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.

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.

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

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

(http://srtm.usgs.gov/) 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.

Major Scientific Discoveries

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.

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

Major Scientific Discoveries

Helen Lane

Laurence Young

William Paloski

Laura Barger

Charles Czeisler

John Charles

Steven Platts

Daniel Feeback

Kenneth Baldwin

Judith Hayes

John Charles

Steven Platts

Helen Lane

Clarence Alfrey

Scott Smith

Brian Crucian

Satish Mehta

Mark Ott

Duane Pierson

Clarence Sams

Janis Connolly

David Fitts

Dane Russo

Vickie Kloeris

John James

Thomas Limero

Mark Ott

Chau Pham

Duane Pierson

Philip Stepaniak

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

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.

Major Scientific Discoveries

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).

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.

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.”

Major Scientific Discoveries

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

Major Scientific Discoveries

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

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.

Major Scientific Discoveries

Nucleus of the

Solitary Tract

Somatic Motor Reexes

Medulla

Inferior Olive

Cerebellar

Cortex

Pons

Vestibular

(Cranial

Nerve VIII)

Nuclei

Abducens

(Cranial

Nerve VI)

Nucleus

Trochlear

(Cranial Nerve IV)

Nucleus

Oculomotor

(Cranial Nerve III)

Nucleus

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.

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.

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.

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.

Major Scientific Discoveries

On a 24-hour external

light-dark cycle, the

body’s circadian clock

remains properly

synchronized

(e.g., hormones like

melatonin are

released at the

appropriate time).

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

desynchronized

(e.g., inappropriately

timed hormone release).

Major Scientific Discoveries

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.

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.

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

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.

Colonel, US Air Force (retired).

Pilot for STS-58 (1993) and

STS-76 (1996).

Commander for STS-90 (1998).

“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.”

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

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.

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.

Major Scientific Discoveries

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.

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.

Major Scientific Discoveries

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.

Treadmill

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.

Major Scientific Discoveries

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).

Rower

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

Velcro

®

strap onto a footplate that

allowed for positioning. The rower used

a magnetic brake to generate resistance.

Summary

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.

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.

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,

Major Scientific Discoveries

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.

Major Scientific Discoveries

Immediately

After Entering

Microgravity

Environment

While in

Prolonged

Microgravity

Landing

Day

Launch

Day

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.

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

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.

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.

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.

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

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.

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.

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

Major Scientific Discoveries

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).

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.

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.

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

Major Scientific Discoveries

determined from the products of energy

metabolism: carbon energy sources like

carbohydrates, protein, or fat + oxygen

(O

2

) = heat + carbon dioxide (CO

2

).

We used two methods for shuttle

flights. For most flights, all the expired

CO

2

was removed by chemical reaction

with lithium hydroxide (LiOH) so the

amount of CO

2

produced during a flight

could be determined. CO

2

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

2

and water loss over 3 to 5 days

of time per astronaut. Astronauts

consumed two stable isotopes (not

radioactive), deuterium and

18

O, and

the levels of these isotopes in urine

were measured over a period of several

days. The O

2

occurs in the CO

2

and

water, but deuterium is only in the

water; thus the method allowed for the

determination of the CO

2

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 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

isotope

15

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.

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.

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

Major Scientific Discoveries

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

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.

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.

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

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)

Protein

12% to 15% of energy intake

< 85 g/d

Water

2,000 ml/d

Na

1,500 to 3,500 mg/d

K

3,500 mg/d

Fe

10 mg/d

Vitamin D

10 ug/d

Calcium

800 to 1,200 mg

Hypersensitivity

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.

Major Scientific Discoveries

Antibodies

Cytokines

Granulocytes

Monocytes

Lymphocytes

B lymphocytes - Humoral immunity

T lymphocytes - Cell-mediated immunity

Natural killer cells - Innate immunity

Innate immunity

Humoral immunity

Cytokines

Antibodies

Humoral immunity

Cytokines

Antibodies

Humoral immunity

ym

L mphocytes

Monocytes

Granulocytes

T lymphocytes - Cell-mediated immunity

Innate immunity

ymphocytes

B lymphocytes - Humoral immunity

Monocytes

Granulocytes

T lymphocytes - Cell-mediated immunity

Innate immunity

B lymphocytes - Humoral immunity

T lymphocytes - Cell-mediated immunity

B lymphocytes - Humoral immunity

Natural killer cells - Innate immunity

Major Scientific Discoveries

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

postherpetic

neuralgia.

Initial stage consists

of burning pain and

sensitive skin.

Weakened

immune system

reawakens

virus.

Dormant

Varicel a

Virus

Nerve Fiber

Primary Disease

(Chicken Pox)

Reactivation

(Shingles)

Stress on the

immune system

allows the latent

virus to reactivate

as shingles.

Shingles

Outbreak

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.

Summary

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.

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.

Major Scientific Discoveries

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.

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,

Velcro

®

, 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.

Major Scientific Discoveries

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.

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.

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.

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

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.

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.

Light-emitting diode (LED) rings mounted on the two shuttle cameras in the aft payload

bay of shuttle.

Maintaining a Healthy Environment During

Spaceflight

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

2

) 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.

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

Freon

®

-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

®

-21

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.

Air

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

2

—a gas

exhaled in large quantities as a result

of human metabolism—from the

atmosphere. By contrast, CO

2

is one

of the most difficult compounds to

deal with in spaceflight. For example,

accumulation of CO

2

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

2

. This involved duct-taping

filters and tubing together to maintain

CO

2

at tolerable levels. Such extreme

measures were not necessary aboard

shuttle; however, if the crew forgot to

change out filters, the CO

2

levels could

have exceeded exposure standards

within a few hours.

Although older limits for CO

2

were

set at 1%, during NASA’s new

standard-setting process with the

National Research Council it became

Major Scientific Discoveries

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

2

, 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

2

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

Major Scientific Discoveries

Major Scientific Discoveries

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.

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.

)

Compounds:

Toluene

Benzene

Ethylbenzene

Xylenes

Post release

62 minutes

9/18/06

Pre-incident

9/04/06

Post release

296 minutes

9/18/06

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.

Water

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.

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

Teflon

®

; 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.

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,

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.

Major Scientific Discoveries

n

Infectious diseases

n

Toxin production

n

Plant diseases

n

Allergies

n

Food spoilage

n

Volatile release

n

Material degradation

n

Immune alteration

n

Environmental

contamination

Astronauts Megan McArthur,

Michael Massimino (center),

and Andrew Feustel

prepare to eat a meal on

the middeck of Atlantis

(STS-125 [2009]).

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 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.

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

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.

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.

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

2

), 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

2

exposure, protection and monitoring in

case of radiation exposure from either

artificial or solar particle events, and the

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

Freon

®

. 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

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.

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.

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.

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.

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

Nomex

®

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.

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.

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.

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

Major Scientific Discoveries

Kenneth Souza

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

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.”

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.

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.

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,

Major Scientific Discoveries

STS-40 (1991) payload

specialist Millie

Hughes-Fulford working

with the Research

Animal Holding Facility.