Why Do We Need
Accurate Topographic
Maps of the Earth?
If you have ever used a global
positioning system for navigation,
you know the value of accurate
maps. But, have you ever wondered
how accurate the height of Mount
Everest is on a map or how its
height was determined? One of the
foundations of many science
disciplines and their applications
to societal issues is accurate
knowledge of the Earth’s surface,
including its topography. Accurate
elevation maps have numerous
common and easily understood
civil and military applications, like
locating sites for communications
towers and ground collision avoidance
systems for aircraft. They are also
helpful in planning for floods,
volcanic eruptions, and other
natural disasters, and even predicting
the viewscape for a planned scenic
highway or trail.
It is hard to imagine that the global
topographic data sets through the
end of the 20th century were quite
limited. Many countries created and
maintained national mapping
databases, but these databases varied
in quality, resolution, and accuracy.
Most did not even use a common
elevation reference so they could not
be easily combined into a more global
map. Space Shuttle radar missions
significantly advanced the science
of Earth mapping.
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What Is
Imaging Radar?
The term radar
stands for Radio
Detection and
Ranging.You have
seen radar images
of weather patterns
on television.
Typical radar works
like a flash camera,
so it can operate
day or night. But,
instead of a lens
and a film, radar
uses an antenna to
send out energy
(“illumination”) and
computer tapes to
record the reflected
“echoes” of pulses of “light” that comprise its image. Radar wavelengths are much
longer than those of visible light so it can “see” through clouds, dust, haze, etc. Radar
antenna alternately transmits and receives pulses at a particular microwave wavelength
(range of 1 cm [0.4 in.] to several meters [feet]).Typical imaging radar systems transmit
around 1,500 high-power pulses per second toward the area or surface to be imaged.
What Is Synthetic Aperture Radar?
When a radar is moving along a track, it is possible to combine the echoes received
at various positions to create a sort of “radar hologram” that can be further processed
into an image.The improved resolution that results would normally require a much
larger antenna, or aperture, thus a “synthetic aperture” is created.
How does radar work? A radar transmits a pulse, then measures
the reflected echo.
“Seeing” Through the Clouds
Shuttle Imaging
Shuttle Imaging
Space Radar
Space Radar
Shuttle Radar
Topography Mission
Space Shuttle Missions:
Advancing Earth Observations and Mapping
Shuttle and Imaging
Radars—A Quiet
Revolution in
Earth Mapping
The First Mission
The Shuttle Imaging Radar-A flew on
Space Shuttle Columbia (Space
Transportation System [STS]-2) in
November 1981. This radar was
comprised of a single-frequency,
single-polarization (L-band
wavelength, approximately 24-cm
[9-in.]) system with an antenna capable
of acquiring imagery at a fixed angle
and a data recorder that used optical
film. Shuttle Imaging Radar-A worked
perfectly, and the radar acquired images
covering approximately 10 million km
(4 million miles
) from regions with
surface covers ranging from tropical
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Major Scientific Discoveries
The Working of Shuttle Imaging Radars
forests in the Amazon and Indonesia
to the completely arid deserts of North
Africa and Saudi Arabia. Analysts
found the data to be particularly
useful in geologic structure mapping,
revealing features like lineaments,
faults, fractures, domes, layered rocks,
and outcrops. There were even land-use
applications since radar is sensitive to
changes in small-scale roughness,
surface vegetation, and human-made
structures. Urban regions backscatter
strongly, either because the walls of
buildings form corner reflectors with
the surface or because of the abundance
of metallic structures—or both.
The Shuttle Imaging Radar-A’s
most important discovery, however,
resulted from a malfunction. STS-2
was planned as a 5-day excursion and
the payload operators generated an
imaging schedule to optimize use of
the radar’s 8-hour supply of film.
But early on, one of the three Orbiter
fuel cells failed, which by mission
rules dictated a minimum-duration
flight—in this case, a bit over 2 days.
So, the operators quickly retooled the
plan to use the film in that time frame
and ended up running the system
whenever the Orbiter was over land.
The result was a number of additional
unplanned image passes over Northern
Africa, including the hyper-arid regions
of the Eastern Sahara.
Space Shuttle’s track at the altitude of 215 km (134 miles) with changing radar antenna look angle
allowed the mapping of swaths up to 100 km (62 miles) wide.
“Radar Rivers” Uncovered
This Sahara region, particularly the
Selima Sand Sheet straddling the
Egypt/Sudan border, is one of the driest
places on our planet. Photographs from
orbit show nothing but vast, featureless
expanses of sand, and with good reason.
The area gets rain no more than two
or three times per century, and rates a
200 on the geological aridity index.
For comparison, California’s Death
Valley—the driest place in the United
States—rates no more than a 7 on the
geological aridity index.
But when scientists got their first
look at the Shuttle Imaging Radar-A
images, they said “Hey, where’s the
sand sheet?” Instead of the expected
dark, featureless plain, they saw
what looked like a network of rivers
and channels that covered virtually
all the imaged area and might extend
for thousands of kilometers (miles).
To everyone’s surprise, the radar
waves had penetrated 5 or more meters
(16 or more feet) of loose, porous
sand to reveal the denser rock, gravel,
and alluvium marking riverbeds
that had dried up and been covered
over tens of thousands of years ago.
Scientists knew the Sahara had not
always been dry because some 50
million years ago, large mammals
roamed its lush savannahs, swamps,
and grasslands. Since then, the region
has fluctuated between wet and dry,
with periods during which rivers
carved a complex drainage pattern
across the entire Northern part of the
continent. The existence of wadis
(dry valleys) carved in Egypt’s nearby
Gilf Kebir Plateau, as well as other
geologic evidence, supports this idea.
Subsequent field expeditions and
excavations verified the existence of
what came to be called the “radar
rivers” and even found evidence of
human habitation in the somewhat
wetter Neolithic period, about 10,000
years ago. This discovery of an
evolving environment was a harbinger
of current concerns about global
climate change, evoking historian Will
Durant’s statement, “Civilization exists
by geological consent, subject to
change without notice.”
The Second Mission
The Shuttle Imaging Radar-B mission
launched October 5, 1984, aboard the
Space Shuttle Challenger (STS-41G)
for an 8-day mission. This radar,
again L-band, was a significant
improvement, allowing multi-angle
imaging—a capability achieved by
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using an antenna that could be
mechanically tilted. It was also
designed as a digital system, recording
echo data to a tape recorder on the
flight deck for subsequent downlink
to the ground but with Shuttle Imaging
Radar-A’s optical recorder included
as a backup. The results, deemed
successful, included the cartography
and stereo mapping effort that
produced early digital-elevation data.
Left: Optical view
of the Sahara region
(Africa) showing
the vast, featureless
expanse of sand.
The white lines depict
the radar flight path.
Right: Radar imagery
over the same region,
taken during STS-2
(1981), reveals the
network of channels
and dried-up rivers
(radar rivers) beneath
the sand sheets,
thereby illustrating
the power of radar
for archeological
Next Generation of Space
Radar Laboratory Missions
The Shuttle Imaging Radar instrument
expanded to include both L-band
(24 cm [9 in.]) and C-band (6 cm
[2 in.]) and, with the inclusion of the
German/Italian X-band (3 cm [1 in.]),
radar. For the first time, an orbiting
radar system not only included three
wavelengths, the instrument was also
fully polarimetric, capable of acquiring
data at both horizontal and vertical
polarizations or anything in between.
It also used the first “phased-array”
antenna, which meant it could be
electronically steered to point at any
spot on the ground without any motion
of the antenna or platform. The
resulting multiparameter images could
be combined and enhanced to produce
some of the most spectacular and
information-rich radar images ever seen.
The Space Radar Laboratory
missions (1 and 2) in 1994 were an
international collaboration among
NASA, the Jet Propulsion Laboratory,
the German Space Agency, and the
Italian Space Agency and constituted
a real quantum leap in radar design,
capability, and performance.
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Major Scientific Discoveries
Tom Jones, PhD
Astronaut on
STS-59 (1994),
STS-68 (1994),
STS-80 (1996), and
STS-98 (2001).
“Space Radar
and -2 orbited
a state-of-the-art multifrequency radar observatory to examine the
changing state of Earth’s surface. Our STS-59 and STS-68 crews were
integral members of the science team. Both missions returned, in total,
more than 100 terabytes of digital imagery and about 25,000 frames
of detailed Earth photography targeted on more than 400 science sites
around the globe.
“For our crews, the missions provided a glorious view of Earth from a
low-altitude, high-inclination orbit. Earth spun slowly by our flight deck
windows, and we took advantage of the panorama with our 14 still and TV
cameras. On September 30, 1994, on Space Radar Laboratory-2, we were
treated to the awesome sight of Kliuchevskoi volcano in full eruption,
sending a jet-like plume of ash and steam 18,288 m (60,000 ft) over
Kamchatka. Raging wildfires in Australia, calving glaciers in Patagonia,
plankton blooms in the Caribbean, and biomass burning in Brazil showed us
yet other faces of our dynamic Earth. These two missions integrated our
crews into the science team as orbital observers, providing ‘ground truth’
from our superb vantage point. Flight plan duties notwithstanding, I found it
hard to tear myself away from the windows and that breathtaking view.
“Both missions set records for numbers of individual Orbiter maneuvers
(470 each) to point the radars, and required careful management of power
resources and space-to-ground payload communications. The
demonstration of precise orbit adjustment burns, enabling repeat-pass
interferometry with the radar, led to successful global terrain mapping by
the Shuttle Radar Topography Mission (STS-99) in 2000.”
The Shuttle Radar
Topography Mission—
A Quantum Leap
in Earth Mapping
The Shuttle Radar Topography
Mission was major a breakthrough in
the science of Earth mapping and
remote sensing—a unique event.
NASA, the Jet Propulsion Laboratory,
the National Geospatial-Intelligence
Agency (formerly the Defense
Mapping Agency Department of
Defense), and the German and Italian
Space Agencies all collaborated to
accomplish the goals of this mission.
The 11-day flight of the Space Shuttle
Endeavour for the Shuttle Radar
Topography Mission acquired a
high-resolution topographic map of
the Earth’s landmass (between 60°N
and 56°S) and tested new technologies
for deployment of large, rigid
structures and measurement of their
distortions to extremely high precision.
How Did the Shuttle Radar
Topography Mission Work?
The heart of this mission was the
deployable mast—a real engineering
marvel. At launch, it was folded up
inside a canister about 3 m (10 ft) long.
The mast had 76 bays made of plastic
struts reinforced with carbon fiber, with
stainless-steel joints at the corners and
titanium wires held taut by 227 kg
(500 pounds) of tension. The strict
requirements of interferometry dictated
that the mast be incredibly rigid and not
flex by more than a few centimeters
(inches) in response to the firing of the
Orbiter’s attitude control vernier jets.
It didn’t. Once in orbit, a helical screw
mechanism pulled the mast open and
unfurled it one “bay” at a time to the
mast’s full length of 60 m (197 ft).
A crucial aspect of the mapping
technique was determination of the
interferometric baseline. The Shuttle
Radar Topography Mission was
designed to produce elevations such
that 90% of the measured points had
absolute errors smaller than 16 m
(52 ft), consistent with National
Mapping Accuracy Standards, and to
do so without using ground truth—
information collected “on location.”
Almost all conventional mapping
techniques fit the results to ground
truth, consisting of arrays of points
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with known locations and elevations,
to remove any residual inaccuracies.
But, because the Shuttle Radar
Topography Mission would be
mapping large regions with no such
known points, the system had to be
designed to achieve that accuracy
using only internal measurements.
This was a major challenge since
analysis showed that a mere
1-arc-second error in our knowledge of
the absolute orientation of the mast
would result in a 1-m (3-ft) error in the
elevation measurements. A1-arc-second
angle over the 60-m (197-ft) baseline
is only 0.3 mm (0.1 in.)—less than the
thickness of a penny.
This problem was solved by
determining the Orbiter’s attitude with
an inertial reference unit borrowed
from another astronomy payload,
augmented with a new star tracker.
To measure any possible bending of
the mast, the borrowed star tracker was
mounted on the main antenna to stare
at a small array of light-emitting diodes
mounted on the other antenna at the
end of the mast. By tracking the diodes
as if they were stars, all mast flexures
could be measured and their effects
removed during the data processing.
The mast-Orbiter combination
measured 72 m (236 ft) from wingtip
to the end of the mast, making it the
largest solid object ever flown in space
at that time. This size created one
interesting problem: The Orbiter had
to perform a small orbit maintenance
burn using the Reaction Control
System about once per day to maintain
the proper altitude, and analysis
showed that the resulting impulse
would generate oscillations in the
mast that would take hours to die out
and be too large for the Shuttle Radar
Topography Mission to operate.
By collaborating, Johnson Space
Center flight controllers and Jet
Propulsion Laboratory mechanical
engineers arrived at a firing sequence
involving a series of pulses that
promised to stop the mast dead at the
end of the burn. They called it the
“flycast maneuver” since it mimicked
the way a fisherman controls a fly rod
while casting. The maneuver involved
some tricky flying by the pilots and
required much practice in the
simulators, but it worked as planned.
It also gave the crew an excuse to wear
fishing gear in orbit—complete with
hats adorned with lures—and produced
some amusing photos.
NASA developed the original flight
plan to maximize the map accuracy by
imaging the entire landscape at least
twice while operating on both
ascending and descending orbits,
The Interferometry Principle
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Major Scientific Discoveries
Major Scientific Discoveries
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but it turned out that a limited region
was covered only once because the
mapping had to be terminated a few
orbits early when the propellant ran
low. This had a minor impact, however,
because even a single image could
meet the accuracy specifications. In
addition, the affected regions were
mostly within the already well-mapped
US terrain near the northern and
southern limits of the orbits where
the swaths converged were covered
as much as 15 to 20 times. In all,
the instrument covered 99.96% of the
targeted landmass.
What Is Radar Interferometry?
When two sets of radar signals are combined, they create interference patterns.
The measurement of this interference is called interferometry.
For example, if someone imagines a person standing with both arms extended to his or
her sides and that person is holding a pebble (representing one radar each) in each
hand but then drops the pebbles into a pond, two rippling concentric circles
(representing radar signals) would emanate from the splash. As the two waves travel
outward, they will eventually combine with each other causing “interference” patterns.
Similar patterns are generated when signals from two radar antennas are combined.
Elevation differences on the surface cause distortions in the fringes that can be
measured to determine the elevations.This was the concept used in the Shuttle Radar
Topographic Mapping mission.
Generating Three-dimensional Images
Radar wavefronts
combine to form
interference pattern.
Interference pattern is distorted by topography.
Processing detects
and removes
fringe distortions.
Residual fringes are topographic contours
used to generate digital elevation map.
How Does Interferometry Work?
This interferometry concept was used in the Shuttle Radar Topography Mapping mission. Radars on
the mast (not to scale) and in the shuttle payload bay were used to map a swath of 225 km (140 miles),
thus covering over 80% of the Earth’s landmass.
Turkey: Mount Ararat was mapped with a Shuttle Radar Topographic Mapping elevation model and draped with a color satellite image. This view has
been vertically exaggerated 1.25 times to enhance topographic expression. This peak is a well-known site for searches for the remains of Noah’s Ark.
The tallest peak rises to 5,165 m (16,945 ft).
Haiti:This pre-earthquake image clearly shows the Enriquillo fault that probably was responsible for the 7.0-magnitude earthquake on January 12, 2010.
The fault is visible as a prominent linear landform that forms a sharp diagonal line at the center of the image. The city of Port-au-Prince is immediately
to the left (North) at the mountain front and shoreline.
Converting Data Sets Into
Real Topographic Maps
NASA assembled a highly effective
computerized production system
to produce topographic maps for users.
Successful completion of radar data
collection from Endeavour’s flight
was a major step, but it was only
the first step. Teams from several
technical areas of microwave
imaging, orbital mechanics, signal
processing, computer image
processing, and networking worked
together to generate the products
that could be used by the public
and other end users. Major steps
included: rectifying the radar data
to map coordinates, generating
mosaics for each continent,
performing quality checks at each
stage, and assessing accuracy.
Results of Shuttle Radar
Topography Mission
The mission collected 12 terabytes
of raw data—about the same
volume of information contained
in the US Library of Congress.
Processing those data into digital
elevation maps took several years,
even while using the latest
supercomputers. Yet, the Shuttle
Radar Topography Mission eventually
produced almost 15,000 data files,
each covering 1° by 1° of latitude
and longitude and covering Earth’s
entire landmass from the tip of
South America to the southern tip
of Greenland. The data were delivered
to both the National Geospatial
Agency and the Land Processes
Distributed Active Archive Center
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at the US Geological Survey’s
EROS (Earth Resources Observation
and Science) Data Center in Sioux
Falls, South Dakota, for distribution
to the public. The maps can be
downloaded from their Web site
( at no charge,
and they are consistently the most
popular data set in their archive.
Elevation accuracy was determined
by comparing the mission’s map to
other higher-resolution elevation maps.
Results confirmed the findings of the
National Geospatial-Intelligence
Agency and the US Geological Survey
that Shuttle Radar Topography Mission
data exceeded their 16-m (52-ft)
height accuracy specification by at
least a factor of 3.
In all, the Shuttle Radar Topography
Mission successfully imaged 80% of
Earth’s landmass and produced
topographic maps 30 times as precise as
the best maps available at that time.
Major Scientific Discoveries
Africa:Tanzania’s Crater Highlands along the East African Rift Valley are depicted here as mapped
with the Shuttle Radar Topographic Mapping elevation model with vertical exaggeration of two times
to enhance topographic variations. Lake Eyasi (top of the image, in blue) and a smaller crater lake are
easily seen in this volcanic region. Mount Loolmalasin (center) is 3,648 m (11,968 ft).
The successful shuttle radar missions
demonstrated the capabilities of Earth
mapping and paved the way for the
Shuttle Radar Topography Mission.
This mission was bold and innovative,
and resulted in vast improvement by
acquiring a new topographic data set
for global mapping. It was an excellent
example of a mission that brought
together the best engineering and the
best science minds to provide uniform
accuracy elevation information for
users worldwide. This success has been
enshrined at the Smithsonian Air and
Space Museum’s Udvar-Hazy Center
in Virginia, where the radar mast and
outboard systems are displayed.
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Charles Elachi, PhD
Director of Jet Propulsion Laboratory
California Institute of Technology.
“The Space Shuttle played a key role, as
the orbiting platform, in advancing the field
of radar observation of the Earth. Five
flights were conducted between 1981 and
2004, each one with successively more
capability. Probably the two most dramatic
advances occurred with: 1) the SIR-C* flight, which demonstrated for the
first time ‘color’ imaging radars with multifrequency/multi-polarization
capability, and it is still considered the ‘gold standard’ for later missions;
and 2) the Shuttle Radar Topography Mission flight, which revolutionized
topographic mapping by acquiring global digital topography data using
interferometric radar. These missions were enabled by the volumetric and
lift capability of the shuttle. These two advances in our ability to map the
Earth will go down in history as two of the most important contributions of
the shuttle to the field of Earth Science.”
* Shuttle Imaging Radar-C
US: California’s San Andreas fault (1,200 km [800 miles]) is one of the longest faults in North America.
This view of a section of it was generated using a Shuttle Radar Topographic Mapping elevation
model and draped with a color satellite image. The view shows the fault as it cuts along the base of
Temblor Range near Bakersfield, California.
Human travel to Mars and beyond is no longer science fiction.
Through shuttle research we know how the body changes, what we
need to do to fix some of the problems or—better yet—prevent them,
the importance of monitoring health, and how to determine the
human body’s performance through the various sequences of launch,
spaceflight, and landing. Basically, we understand how astronauts
keep their performance high so they can be explorers, scientists,
and operators.
Astronauts change physically during spaceflight, from their brain,
heart, blood vessels, eyes, and ears and on down to their cells.
Many types of research studies validated these changes and
demonstrated how best to prevent health problems and care for the
astronauts before, during, and after spaceflight.
During a shuttle flight, astronauts experienced a multitude of
gravitational forces. Earth is 1 gravitational force (1g); however,
during launch, the forces varied from 1 to 3g. During a shuttle’s
return to Earth, the forces varied from nearly zero to 1.6g, over
approximately 33 minutes, during the maneuvers to return. In all,
the shuttle provided rather low gravitational forces compared with
other rocket-type launches and landings.
The most pervasive physiological human factor in all spaceflight,
however, is microgravity. An astronaut perceives weightlessness and
floats along with any object, large or small. The microgravity
physiological changes affect the human body, the functions within the
space vehicle, and all the fluids, foods, water, and contaminants.
We learned how to perform well in this environment through the
Space Shuttle Program. This information led to improvements in
astronauts’health care not only during shuttle flights but also for the
International Space Station (ISS) and future missions beyond
low-Earth orbit. Shuttle research and medical care led directly to
improved countermeasures used by ISS crew members. No shuttle
mission was terminated due to health concerns.
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Major Scientific Discoveries
Astronaut Health
and Performance
Helen Lane
Laurence Young
How Humans Adapt to Spaceflight:
Physiological Changes
Vision, Orientation, and Balance
William Paloski
Laura Barger
Charles Czeisler
Muscle and Exercise
John Charles
Steven Platts
Daniel Feeback
Kenneth Baldwin
Judith Hayes
John Charles
Steven Platts
Nutritional Needs in Space
Helen Lane
Clarence Alfrey
Scott Smith
Immunology and Infectious Diseases
Brian Crucian
Satish Mehta
Mark Ott
Duane Pierson
Clarence Sams
Habitability and Environmental Health
Janis Connolly
David Fitts
Dane Russo
Vickie Kloeris
Environmental Health
John James
Thomas Limero
Mark Ott
Chau Pham
Duane Pierson
Astronaut Health Care
Philip Stepaniak
How Humans Adapt
to Spaceflight:
Physiological Changes
Vision, Orientation, and Balance
Change in Microgravity
Gravity is critical to our existence.
As Earthlings, we have come to rely on
Earth’s gravity as a fundamental
reference that tells us which way is
down. Our very survival depends on
our ability to discern down so that we
can walk, run, jump, and otherwise
move about without falling. To
accomplish this, we evolved specialized
motion-sensing receptors in our inner
ears—receptors that act like biological
guidance systems. Among other things,
these receptors sense how well our
heads are aligned with gravity. Our
brains combine these data with visual
information from our eyes, pressure
information from the soles of our feet
(and the seats of our pants), and
position and loading information from
our joints and muscles to continuously
track the orientation of our bodies
relative to gravity. Knowing this, our
brains can work out the best strategies
for adjusting our muscles to move our
limbs and bodies about without losing
our balance. And, we don’t even have
to think about it.
At the end of launch phase, astronauts
find themselves suddenly thrust into
the microgravity environment. Gravity,
the fundamental up/down reference
these astronauts relied on throughout
their lives for orientation and
movement, suddenly disappears.
As you might expect, there are a
number of immediate consequences.
Disorientation, perceptual illusions,
motion sickness, poor eye-head/eye-
hand coordination, and whole-body
movements are issues each astronaut
has to deal with to some degree.
One thing we learned during the shuttle
era, though, is that astronauts’ nervous
systems adapt very quickly. By the
third day of flight, most crew members
overcame the loss of gravitational
stimulation. Beyond that, most
exhibited few functionally significant
side effects. The downside to this rapid
adaptation was that, by the time a
shuttle mission ended and the
astronauts returned to Earth, they had
forgotten how to use gravity for
orientation and movement. So, for the
first few days after return, they suffered
again from a multitude of side effects
similar to those experienced at the
beginning of spaceflight. During the
Earth-readaptation period, these
postflight affects limited some types of
physical activities, such as running,
jumping, climbing ladders, driving
automobiles, and flying planes.
The Space Shuttle––particularly
when carrying one of its Spacelab
or Spacehab modules and during
the human-health-focused,
extended-duration Orbiter medical
missions (1989 through 1995)––
provided unique capabilities to study
neurological adaptation to space.
By taking advantage of the shuttle’s
ability to remove and then reintroduce
the fundamental spatial orientation
reference provided by gravity, many
researchers sought to understand
the brain mechanisms responsible for
tracking and responding to this
Major Scientific Discoveries
Page 371
stimulus. Other researchers used these
stimuli to investigate fundamental and
functional aspects of neural adaptation,
while others focused on the operational
impacts of these adaptive responses
with an eye toward reducing risks to
space travelers and enabling future
missions of longer duration.
Laurence Young, ScD
Principal investigator or
coinvestigator on seven space
missions, starting with STS-9 (1983).
Alternate payload specialist on
STS-58 (1993).
Founding director of the National
Space Biomedical Research Institute.
Apollo Program professor of
astronautics and professor of health
sciences and technology at
Massachusetts Institute of Technology.
“The Space Shuttle Program provided a golden era for life sciences research.
The difference between science capabilities on spacecraft before and after the
Space Shuttle is enormous: it was like doing science in a telephone booth in the
Gemini-Apollo era while shuttle could accommodate a school-bus-size laboratory.
This significantly added to the kind of research that could be done in space.
We had enormous success in life sciences, especially with the Spacelabs, for
quality of instrumentation, their size, and opportunity for repeated measurements
on the astronauts on different days of flight and over many different flights
including Space Life Sciences flights 1 and 2 and ending with Neurolab.
“Our research led to a much more complete understanding of the neurovestibular
changes in spaceflight and allowed us to know what issues require
countermeasures or treatment, such as space motion sickness, as well as what
research needed to continue in Earth laboratories, such as the role of short radius
centrifuges for intermittent artificial gravity to support a Mars exploration mission.”
Space Motion Sickness
What Is Space Motion Sickness?
Many people experience motion
sickness while riding in vehicles ranging
from automobiles to airplanes to boats
to carnival rides. Its symptoms include
headache, pallor, fatigue, nausea, and
vomiting. What causes motion sickness
is unknown, but it is clearly related to
the nervous system and almost always
involves the specialized motion-sensing
receptors of the inner ear, known as the
vestibular system.
The most popular explanation for
motion sickness is the sensory-conflict
theory. This theory follows from
observations that in addition to planning
the best strategies for movement control,
the brain also anticipates and tracks the
outcome of the movement commands
it issues to the muscles. When the
tracked outcome is consistent with the
anticipated outcome, everything
proceeds normally; however, when
the tracked outcome is inconsistent, the
brain must take action to investigate
what has gone wrong. Sensory conflict
occurs when some of the sensory
information is consistent with the
brain’s anticipated outcome and some
information is inconsistent. This might
occur in space, for example, when
the brain commands the neck muscles
to tilt the head. The visual and neck
joint receptors would provide immediate
feedback indicating that the head has
tilted, but because gravity has been
reduced, some of the anticipated signals
from the inner ear would not arrive.
Initially, this would cause confusion,
disorientation, and motion sickness
symptoms. Over time, however, the
brain would learn not to anticipate this
inner-ear information during head tilts
and the symptoms would abate.
How Often Do Astronauts Have
Space Motion Sickness?
Many astronauts report motion sickness
symptoms just after arrival in space and
again just after return to Earth. For
example, of the 400 crew members who
flew on the shuttle between 1981 and
1998, 309 reported at least some motion
sickness symptoms, such as stomach
awareness, headache, drowsiness,
pallor, sweating, dizziness, and, of
course, nausea and vomiting. For most
astronauts, this was a short-term
problem triggered by the loss of gravity
stimuli during ascent to orbit and, again,
by the return of gravity stimuli during
descent back to Earth. It usually lasted
only through the few days coinciding
with neural adaptations to these gravity
transitions. While the symptoms of
space motion sickness were quite
similar to other types of motion
sickness, its incidence was not predicted
by susceptibility to terrestrial forms,
such as car sickness, sea sickness, air
sickness, or sickness caused by carnival
rides. To complicate our understanding
of the mechanisms of space motion
sickness further, landing-day motion
sickness was not even predicted by the
incidence or severity of early in-flight
motion sickness. The only predictable
aspect was that repeat flyers usually had
fewer and less severe symptoms with
each subsequent flight.
How Do Astronauts Deal With
Space Motion Sickness?
Crew members can limit head
movements during the first few days of
microgravity and during return to Earth
to minimize the symptoms of space
motion sickness. For some astronauts,
drugs are used to reduce the symptoms.
Promethazine-containing drugs
emerged as the best choice during the
early 1990s, and were frequently used
throughout the remaining shuttle
flights. Scientists also investigated
preflight adaptation training in devices
that simulate some aspects of the
sensory conflicts during spaceflight, but
more work is necessary before
astronauts can use this approach.
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Some crew members experience height vertigo or acrophobia during extravehicular activities.
Astronaut Stephen Robinson is anchored by a foot restraint on the International Space Station Robotic
Arm during STS-114 (2005).
Spatial Disorientation:
Which Way Is Down?
Astronauts entering the microgravity
environment of orbital spaceflight for
the first time report many unusual
sensations. Some experience a sense of
sustained tumbling or inversion (that is,
a feeling of being upside down). Others
have difficulty accepting down as being
the direction one’s feet are pointing,
preferring instead to consider down in
terms of the module’s orientation
during preflight training on the ground.
Almost all have difficulty figuring out
how much push-off force is necessary
to move about in the vehicle. While
spacewalking (i.e., performing
extravehicular activities [EVAs]), many
astronauts report height vertigo—a
sense of dizziness or spinning—that
is often experienced by individuals on
Earth when looking down from great
heights. Some astronauts also
experienced transient acrophobia—an
overwhelming fear of falling toward
Earth—which can be terrifying.
After flight, crew members also
experience unusual sensations. For
example, to many crew members
everyday objects (e.g., apples,
cameras) feel surprisingly heavy.
Also, when walking up stairs, many
experience the sensation that they are
pushing the stairs down rather than
pushing their bodies up. Some feel
an overwhelming sense of translation
(sliding to the side) when rounding
corners in a vehicle. Many also
have difficulty turning corners while
walking, and some experience
difficulty while bending over to
pick up objects. Early after return to
Earth, most are unable to land from
a jump; many report a sensation
that the ground is coming up rapidly
to meet them. For the most part,
all of these sensations abate within
a few days; however, there have
been some reports of “flashbacks”
occurring, sometimes even weeks
after a shuttle mission.
Dafydd (Dave) Williams, MD
Canadian astronaut on STS-90 (1998)
and STS-118 (2007).
“Humans adapt remarkably well to
the physiologic challenges associated
with leaving the Earth’s gravitational
environment. For me, these started at
main engine cutoff. After 7 minutes of the 8½-minute ride, G forces pushed
me like an elephant sitting on my chest. The crushing pressure resolved as
I was thrown forward against my harness when the main engines shut down.
This created a sense of tumbling, head over heels, identical to performing
somersaults as a child. I pulled myself down in the shuttle seat to re-create the
gravitational sense of sitting in a chair and the tumbling stopped. I had
experienced my first illusion of spaceflight!
“On the first day, many changes took place. My face felt puffy. I had a mild
headache. Over the first few days, I experienced mild low back pain. Floating
freely inside the shuttle with fingertip forces gently propelling us on a
somewhat graceful path reminded me of swimming underwater—with the
notable absence of any resistance.
“During re-entry into the Earth’s atmosphere, I felt the forces of gravity gradually
building. Standing on the middeck after landing, I felt gravitationally challenged.
As I walked onto the crew transfer vehicle I felt as though my arms weighed
twice what they normally do. Moving my head created an instant sense of vertigo.
“On my second spaceflight, when I arrived in space it seemed like I had never left
and as I floated gracefully, looking back at Earth, it reminded me that I will always
remain a spacefarer at heart.”
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Page 373
moving or the object we wish to see
is moving. Under these dynamic visual
conditions, even people with 20/20
vision will see poorly if they can’t keep
the image of interest stabilized on
their retinas. To do this while walking,
running, turning, or bending over, we
have evolved complex neural control
systems that use information from the
vestibular sensors of the inner ear to
automatically generate eye movements
that are equal and opposite to any
head movements. On Earth, this
maintains a stable image on the retina
whenever the head is moving.
Since part of this function depends on
how the inner ear senses gravity,
scientists were interested in how it
changes in space. Many experiments
performed during and just after shuttle
missions examined the effects of
spaceflight on visual acuity. Static
visual acuity changed mildly, mainly
because the headward fluid shifts
during flight cause the shape of the
eyes to change. Dynamic visual acuity,
on the other hand, was substantially
disrupted early in flight and just after
return to Earth. Even for simple
dynamic vision tasks, such as pursuing
a moving target without moving the
head, eye movements were degraded.
But the disruption was found to be
greatest when the head was moving,
especially in the pitch plane (the plane
your head moves in when you nod it
to indicate “yes”). Scientists found that
whether pursuing a target, switching
vision to a new target of interest (the
source of a sudden noise, for instance),
or tracking a stationary target while
moving (either voluntarily or as a result
of vehicle motion), eye movement
control was inaccurate whenever the
head was moving.
Vision (eye movements) and
orientation perceptions are disrupted
during spaceflight. Scientists found
that some kinds of anticipatory actions
are inaccurate during flight. The
impact of these changes on shuttle
operations was difficult to assess. For
example, while it appears that some
shuttle landings were not as accurate as
preflight landings in the Shuttle
Training Aircraft, many confounding
factors (such as crosswinds and
engineering anomalies) precluded
rigorous scientific evaluation. It
appears that the highly repetitive
training crew members received just
before a shuttle mission might have
helped offset some of the physiological
changes during the flight. Whether the
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Major Scientific Discoveries
Payload specialist James Pawelczyk, STS-90 (1998).
positive effects of this training will
persist through longer-duration flights
is unknown. At this point, training is
the only physiological countermeasure
to offset these potential problems.
Eye-Hand Coordination
Catching a ball is easy for most
people on Earth. Yet, we don’t
usually realize how much work
our brains do to predict when
and where the ball will come
down, get our hand to that
exact place at the right time,
and be sure our fingers grab
the ball when it arrives.
Because of the downward
acceleration caused by gravity,
the speed of a falling object
increases on Earth. Scientists
think that the brain must
anticipate this to be able to
catch a ball. Objects don’t fall in
space, however. So, scientists
wondered how well people
could catch objects without
gravity. To find out, astronauts
were asked to catch balls launched from a spring-loaded canon that “dropped” them
at a constant speed rather than a constant acceleration as on Earth. In flight, the
astronauts always caught the balls, but their timing was a little bit off. They reacted as
if they expected the balls to move faster than they did, suggesting that their brains
were still anticipating the effects of gravity. The astronauts eventually adapted, but
some of the effects were still evident after 15 days in space. After flight, the
astronauts were initially surprised by how fast the balls fell, but they readapted very
quickly. This work showed that, over time in microgravity, astronauts could make
changes in their eye-hand coordination, but that it took time after a gravity transition
for the brain to accurately anticipate mechanical actions in the new environment.
Eye-Hand Coordination:
Changes in Visual Acuity and
Manual Control
Manual control of vehicles and other
complex systems depends on accurate
eye-hand coordination, accurate
perception of spatial orientation, and
the ability to anticipate the dynamic
response of the vehicle or system to
manual inputs. This function was
extremely important during shuttle
flights for operating the Shuttle Robotic
Arm, which required high-level
coordination through direct visual,
camera views, and control feedback.
It was also of critical importance to
piloting the vehicle during rendezvous,
docking, re-entry, and landing.
Clear vision begins with static visual
acuity (that is, how well one can see
an image when both the person and the
image are stationary). In most of our
daily activities, however, either we are
Postflight Balance and Walking
When sailors return to port following a
long sea voyage, it takes them some
time to get back their “land legs.” When
astronauts returned to Earth following a
shuttle mission, it took them some time
to get back their “ground legs.” On
landing day, most crew members had
a wide-based gait, had trouble turning
corners, and could not land from a
jump. They didn’t like bending over
or turning their heads independent
of their torsos. Recovery usually took
about 3 days; but the more time the
crew member spent in microgravity,
the longer it took for his or her balance
and coordination to return to normal.
Previous experience helped, though;
for most astronauts, each subsequent
shuttle flight resulted in fewer postflight
effects and a quicker recovery.
Scientists performed many experiments
before and after shuttle missions to
understand the characteristics of these
transient postflight balance and gait
disorders. By using creative
experimental approaches, they showed
that the changes in balance control
were due to changes in the way the
brain uses inner-ear information
during spaceflight. As a result, the
crew members relied more on visual
information and body sense information
from their ankle joints and the bottoms
of their feet just after flight. Indeed,
when faced with a dark environment
(simulated by closing their eyes), the
crew members easily lost their balance
on an unstable surface (like beach
sand, deep grass, or a slippery shower
floor), particularly if they made any
head movements. As a result, crew
members were restricted from certain
activities for a few days after shuttle
flights to help them avoid injuring
themselves. These activities included
the return to flying aircraft.
In summary, experiments aboard
the Space Shuttle taught us many
things about how the nervous system
uses gravity, how quickly the nervous
system can respond to changes in
gravity levels, and what consequences
flight-related gravity changes might
have on the abilities of crew members
to perform operational activities.
We know much more now than we
did when the Space Shuttle Program
started. But, we still have a lot to learn
about the impacts of long-duration
microgravity exposures, the effects
of partial gravity environments, such
as the moon and Mars, and how to
develop effective physiological
countermeasures to help offset some
of the undesirable consequences
of spaceflight on the nervous system.
These will need to be tackled for
space exploration.
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Page 375
Nucleus of the
Solitary Tract
Somatic Motor Reexes
Inferior Olive
Nerve VIII)
Nerve VI)
(Cranial Nerve IV)
(Cranial Nerve III)
Locus Coeruleus
Extrinsic eye muscles receive
signals from the brain stem.
Vestibule of the inner ear
sends signals to the brain stem.
For us to see clearly, the image of interest must be focused precisely on a small region of the
retina called the fovea. This is particularly challenging when our heads are moving (think about
how hard it is to make a clear photograph if your camera is in motion). Fortunately, our nervous
systems have evolved very effective control loops to stabilize the visual scene in these
instances. Using information sensed by the vestibular systems located in our inner ears, our
brains quickly detect head motion and send signals to the eye muscles that cause compensatory
eye movements. Since the vestibular system senses gravity as well as head motion,
investigators performed many experiments aboard the shuttle to determine the role of gravity in
the control of eye movements essential for balance. They learned that the eye movements used
to compensate for certain head motions were improperly calibrated early in flight, but they
eventually adapted to the new environment. Of course, after return to Earth, this process had to
be reversed through a readaptation process.
Adapted from an il ustration by Wil iam Scavone, Kestrel Il ustration.
Balance: Eye, Ear, and Brain Working in Concert
Sleep Quality and Quantity on
Space Shuttle Missions
Many people have trouble sleeping
when they are away from home or in
unusual environments. This is also true
of astronauts. When on a shuttle
mission, however, astronauts had to
perform complicated tasks requiring
optimal physical and cognitive abilities
under sometimes stressful conditions.
Astronauts have had difficulty
sleeping from the beginning of human
spaceflight. Nearly all Apollo crews
reported being tired on launch day and
many gave accounts of sleep disruption
throughout the missions, including
some reporting continuous sleep
periods lasting no more than 3 hours.
Obtaining adequate sleep was also a
serious challenge for many crew
members aboard shuttle missions.
Environmental Factors
Several factors negatively affect
sleep: unusual light-dark cycles, noise,
and unfavorable temperatures. All of
these factors were present during
shuttle flights and made sleep difficult
for crew members. Additionally, some
crew members reported that work stress
further diminished sleep.
When astronauts completed a daily
questionnaire about their sleep, almost
60% of the questionnaires indicated
that sleep was disturbed during the
previous night. Noise was listed as
the reason for the sleep disturbance
approximately 20% of the time. High
levels of noise negatively affect both
slow-wave (i.e., deep sleep important
for physical restoration) and REM
(Rapid Eye Movement) sleep (i.e.,
stage at which most dreams occur and
important for mental restoration),
diminishing subsequent alertness,
cognition, and performance. A
comfortable ambient temperature
is also important for promoting
sleep. On the daily questionnaire,
approximately15% of the disturbances
were attributed to the environment
being too hot and approximately15%
of the disturbances were attributed
to it being too cold. Thus, the shuttle
environment was not optimal for sleep.
Circadian Rhythms
Appropriately timed circadian rhythms
are important for sleep, alertness,
performance, and general good health.
Light is the most important time cue to
the body’s circadian clock, which has a
natural period of about 24.2 hours.
Normally, individuals sleep when it is
dark and are awake when it is light.
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Major Scientific Discoveries
Earth Conditions
On a 24-hour external
light-dark cycle, the
body’s circadian clock
remains properly
(e.g., hormones like
melatonin are
released at the
appropriate time).
Space Conditions
On the Orbiter’s
90-minute light-dark
cycle, weak interior
ambient light may not
sufficiently cue the
body’s circadian clock,
which may then become
(e.g., inappropriately
timed hormone release).
Comparison of Earth and Space Sleep Cycles
Major Scientific Discoveries
Page 377
This 24-hour pattern resets the body’s
clock each day and keeps all of the
body’s functions synchronized,
maximizing alertness during the day
and consolidating sleep at night. Unlike
the 24-hour light-dark cycle that we
experience on Earth, shuttle crew
members experience 90-minute light-
dark cycles as they orbited the Earth.
Not only is the timing of light
unsuitable, but the low intensity of the
light aboard the shuttle may have
contributed to circadian misalignment.
Light levels were measured in the
various compartments of the shuttle
during Space Transportation System
(STS)-90 Neurolab (1998) and STS-95
(1998) missions. In the Spacelab, light
levels were constant and low
(approximately 10 to 100 lux) during the
working day. In the middeck, where the
crew worked, ate, and slept, the light
levels recorded were relatively constant
and very dim (1 to 10 lux). Laboratory
data showed that these light levels are
insufficient to entrain the human
circadian pacemaker to non-24-hour
sleep-wake schedules. Normal room
lighting (200 to 300 lux) would be
required to keep the circadian system
aligned under 24-hour light-dark cycles.
Crew members also were often
scheduled to work on 23.5-hour days or
had to shift their sleep-wake schedule
several hours during flight. Moreover,
deviations from the official schedule
were frequently required by operational
demands typical of space exploration.
Therefore, the crew members’circadian
rhythms often became misaligned,
resulting in them having to sleep during
a time when their circadian clock was
promoting alertness, much as a shift
worker on Earth.
Actually, difficulties with sleep began
even before the shuttle launched.
Often in the week prior to launch
crew members had to shift their
sleep-wake schedule, sometimes up
to 12 hours. This physiological
challenge, associated with sleep
disruption, created “fatigue pre-load”
before the mission even began.
All US crew members participated in
the Crew Health Stabilization Program
where they were housed together for
7 days prior to launch to separate
them from potential infectious disease
from people and food. During this
quarantine period, scientists at
Harvard Medical School, in association
with NASA, implemented a
bright-light treatment program for crew
members of STS-35 (1990), the first
Space Shuttle mission requiring both
dual shifts and a night launch.
Scheduled exposure to bright light
(about 10,000 lux—approximately the
brightness at sunrise), at appropriate
times throughout the prelaunch
period at Johnson Space Center and
Kennedy Space Center, was used
to prepare shuttle crew members of
the Red Team of STS-35 for both their
night launch and their subsequent
night-duty shift schedule in space.
A study confirmed that the prescribed
light exposure during the prelaunch
quarantine period successfully induced
circadian realignment in this crew.
Bright lights were installed at both
centers’ crew quarters in 1991 for use
when shuttle flights required greater
than a 3-hour shift in the prelaunch
sleep-wake cycle.
Studies of Sleep in Space
NASA studied sleep quality and
quantity and investigated the
underlying physiological mechanisms
associated with sleep loss as well as
countermeasures to improve sleep
and ultimately enhance alertness and
performance in space. Scientists
conducted a comprehensive sleep
study on STS-90 and STS-95
missions using full polysomnography,
which monitors brain waves, tension
in face muscles, and eye movements,
and is the “gold standard” for
evaluating sleep. Scientists also
made simultaneous recordings of
multiple circadian variables such as
body temperature and cortisol, a
salivary marker of circadian rhythms.
This extensive study included
performance assessments and the
first placebo-controlled, double-blind
clinical trial of a pharmaceutical
(melatonin) during spaceflight. Crew
members on these flights experienced
circadian rhythm disturbances,
sleep loss, and decrements in
neurobehavioral performance.
For another experiment, crew members
wore a watch-like device, called an
actigraph, on their wrists to monitor
sleep. The actigraph contained an
accelerometer that measured wrist
motion. From that recorded motion
scientists were able to use software
algorithms to estimate sleep duration.
Fifty-six astronauts (approximately
60% of the Astronaut Corps between
2001 and 2010) participated in this
study. Average nightly sleep duration
across multiple shuttle missions was
approximately 6 hours. This level
of sleep disruption has been associated
with cognitive performance deficits
in numerous ground-based laboratory
and field studies.
Pharmaceuticals were the most
widespread countermeasure for sleep
disruption during shuttle flights. Indeed,
more than three-quarters of astronauts
reported taking sleep medications
during missions. Astronauts took sleep
medications during flight half the time.
Wake-promoting therapeutics gained in
popularity as well, improving alertness
after sleep-disrupted nights.
Although sleep-promoting medication
use was widespread in shuttle
crew members, investigations need
to continue to determine the most
acceptable, feasible, and effective
methods to promote sleep in future
missions. Sleep monitoring is ongoing
in crew members on the International
Space Station (ISS) where frequent
shifts in the scheduled sleep-wake
times disrupt sleep and circadian
alignment. Sleep most certainly will
also be an issue when space travel
continues beyond low-Earth orbit.
Private sleep quarters will probably not
be available due to space and mass
issues. Consequently, ground-based
studies continue to search for the most
effective, least invasive, and least
time-consuming countermeasures to
improve sleep and enhance alertness
during spaceflight. Currently, scientists
are trying to pinpoint the most effective
wavelength of light to use to ensure
alignment of the circadian system and
improve alertness during critical tasks.
Spaceflight Changes Muscle
Within the microgravity environment
of space, astronauts’ muscles are said
to be “unweighted” or “unloaded”
because their muscles are not required
to support their body weight. The
unloading of skeletal muscle during
spaceflight, in what is known as
“muscle atrophy,” results in remodeling
of muscle (atrophic response) as an
adaptation to the spaceflight. These
decrements, however, increase the
risk of astronauts being unable to
adequately perform physically
demanding tasks during EVAs or after
abrupt transitions to environments
of increased gravity (such as return to
Earth at the end of a mission).
A similar condition, termed “disuse
muscle atrophy,” occurs any time
muscles are immobilized or not used as
the result of a variety of medical
conditions, such as wearing a cast or
being on bed rest for a long time. Space
muscle research may provide a better
understanding of the mechanisms
underlying disuse muscle atrophy,
which may enable better management
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Major Scientific Discoveries
of these patients. In the US human
space program, the only tested in-flight
preventive treatment for muscle atrophy
has been physical exercise. In-flight
exercise hardware and protocols varied
from mission to mission, somewhat
dependent on mission duration as well
as on the internal volume of the
spacecraft. Collective knowledge gained
from these shuttle missions aided in the
evolution of exercise hardware and
protocols to prevent spaceflight-induced
muscle atrophy and the concomitant
deficits in skeletal muscle function.
Richard Searfoss
Colonel, US Air Force (retired).
Pilot for STS-58 (1993) and
STS-76 (1996).
Commander for STS-90 (1998).
Perspectives on
“I was privileged to
command STS-90
Neurolab, focusing on the effects of weightlessness on the brain and nervous
system. Although my technical background is in engineering and flight test, it was
still incredibly rewarding to join a dedicated team that included not just NASA but
the National Institutes of Health and top researchers in the world to strive with
disciplined scientific rigor to really understand some of the profound changes to
living organisms that take place in the unique microgravity environment. I viewed
my primary role as science enabler, calling on my operational experience to build
the team, lead the crew, and partner with the science community to accomplish the
real ‘mission that mattered.’
“Even though at the time STS-90 flew on Columbia humans had been flying to
space nearly 40 years, much of our understanding of the physiological effects was
still a mystery. Neurolab was extremely productive in unveiling many of those
mysteries. The compilation of peer-reviewed scientific papers from this mission
produced a 300-page book, the only such product from any Space Shuttle mission.
I’ll leave it to the scientists to testify to the import, fundamental scientific value, and
potential for Earth-based applications from Neurolab. It’s enough for me to realize
that my crew played an important role in advancing science in a unique way.
“With STS-90 as the last of 25 Spacelab missions, NASA reached a pinnacle of
overall capability to meld complex, leading-edge science investigations with
the inherent challenges of operating in space. Building on previous Spacelab
flights, Neurolab finished up the Spacelab program spectacularly, with scientific
results second to none. What a joy to be part of that effort! It was unquestionably
the honor of my professional life to be a member of the Neurolab team in my
role as commander.”
How Was Muscle Atrophy Measured,
and What Were the Results?
Leg and Back Muscle Size Decreases
Loss of muscle and strength in the lower
extremities of astronauts was initially
found in the Gemini (1962-1966) and
Apollo missions (1967-1972) and was
further documented in the first US space
station missions (Skylab, 1973-1974)
of 28, 59, and 84 days’ duration.
NASA calculated crude muscle volumes
by measuring the circumference of the
lower and upper legs and arms at
multiple sites.
For shuttle astronauts, more
sophisticated, accurate, and precise
measures of muscle volume were made
by magnetic resonance imaging (MRI).
MRI is a common diagnostic medical
procedure used to image patient’s
internal organs that was adapted to
provide volume measurements of a
crew member’s lower leg, thigh, and
back muscles before and after flight.
The leg muscle volume was evaluated
in eight astronauts (seven males and
one female, age range 31 to 39 years)
who flew on either one of two 9-day
missions. Scientists obtained MRI
scans of multiple leg cross sections
prior to flight and compared them
to scans obtained at 2 to 7 days after
flight. The volumes of various leg
muscles were reduced by about 4%
to 6% after spaceflight. In another
study of longer missions (9 to 16 days’
duration—two males and one female,
mean age 41 years), the losses were
reported to be greater, ranging from
5.5% to 15.9% for specific leg
muscles. This study found that daily
volume losses of leg muscles
normalized for duration of flight were
from 0.6% to 1.04% per mission day.
Muscle Strength Decreases
Decreases in muscle strength persisted
throughout the shuttle period in spite
of various exercise prescriptions.
Measurements of muscle strength,
mass, and performance helped
NASA determine the degree of
muscle function loss and assess the
efficacy of exercise equipment and
determine whether exercise protocols
were working as predicted.
Muscle strength, measured with a
dynamometry (an instrument that
measures muscle-generated forces,
movement velocity, and work) before
launch and after landing consistently
showed loss of strength in muscles that
extend the knee (quadriceps muscles)
by up to 12% and losses in trunk
flexor strength of as much as 23%.
The majority of strength and endurance
losses occurred in the trunk and leg
muscles (the muscle groups that are
active in normal maintenance of posture
and for walking and running) with
little loss noted in upper body and arm
muscle strength measurements. In
contrast, four STS-78 (1996) astronauts
had almost no decrease in calf muscle
strength when they participated
voluntarily in high-volume exercise
in combination with the in-flight,
experiment-specific muscle strength
performance measurements. This
preliminary research suggested that such
exercises may prevent loss of muscle
function leading to implementation of
routine combined aerobic and resistive
exercise for ISS astronauts.
Muscle Fiber Changes in Size and Shape
An “average” healthy person has
roughly equal numbers of the two
major muscle fiber types (“slow” and
“fast” fibers). Slow fibers contract
(shorten) slowly and have high
endurance (resistance to fatigue) levels.
Fast fibers contract quickly and fatigue
readily. Individual variation in muscle
fiber type composition is genetically
(inherited) determined. The
compositional range of slow fibers in
the muscles on the front of the thigh
(quadriceps muscles) in humans can
vary between 20% and 95%, a
percentage found in many marathon
runners. On the other hand, a
world-class sprinter or weight lifter
would have higher proportions of fast
fibers and, through his or her training,
these fibers would be quite large
(higher cross-sectional diameter or
area). Changing the relative proportions
of the fiber types in muscles is possible,
but it requires powerful stimulus
such as a stringent exercise program
or the chronic unloading profile that
occurs in microgravity. NASA was
interested in determining whether there
were any changes in the sizes or
proportions of fiber types in astronauts
during spaceflight.
In the only biopsy study of US
astronauts to date, needle muscle
biopsies from the middle of the vastus
lateralis muscle (a muscle on the side
of the thigh) of eight shuttle crew
members were obtained before launch
(3 to 16 weeks) and after landing
(within 3 hours) for missions ranging
in duration from 5 to 11 days. Three of
the eight crew members (five males and
three females, age range 33 to 47 years)
Major Scientific Discoveries
Page 379
flew 5-day missions while the other
five crew members completed 11-day
flights. Five of the eight crew members
did not participate in other medical
studies that might affect muscle fiber
size and type. NASA made a variety of
measurements in the biopsy samples,
including relative proportions of the
two major muscle fiber types, muscle
fiber cross-sectional area by muscle
fiber type, and muscle capillary (small
blood vessel) density. Slow fiber-type
cross-sectional area decreased by
15% as compared to a 22% decrease
for fast fiber muscle fibers. Biopsy
samples from astronauts who flew on
the 11-day mission showed there were
relatively more fast fiber types and
fewer slow fiber types, and the density
of muscle capillaries was reduced
when the samples taken after landing
were compared to those taken before
launch. NASA research suggests that
fiber types can change in microgravity
due to the reduced loads. This has
implications for the type and volume
of prescriptive on-orbit exercise.
Research conducted during the shuttle
flights provided valuable insight into
how astronauts’ muscles responded
to the unloading experienced while
living and working in space. Exercise
equipment and specific exercise
therapies developed and improved on
during the program are currently in
use on the ISS to promote the safety
and health of NASA crew members.
The “Why” and “How” of
Exercise on the Space Shuttle
Why Exercise in Space?
Just as exercise is an important
component to maintain health here on
Earth, exercise plays an important role
in maintaining astronaut health and
fitness while in space. While living in
space requires very little effort to
maneuver around, the lack of gravity
can decondition the human body.
Knowledge gained during the early
years of human spaceflight indicated an
adaptation to the new environment.
While the empirical evidence was
limited, the biomedical data indicated
that microgravity alters the
musculoskeletal, cardiovascular, and
neurosensory systems. In addition, the
responses to spaceflight varied from
person to person. Space adaptation was
highly individualized, and some human
systems adjusted at different rates.
Overall, these changes were considered
to have potential implications on
astronaut occupational performance as
well as possible impacts to crew health
and safety. There was concern that
space-related deconditioning could
negatively influence critical space
mission tasks, such as construction of
the space station, repair of the orbiting
Hubble Space Telescope, piloting and
landing operations, and the ability to
egress in an emergency.
Historically, NASA worked on
programs to develop a variety of
strategies to prevent space
deconditioning, thus migrating toward
the use of exercise during spaceflight
to assure crew member health and
fitness. In general, exercise offered
a well-understood approach to fitness
on Earth, had few side effects, and
provided a holistic approach for
addressing health and well-being, both
physically and psychologically.
NASA scientists conducted experiments
in the 1970s to characterize the effects
of exercise during missions lasting 28,
56, and 84 days on America’s first
orbiting space station—Skylab. This
was the first opportunity for NASA to
study the use of exercise in space. These
early observations demonstrated that
exercise modalities and intensity could
improve the fitness outcomes of
astronauts, even as missions grew in
length. Armed with information from
Skylab, NASA decided to provide
exercise on future shuttle missions to
minimize consequences that might
be associated with spaceflight
deconditioning to guarantee in-flight
astronaut performance and optimize
postflight recovery.
Benefits of Exercise
Space Shuttle experience demonstrated
that for the short-duration shuttle
flights, the cardiovascular adaptations
did not cause widespread significant
problems except for the feelings of
light-headedness—and possibly
fainting—in about one-fifth of the
astronauts and a heightened concern
over irregular heartbeats during
spacewalks. During the Space Shuttle
Program, however, it became clear
from these short-duration missions that
exercise countermeasures would be
required to keep astronauts fit during
long-duration spaceflights. Although
exercise was difficult in the shuttle,
simple exercise devices were the
stationary bike, a rowing machine, and
a treadmill. Astronauts, like those from
Skylab, found it difficult to raise their
heart rate high enough for adequate
exercise. NASA demonstrated that
in-flight exercise could be performed
and helped maintain some aerobic
fitness, but much research remained to
be done. This finding led to providing
the ISS with a bicycle ergometer, a
treadmill, and a resistive exercise
device to ensure astronaut fitness.
Deconditioning due to a lack of
aerobic exercise is a concern in the
area of EVAs, as it could keep the
astronaut from performing spacewalks
and other strenuous activities. Without
enough in-flight aerobic exercise,
astronauts experienced elevated heart
rates and systolic blood pressures.
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The deconditioned cardiovascular
system must work harder to do the
same or even less work (exercise) than
the well-conditioned system.
Exercise capacity was measured
preflight on a standard upright bike.
Exercise was stepped up every
3 minutes with an increase in
workload. Maximal exercise was
determined preflight by each
astronaut’s maximum volume of
oxygen uptake. A conditioned
astronaut may have little increase
in heart rate above sitting when he
or she is walking slowly. The heart
rate and systolic blood pressure (the
highest blood pressure in the arteries,
just after the heartbeats during each
cardiac cycle) increase as the astronaut
walks fast or runs until the heart rate
cannot increase any more.
In-flight exercise testing showed that
crew members could perform at 70% of
the preflight maximum exercise level
with no significant issues. This allowed
mission planners to schedule EVAs
and other strenuous activities that did
not overtax the astronauts’capabilities.
How Astronauts Exercised on the
Space Shuttle
Because of the myriad restrictions
about what can be launched within a
space vehicle, tremendous challenges
exist related to space exercise
equipment. Systems need to be portable
and lightweight, use minimal electrical
power, and take up limited space
during use and stowage. In addition,
operation of exercise equipment in
microgravity is inherently different
than it is on Earth. Refining the
human-to-machine interfaces for
exercise in space was a challenging task
tested throughout the shuttle missions.
Providing exercise concepts with the
appropriate physical training stimulus
to maintain astronaut performance that
operates effectively in microgravity
proved to be a complex issue.
Exercise systems developed for shuttle
included: treadmill, cycle ergometer,
and rower. The devices offered exercise
conditioning that simulated ambulation,
cycling, and rowing activities. All
exercise systems were designed for
operations on the shuttle middeck;
however, the cycle could also be used
on the flight deck so that astronauts
could gaze out the overhead windows
during their exercise sessions.
Each of the three systems had its own
challenges for making Earth-like
exercise feasible while in space within
the limits of the shuttle vehicle. Most
traditional exercise equipment has the
benefit of gravity during use, while
spaceflight systems require unique
approaches to exercise for the astronaut
users. While each system had its unique
issues for effective space operations,
the exercise restraints were some of the
biggest challenges during the program.
These restraints included techniques
for securing an astronaut to the exercise
device itself to allow for effective
exercise stimuli.
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Ken Baldwin, PhD
Principal investigator on three
Spacelab missions—STS-40
(1991), STS-58 (1993), and STS-90
(1998)—and a Physiological
Anatomical Rodent Experiment.
Muscle Team leader, 2001-2009,
for the National Space Biomedical
Research Institute.
“The space life sciences missions (STS-40, STS-58, and STS-90) provided a
state-of-the-art laboratory away from home that enabled scientists to customize
their research studies in ways that were unheard of prior to the Space Shuttle
Program. In using such a laboratory, my research generated unique insights
concerning the remodeling of muscle structure and function to smaller, weaker,
fatigue-prone muscles with a contractile phenotype that was poorly suitable to
apposing gravity. These unique findings became the cornerstone of
recommendations that I spearheaded to redesign the priority of exercise during
spaceflight from one of an aerobic exercise focus (treadmill and cycling exercise) to
a greater priority of exercise paradigms favoring heavy-resistance exercise in order
to prevent muscle atrophy in microgravity. Additionally, our group also made an
important discovery in ground-based research supported by NASA’s National Space
Biomedical Research Institute showing that it is not necessarily the contraction
mode that the muscles must be subjected to, but rather it is the amount and volume
of mechanical force that the muscle must generate within a given contraction
mode in order to maintain normal muscle mass. Thus, the early findings aboard the
Space Shuttle have served as a monument for guiding future research to expand
humankind’s success in living productively on other planets under harsh conditions.”
In-flight exercise quality and quantity
were measured on all modalities
using a commercial heart rate monitor
for tracking work intensity and
exercise duration. This allowed for a
common measure across devices. Heart
rate is a quality indicator of exercise
intensity and duration (time) is a gauge
of exercise quantity––common
considerations used for generating
exercise prescriptions. Research
showed that target heart rates could be
achieved using each of the three types
of exercise during spaceflight.
Running and walking on a treadmill in
the gym can be computer controlled
with exercise profiles that alter speed
and grade. The shuttle treadmill had
limits to its tread length and speed
and had no means for altering grade.
Treadmill ambulation required the
astronaut to wear a complex over-the-
shoulder bungee harness system that
connected to the treadmill and held the
runner in place during use. Otherwise,
the runner would propel off the tread
with the first step. While exercise
target heart rates were achieved, the
treadmill length restricted gait length
and the harness system proved quite
uncomfortable. This information was
captured as a major lesson learned for
the development of future treadmill
systems for use in space.
Cycle Ergometer
The shuttle cycle ergometer (similar
to bicycling) operated much like the
equipment in a gym. It used a
conventional flywheel with a braking
band to control resistance via a small
motor with a panel that displayed the
user’s speed (up to 120 rpm) and
workload (up to 350 watts). The
restraint system used commercial
pedal-to-shoe bindings, or toe clips,
that held the user to the cycle while
leaning on a back pad in a recumbent
position. The cycle had no seat,
however, and used a simple lap belt to
stabilize the astronaut during aerobic
exercise. While the cycle offered great
aerobic exercise, it was also used for
prebreathe operations in preparation
for EVAs. The prebreathe exercise
protocol allowed for improved nitrogen
release from the body tissues to
minimize the risk of tissue bubbling
during the EVA that could result in
decompression sickness or “the bends.”
Exercise accelerated, “washout”
nitrogen that may bubble in the tissues
during EVA, causing decompression
sickness and, thereby, terminating the
EVA and risking crew health.
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The evolution of types of exercise: running, rowing, and cycling from Earth to space
configurations. Astronaut Jerry Linenger running during STS-64 (1994),Astronaut Robert
Cabana rowing on STS-53 (1992), and Astronaut Catherine Coleman cycling on STS-73 (1995).
“Shuttle left a legacy, albeit incomplete, of the theory and
practice for exercise countermeasures in space.”
William Thornton, MD, astronaut, principal investigator and original inventor of the shuttle treadmill.
The rower offered total body aerobic
exercise, similar to gym rowers. It also
had limited capability for resistance
exercise. Similar to the cycle, it was
seatless since the body floats. The
astronaut’s feet were secured with a
strap onto a footplate that
allowed for positioning. The rower used
a magnetic brake to generate resistance.
In summary, exercise during Space
Shuttle flights had physical and
psychological benefits for astronauts.
In general, it showed that astronauts
could reduce the deconditioning effects
that may alter performance of critical
mission tasks using exercise in space,
even on the relatively short shuttle
missions. As a result, a “Flight Rule”
was developed that mandated
astronauts exercise on missions longer
than 11 days to maintain crew health,
safety, and performance.
Each device had the challenge of
providing an appropriate exercise
stimulus without the benefit of gravity
and had a unique approach for on-orbit
operations. Engineers and exercise
physiologists worked closely together to
develop Earth-like equipment for the
shuttle environment that kept astronauts
healthy and strong.
Cardiovascular: Changes
in the Heart and Blood Vessels
That Affect Astronaut Health
and Performance
The cardiovascular system, including
the heart, lungs, veins, arteries, and
capillaries, provides the cells of the
body with oxygen and nutrients and
allows metabolic waste products
to be eliminated through the kidneys
(as urine) and the gastrointestinal tract.
All of this depends on a strong heart
to generate blood pressure and a
healthy vascular system to regulate
the pressure and distribute the blood,
as needed, throughout the body via
the blood vessels.
For our purposes, the human body
is essentially a column of fluid; the
hydrostatic forces that act on this
column, due to our upright posture
and bipedal locomotion, led to a
complex system of controls to
maintain—at a minimum—adequate
blood flow to the brain.
On Earth, with its normal gravity,
all changes in posture—such as when
lying down, sitting, or standing as
well as changes in activity levels such
as through exercising—require the
heart and vascular system to regulate
blood pressure and distribution by
adjusting the heart rate (beats per
minute), amount of blood ejected by
the heart (or stroke volume), and
constriction or dilation of the
distributing arteries. These adjustments
assure continued consciousness by
providing oxygen to the brain or
continued ability to work, with oxygen
going to the working muscles.
Removing the effects of gravity during
spaceflight and restoring gravity after a
period of adjustment to weightlessness
present significant challenges to
the cardiovascular control system.
The cardiovascular system is stressed
very differently in spaceflight, where
body fluids are shifted into the head
and upper body and changes in
posture do not require significant
responses because blood does not
drain and pool in the lower body.
Although the cardiovascular system
is profoundly affected by spaceflight,
the basic mechanisms involved are still
not well understood.
During the shuttle era, flight-related
cardiovascular research focused on
topics that could benefit the safety and
well-being of crew members while also
revealing the mechanisms underlying
the systemic adjustments to spaceflight.
NASA researchers studied the
immediate responses to the effects of
weightlessness during Space Shuttle
flights and the well-developed systemic
adjustments that followed days and
weeks of exposure. Most
such research related to the loss of
orthostatic tolerance after even brief
flights and to the development of
potentially detrimental disturbances in
cardiac rhythm during longer flights.
Scientists also evaluated the usefulness
of several interventions such as exercise,
fluid ingestion, and landing-day gravity
suits (g-suits) in protecting the
astronauts’capacities for piloting the
Orbiter—an unpowered, 100-ton
glider—safely to a pinpoint landing,
and especially for making an unaided
evacuation from the Orbiter if it landed
at an alternate site in an emergency.
Orthostatic Intolerance:
Feeling Light-headed and Fainting
on Standing Upright
One of the most important changes
negatively impacting flight operations
and crew safety is landing day
orthostatic intolerance. Astronauts who
have orthostatic intolerance (literally,
the inability to remain standing upright)
cannot maintain adequate arterial blood
pressure and have decreased brain blood
levels when upright, and they experience
light-headedness and perhaps even
fainting. This may impair their ability
to stand up and egress the vehicle after
landing, and even to pilot the vehicle
while seated upright as apparent gravity
increases from weightlessness to 1.6g
during atmospheric re-entry.
The orthostatic intolerance condition
is complicated and multifactorial.
Its hallmarks are increased heart rate,
decreased systolic blood pressure,
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and decreased stroke volume during
5 minutes of standing shortly after
landing. The decrease in blood volume
frequently observed is an important
initiating event in the etiology of
orthostatic intolerance, but it is the
subsequent effects and the
physiological responses (or lack
thereof) to those effects that may result
in orthostatic intolerance after shuttle
flights. This is highlighted by the fact
that while all shuttle crew members
who were tested had low blood volume
on landing day, only one-quarter of
them developed orthostatic intolerance
during standing or head-up tilting.
The group of astronauts that developed
orthostatic intolerance lost comparable
amounts of plasma (the watery
portion of the blood, which the body
can adjust quickly) to the group that
did not develop orthostatic intolerance.
But, the group that was not susceptible
had a more pronounced increase in
the functioning of the sympathetic
nervous system, which is important
in responding to orthostatic stress
after returning to Earth. Thus, it is not
the plasma volume loss alone that
causes light-headedness but the lack
of compensatory activation of the
sympathetic system.
Another possible mechanism for
post-spaceflight orthostatic hypotension
(low blood pressure that causes
fainting) is cardiac atrophy and the
resulting decrease in stroke volume
(the amount of blood pushed out of the
heart at each contraction). Orthostatic
hypotension occurs if the fall in stroke
volume overwhelms normal
compensatory mechanisms such as an
increase in heart rate or constriction in
the peripheral blood vessels in the
arms, legs, and abdomen.
The vast majority of astronauts have
been male. Consequently, any
conclusions drawn regarding the
physiological responses to spaceflight
are male biased. NASA recognized
significant differences in how men and
women respond to spaceflight,
including the effects of spaceflight on
cardiovascular responses to orthostatic
stress. More than 80% of female crew
members tested became light-headed
during postflight standing as compared
to about 20% of men tested, confirming
a well-established difference in the
non-astronaut population. This is an
important consideration for prevention,
as treatment methods may not be
equally effective for both genders.
How Can This Risk be Changed?
While orthostatic intolerance is
perhaps the most comprehensively
studied cardiovascular effect of
spaceflight, the mechanisms are not
well understood. Enough is known
to allow for the implementation of
some countermeasures, yet none of
these countermeasures have been
completely successful at eliminating
spaceflight-induced orthostatic
intolerance following spaceflight.
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After Entering
While in
The distribution of blood changes in microgravity more in the upper torso and less in the
legs. At landing, the astronaut is light-headed because of less blood and the pooling of
the blood in the feet.
Blood Volume Changes During Spaceflight
In 1985, ingestion of fluid and salt
(or “fluid loading”) prior to landing
became a medical requirement through
a Flight Rule given the demonstrated
benefits and logic that any problem
caused—at least in part—by a loss in
plasma volume should be resolved—
at least in part—by fluid restoration.
Starting about 2 hours before landing,
astronauts ingest about 1 liter (0.58 oz)
of water along with salt tablets.
Subsequent refinements to enhance
palatability and tolerance include the
addition of sweeteners and substitution
of bouillon solutions. Of course, any
data on plasma volume acquired after
1985 do not reflect the unaltered landing
day deficit. But, in spite of the fluid
loading, astronauts still returned from
shuttle missions with plasma volume
deficits ranging from 5% to 19% as well
as with orthostatic intolerance.
Shuttle astronauts returned home
wearing a lower-body counterpressure
garment called the anti-g suit. These
suits have inflatable bladders at the
calves, thighs, and lower abdomen
that resist blood pooling in those areas
and force the blood toward the head.
The bladders can be pressurized from
25 mmHg (0.5 psi) to 130 mmHg
(2.5 psi). In addition, ISS crew
members landing on the shuttle used
recumbent seats (as opposed to the
upright seats of the shorter-duration
shuttle crews) and only inflated their
suit minimally to 25 mmHg (0.5 psi).
All astronauts deflated their anti-g suit
slowly after the shuttle wheeled to a
stop to allow their own cardiovascular
systems time to readjust to the pooling
effects of Earth’s gravity.
Other treatments for orthostatic
intolerance were also evaluated during
the program. A technique called
“lower body negative pressure,”
which used slight decompression of
an airtight chamber around the
abdomen and legs to pool blood there
and thus recondition the cardiovascular
system, showed promise in ground
studies but was judged too
cumbersome and time consuming for
routine shuttle use. A much simpler
approach used a medication known as
fludrocortisone, a synthetic
corticosteroid known to increase fluid
retention in patients on Earth. It proved
unsuccessful, however, when it was not
well-tolerated by crew members and
did not produce any differences in
plasma volume or orthostatic tolerance.
Thus, the countermeasures tested were
not successful in preventing postflight
orthostatic intolerance, at least not
in an operationally compatible manner.
The knowledge gained about
spaceflight-induced cardiovascular
Major Scientific Discoveries
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changes and differences between
orthostatic tolerance groups, however,
provided a base for development of
future pharmacological and mechanical
countermeasures, which will be
especially beneficial for astronauts on
long-duration missions on space
stations and to other planets.
How Red Blood Cells Are Lost
in Spaceflight
What do astronauts, people
traveling from high altitudes to
sea level, and renal (kidney)
failure patients have in common?
All experience changes in red
blood cell numbers due to changes
in the hormone erythropoietin,
synthesized in the kidneys.
Red blood cells bring oxygen to tissues. When astronauts enter microgravity
or high-altitude residents travel to sea level, the body senses excess red blood cells.
High-attitude residents produce an increased number because of decreased ambient
oxygen levels but, at sea level, excess cells are not needed. Astronauts experience
a 15% decrease in plasma volume as the body senses an increase in red blood cells
per volume of blood. In these situations, erythropoietin secretion from the kidneys
ceases. Prior to our research, we knew that when erythropoietin secretion stops, the
bone marrow stops production of pre red blood cells and an increase in programmed
destruction of these cells occurs.
Another function was found in the absence of erythropoietin, the loss of the newly
secreted blood cells from the bone marrow—a process called neocytolysis. Since
patients with renal failure are unable to synthesize erythropoietin, it is administered at
the time of renal dialysis (a process that replaces the lost kidney functions); however,
blood levels of erythropoietin fell rapidly between dialysis sessions, and neocytolysis
occurs. Thus, the development of long-lasting erythropoietin now prevents
neocytolysis in these patients. Erythropoietin is, therefore, important for human
health—in space and on Earth—and artificial erythropoietin is essential for renal
failure patients.
Cardiovascular Changes During
Headward fluid shift was inferred
from reports containing astronaut
observations of puffy faces and skinny
legs, and was long believed to be the
initiating event for subsequent
cardiovascular responses to spaceflight.
The documentation of this shift was
an early goal of Space Shuttle-era
investigators, who used several
techniques to do so. Direct measurement
of peripheral venous blood pressure in
an arm vein (assumed to reflect central
venous pressure in the heart, an
indication of headward fluid shift) was
done in 1983 during in-flight blood
collections. Actual measurement of
central venous pressure was done on a
small number of astronauts on dedicated
space life sciences Spacelab missions
starting in 1991. These studies, and
particularly the direct central venous
pressure measurements, demonstrated
that central venous pressure was
elevated in recumbent crew members
even before launch, and that it increased
acutely during launch with acceleration
loads of up to three times Earth’s
surface gravity. This increased the
weight of the column of blood in the
legs “above” the heart and the central
venous pressure decreased to below
baseline values immediately on
reaching orbit. Investigators realized
that the dynamics of central blood
volume changes were more complex
than originally hypothesized.
By measuring and recording arterial
blood pressures, heart rate, and rhythm,
two-dimensional echocardiography
demonstrated the variety of changes
in the cardiovascular system in flight.
In-flight heart rate and systolic and
diastolic blood pressure decreased when
compared to the preflight values. During
re-entry into Earth’s atmosphere, these
values increased past their preflight
baseline, reaching maximal values at
peak deceleration loading. When crew
members stood upright for the first time
after landing, both systolic and diastolic
pressures significantly decreased from
their seated values and the decrease in
diastolic pressure was greater in crew
members who did not fully inflate their
g-suits. Systolic pressure and heart rate
returned to preflight values within an
hour of landing, whereas all other
spaceflight-induced cardiovascular
changes were reversed within a week
after landing. Furthermore, stress
hormones such as adrenaline
(involved in the primal “fight or flight
response”) were increased postflight,
whether the astronauts were resting
supine or standing.
So, What Does This Mean?
During weightlessness, there is reduced
postural stress on the heart. As expected,
the cardiovascular response is muted:
blood pressure and heart rate are lower
in the resting astronaut than before
flight. The volume of blood ejected from
the heart with each beat initially
increases because of the headward fluid
shift, but it becomes lower than preflight
levels after that due to the decreased
blood volume.
Cardiac Rhythm Disturbances
Contrary to popular opinion, shuttle
astronauts were not monitored
extensively throughout their flights.
Electrocardiograms were recorded and
transmitted for crew health assurance
only on up to two crew members
(out of crews numbering up to seven)
and only during launch and landing
through the 14th shuttle mission,
STS-41G (1984). Subsequently, given
the established confidence that healthy
astronauts could tolerate spaceflight
without difficulty, the requirement for
even such minimal medical monitoring
was eliminated. Later, a purpose-built
system for on-board recording of
electrocardiograms and blood pressure
was used on select volunteer astronauts
between 1989 and 1994.
At present, there is little evidence to
indicate that cardiovascular changes
observed in spaceflight increase
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Major Scientific Discoveries
In the Spacelab (laboratory in Orbiter payload bay) Astronaut Rhea Seddon, MD, measures cardiac
function on Martin Fettman during Columbia life sciences mission STS-58 (1993) .
susceptibility to life-threatening
disturbances in cardiac rhythms.
Certain findings, however, suggest that
significant cardiac electrical changes
occurred during short and long flights.
NASA systematically studied cardiac
rhythm disturbances during some
shuttle missions in response to medical
reports of abnormal rhythms in nine of
14 spacewalking astronauts between
1983 and 1985. In subsequent studies on
12 astronauts on six shuttle flights,
investigators acquired 24-hour
continuous Holter recordings of the
electrocardiograms during and after
altitude chamber training, then again
30 days before launch, during and after
each EVA, and after return to Earth.
These investigators observed no change
in the number of premature contractions
per hour during flight compared to
preflight or postflight. Given the fact
that these data disagreed with other
previous reports on astronauts, the
investigators recommended that further
study was required.
The Space Shuttle provided many
opportunities to study the
cardiovascular system due to the high
number of flights and crew members,
along with an emphasis on life sciences
research. This research provided a
better understanding of the changes
in spaceflight and provided focus for
the ISS research program.
Nutritional Needs in Space
Do Astronauts Have Special
Nutritional Needs?
If elite athletes like Olympians have
special nutritional needs, do astronauts
too? During the shuttle flights,
nutrition research indicated that, in
general, the answer is no. Research,
however, provided the groundwork for
long-duration missions, such as for the
ISS and beyond. Additionally, as the
expression goes, while good nutrition
will not make you an Olympic-quality
athlete, inadequate nutrition can ruin an
Olympic-quality athlete.
Nutritional needs drive the types and
amounts of food available on orbit.
Since shuttle flights were short (1 to
2 weeks), nutritional needs were more
like those required for a long camping
trip. Accordingly, NASA’s research
focused on the most important nutrients
that related to the physiological
changes that microgravity induced for
such short missions. The nutrients
studied were water, energy (calories),
sodium, potassium, protein, calcium,
vitamin D, and iron.
Many astronauts eat and drink less in
flight, probably due to a combination of
reduced appetite and thirst, high stress,
altered food taste, and busy schedules.
Because the success of a flight is based
on the primary mission, taking time for
eating may be a low priority. Astronauts
are healthy adults, so NASA generally
uses Earth-based dietary nutrient
recommendations; however, researchers
commonly found inadequate food
intake and corresponding loss of
body weight in astronauts. This
observation led to research designed
to estimate body water and energy
needed during spaceflight.
How Much Water Should an
Astronaut Consume?
Water intake is important to prevent
dehydration. About 75% of our bodies
is water, located mostly in muscles.
The fluid in the blood is composed of
a noncellular component (plasma) and a
cellular component (red blood cells).
NASA measured the various body water
compartments using dilution techniques:
total body water; extracellular volume
(all water not in cells), plasma volume,
and blood volume. Because of the lack
of strong gravitational force, a shift of
fluid from the lower body to the upper
body occurs. This begins on the launch
pad, when crew members may lie on
their backs for 2 to 3 hours for many
flights. Scientists hypothesize that the
brain senses this extra upper-level body
water and adapts through reduced thirst
and, sometimes, increased losses through
the kidney—urine. An initial reduction
of about15% water (0.5 kg [1.15 pounds])
occurred in the plasma in flight, thus
producing a concentrated blood that is
corrected by reducing the levels of red
blood cells through a mechanism that
reduces new blood cells. Soon after
entering space, these two compartments
(plasma and red blood cells) return to
the same balance as before flight but
with about 10% to 15% less total
volume in the circulation than before
flight. Through unknown mechanisms,
extracellular fluid is less and total body
water does not change or may decrease
slightly, 2% to 3% (maximum loss of
1.8 kg [4 pounds]). From this NASA
scientists inferred that the amount of
intracellular fluid is increased,
although this has not been measured.
These major fluid shifts affect thirst
and, potentially, water requirements
as well as other physiological functions.
Water turnover decreases due to a
lower amount of water consumed
and decreased urine volume—both
occur in many astronauts during
spaceflight. Since total body water
does not change much, recommended
water intakes are around 2,000 ml/d
(68 oz, or 8.5 cups). Astronauts may
consume this as a combination of
beverages, food, and water.
Because of potentially reduced thirst
and appetite, astronauts must make an
effort to consume adequate food and
water. Water availability on the shuttle
was never an issue, as the potable
water was a by-product of the fuel
cells.With flights to the Russian space
station Mir and the ISS, the ability to
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transfer water to these vehicles
provided a tremendous help as the
space agencies no longer needed to
launch water, which is very heavy.
A much-improved understanding of
water loss during EVAs occurred
during the shuttle period. This
information led to the ISS EVA
standards. Dehydration may increase
body heat, causing dangerously high
temperatures. Therefore, adequate
water intake is essential during EVAs.
NASA determined how much water
was needed for long EVAs (6 hours
outside the vehicle, with up to 12 hours
in the EVA suit). Due to the concern
for dehydration, water supplies
were 710 to 946 ml (24 to 32 oz, or
3 to 4 cups) in the in-suit drink bag
(the only nutrition support available
during EVA).
How Spaceflight Affects
Kidney Function
Does the headward fluid shift decrease
kidney function? The kidneys depend
on blood flow, as it is through plasma
that the renal system removes just the
right amount of excess water, sodium,
metabolic end products like urea and
creatinine, as well as other metabolic
products from foods and contaminates.
So, what is the affect of reduced heart
rates and lower blood volumes?
Astronauts on several Spacelab flights
participated in research to determine
any changes in renal function and the
hormones that regulate this function.
When the body needs to conserve
water, such as when sweating or not
hydrating enough, a hormone called
antidiuretic hormone prevents water
loss. Similarly, when the body has too
little sodium, primarily due to diet and
sweating, aldosterone keeps sodium
loss down. All the experiments showed
that these mechanisms worked fine in
spaceflight. We learned not to worry
about the basic functions of the kidney.
Renal Stones
As stated, the kidney controls excess
water. But, what happens if a crew
member is dehydrated due to sweating
or not consuming enough water? During
spaceflight, urine becomes very
concentrated with low levels of body
water. This concentrated urine is doubly
changed by immediately entering
microgravity, and the bone starts losing
calcium salts. Although these losses
were not significant during the short
shuttle flights, this urinary increase had
the potential to form calcium oxalate
renal stones. Furthermore, during
spaceflight, protein breakdown increases
due to muscle atrophy and some of the
end products could also promote renal
stones. Due to the potential problem of
renal stones, crew members were
strongly encouraged to consume more
water than their thirst dictated. This
work led to the development of
countermeasures for ISS crew members.
Sodium and Potassium: Electrolytes
Important for Health
The electrolytes sodium (Na) and
potassium (K) are essential components
of healthy fluid balance; Na is a
primarily extracellular ion while K is
a primarily intracellular ion. They
are essential for osmotic balance, cell
function, and many body chemical
reactions. K is required for normal
muscle function, including the heart.
With changes in fluid balance, what
happens to these electrotypes,
especially in their relationship to
kidney and cardiovascular function?
Total body water levels change with
changes in body weight. With weight
loss, liver glycogen (polymers of
glucose) stores that contain significant
associate water are lost, followed by
tissue water—fat 14% and lean body
mass 75% water. Antidiuretic hormone
conserves body water. Aldosterone
increases the volume of fluid in the
body and drives blood pressure up,
while atrial natriuretic peptide controls
body water, Na, K, and fat (adiposity),
thereby reducing blood pressure.
In the first few days of spaceflight,
antidiuretic hormone is high but it then
readjusts to controlling body water.
Aldosterone and atrial natriuretic
peptide reflect Na and water intakes to
prevent high blood pressure.
Research from several Spacelab
missions demonstrated that in
microgravity, astronauts’ bodies are
able to adjust to the changes induced
by microgravity, high Na intakes,
and the stress of spaceflight. During
spaceflight, Na intakes are generally
high while K intakes are low as
compared to needs. The astronauts
adjust to microgravity within a few
days. Although astronauts have less
body water and a headward shift of
water, these regulatory hormones
primarily reflect dietary intakes.
The implications of these data for
long-duration flights, such as the ISS,
remain unknown. While on Earth, high
Na intakes are most often associated
with increasing blood pressure. Such
intakes also may exacerbate bone loss,
which is a problem for astronauts on
long-duration spaceflights.
How Many Calories Do Astronauts
Need in Spaceflight?
Because astronauts eat less, research
determined the energy level (calories)
needed during spaceflight. For selected
missions, astronauts completed food
records with a bar code reader to obtain
good information about dietary intake
during spaceflights. These studies
showed that most astronauts ate less
than their calculated energy needs—on
average, about 25% less.
Scientists completed two types of
research for measuring astronauts’
body energy use. Energy can be
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Major Scientific Discoveries
determined from the products of energy
metabolism: carbon energy sources like
carbohydrates, protein, or fat + oxygen
) = heat + carbon dioxide (CO
We used two methods for shuttle
flights. For most flights, all the expired
was removed by chemical reaction
with lithium hydroxide (LiOH) so the
amount of CO
produced during a flight
could be determined. CO
that was
absorbed into the LiOH could be
measured at the end of the flight to
determine the energy use by the crew
over the entire mission. The second
method was to determine the amount
of CO
and water loss over 3 to 5 days
of time per astronaut. Astronauts
consumed two stable isotopes (not
radioactive), deuterium and
O, and
the levels of these isotopes in urine
were measured over a period of several
days. The O
occurs in the CO
water, but deuterium is only in the
water; thus the method allowed for the
determination of the CO
produced by
an astronaut. Surprisingly for both
methods, the levels of energy used were
the same in flight as on Earth. As a
result of this research, NASA dietitians
use gender and weight, along with
allowing for moderate activity values,
to calculate astronauts’ energy needs for
spaceflight. This method has worked
for many years to ensure adequate
provision of space foods.
One of the major contributions of EVA
research is the increased ability to
predict energy expenditure during
spacewalks. EVAs were routinely
conducted from the shuttle. Energy
expenditure was important for both suit
design and dietary intakes before and
after a spacewalk. After conducting
thousands of EVA hours, NASA
knows that the energy expenditure
was not high for a short period of time,
similar to walking 4 to 6.4 kph
(2.5 to 4.0 mph). Nearly all EVAs
lasted around 6 hours, however, and
thus energy expenditure added up to
a fairly high level. The lower energy
levels occurred when crew members
were within the payload bay, primarily
doing less-demanding work for short
periods. With the construction of the
ISS, EVA activity increased along
with duration to about 4 to 8 kJ/hr (250
to 500 kcal/hr). For an 8-hour EVA,
this was significant. Of course, as
previously described, increased energy
expenditure increased water needs.
Protein and Amino Acids: Essential
for Maintenance of Muscle Function
Protein and its components (amino
acids) are essential for all body
chemical reactions, structure, and
muscles. In spaceflight, total body
protein turnover increases as measured
by the loss of the orally ingested stable
N-glycine, which was
measured in body tissues such as saliva
and blood. Glycine is an amino acid
that occurs abundantly in proteins, so
changes in blood levels indicate the
amount of glycine moved to the tissues
for protein syntheses. Some of the
increased turnover may be due to the
catabolic state of weight loss found
with many astronauts due to
lower-than-needed energy intakes.
There is evidence, even with short-term
shuttle flights, that skeletal muscle
function decreases. The mild stress of
spaceflight found with hard-working
astronauts may increase protein
breakdown. Increased stress was
determined by increased levels of blood
and urinary cortisol. Dietary protein
levels are already high in spaceflight.
Protein recommendations are the same
as ground-based dietary guidelines.
Bones Need Calcium and Vitamin D
Studies with Skylab astronauts in the
1970s and shuttle crew members found
calcium (Ca) losses increased during
flight, probably through removal from
bone. NASA confirmed this initial
observation of bone loss in the 1990s by
using the latest biological markers
technology. In fact, research showed
that as soon as the astronauts arrived in
space, they started losing bone.
Vitamin D is essential for the body
to absorb the dietary Ca that is used for
bone and other tissue functions.
Vitamin D syntheses occur in the skin
during exposure to sunlight. In
spacecraft, however, sunlight is not
tolerated: the rays are too strong
because flights take place above the
protective atmosphere. Studies
completed during the Shuttle-Mir and
European Space Agency research
programs showed low vitamin D levels
could be a problem for Ca absorption
and good bone health. A vitamin D
supplement is provided for ISS
long-duration spaceflights.
Too Much Iron May Be Toxic
Changes in astronaut’s red blood cells
and iron (Fe) levels are similar to those
of a person who lives at a high altitude
(e.g., 3,658 m [12,000 ft]) coming to
sea level. Both have too much available
Fe (i.e., not bound up in red blood cells).
Fe is an important part of red blood
cells that brings oxygen from the
lungs to the tissues. Low levels of red
blood cells cause fatigue. The initial
decrease in plasma volume produces
an increased concentration of red
blood cells. The body may then
perceive too many red blood cells
and make adjustments accordingly.
A12% to 14% decrease in the
number of red blood cells occurs
within a couple of weeks of spaceflight.
To maintain the correct percent of
red blood cells (about 37% to 51% of
the blood), newly formed red blood
cells are destroyed until a new
equilibrium is achieved. The red
blood cell Fe is released back into the
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blood and tissues, and no mechanism
except bleeding can reduce the level of
body Fe. Excess Fe could potentially
have toxic effects, including tissue
oxidation and cardiovascular diseases.
Shuttle research showed that the dietary
Fe need is below that needed on Earth
because of the reduced need for red
blood cell production.
Summary of Nutritional Needs Found
for Space Shuttle Astronauts
Changes in Immunity
and Risk of Infectious Disease
During Spaceflight
Humans are healthy most of the time,
despite being surrounded by potentially
infectious bacteria, fungi, viruses, and
parasites. How can that be? The answer
is the immune system. This highly
complex and evolved system is our
guardian against infectious diseases
and many cancers. It is essential that
astronauts have a robust, fully
functional immune system just as it
is for us on Earth. Astronauts are very
healthy, exquisitely conditioned, and
well nourished—all factors promoting
healthy immunity. In addition,
exposures to potential microbial
pathogens are limited by a series of
controls. All shuttle consumables
(e.g., drinking water and food) and
environment (breathing air and
surfaces) are carefully examined to
ensure the health and safety of the
astronauts. Preflight restrictions are in
place to limit exposure of astronauts to
ill individuals. This system works very
well to keep astronauts healthy before,
during, and after spaceflight. Since
spaceflight is thought to adversely affect
the immune system and increase disease
potential of microorganisms, the shuttle
served as a platform to study immunity
and microbes’ability to cause disease.
The Immune System
Your immune system quietly works
for you, a silent army within your body
protecting you from microorganisms
that can make you sick. If it is
working well, you never know it.
But, when it’s not working well, you
will probably feel it.
The human immune system consists of
many distinct types of white blood cells
residing in the blood, lymph nodes, and
various body tissues. The white blood
cells of the immune system function in
a coordinated fashion to protect the host
from invading pathogens (bacteria,
fungi, viruses, and parasites).
There are various elements of immunity.
Innate immunity is the first line of
defense, providing nonspecific killing of
microbes. The initial inflammation
associated with a skin infection at a
wound site is an example of innate
immunity, which is primarily mediated
by neutrophils, monocytes, and
macrophages. Cell-mediated immunity
provides a specific response to a
particular pathogen, resulting in
immunologic “memory” after which
immunity to that unique pathogen is
conferred. This is the part of the
immune system that forms the basis of
how vaccines work. T cells are part of
cell-mediated immunity, while B cells
provide the humoral immune response.
Humoral immunity is mediated by
soluble antibodies—highly specific
antimicrobial proteins that help
eliminate certain types of pathogens and
persist in the blood to guard against
future infections. Upon initial exposure
to a unique pathogen such as a herpes
virus, the number of specific types of
T and B cells expands in an attempt to
eliminate the infection. Afterward,
smaller numbers of memory cells
continue to patrol the body, ever vigilant
for another challenge by that particular
pathogen. An immune response can
be too strong at times, leading to
self-caused illness without a pathogen.
Examples of this are allergies and
autoimmune diseases. At other times
an immune response is not strong
enough to fight an infection
(immunodeficiency). Acquired
Immunodeficiency Syndrome (AIDS)
and cancer chemotherapy are both
examples of immunodeficiency
conditions caused by the loss of one or
more types of immune cells.
Spaceflight-associated Changes
in Immune Regulation
Changes in regulation of the immune
system are found with both short- and
long-duration spaceflight. Studies
demonstrated that reduced cell mediated
immunity and increased reactivation of
latent herpes viruses occur during flight.
In contrast, humoral (antibody)
immunity was found to be normal when
astronauts were immunized during
spaceflight. Other shuttle studies
showed reduced numbers of T cells and
natural killer cells (a type of white
blood cell important for fighting cancer
and virally infected cells), altered
distribution of the circulating leukocyte
(white blood cell) subsets, altered stress
hormone levels, and altered cytokine
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Major Scientific Discoveries
levels. Reduced antimicrobial functions
of monocytes, neutrophils, and natural
killer cells also occur when measured
soon after spaceflight. Cytokines are
small proteins produced by immune
cells; they serve as molecular
messengers that control the functions
of specialized immune cells. Cytokines
are released during infection and serve
to shape the immune response. There
are many cytokines, and they can be
grouped in several ways. Th1 cytokines
are produced by specialized T cells
to promote cell-mediated immunity,
whereas Th2 cytokines promote
humoral immunity. One hypothesis to
explain immune dysregulation during
spaceflight is a shift in the release of
cytokines from Th1 toward Th2
cytokines. Data gained from the shuttle
research support this theory.
Energy men
70 kg (154 pounds)
12.147 MJ/d (2,874 kcal/d)
Energy women
60 kg (132 pounds)
9.120 MJ/d (2,160 kcal/d)
12% to 15% of energy intake
< 85 g/d
2,000 ml/d
1,500 to 3,500 mg/d
3,500 mg/d
10 mg/d
Vitamin D
10 ug/d
800 to 1,200 mg
Selected Space Shuttle
Immune Studies
Hypersensitivity occurs when the
immune response to a common antigen
is much stronger than normal. Usually,
this manifests itself as a rash and is
commonly measured via skin testing.
Briefly, seven common antigens,
bacteria, Proteus (common in urinary
track infections), Streptococcus,
tuberculin and Trichophyton (skin
diseases), and yeast, Candida (known to
increase in the immune compromised),
are injected into the forearm skin.
For most normal individuals, the
cell-mediated arm of the immune
system reacts to these antigens within
2 days, resulting in a visible red,
raised area at the site of the injections.
These reactions are expected and
represent a healthy immune response.
The red, raised circular area for each
antigen can be quantified. To test
astronauts, antigens were injected
46 hours before landing, and the
evaluation of the reaction took place
2 hours after landing. Data showed
that, as compared to preflight baseline
testing, the cell-mediated immunity
was significantly reduced during flight.
Both the number of reactions and the
individual reaction size were reduced
during flight. These data indicated for
the first time that immunity was reduced
during short-duration spaceflight. Any
associated clinical risks were unknown
at the time. The possibility that this
phenomenon would persist for
long-duration flight was also unknown.
Similar reductions in cell-mediated
immunity were reported in Russian
cosmonauts during longer missions.
Studies of the Peripheral
Mononuclear Cells
Peripheral mononuclear cells are
blood immune cells. Their numbers
are a measure of the current immune
status of a subject. During the latter
stages of the 11-day STS-71 (1995)
shuttle mission, the shuttle astronauts
and the returning long-duration
astronauts (from Mir space station)
stained samples of their peripheral
blood immune cells with various
dyes using unique and patented
equipment developed at Johnson
Space Center. These data showed that
the major “bulk” levels of peripheral
blood immune cells did not appear to
be altered during flight.
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comprises the cells and mechanisms that defend the host from
infection by other organisms, in a nonspecific manner, and are found in all classes of plant
and animal life.
Red Blood Cells
White Blood Cells
B lymphocytes - Humoral immunity
T lymphocytes - Cell-mediated immunity
Natural killer cells - Innate immunity
Innate immunity
Humoral immunity
Humoral immunity
Humoral immunity
White Blood Cells
L mphocytes
White Blood Cells
T lymphocytes - Cell-mediated immunity
Innate immunity
B lymphocytes - Humoral immunity
T lymphocytes - Cell-mediated immunity
Innate immunity
B lymphocytes - Humoral immunity
T lymphocytes - Cell-mediated immunity
B lymphocytes - Humoral immunity
Red Blood Cells
Natural killer cells - Innate immunity
Innate immunity
Humoral immunity
(involving substances found in the humours, or body fluids) is
mediated by secreted antibodies that are produced by B lymphocytes and bind to antigens
on the surfaces of invading microbes, which marks the microbes for destruction.
Cell-mediated immunity
is an immune response that involves the activation of
macrophages, natural killer cells, antigen-specific cytotoxic T lymphocytes, and the release
of various cytokines in response to an antigen.
Immunity Components of Blood
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Major Scientific Discoveries
Herpes Viruses Become Active During Spaceflight
Childhood chicken pox
becomes dormant in
the nervous system.
Hair Shaft
Skin Surface
Blisters resembling
chicken pox
develop and ll
with pus.
Blisters eventually
burst, crust over,
and heal.
Nerve damage
can cause
Initial stage consists
of burning pain and
sensitive skin.
immune system
Varicel a
Nerve Fiber
Primary Disease
(Chicken Pox)
Stress on the
immune system
allows the latent
virus to reactivate
as shingles.
Herpes viruses, the most commonly
recognized latent viruses in humans,
cause specific primary diseases
(e.g., chicken pox), but may remain inactive
in nervous tissue for decades. When
immune response is diminished by stress
or aging, latent viruses reactivate and
cause disease (e.g., shingles).
Epstein-Barr virus reactivated and appeared
in astronauts’ saliva in large numbers
during spaceflight. Saliva collected during
the flight phase contained tenfold more virus
than saliva collected before or after flight.
This finding correlated with decreased
immunity in astronauts during flight.The
causes of reduced immunity are unknown,
but stress associated with spaceflight
appears to play a prominent role, as the
levels of stress hormones increase during
spaceflight.The resulting decreased
immunity allows the viruses to multiply
and appear in saliva.The mechanism for
Epstein-Barr virus reactivation seems to be
a reduction in the number of virus-specific
T cells leading to decreased ability to keep
Epstein-Barr virus inactive.
Cytomegalovirus, another latent virus,
also reactivated and appeared in astronaut
urine in response to spaceflight. Healthy
individuals rarely shed cytomegalovirus
in urine, but the virus is commonly found in
those with compromised immunity.
Scientists also studied Varicella-Zoster
virus, the causative agent of chicken pox
and shingles. These astronaut studies were
the first reports of the presence of this
infectious virus in saliva of asymptomatic
individuals. A rapid, sensitive test for
use in doctors’ offices to diagnose shingles
and facilitate early antiviral therapy
resulting in reductions in nerve damage
was a product of this study.
Role of Varicella-Zoster Virus in Chicken Pox and Shingles
The laboratory capabilities of the
Space Shuttle allowed our first
systematic assessment of the effects
of space travel on the human immune
system. Most indicators of immunity
were altered during short-duration
spaceflight, which is a uniquely
stressful environment. These stressors
were likely major contributors to the
observed changes in immunity and the
increased viral reactivation. Latent
viruses were shown to be sensitive
indicators of immune status. Bacterial
pathogens were also shown to be more
virulent during spaceflight. It is
unknown whether these are transient
effects or whether they will persist for
long-duration missions. These
important data will allow flight
surgeons to determine the clinical risk
for exploration-class space missions
(moon, Mars) related to immunology,
and to further the development of
countermeasures for those risks.
These studies and the hardware
developed to support them serve as
the platform from which new studies
on board the ISS were initiated.
It is expected that the ISS studies will
allow a comprehensive assessment
of immunity, stress, latent viral
reactivation, and bacterial virulence
during long-duration spaceflight.
Habitability and
Environmental Health
The shuttle contributed significantly
to advances in technologies and
processes to improve the habitability
of space vehicles and enable humans
to live and work productively in space.
These shuttle-sponsored advances
played a key role in our coming to
view living and working in space as
not only possible but also achievable
on a long-term basis.
Habitability can be defined as the
degree to which an environment meets
an individual’s basic physiological and
psychological needs. It is affected by
multiple factors, including the size of
the environment relative to the number
of people living and working there
and the activities to be undertaken.
Other habitability factors include air,
water, and food quality as well as
how well the environment is designed
and equipped to facilitate the work that
is to be done.
Resource limitations conspire to
severely limit the habitability of space
vehicles. Spacecraft usually provide
minimal volume in which crew
members can live and work due to
the high cost of launching mass into
space. The spacecraft’s environmental
control system is usually closed to
some degree, meaning that spacecraft
air and water are recycled and their
quality must be carefully maintained
and monitored. It may be several
months between when food is prepared
and when it is consumed by a space
crew. There is normally a limited fresh
resupply of foods. Care must be taken
to assure the quality of the food before
it is consumed.
The following sections illustrate some
of the technologies and processes that
contributed to the habitability of the
shuttle and provided a legacy that will
help make it possible for humans to live
safely and work productively in space.
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On STS-90 (1998), three Space Shuttle Columbia crew members—Astronauts James Pawelczyk,
Richard Searfoss, and Richard Linnehan—meet on the middeck, where the crew ate, slept, performed
science, prepared for extravehicular activities (spacewalks), exercised, took care of personal hygiene
needs, and relaxed.
Innovations Improve Habilitability
Restraints and Mobility Aids
One of the most successful aids
developed through the program, and one
that will be used on future spacecraft, to
support crew member physical stability
in microgravity is foot restraints.
It is nearly impossible to accomplish
tasks in microgravity without stabilizing
one’s feet. NASA scientists developed
several designs to make use of the
body’s natural position while in space.
One design has foot loops and
two-point leg/foot restraints used while
a crew member works at a glove box.
These restraints stabilize a crew
member. The effectiveness of a restraint
system relates to the simplicity of
design, comfort, ease of use,
adjustability, stability, durability, and
flexibility for the range of the task.
Other restraint systems developed
include handrails, bungee cords,
, and flexible brackets.
Furthermore, foot restraints aid in
meeting other challenges such as limited
visibility and access to the activity area.
The latter difficulties can lead to
prolonged periods of unnatural postures
that may potentially harm muscles or
exacerbate neurological difficulties.
Cursor Control Devices
The shuttle spacecraft environment
included factors such as complex
lighting scenarios, limited habitable
volume, and microgravity that could
render Earth-based interface designs
less than optimal for space applications.
Research in space human factors
included investigating ways to optimize
interfaces between crew members and
spacecraft hardware, and the shuttle
proved to be an excellent test bed for
evaluating those interfaces.
For example, while computer use is
quite commonplace today, little was
known about how, or if, typical cursor
control devices used on Earth would
work in space. NASA researchers
conducted a series of experiments to
gather information about the desirable
and undesirable characteristics of cursor
control devices using high-fidelity
environments. Experiments began in
ground laboratories and then moved to
the KC-135 aircraft for evaluation in a
short-duration microgravity environment
during parabolic flight. The experiments
culminated with flight experiments on
board Space Transportation System
(STS)-29 (1989), STS-41(1990), and
STS-43 (1991). These evaluations and
experiments used on-board crew
members to take the devices through
the prescribed series of tasks.
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Major Scientific Discoveries
Without Constraints
On STS-73 (1995) Astronaut Kathryn Thornton
works at the Drop Physics Module on board
the Spacelab science module located in
the cargo bay of the Earth-orbiting shuttle.
Notice that Dr. Thornton is anchoring her body
by using a handrail for her feet and right hand.
This leaves only one free hand to accomplish
her tasks at that workstation and would
be an uncomfortable position to hold for a
long period of time.
With Constraints
Also on STS-73,Astronaut Catherine Coleman
uses the advanced lower body extremities
restraint at the Spacelab glove box.
With Dr. Coleman’s feet and knees anchored
for body stability, she has both hands free
to work for longer periods, providing her
stability and comfort.
Example of a cursor control device with a trackball
as used with ungloved and gloved hands.
Anchoring Improves Performance
It cannot be assumed that computer
equipment, like cursor control devices
(e.g., a trackball, an optical mouse),
used on Earth will behave the same way
in space. Not only does microgravity
make items “float,” in general the
equipment might be used while a crew
member is wearing gloves—and the
gloves could be pressurized at the time.
For example, a trackball has a certain
amount of movement allowed within its
casing. In space, the ball will float,
making it much more difficult to use the
trackball and be accurate. During
STS-43, the shuttle crew worked with
a trackball that was modified to reduce
the “play,” and they reported that the
mechanism worked well. This
modification resulted in the fastest and
most accurate responses.
Those tests in the flight environment
paved the way for the types of
equipment chosen for the International
Space Station (ISS). The goal was to
provide the best equipment to ensure
quick and precise execution of tasks
by crew members. As computer
technology advances, NASA will
continue investigations involving
computer hardware as spacecraft and
habitats are developed.
Shuttle Food System Legacy
Does NASA have a grocery store in
space? The answer is no. One
significant change NASA made to
the space food system during the
Space Shuttle Program, however,
was the addition of a unique bar code
on each food package to facilitate
on-orbit science.
When crew members began
participating in experiments on orbit
that required them to track their food
consumption, a method was needed that
would promote accurate data collection
while minimizing crew time; thus, the
Major Scientific Discoveries
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bar code. Crew members simply used a
handheld scanning device to scan
empty food packages after meals. The
device automatically recorded meal
composition and time of consumption.
Not only did bar codes facilitate
science, they also had the additional
benefit of supporting the Hazard
Analysis and Critical Control Point
program for space food.
Hazard Analysis and Critical Control
Point is a food safety program
developed for NASA’s early space
food system. Having a unique bar code
on each food package made it easy to
scan the food packages as they were
stowed into the food containers prior
to launch. The unique bar code could
be traced to a specific lot of food.
This served as a critical control point
in the event of a problem with a food
product. If a problem had arisen,
the bar code data collected during the
scanning could have been used to
locate every package of food from that
same lot, making traceability much
easier and more reliable. This system
of bar coding food items carried over
into the ISS food system.
Food preparation equipment also
evolved during the shuttle era. The
earliest shuttles flew with a portable
water dispenser and a suitcase-sized
food warmer. The first version of the
portable water dispenser did not
measure, heat, or chill water, but it did
allow the crew to inject water into foods
and beverages that required it. This
dispenser was eventually replaced by
a galley that, in addition to measuring
and injecting water, chilled and heated
it as well. The shuttle galley also
included an oven for warming foods
to serving temperature. Ironically,
the food preparation system in use
on the ISS does not include chilled
water and, once again, involves the
use of the suitcase-sized food warmer
for heating US food products.
Food packaging for shuttle foods also
changed during the course of the
program. The original rigid, rectangular
plastic containers for rehydratable
foods and beverages were replaced
by flexible packages that took up less
room in storage and in the trash.
The increase in crew size and mission
duration that occurred during the
program necessitated this change.
These improvements continue to
benefit the ISS food system.
White Light-emitting Diode Illuminators
As the shuttle orbited Earth, the crew experienced a sunrise and sunset every 45
minutes on average. This produced dramatic changes in lighting conditions, making
artificial light sources very important for working in space.
Because of power and packaging constraints during the Space Shuttle Program, most
artificial lights were restricted to fixed locations. With the assembly of the International
Space Station and the maintenance of the Hubble Space Telescope, NASA felt it
would be a great improvement to have lights mounted on all of the shuttle cameras.
These light sources had to be durable, lightweight, and low in power requirements—
the characteristics of light-emitting diodes (LEDs).
In 1995, NASA began using white LED lights for general illumination in camera
systems several years in advance of industry. These early lights were designed as
rings mounted around the lens of each camera. The four payload bay cameras were
equipped with four LED light systems capable of being pointed with the pan-and-tilt
unit of each camera. NASA also outfitted the two robotic arm cameras with LED rings.
In June 1998, the first white 40 LED illumination system was flown. In May 1999,
white 180 LED illuminators were flown. These lighting systems remained in use on
all shuttle flights.
LED rings
Light-emitting diode (LED) rings mounted on the two shuttle cameras in the aft payload
bay of shuttle.
Environmental Conditions
Maintaining a Healthy Environment During
The shuttle crew compartment felt like
an air-conditioned room to astronauts
living and working in space, and the
Environmental Control and Life
Support System created that habitable
environment. In fact, this system
consisted of a network of systems that
interacted to create such an environment,
in addition to cooling or heating
various Orbiter systems or components.
The network included air revitalization,
water coolant loop, active thermal
control, atmosphere revitalization
pressure control, management of supply
and wastewater, and waste collection.
The Air Revitalization System assured
the safety of the air supply by using
lithium hydroxide to maintain carbon
dioxide (CO
) and carbon monoxide at
nontoxic levels. It also removed odors
and trace contaminants through active
charcoal, provided ventilation in the
crew compartment via a network of
fans and ducting, controlled the cabin’s
relative humidity (30% to 75%) and
temperature (18°C [65°F] to 27°C
[80°F]) through cabin heat exchangers
for additional comfort, and supplied air
cooling to various flight deck and
middeck electronic avionics as well as
the crew compartment.
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Major Scientific Discoveries
On STS-122 (2007),Astronaut Leland Melvin enjoys his dessert of rehydrated peach ambrosia.
Also shown is the pair of scissors that is needed to open the pouch. On the pouch is a bar code
that is used to track the food. The blue Velcro
allows the food to be attached to the walls.
The water coolant loop system
collected heat from the crew
compartment cabin heat exchanger
and from some electronic units within
the crew compartment. The system
transferred the excess heat to the
water coolant/Freon
-21 coolant loop
heat exchanger of the Active Thermal
Control System, which then moved
excess heat from the various Orbiter
systems to the system heat sinks using
-21 as a coolant.
During ground operations, the ground
support equipment heat exchanger in the
Orbiter’s Freon
-21 coolant loops
rejected excess heat from the Orbiter
through ground systems cooling. Shortly
after liftoff, the flash evaporator
(vaporization under reduced pressure)
was activated and provided Orbiter heat
rejection of the Freon
-21 coolant loops
through water boiling. When the Orbiter
was on orbit and the payload bay doors
were opened, radiator panels on the
underside of the doors were exposed to
space and provided heat rejection.
If combinations of heat loads and the
Orbiter attitude exceeded the capacity of
the radiator panels during on-orbit
operations, the flash evaporator was
activated to meet the heat rejection
requirements. At the end of orbital
operations, through deorbit and re-entry,
the flash evaporator was again brought
into operation until atmospheric
pressure, about 30,480 m (100,000 ft)
and below, no longer permitted the flash
evaporation process to provide adequate
cooling. At that point, the ammonia
boilers rejected heat from the Freon
coolant loops by evaporating ammonia
through the remainder of re-entry,
landing, and postlanding until ground
cooling was connected to the ground
support equipment heat exchanger.
Atmosphere revitalization pressure
control kept cabin pressure around
sea-level pressure, with an average
mixture of 80% nitrogen and 20%
oxygen. Oxygen partial pressure was
maintained between 20.3 kPa (2.95
pounds per square inch, absolute [psia])
and 23.8 kPa (3.45 psia), with sufficient
nitrogen pressure of 79.3 kPa (11.5
psia) added to achieve the cabin total
pressure of 101.3 kPa (14.7 psia)
+/-1.38 kPa (0.2 psia). The Pressure
Control System received oxygen from
two power reactant storage and
distribution cryogenic oxygen systems
in the mid-fuselage of the Orbiter.
Nitrogen tanks, located in the
mid-fuselage of the Orbiter, supplied
gaseous nitrogen—a system that was
also used to pressurize the potable and
wastewater tanks located below the
crew compartment middeck floor.
Three fuel-cell power plants produced
the astronauts’ potable water, to which
iodine was added to prevent bacterial
growth, that was stored in water tanks.
Iodine functions like the chlorine that
is added to municipal water supplies,
but it is less volatile and more stable
than chlorine. Condensate water and
human wastewater were collected
into a wastewater tank, while solid
waste remained in the Waste Collection
System until the Orbiter was serviced
during ground turnaround operations.
Space Shuttle Environmental Standards
We live on a planet plagued with air
and water pollution problems because
of the widespread use of chemicals for
energy production, manufacturing,
agriculture, and transportation. To
protect human health and perhaps the
entire planet, governmental agencies
set standards to control the amount
of potentially harmful chemicals that
can be released into air and water
and then monitor the results to show
compliance with standards. Likewise,
on the shuttle, overheated electronics,
systems leaks, propellants, payload
chemicals, and chemical leaching
posed a risk to air and water quality.
Standards were necessary to define
safe air and water, along with
monitoring systems to demonstrate a
safe environment.
Both standards and methods as well
as instruments to measure air quality
were needed to ensure air quality. For
the shuttle, NASA had a formalized
process for setting spacecraft
maximum allowable concentrations.
Environmental standards for astronauts
must consider the physiological effects
of spaceflight, the continuous nature of
airborne exposures, the aversion to
drinking water with poor aesthetic
properties, and the reality that astronauts
could not easily leave a vehicle if it
were to become dangerously polluted.
On Earth, plants remove CO
—a gas
exhaled in large quantities as a result
of human metabolism—from the
atmosphere. By contrast, CO
is one
of the most difficult compounds to
deal with in spaceflight. For example,
accumulation of CO
was a critical
problem during the ill-fated Apollo 13
return flight. As the disabled spacecraft
returned to Earth, the crew had to
implement unanticipated procedures to
manage CO
. This involved duct-taping
filters and tubing together to maintain
at tolerable levels. Such extreme
measures were not necessary aboard
shuttle; however, if the crew forgot to
change out filters, the CO
levels could
have exceeded exposure standards
within a few hours.
Although older limits for CO
set at 1%, during NASA’s new
standard-setting process with the
National Research Council it became
Major Scientific Discoveries
Page 397
clear that 1% was too high and,
therefore, the spacecraft maximum
allowable concentration was reduced
to 0.7 %. Even this lower value proved
to be marginal under some conditions.
For example, the shuttle vehicle did
not have the capability to measure local
pockets of CO
, and those pockets
could contain somewhat higher levels
than were found in the general air.
That was especially true in the absence
of gravity where convection was not
available to carry warm, exhaled air
upward from the astronaut’s breathing
zone. Use of a light-blocking curtain
during a flight caused the crew to
experience headaches on awakening,
and this was attributed to accumulation
of CO
because the crew slept in a
confined space and the curtain
obstructed normal airflow.
Setting air quality standards for
astronaut exposures to toxic
compounds is not a precise science
and is complicated. NASA partnered
with the National Research Council
Committee on Toxicology in 1989
to set and rigorously document air
quality standards for astronauts during
shuttle spaceflight.
The spaceflight environment is like
Earth in that exposure standards can
control activities when environmental
monitors suggest the need for control.
For example, youth outdoor sports
activities are curtailed when ozone
levels exceed certain standards on
Earth. Likewise, spacecraft maximum
allowable concentrations for carbon
monoxide, a toxic product of
combustion, were used to determine
criteria for the use of protective masks
in the event of an electrical burn.
The shuttle Flight Rules provided the
criteria. Ranges for environmental
monitoring instruments were also based
on spacecraft maximum allowable
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Measuring Airborne Volatile Organic Compounds
Volatile organic compounds are airborne contaminants that pose
a problem in semi-closed systems such as office buildings with
contributions from carpets, furniture, and paper products as well
as in closed systems such as airplanes and spacecraft. These
contaminates cause headaches, eye and skin irritation, dizziness,
and even cancer.
NASA needed to be able to measure such compounds for the
International Space Station (ISS), a long-term closed living situation.
Therefore, in the latter 1990s, the shuttle was used as a test bed
for instruments considered for use on the ISS.
Shuttle flights provided the opportunity to assess the performance
of a volatile organic analyzer-risk mitigation experiment in
microgravity on STS-81 (1997) and STS-89 (1998). Results
confirmed component function and improved the instrument built
for ISS air monitoring.
The volatile organic analyzer
operated episodically on ISS
since 2001 and provided
timely and valuable
information during the
Elektron (Russian oxygen
generation system) incident in
September 2006 when the
crew tried to restart the
Elektron and saw what
appeared to be smoke
emanating from the device.
The volatile organic analyzer
collected and analyzed
samples prior to the event and
during cleanup. Data showed
that the event had started
before the crew noticed the
smoke, but the concentrations
of the contaminants released
were not a health hazard.
Combustion Product Analyzer Ensured
Crew Breathed Clean Air After Small
Fire in Russian Space Station
The combustion product analyzer flew on every Space Shuttle flight from 1990
through 1999 and proved its value during the Shuttle-Mir Program (1995-1998).
On the seventh joint mission in 1998, no harm seemed to have occurred during an
inadvertent valve switch on an air-purifying scrubber. In fact, during this time, the
crew—including American Andrew Thomas—participated in a video presentation
transmitted back to Earth; however, shortly after the valve switch, the crew
experienced headaches. As on Earth, when occupants of a house or building
experience headaches simultaneously, it can indicate that the air has been severely
degraded. The crew followed procedures and activated the combustion product
analyzer, designed to detect carbon monoxide (CO), hydrogen cyanide, hydrogen
chloride, and hydrogen fluoride. The air contained over 500 parts per million of CO,
significantly above acceptable concentrations. This high concentration was produced
by hot air flowing through a paper filter and charcoal bed and then into the cabin
when the valve was mistakenly switched on. The combustion product analyzer was
used to follow the cleanup of the CO. Archival samples confirmed the accuracy of the
analyzer’s results. The success of this analyzer and its successor—the compound
specific analyzer-combustion products—led to the inclusion of four units (compound
specific analyzer-combustion products) on the International Space Station and a
combustion products analyzer on future crew exploration vehicles.
Commander Robert Gibson and Astronaut Jan Davis check the
combustion product analyzer during STS-47 (1992).
During the STS-89 shuttle dock
with Russian space station Mir,
Astronaut Bonnie Dunbar goes
through her checklist to start
the volatile organic analyzer
sample acquisition sequence.
This chart plots the course of the
Elektron incident showing the
concentrations of toluene, benzene,
ethylbenzene, and xylenes—all
serious toxins—released into the
air. In 2004, the levels of the four
contaminates were very low, as
measured by the volatile organic
analyzer and grab samples returned
to Earth for analysis. During the
incident, the analyzer measured
increases in the four compounds.
Grab samples confirmed the higher
levels for these compounds and
verified that the analyzer had
worked. The next available data
showed the contaminants had
returned to very low levels.
Contaminants: Elektron Incident on
the Russian Space Station Mir
Post release
62 minutes
Post release
296 minutes
concentrations. For example, the
monitoring requirements for hydrogen
cyanide, another toxic combustion
product, were based on spacecraft
maximum allowable concentrations to
determine how sensitive the monitor
must be. By analogy with Earth-based
environmental monitoring, spaceflight
monitors needed the ability to indicate
when safe conditions had returned so
that normal operations could resume.
NASA recognized the need for unique
water-quality standards. Although the
effort to set specific water-quality
standards, called spacecraft water
exposure guidelines, did not begin until
2000, NASA quickly realized the value
of these new limits. One of the first
spacecraft water-exposure guidelines
set was for nickel, a slightly toxic metal
often found in water that has been held
in metal containers for some time.
The primary toxic effect of concern was
nickel’s adverse effect on the immune
system. High nickel levels had been
observed from time to time in the shuttle
water system based on the existing
requirements in NASA documents.
This sometimes caused expensive and
schedule-breaking activity at Kennedy
Space Center to deal with these events.
When National Research Council
experts accepted a new, higher
standard, the old standard was no
longer applied to shuttle water and the
nickel “problem” became history.
Toxicants From Combustion
Fire is always a concern in any
environment, and a flame is sometimes
difficult to detect. First responders
must have instruments to quickly
assess the contaminants in the air on
arriving at the scene of a chemical
spill, fire, or building where occupants
have been overcome by noxious
fumes. Additionally, these instruments
must be capable of determining when
the cleanup efforts have made it safe
for unprotected people to return. When
a spill, thermodegradation, or unusual
odor occurs on a spacecraft, crew
members are the first responders.
They need the tools to assess the
situation and track the progress of the
cleanup. As a result of shuttle
experiments, NASA was able to
provide crews with novel instruments
to manage degradations in air quality
caused by unexpected events.
The combustion products
analyzer addressed spacecraft
thermodegradations events, which
can range from overheated wiring to
a full-fledged fire. Fire in a sealed,
remote capsule is a frightening event.
A small event—overheated wire
(odor produced)—occurred on
STS-6 (1983), but it wasn’t until 1988,
when technology advances improved
the reliability and shrank the size of
monitors, that a search for a
combustion products analyzer was
initiated. Before the final development
of the analyzer, however, a more
significant event occurred on STS-28
(1989) that hastened the completion of
the instrument. On STS-28, a small
portion of teleprinter cable pyrolyzed
and the released contaminants could
have imperiled the crew if more of the
cable had burned. The combustion
products analyzer requirements were to
measure key contaminants in the air
following thermodegradation incidents,
track the effectiveness of cleanup
efforts, and determine when it was safe
to remove protective gear.
Toxic containments may be released
from burning materials depending
on the type of materials and level of
oxygen. For spaceflight, NASA
identified five marker compounds:
carbon monoxide (odorless and
colorless gas) released from most
thermodegradation events; hydrogen
chloride released from polyvinyl
chloride; hydrogen fluoride and
carbonyl fluoride associated with
; and hydrogen cyanide released
from Kapton
-coated wire and
polyurethane foam. The concentration
range monitored for each marker
compound was based on the established
spacecraft maximum allowable
concentrations at the low end and, at
the other end of the range, an estimated
highest concentration that might be
released in a fire.
An upgraded combustion product
analyzer is now used on the ISS,
demonstrating that the technology and
research on fire produced methods that
detect toxic materials. The results
indicate when it is safe for the astronauts
to remove their protective gear.
Safeguarding the Astronauts
From Microorganisms—
Prevention of Viral, Bacterial,
and Fungal Diseases
Certain bacteria, fungi, and viruses
cause acute diseases such as upper
respiratory problems, lung diseases,
and gastrointestinal disease as well as
chronic problems such as some
cancers and serious liver problems.
In space, astronauts are exposed to
microorganisms and their by-products
from the food, water (both used
for food and beverage rehydration,
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Major Scientific Discoveries
and for personal hygiene), air,
interior surfaces, and scientific
investigations that include animals
and microorganisms. The largest
threat to the crew members, however,
is contact with their crewmates.
The shuttle provided an opportunity
to better understand the changes in
microbiological contamination
because, unlike previous US spacecraft
for human exploration, the shuttle
was designed to be used over many
years with limited refurbishment
between missions. Risks associated
with the long-term accumulation
of microorganisms in a crewed
compartment were unknown at the
start of the shuttle flights; however,
many years of studying these
microorganisms produced changes that
would prevent problems for the ISS
and the next generation of crewed
vehicles. With assistance from industry
and government standards (e.g.,
Environmental Protection Agency)
and expert panels, NASA established
acceptability limits for bacteria and
fungi in the environment (air and
surfaces) and consumables (food
and water). Preflight monitoring for
spaceflight was thorough and included
the crew, spaceflight food, potable
water, and vehicle air and surfaces
to ensure compliance with these
acceptability standards. NASA
reviewed all flight payloads for
biohazardous materials. Space Shuttle
acceptability limits evolved with
time and were later used to develop
contamination limits for the ISS and
the next generation of crewed vehicles.
Microbial growth in the closed
environment of spacecraft can lead to
a wide variety of adverse effects
including infections as well as the
release of volatile organics, allergens,
and toxins. Biodegradation of critical
materials, life support system fouling,
and bio-corrosion represent other
potential microbial-induced problems.
Shuttle crew members sometimes
reported dust in the air and occasional
eye irritation. In-flight monitoring
showed increased bacterial levels in the
shuttle air as the number of days in
space increased. Dust, microbes, and
even water droplets from a simple
sneeze settle out on Earth. The human
body alone sheds about 1 billion skin
cells every week. Particles remain
suspended in space and carry
microorganisms and allergens that pose
a health risk to the crew.
The shuttle’s air filters were
designed to remove particles greater
than 70 micrometers. The filters
removed most skin cells (approximately
100 micrometers) and larger airborne
contaminants (e.g., lint); however,
they did not quickly remove smaller
contaminants such as bacteria, viruses,
and particulates. When the shuttle was
modified for longer flights of up to
2 weeks, an auxiliary cabin air cleaner
provided filtration that removed
particles over 1 micrometer. As the
air recirculated through the vehicle,
the filter captured skin cells, lint,
microorganisms, and other debris.
This resulted in much-improved
air quality. These high-efficiency
particulate air (HEPA) filters
(99.97% efficient at removing
particles >0.3 micrometers) provide
dust- and microbe-free air. This led
to the inclusion of HEPA filters in
the Air Revitalization System on the
ISS where monitoring has shown that
air quality has been maintained below
stringent microbial requirements.
HEPA filters are also planned for
other crewed vehicles.
Microbial growth can result in
volatile chemicals that can produce
objectionable odors or irritants. For
example, during the STS-55 (1993)
mission, the crew reported a noxious
odor that was later found by extensive
ground studies to be a mixture of
three dimethyl sulfides resulting from
the bacterial metabolism of urine in
a waste storage container.
These challenges provided
opportunities for improvements that
served as “lessons learned,” which were
applied to all future missions. Lessons
learned from the shuttle experiences
led to NASA’s current approach of
prevention first and mitigation second.
Many microbiological risks associated
with living in space can be prevented
or mitigated to acceptable levels
through engineering approaches.
Prevention strategy begins with the
design phase and includes steps that
discourage excessive microbial
growth. Use of antimicrobial materials,
maintaining relative humidity below
70%, avoiding condensation buildup,
implementing rigorous housekeeping,
maintaining air and water filtration,
and judicially using disinfectants
are effective steps limiting the
adverse effects of microorganisms.
In all, the microbiological lessons
learned from the Space Shuttle era
resulted in improved safety for all
future spacecraft.
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Adverse Effects of Microorganisms
Infectious diseases
Toxin production
Plant diseases
Food spoilage
Volatile release
Material degradation
Immune alteration
Astronauts Megan McArthur,
Michael Massimino (center),
and Andrew Feustel
prepare to eat a meal on
the middeck of Atlantis
(STS-125 [2009]).
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Major Scientific Discoveries
As illustrated, a
high-efficiency particulate
air (HEPA) filter removes
particles from recirculated
air, resulting in improved
air quality. The HEPA filter
in the air-purification
system on the International
Space Station (ISS), as
pictured below, is of a
higher quality than
purification systems used
in offices and homes.
HEPA Filter on the ISS
Astronaut Health Care
Astronaut health care includes all issues
that involve flight safety, physiological
health, and psychological health.
During the Space Shuttle Program,
space medicine was at the “heart” of
each issue.
Space medicine evolved during the
shuttle’s many transitional phases, from
the experimental operational test vehicle
to pre-Challenger (1986) accident,
post-Challenger accident, unique
missions such as Department of Defense
and Hubble, Spacelab/Spacehab,
Extended Duration Orbiter Project,
Shuttle–Mir, Shuttle-International Space
Station (ISS), post-Columbia (2003)
accident and, finally, the ISS assembly
completion. All of these evolutionary
phases required changes in the selection
of crews for spaceflight, preparation
for spaceflight, on-orbit health care, and
postflight care of the astronauts.
Astronauts maintained their flight
status, requiring both ambulatory
and preventive medical care of their
active and inactive medical conditions.
Preflight, on-orbit, and postflight
medical care and operational space
medicine training occurred for all
flights. The medical team worked with
mission planners to ensure that all
facets of coordinating the basic tenets
of personnel, equipment, procedures,
and communications were included
in mission support. During the shuttle
era, the Mission Control Center was
upgraded, significantly improving
communications among the shuttle
flight crew, medical team, and other
flight controllers with the flight director
for the mission. Additionally, the
longitudinal study of astronaut health
began with all medical data collected
during active astronaut careers. NASA
used post-retirement exams, conducted
annually, to study the long-term effect
of short-duration spaceflight on crews.
Astronaut Selection and
Medical Standards
Due to increasing levels of flight
experience and changes in medical
delivery, medical standards for
astronaut selection evolved over the
shuttle’s 30 years, as it was important
that the selected individuals met certain
medical criterion to be considered as
having the “right stuff.” The space
agency initially adopted these standards
from a combination of US Air Force,
US Navy, and Federal Aviation
Administration as well as previous
standards from the other US space
programs. The shuttle medical
standards were designed to support
short-duration spaceflights of as many
as 30 days. NASA medical teams, along
with experts in aerospace medicine
and systems specialties, met at least
every 2 years to review and update
standards according to a combination
of medical issues related to flights and
the best evidence-based medicine at
that time. These standards were very
strict for selection, requiring optimum
health, and they eventually led to
Major Scientific Discoveries
Page 403
the ISS medical requirements for
long-duration spaceflight.
Preventive medicine was the key to
success. Astronauts had an annual
spaceflight certification physical
exam to ensure they remained healthy
for spaceflight, if assigned. Also, if a
potential medical condition or problem
was diagnosed, it was treated
appropriately and the astronaut was
retained for spaceflight. Medical exams
were completed 10 days prior to launch
and again at 2 days prior to launch to
ensure that the astronaut was healthy
and met the Flight Readiness Review
requirements for launch. Preventive
health successfully kept almost 99% of
the astronauts retained for spaceflight
duties during their careers with NASA.
Space Adaptation Syndrome
The first thing an astronaut noticed was a fluid shift from his or her lower extremities
to his or her torso and upper bodies, resulting in a facial fullness. Ultimately, this fluid
shift caused a stretch on the baroreceptors in the arch of the aorta and carotid arteries
and the astronaut would lose up to 1.5 to 2 L (1.6 to 2.1 qt) of fluid.
Secondly, over 80% of crew members experienced motion sickness, from loss of
appetite to nausea and vomiting. Basic prevention included attempting to maintain an
Earth-like orientation to the vehicle. Also, refraining from exaggerated movements
helped. If symptoms persisted despite preventive measures, medications in an oral,
suppository, or injectable form were flown to treat the condition.
The next thing crew members noticed was a change in their musculoskeletal system.
In space, the human body experiences a lengthening and stretching of tendons and
ligaments that hold bones, joints, and muscles together. Also, there was an unloading
of the extensor muscles that included the back of the neck and torso, buttocks, and
back of the thighs and calves. Preventive measures and treatment included on-orbit
exercise, together with pain medications.
Additional changes were a mild decrease in immune function, smaller blood cell
volume, and calcium loss. Other problems included headache, changes in visual acuity,
sinus congestion, ear blocks, nose bleeds, sore throats, changes in taste and smell,
constipation, urinary infections and difficulty in urination, fatigue, changes in sleep
patterns with retinal flashes during sleep, minor behavioral health adjustment reactions,
adverse reactions to medications, and minor injuries.
Crew Preparation for Flight
Approximately 9 months prior to each
shuttle flight, the medical team and
flight crew worked together to resolve
any medical issues. The flight medical
team provided additional medical
supplies and equipment for the crew’s
active and inactive medical problems.
Spaceflight inspired some exceptional
types of medical care. Noise was a
hazard and, therefore, hearing needed
to be monitored and better hearing
protection was included. Due to the
presence of radiation, optometry was
important for eye health and for
understanding the impact of radiation
exposure on cataract development.
Also, in space visual changes occurred
with elongation of the eye, thus
requiring special glasses prescribed
for flight. All dental problems needed
to be rectified prior to flight as well.
Behavioral health counseling was
also available for the crews and their
families, if required. This program,
along with on-orbit support,
provided the advantage of improved
procedures and processes such as a
family/astronaut private communication
that allowed the astronaut another
avenue to express concerns.
Over the course of the Space Shuttle
Program, NASA provided improved
physical conditioning and rehabilitation
medicine throughout the year to keep
crews in top physical shape. Before and
during all shuttle flights, the agency
provided predictions on solar activity
and accumulation of the radiation
astronauts received during their careers
to help them limit their exposure.
Prior to a shuttle mission, NASA
trained all astronauts on the effects of
microgravity and spaceflight on their
bodies to prepare them for what to
expect in the environment and during
the physiological responses to
microgravity. The most common
medical concerns were the space
adaptation syndrome that included
space motion sickness and the
cardiovascular, musculoskeletal, and
neurovestibular changes on orbit. Other
effects such as head congestion,
headaches, backaches, gastrointestinal,
genitourinary, crew sleep, rest, fatigue,
and handling of injuries were also
discussed. The most common
environmental issues were radiation,
the biothermal considerations of heat
and cold stress, decompression sickness
from an extravehicular activity (EVA),
potable water contamination, carbon
dioxide (CO
), and other toxic
exposures. Re-entry-day (return to
Earth) issues were important because
the crew transitioned quickly from
microgravity into a hypergravity,
then into a normal Earth environment.
Countermeasures needed to be
developed to overcome this rapid
response by the human body. These
countermeasures included the control
of cabin temperature, use of the g-suit,
and entry fluid loading, which helped
restore fluid in the plasma volume that
was lost on orbit during physiological
changes to the cardiovascular system.
It was also important to maximize the
health and readaptation of the crew on
return to Earth in case emergency
bailout, egress, and escape procedures
needed to be performed.
The addition of two NASA-trained crew
medical officers further improved
on-orbit medical care. Training included
contents of the medical kits with an
understanding of the diagnostic and
therapeutic procedures contained within
the medical checklist. These classes
were commonly referred to as “4 years
of medical school in three 2-hour
sessions.” Crew medical officers learned
basic emergency and nonemergency
procedures common to spaceflight.
This training included how to remove
foreign bodies from the eye; treat ear
blocks and nose bleeds; and start IVs
and give medications that included IV,
intramuscular, and subcutaneous
injections and taught the use of oral
and suppository intake. Emergency
procedures included training in
cardiopulmonary resuscitation, airway
management and protection, wound
care with Steri-Strip
and suture repair,
bladder catheterization, and needle
thoracentesis. NASA taught special
classes on how to mitigate the possibility
of decompression sickness from an
EVA. This incorporated the use of
various EVA prebreathe protocols
developed for shuttle only or shuttle-ISS
docking missions. Crews were taught to
recognize decompression sickness and
how to medically manage this event by
treating and making a disposition of the
crew member if decompression sickness
occurred during an EVA.
Environmental exposure specialty
classes included the recognition and
management of increased CO
exposure, protection and monitoring in
case of radiation exposure from either
artificial or solar particle events, and the
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Major Scientific Discoveries
biothermal consideration of heat stress
in case the Orbiter lost its ability to
maintain cooling. Toxicology exposure
specialty classes focused on generic
toxic compounds unique to the Orbiter
and included hypergolic exposure to
hydrazines and nitrogen tetroxide,
ammonia, and halogenated
hydrocarbons such as halon and
. Certain mission-specific toxic
compounds were identified and
antidotes were flown in case of crew
exposure to those compounds. NASA
trained crew members on how to use the
toxicology database that enabled them
to readily identify the exposed material
and then provide protection to
themselves during cleanup of toxic
compounds using a specialty
contamination cleanup kit. Astronauts
were also trained on fire and smoke
procedures such as the rapid quick-don
mask for protection while putting out
the fire and scrubbing the cabin
atmosphere. In such an incident, the
atmosphere was monitored for carbon
monoxide, hydrogen cyanide, and
hydrogen chloride. When those levels
were reduced to nontoxic levels, the
masks were removed.
The potable water on the shuttle was
monitored 15 and 2 days preflight to
ensure quality checks for iodine levels,
microbes, and pH. Crews were
instructed in limiting their iodine
(bacteriostatic agent added to stored
shuttle water tank) intake by
installing/reinstalling a galley iodine-
reduction assembly device each day that
limited their intake of iodine from the
cold water. The crews also learned how
to manage the potable water tank in case
it became contaminated on orbit.
Over the course of the program, NASA
developed Flight Rules that covered
launch through recovery after landing
and included risky procedures such as
EVAs. These rules helped prevent
medical conditions and were approved
through a series of review boards that
included NASA missions managers,
flight directors, medical personnel, and
outside safety experts. The Flight Rules
determined the preplanned decision on
how to prevent or what to do in case
something went wrong with the shuttle
systems. Other controlled activities
were rules and constraints that protected
and maintained the proper workload,
rest, and sleep prior to flight and for
on-orbit operations during the presleep,
Major Scientific Discoveries
Page 405
work, and post-sleep periods. The
flight-specific sleep and work schedule
was dependent on the launch time and
included the use of bright and dim
lights, naps, medications, and shifts in
sleep and work patterns. NASA
developed crew schedules to prevent
crew fatigue—an important constraint
for safety and piloted return.
Although implemented in the Apollo
Program, preflight crew quarantine
proved to be essential during the Space
Shuttle Program to prevent infectious
disease exposure prior to launch. The
quarantine started 7 days prior to
launch. At that point, all crew contacts
were monitored and all contact
personnel received special training in
the importance of recognizing the signs
and symptoms of infectious disease,
thus limiting their contact with the
flight crew if they became sick. This
program helped eliminate the exposure
of an infectious disease that would
delay launch and was successful in that
only one flight had to be delayed
because of a respiratory illness.
Shuttle Medical Kit
The Shuttle Orbiter Medical System had generic and accessory items and provided
basic emergency and nonemergency medical care common to spaceflight. The
contents focused on preventing illnesses and infection as well as providing pain
control. It also provided basic life support to handle certain life-threatening
emergencies, but it did not have advanced cardiac life support capabilities. Initially, it
included two small kits of emergency equipment, medications, and bandages; however,
this evolved into a larger array of sub packs as operational demands required during
the various phases of the program. The generic equipment remained the same for
every flight, but accessory kits included those mission-specific items tailored for the
crew’s needs. Overall, the Shuttle Orbiter Medical System included: a medical checklist
that helped the on-board crew medical officers diagnose and treat on-orbit medical
problems; an airway sub pack; a drug sub pack; an eye, ear, nose, throat, and dental
sub pack; an intravenous sub pack; saline supply bags; a trauma sub pack; a sharps
container; a contamination cleanup kit; patient and rescue restraints; and an
electrocardiogram kit.
Readiness for Launch and
On-orbit Health Care
Launch day is considered the most
risky aspect of spaceflight. As such,
medical teams were positioned to work
directly with mission managers as well
as the shuttle crew during this critical
stage. On launch day, one crew medical
doctor was stationed in the Launch
Control Center at Kennedy Space
Center (KSC) with KSC medical
emergency care providers. They had
direct communication with Johnson
Space Center Mission Control, Patrick
Air Force Base located close to KSC,
alternate landing sites at Dryden Flight
Research Center/Edwards Air Force
Base, White Sands Space Harbor, and
transoceanic abort landing medical
teams. Another crew medical doctor
was pre-staged near a triage site with
the KSC rescue forces and trauma teams
at a site determined by wind direction.
Other forces, including military
doctors and US Air Force pararescuers
in helicopters, stood on “ready alert” for
any type of launch contingency.
Once launch occurred and the crew
reached orbit in just over 8 minutes,
physiologic changes began. Every
crew member was unique and
responded to these changes differently
on a various scale.
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Major Scientific Discoveries
Prior to the 1990s’
Extended Duration
Operations Program,
immediate postflight
care was conducted
in the “white room” or on a small stairwell platform that mated with the port-side
hatch of the shuttle. Typically, astronaut support personnel, a “suit” technician, and
the crew medical team entered the shuttle, postlanding. If a medical condition occurred
and a crew member had problems readapting to the Earth environment, this care was
conducted in the shuttle interior or on the platform of the “white room” stairwell. One
major improvement to landing-day medical care was the change to a mobile postflight
crew transport vehicle. This vehicle was redesigned to mate with the Orbiter and
provided private transport of the crew to a location where they could receive better
care, if required. The vehicle was outfitted with lounge chairs, a rest room, gurneys,
and medical supplies. The crew could first be stabilized. Then, those who didn’t need to
remain on board for research testing could perform a crew walk around the Orbiter.
The crew transport vehicle was first used with STS-40 at Dryden Flight Research
Center (DFRC), California, in 1991 and supported all subsequent shuttle flights at both
DFRC and Kennedy Space Center, Florida.
Crew Transport Vehicle
All medical conditions were discussed
during a private medical communication
with the crew every flight day. The
results at the end of a discussion were
one of the following: no mission impact
(the majority); possible mission impact;
or mission impact. With possible
mission impacts, further private
discussion with the crew and flight
director, other crew members, and other
medical care specialists occurred.
Fortunately for the program, all possible
mission impacts were resolved with
adjustments to the timeline and duties
performed by the crew so the mission
could continue to meet its objectives.
If a mission impact were to occur,
changes would be made public but not
the specifics of those changes. Due to
the Medical Privacy Act of 1974, details
of these private medical conferences
could not be discussed publicly.
Private family communication was
another important aspect,
psychologically, of on-orbit health
care. Early in the program, this was
not performed but, rather, was
implemented at the start of the
Extended Duration Orbiter Medical
Project (1989-1996) and involved
flights of 11 days or longer.
The second riskiest time of spaceflight
was returning to Earth. To overcome
hypotension or low blood pressure
during re-entry, the crew employed
certain countermeasures. The crew
would fluid load to restore the lost
plasma volume by ingesting 237 ml
(8 oz) of water with two salt tablets
every 15 minutes, starting 1 hour prior
to the time of deorbit ignition and to
finish this protocol by entry interface
(i.e., the period right before the final
return stage) for a total fluid loading
time of 90 minutes. Body weight
determined the total amount ingested.
After the Challenger accident, NASA
developed a launch and re-entry suit
that transitioned from the standard
flight suit, to a partial pressure
suit, then on to a full pressure suit
called the advanced crew escape suit.
An incorporated g-suit could be used to
compress lower extremities and the
abdomen, which prevented fluid from
accumulating in those areas. Another
post-Challenger accident lesson learned
was to cool the cabin and incorporate
the liquid cooling within the launch and
re-entry suit to prevent heat loads that
could possibly compromise the landing
performance of the vehicle by the
commander and pilot (second in
command). Finally, each crew member
used slow, steady motions of his or her
head and body to overcome the
neurovestibular changes that occurred
while transitioning from a microgravity
to an Earth environment. All items
were important that assisted the crew
in landing the vehicle on its single
opportunity in a safe manner.
Postflight Care
Once the landed shuttle was secured
from any potential hazards, the medical
team worked directly with returning
crew members. Therefore, medical
teams were stationed at all potential
landing sites—KSC in Florida, Dryden
Flight Research Center in California,
and White Sands in New Mexico.
When the crew returned to crew
quarters, they reunited with their
families and then completed a postflight
exam and mini debrief. Crew members
were advised not to drive a vehicle
for at least 1 day and were restricted
from aircraft flying duties due to
disequilibrium—problems with spatial
and visual orientation. NASA
performed another postflight exam and
a more extensive debrief at return plus
3 days and, if passed, the crew member
was returned to aircraft flight duties.
Mission lessons learned from debriefs
were shared with the other crew
medical teams, space medicine
researchers, special project engineers,
and the flight directors. All of these
lessons learned over time, especially
during the transitional phases of the
program, continued to refine astronaut
health and medical care.
Accidents and Emergency
Return to Earth
Main engine or booster failures could
have caused emergency returns to KSC
or transoceanic abort landing sites.
NASA changed its handling of
post-accident care after the two shuttle
accidents. Procedures specific for the
medical team were sessions on
emergency medical services with the
US Department of Defense Manned
Spaceflight Support Office and
included search and rescue and medical
evacuation. This support and training
evolved tremendously after the
Challenger and Columbia accidents,
incorporating lessons learned. It mainly
included upgrades in training on crew
equipment that supported the scenarios
of bailout, egress, and escape.
The Future of Space Medicine
NASA’s medical mission continues to
require providing for astronaut health
and medical care. Whatever the future
milestones are for the US space
program, the basic tenets of selecting
healthy astronaut candidates by having
strict medical selection standards and
then retaining them through excellent
preventive medical care are of utmost
importance. Combining these with
the operational aspects of coordinating
all tenets of understanding the
personnel, equipment, procedures,
and communications within the
training to prepare crews for flight will
enhance the success of any mission.
At the closing stages of the Space
Shuttle Program, no shuttle mission
was terminated or aborted because of
a medical condition, and this was a
major accomplishment.
Major Scientific Discoveries
Page 407
The Space Shuttle brought a new dimension to the study of biology in space.
Prior to the shuttle, scientists relied primarily on uncrewed robotic spacecraft
to investigate the risks associated with venturing into the space environment.
Various biological species were flown because they were accepted as models
with which to study human disease and evaluate human hazards. The results
from the pioneering biological experiments aboard uncrewed robotic spacecraft
not only provided confidence that humans could indeed endure the rigors of
spaceflight, they also formed the foundation on which to develop risk mitigation
procedures; i.e., countermeasures to the maladaptive physiological changes the
human body makes to reduced gravity levels. For example, the musculoskeletal
system reacts by losing mass. This may pose no hazard in space; however, on
returning to Earth after long spaceflights, such a reaction could result in an
increased risk of bone fractures and serious muscle atrophy.
Unfortunately, most biological research in uncrewed spacecrafts was limited to
data that could only be acquired before and/or after spaceflight. With crew
support of the experiments aboard the Space Shuttle and Spacelab, and with
adequate animal housing and lab support equipment, scientists could train the
crew to obtain multiple biospecimens during a flight, thus providing windows
into the adaptation to microgravity and, for comparison, to samples obtained
during readaptation to normal terrestrial conditions postflight.
With the Space Shuttle and its crews, earthbound scientists had surrogates in
orbit—surrogates who could be their eyes and hands within a unique
laboratory. The addition of Spacelab and Spacehab, pressurized laboratory
modules located in the shuttle payload bay, brought crews and specialized
laboratory equipment together, thus enabling complex interactive biological
research during spaceflight. Crew members conducted state-of-the-art
experiments with a variety of species and, in the case of human research, served
as test subjects to provide in-flight measurements and physiological samples.
In addition to the use of biological species to evaluate human spaceflight risks,
research aboard the shuttle afforded biologists an opportunity to examine the
fundamental role and influence of gravity on living systems. The results of such
research added new chapters to biology textbooks. Life on Earth originated
and evolved in the presence of a virtually constant gravitational field, but
leaving our planet of origin creates new challenges that living systems must
cope with to maintain the appropriate internal environment necessary for
health, performance, and survival.
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Major Scientific Discoveries
The Space
A Platform
That Expanded
the Frontiers
of Biology
Kenneth Souza
How Does Gravity
Affect Plants
and Animals?
Throughout the course of evolution,
gravity has greatly influenced the
morphology, physiology, and behavior
of life. For example, a support
structure—i.e., the musculoskeletal
system—evolved to support body
mass as aquatic creatures transitioned
to land. To orient and ambulate,
organisms developed ways to sense
the gravity vector and translate this
information into a controlled response;
hence, the sensory-motor system
evolved. To maintain an appropriate
blood supply and pressure in the
various organs of the mammalian
body, a robust cardiovascular system
developed. Understanding how
physiological systems sense, adapt,
and respond to very low gravity cannot
be fully achieved on the ground; it
requires the use of spaceflight as a
tool. Just as we need to examine the
entire light spectrum to determine
how the visual organs of living
systems work, so too we must use
the complete gravity spectrum, from
hypogravity to hypergravity, to
understand how gravity influences
life both on and off the Earth.
Space biologists have identified and
clarified the effects of spaceflight
on a few representative living systems,
from the cellular, tissue, and system
level to the whole organism. NASA
achieved many “firsts” as well as
other major results that advanced our
understanding of life in space and on
Earth.The agency also achieved many
technological advances that provided
life support for the study of the various
species flown.
Major Scientific Discoveries
Page 409
Baruch Blumberg, MD
Nobel Prize winner in medicine, 1976.
Professor of Medicine
Fox Chase Cancer Center.
Former director of Astrobiology
Ames Research Center, California.
“The United States and other
countries are committed to space
travel and to furthering the human
need to explore and discover.
Since April 12, 1981, the
shuttle has been the major portal to space for humans; its crews have built the
International Space Station (ISS), a major element in the continuum that will allow
humans to live and work indefinitely beyond their planet of origin. The shuttle
has provided the high platform that allows observations in regions that were
previously very difficult to access. This facilitates unique discoveries and reveals
new mysteries that drive human curiosity.
“In the final paragraph of Origin of Species Darwin wrote:
There is grandeur in this view of life, with its several powers, having been
originally breathed by the Creator into a few forms or into one; and that,
whilst this planet has gone circling on according to the fixed law of gravity,
from so simple a beginning endless forms most beautiful and most
wonderful have been, and are being evolved.
“The shuttle and the ISS now provide a means to study life and its changes
without the constraints of gravity. What will be the effect of this stress never
before experienced by our genome and its predecessors (unless earlier forms
of our genes came to Earth through space from elsewhere) on physiology, the cell,
and molecular biology? Expression of many genes is altered in the near-zero
gravity; how does this conform to the understanding of the physics of gravity at
molecular and atomic dimensions?
“In time, gravity at different levels, at near-zero on the ISS, at intermediate
levels on the moon and Mars, and at one on Earth, can provide the venues to
study biology at different scales and enlarge our understanding of the nature
of life itself.”
Gravity-sensing Systems—
How Do Plants and
Animals Know Which Way
Is Down or Up?
As living systems evolved from simple
unicellular microbes to complex
multicellular plants and animals, they
developed a variety of sensory organs
that enabled them to use gravity for
orientation. For example, plants
developed a system of intracellular
particles called statoliths that, upon
seed germination, enabled them to
sense the gravity vector and orient their
roots down into the soil and their shoots
up toward the sun. Similarly, animals
developed a variety of sensory systems
(e.g., the vestibular system of the
mammalian inner ear) that enabled
them to orient with respect to gravity,
sense the body’s movements, and
transduce and transmit the signal to the
brain where it could be used together
with visual and proprioceptive inputs
to inform the animal how to negotiate
its environment.
Why Do Astronauts Get Motion
Sickness in Spaceflight?
One consequence of having
gravity-sensing systems is that while
living in microgravity, the normal
output from the vestibular system is
altered, leading to a confusing set of
signals of the organism’s position
and movement. Such confusion is
believed to result in symptoms not too
different from the typical motion
sickness experienced by seafarers on
Earth. This affliction, commonly
termed “space motion sickness,”
affects more than 80% of astronauts
and cosmonauts during their first few
days in orbit. Interestingly, one of
the two monkeys flown in a crewed
spacecraft, the Space Transportation
System (STS)-51B (1985) Spacelab-3
mission, displayed symptoms
resembling space motion sickness
during the first few days of spaceflight.
The basic process of space motion
sickness became one of the main
themes of the first two dedicated space
life sciences missions: STS-40 (1991)
and STS-58 (1993). Scientists gained
insights into space motion sickness
by probing the structural changes that
occur in the vestibular system of the
mammalian balance organs. Using
rodents, space biologists learned for
the first time that the neural hair cells
of the vestibular organ could change
relatively rapidly to altered gravity.
Such neuroplasticity was evident in
the increased number of synapses
(specialized junctions through
which neurons signal to each other)
between these hair cells and the
vestibular nerve that occurred as the
gravity signal decreased. In effect,
the body tried to turn up the gain to
receive the weaker gravitational signal
in space. This knowledge enabled
medical doctors and crew members
to have a better understanding of why
space motion sickness occurs.
Is Gravity Needed for
Successful Reproduction?
Amphibian Development
Studies of the entire life span of living
systems can provide insights into the
processes involved in early development
and aging. The Frog Embryology
Experiment flown on STS-47 (1992)
demonstrated for the first time that
gravity is not required for a vertebrate
species, an amphibian, to ovulate,
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Major Scientific Discoveries
STS-40 (1991) payload
specialist Millie
Hughes-Fulford working
with the Research
Animal Holding Facility.