and the back room flight controllers,
just as if the Sim were the real thing.
Sims allowed the flight control team
and the astronauts to familiarize
themselves with the specifics of the
missions and with each other. These
activities were just as much
team-building exercises as they were
training exercises in what steps to take
and the decisions required for a variety
of issues, any of which could have had
catastrophic results. Of course, the best
part of a simulation was that it was not
real. So if a flight controller or an
astronaut made a mistake, he or she
could live and learn while becoming
better prepared for the real thing.
Training to become a flight controller
began long before a mission flew.
Flight controllers had to complete a
training flow and certification process
before being assigned to a mission.
The certification requirements varied
depending on the level of responsibility
of the position. Most trainees began
by reading technical manuals related
to their area of flight control (i.e.,
electrical, environmental, consumables
manager or guidance, navigation, and
controls system engineer), observing
currently certified flight controllers
during simulations, and performing
other hands-on activities appropriate
to their development process. As the
trainee became more familiar with
the position, he or she gradually
began participating in simulations
until an examination of the trainee’s
performance was successfully
completed to award formal
certification. Training and development
was a continually improving process
that all flight controllers remained
engaged in whether they were assigned
to a mission or maintaining proficiency.
A flight controller also had the option
to either remain in his or her current
position or move on to a more
challenging flight control position
with increased responsibilities, such as
those found in the front room. An
ascent phase, front room flight control
position was typically regarded as
having the greatest level of
responsibility because this flight
controller was responsible for the
actions of his or her team in the back
room during an intense and
time-critical phase of flight. Similarly,
the flight director was responsible for
the entire flight control team.
Flight Techniques
The flight techniques process helped
develop the procedures, techniques,
and rules for the vehicle system,
payload, extravehicular activities
(EVAs), and robotics for the flight
crew, flight control team, flight
designers, and engineers. NASA
addressed many topics over the course
of the Space Shuttle Program, including
abort modes and techniques, vehicle
power downs, system loss integrated
manifestations and responses, risk
assessments, EVA and robotic
procedures and techniques, payload
deployment techniques, rendezvous and
docking or payload capture procedures,
weather rules and procedures, landing
site selection criteria, and others.
Specific examples involving the ISS
were the development of techniques
to rendezvous, conduct proximity
operations, and dock the Orbiter
while minimizing plume impingement
contamination and load imposition.
Crew Procedures
Prior to the first shuttle flight, NASA
developed and refined the initial launch,
orbit, and re-entry crew procedures, as
documented in the Flight Data File. This
document evolved and expanded over
time, especially early in the program,
as experience in the real operational
environment increased rapidly.
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Flight Rules
Part of the planning process included writing Flight Rules. Flight Rules were a key
element of the real-time flight control process and were predefined actions to
be taken, given certain defined circumstances. This typically meant that rules were
implemented, as written, during critical phases such as launch and re-entry into
Earth’s atmosphere. Generally, during the orbit phase, there was time to evaluate
exact circumstances. The Flight Rules defined authorities and responsibilities
between the crew and ground, and consisted of generic rules, such as system loss
definition, system management, and mission consequence (including early mission
termination) for defined failures.
For each mission, lead flight directors and their teams identified flight-specific mission
rules to determine how to proceed if a failure occurred. These supplemented the
larger book of generic flight rules. For instance, how would the team respond if the
payload bay doors failed to open in orbit? The rules minimized real-time rationalization
because the controllers thoroughly reviewed and simulated requirements and
procedures before the flight.
The three major flight phases—
ascent, orbit, and re-entry—often
required different responses to the
same condition, many of which were
time critical. This led to the
development of different checklists
for these phases. New vehicle
features such as the Shuttle Robotic
Arm and the airlock resulted in
additional Flight Data File articles.
Some of these, such as the
malfunction procedures, did not
change unless the underlying system
changed or new knowledge was
gained, while flight-specific articles,
such as the flight plan, EVA, and
payload operations checklists, changed
for each flight. The Flight Data File
included in-flight maintenance
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procedures based on experience from
the previous programs. Checklist
formats and construction standards
were developed and refined in
consultation with the crews. NASA
modeled the pocket checklists, in
particular, after similar checklists
used by many military pilots for their
operations. Flight versions of the cue
cards were fitted with Velcro
and some were positioned in critical
locations on the various cockpit panels
for instantaneous reference.
In addition, the crew developed quick-
reference, personal crew notebooks that
included key information the crew
member felt important, such as emails
or letters from individuals or
organizations. During ISS missions,
the crews established a tradition where
the shuttle crew and the ISS crew
signed or stamped the front of each
other’s notebook.
Once the official Flight Data File was
completed, crew members reviewed the
flight version one last time and often
added their own notes on various
pages. All information was then copied
and the flight versions of the Flight
Data File were loaded on the shuttle.
Multiple copies of selected Flight
Data File books were often flown to
enhance on-board productivity.
All flight control team members and
stakeholders, including the capsule
communicator and flight director,
had nearly identical copies of the
Flight Data File at their consoles.
This was to ensure the best possible
communications between the space
vehicle and the flight control team.
The entire flown Flight Data File with
crew annotations, both preflight and
in-flight, was recovered Postflight and
archived as an official record.
Commander Mark Kelly’s personal crew notebook from STS-124.
A "fish-eye"? lens on a digital still
camera was used to record this
image of the STS-124 and
International Space Station (ISS)
Expedition 17 crew members as they
share a meal on the middeck of the
Space Shuttle Discovery while
docked with the ISS. Pictured
counterclockwise (from the left
bottom):Astronaut Mark Kelly,
STS-124 commander; Russian
Federal Space Agency Cosmonaut
Sergei Volkov, Expedition 17
commander; Astronaut Garrett
Reisman; Russian Federal Space
Agency Cosmonaut Oleg Kononenko,
Astronaut Gregory Chamitoff,
Expedition 17 flight engineers;
Astronaut Michael Fossum, Japan
Aerospace Exploration Agency
Astronaut Akihiko Hoshide,Astronaut
Karen Nyberg; and Astronaut
Kenneth Ham, pilot.
Detailed Trajectory Planning
Trajectory planning efforts, both
preflight and in real time, were major
activities. Part of the preflight effort
involved defining specific parameters
called I-loads, which defined elements
of the ascent trajectory control
software, some of which were defined
and loaded on launch day via the
Day-of-Launch I-Load Update system.
The values of these parameters were
uniquely determined for each flight
based on the time of year, specific
flight vehicle, specific main engines,
mass properties including the specific
Solid Rocket Boosters (SRBs), launch
azimuth, and day-of-launch wind
measurements. It was a constant
optimization process for each flight
to minimize risk and maximize
potential success. Other constraints
were space radiation events,
predictable conjunctions, and
predictable meteoroid events, such as
the annual Perseid meteor shower
period in mid August. The mission
operations team developed the Flight
Design Handbook to document, in
detail, the process for this planning.
Re-entry trajectory planning was
initially done preflight and was
continuously updated during a mission.
NASA evaluated daily landing site
opportunities for contingency deorbit
purposes, and continuously tracked
mass properties and vehicle center of
gravity to precisely predict deorbit burn
times and re-entry maneuvers. After the
Columbia accident (STS-107) in 2003,
the agency established new ground
rules to minimize the population
overflown for normal entries.
Planning also involved a high level
of NASA/Department of Defense
coordination, particularly following
the Challenger accident (STS-51L)
in 1986. This included such topics
as threat and warning, orbital debris,
and search and rescue.
Orbiter and Payload
Systems Management
Planning each mission required
management of on-board consumables
for breathing oxygen, fuel cell
reactants, carbon dioxide, potable
water and wastewater, Reaction
Control System and Orbital
Maneuvering System propellants,
Digital Auto Pilot, attitude constraints,
thermal conditioning, antenna
pointing, Orbiter and payload data
recording and dumping, power downs,
etc. The ground team developed and
validated in-flight maintenance
activities, as required, then put these
activities in procedure form and
uplinked the activity list for crew
execution. There was an in-flight
maintenance checklist of predefined
procedures as well as an in-flight
maintenance tool kit on board for
such activities. Unique requirements
for each flight were planned preflight
and optimized during the flight by
the ground-based flight control team
and, where necessary, executed by the
crew on request.
Astronaut Training
Training astronauts is a continually
evolving process and can vary
depending on the agency’s objectives.
Astronaut candidates typically
completed 1 year of basic training,
over half of which was on the shuttle.
This initial year of training was
intended to create a strong foundation
on which the candidates would build
for future mission assignments.
Astronaut candidates learned about
the shuttle systems, practiced operation
of the shuttle in hands-on mock-ups,
and trained in disciplines such as space
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and life sciences, Earth observation,
and geology. These disciplines helped
develop them into “jacks-of-all-trades."?
Flight assignment typically occurred
1 to 1½ years prior to a mission. Once
assigned, the crew began training for the
specific objectives and specialized
needs for that mission. Each crew had a
training team that ensured each crew
member possessed an accurate
understanding of his or her assignments.
Mission-specific training was built off
of past flight experience, if any, and
basic training knowledge. Crew
members also received payload training
at the principal investigator’s facility.
This could be at a university, a national
facility, an international facility, or
another NASA facility. Crew members
were the surrogates for the scientists
and engineers who designed the
payloads, and they trained extensively
to ensure a successfully completed
mission. As part of their training for the
payloads, they may have actually spent
days doing the operations required for
each day’s primary objectives.
Crew members practiced mission
objectives in simulators both with and
without the flight control teams in
Mission Control. Astronauts trained in
Johnson Space Center’s (JSC’s) Shuttle
Mission Simulator, shuttle mock-ups,
and the Shuttle Engineering Simulator.
The Shuttle Mission Simulator
contained both a fixed-base and a
motion-based high-fidelity station.
The motion-based simulator duplicated,
as closely as possible, the experience
of launch and landing, including the
release of the SRBs and External
Tank (ET) and the views seen out the
Orbiter windows. Astronauts practiced
aborts and disaster scenarios in this
simulator. The fixed-base simulator
included a flight deck and middeck,
where crews practiced on-orbit
activities. To replicate the feeling of
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space, the simulator featured views of
space and Earth outside the mock-up’s
windows. Astronauts used the
full-fuselage mock-up trainer for a
number of activities, including
emergency egress practice and EVA
training. Crew compartment trainers
(essentially the flight deck and the
middeck) provided training on Orbiter
stowage and related subsystems.
A few months before liftoff, the crew
began integrated simulations with the
flight control teams in the Mission
Control Center. These simulations
prepared the astronauts and the flight
control teams assigned to the mission to
safely execute critical aspects of the
mission. They were a crucial step in
flight preparation, helping to identify
any problems in the flight plan.
With the exception of being in Earth
environment, integrated simulations
were designed to look and feel as
they would in space, except equipment
did not malfunction as frequently in
space as it did during simulations.
Elaborate scripts always included a
number of glitches, anomalies, and
failures. Designed to bring the on-orbit
and Mission Control teams together to
work toward a solution, integrated
simulations tested not only the crews
and controllers but also the
mission-specific Flight Rules.
An important part of astronaut crew
training was a team-building activity
completed through the National
Outdoor Leadership School. This
involved a camping trip that taught
astronaut candidates how to be leaders
as well as followers. They had to learn
to depend on one another and balance
each other’s strengths and weaknesses.
The astronaut candidates needed to
learn to work together as a crew and
eventually recognize that their crew was
their family. Once a crew was assigned
to a mission, these team-building
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activities became an important part of
the mission-specific training flow.
Teamwork was key to the success of a
shuttle mission.
When basic training was complete,
astronauts received technical
assignments; participated in simulations,
support boards, and meetings; and made
public appearances. Many also began
specialized training in areas such as
EVA and robotic operations. Extensive
preflight training was performed when
EVAs were required for the mission.
Each astronaut candidate completed
an EVA skills program to determine his
or her aptitude for EVA work. Those
continuing on to the EVA specialty
completed task training and systems
training, the first of which was specific
to the tasks completed by an astronaut
during an EVA while the latter focused
on suit operations. Task training
included classes on topics such as the
familiarization and operation of tools.
For their final EVA training, the
astronauts practiced in a swimming
pool that produced neutral buoyancy,
which mimicked some aspect of
microgravity. Other training included
learning about their EVA suits, the use
of the airlock in the Orbiter or ISS, and
the medical requirements to prevent
decompression sickness.
Mission-specific EVA training
typically began 10 months before
launch. An astronaut completed seven
neutral buoyancy training periods
for each spacewalk that was considered
complex, and five training periods
for noncomplex or repeat tasks.
The last training runs before launch
were usually completed in the order
in which they would occur during the
mission. Some astronauts found that
the first EVA was more intimidating
than the others simply because it
represented that initial hurdle to
overcome before gaining their rhythm.
This concern was eased by practicing
an additional Neutral Bouyancy
Laboratory training run for their first
planned spacewalk as the very last
training run before launch.
EVA and robotic operations were
commonly integrated, thereby
creating the need to train both
specialties together and individually.
The robotic arm operator received
specialized training with the arm
on the ground using skills to mimic
microgravity and coordination
through a closed-circuit television.
EVA training was also accomplished in
the Virtual Reality Laboratory, which
was similarly used for robotic training.
The Virtual Reality Laboratory
complemented the underwater training
with a more comfortable and flexible
environment for reconfiguration
changes. Virtual reality software was
also used to increase an astronaut’s
situational awareness and develop
effective verbal commands as well as to
familiarize him or her with mass
handling on the arm and r-bar pitch
maneuver photography training.
T-38 aircraft training was primarily
used to keep astronauts mentally
conditioned to handle challenging,
real-time situations. Simulators were an
excellent training tool, but they were
limited in that the student had the
comfort of knowing that he or she was
safely on the ground. The other benefit
of T-38 training was that the aircraft
permitted frequent and flexible travel,
which was necessary to accommodate
an astronaut’s busy training schedule.
Team Building
Commander Mark Kelly took his crew and the lead International Space Station flight
director to Alaska for a 10-day team-building exercise in the middle of mission
training. These exercises were important, Kelly explained, as they provided crews
with the “opportunity to spend some quality time together in a stressful environment"
and gave the crews an opportunity to develop leadership skills. Because shuttle
missions were so compressed, Kelly wanted to determine how his crew would react
under pressure and strain. Furthermore, as a veteran, he knew the crew members
had to work as a team. They needed to learn more about one another to perform
effectively under anxious and stressful circumstances. Thus, away from the
conveniences of everyday life, STS-124’s crew members lived in a tent, where
they could “practice things like team building, Expedition behavior, and working out
conflicts." Building a team was important not only to Kelly, but also to the lead
shuttle flight director who stressed the importance of developing “a friendship and
camaraderie with the crew." To build that support, crew members frequently
gathered together for social events after work. A strong relationship forged between
the flight control team and crews enabled Mission Control to assess how the
astronauts worked and how to work through stressful situations.
The STS-124 crew members celebrate the end of formal crew training with a cake-cutting
ceremony in the Jake Garn Simulation and Training Facility at Johnson Space Center. Pictured
from the left:Astronauts Mark Kelly, commander; Ronald Garan, mission specialist; Kenneth
Ham, pilot; Japan Aerospace Exploration Agency Astronaut Akihiko Hoshide,Astronauts Michael
Fossum, Karen Nyberg, and Gregory Chamitoff, all mission specialists. The cake-cutting tradition
shows some of the family vibe between the training team and crew as they celebrate key
events in an assigned crew training flow.
Shuttle Training Aircraft
Commanders and pilots used
the Shuttle Training Aircraft—
a modified Gulfstream-2
aircraft—to simulate landing
the Orbiter, which was often
likened to landing a brick,
especially when compared
with the highly maneuverable
high-speed aircraft that
naval aviators and pilots had
flown.The Shuttle Training
Aircraft mimicked the flying
characteristics of the shuttle,
and the left-hand flight
deck resembled the Orbiter.
Trainers even blocked the
windows to simulate the limited view that a pilot experienced during the landing. During
simulations at the White Sands Space Harbor in New Mexico, the instructor sat in the
right-hand seat and flew the plane into simulation.The commander or pilot, sitting in the
left-hand seat, then took the controls.To obtain the feel of flying a brick with wings, he or
she lowered the main landing gear and used the reverse thrusters. NASA requirements
stipulated that commanders complete a minimum of 1,000 Shuttle Training Aircraft
approaches before a flight. Even Commander Mark Kelly—a pilot for two shuttle
missions, a naval aviator, and a test pilot with over 5,000 flight hours—recalled that he
completed at least “1,600 approaches before [he] ever landed the Orbiter." He conceded
that the training was “necessary because the Space Shuttle doesn’t have any engines
for landing.You only get one chance to land it.You don’t want to mess that up."
Two aircraft stationed at Ellington Air Force Base for
Johnson Space Center are captured during a training
and familiarization flight over White Sands, New Mexico.
The Gulfstream aircraft (bottom) is NASA’s Shuttle
Training Aircraft and the T-38 jet serves as a chase plane.
Flight Simulation Training
For every hour of flight, the STS-124 crew spent 6 hours training on the ground for
a total of about 1,940 hours per crew member.This worked out to be nearly a year of
8-hour workdays.
Commander Mark Kelly and Pilot Kenneth Ham practiced rendezvousing and docking
with the space station on the Shuttle Engineering Simulator, also known as the dome,
numerous times (on weekends and during free time) because the margin of error
was so small.
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The Space Shuttle and Its Operations
In Need of a
Just a few days before liftoff of
STS-124, the space station’s toilet
broke. This added a wrinkle to
the flight plan redrafted earlier. Russia
delivered a spare pump to Kennedy
Space Center, and the part arrived
just in time to be added to Discovery’s
middeck. Storage space was always
at a premium on missions. The
last-minute inclusion of the pump
involved some shifting and the
removal of 15.9 kg (35 pounds) of
cargo, including some wrenches
and air-scrubber equipment. This
resulted in changes to the flight
plan—Discovery’s crew and the
station members would use the
shuttle’s toilet until station’s could be
used. If that failed, NASA packed
plenty of emergency bags typically
used by astronauts to gather in-flight
urine specimens for researchers.
When the crew finally arrived and
opened the airlock, Commander
Mark Kelly joked,“Hey, you looking for
a plumber?" The crews, happy to see
each other, embraced one another.
Prior to launch, astronauts walk around their
launch vehicle at Kennedy Space Center.
There were roughly two dozen T-38
aircraft at any time, all of which were
maintained and flown out of Ellington
Field in Houston, Texas. As part of
astronaut candidate training, they
received T-38 ground school, ejection
seat training, and altitude chamber
training. Mission specialists frequently
did not have a military flying
background, so they were sent to
Pensacola, Florida, to receive survival
training from the US Navy. As with
any flight certification, currency
requirements were expected to be
maintained. Semiannual total T-38 flying
time minimum for a pilot was 40 hours.
For a mission specialist, the minimum
flight time was 24 hours. Pilots were
also required to meet approach and
landing minimum flight times.
Launching the Shuttle
Launch day was always exciting. KSC’s
firing room controlled the launch,
but JSC’s Mission Operations intently
watched all the vehicle systems.
The Mission Control Center was filled
with activity as the flight controllers
completed their launch checklists. For
any shuttle mission, the weather was
the most common topic of discussion
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and the most frequent reason why
launches and landings were delayed.
Thunderstorms could not occur too
close to the launch pad, crosswinds had
to be sufficiently low, cloud decks
could not be too thick or low, and
visibility was important. Acceptable
weather needed to be forecast at the
launch site and transatlantic abort
landing sites as well as for each ascent
abort option.
Not far from the launch pad, search
and rescue forces were always on
standby for both launch and landing.
This included pararescue jumpers to
retrieve astronauts from the water if a
bailout event were to occur. The more
well-known assets were the support
ships, which were also supported by
each of the military branches and the
US Coast Guard. This team of
search-and-rescue support remained on
alert throughout a mission to ensure the
safe return of all crew members.
Shortly before a launch, the KSC launch
director polled the KSC launch control
room along with JSC Mission Control
for a “go/no go" launch decision.
The JSC front room flight controllers
also polled their back room flight
controllers for any issues. If no issues
were identified, the flight controllers,
representing their specific discipline,
responded to the flight director with a
“go." If an issue was identified, the
flight controller was required to state
“no go" and why. Flight Rules existed
to identify operational limitations,
but even with these delineations the
decision to launch was never simple.
Crew Prepares for Launch
With all systems “go" and launch weather acceptable, STS-124 launched on May 31, 2008, marking
the 26th shuttle flight to the International Space Station.Three hours earlier, technicians had
strapped in seven astronauts for NASA’s 123rd Space Shuttle mission. Commander Mark Kelly was a
veteran of two shuttle missions. By contrast, the majority of his crew consisted of rookies—Pilot
Kenneth Ham along with Astronauts Karen Nyberg, Ronald Garan, Gregory Chamitoff, and Akihiko
Hoshide of the Japan Aerospace Exploration Agency.Although launch typically represented the
beginning of a flight, more than 2 decades of work went into the coordination of this single mission.
After suiting up, STS-124 crew members exited the Operations and Checkout Building to board the
Astrovan, which took them to Launch Pad 39A for the launch of Space Shuttle Discovery. On the right
(front to back):Astronauts Mark Kelly, Karen Nyberg, and Michael Fossum. On the left (front to back):
Astronauts Kenneth Ham, Ronald Garan,Akihiko Hoshide, and Gregory Chamitoff.
The Countdown Begins
The primary objective of the STS-124 mission was to deliver Japan’s Kibo module to
the International Space Station. As Commander Mark Kelly said, “We’re going to deliver
Kibo, or hope, to the space station, and while we tend to live for today, the discoveries
from Kibo will certainly offer hope for tomorrow." The Japanese module is an
approximately 11-m (37-ft), 14,500-kg (32,000-pound) pressurized science laboratory,
often referred to as the Japanese Pressurized Module. This module was so large that
the Orbiter Boom Sensor System had to be left on orbit during STS-123 (2008) to
accommodate the extra room necessary in Discovery’s payload bay.
During the STS-124 countdown, the area experienced some showers. By launch time,
however, the sea breeze had pushed the showers far enough away to eliminate any
concerns.The transatlantic abort landing weather proved a little more challenging, with
two of the three landing sites forecasted to have weather violations. Fortunately, Moron Air
Base, Spain, remained clear and became the chosen transatlantic abort landing site.
Space Shuttle Discovery and its seven-member
STS-124 crew head toward low-Earth orbit and
a scheduled link-up with the International
Space Station.
Ground Facilities Operations
The Mission Control Center relied on
the NASA network, managed by
Goddard Space Flight Center (GSFC),
to route the spacecraft downlink
telemetry, tracking, voice, and
television and uplink voice, data, and
command. The primary in-flight link
was to/from the Mission Control Center
to the White Sands Ground Terminal
up to the tracking and data relay
satellites and then to/from the Orbiter.
In addition, there were still a few
ground sites with a direct linkage
to/from the Orbiter as well as specific
C-band tracking sites for specific phases
as needed. The preflight planning
function included arranging for flight-
specific support from all these ground
facilities and adjusting them, as
necessary, based on in-flight events. The
readiness of all these support elements
for each flight was certified by the
GSFC network director at the Mission
Operations Flight Readiness Review.
The Mission Control Center was the
focus of shuttle missions during the
flight phase. Control of the mission and
communication with the crew
transferred from the KSC firing room to
the JSC Mission Control Center at main
engine ignition. Shuttle systems data,
voice communications, and television
were relayed almost instantaneously to
the Mission Control Center through the
NASA ground and space networks. In
many instances, external facilities such
as MSFC and GSFC as well as US Air
Force and European Space Agency
facilities also provided support for
specific payloads. The facility support
effort, the responsibility of the
operations support team, ensured the
Mission Control Center and all its
interfaces were ready with the correct
software, hardware, and interfaces to
support a particular flight.
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The Mission Control Center front room houses the capsule communicator, flight director and deputy, and leads for all major systems such as avionics, life
support, communication systems, guidance and navigation, extravehicular activity lead and robotic arm, propulsion and other expendables, flight surgeon,
and public affairs officer. These views show the extensive support and consoles. Left photo: At the front of the operations center are three screens.
The clocks on the left include Greenwich time, mission elapsed time, and current shuttle commands. A map of the world with the shuttle position-current
orbit is in the center. The right screen shows shuttle attitude. Center photo: Flight Director Norman Knight (right) speaks with one of the leads at the
support console. Right photo: Each console in the operations center has data related to the lead’s position; e.g., the life support position would have the
data related to Orbiter air, water, and temperature readings and the support hardware functions.
Just before shuttle liftoff, activity in the
Mission Control Center slowed and the
members of the flight control team
became intently focused on their
computer screens. From liftoff, the
performance of the main engines, SRBs,
and ET were closely observed with the
team ready to respond if anything
performed off-nominally. If, for
example, a propulsion failure occurred,
the flight control team would identify a
potential solution that may or may not
require the immediate return of the
Orbiter to the ground. If the latter were
necessary, an abort mode (i.e., return to
launch site, transatlantic abort landing)
and a landing site would be selected.
The electrical systems and the crew
environment also had to function
correctly while the Orbiter was guided
into orbit. For the entire climb to orbit,
personnel in the Mission Control Center
remained intensely focused. Major
events were called out during the ascent.
At almost 8½ minutes, when target
velocity was achieved, main engine
cutoff was commanded by the on-board
computers and flight controllers
continued verifying system
performance. Every successful launch
was an amazing accomplishment.
Before and after a shuttle launch, KSC
personnel performed walkdowns of the
launch pad for a visual inspection of
any potential debris sources. Shuttle
liftoff was a dynamic event that could
cause ice/frost or a loose piece of
hardware to break free and impact the
Orbiter. Finding these debris sources
and preventing potential damage was
important to the safety of the mission.
Debris Impact on the Orbiter
Debris from launch and on orbit could
make the Orbiter unable to land. The
Orbiter could also require on-orbit repair.
Ascent Inspection
After the Columbia accident (2003),
the shuttle was closely observed during
the shuttle launch and for the duration
of the ascent phase by a combination of
ground and vehicle-mounted cameras,
ground Radio Detection and Ranging,
and the Wing Leading Edge Impact
Detection System. The ground cameras
were located on the fixed service
structure, the mobile launch platform,
around the perimeter of the launch
pad, and on short-, medium-, and
long-range trackers located along the
Florida coast. The ground cameras
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provided high-resolution imagery of
liftoff and followed the vehicle through
SRB separation and beyond. The
vehicle-mounted cameras were
strategically placed on the tank,
boosters, and Orbiter to observe the
condition of specific areas of interest
and any debris strikes. The crew took
handheld video and still imagery of the
tank following separation when lighting
conditions permitted. This provided
another source of information to
confirm a clean separation or identify
any suspect areas on the tank that might
potentially represent a debris concern
for the Orbiter Thermal Protection
System. The Wing Leading Edge Impact
Detection System used accelerometers
mounted within the Orbiter’s wing
leading edge to monitor for impacts
throughout the ascent and orbit phases,
power permitting.
The world’s largest C-band radar and
two X-band radars played an integral
role in the ascent debris observation
through a valuable partnership with the
US Navy. The C-band radar watched
for falling debris near the Orbiter, and
the X-band radar further interpreted the
velocity characteristics of any debris
events with respect to the vehicle’s
motion. The X-band radars were on
board an SRB recovery ship located
downrange of the launch site and
a US Army vessel south of the
groundtrack. The US Navy C-band
radar sat just north of KSC.
Data collected from ground and
vehicle-mounted cameras, ground
radar, and the Wing Leading Edge
Impact Detection System created a
comprehensive set of ascent data.
Data were sent to the imagery analysis
teams at JSC, KSC, and MSFC for
immediate review. Each team had its
area of specialty; however, intentional
overlap of the data analyses existed
as a conservative measure. As early as
1 hour after launch, these teams of
imagery specialists gathered in a dark
room with a large screen and began
reviewing every camera angle captured.
They watched the videos in slow
motion, forward, and backward as
many times as necessary to thoroughly
analyze the data. The teams were
looking for debris falling off the vehicle
stack or even the pad structure that
may have impacted the Orbiter. If the
team observed or even suspected a
debris strike on the Orbiter, the team
reported the location to the mission
management team and the Orbiter
damage assessment team for on-orbit
inspection. The damage assessment
team oversaw the reported findings of
the on-orbit imagery analysis and
delivered a recommendation to the
Orbiter Project Office and the mission
management team stating the extent
of any damage and the appropriate
forward action. This cycle of
obtaining imagery, reviewing imagery,
and recommending forward actions
continued throughout each phase of
the mission.
On-orbit Inspections
The ISS crew took still images of the
Orbiter as it approached the station
and performed maneuvers, exposing
the underside tiles. Pictures were also
taken of the ET umbilical doors to
verify proper closure as well as photos
of the Orbiter’s main engines, flight
deck windows, Orbital Maneuvering
System pods, and vertical stabilizer.
The shuttle crew photographed the
pods and the leading edge of the
vertical stabilizer from the windows
of the flight deck. The ISS crew took
still images of the Orbiter. All images
were downlinked for review by the
damage assessment team.
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The Space Shuttle and Its Operations
Orbiter Survey
The Orbiter survey included the
Orbiter’s crew cabin Thermal
Protection System and the
wing leading edge and nose
cap reinforced carbon-carbon
using the Shuttle Robotic
Arm and the Orbiter Boom
Sensor System. The survey
involved detailed scanning
in a specified pattern and required most of the day to complete. A focused inspection
was only performed when a suspect area was identified and more detailed information
was required to determine whether a repair or alternative action was necessary.
Due to the unique nature of the STS-124 mission, the Shuttle Robotic Arm was used
instead of the Orbiter Boom Sensor System. Astronaut Karen Nyberg operated the
robotic arm for the inspection of the Thermal Protection System. The nose cap and
wing leading edge reinforced carbon-carbon survey was scheduled for post undock
after the Orbiter Boom Sensor System had been retrieved during a Flight Day 4
extravehicular activity.
Astronaut Karen Nyberg, STS-124, works the controls
on the aft flight deck of Space Shuttle Discovery during
Flight Day 2 activities.
For all missions to the ISS that took
place after the Columbia accident, late
inspection was completed after the
Orbiter undocked. This activity
included a survey of the reinforced
carbon-carbon to look for any
micrometeoroid orbital debris damage
that may have occurred during the time
on orbit. Since the survey was only of
the reinforced carbon-carbon, it took
less time to complete than did the
initial on-orbit survey. As with the
Flight Day 2 survey, the ground teams
compared the late inspection imagery
to Flight Day 2 imagery and either
cleared the Orbiter for re-entry or
requested an alternative action.
On-orbit Activities
Extravehicular Activity Preparation
For missions that had EVAs, the
day after launch was reserved for
extravehicular mobility unit checkout
and the Orbiter survey. EVA suit
checkout was completed in the
airlock where the suit systems were
verified to be operating correctly.
Various procedures developed over
the nearly 30-year history for an EVA
mission were implemented to prevent
decompression sickness and ensure
the crew and all the hardware were
ready. The day of the EVA, both
crew members suited up with the
assistance of the other crew members
and then left the airlock. EVAs
involving the Shuttle Robotic Arm
required careful coordination between
crew members. This was when the
astronauts applied the meticulously
practiced verbal commands.
For missions to the ISS, the primary
objective of Flight Day 3 was to
rendezvous and dock with the ISS.
As the Orbiter approached the ISS, it
performed a carefully planned series
of burns to adjust the orbit for a
smooth approach to docking.
On-orbit Operations
Within an hour of docking with the
ISS, the hatch opened and the shuttle
crew was welcomed by the ISS crew.
For missions consisting of a crew
change, the first task was to transfer
the custom Soyuz seat liners to crew
members staying on station. Soyuz is
the Russian capsule required for
emergency return to Earth and for crew
rotations. Completion of this task
marked the formal change between the
shuttle and ISS crews.
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A Flawless Rendezvous
On day three, STS-124 rendezvoused and docked with the space station. About 182 m
(600 ft) below the station, Commander Mark Kelly flipped Discovery 360 degrees so
that the station crew members could photograph the underbelly of the shuttle.
Following the flip, Kelly conducted a series of precise burns with the Orbital
Maneuvering System, which allowed the shuttle—flying about 28,200 km/hr (17,500
mph)—to chase the station, which was traveling just as fast. Kelly, who had twice
flown to the station, described the moment: “It’s just incredible when you come 610 m
(2,000 ft) underneath it and see this giant space station. It’s just an amazing sight."
Once the Orbiter was in the same orbit with the orbiting lab, Kelly nudged the vehicle
toward the station. As the vehicle moved, the crew encountered problems with the
Trajectory Control System, a laser that provided range and closure rates. This system
was the primary sensor, which the crew members used to gauge how far they were
from the station. Luckily, the crew had simulated this failure numerous times, so the
malfunction had no impact on the approach or closure. The lead shuttle flight director
called the rendezvous “absolutely flawless." Upon docking ring capture, the crew
congratulated Kelly with a series of high fives.
Trust and Respect Do Matter
During activation of the Japanese Experiment Module, the flight controllers in Japan
encountered a minor hiccup.As the crew attached the internal thermal control system
lines, ground controllers worried that there was an air bubble in the system’s lines,
which could negatively impact the pump’s performance. Controllers in Houston,Texas,
and Tsukuba, Japan, began discussing options.The International Space Station (ISS)
flight director noticed that the relationship she had built with the Japanese “helped
immensely."The thermal operations and resource officer had spent so many years
working closely with his Japan Aerospace Exploration Agency counterpart that, when it
came time to decide to use the nominal plan or a different path,“the respect and trust
were there," and the Japanese controllers agreed with his recommendations to stay with
the current plan.“I think," the ISS flight director said,“that really set the mission on the
right course, because then we ended up proceeding with activation."
Every mission included some
housekeeping and maintenance. New
supplies were delivered to the station
and old supplies were stowed in
the Orbiter for return to Earth.
Experiments that completed their stay
on board the ISS were also returned
home for analyses of the microgravity
environment’s influence.
Returning Home
If necessary, a flight could be extended
to accommodate extra activities and
weather delays. The mission
management team decided on flight
extensions for additional activities
where consideration was given for
impacts to consumables, station
activities, schedule, etc. Landing was
typically allotted 2 days with multiple
opportunities to land. NASA’s
preference was always to land at KSC
since the vehicle could be processed at
that facility; however, weather would
sometimes push the landing to Dryden
Flight Research Center/Edwards Air
Force Base. If the latter occurred, the
Orbiter was flown back on a modified
Boeing 747 in what was referred to as
a “ferry flight."
Once the Orbiter landed and rolled to
a stop, the Mission Control Center
turned control back to KSC. After
landing, personnel inspected the
Orbiter for any variations in Thermal
Protection System and reinforced
carbon-carbon integrity. More imagery
was taken for comparison to on-orbit
imagery. Once the Orbiter was at the
Orbiter Processing Facility, its
cameras were removed for additional
imagery analysis and the repairs began
in preparation for another flight.
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The Space Shuttle and Its Operations
After nearly 9 days at the space station, the crew of STS-124 undocked and said
farewell to Gregory Chamitoff, who would be staying on as the flight engineer for the
Expedition crew, and the two other crew members. When watching the goodbyes on
video, it appeared as if the crew said goodbye, closed the hatch, and dashed away from
the station. “It’s more complicated than that," Commander Mark Kelly explained. “You
actually spend some time sitting on the Orbiter side of the hatch." About 1 hour passed
before the undocking proceeded. Afterward, the crew flew around the station and then
completed a full inspection of the wing’s leading edge and nose cap with the boom.
The crew began stowing items like the Ku-band antenna in preparation for landing on
June 15. On the day of landing, the crew suited up and reconfigured the Orbiter from a
spaceship to an airplane.The re-entry flight director and his team worked with the crew
to safely land the Orbiter, and continually monitored weather conditions at the three
landing sites.With no inclement weather at Kennedy Space Center, the crew of STS-124
was “go" for landing.The payload bay doors were closed several minutes before deorbit
burn.The crew then performed checklist functions such as computer configuration,
auxiliary power unit start, etc. Sixty minutes before touchdown the deorbit burn was
performed.After the Columbia accident, the re-entry profiles for the Orbiter changed so
that the crew came across the Gulf of Mexico, rather than the United States.As the
Orbiter descended, the sky turned from pitch black to red and orange. Discovery hit the
atmosphere at Mach 25 and a large fireball surrounded the glider. It rapidly flew over
Mexico. By the time it passed over Orlando, Florida, the Orbiter slowed.As they
approached the runway, Kelly pulled the nose up and lowered the landing gear. On
touchdown—after main gear touchdown but before nose gear touchdown—he deployed
a parachute, which helped slow the shuttle as it came to a complete stop.
Returning to Earth
Space Shuttle Discovery’s drag chute is deployed as the spacecraft rolls toward a stop on
runway 15 of the Shuttle Landing Facility at Kennedy Space Center, concluding the 14-day
STS-124 mission to the International Space Station.
Solid Foundations Assured
Two pioneers of flight operations,
Christopher Kraft and Gene Kranz,
established the foundations of shuttle
mission operations in the early human
spaceflight programs of Mercury,
Gemini, and Apollo. Their “plan, train,
fly" approach made controllers tough
and competent, “flexible, smart, and
quick on their feet in real time," recalled
the lead flight director for STS-124
(2008). That concept, created in the
early 1960s, remained the cornerstone
of mission operations throughout the
Space Shuttle Program, as exemplified
by the flight of STS-124.
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The Shuttle Carrier Aircraft transported the Space Shuttle Endeavour from Dryden Research Center,
California, back to Kennedy Space Center, Florida.
Endeavour touches down at Dryden Flight Research Center located at Edwards Air Force Base in
California to end the STS-126 (2008) mission.
A dramatic expansion in extravehicular activity (EVA)—or
“spacewalking"—capability occurred during the Space Shuttle
Program; this capability will tremendously benefit future space
exploration. Walking in space became almost a routine event during
the program—a far cry from the extraordinary occurrence it had been.
Engineers had to accommodate a new cadre of astronauts that included
women, and the tasks these spacewalkers were asked to do proved
significantly more challenging than before. Spacewalkers would be
charged with building and repairing the International Space Station.
Most of the early shuttle missions helped prepare astronauts, engineers,
and flight controllers to tackle this series of complicated missions
while also contributing to the success of many significant national
resources—most notably the Hubble Space Telescope. Shuttle
spacewalkers manipulated elements up to 9,000 kg (20,000 pounds),
relocated and installed large replacement parts, captured and repaired
failed satellites, and performed surgical-like repairs of delicate solar
arrays, rotating joints, and sensitive Orbiter Thermal Protection System
components. These new tasks presented unique challenges for the
engineers and flight controllers charged with making EVAs happen.
The Space Shuttle Program matured the EVA capability with advances in
operational techniques, suit and tool versatility and function, training
techniques and venues, and physiological protocols to protect astronauts
while providing better operational efficiency. Many of these advances
were due to the sheer number of EVAs performed. Prior to the start
of the program, 38 EVAs had been performed by all prior US spaceflights
combined. The shuttle astronauts accomplished 157 EVAs.
This was the primary advancement in EVA during the shuttle era—
an expansion of capability to include much more complicated and difficult
tasks, with a much more diverse Astronaut Corps, done on a much more
frequent basis. This will greatly benefit space programs in the future as they
can rely on a more robust EVA capability than was previously possible.
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The Space Shuttle and Its Operations
Operations and
Nancy Patrick
Joseph Kosmo
James Locke
Luis Trevino
Robert Trevino
Extravehicular Activity
If We Can Put a Human on
the Moon, Why Do We Need to
Put One in the Payload Bay?
The first question for program
managers at NASA in regard to
extravehicular activities (EVAs) was:
Are they necessary? Managers
faced the challenge of justifying the
added cost, weight, and risk of putting
individual crew members outside
and isolated from the pressurized
cabin in what is essentially a personal
spacecraft. Robotics or automation are
often considered alternatives to sending
a human outside the spacecraft;
however, at the time the shuttle was
designed, robotics and automation were
not advanced enough to take the place
of a human in all required external
tasks. Just as construction workers and
cranes are both needed to build
skyscrapers, EVA crew members and
robots are needed to work in space.
Early in the Space Shuttle Program,
safety engineers identified several
shuttle contingency tasks for which
EVA was the only viable option.
Several shuttle components could
not meet redundancy requirements
through automated means without an
untenable increase in weight or system
complexity. Therefore, EVA was
employed as a backup. Once EVA
capability was required, it became a
viable and cost-effective backup
option as NASA identified other
system problems. Retrieval or repair
of the Solar Maximum Satellite
(SolarMax) and retrieval of the Palapa
B2 and Westar VI satellites were EVA
tasks identified very early in the
program. Later, EVA became a standard
backup option for many shuttle
payloads, thereby saving cost and
resolving design issues.
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Gregory Harbaugh
Astronaut on STS-39 (1991), STS-54
(1993), and STS-82 (1997).
Manager, Extravehicular Activity (EVA)
Office (1997-2001).
“In my opinion, one of the major
achievements of the Space Shuttle
era was the dramatic enhancement
in productivity, adaptability, and
efficiency of EVA, not to mention
the numerous EVA-derived
accomplishments. At the beginning
of the shuttle era, the extravehicular
mobility unit had minimal capability for tools, and overall utility of EVA was
limited. However, over the course of the program EVA became a planned event
on many missions and ultimately became the fallback option to address a
multitude of on-orbit mission objectives and vehicle anomalies. Speaking as the
EVA program manager for 4 years (1997-2001), this was the result of incredible
reliability of the extravehicular mobility unit thanks to its manufacturers
(Hamilton Sundstrand and ILC Dover), continuous interest and innovation led by
the EVA crew member representatives, and amazing talent and can-do spirit of
the engineering/training teams. In my 23 years with NASA, I found no team of
NASA and contractor personnel more technically astute, more dedicated, more
innovative, or more ultimately successful than the EVA team.
EVA became an indispensible part of the Space Shuttle Program. EVA could and
did fix whatever problems arose, and became an assumed tool in the holster
of the mission planners and managers. In fact, when I was EVA program
manager we had shirts made with the acronym WOBTSYA—meaning ‘we’ve
only begun to save your Alpha’ (the ISS name at the time). We knew when called
upon we could handle just about anything that arose."
Automation and
Extravehicular Activity
EVA remained the preferred method
for many tasks because of its
efficiency and its ability to respond to
unexpected failures and contingencies.
As amazing and capable as robots
and automation are, they are typically
efficient for anticipated tasks or those
that fall within the parameters of
known tasks. Designing and certifying
a robot to perform tasks beyond
known requirements is extremely
costly and not yet mature enough to
replace humans.
Robots and automation streamlined
EVA tasks and complemented EVA,
resulting in a flexible and robust
capability for building, maintaining,
and repairing space structures and
conducting scientific research.
Designing the Spacesuit for
the Space Shuttle
Once NASA established a requirement
for EVA, engineers set out to design
and build the hardware necessary
to provide this capability. Foremost,
a spacesuit was required to allow a
crew member to venture outside the
pressurized cabin. The Gemini and
Apollo spacesuits were a great
starting point; however, many changes
were needed to create a workable
suit for the shuttle. The shuttle suit
had to be reusable, needed to fit many
different crew members, and was
required to last for many years
of repeated use. Fortunately, engineers
were able to take advantage of
advanced technology and lessons
learned from earlier programs to meet
these new requirements.
The cornerstone design requirement
for any spacesuit is to protect the crew
member from the space environment.
Suit Environment as Compared
to Space Environment
The target suit pressure was an
exercise in balancing competing
requirements. The minimum pressure
required to sustain human life is
21.4 kPa (3.1 psi) at 100% oxygen.
Higher suit pressure allows better
oxygenation and decreases the risk of
decompression sickness to the EVA
crew member. Lower suit pressure
increases crew member flexibility
and dexterity, thereby reducing crew
fatigue. This is similar to a water hose.
A hose full of water is difficult to
bend or twist, while an empty hose
is much easier to move around.
Higher suit pressures also require
more structural stiffening to maintain
suit integrity (just as a thicker
balloon is required to hold more air).
This further exacerbates the decrease
in flexibility and dexterity. The final
suit pressure selected was 29.6 kPa
(4.3 psi), which has proven to be a
reasonable compromise between these
competing constraints.
The next significant design
requirements came from the specific
mission applications: what EVA tasks
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were required, who would perform
them, and to what environmental
conditions the spacewalkers would be exposed.
Image: Contingency extravehicular activity:Astronaut Scott Parazynski, atop the Space Station Robotic Arm
and the Shuttle Robotic Arm extension, the Orbiter Boom Sensor System, approaches the International
Space Station solar arrays to repair torn sections during STS-120 (2009).
Suit Environment
23.44 kPa-27.57 kPa
(3.4-4.4 psi)
1 Pa
(1.45 x10
Managers decided that the
shuttle spacesuit would only be
required to perform in microgravity
and outside the shuttle cabin. This
customized requirement allowed
designers to optimize the spacesuit.
The biggest advantage of this approach
was that designers didn’t have to worry
as much about the mass of the suit.
Improving mobility was also a design
goal for the shuttle extravehicular
mobility unit (i.e., EVA suit). Designers
added features to make it more flexible
and allow the crew member greater
range of motion than with previous
suits. Bearings were included in the
shoulder, upper arm, and waist areas to
provide a useful range of mobility.
The incorporation of the waist bearing
enabled the EVA crew member to rotate.
Shuttle managers decided that, due to
the duration of the program, the suit
should also be reusable and able to fit
many different crew members. Women
were included as EVA crew members
for the first time, necessitating unique
accommodations and expanding the size
range required. The range had to cover
from the 5% American Female to the
95% American Male with variations in
shoulders, waist, arms, and legs.
A modular “tuxedo" approach was used
to address the multi-fit requirement.
Tuxedos use several different pieces,
which can be mixed and matched to
best fit an individual—one size of
pants can be paired with a different
size shirt, cummerbund, and shoes to
fit the individual. The EVA suit used a
modular design, thereby allowing
various pieces of different sizes
to achieve a reasonably good fit.
The design also incorporated a
custom-tailoring capability using
inserts, which allowed a reasonably
good fit with minimal modifications.
While the final design didn’t
accommodate the entire size range
of the Astronaut Corps, it was flexible
enough to allow for a wide variety of
crew members to perform spacewalks,
especially those crew members who had
the best physical attributes for work on
the International Space Station (ISS).
One notable exception to this modular
approach was the spacesuit gloves.
Imagine trying to assemble a bicycle
while wearing ski gloves that are too
large and are inflated like a balloon.
This is similar to attempting EVA tasks
like driving bolts and operating latches
while wearing an ill-fitting glove.
Laser-scanning technology was used
to provide a precise fit for glove
manufacture patterns. Eventually,
it became too expensive to maintain
a fully customized glove program.
Engineers were able to develop a set
of standard sizes with adjustments at
critical joints to allow good dexterity
at a much lower cost. In contrast, a
single helmet size was deemed
sufficient to fit the entire population
without compromising a crew
member’s ability to perform tasks.
The responsibility for meeting the
reuse requirement was borne primarily
by the Primary Life Support System, or
“backpack," which included equipment
within the suit garment to control
various life functions. The challenge
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for Primary Life Support System
designers was to provide a multiyear,
25-EVA system. This design challenge
resulted in many innovations over
previous programs.
Crew Member Size Variations and Ranges
One area that had to be improved to
reduce maintenance was body
temperature control. Both the Apollo
and the shuttle EVA suit used a
water cooling system with a series of
tubes that carried chilled water and
oxygen around the body to cool and
ventilate the crew member. The shuttle
EVA suit improved on the Apollo
design by removing the water tubes
from the body of the suit and putting
them in a separate garment—the
liquid cooling ventilation garment.
This garment was a formfitting,
stretchable undergarment (think long
johns) that circulated water and oxygen
supplied by the Primary Life Support
System through about 91 m (300 ft) of
flexible tubing. This component of the
suit was easily replaceable,
inexpensive, easy to manufacture, and
available in several sizes.
Materials changes in the Primary Life
Support System also helped to reduce
maintenance and refurbishment
requirements. Shuttle designers replaced
the tubing in the liquid cooling
ventilation garment with ethylene vinyl
acetate to reduce impurities carried by
the water into the system. The single
change that likely contributed the most
toward increasing component life and
reducing maintenance requirements
was the materials selection for the
Primary Life Support System water
tank bladder. The water tank bladder
expanded and contracted as the water
quantity changed during the EVA, and
functioned as a barrier between the
water and the oxygen system. Designers
replaced the molded silicon bladder
material with Flourel
, which leached
fewer and less-corrosive effluents
and was half as permeable to water,
resulting in dryer bladder cavities.
This meant less corrosion and cleaner
filters—all resulting in longer life and
less maintenance.
Using the Apollo EVA suit as the basis
for the shuttle EVA suit design saved
time and money. It also provided a
better chance for success by using
proven design. The changes that were
incorporated, such as using a modular
fit approach, including more robust
materials, and taking advantage of
advances in technology, helped meet
the challenges of the Space Shuttle
Program. These changes also resulted in
a spacesuit that allowed different types
of astronauts to perform more difficult
EVA tasks over a 30-year program with
very few significant problems.
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The Space Shuttle and Its Operations
Extravehicular Mobility Unit
February 8, 2007:Astronaut
Michael Lopez-Alegria,
International Space Station
Expedition 14 commander,
dons a liquid cooling
and ventilation garment
to be worn under the
extravehicular mobility unit.
Here, he is preparing for
the final of three sessions
of extravehicular activity (EVA)
in 9 days.
Extravehicular Activity
Mission Operations and
Training—All Dressed Up,
Time to Get to Work
If spacesuit designers were the outfitters
of spacewalks, flight controllers, who
also plan the EVAs and train the crew
members, were the choreographers.
Early in the program, EVAs resembled
a solo dancer performing a single
dance. As flights became more
complicated, the choreography became
more like a Broadway show—several
dancers performing individual
sequences, before coming together to
dance in concert. On Broadway, the
individual sequences have to be
choreographed so that dancers come
together at the right time. This
choreography is similar to developing
EVA timelines for a Hubble repair or an
ISS assembly mission. The tasks had to
be scheduled so that crew members
could work individually when only one
person was required for a task, but
allow them to come together when they
had a jointly executed task.
The goal was to make timelines as
efficient as possible, accomplish as
many tasks as possible, and avoid
one crew member waiting idle until
the other crew member finished a task.
The most significant contribution of
EVA operations during the shuttle era
was the development of this ability to
plan and train for a large number of
interdependent and challenging EVA
tasks during short periods of time.
Over time, the difficulty increased to
require interdependent spacewalks
within a flight and finally
interdependent spacewalks between
flights. This culminated in the
assembly and maintenance of the ISS,
which required the most challenging
series of EVAs to date.
The first shuttle EVAs were devoted
to testing the tools and suit equipment
that would be used in upcoming
spacewalks. After suit/airlock problems
scrubbed the first attempt, NASA
conducted the first EVA since 1974
during Space Transportation System
(STS)-6 on April 7,1983. This EVA
practiced some of the shuttle
contingency tasks and exercised the
suit and tools. The goal was to gain
confidence and experience with the new
EVA hardware. Then on STS-41B
(1984), the second EVA flight tested
some of the critical tools and techniques
that would be used on upcoming
spacewalks to retrieve and repair
satellites. One of the highlights was a
test of the manned maneuvering unit, a
jet pack designed to allow EVA crew
members to fly untethered, retrieve
satellites, and return with the satellite to
the payload bay for servicing. The
manned maneuvering unit allowed an
EVA crew member to perform precise
maneuvering around a target and dock
to a payload in need of servicing.
Shuttle Robotic Arm
Another highlight of the STS-41B
EVAs was the first demonstration of
an EVA crew member performing tasks
while positioned at the end of the
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Page 115
Shuttle Robotic Arm. This capability
was a major step in streamlining EVAs
to come as it allowed a crew member to
be moved from one worksite to another
quickly. This capability saved the effort
required to swap safety tethers during
translation and set up and adjust foot
restraints—sort of like being able to
roll a chair to move around an office
rather than having to switch from chair
to chair. It was also a first step in
evaluating how an EVA crew member
affected the hardware with which he or
she interacted.
The concern with riding the Shuttle
Robotic Arm was ensuring that the
EVA crew member did not damage the
robotic arm’s shoulder joint by
imparting forces and moments at the
end of the 15-m (50-ft) boom that didn’t
have much more mass than the crew
member. Another concern was the
motion that the Shuttle Robotic Arm
could experience under EVA
loads—similar to how a diving board
bends and flexes as a diver bounces on
its end. Too much motion could make it
too difficult to perform EVA tasks and
too time consuming to wait until the
motion damps out. Since the arm joints
were designed to slip before damage
could occur and crew members would
be able to sense a joint slip, the belief
was that the arm had adequate
safeguards to preclude damage.
Allowing a crew member to work from
the end of the arm required analysis of
the arm’s ability to withstand EVA crew
member forces. Since both the Shuttle
Robotic Arm and the crew member
were dynamic systems, the analysis
could be complicated; however, experts
agreed that any dynamic EVA load case
with a static Shuttle Robotic Arm would
be enveloped by the case of applying
brakes to the arm at its worst-case
runaway speed with a static EVA crew
member on the end. After this analysis
demonstrated that the Shuttle Robotic
Arm would not be damaged, EVA crew
members were permitted to work on it.
Working from the Shuttle Robotic
Arm became an important technique
for performing EVAs.
Astronaut Bruce McCandless on STS 41B (1984) in the nitrogen-propelled manned maneuvering unit,
completing an extravehicular activity. McCandless is floating without tethers attaching him to the shuttle.
Satellite Retrieval and Repair
Once these demonstrations and tests
of EVA capabilities were complete, the
EVA community was ready to tackle
satellite repairs. The first satellite to
be repaired was SolarMax, on STS-41C
(1984), 1 year after the first shuttle
EVA. Shortly after STS-41B landed,
NASA decided to add retrieval of
Palapa B2 and Westar VI to the shuttle
manifest, as the satellites had failed
shortly after their deploy on that
flight. While these early EVAs were
ultimately successful, they did not go
as originally planned.
NASA developed several new tools
to assist in the retrieval. For SolarMax,
the trunnion pin attachment device
was built to attach to the manned
maneuvering unit on one side and then
mate to the SolarMax satellite
on the other side to accommodate the
towing of SolarMax back to the
payload bay. Similarly, an apogee
kick motor capture device (known
as the “stinger") was built to attach to
the manned maneuvering unit to mate
with the Palapa B2 and Westar VI
satellites. An a-frame was also provided
to secure the Palapa B and Westar
satellites in the payload bay. All was
ready for the first operational EVAs;
however, engineers, flight controllers,
and managers would soon have their
first of many experiences
demonstrating the value of having a
crew member in the loop.
When George Nelson flew the manned
maneuvering unit to SolarMax during
STS-41C, the trunnion pin attachment
device jaws failed to close on the
service module docking pins. After
several attempts to mate, the action
induced a slow spin and eventually an
unpredictable tumble. SolarMax was
stabilized by ground commands from
Goddard Space Flight Center during
the crew sleep period. The next day,
Shuttle Robotic Arm operator Terry
Hart grappled and berthed the
satellite—a procedure that flight
controllers felt was too risky preflight.
EVA crew members executed a second
EVA to complete the planned repairs.
The STS-51A (1984) Palapa B2/Westar
VI retrieval mission was planned,
trained, and executed within 10 months
of the original satellite failures.
In the wake of the problem retrieving
SolarMax, flight planners decided
to develop backup plans in case the
crew had problems with the stinger
or a-frame. Joseph Allen flew the
manned maneuvering unit/stinger
and mated it to the Palapa B2 satellite;
however, Dale Gardner, working off
the robotic arm, was unable to attach
the a-frame device designed to assist
in handling the satellite. The crew
resorted to a backup plan, with
Gardner grasping the satellite then
slowly bringing it down and securing
it for return to Earth. On a subsequent
EVA, Gardner used the manned
maneuvering unit and stinger to
capture the Westar VI satellite, and the
crew used the Shuttle Robotic Arm to
maneuver it to the payload bay where
the EVA crew members secured it.
Although the manned maneuvering unit
was expected to be used extensively,
the Shuttle Robotic Arm proved more
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The Space Shuttle and Its Operations
efficient because it had fewer
maintenance costs and less launch mass.
The next major EVA missions were
STS-51D and STS-51I, both in 1985.
STS-51D launched and deployed
Syncom-IV/Leasat 3 satellite, which
failed to activate after deployment.
The STS-51D crew conducted the first
unscheduled shuttle EVA. The goal
was to install a device on the Shuttle
Robotic Arm that would be used to
attempt to flip a switch to activate the
satellite. Although the EVA was
successful, the satellite did not activate
and STS-51I was replanned to attempt
to repair the satellite. STS-51I was
executed within 4 months of STS-51D,
and two successful EVAs repaired it.
These early EVA flights were
significant because they established
many of the techniques that would be
used throughout the Space Shuttle
Program. They also helped fulfill the
promise that the shuttle was a viable
option for on-orbit repair of satellites.
EVA flight controllers, engineers, and
astronauts proved their ability to
respond to unexpected circumstances
and still accomplish mission objectives.
EVA team members learned many
things that would drive the program and
payload customers for the rest of the
program. They learned that moving
massive objects was not as difficult as
expected, and that working from the
Shuttle Robotic Arm was a stable way
of positioning an EVA crew member.
Over the next several years, EVA
operations were essentially a further
extension of the same processes and
operations developed and demonstrated
on these early flights.
During the early part of the Space
Shuttle Program, EVA was considered to
be a last resort because of inherent risk.
As the reliability and benefits of EVA
were better understood, however,
engineers began to have more
confidence in it. They accepted that EVA
could be employed as a backup means,
be used to make repairs, or provide a
way to save design complexity.
Engineers were able to take advantage
of the emerging EVA capability in the
design of shuttle payloads. Payload
designers could now include manual
EVA overrides on deployable systems
such as antennas and solar arrays instead
of adding costly automated overrides.
Spacecraft subsystems such as batteries
and scientific instruments were designed
to be repaired or replaced by EVA.
Hubble and the Compton Gamma Ray
Observatory were two notable science
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satellites that were able to use a
significant number of EVA-serviceable
components in their designs.
Astronauts George Nelson (right) and James van Hoften captured Solar Maximum Satellite in the
aft end of the Challenger’s cargo bay during STS-41C (1984). The purpose was to repair the satellite.
They used the mobile foot restraint and the robotic arm for moving about the satellite.
EVA flight controllers and engineers
began looking ahead to approaching
missions to build the ISS. To prepare
for this, program managers approved
a test program devoted to testing tools,
techniques, and hardware design
concepts for the ISS. In addition to
direct feedback to the tool and station
hardware designs, the EVA community
gained valuable experience in
planning, training, and conducting
more frequent EVAs than in the early
part of the program.
Hubble Repair
As NASA had proven the ability to
execute EVAs and accomplish some
remarkable tasks, demand for the
EVA resource increased sharply on
the agency. One of the most dramatic
and demanding EVA flights began
development shortly after the
deployment of Hubble in April 1990.
NASA’s reputation was in jeopardy
from the highly publicized Hubble
failure, and the scientific community
was sorely disappointed with the
capability of the telescope. Hubble was
designed with several servicing missions
planned, but the first mission—to
restore its optics to the expected
performance—took on greater
significance. EVA was the focal point
in recovery efforts. The mission took
nearly 3 years to plan, train, and develop
the necessary replacement parts.
The Hubble repair effort required
significant effort from most resources
in the EVA community. Designers from
Goddard Space Flight Center, Johnson
Space Center, Marshall Space Flight
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The Space Shuttle and Its Operations
Center, and the European Space
Agency delivered specialized tools and
replacement parts for the repair.
Approximately 150 new tools and
replacement parts were required for this
mission. Some of these tools and parts
were the most complicated ones
designed to date. Flight controllers
concentrated on planning and training
the unprecedented number of EVA
tasks to be performed—a number
that continued to grow until launch.
What started as a three-EVA mission
had grown to five by launch date.
The EVA timeliners faced serious
challenges in trying to accomplish so
many tasks, as precious EVA resources
were stretched to the limit.
New philosophies for managing EVA
timelines developed in response to
the growing task list. Until then, flight
controllers included extra time in
timelines to ensure all tasks would be
completed, and crews were only trained
in the tasks stated in those timelines.
For Hubble, timelines included less
flexibility and crews were trained on
extra tasks to make sure they could get
as much done as possible. With the next
servicing mission years away, there
was little to lose by training for extra
tasks. To better ensure the success of
the aggressive timelines, the crew
logged more than twice the training
time as on earlier flights.
When astronauts were sent to the
Hubble to perform its first repair,
engineers became concerned that the
crew members would put unacceptable
forces on the great observatory.
Engineers used several training
platforms to measure forces and
moments from many different crew
members to gain a representative set
of both normal and contingency EVA
tasks. These cases were used to
analyze Hubble for structural integrity
and to sensitize EVA crew members
to where and when they needed to be
careful to avoid damage.
EVA operators also initiated three key
processes that would prove very
valuable both for Hubble and later
for ISS. Operators and tool designers
requested that, during Hubble
assembly, all tools be checked for fit
against all Hubble components and
replacement parts. They also required
extensive photography of all Hubble
components and catalogued the
images for ready access to aid in
real-time troubleshooting. Finally,
engineers analyzed all the bolts that
would be actuated during the repair
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to provide predetermined responses to
problems operating bolts—data like
the maximum torque allowed across
the entire thermal range. Providing
these data and fit checks would become
a standard process for all future
EVA-serviceable hardware.
The first Hubble repair mission
was hugely successful, restoring
Hubble’s functionality and NASA’s
reputation. The mission also flushed
out many process changes that the
EVA community would need to adapt
as the shuttle prepared to undertake
assembly of the ISS. What had been a
near disaster for NASA when Hubble
was deployed turned out to be a
tremendous opportunity for engineers,
flight controllers, and mission
managers to exercise a station-like
EVA mission prior to when such
missions would become routine. This
mission helped demonstrate NASA’s
ability to execute a complex mission
while under tremendous pressure to
restore a vital international resource.
Fatigue—A Constant Concern During
Extravehicular Activity
Why are extravehicular activities (EVAs) so fatiguing if nothing has any weight in
Lack of suit flexibility and dexterity forces the wearer to exert more energy to perform
tasks. With the EVA glove, the fingers are fixed in a neutral position. Any motion that
changes the finger/hand position requires effort.
Lack of gravity removes leverage. Normally, torque used to turn a fastener is opposed
by a counter-torque that is passively generated by the weight of the user. In
weightlessness, a screwdriver user would spin aimlessly unless the user’s arm and
body were anchored to the worksite, or opposed the torque on the screwdriver with an
equal muscular force in the opposite direction. Tool use during EVAs is accomplished
by direct muscle opposition with the other arm, locking feet to the end of a robotic arm,
or rigidly attaching the suit waist to the worksite. EVA tasks that require many
hand/arm motions over several hours lead to significant forearm fatigue.
The most critical tasks—ingressing the airlock, shutting the hatch, and reconnecting
the suit umbilical line— occur at the end of an EVA. Airlocks are cramped and tasks
are difficult, especially when crew members are fatigued and overheated. Overheating
occurs because the cooling system must be turned off before an astronaut can enter
the airlock. The suit does not receive cooling until the airlock umbilical is connected.
The helmet visor can fog over at this point, making ingress even more difficult.
Along with crew training, medical doctors and the mission control team monitor
exertion level, heart rate, and oxygen usage. Communication between ground personnel
and astronauts is essential in preventing fatigue from having disastrous consequences.
STS-49 significantly impacted planning for future EVAs. It was the most aggressive
EVA flight planned, up to that point, with three EVAs scheduled. Engineers designed
a bar with a grapple fixture to capture Intelsat and berth it in the payload bay.
The data available on the satellite proved inadequate and it was modeled incorrectly
for ground simulations. After two EVA attempts to attach the capture bar, flight
controllers looked at other options.
The result was an unprecedented three-man EVA using space hardware to build
a platform for the crew members, allowing them to position themselves in a triangle
formation to capture the Intelsat by hand. This required an intense effort by ground
controllers to verify that the airlock could fit three crew members, since it was
only designed for two, and that there were sufficient resources to service all three.
Additional analyses looked at whether there were sufficient handholds to grasp
the satellite, that satellite temperatures would not exceed the glove temperature limits,
and that structural margins were sufficient. Practice runs on the ground convinced
ground operators that the operation was possible. The result was a successful capture
and repair during the longest EVA in the shuttle era.
Three Spacewalkers Capture Satellite
Astronauts Rick Hieb on the starboard payload bay mounted foot restraint work station,
Bruce Melnick with his back to the camera, and Tom Akers on the robotic arm mounted foot
restraint work station—on the backside of the Intelsat during STS-49 (1992).
Flight Training
Once NASA identified the tasks for a
shuttle mission, the crew had to be
trained to perform them. From past
programs, EVA instructors knew that
the most effective training for
microgravity took place under water,
where hardware and crew members
could be made neutrally buoyant. The
Weightless Environment Training
Facility— a swimming pool that
measured 23 m (75 ft) long, 15 m (50 ft)
wide, and 8 m (25 ft) deep—was the
primary location for EVA training early
in the Space Shuttle Program. The
Weightless Environment Training
Facility contained a full-size mock-up
of the shuttle payload bay with all
EVA interfaces represented. In the same
manner that scuba divers use buoyancy
compensation vests and weights, crew
members and their tools were
configured to be neutrally buoyant
through the use of air, foam inserts,
and weights. This enabled them
to float suspended at the worksite, thus
simulating a weightless environment.
Crew members trained an average of
10 hours in the Weightless Environment
Training Facility for every 1 hour of
planned on-orbit EVA. For complicated
flights, as with the first Hubble repair
mission, the training ratio was increased.
Later, EVA training moved to a new,
larger, and more updated water tank—
the Neutral Buoyancy Laboratory—to
accommodate training on the ISS.
A few limitations to the neutral
buoyancy training kept it from being a
perfect zero-gravity simulation. The
water drag made it less accurate for
simulating the movement of large
objects. And since they were still in a
gravity environment, crew members
had to maintain a “heads-up"
orientation most of the time to avoid
blood pooling in the head. So mock-ups
had to be built and oriented to allow
crew members to maintain this position.
The gravity environment of the water
tank also contributed to shoulder
injuries—a chronic issue, especially in
the latter part of the program. Starting
in the mid 1990s, several crew
members experienced shoulder injuries
during the course of their EVA training.
This was due to a design change
made at that time to the extravehicular
mobility unit shoulder joint. The
shoulder joint was optimized for
mobility, but designers noticed wear
in the fabric components of the
original joint. To avoid the risk of a
catastrophic suit depressurization,
NASA replaced the joint with a scye
bearing that was much less subject
to wear but limited to rotation in a
single plane, thus reducing the range
of motion. The scye bearing had to be
placed to provide good motion for
work and allow the wearer to don the
extravehicular mobility unit through
the waist ring (like putting on a shirt),
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which placed the arms straight up
alongside the head. Placement of the
shoulder joint was critical to a good fit,
but there were only a few sizes of
upper torsos for all crew members.
Astronaut John Grunsfeld, working from the end of the Shuttle Robotic Arm, installs replacement parts
on the Hubble Space Telescope during the final repair mission, STS-125 (2009).
Some crew members had reasonably
good fit with the new joint, but others
suffered awkward placement of the
ring, which exerted abnormal forces on
the shoulders. This was more a
problem during training, when stress
on the shoulder joint was increased
due to gravity.
On Earth, the upper arm is held fairly
close to the body during work
activities. The shoulder joint is least
prone to injury in this position under
gravity. In space, the natural position
of the arms is quite different, with
arms extended in front of the torso.
Shoulders were not significantly
stressed by EVA tasks performed in
microgravity. In ground training,
however, it was difficult to make
EVA tools and equipment completely
neutrally buoyant, so astronauts often
held heavy tools with their shoulders
fully extended for long periods. Rotator
cuff injuries, tendonitis, and other
shoulder injuries occurred despite best
efforts to prevent them. The problem
was never fully resolved during the
shuttle era, given the design limitations
of the EVA suit and the intensity of
training required for mission success.
The Precision Air Bearing Floor, also
used for EVA training, is a 6-m (20-ft)
by 9-m (30-ft), highly polished steel
floor that works on the same principles
as an air hockey table. Large mock-ups
of flight hardware were attached to steel
plates that had high-pressure air forced
through tubes that ran along the bottom
and sides. These formed a cushion under
the mock-up that allowed the mock-up
to move easily in the horizontal plane,
simulating zero-gravity mass handling.
Despite the single plane limitation of the
Precision Air Bearing Floor, when
combined with neutral buoyancy
training the two facilities provided
comprehensive and valuable training of
moving large objects.
Another training and engineering
platform was the zero-gravity aircraft.
This specially outfitted KC-135
(later replaced by a DC-9) aircraft was
able to fly a parabolic trajectory that
provided approximately 20 seconds of
microgravity on the downward slope,
similar to the brief periods experienced
on a roller coaster. This platform was
not limited by water drag as was the
Weightless Environment Training
Facility, or to single plane evaluations
as was the Precision Air Bearing Floor;
however, it was only effective for
short-duration tasks. Therefore, the
zero-gravity aircraft was only used for
short events that required a
high-fidelity platform.
Extravehicular Activity Tools
EVA tools and support equipment are
the Rodney Dangerfield of spacewalks.
When they work, they are virtually
unnoticed; however, when they fail to
live up to expectations, everyone knows.
Looking at the cost of what appear to be
simple tools, similar to what might be
found at the local hardware store, one
wonders why they cost so much and
don’t always work. The reality is that
EVA tool engineers had a formidable
task—to design tools that could operate,
in vacuum, in temperatures both colder
than the Arctic and as hot as an oven,
and be operable by someone wearing the
equivalent of several pairs of ski gloves,
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in vacuum, while weightless. These
factors combined to produce a set of
competing constraints that was difficult
to balance. When adding that the
complete space environment cannot be
simulated on the ground, the challenge
for building specialized tools that
perform in space became clear. Any
discussion of tools invariably involves
the reasons why they fail and the lessons
learned from those failures.
EVA tools are identified from two
sources: the required EVA tasks, and
engineering judgment on what general
tools might be useful for unplanned
events. Many of the initial tools were
fairly simple—tethers, foot restraints,
sockets, and wrenches. There were also
specialized tools devoted to closing and
latching the payload bay doors. Many
tools were commercial tools available
to the public but that were modified for
use in space. This was thought to be a
cost savings since they were designed
for many of the same functions. These
tools proved to be adequate for many
uses; however, detailed information
was often unavailable for commercial
tools and they did not generally hold up
to the temperature extremes of space.
Material impurities made them
unpredictable at cold temperatures and
lubricants became too runny at high
temperatures, causing failures.
Therefore, engineers moved toward
custom tools made with high-grade
materials that were reliable across the
full temperature range.
Trunnion pin attachment device,
a-frame, and capture bar problems on
the early satellite repair flights were
found to be primarily due to incorrect
information on the satellite interfaces.
Engineers determined that interfering
objects weren’t represented on
satellite design drawings. After these
events, engineers stepped up efforts
to better document EVA interfaces,
but it is never possible to fully
document the precise configuration
of any individual spacecraft.
Sometimes drawings include a range of
options for components for which
many units will be produced, and
that will be manufactured over a long
period of time. Designers must also
have the flexibility to perform quick
fixes to minor problems to maintain
launch schedules. The balance between
providing precise documentation
and allowing design and processing
flexibility will always be a
judgment call and will, at times,
result in problems.
Engineers modified tools as they
learned about the tools’performance in
space. White paint was originally used
as a thermal coating to keep tools from
getting too hot. Since tools bump
against objects and the paint tends to
chip, the paint did not hold up well
under normal EVA operations.
Engineers thus switched to an anodizing
process (similar to electroplating) to
make the tools more durable. Lubricants
were also a problem. Oil-based
lubricants would get too thick in cold
temperatures and inhibit moving parts
from operating. In warm environments,
the lubricants would become too thin.
Dry-film lubricants (primarily
, which acts like Teflon
frying pans) became the choice for
almost all EVA tools because they are
not vulnerable to temperature changes
in the space environment.
Astronaut Dafydd Williams, STS-118, representing the Canadian Space Agency, is wearing a training
version of the extravehicular mobility unit spacesuit while participating in an underwater simulation
of extravehicular activity in the Neutral Buoyancy Laboratory near Johnson Space Center.
Scuba-equipped divers are in the water to assist Williams in his rehearsal, intended to help
prepare him for work on the exterior of the International Space Station. Observe Williams holding
the Pistol Grip Tool in his left hand with his shoulder extended. This position causes shoulder pain
during training in neutral bouyancy.
Pistol Grip Tool
Some of the biggest problems with
tools came from attempting to expand
their use beyond the original purpose.
Sometimes new uses were very similar
to the original use, but the details were
different—like trying to use a hacksaw
to perform surgery. The saw is designed
for cutting, but the precision required is
extremely different. An example is the
computerized Pistol Grip Tool, which
was developed to actuate bolts while
providing fairly precise torque
information. This battery-operated tool
was similar to a powered screwdriver,
but had some sophisticated features
to allow flexibility in applying and
measuring different levels of torque or
angular rotation. The tool was designed
for Hubble, and the accuracy was more
than adequate for Hubble. When ISS
required a similar tool, the program
chose to purchase several units of the
Hubble power tool rather than design a
new tool specific to ISS requirements.
The standards for certification and
documentation were different for
Hubble. ISS had to reanalyze bolts,
provide for additional ground and
on-orbit processing of the Pistol Grip
Tool to meet ISS accuracy needs, and
provide additional units on orbit to
meet fault tolerance requirements and
maintain calibration.
The use of the Pistol Grip Tool for
ISS assembly also uncovered another
shortcoming with regard to using a tool
developed for a different spacecraft.
The Pistol Grip Tool was advertised as
having an accuracy of 10% around the
selected torque setting. This accuracy
was verified by setting the Pistol Grip
Tool in a fixed test stand on the ground
where it was held rigidly in place. This
was a valid characterization when used
on Hubble where EVA worksites were
designed to be easily accessible and
where the Pistol Grip Tool was used
directly on the bolts. It was relatively
easy for crew members to center the
tool and hold it steady on any bolt. ISS
worksites were not as elegant as Hubble
worksites, however, since ISS is such
a large vehicle and the Pistol Grip Tool
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often had to be used with socket
extensions and other attachments that
had inaccuracies of their own. Crew
members often had to hold the tool off
to the side with several attachments,
and the resulting side forces could
cause the torque measured by the tool
to be very different than the torque
actually applied. Unfortunately, ISS
bolts were designed and analyzed to the
advertised torque accuracy for Hubble
and they didn’t account for this
“man-in-the-loop" effect. The result
was a long test program to characterize
the accuracy of the Pistol Grip Tool
when used in representative ISS
worksites, followed by analysis of the
ISS bolts to this new accuracy.
To focus only on tool problems,
however, is a disservice. It’s like
winning the Super Bowl and only
talking about the fumbles. While use
of the Pistol Grip Tool caused some
problems as NASA learned about
its properties, it was still the most
sophisticated tool ever designed for
EVA. It provided a way to deliver
a variety of torque settings and
accurately measure the torque
delivered. Without this tool, the
assembly and maintenance of the
ISS would not have been possible.
Extravehicular Activity Tools
Astronaut Rick Mastracchio, STS-118 (2007), is shown using several extravehicular activity (EVA) tools while working on construction and maintenance
of the International Space Station during the shuttle mission’s third planned EVA activity.
Other Tools
NASA made other advancements in
tool development as well. Tools built
for previous programs were generally
simple tools required for collecting
geology samples. While there weren’t
many groundbreaking discoveries
in the tool development area, the
advances in tool function, storage,
and transport greatly improved EVA
efficiency during the course of the
program. The fact that Henry Ford
didn’t invent the internal combustion
engine doesn’t mean he didn’t make
tremendous contributions to the
automobile industry.
One area where tool engineers
expanded EVA capabilities was in
astronaut translation and worksite
restraint. Improvements were made to
the safety tether to include a more
reliable winding device and locking
crew hooks to prevent inadvertent
release. Engineers developed portable
foot restraints that could be moved
from one location to another, like
carrying a ladder from site to site.
The foot restraints consisted of a boot
plate to lock the crew member’s feet in
place and an adjustment knob to adjust
the orientation of the plate for better
positioning. The foot restraint had a
probe to plug into a socket at the
worksite. These foot restraints gave
crew members the stability to work in
an environment where unrestrained
crew members would have otherwise
been pushed away from the worksite
whenever they exerted force.
The portable foot restraints were an
excellent starting point, but they
required a fair amount of time to move.
They also became cumbersome when
crew members had to work in many
locations during a single EVA (as with
the ISS). Engineers developed tools that
could streamline the time to stabilize
at a new location. The Body Restraint
Tether is one of these tools. This tool
consists of a stack of balls connected
through its center by a cable with a
clamp on one end to attach to a handrail
and a bayonet probe on the other end
to attach to the spacesuit. Similar to
flexible shop lights, the Body Restraint
Tether can be bent and twisted to the
optimum position, then locked in that
position with a knob that tightens the
cable. The Body Restraint Tether is a
much quicker way for crew members to
secure themselves for lower-force tasks.
Another area where tool designers
made improvements was tool stowage
and transport. Crew members had to
string tools to their suits for transport
until designers developed sophisticated
tool bags and boxes that allowed crews
to carry a large number of tools and
use the tools efficiently at a worksite.
The Modular Mini Workstation—the
EVA tool belt—was developed to
attach to the extravehicular mobility
unit and has become invaluable to
conducting spacewalks. Specific tools
can be attached to the arms on the
workstation, thereby allowing ready
access to the most-used tools. Various
sizes of tool caddies and bags also
help to transport tools and EVA “trash"
(e.g., launch restraints).
Space Shuttle Program tool designers
expanded tool options to include
computer-operated electronics and
improved methods for crew restraint,
tool transport, and stowage. While
there were hiccups along the way, the
EVA tools and crew aids performed
admirably and expanded NASA’s
ability to perform more complicated
and increasingly congested EVAs.
Extravehicular Activity During
Construction of the
International Space Station
From 1981 through 1996, the Space
Shuttle Program accomplished 33
EVAs. From 1997 through 2010, the
program managed 126 EVAs devoted
primarily to ISS assembly and
maintenance, with several Hubble
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The Space Shuttle and Its Operations
Space Telescope repair missions also
included. Assembly and maintenance of
the ISS presented a series of challenges
for the program. EVA tools and suits
had to be turned around quickly and
flawlessly from one flight to the next.
Crew training had to be streamlined
since several flights would be training
at the same time and tasks were
interdependent from one flight to the
next. Plans for one flight, based on
previous flight results, could change
drastically just months (or weeks)
before launch. Sharing resources with
the International Space Station Program
was also new territory—the same tools,
spacesuits, and crew members would
serve both programs after the ISS
airlock was installed.
Extravehicular Loads for
Structural Requirements
The EVA loads development program,
first started for the Hubble servicing
missions, helped define the ISS
structural design requirements. ISS was
the first program to have extensive
EVA performed on a range of structural
interfaces. The load cases for Hubble
repair had to protect the telescope
for a short period of EVA operations
and for a finite number of well-known
EVA tasks.
ISS load cases had to have sufficient
margin for tasks that were only partially
defined at the time the requirements
were fixed, to protect for hundreds of
EVAs over the planned life of the ISS.
The size of ISS was also a factor.
An EVA task on one end of the truss
structure could be much more
damaging than the same task closer to
the center (just like bouncing on the
end of a diving board creates more
stress at the base than bouncing on the
base itself). EVA loads had to account
for intentional tasks (e.g., driving bolts)
and unintentional events (e.g., pushing
away from a rotating structure to avoid
collision). Engineers had to protect
for a reasonable set of EVA scenarios
without overly restricting the ISS
design to protect against simultaneous
low-probability events. This required
an iterative process that included
working with ISS structures experts
to zero in on the right requirements.
A considerable test program—using a
range of EVA crew members executing
a variety of tasks in different ground
venues—characterized the forces and
The Space Shuttle and Its Operations
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moments that an EVA crew member
could impart. The resulting cases were
used throughout the programs to
evaluate new tasks when the tasks
were needed. While the work was done
primarily for ISS, the loads that had
been developed were used extensively
in the post-Columbia EVA inspection
and repair development.
Medical Risks of Extravehicular
Activity—Decompression Sickness
One risk spacewalkers share with scuba divers is decompression sickness, or “the
bends." “The bends" name came from painful contortions of 19th-century underwater
caisson workers suffering from decompression sickness, which occurs when nitrogen
dissolves in blood and tissues while under pressure, and then expands when pressure
is lowered. Decompression sickness can occur when spacewalkers exit the pressurized
spacecraft into vacuum in a spacesuit
Decompression sickness can be prevented if nitrogen tissue concentrations are lowered
prior to reducing pressure. Breathing 100% oxygen causes nitrogen to migrate from
tissues into the bloodstream and lungs, exiting the body with exhaling.The first
shuttle-based extravehicular activities used a 4-hour in-suit oxygen prebreathe.This idle
time was inefficient and resulted in too long a crew day. New solutions were needed.
One solution was to lower shuttle cabin pressure from its nominal pressure of 101.2 kPa
(14.7 psi) to 70.3 kPa (10.2 psi) for at least 12 hours prior to the EVA. This reduced
cabin pressure protocol was efficient and effective, with only 40 minutes prebreathe.
Shuttle EVA crew members working International Space Station (ISS) construction
required a different approach. It is impossible to reduce large volume ISS pressure to
70.3 kPa (10.2 psi). To increase the rate of nitrogen release from tissues, crew
members exercised before EVA while breathing 100% oxygen. This worked, but it
added extra time to the packed EVA day and exhausted the crew. Planners used the
reduced cabin pressure protocol by isolating EVA crew members in the ISS airlock
the night before the EVA and lowering the pressure to 70.3 kPa (10.2 psi). This worked
well for the remainder of ISS EVAs, with no cases of decompression sickness
throughout the Space Shuttle Program.
Rescue From Inadvertent Release
NASA always provided for rescue of an
accidentally released EVA crew member
by maintaining enough fuel to fly to him
or her. Once ISS assembly began,
however, the Orbiter was docked during
EVAs and would not have been able to
detach and pursue an EVA crew member
in time. The ISS Program required a
self-rescue jet pack for use during ISS
EVAs. The Simplified Aid for EVA
Rescue was designed to meet this
requirement. Based on the manned
maneuvering unit design but greatly
simplified, the Simplified Aid for
EVA Rescue was a reliable, nitrogen-
propelled backpack that provided
limited capability for a crew member to
stop and fly back to the station or
Orbiter. It was successfully tested on
two shuttle flights when shuttle rescue
was still possible if something went
wrong. Fortunately, the Simplified Aid
for EVA Rescue never had to be
employed for crew rescue.
Extravehicular Activity Suit
Life Extension and Multiuse
Certification for International
Space Station Support
A significant advancement for the
EVA suit was the development of a
regenerable carbon dioxide removal
system. Prior to the ISS, NASA used
single-use lithium hydroxide canisters
for scrubbing carbon dioxide during an
EVA. Multiple EVAs were routine
during flights to the ISS. Providing a
regenerative alternative using silver
oxide produced significant savings in
launch weight and volume. These
canisters could be cleaned in the ISS
airlock regenerator, thereby allowing
the canisters to be left on orbit rather
than processed on the ground and
launched on the shuttle. This
capability saved approximately 164 kg
(361 pounds) up-mass per year.
Training Capability Enhancements
During the early shuttle missions, the
Weightless Environment Training
Facility and Precision Air Bearing
Facility were sufficient for crew
training. To prepare for space station
assembly, however, virtually every
mission would include training for
three to five EVAs—often with two
EVA teams—with training for three to
five flights in progress simultaneously.
To do this, NASA built the Neutral
Buoyancy Laboratory to accommodate
EVA training for both the Space
Shuttle and ISS Programs. At 62 m
(202 ft) long, 31 m (102 ft) wide,
and 12 m (40 ft) deep, the Neutral
Buoyancy Laboratory is more than
twice the size of the previous
facility, and it dramatically increased
neutral buoyancy training capability.
It also allowed two simultaneous
simulations to be conducted using
two separate control rooms to manage
each individual event.
Trainers took advantage of other
resources not originally designed for
EVA training. The Virtual Reality
Laboratory, which was designed
primarily to assist in robotic operations,
Page 126
became a regular EVA training venue.
This lab helped crew members train in
an environment that resembled the space
environment, from a crew member’s
viewpoint, by using payload and vehicle
engineering models working with
computer software to display a view that
changed as the crew member “moved"
around the space station.
The Space Shuttle and Its Operations
Astronaut Douglas Wheelock, STS-120 (2007), uses virtual reality hardware in the Space Vehicle
Mockup Facility at Johnson Space Center to rehearse some of his duties on the upcoming mission to
the International Space Station.
The Virtual Reality Laboratory also
provided mass simulation capability
by using a system of cables and pulleys
controlled by a computer as well as
special goggles to give the right visual
cues to the crew member, thus
allowing him or her to get a sense of
moving a large object in a microgravity
environment. Most of the models used
in the Virtual Reality Laboratory were
actually built for other engineering
facilities, so the data were readily
available and parameters could be
changed relatively quickly to account
for hardware or environment changes.
This gave the lab a distinct advantage
over other venues that could not
accommodate changes as quickly.
In addition to the new training venues,
changes in training philosophy were
required to support ISS assembly.
Typically, EVA crew training began at
least 1 year prior to the scheduled
launch. Therefore, crew members for
four to five missions would have to
train at the same time, and the tasks
required were completely dependent on
the previous flights’ accomplishments.
A hiccup in on-orbit operations could
cascade to all subsequent flights,
changing the tasks that were currently
in training. In addition, on-orbit ISS
failures often resulted in changes to the
tasks, as repair of those components
may have taken a higher priority.
To accommodate late changes, flight
controllers concentrated on training
individual tasks rather than timelines
early in the training schedule. They also
engaged in skills training—training the
crew on general skills required to
perform EVAs on the ISS rather than
individual tasks. Flight controllers still
developed timelines, but they held off
training the timelines until closer to
flight. Crews also trained on “get-
ahead" tasks—those tasks that did not
fit into the pre-mission timelines but
that could be added if time became
available. This flexibility provided time
to allow for real-time difficulties.
Extravehicular Activity
Participation in Return to
Flight After Space Shuttle
Columbia Accident
One other significant EVA
accomplishment was the development
of a repair capability for the Orbiter
Thermal Protection System after the
Space Shuttle Columbia accident in
2003. This posed a significant
challenge for EVA for several reasons.
The Thermal Protection System was a
complex design that was resistant to
high temperatures but was also
delicate. It was located in areas under
the fuselage that was inaccessible to
EVA crew members. The materials
used for repair were a challenge to
work with, even in an Earth
environment, since they did not adhere
well to the damage. Finally, the repair
had to be smooth since even very small
rough edges or large surface deviations
could cause turbulent airflow behind
the repair, like rocks disrupting flow
in a stream. Turbulent flow increased
surface heating dramatically, with
potentially disastrous results. These
challenges, along with the schedule
pressure to resume building and
resupplying the ISS, made Thermal
Protection System repair a top priority
for EVA for several years.
The process included using repair
materials that engineers originally
began developing at the beginning of
the program that now had to be refined
and certified for flight. Unique tools
and equipment, crew procedures, and
methods to ensure stabilizing the crew
member at the worksite were required
to apply the material. The tools
mixed the two-part silicone rubber
repair material but also kept it from
hardening until it was dispensed in
The Space Shuttle and Its Operations
Page 127
the damage area. The tools also
maintained the materials within a fairly
tight thermal range to keep them
viable. Engineers were able to avoid
the complexity of battery-powered
heaters by selecting materials and
coatings to passively control the
material temperature. The reinforced
carbon-carbon Thermal Protection
System (used on the wing leading
edge) repair required an additional set
of tools and techniques with similar
considerations regarding precision
application of sensitive materials.
Astronauts Robert Curbeam (foreground) and
Rex Walheim (background) simulate tile repair,
using materials and tools developed after the
Space Shuttle Columbia accident, on board the
zero-gravity training aircraft KC-135.
Getting a crew member to the worksite
proved to be a unique challenge. NASA
considered several options, including
using the Simplified Aid for EVA
Rescue with restraint aids attached by
adhesives. Repair developers
determined, however, that the best
option was to use the new robotic arm
extension boom provided for Orbiter
inspection. The main challenge to using
the extension boom was proving that it
was stable enough to conduct repairs,
and that the forces the EVA crew
member imparted on the boom would
not damage the boom or the arm.
These concerns were similar to those
involved with putting a crew member
on a robotic arm, but the “diving board"
was twice as long. The EVA loads
work performed earlier provided a
foundation for the process by which
EVA loads could be determined for
this situation; however, the process
had to be modified since the work
platform was much more flexible.
Previous investigations into EVA
loads usually involved a crew member
imparting loads into a fixed platform.
When the loads were continuously
applied to the boom/arm configuration,
they resulted in a large (about 1.2 m
[4 ft]) amount of sway as well as
structural concerns for the arm and
boom. Engineers knew that the
boom/arm configuration was more like
a diving board than a floor, meaning
that the boom would slip away as force
was applied, limiting the force a crew
member could put into the system.
Engineers developed a sophisticated
boom/arm simulator and used it on the
precision air bearing floor to measure
EVA loads. These tests provided the
data for analysis of the boom/arm
motion. The work culminated in a flight
test on STS-121 (2006), which
demonstrated that the boom/arm was
stable enough for repair and able to
withstand reasonable EVA motions
without damage.
Although the repair capability was
never used, both the shuttle and the
space station benefited from the repair
development effort. Engineers made
several minor repairs to the shuttle
Thermal Protection System that would
not have been possible without
demonstrating that the EVA crew
member could safely work near the
fragile system. The boom was also used
on the Space Station Robotic Arm to
conduct a successful repair of a
damaged station solar array wing that
was not reachable any other way.
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The Space Shuttle and Its Operations
Astronaut Piers Sellers, STS-121 (2006), wearing a training version of the extravehicular mobility unit,
participates in an extravehicular activity simulation while anchored on the end of the training version
of the Shuttle Robotic Arm in the Space Vehicle Mockup Facility at Johnson Space Center (JSC).
The arm has an attached 15-m (50-ft) boom used to reach underneath the Orbiter to access tiles.
Lora Bailey (right), manager, JSC Engineering Tile Repair, assisted Sellers.
The legacy of EVA during the Space
Shuttle Program consists of both the
actual work that was done and the
dramatic expansion of the EVA
capability. EVA was used to successfully
repair or restore significant national
resources to their full capacity, such
as Hubble, communications satellites,
and the Orbiter, and to construct the
ISS. EVA advanced from being a minor
capability used sparingly to becoming
a significant part of almost every
shuttle mission, with an increasing
list of tasks that EVA crew members
were able to perform. EVA tools and
support equipment provided more
capability than ever before, with
battery-powered and computer-
controlled tools being well understood
and highly reliable.
Much was learned about what an
EVA crew member needs to survive
and work in a harsh environment
as well as how an EVA crew member
affected his or her environment.
This tremendous expansion in EVA
capability will substantially benefit
the future exploration of the solar
system as engineers design vehicles
and missions knowing that EVA crew
members are able to do much more
than they could at the beginning of the
Space Shuttle Program.
The Space Shuttle and Its Operations
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April 1983: First Shuttle EVA (STS-6)
April 1984: Shuttle EVA Repair,
SolarMax (STS-41C)
November 1984: Palapa, Westar
Retrieval EVAs (STS-51A)
August 1985: First Shuttle
Unscheduled EVA, Least
Deploy (STS-51I)
April 1991: First EVA After Challenger
Accident, Compton Gamma Ray Observatory
Unscheduled EVA (STS-37)
May 1992: First Three-person EVA,
Intelsat Retrieval, and Repair EVAs (STS-49)
December 1993:
First Hubble Space Telescope
Repair Mission (STS-61)
December 1998:
First ISS Assembly
EVA (STS-88)
December 2000: First ISS Unscheduled
EVA, Solar Array Repair (STS-97)
July 2005: First EVA
After Columbia Accident,
First EVA on Orbiter
Belly to Remove
Protruding Gap Filler
February 1,
January 28, 1986:
Challenger Accident
October 2007: First EVA
from Orbiter Inspection
and Repair Boom to Repair
ISS Solar Array Blanket
Gemini — 9
Apollo — 19
Shuttle (including EVAs while at ISS) — 157
= Shuttle Stand-alone EVAs
= Shuttle EVAs while at ISS
Skylab — 10
ISS Stand-alone — 19
EVA = Extravehicular Activity
ISS = International Space Station
Major Extravehicular Activity Milestones
Since its inception, the International Space Station (ISS) was destined
to have a close relationship with the Space Shuttle. Conceived for very
different missions, the two spacecraft drew on each other’s strengths
and empowered each other to achieve more than either could alone.
The shuttle was the workhorse that could loft massive ISS elements into
space. It could then maneuver, manipulate, and support these pieces
with power, simple data monitoring, and temperature control until the
pieces could be assembled. The ISS gradually became the port of call
for the shuttles that served it.
The idea of building a space station dates back to Konstantin
Tsiolkovsky’s writings in 1883. A space station would be a small colony
in space where long-term research could be carried out. Visionaries in
many nations offered hundreds of design concepts over the next century
and a half, and a few simple outposts were built in the late 20th
century. The dreams of an enduring international space laboratory
coalesced when the shuttle made it a practical reality.
As a parent and child grow, so too did the relationship between the
shuttle and the ISS as the fledgling station grew out of its total
dependence on the shuttle to its role as a port of call. The ISS soon
became the dominant destination in the heavens, hosting vehicles
launched from many spaceports in four continents below, including
shuttles from the Florida coast.
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The Space Shuttle and Its Operations
Shuttle Builds
the International
Space Station
John Bacon
Melanie Saunders
Improvements to the Shuttle
Facilitated Assembly of
the International Space Station
Lee Norbraten
Financial Benefits of the
Space Shuttle for the United States
Melanie Saunders
Psychological Support—
Lessons from Shuttle-Mir
to International Space Station
Albert Holland
Creating the
International Space
Station Masterpiece—
in Well-planned
Building this miniature world in the
vacuum of space was to be the largest
engineering challenge in history. It was
made possible by the incomparable
capabilities of the winged fleet of
shuttles that brought and assembled the
pieces. The space station did not spring
into being “out of thin air." Rather, it
made use of progressively sophisticated
engineering and operations techniques
that were matured by the Space Shuttle
Program over the preceding 17 years.
This evolution began before the first
International Space Station (ISS)
assembly flight ever left the ground—
or even the drawing board.
Early Tests Form a Blueprint
NASA ran a series of tests beginning
with a deployable solar power wing
experiment on Discovery’s first flight
(Space Transportation System
[STS]-41D in 1984) to validate the
construction techniques that would be
used to build the ISS. On STS-41G
(1984), astronauts demonstrated the
safe capability for in-space resupply
of dangerous rocket propellants in a
payload bay apparatus. Astronauts
practiced extravehicular activity
(EVA) assembly techniques for
space-station-sized structures in
experiments aboard STS-61B (1985).
Several missions tested the performance
of large heat pipes in space. NASA
explored mobility aids and EVA
handling limits during STS-37 (1991).
In April 1984, STS-41C deployed
one of the most important and
comprehensive test programs—the
Long Duration Exposure Facility.
STS-32 retrieved the facility in January
1990, giving critical evidence of the
performance and degradation timeline of
materials in the low-Earth environment.
It was a treasure trove of data about
the micrometeoroid orbital debris
threat that the ISS would face. NASA’s
ability to launch such huge test fixtures
and to examine them back on Earth
after flight added immensely to the
engineers’understanding of the
technical refinements that would be
necessary for the massively complicated
ISS construction.
The next stage in the process would
involve an international connection and
the coming together of great scientific
and engineering minds.
Spacelab and Spacehab Flights
Skylab had been an interesting first
step in research but, after the Saturn V
production ceased, all US space station
designs would be limited to something
similar to the Orbiter’s 4.6-m (15-ft.)
payload bay diameter. The shuttle
had given the world ample ways
to evolve concepts of space station
modules, including a European Space
Agency-built Spacelab and an
American-built Spacehab. Each module
rode in the payload bay of the Orbiter.
These labs had the same outer diameter
as subsequent ISS modules.
The shuttle could provide the necessary
power, communications, cooling,
and life support to these laboratories.
Due to consumables limits, the shuttle
could only keep these labs in orbit
for a maximum of 2 weeks at a time.
Through the experience, however,
The Space Shuttle and Its Operations
Page 131
astronaut crews and ground engineers
discovered many issues of loading and
deploying real payloads, establishing
optimum work positions and locations,
clearances, cleanliness, mobility,
environmental issues, etc.
Space Shuttle Atlantis (STS-71) is docked with the Russian space station Mir (1995). At the time,
Atlantis and Mir had formed the largest spacecraft ever in orbit. Photo taken from Russian Soyuz vehicle
as shuttle begins undocking from Mir. Photo provided to NASA by Russian Federal Space Agency.
In 1994, the funding of the Space
Station Program passed the US Senate
by a single vote. Later that year,
Vice President Al Gore and Russian
Deputy Premier Viktor Chernomyrdin
signed the agreement that redefined
both countries’ space station programs.
That agreement also directed the US
Space Shuttle Program and the Russian
space program to immediately hone
the complex cooperative operations
required to build the new, larger-than-
dreamed space station. That operations
development effort would come through
a series of increasingly complex flights
of the shuttle to the existing Russian
space station Mir. George Abbey,
director of Johnson Space Center,
provided the leadership to ensure the
success of the Shuttle-Mir Program.
The Space Shuttle Program immediately
engaged Mir engineers and the Moscow
Control Center to begin joint operations
planning. Simultaneously, engineers
working on the former US-led Space
Station Program, called Freedom, went
to work with their counterparts who
had been designing and building Mir’s
successor—Mir-II. The new joint
program was christened the ISS
Program. Although NASA’s Space
Shuttle and ISS Programs emerged as
flagships for new, vigorous international
cooperation with the former Soviet
states, the immediate technical
challenges were formidable. The Space
Shuttle Program had to surmount many
of these challenges on shorter notice
than did the ISS Program.
Striving for Lofty Heights—
And Reaching Them
The biggest effect on the shuttle in
this merged program was the need to
reach a higher-inclination orbit that
could be accessed from Baikonur
Cosmodrome in Kazakhstan. At an
inclination of 51.6 degrees to the
equator, this new orbit for the ISS
would not take as much advantage of
the speed of the Earth’s rotation toward
the East as had originally been planned.
Instead of launching straight eastward
and achieving nearly 1,287 km/hour
(800 mph) from Earth’s rotation, the
shuttle now had to aim northward
to meet the vehicles launched from
Baikonur, achieving a benefit of only
901 km/hour (560 mph). The speed
difference meant that each shuttle could
carry substantially less mass to orbit for
the same maximum propellant load. The
Mir was already in such an orbit, so the
constraint was in place from the first
flight (STS-63 in 1995).
The next challenge of the 51.6-degree
orbit was a very narrow launch window
each day. In performing a rendezvous,
the shuttle needed to launch close to
the moment when the shuttle’s launch
pad was directly in the same flat plane
as the orbit of the target spacecraft.
Typically, there were only 5 minutes
when the shuttle could angle enough
to meet the Russian orbit.
Thus, in a cooperative program with
vehicles like Mir (and later the ISS), the
shuttle had only a tiny “window" each
day when it could launch. The brief
chance to beat any intermittent weather
meant that the launch teams and
Mission Control personnel often had to
wait days for acceptable weather during
the launch window. As a result of the
frequent launch slips, the Mir and ISS
control teams had to learn to pack days
with spontaneous work schedules for
the station crew on a single day’s
notice. Flexibility grew to become a
high art form in both programs.
Once the shuttle had launched into the
orbit plane of the Mir, it had to catch
up to the station before it could dock
and begin its mission at the outpost.
Normally, rendezvous and docking
would be completed 2 days after
launch, giving the shuttle time to make
up any differences between its location
around the orbit compared to where
the Mir or ISS was positioned at the
time of launch, as well as time for
ground operators to create the precise
maneuvering plan that could only be
perfected after the main engines cut
off 8½ minutes after launch.
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The Space Shuttle and Its Operations
Astronaut Shannon
Lucid floats in the
tunnel that connects
Atlantis’ (STS-79
[1996]) cabin to the
Spacehab double
module in the cargo
bay. Lucid and her
crew mates were
already separated
from the Russian
space station Mir
and were completing
chores before their
return to Earth.
Generally, the plan was to launch
then execute the lengthy rendezvous
preparation the day after launch.
The shuttle conducted the last stages of
the rendezvous and docking the next
morning so that a full day could be
devoted to assembly and cargo transfer.
This 2-day process maximized the
available work time aboard the station
before the shuttle consumables gave
out and the shuttle had to return to
Earth. The Mir and ISS teams worked
in the months preceding launch to
place their vehicles in the proper phase
in their respective orbits, such that this
2-day rendezvous was always possible.
Arriving at the rendezvous destination
was only the first step of the journey.
The shuttle still faced a formidable
hurdle: docking.
Docking to Mir
The American side had not conducted
a docking since the Apollo-Soyuz
Test Project of 1975. Fortunately,
Moscow’s Rocket and Space
Corporation Energia had further
developed the joint US-Russian
docking system originally created for
the Apollo-Soyuz Test Project in
anticipation of their own shuttle—the
Buran. Thus, the needed mechanism
was already installed on Mir.
The Russians had a docking mechanism
on their space station in a 51.6-degree
orbit, awaiting a shuttle. That
mechanism had a joint US-Russian
design heritage. The Americans had a
fleet of shuttles that needed to practice
servicing missions to a space station
in a 51.6-degree orbit. In a surprisingly
rapid turn of events, the US shuttle’s
basic design began to include a
sophisticated Russian mechanism. That
mechanism would remain a part of
most of the shuttle’s ensuing missions.
The mechanism—called an
Androgynous Peripheral Docking
System—became an integral part of
the shuttle’s future. It looked a little
like a three-petal artichoke when seen
from the side. US engineers were
challenged to work scores of details
and unanticipated challenges to
incorporate this exotic Russian
apparatus in the shuttle. The bolts that
held the Androgynous Peripheral
Docking System to the shuttle were
manufactured according to Système
International (SI, or metric) units
whereas all other shuttle hardware and
tools were English units. For the first
time, the US space program began to
create hardware and execute operations
in SI units—a practice that would
become the norm during the ISS era.
All connectors in the cabling were
of Russian origin and were unavailable
in the West. Electrical and data
interfaces had to be made somewhere.
The obvious solution would be to
put a US connector on the “free" end
of each cable that led to the docking
system. Each side could engineer
from there to its own standards and
hardware. Yet, even that simple plan
had obstacles. Whose wire would
be in the cable?
The Russian wires were designed to
be soldered into each pin and socket
while the US connector pins and sockets
were all crimped under pressure to their
wires in an exact fit. US wire had nickel
plating, Russian wire did not. US wire
could not be easily soldered into
Russian connector pins, and Russian
wire could not be reliably crimped into
American connector pins. Ultimately,
unplated Russian wire was chosen
and new techniques were certified to
assure a reliable crimped bond at each
American pin. Even though the
Russian system and the shuttle were
both designed to operate at 28 volts,
direct current (Vdc), differences in the
grounding strategy required extensive
discussions and work.
The Space Shuttle Atlantis (STS-71)
arrived at the Mir on June 29, 1995,
with the international boundary drawn
at the crimped interface to a Russian
wire in every US connector pin and
socket. US 28-Vdc power flowed
in every Russian Androgynous
Peripheral Docking System electronic
component, beginning a new era in
international cooperation. And this
happened just in time, as the US and
partners were poised to begin work on a
project of international proportions.
The Space Shuttle and Its Operations
Page 133
View of the Orbiter
Docking System that
allowed the shuttle
to attach to the
International Space
Station. This close-up
image shows the
payload bay closeout
on STS-130 (2010).
Construction of
the International
Space Station Begins
The International Space Station (ISS)
was a new kind of spacecraft that
would have been impossible without
the shuttle’s unique capabilities; it
was the first spacecraft designed to be
assembled in space from components
that could not sustain themselves
independently. The original 1984
International Freedom Space Station—
already well along in its manufacture—
was reconfigured to be the forward
section of the ISS.The Freedom
heritage was a crucial part of ISS plans,
as its in-space construction was a
major goal of the program. All previous
spacecraft had either been launched
intact from the ground (such as the
shuttle itself, Skylab, or the early
Salyut space stations) or made of fully
functional modules, each launched
intact from the ground and hooked
together in a cluster of otherwise
independent spacecraft.
The Mir and the late-era Salyut stations
were built from such self-contained
spacecraft linked together. Although
these Soviet stations were big, they were
somewhat like structures built primarily
out of the trucks that brought the pieces
and were not of a monolithic design.
Only about 15% of each module could
be dedicated to science. The rest of the
mass was composed of the infrastructure
needed to get the mass to the station.
The ISS would take the best features
of both the merged Mir-II and the
Freedom programs. It would use
proven Russian reliability in logistics,
propulsion, and basic life support and
enormous new capabilities in US power,
communications, life support, and
thermal control. The integrated Russian
modules helped to nurture the first few
structural elements of the US design
until the major US systems could be
carried to the station and activated.
These major US systems were made
possible by assembly techniques
enabled by the shuttle. The United
States could curtail expensive and
difficult projects in both propulsion and
crew rescue vehicles and stop worrying
about the problem of bootstrapping
their initial infrastructure, while the
Russians would be able to suspend
sophisticated-but-expensive efforts in
in-space construction techniques, power
systems, large gyroscopes, and robotics.
What emerged out of the union of
the Freedom and the Mir-II programs
was a space station vastly larger and
more robust (and more complicated)
than either side had envisioned.
The Pieces Begin to
Come Together
Although the ISS ultimately included
several necessary Mir-style modules
in the Russian segment, the other
partner elements from the United States,
Canada, European Space Agency, Italy,
and Japan were all designed with the
shuttle in mind. Each of these several
dozen components was to be supported
by the shuttle until each could be
supported by the ISS infrastructure.
These major elements typically
required power, thermal control, and
telemetry support from the shuttle.
Not one of these chunks could make
it to the ISS on its own, nor could any
be automatically assembled into the
ISS by itself. Thus, the shuttle enabled
a new era of unprecedented in situ
construction capability.
The Space Shuttle and Its Operations
This timeline represents the Space Shuttle
fleet’s delivery and attachment of several
major components to the International
Space Station. The specific components
are outlined in red in each photo.
Discovery (STS-92) delivered Z1 truss and
antenna (top) and one of the mating adapters.
Discovery (STS-96) brought US-built Unity
node, which attached to Russian-built Zarya.
Endeavour (STS-97) delivered new
solar array panels.
Because it grew with every mission,
the ISS presented new challenges to
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spacecraft engineering in general and
to the shuttle in particular. With each
new module, the spacecraft achieved
more mass, a new center of mass, new
antenna blockages, and some enhanced
or new capability and constraints.
During the assembly missions, the
shuttle and the ISS would each need
to reconfigure the guidance, navigation,
and control software to account for
several different configurations.
Each configuration needed to be
analyzed for free flight, initial docked
configuration with the arriving
element still in the Orbiter payload bay,
and final assembled and mated
configuration with the element in its
ISS position. There were usually one
or two intermediate configurations with
the element robotically held at some
distance between the cargo bay and its
final destination.
Consequently, crews had to update
a lot of software many times during
the mission. At each step, both the
ISS and the shuttle experienced a new
and previously unflown shape and
size of spacecraft.
Even the most passive cargos
involved active participation from the
shuttle. For example, in the extremely
cold conditions in space, most cargo
elements dramatically cooled
throughout the flight to the ISS. On
previous space station generations like
Skylab, Salyut, and Mir, such modules
needed heaters, a control system to
regulate them, and a power supply to
run them both. These functions all
passed to the shuttle, allowing an
optimized design of each ISS element.
Each mission, therefore, had a kind of
special countdown called the “Launch to
Activation" timeline. This unique
timeline for every cargo considered how
long it would take before such
temperature limits were reached.
Sometimes, the shuttle’s ground support
systems would heat the cargo in the
payload bay for hours before the launch
to gain some precious time in orbit.
Other times electric heaters were
provided to the cargo element at the
expense of shuttle power. At certain
times the shuttle would spend extra time
pointing the payload bay intentionally
toward the sun or the Earth during the
long rendezvous with the ISS. All these
activities led to a detailed planning
process for every flight that involved
thermal systems, attitude control,
robotics, and power.
The growth of the ISS did not come
at the push of a button or even solely
at the tip of a remote manipulator.
The assembly tasks in orbit involved a
combination of docking, berthing,
automatic capture, automatic
deployment, and good old-fashioned
elbow grease.
The shuttle had mastered the rendezvous
and docking issues in a high-inclination
orbit during the Mir Phase 1Program.
However, just getting there and getting
docked would not assemble the ISS.
Berthing and several other attachment
techniques were required.
Docking and Berthing
Docking and berthing are conceptually
similar methods of connecting a
pressurized tunnel between two
objects in space. The key differences
arise from the dynamic nature of the
docking process with potentially large
residual motions. In addition, under
docking there is a need to complete
the rigid structural mating quickly.
Such constraints are not imposed on
the slower, robotically controlled
berthing process.
Docking spacecraft need to mate
quickly so that attitude control can be
restored. Until the latches are secured,
The Space Shuttle and Its Operations
Page 135
there is very little structural strength at
the interface. Therefore, neither vehicle
attempts to fire any thrusters or exert
any control on “the stack." During
this period of free drift, there is no
telling which attitude can be expected.
The sun may consequently end up
pointing someplace difficult, such
as straight onto a radiator or edge-on
to the arrays. Thus, it pays to get
free-flying vehicles latched firmly
together as quickly as possible.
Atlantis (STS-98) brought Destiny laboratory.
Endeavour (STS-100) delivered and attached
Space Station Robotic Arm.
Atlantis (STS-104) delivered Quest airlock.
Due to the large thermal differences—
up to 400°C (752°F) between sun-facing
metal and deep-space-facing metal—
the thermal expansion of large metal
surfaces can quickly make the precise
alignment of structural mating hooks or
bolts problematic, unless the metal
surfaces have substantial time to reach
the same temperature. As noted, time is
of the essence. Hence, docking
mechanisms were forced to be small—
about the size of a manhole—due to
this need to rapidly align in the
presence of large thermal differences.
A docking interface is a sophisticated
mechanism that must accomplish many
difficult functions in rapid succession.
It must mechanically guide the
approaching spacecraft from its first
contact into a position where a “soft
capture" can be engaged. Soft capture
is somewhat akin to the moment when
a large ship first tosses its shore lines
to dock hands on the pier; it serves
only to keep the two vehicles lightly
connected while the next series of
functions is completed.
The mechanism must next damp out
leftover motions in X, Y, and Z axes
as well as damp rotational motions
in pitch, yaw, and roll while bringing
the two spacecraft into exact
alignment. This step was a particular
challenge for shuttle dockings. For the
first time in space history, the docking
mechanism was placed well away
from the vehicle’s center of gravity.
Sufficient torque had to be applied at
the interface to overcome the large
moment of the massive shuttle as it
damped its motion.
Next, the mechanism had to retract,
pulling the two spacecraft close enough
together that strong latches could
engage. The strong latches clamped
the two halves of the mechanism
together with enough force to compress
the seals. These latches held the
halves together against the huge force
of pressure that would try to push them
apart once the hatches were opened
inside. While this final cinching of
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The Space Shuttle and Its Operations
the latches happened, hundreds of
electrical connections and even a
few fluid transfer lines had to be
automatically and reliably connected.
Finally, there had to be a means to let
air into the space between the hatches,
and all the hardware that had been
filling the tunnel area had to be
removed before crew and cargo could
freely transit between the spacecraft.
Atlantis (STS-110) delivered S0 truss.
Atlantis (STS-112) brought S1 truss.
Endeavour (STS-113) delivered P1 truss.
Astronaut Peggy Whitson, Expedition 16 commander, works on Node 2 outfitting in the vestibule between
the Harmony node and Destiny laboratory of the International Space Station in November 2007.
Once docked, the shuttle and
station cooperated in a gentler way
called berthing, which led to much
larger passageways.
Berthing was done under the control
of a robotic arm. It was the preferred
method of assembling major modules
of the ISS. The mechanism halves
could be held close to each other
indefinitely to thermally equilibrate.
The control afforded by the robotic
positioning meant that the final
alignment and damping system in
berthing could be small, delicate, and
lightweight while the overall tunnel
could be large.
In the case of the ISS, the berthing
action only completed the hard
structural mating and sealing, unlike
docking, where all utilities were
simultaneously mated. All berthing
interface utilities were subsequently
hooked between the modules in the
pressurized tunnel (i.e., in a
“shirtsleeve" environment). During
extravehicular activities (EVAs),
astronauts connected major cable routes
only where necessary.
The interior cables and ducts connected
in a vestibule area inside the sealing
rings and around the hatchways.
This arrangement allowed thousands
of wires and ducts to course through
the shirtsleeve environment where they
could be easily accessed and maintained
while allowing the emergency closure
of any hatch in seconds. This hatch
closure could be done without the need
to clear or cut cables that connected the
modules. This “cut cable to survive"
situation occurred, at great peril to the
crew, for several major power cables
across a docking assembly during the
Mir Program.
Robotic Arms Provide
Necessary Reach
The assembly of the enormous ISS
required that large structures were
placed with high precision at great
distance from the shuttle’s payload
bay. As the Shuttle Robotic Arm
could only reach the length of the
payload bay, the ISS needed a
second-generation arm to position its
assembly segments and modules for
subsequent hooking, berthing, and/or
EVA bolt-downs.
Building upon the lessons learned
from the shuttle experience, the same
Canadian Space Agency and contractor
team created the larger, stiffer, and
more nimble Space Station Robotic
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Page 137
Arm, also known as the “big arm."
The agency and team created a 17-m
(56-ft) arm with seven joints. The
completely symmetric big arm was
also equipped with the unique ability to
use its end effector as a new base of
operations, walking end-over-end
around the ISS. Together with a mobile
transporter that could carry the new
arm with a multiton cargo element at
its end, the ISS robotics system worked
in synergy with the Shuttle Robotic
Arm to maneuver all cargos to their
final destinations.
The Unity connecting module is being put
into position to be mated to Endeavour’s
(STS-88 [1998]) docking system in the cargo
bay. This mating was the first link in a long chain
of events that led to the eventual deployment
of the connected Unity and Zarya modules.
Atlantis (STS-115) brought P3/P4 truss.
Discovery (STS-116) delivered P5 truss.
Atlantis (STS-117) delivered S3/S4 truss and
another pair of solar arrays.
The Space Station Robotic Arm could
grip nearly every type of grapple
fixture that the shuttle’s system could
handle, which enabled the astounding
combined robotic effort to repair a
torn outboard solar array on STS-120
(2007). On that memorable mission,
the Space Station Robotic Arm
“borrowed" the long Orbiter Boom
Sensor System, allowing an
unprecedented stretch of 50 m (165 ft)
down the truss and 27 m (90 ft) up to
reach the damage.
The Space Station Robotic Arm was
robust. Analysis showed that it was
capable of maneuvering a fully loaded
Orbiter to inspect its underside from
the ISS windows.
The robotic feats were amazing
indeed—and unbelievable at times—
yet successful construction of the
ISS depended on a collaboration of
human efforts, ingenuity, and a host
of other “nuts-and-bolts" mechanisms
and techniques.
Other Construction
The many EVA tests conducted by
shuttle crews in the 1980s inspired ISS
designers to create several simplifying
construction techniques for the
enormous complex. While crews
assembled the pressurized modules
using the Common Berthing
Mechanism, they had to assemble major
external structures using a simple large-
hook system called the Segment-to-
Segment Attachment System designed
for high strength and rapid alignment.
The Segment-to-Segment Attachment
System had many weight and
reliability enhancements resulting from
the lack of a need for a pressurized
seal. Such over-center hooks were
used in many places on the ISS exterior.
In major structural attachments
(especially between segments of the
100-m [328-ft] truss), the EVA crew
additionally drove mechanical bolts
between the segments. The crew then
attached major appendages and
payloads with a smaller mechanism
called a Common Attachment System.
Where appropriate, major systems were
automatically deployed or retracted
from platforms that were pre-integrated
to the delivered segment before launch.
The solar array wings were deployed by
swinging two half-blanket boxes open
from a “folded hinge" launch position
and then deploying a collapsible mast to
extend and finally to stiffen the blankets.
Like the Russian segment’s smaller
solar arrays, the tennis-court-sized
US thermal radiators deployed
automatically with an extending
scissor-like mechanism.
Meanwhile, the ISS design had to
accommodate the shuttle. It needed to
provide a zigzag tunnel mechanism
(the Pressurized Mating Adapter) to
optimize the clearance to remove
payloads from the bay after the shuttle
had docked. ISS needed to withstand
the shuttle’s thruster plumes for heating,
loads, contamination, and erosion. It
also had to provide the proper electrical
grounding path for shuttle electronics,
even though the ISS operated at a
significantly higher voltage.
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The Space Shuttle and Its Operations
Endeavour (STS-118) delivered the
S5 truss segment.
Discovery (STS-120) brought Harmony
Node 2 module.
Atlantis (STS-122) delivered European Space
Agency’s Columbus laboratory.
Further Improvements
Facilitate Collaboration
Between Shuttle and Station
The ISS needed a tiny light source that
could be seen at a distance of hundreds
of miles by the shuttle’s star tracker so
that rendezvous could be conducted.
The ISS was so huge that in sunlight it
would saturate the star trackers of the
shuttle, which were accustomed to
seeking vastly dimmer points of light.
Thus, the shuttle’s final rendezvous
with the ISS involved taking a relative
navigational “fix" on the ISS at night,
when the ISS’s small light bulb
approximated the light from a star.
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Endeavour (STS-123) brought Kibo Japanese
Experiment Module.
Endeavour (STS-123) also delivered Canadian-
built Special Purpose Dextrous Manipulator.
Discovery (STS-124) brought Pressurized
Module and robotic arm of Kibo Japanese
Experiment Module.
NASA had to improve Space Shuttle
capability before the International Space
Station (ISS) could be assembled. The
altitude and inclination of the ISS orbit
required greater lift capability by the
shuttle, and NASA made a concerted effort
to reduce the weight of the vehicle.
Engineers redesigned items such as crew
seats, storage racks, and thermal tiles.
The super lightweight External Tank
allowed the larger ISS segments to be
launched and assembled. Modifications
to the ascent flight path and the firing of
Orbital Maneuvering System engines
alongside the main engines during ascent
provided a more efficient use of propellant.
Launch reliability was another concern.
For the shuttle to rendezvous with the
ISS, the launch window was limited to a
period of about 5 minutes, when the launch
pad on the rotating Earth was aligned
with the ISS orbit. By rearranging the
prelaunch checklist to complete final tests
earlier and by adding planned hold periods
to resolve last-minute technical concerns,
the 5-minute launch window could be met
with high reliability.
Finally, physical interfaces between the
shuttle and the ISS needed to be
coordinated. NASA designed docking
fixtures and transfer bags to
accommodate the ISS. The agency
modified the rendezvous sequence to
prevent contamination of the ISS by
the shuttle thrusters. In addition, NASA
could transfer electrical power from the
ISS to the shuttle. This allowed the shuttle
to remain docked to the ISS for longer
periods, thus maximizing the work that
could be accomplished.
Improvements to the Shuttle Facilitated Assembly of the
International Space Station
Astronaut Carl Walz, Expedition 4 flight
engineer, stows a small transfer bag into a
larger cargo transfer bag while working in the
International Space Station Unity Node 1 during
joint docked operations with STS-111 (2002).
Other navigational aids were mounted
on the ISS as well. These aids included a
visual docking target that looked like a
branding iron of the letter “X" erected
vertically from a background plate in the
center of the hatch. Corner-cube glass
reflectors were provided to catch a laser
beam from the shuttle and redirect it
straight back to the shuttle. This
remarkable optical trick is used by
several alignment systems, including the
European Space Agency’s rendezvous
system that targeted other places on the
ISS. Thus, it was necessary to carefully
shield the different space partners’
reflectors from the beams of each
other’s spacecraft during their respective
final approaches to the ISS. Otherwise
a spacecraft might “lock on" to the
wrong place for its final approach.
As the station grew, it presented new
challenges to the shuttle’s decades-old
control methods. The enormous solar
arrays, larger than America’s Cup yacht
sails, caught the supersonic exhaust
from the shuttle’s attitude control jets
and threatened to either tear or
accelerate the station in some strange
angular motion. Thus, when the shuttle
was in the vicinity of or docked to the
ISS, a careful ballet of shuttle engine
selection and ISS array positions was
always necessary to keep the arrays
from being damaged.
This choreography grew progressively
more worrisome as the ISS added
more arrays. It was particularly
difficult during the last stages of
docking and in the first moments of
a shuttle’s departure, when it was
necessary to fire thrusters in the general
direction of the station.
There were also limits as to how soon
a shuttle might be allowed to fire an
engine after it had just fired one.
It was possible that the time between
each attitude correction pulse could
match the natural structural frequency
of that configuration of the ISS. This
pulsing could amplify oscillations to
the point where the ISS might break if
protection systems were not in place.
Of course, this frequency changed each
time the ISS configuration changed.
Thus, the shuttle was always loading
new “dead bands" in its control logic to
prevent it from accidentally exciting
one of these large station modes.
In all, the performances of all the
“players" in this unfolding drama were
stellar. The complexity of challenges
required flexibility and tenacity.
The shuttle not only played the lead
in the process, it also served in
supporting roles throughout the entire
construction process.
The Roles of
the Space Shuttle
Program Throughout
Logistics Support—
Expendable Supplies
The shuttle was a workhorse that
brought vast quantities of hardware
and supplies to the International Space
Station (ISS). Consumables and spare
parts were a key part of that manifest,
with whole shuttle missions dedicated
to resupply. These missions were called
“Utilization and Logistics Flights."
All missions—even the assembly
flights—contributed to the return of
trash, experiment samples, completed
experiment apparatus, and other items.
Unique Capacity to
Return Hardware and
Scientific Samples
Perhaps the greatest shuttle contribution
to ISS logistics was its unsurpassed
capability to return key systems and
components to Earth. Although most of
the ISS worked perfectly from the start,
the shuttle’s ability to bring components
and systems back was essential in
rapidly advancing NASA’s engineering
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The Space Shuttle and Its Operations
knowledge in many key areas. This
allowed ground engineers to thoroughly
diagnose, repair, and sometimes
redesign the very heart of the ISS.
The shuttle upmass was a highly
valued financial commodity within
the ISS Program, but its recoverable
down-mass capability was unique,
hotly pursued, and the crown jewel
at the negotiation table. As it became
clear that more and more partners
would have the capability to deliver
cargo to the ISS but only NASA
retained any significant ability to
return cargo intact to Earth, the cachet
only increased. Even the Russian
partner—with its own robust resupply
capabilities and long, proud history
in human spaceflight—was seduced
by the lure of recoverable down mass
and agreed that its value was twice
that of 1 kg (2.2 pounds) of upmass.
NASA negotiators had a particular
fondness for this one capability that
the Russians seemed to value higher
than their own capabilities.
Discovery (STS-119) brought
S6 truss segment.
Endeavour (STS-127) delivered Kibo Japanese
Experiment Module Exposed Facility and
Experiment Logistics Module Exposed Section.
Endeavour (STS-130) delivered Node 3
with Cupola.
Symbiotic Relationship
Between Shuttle and the
International Space Station
Over time the two programs developed
several symbiotic logistic relationships.
The ISS was eager to take the
pure-water by-product of the shuttle’s
fuel cell power generators because
water is the heaviest and most vital
consumable of the life support system.
The invention of the Station to Shuttle
Power Transfer System allowed the
shuttle to draw power from the ISS
solar arrays, thereby conserving its own
oxygen and hydrogen supplies and
extending its stay in orbit.
The ISS maintained the shared
contingency supply of lithium hydroxide
canisters for carbon dioxide scrubbing
by both programs, allowing more
cargo to ride up with the shuttle on
every launch in place of such canisters.
The shuttle would even carry precious
ice cream and frozen treats for the ISS
crews in freezers needed for the return
of frozen medical samples.
The shuttle would periodically reboost
the ISS, as needed, using any leftover
propellant that had not been required for
contingencies.The shuttle introduced air
into the cabin and transferred
compressed oxygen and nitrogen to the
ISS tanks as its unused reserves allowed.
ISS crews even encouraged shuttle
crews to use their toilet so that the
precious water could be later recaptured
from the wastes for oxygen generation.
The ISS kept stockpiles of food, water,
and essential consumables that were
collectively sufficient to keep a guest
crew of seven aboard for an additional
30 days—long enough for a rescue
shuttle to be prepared and launched to
the ISS in the event a shuttle already at
the station could not safely reenter the
Earth’s atmosphere.
Extravehicular Activity by
Space Shuttle Crews
Even with all of the automated and
robotic assembly, a large and complex
vehicle such as the ISS requires an
enormous amount of manual
assembly—much of it “hands on"—
in the harsh environment of space.
Spacewalking crews assembled the
ISS in well over 100 extravehicular
activity (EVA) sessions, usually lasting
5 hours or more. EVA is tiring, time
consuming, and more dangerous than
routine cabin flight. It is also
exhilarating to all involved. Despite
the dangers of EVA, the main role for
shuttle in the last decade of flight was
to assemble the ISS. Therefore, EVAs
came to dominate the shuttle’s activities
during most station visits.
These shuttle crew members were
trained extensively for their respective
missions. NASA scripted the shuttle
flights to achieve ambitious assembly
objectives, sometimes requiring four
EVAs in rapid succession. The level of
proficiency required for such long,
complicated tasks was not in keeping
with the ISS training template.
Therefore, the shuttle crews handled
most of the burden. They trained until
mere days before launch for the
marathon sessions that began shortly
after docking.
Shuttle Airlock
Between assembly flights STS-97
(2000) and STS-104 (2001)—the first
time a crew was already aboard the ISS
to host a shuttle and the flight when
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The Space Shuttle and Its Operations
the ISS Quest airlock was activated,
respectively—the shuttle crews were
hampered by a short-term geometry
problem. The shuttle’s airlock was part
of the docking tunnel that held the two
spacecraft together, so in that period the
shuttle crew had to be on its side of
the hatch during all such EVAs in case
of an emergency departure. Further,
the preparations for EVA required that
the crew spend many hours at reduced
pressure, which was accomplished
prior to Quest by dropping the entire
shuttle cabin pressure. Since the ISS
was designed to operate at sea-level
atmosphere, it was necessary to keep
the shuttle and station separated by
closed hatches while EVAs were in
preparation or process. This hampered
the transfer of internal cargos and other
intravehicular activities.
Clayton Anderson
Astronaut on STS-117 (2007) and STS-131 (2010).
Spent 152 days on the International Space Station
before returning on STS-120 (2007).
“Life was good on board the International Space Station (ISS).
Time typically passed quickly, with much to do each day.
This was especially true when an ISS crew prepared to
welcome ‘interplanetary guests’…or more specifically, a
Space Shuttle crew! During my 5-month ISS expedition, our
‘visitors from another planet’ included STS-117 (my ride up),
STS-118, and STS-120 (my ride down).
“While awaiting a shuttle’s arrival, ISS crews prepared in
many ways. We may have said goodbye to ‘trash-collecting
tugs’ or welcomed replacement ships (Russian Progress,
European Space Agency Automated Transfer Vehicle, and the
Japanese Aerospace Exploration Agency H-II Transfer Vehicle)
fully stocked with supplies. Just as depicted in the movies, life
on the ISS became a little bit like Grand Central Station!
“Prepping for a shuttle crew was not trivial. It was
reminiscent of work you might do when guests are coming
to your home! ISS crews ‘pre-packed…,’ gathering loads
of equipment and supplies no longer needed that must be
disposed of or may be returned to Earth…like cleaning
house! This wasn’t just ‘trash disposal’—sending a vehicle
to its final rendezvous with the fiery friction of Earth’s
atmosphere. Equipment could be returned on shuttle to
enable refurbishment for later use or analyzed by experts
to figure out how it performed in the harsh environment of
outer space. It was also paramount to help shuttle crews by
prepping their spacewalking suits and arranging the special
tools and equipment that they would need. This allowed
them to ‘jump right in’ and start their work immediately
after crawling through the ISS hatch! Shuttle flights were
all about cramming much work into a short timeframe!
The station crew did their part to help them get there!
“The integration of shuttle and ISS crews was like forming
an ‘All-Star’ baseball team. In this combined form, wonderful
things happened. At the moment hatches swung open,
a complicated, zero-gravity dance began in earnest and a
well-oiled machine emerged from the talents of all on board
executing mission priorities flawlessly!
“Shuttle departure was a significant event. I missed
my STS-117 and STS-118 colleagues as soon as they left!
I wanted them to stay there with me, flying through the
station, moving cargo to and fro, knocking stuff from the
walls! The docked time was grand…we accomplished so
much. To build onto the ISS, fly the robotic arm, perform
spacewalks, and transfer huge amounts of cargo and supplies,
we had to work together, all while having a wonderfully good
time. We talked, we laughed, we worked, we played, and we
thoroughly enjoyed each other’s company. That is what
camaraderie and ‘crew’ was all about. I truly hated to see
them go. But then they were home…safe and sound with
their feet firmly on the ground. For that, I was always grateful,
yet I must admit that when a crew departed I began to
think more of the things that I did not have in orbit, some
354 km (220 miles) above the ground.
“Life was good on board the ISS…I cherished every single
minute of my time in that fantastic place."
Astronaut Clayton Anderson, Expedition 15 flight engineer, smiles
for a photo while floating in the Unity node of the International
Space Station.
International Space Station Airlock
On assembly flight 7A (STS-104), the
addition of the joint airlock Quest
allowed shuttle crews to work in
continuous intravehicular conditions
while their EVA members worked
outside. Even in this airlock, shuttle
crews continued to conduct the majority
of ISS EVAs and shuttles provided the
majority of the gases for this work.
Docked shuttles could replenish the
small volume of unrecoverable air that
could not be compressed from the
airlock. The prebreathe procedure of
pure oxygen to the EVA crew also was
supported by shuttle reserves through a
system called Recharge Oxygen Orifice
Bypass Assembly. This system was
delivered on STS-114 (2005) and used
for the first time on STS-121(2006).
Finally, the shuttle routinely
repressurized the ISS high-pressure
oxygen and nitrogen tanks and/or the
cabin itself prior to leaving. The ISS
rarely saw net losses in its on-board
supplies, even in the midst of such
intense operations. Fewer ISS
consumables were thus used whenever
a shuttle could support the EVAs.
The Shuttle as Crew Transport
Although many crews came and went
aboard the Russian Soyuz rescue craft,
the shuttle assisted the ISS crew
rotations at the station during early
flights. This shuttle-based rotation of
ISS crew had several significant
drawbacks, however, and the practice
was abandoned in later flights.
Launch and re-entry suits needed to be
shared or, worse, spared on the Orbiter
middeck to fit the arriving and departing
crew member. Different Russian suits
were used in the Soyuz rescue craft, so
those suits had to make the manifest
somewhere. Further, a special custom-fit
seat liner was necessary to allow each
crew member to safely ride the Soyuz
to an emergency landing. This seat liner
had to be ferried to the ISS with each
new crew member who might use the
Soyuz as a lifeboat. Thus, a lot of
duplication occurred in the hardware
required for shuttle-delivered crews.
Shuttle Launch Delays
As a shuttle experienced periodic
delays of weeks or even months from
its original flight plan, it was necessary
to replan the activities of ISS crews
who were expecting a different crew
makeup. Down-going crews sometimes
found their “tours of duty" had
been extended. Arriving crews found
their tours of duty shortened and their
work schedule compressed. As the
construction evolved, the shuttle carried
a smaller fraction of the ISS crew.
The Space Shuttle and Its Operations
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Left photo: Astronauts John Olivas (top) and Christer Fuglesang pose for a photo in the STS-128 (2009) Space Shuttle airlock.
Right photo: Astronauts Garrett Reisman (left) and Michael Good—STS-132 (2010)—pose for a photo between two extravehicular mobility units in the
International Space Station (ISS) Quest airlock. By comparison, the Quest airlock is much larger and thus allows enough space for the prebreathe needed
to prevent decompression sickness to occur in the airlock, isolated from the ISS.
Whenever NASA scrubbed a launch
attempt for even 1 day, the scrub
disrupted the near-term plan on board
the ISS. Imagine the shuttle point of
view in such a scrub scenario: “We’ll
try again tomorrow and still run exactly
the script we know."
Now imagine the ISS point of view in
the same scenario: “We’ve been
planning to take 12 days off from our
routine to host seven visitors at our
home. These visitors are coming to
rehab our place with a major new
home addition. We need to wrap up
any routine life we’ve established and
conclude our special projects and
then rearrange our storage to let these
seven folks move back and forth, start
packing things for the visitors to take
with them, and reconfigure our wiring
and plumbing to be ready for them to
do their work. Then we must sleep
shift to be ready for them at the strange
hour of the day that orbital mechanics
says that they can dock. Two days
before they are to get here, they tell us
that they’re not coming on that day.
For the next week or so of attempts,
they will be able to tell us only at the
moment of launch that they will in fact
be arriving 2 days later."
At that juncture, did ISS crew members
sleep shift? Did they shut down the
payloads and rewire for the shuttle’s
arrival? Did they try to cram in one
more day of experiments while they
waited? Did they pack anything at all?
This was the type of dilemma that
crews and planners faced leading
up to every launch. Therefore, a few
weeks before each launch, ISS
planners polled the technical teams
for the tasks that could be put on the
“slip schedule," such as small tasks
or day-long procedures that could
be slotted into the plan on very short
notice. Some of these tasks were
complex, like tearing down a piece
of exercise equipment and then
refurbishing it; not the sort of thing
they could just dive in and do without
reviewing the procedures.
Shuttle Helps Build
International Partnerships
Partnering With the Russians
It is hard to overstate the homogenizing
but draconian effect that the shuttle
initially had on all the original
international partners who had joined
the Freedom Space Station Program or
who took part in other cooperative
spaceflights and payloads. The shuttle
was the only planned way to get their
hardware and astronauts to orbit.
Thus, “international integration" was
decidedly one-sided as NASA engineers
and operators worked with existing
partners to meet shuttle standards.
Such standards included detailed
specifications for launch loads
capability, electrical grounding and
power quality, radio wave emission
and susceptibility limits, materials
outgassing limits, flammability limits,
toxicity, mold resistance, surface
temperature limits, and tens of
thousands of other shuttle standards.
The Japanese H-II Transfer Vehicle
and European Space Agency’s (ESA’s)
Automated Transfer Vehicle were
not expected until nearly a decade
after shuttle began assembly of the
ISS. Neither could carry crews, so all
astronauts, cargoes, supplies, and
structures had to play by shuttle’s rules.
Then the Earth Moved
The Russians and Americans started
working together with a series of
shuttle visits to the Russian space
station Mir. There was more at stake
than technical standards.
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The Space Shuttle and Its Operations
Michael Foale, PhD
Astronaut on STS-45 (1992),
STS-56 (1993), STS-63
(1995), STS-84 (1997), and
STS-103 (1999).
Spent 145 days on Russian
space station Mir before
returning on STS-86 (1997).
Spent 194 days as
commander of Expedition 8
on the International Space
Station (2003-2004).
“When we look back 50 years to this time, we won't remember the experiments
that were performed, we won't remember the assembly that was done.
What we will know was that countries came together to do the first joint
international project, and we will know that that was the seed that started us
off to the moon and Mars."
On board the International Space Station,Astronaut Michael
Foale fills a water microbiology bag for in-flight analysis.
Leadership roles were more equitably distributed
and cooperation took on a new
diplomatic flavor in a true partnership.
In the era following the fall of the
Berlin Wall (1989) along with the end
of Soviet communism and the Soviet
Union itself, the US government seized
the possibility of achieving two key
goals—the seeding of a healthy
economy in Russia through valuable
western contracts, and the prevention
of the spread of the large and
now-saleable missile and weapon
technology to unstable governments
from the expansive former Soviet
military-industrial complex that was
particularly cash-strapped. The creation
of a joint ISS was a huge step toward
each of those goals, while providing
the former Freedom program with an
additional logistics and crew transport
path. It also provided the Russian
government a huge boost in prestige as
a senior partner in the new worldwide
partnership. That critical role made
Russian integration the dominant
focus of shuttle integration, and it
subsequently changed the entire US
perspective on international spaceflight.
Two existing spacecraft were about to
meet, and engineers in each country had
to satisfy each other that it was
safe for each vehicle to do so. Neither
side could be compelled to simply
accept the other’s entire system of
standards and practices. The two sides
certainly could not retool their
programs, even if they had wanted to
accept new standards. Tens of thousands
of agreements and compromises had to
be reached, and quickly. Only where
absolutely necessary did either side
have to retest its hardware to a new
standard. During the Mir Phase 1
Program, the shuttle encountered the
new realities of cooperative spaceflight
and set about the task of defining new
ways of doing business.
It was difficult but necessary to
compare every standard for mutual
acceptability. In most cases, the intent of
the constraint was instantly compatible
and the implementation was close
enough to sidestep an argument. The
standards compatibility team worked
tirelessly for 4 years to allow cross
certification. This was an entirely new
experience for the Americans.
As difficult as the technical
requirements were, an even more
fundamental issue existed in the
documents themselves. The Russians
had never published in English and,
similarly, the United States had not
published in Cyrillic, the alphabet of
the Russian language. Chaos might
immediately ensue in the computers
that tracked each program’s data.
Communicating With Multiple Alphabets
The space programs needed something
robust to handle multiple alphabets,
and they needed it soon. In other words,
the programs needed more bytes for
every character. Thus, the programs
became early adopters of the system
that several Asian nations had been
forced to adopt as a national standard
to capture the 6,000+ characters of
kanji—pictograms of Chinese origin
used in modern Japanese writing.
The Universal Multiple-Octet Coded
Character Set—known in one
ubiquitous word processing
environment as “Unicode" and
standardized worldwide as International
Standards Organization (ISO) Standard
10646—allowed all character sets of
the world to be represented in all
desired fonts. Computers in space
agencies around the world quickly
modified to accept the new character
ISO Standard, and instantly the cosmos
was accessible to the languages of all
nations. This also allowed a common
lexicon for acronyms.
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Financial Benefits of the Space Shuttle
for the United States
Just as the International Space Station (ISS) international agreements called for each
partner to meet its obligations to share in common operations costs such as propellant
delivery and reboost, the agreements also required each partner to bear the cost of
delivering its contributions and payloads to orbit and encouraged use of barter. As a
result, the European Space Agency (ESA) and the Japan Aerospace Exploration Agency
(JAXA) took on the obligation to build some of the modules within NASA’s contribution
as payment in kind for the launch of their laboratories. In shifting the cost of
development and spares for these modules to the international partners—and without
taking on any additional financial obligation for the launch of the partner labs—NASA
was able to provide much-needed fiscal relief to its capped “build-to-cost"
development budget in the post-redesign years. The Columbus laboratory took a
dedicated shuttle flight to launch. In return, ESA built Nodes 2 and 3 and some
research equipment. The Japanese Experiment Module that included Kibo would take
2.3 shuttle flights to place in orbit. JAXA paid this bill by building the Centrifuge
Accommodation Module (later deleted from the program by NASA after the Vision for
Space Exploration refocused research priorities on the ISS) and by providing other
payload equipment and a non-ISS launch.
National Perceptions
The Russians had a highly “industrial"
approach to operating a spacecraft.
Their cultural view of a space station
appeared to most Americans to be
more as a facility for science, not
necessarily a scientific wonder unto
itself. Although the crews continued
to be revered as Russian national
heroes, the spacecraft on which they
flew never achieved the kind of iconic
status that the Space Shuttle or the
ISS achieved in the United States.
By contrast, the American public was
more likely to know the name of the
particular one of four Orbiters flying
the current mission than the names
of the crew members aboard.
Although the Soyuz was reliable, it was
a small capsule—so small that it limited
the size of crews that could use it as a
lifeboat. All crew members required
long stays in Russia to train for Soyuz
and many Russian life-critical systems.
This was in addition to their US
training and short training stays with
the other partners. Overall, however,
the benefits of having this alternate
crew and supply launch capability were
abundantly clear in the wake of the
Columbia (STS-107) accident in 2003.
The Russians launched a Progress
supply ship to the ISS within 24 hours
and then launched an international crew
of Ed Lu and Yuri Malenchenko exactly
10 weeks after the accident. Both crew
members wore the STS-107 patch on
their suits in tribute to their fallen
comrades. After the Columbia accident,
the Russians launched 14 straight
uncrewed and crewed missions to
continue the world’s uninterrupted
human presence in space before the
shuttle returned to share in those duties.
Other Faces on
the International Stage
All the while, teams of specialists from
the Canadian Space Agency, Japanese
Space Exploration Agency, Italian
Space Agency, and ESA each worked
side-by-side with NASA shuttle and
station specialists at Kennedy Space
Center to prepare their modules for
launch aboard the shuttle. Shortly after
the delivery of the ESA Columbus
laboratory on STS-122 (2008) and the
Japanese Kibo laboratory on STS-124
(2008), each agency’s newly developed
visiting cargo vehicle joined the fleet.
The Europeans had elected to dock
their Automated Transfer Vehicle at the
Russian end of the station, whereas
the Japanese elected to berth their
vehicle—the H-II Transfer Vehicle—
to the station. The manipulation of
the H-II Transfer Vehicle and its
berthing to the ISS were similar to
the experience of all previous modules
that the shuttle had brought to the space
station. The big change was that the
vehicle had to be grabbed in free flight
by the station arm—a trick previously
only performed by the much more
nimble shuttle arm. NASA ISS
engineers and Japanese specialists
worked for years with shuttle robotics
veterans to develop this exotic
procedure for the far-more-sluggish ISS.
The experience paid off. In the grapple
of H-II Transfer Vehicle 1 in 2009,
and following the techniques first
pioneered by shuttle, the free-flight
grapple and berth emerged as the
attachment technique for the upcoming
fleet of commercial space transports
expected at the ISS.
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The Space Shuttle and Its Operations
“For Shuttle ESA was a junior partner, but now
with ISS we are equal partners"
—Volker Damann, ESA
Russian Federal Space Agency
European Space Agency
Canadian Space Agency
National Aeronautics and
Space Administration
Japan Aerospace Exploration Agency
From Shuttle-Mir
to International
Space Station—
Crews Face Additional
The Shock of Long-Duration
NASA had very little experience with
the realities of long-term flight. Since
the shuttle’s inception, the shuttle team
had been accustomed to planning
single-purpose missions with tight
scripts and well-identified manifests.
The shuttle went through time-critical
stages of ascent and re-entry into Earth’s
atmosphere on every flight, with limited
life-support resources aboard. Thus, the
overall shuttle culture was that every
second was crucial and every step was
potentially catastrophic. It took a while
for NASA to become comfortable with
the concept of “time to criticality,"
where systems aboard a large station did
not necessarily have to have immediate
consequences. These systems often
didn’t even have immediate failure
recovery requirements.
For instance, the carbon dioxide
scrubber or the oxygen generator could
be off for quite some time before the
vast station atmosphere had to be
adjusted. What mattered most was
flexibility in the manifest to get needed
parts up to space. The shuttle’s self-
contained missions with well-defined
manifests were not the best experience
base for this pipeline of supplies.
New Realities
Russia patiently guided shuttle and then
International Space Station (ISS) teams
through these new realities. The
delivery of parts, while always urgent,
was handled in stride and with great
flexibility. Their flexible manifesting
practices were a shock to veteran
shuttle planners. The Soyuz and the
uncrewed Progress were particularly
reliable at getting off the pad on time,
come rain, sleet, wind, or clouds. This
reliability came from the Russians’
simple capsule-on-a-missile heritage,
and allowed mission planners to
pinpoint spacecraft arrivals and
departures months in advance. The
cargos aboard the Progress, however,
were tweaked up until the final day as
dictated by the needs at the destination,
just as overnight packages are
identified and manifested until the
final minutes aboard a regularly
scheduled airline flight. In contrast,
the shuttle’s heritage was one of
well-defined cargos with launch dates
that were weather-dependent.
Prior to the Mir experience, the shuttle
engineers had maintained stringent
manifesting deadlines to keep the
weight and balance of the Orbiter
within tight constraints and to handle
the complex task of verifying the
structural loads during ascent for the
unique mix of items bolted to structures
that would press against their fittings in
the payload bay in nonlinear ways.
Nonlinearity was a difficult side effect
of the way that heavy loads had to be
distributed. The load that each part of
the structure would see was completely
dependent on the history of the loads it
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had seen recently. If a load was moved,
removed, or added to any of the cargo,
it could invalidate the analysis.
This was an acceptable way of
operating a stand-alone mission until
one faced a manifesting crisis such as
the loss of an oxygen generator or a
critical computer on the space station.
Shortly after starting the Mir Phase I
Program, the pressures of emergency
manifest demands led to a new
suite of tools and capabilities for
the shuttle team. Engineers developed
new computer codes and modeling
techniques to rapidly reconfigure
the models of where the masses
were attached and to show how the
shuttle would respond as it shook
during launch. Items as heavy as
250 kg (551 pounds) were swapped
out in the cargo within months or
weeks of launch. In some cases, items
as large as suitcases were swapped out
within hours of launch.
During the ISS Program, Space
Transportation System (STS)-124
carried critical toilet repair parts that had
been hand-couriered from Russia during
the 3-day countdown. The parts had to
go in about the right place and weigh
about the same amount as parts removed
from the manifest for the safety analysis
to be valid. Nevertheless, on fewer than
72 hours’notice, the parts made it from
Moscow to space aboard the shuttle.
Unheeded Skylab Lesson: Take a Break!
The US planners might be applauded for their optimism and ambition in scheduling
large workloads for the crew, but they had missed the lesson of a previous generation
of planners resulting from the “Skylab Rebellion." This rebellion occurred when the
Skylab-4 crew members suddenly took a day off in response to persistent over-tasking
by the ground planners during their 83-day mission. From “Challenges of Space
Exploration" by Marsha Freeman:
“At the end of their sixth week aboard Skylab, the third crew went on
strike. Commander Carr, science pilot Edward Gibson, and Pogue stopped
working, and spent the day doing what they wanted to do. As have almost
all astronauts before and after them, they took the most pleasure and
relaxation from looking out the windows at the Earth, taking a lot of
photographs. Gibson monitored the changing activity of the Sun, which had
also been a favourite pastime of the crew."
It is both ironic and instructive to note that during the so-called “rebellion," the crew
members actually filled their day off with intellectually stimulating activities that were
also of scientific use. Although these activities of choice were not the ones originally
scripted, they were a form of mental relaxation for these exhausted but dedicated
scientists. The crew members of Skylab-4 just needed some time to call their own.
The continuous nature of space station
operations led to significant
philosophical changes in NASA’s
training and operations. A major facet
of the training adjustment had to do
with the emotional nature of
long-duration activities. Short-duration
shuttle missions could draw on
the astronauts’ emotional “surge"
capability to conduct operations for
extended hours, sleep shift as
necessary, and develop proficiency
in tightly scripted procedures. It was
like asking performers to polish a
15-day performance, with up to 2 years
of training to perfect the show.
Astronauts spent about 45 days of
training for each day on orbit. They
would have time to rest before and after
the mission, with short breaks, if any,
included in their timeline.
That would be a lot of training for a
half-year ISS expedition. The crew
would have to train for over 22 years
under that model. One way to put the
training issue into perspective is to
realize that most ISS expedition
members expect to remain about 185
days in orbit. This experience, per crew
member, is equal to the combined Earth
orbital, lunar orbital, and trans-lunar
experience accumulated by all US
astronauts until the moment the United
States headed to the moon on Apollo 11.
Thus, each such Mir (or ISS) crew
member matched the accumulated total
crew experience of the first 9 years of
the US space effort.
With initially three and eventually six
long-duration astronauts permanently
aboard the ISS, the US experience in
space grew at a rapidly expanding rate.
By the middle of ISS Expedition 5
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(2002), only 2½ years into the ISS
occupation, the ISS expedition crews
had worked in orbit longer than
crews had worked aboard all other
US-operated space missions in the
previous 42 years, including the
shuttle’s 100+ flights. Clearly, the
training model had to change.
Shuttle operations were like a
decathlon of back-to-back sporting
events—all intense, all difficult, and
all in a short period of time—while
space station operations were more
like an ongoing trek of many months,
requiring a different kind of stamina.
ISS used the “surge" of specialized
training by the shuttle crews to execute
most of the specialized extravehicular
activities (EVAs) to assemble the
vehicle. The station crew training
schedule focused on the necessary
critical-but-general skills to deal
with general trekking as well as
a few planned specific tasks for that
expedition. Only rarely did ISS crews
take on major assembly tasks in the
period between shuttle visits (known
in the ISS Program as “the stage").
Another key in the mission scripting
and training problem was to consider
when and how that “surge capability"
could be requested of the ISS crew.
That all depended on how long that
crew would be expected to work at the
increased pace, and how much rest the
crew members had had before that
period. Nobody can keep competing in
decathlons day after day; however, such
periodic surges were needed and would
need to be compensated by periodic
holidays and recovery days.
Humans need a balanced workday with
padding in the schedule to freshen up
after sleep, read the morning news, eat,
exercise, sit back with a good movie,
write letters, create, and generally
relax before sleep, which should be a
minimum of 8 hours per night for
long-term health. The Russians had
warned eager US mission planners that
their expectations of 10 hours of
productive work from every crew
member every day, 6 days per week
was unrealistic. A 5-day workweek
with 8-hour days (with breaks), plus
periodic holidays, was more like it.
The Space Shuttle and Its Operations
Posing in Node 2 during STS-127 (2009)/Expedition 20 Joint Operations: Front row (left to right):
Expedition 20 Flight Engineer Robert Thirsk (Canadian Space Agency); STS-127 Commander Mark
Polansky; Expedition 19/20 Commander Gennady Padalka (Cosmonaut); and STS-127 Mission
Specialist David Wolf. Second row (left to right):Astronaut Koichi Wakata (Japanese Aerospace
Exploration Agency); Expedition 19/20 Flight Engineer Michael Barratt; STS-127 Mission Specialist
Julie Payette (Canadian Space Agency); STS-127 Pilot Douglas Hurley; and STS-127 Mission Specialist
Thomas Marshburn. Back row (left to right): Expedition 20/21 Flight Engineer Roman Romanenko
(Cosmonaut); STS-127 Mission Specialist Christopher Cassidy; Expedition 20 Flight Engineer Timothy
Kopra; and Expedition 20 Flight Engineer Frank De Winne (European Space Agency).
Different Attitude and Planning
of Timelines
The ISS plan eventually settled in
exactly as the veteran Russian planners
had recommended. That is not to say
that ISS astronauts took all the time
made available to them for purely
personal downtime. These are some of
the galaxy’s most motivated people, so
several “unofficial" ways evolved to let
them contribute to the program beyond
the scripted activities, but only on a
voluntary basis.
The ISS planners ultimately learned
one productivity technique from the
Russians and the crews invented
another. At the Russians’ suggestion,
the ground added a “job jar" of tasks
with no particular deadline. These tasks
could occupy the crew’s idle hours.
If a job-jar item had grown too stale
and needed doing soon, it found its way
onto the short-term plan. Otherwise,
the job jar (in reality, a computer file
of good “things to do") was a useful
means to keep the crew busy during
off-duty time. The crew was inventive,
even adding new education programs
to such times.
Tasks vs. Skills
Generally, training for both the ground
and the crew was skills oriented for
station operations and task oriented for
shuttle operations. The trainers grew
to rely on electronic file transfers of
intricate procedures, especially videos,
to provide specialized training on
demand. These were played on on-board
notebook computers for the station
crew but occasionally for the shuttle
crews as well. This training was useful
in executing large tasks on the slip
schedule, unscheduled maintenance, or
on contingency EVAs scheduled well
after the crew arrival on station.
Station crews worked on generic
EVA skills, component replacement
techniques, maintenance tasks, and
general robotic manipulation skills.
Many systems-maintenance skills
needed to be mastered for such a
huge “built environment." The station
systems needed to closely replicate
a natural existence on Earth, including
air and water revitalization, waste
management, thermal and power
control, exercise, communications
and computers, and general cleaning
and organizing.
The 363-metric-ton (400-ton) ISS
had a lot of hardware in need of routine
inspection and maintenance that, in
shuttle experience, was the job of
ground technicians—not astronauts.
These systems were the core focus of
ISS training. There were multiple
languages and cultures to consider
(most crew members were multilingual)
and usually two types of everything:
two oxygen generators; two condensate
collectors; two carbon dioxide
separators; multiple water systems;
different computer architectures; and
even different food rations. Each ISS
crew member then trained extensively
for the specific payloads that would be
active during his or her stay on orbit.
Scores of payloads needed operators
and human subjects. Thus, it took about
3 years to prepare an astronaut for
long-duration flight.
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Page 149
Major Missions of
Shuttle Support
By May 2010, the shuttle had flown
34 missions to the International Space
Station (ISS). Although no human
space mission can be called “routine,"
some missions demonstrated
particular strengths of the shuttle and
her crews—sometimes in unplanned
heroics. A few such missions are
highlighted to illustrate the high
drama and extraordinary achievement
of the shuttle’s 12-year construction
of the ISS.
STS-88—The First Big Step
The shuttle encountered the full suite
of what would soon be routine
challenges during its first ISS assembly
mission—Space Transportation System
(STS)-88 (1998). The narrow launch
window required a launch in the middle
of the night. This required a huge sleep
shift. The cargo element (Node 1 with
two of the three pressurized mating
adapters already attached) needed to be
warmed in the payload bay for hours
before launch to survive until the
heaters could be activated after the first
extravehicular activity (EVA). The
rendezvous was conducted with the
cargo already erected in a 12-m (39-ft)
tower above the Orbiter docking
mechanism. This substantially changed
the flight characteristics of the shuttle
and blocked large sections of the sky as
seen from the Orbiter’s high-gain
television antenna.
The rendezvous required the robotic
capture of the Russian-American
bridge module: the FGB named
Zarya. (Zarya is Russian for “sunrise."
“FGB" is a Russian acronym for the
generic class of spacecraft—a
Functional Cargo Block—on which the
Zarya had been slightly customized.)
Due to the required separation of the
robotic capture of the FGB from the
shuttle’s cargo element, Space Shuttle
Endeavour needed to extend its arm
nearly to its limit just to reach the
free-flying FGB. Even so, the arm
could only touch Zarya’s forward end.
In the shuttle’s first assembly act of
the ISS Program, Astronaut Nancy
Currie grappled the heaviest object
the Shuttle Robotic Arm had ever
manipulated, farther off-center than
any object had ever been manipulated.
Because of the blocked view of the
payload bay (obstructed by Node 1 and
the Pressurized Mating Adapter 2), she
completed this grapple based on
television cues alone—another first.
After the FGB was positioned above
the top of the cargo stack, the shuttle
used new software to accommodate the
large oscillations that resulted from the
massive off-center object as it moved.
Next, the shuttle crew reconnected the
Androgynous Peripheral Docking
System control box to a second
Androgynous Peripheral Docking
System cable set and prepared to drive
the interface between the Pressurized
Mating Adapter 1 and the FGB. Finally,
Currie limped the manipulator arm
while Commander Robert Cabana
engaged Endeavour’s thrusters and flew
the Androgynous Peripheral Docking
System halves together. The successful
mating was followed by a series of
three EVAs to link the US and Russian
systems together and to deploy two
stuck Russian antennas.
This process required continuous
operation from two control centers, as
had been practiced during the Mir
Phase I Program.
Before departing, the shuttle (with yet
another altitude-control software
configuration) provided a substantial
reboost to the fledgling ISS. At a press
conference prior to the STS-88 mission,
Lead Flight Director Robert Castle
called it “…the most difficult mission
the shuttle has ever had to fly, and the
simplest of all the missions it will have
to do in assembling the ISS." He was
correct. The shuttle began an ambitious
series of firsts, expanding its capabilities
with nearly every assembly mission.
STS-97—First US Solar Arrays
STS-97 launched in November 2000
with one of its heaviest cargos: the
massive P6 structural truss; three
radiators; and two record-setting
solar array wings. At nearly 300 m
(3,229 ft²) each, the solar wings could
each generate more power than any
spacecraft in history had ever used.
After docking in an unusual-but-
necessary approach corridor that
arrived straight up from below the ISS,
Endeavour and her US/Canadian crew
gingerly placed the enormous mast high
above the Orbiter and seated it with the
first use of the Segment-to-Segment
Attachment System.
The first solar wing began to
automatically deploy as scheduled,
just as the new massive P6 structure
began to block the communications
path to the Tracking and Data Relay
Satellites. The software dutifully
switched off the video broadcast so as
not to beam high-intensity television
signals into the structure. When the
video resumed, ground controllers saw
a disturbing “traveling wave" that
violently shook the thin wing as it
unfolded. Later, it was determined that
lubricants intended to assist in
deployment instead added enough
surface tension to act as a delicate
adhesive. This subtle sticking kept the
fanfolds together in irregular clumps
rather than letting them gracefully
unfold out of the storage box. The
clumps would be carried outward in
the blanket and then would release
rapidly when tension built up near the
final tensioning of the array.
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Robert Cabana
Colonel, US Marine Corps (retired).
Pilot on STS-41 (1990) and STS-53 (1992).
Commander on STS-65 (1994) and STS-88 (1998).
Reflections on
the International Space Station
“Of all the missions that have been accomplished by the Space
Shuttle, the assembly of the International Space Station (ISS)
certainly has to rank as one of the most challenging and
successful. Without the Space Shuttle, the ISS would not be
what it is today. It is truly a phenomenal accomplishment,
especially considering the engineering challenge of assembling
hardware from all parts of the world, on orbit, for the first time
and having it work. Additionally, the success is truly amazing
when one factors in the complexity of the cultural differences
between the European Space Agency and all its partners,
Canada, Japan, Russia, and the United States.
“When the Russian Functional Cargo Block, also known
as Zarya, which means sunrise in Russian, launched on
November 20, 1998, it paved the way for the launch of Space
Shuttle Endeavour carrying the US Node 1, Unity. The first
assembly mission had slipped almost a year, but in December
1998, we were ready to go. Our first launch attempt on
December 3 was scrubbed after counting down to 18 seconds
due to technical issues with the Auxiliary Power Units.
It was a textbook count for the second attempt on the night
of December 4, and Endeavour performed flawlessly.
“Nancy Currie carefully lifted Unity out of the bay and we
berthed it to Endeavour’s docking system with a quick pulse
of our engines once it was properly positioned. With that
task complete, we set off for the rendezvous and capture of
Zarya. The handling qualities of the Orbiter during rendezvous
and proximity operations are superb and amazingly precise.
Once stabilized and over a Russian ground site, we got
the ‘go’ for grapple, and Nancy did a great job on the arm
capturing Zarya and berthing it to Unity high above the Orbiter.
This was the start of the ISS, and it was the shuttle, with its
unique capabilities, that made it all possible.
“On December 10, Sergei Krikalev and I entered the ISS for
the first time. What a unique and rewarding experience it was
to enter this new outpost side by side. It was a very special 2
days that we spent working inside this fledgling space station.
“We worked and talked late into the night about what this
small cornerstone would become and what it meant for
international cooperation and the future of exploration
beyond our home planet. I made the first entry into the
log of the ISS that night, and the whole crew signed it the
next day. It is an evening I’ll never forget.
“Since that
flight, the ISS
has grown
to reach its full
potential as
a world-class
facility and an
proving ground
for operations
in space. As it passes overhead, it is the brightest star in the
early evening and morning skies and is a symbol of the
preeminent and unparalleled capabilities of the Space Shuttle."
Robert Cabana (left), mission commander, and Sergei Krikalev,
Russian Space Agency mission specialist, helped install equipment
aboard the Russian-built Zarya module and the US-built Unity module.
The deployment was stopped and a
bigger problem became apparent.
The wave motion had dislodged the
key tensioning cable from its pulley
system and the array could not be fully
tensioned. The scenario was somewhat
like a huge circus tent partially erected
on its poles, with none of the ropes
pulled tight enough to stretch the tent
into a strong structure. The whole thing
was in danger of collapsing, particularly
if the shuttle fired jets to leave. Rocket
plumes would certainly collapse the
massive wings. If Endeavour left
without tensioning the array, another
shuttle might never be able to arrive
unless the array was jettisoned.
Within hours, several astronauts and
engineers flew to Boeing Rocketdyne
in Canoga Park, California, to
develop special new EVA techniques
with the spare solar wing. A set of
tools and at least three alternate plans
were conceived in Houston,Texas, and
in California. By the time the crew
woke up the next morning, a special
EVA had been scripted to save the
array. Far beyond the reach of the
Shuttle Robotic Arm, astronauts Joseph
Tanner and Carlos Noriega crept slowly
along the ISS to the array base and
gently rethreaded the tension cable
back onto the pulleys. They used
techniques developed overnight in
California that were relayed in the
form of video training to the on-board
notebook computers.
Meanwhile, engineers rescripted
the deployment of the second wing to
minimize the size of the traveling
waves. The new procedures worked.
As STS-97 departed, the ISS had
acquired more electric power than any
prior spacecraft and was in a robust
configuration, ready to grow.
STS-100—An Ambitious
Agenda, and an
Unforeseen Challenge
STS-100 launched with a four-nation
crew in April 2001 to deliver the
Space Station Robotic Arm and the
Raffaello Italian logistics module
with major experiments and supplies
for the new US Destiny laboratory,
which had been delivered in February.
The Space Station Robotic Arm
deployed worked well, guided by
Canada’s first spacewalker, Chris
Hadfield. Hadfield reconnected a
balky power cable at the base of the
Space Station Robotic Arm to give the
arm the required full redundancy.
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Psychological Support—
Lessons From Shuttle-Mir to International Space Station
Using crew members’ experiences from flying on Mir long-duration flights, NASA’s
medical team designed a psychological support capability. The Space Shuttle began
carrying psychological support items to the International Space Station (ISS) from
the very beginning. Prior to the arrival of the Expedition 1 crew, STS-101 (2000)
and STS-106 (2000) pre-positioned crew care packages for the three crew members.
Subsequently, the shuttle delivered 36 such packages to the ISS. The shuttle
transported approximately half
of all the packages that were
sent to the ISS during that
era. The contents were tailored
to the individual (and crew).
Packages contained music
CDs, DVDs, personal items,
cards, pictures, snacks,
specialty foods, sauces, holiday
decorations, books, religious
supplies, and other items.
The shuttle delivered a guitar (STS-105 [2001]), an electronic keyboard (STS-108
[2001]), a holiday tree (STS-112 [2002]), external music speakers (STS-116 [2006]),
numerous crew personal support drives, and similar nonwork items. As
communications technology evolved, the shuttle delivered key items such as the
Internet Protocol telephones.
The shuttle also brought visitors and fellow space explorers to the dinner table of
the ISS crews. In comparison to other vehicles that visited the space station, the
shuttle was self-contained. It was said that when the shuttle visited, it was like having
your family pull up in front of your home in their RV—they arrived with their own
independent sleeping quarters, galley, food, toilet, and electrical power. This made a
shuttle arrival a very welcome thing.
Raffaello was successfully berthed
and the mission went smoothly until a
software glitch in the evolving ISS
computer architecture brought all ISS
communications to a halt, along with
the capability of the ground to
command and control the station.
Coordinating through the shuttle’s
communications systems, the station,
shuttle, and ground personnel organized
a dramatic restart of the ISS.
A major control computer was rebuilt
using a payload computer’s hard drive,
while the heartbeat of the station was
maintained by a tiny piece of rescue
software—appropriately called “Mighty
Mouse"—in the lowest-level computer
on the massive spacecraft. Astronaut
Susan Helms directly commanded the
ISS core computers through a notebook
computer. That job was normally
assigned to Mission Control. Having
rescued the ISS computer architecture,
the ISS crew inaugurated the new
Space Station Robotic Arm by using
it to return its own delivery pallet to
Endeavour’s cargo bay. Through a mix
of intravehicular activity, EVA, and
robotic techniques shared across four
space agencies, the ISS and Endeavour
each ended the ambitious mission more
capable than ever.
By 2007, with the launch of STS-120,
ISS construction was in its final stages.
Crew members encountered huge
EVA tasks in several previous flights,
usually dealing with further problems
in balky ISS solar arrays. A severe
Russian computer issue had occurred
during flight STS-117 in June of that
year, forcing an international problem
resolution team to spring into action
while the shuttle took over attitude
control of the station.
STS-120, however, was to be one for
the history books. It was already
historic in that by pure coincidence
both the shuttle and the station were
commanded by women. Pamela Melroy
commanded Space Shuttle Discovery
and Peggy Whitson commanded the
ISS. Further, the Harmony connecting
node would need to be relocated during
the stage in a “must succeed" EVA.
During that EVA, the ISS would briefly
be in an interim configuration where
the shuttle could not dock to the ISS.
On this flight, the ISS would finally
achieve the full complement of solar
arrays and reach its full width.
Shortly after the shuttle docked, the ISS
main array joint on the starboard side
exhibited a problem that was traced to
crushed metal grit from improperly
treated bearing surfaces that fouled the
whole mechanism. While teams worked
to replan the mission to clean and
lubricate this critical joint, a worse
problem came up. The outermost solar
array ripped while it was being
deployed. The wing could not be
retracted or further deployed without
sustaining greater damage. It would be
destroyed if the shuttle tried to leave.
The huge Space Station Robotic Arm
could not reach the distant tear, and
crews could not safely climb on the
160-volt array to reach the tear.
In an overnight miracle of cooperation,
skill, and ingenuity, ISS and shuttle
engineers developed a plan to extend
the Space Station Robotic Arm’s reach
using the Orbiter Boom Sensor System
with an EVA astronaut on the end.
The use of the boom on the shuttle’s
arm for contingency EVA had been
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validated on the previous flight. The
new technique using the Space Station
Robotic Arm and boom would barely
reach the damaged area with the
tallest astronaut in the corps—Scott
Parazynski—at its tip in a portable foot
restraint. This technique came with the
risk of potential freezing damage to
some instruments at the end of the
Orbiter Boom Sensor System.
Overnight, Commander Whitson and
STS-120 Pilot George Zamka
manufactured special wire links that
had been specified to the millimeter
in length by ground crews working with
a spare array.
In one of the most dramatic repairs
(and memorable images) in the history
of spaceflight, Parazynski, surrounded
by potentially lethal circuits, rode the
boom and arm combination on a
record-tying fifth single-mission EVA
to the farthest edge of the ISS. Once
there, he carefully “stitched" the vast
array back into perfect shape and
strength with the five space-built links.
These few selected vignettes cannot
possibly capture the scope of the ISS
assembly in the vacuum of space. Each
shuttle mission brought its own drama
and its own major contributions to the
ISS Program, culminating in a new
colony in space, appearing brighter to
everyone on Earth than any planet. This
bright vision would never have been
possible without the close relationship—
and often unprecedented cooperative
problem solving—that ISS enjoyed
with its major partner from Earth.
Raffaello, the Italian logistics module, flies in the
payload bay on STS-100 in 2001.
Astronaut Pamela
Melroy (left), STS-120
(2007) commander,
and Peggy Whitson,
Expedition 16
commander, pose
for a photo in the
Pressurized Mating
Adapter of the
International Space
Station as the
shuttle crew members
exit the station to
board Discovery for
their return trip home.
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While anchored to a foot restraint on the end of the Orbiter Boom Sensor System,Astronaut Scott
Parazynski, STS-120 (2007), assesses his repair work as the solar array is fully deployed during the
mission's fourth session of extravehicular activity while Discovery is docked with the International
Space Station. During the 7-hour, 19-minute spacewalk, Parazynski cut a snagged wire and installed
homemade stabilizers designed to strengthen the damaged solar array's structure and stability
in the vicinity of the damage. Astronaut Douglas Wheelock (not pictured) assisted from the truss by
keeping an eye on the distance between Parazynski and the array.
When humans learn how to manipulate
any force of nature, it is called
“technology," and technology is the
fabric of the modern world and its
economy. One such force—gravity—
is now known to affect physics,
chemistry, and biology more
profoundly than the forces that have
previously changed humanity, such as
fire, wind, electricity, and biochemistry.
Humankind’s achievement of an
international, permanent platform in
space will accelerate the creation of
new technologies for the cooperating
nations that may be as influential as
the steam engine, the printing press,
and fire. The shuttle carried the
modules of this engine of invention,
assembled them in orbit, provided
supplies and crews to maintain it, and
even built the original experience base
that allowed it to be designed.
Over the 12 years of coexistence,
and even further back in the days
when the old Freedom design was
first on the drawing board, the
International Space Station (ISS)
and Space Shuttle teams learned a lot
from each other, and both teams and
both vehicles grew stronger as a
result. Like a parent and child, the
shuttle and station grew to where the
new generation took up the journey
while the accomplished veteran eased
toward retirement.
The shuttle’s true legacy does not live
in museums. As visitors to these
astounding birds marvel up close at
these engineering masterpieces, they
need only glance skyward to see the
ongoing testament to just a portion of
the shuttles’ achievements. In many
twilight moments, the shuttle’s greatest
single payload and partner—the
stadium-sized ISS—flies by for all to
see in a dazzling display that is brighter
than any planet.
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Image of the International Space Station, as photographed from STS-132 (2010), with all of the modules, trusses, and solar panels in place.
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