Life in Extreme Environments: How Will Humans Perform on Mars?
Dava J. Newman
Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge MA
ABSTRACT
capabilities relative to the effects of partial gravity on human
locomotion will enhance the integration of humans and machines
for future missions.
This review of astronaut extravehicular activity
(EVA) and the details of American and Soviet/Russian
spacesuit design focuses on design recommendations to
enhance astronaut safety and effectiveness. Innovative
spacesuit design is essential, given the challenges of
future exploration-class missions in which astronauts will
be called upon to perform increasingly complex and
physically demanding tasks in the extreme environments
of microgravity and partial gravity.
THE SPACE SHUTTLE AND MIR SPACE STATION
INTRODUCTION
Since the beginning of human exploration above Earth’s
atmosphere, our main challenge has been to supply the explorer
with the basic necessities for life support that nature normally
provides. Unprotected by a spacecraft or spacesuit, anyone
encountering the near-vacuum of space would survive only a few
minutes. Body fluids would vaporize in the absence of pressure
and an atmosphere, and gas that would quickly expand in the
lungs and other tissues would prevent circulation and
respiration.
This paper focuses on the demands faced by astronauts
when they leave their spacecrafts and perform extravehicular
activities (EVA) in space, and on the evolutionary design of
spacesuits to meet these needs. These suits comprise a
necessary operational resource for the long-duration missions
that will establish human presence beyond Earth. The different
spacesuit choices pursued by the American and Soviet/Russian
space programs provide the basis for case studies relative to the
design of human space exploration systems. Many factors
bearing on the challenge of keeping humans alive and functioning
optimally in space will be considered in the following discussion,
including atmosphere composition and pressure, thermal control,
radiation protection, human physiology, and human performance
in partial gravity.
Human presence on space missions offers many advantages
to ensure mission success: flexibility and dexterous
manipulation, human visual interpretation and cognitive ability,
and real-time approaches to problems. However, there are
factors that may degrade human performance. These include
pressure-suit encumbrance, prebreathe requirements, insufficient
working volume, limited duration, sensory deprivation, and poor
task or tool design (NASA, 1989). In addition to microgravity
performance, the partial-gravity environments of the moon and
Mars require advanced technology, hardware, and performance
capabilities for successful space endeavors. While EVA, as well
as robotics and automation, expand the scope of space
operations, a more thorough understanding of astronaut
Many of the tasks accomplished onboard the Space
Shuttle—the world's first reusable spacecraft and one of
NASA's foremost projects—have furthered space exploration
and enhanced the quality of life on Earth. The Space Shuttle is
the first U.S. vehicle with a standard sea-level atmospheric
pressure and composition. (Mercury, Gemini, and Apollo all
operated at 33.4 kPa [5 psi or 0.33 atm] pressure and 100%
oxygen composition.) The Space Shuttle’s capabilities allow
scientists routinely to conduct experiments that explore the
effects of the space environment, particularly microgravity, on
human physiology under conditions that cannot be duplicated on
Earth.
Between March 1995 and May 1998, NASA astronauts
flew onboard the Russian space station Mir in a collaborative
effort with the Russian space program. The NASA program that
has supported this endeavor, commonly known as International
Space Station Phase 1 (or Shuttle-Mir), has encompassed 11
Space Shuttle and joint Soyuz flights. The international program
has resulted in joint space experience for the crew and the start
of joint scientific research. Shuttle-Mir participants (crew
members, principal investigators, and mission control staff)
investigated vital questions about the future of human life in
space. Mir has been a test site for three main areas of experience
and investigation:
•
Designing, Building, and Staffing the International Space Station
Participants have drawn from the experience and
resources of many nations to learn from one another,
and also to learn how to work together.
• Investigation
Mir has offered a unique opportunity for long-duration
data gathering. Station designers have used Mir as a test
site for space station hardware, materials, and
construction methods. Mir crew members have utilized
the microgravity environment to conduct scientific
investigations into biological and materials studies.
• Operation
In the almost 40-year history of human spaceflight, no
previous program has required so many transport
vehicles and so much interdependent operation between
organizations. Shuttle-Mir experience has given
participants an opportunity to prepare for the
formidable cooperative effort required on the
International Space Station.
Gravitational and Space Biology Bulletin 13(2), June 2000
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ASTRONAUT PERFORMANCE FROM MIR TO MARS
A Case Study: MIT’s Enhanced Dynamic Load Sensors
(EDLS) Experiment on Mir
One of the key missions of the International Space Station
(ISS) is to perform microgravity experiments that require a
quiescent environment (~10-4 to 10-7 g); that is, to perform
experiments that make use of the almost complete absence of
any accelerations as a vehicle orbits the Earth. For this reason,
we conduct spaceflight experiments for the ISS program that
investigate how astronauts move around in space and how they
may disturb the spacecraft microgravity environment. While
some microgravity experiments can be fully automated, many
require astronauts to execute or supervise them. We have wanted
to ensure that these astronauts, who play a critical role in the
success of the experiments, are not a significant source of
disturbance to the spacecraft acceleratory environment.
When astronauts move inside the cabin of a spacecraft,
they impart impulses to the vehicle. From vehicle and
environmental parameters, we can estimate external disturbances,
such as aerodynamic drag and solar pressure, quite easily.
Similarly, we can predict interior disturbances caused by
operating mechanical equipment, such as pumps and fans.
However, the inherent randomness of astronaut-induced
disturbances makes their analysis a far more challenging task.
Phase I of the ISS program gave seven American
astronauts the opportunity to conduct long-duration spaceflight
experiments on the Russian space station Mir, and within the
framework of the program, Massachusetts Institute of
Technology (MIT) conducted the Enhanced Dynamic Load
Sensors (EDLS) experiment on Mir to quantify astronautinduced disturbances to the microgravity environment. The
experiment was designed with two objectives:
1. Primarily, to assess nominal astronautinduced forces and torques during longduration space station missions by
measuring everyday activities and induced
loads (using smart sensors, called
“restraints”).
2. Secondarily, to gain a detailed
understanding of the how astronauts devise
strategies for moving around in
microgravity as they propel themselves
with their hands and float from module to
module.
The experimental set-up consisted of four load sensors and a
specially-designed computer. The sensors included an
instrumented handhold and two instrumented foot restraints,
which provided the same functionality as the hand rail and foot
loops built into the Space Shuttle Orbiter and the Mir orbital
complex, and an instrumented push-off pad envisioned as the
kind of flat surface from which astronauts propel themselves
with their hands or feet.
The astronauts were instructed to activate the computer
and go about their regular on-orbit activities.
a
b
.
Figure 1 . MIT’s Enhanced Dynamic Load Sensors (EDLS)
on Mir. (a) A Shuttle-Mir crew member using the EDLS
handhold on Mir. (b) Four EDLS, force sensors that were
used in the Priroda and Mir Base Block modules.
Whenever the computer detected that the measured forces and
torques exceeded a specified threshold force, data were recorded
on the storage medium (Figures1a and b). The experiment was
conducted during the stay of U.S. astronauts Shannon Lucid
(March–September 1996) and Jerry Linenger (January–May
1997) aboard Mir. The overall data recording time was 133 hours
over the two periods. The storage media with the data were
returned to Earth via the Space Shuttle in 1998. Table 1 shows
the seven typical astronaut motions used for locomotion
(including floating) in microgravity. These motions are quite
different from the standing, walking, and running that constitute
bipedal motion on the Earth.
Video recordings of astronauts moving in the modules and using
restraint and mobility aids on the NASA 2 and NASA 4
missions let us identify several typical astronaut motions and
quantify the associated load levels exerted on the spacecraft. It
was found that
• for 2,806 astronaut activities recorded by the foot
restraints and handhold sensor, the highest force
magnitude was 137 N;
36
Gravitational a nd Space Biology Bulletin 13(2), June 2000
ASTRONAUT PERFORMANCE FROM MIR TO MARS
Table 1. Characteristic Astronaut Motions
Characteristic Motion
Description
Landing
Flying across module and landing
Push off
Pushing off and flying
Flexion/Extension
Flexing or extending limb
Single Support
Using one limb for support
Double Support
Using two limbs for support
Twisting
Twisting body motion
Reorienting
Usually small corrections for posture control
• ~99% of the time, the maximum force magnitude was
below 90 N; ~96% of the time, the maximum force
magnitude was below 60 N;
• for 95% of the astronaut motions, the root mean
square force level was below 9.0 N;
• the average momentum imparted by the astronauts on
the Mir space station was 83±228 kg· m/s.
It can be concluded that expected astronaut-induced loads on the
ISS from usual astronaut intravehicular activity are considerably
less than previously thought and will not significantly disturb
the ISS microgravity environment (Amir and Newman, 2000).
These are very low forces when compared to typical Earth
forces. Actually, they are an order of magnitude less. (Consider
that a person with a mass of 52 kg exerts 1 BW, or 510 N with
every step he or she takes, and then think about how many
steps a person takes every day.) Essentially, the data prove that
astronauts in microgravity adopt the appropriate strategy for
their new weightless environment and use “finger push-offs” and
“toe-offs” as they move about in space. After living in space for
months, astronauts, like highly trained athletes or professional
ballet dancers, move about with grace and control. They go
about their daily activities exerting very low forces on the
microgravity environment they inhabit.
will learn how to live and work “off planet” in an international
way.
The Skylab and Mir space station experiences
demonstrated that crew members become very skilled in
performing tasks on long-duration missions. After approximately 60 days in orbit, a crew member’s knowledge
encompasses the laboratory, stowage locations, procedures,
personal dynamics among colleagues, and many other elements.
This experience-based knowledge and understanding is
considerable when compared to what can be learned in missions
that last only two weeks or less. Crew members on longduration missions also have time to fully adapt to space (e.g., to
sleep well, eat well, and exercise regularly).
The completed ISS will be powered by almost an acre of
solar panels and have a mass of almost one million pounds, and
the station’s pressurized volume will be roughly equivalent to
the space inside two jumbo jets. The U.S. habitation module to
to be delivered by the final ISS assembly mission will have
enhanced accommo-dations and will provide for as many as
seven crew members.
The ISS is where key biomedical, life support, and human
factors questions must be answered to ensure crew health, wellbeing, and productivity for future exploration missions.
EXTRAVEHICULAR ACTIVITY (EVA)
THE INTERNATIONAL SPACE STATION
The ISS will offer a world-class research laboratory in low
earth orbit. Once assembled, it will afford scientists, engineers,
and entrepreneurs an unprecedented platform on which to
perform complex, long-duration, and repeatable experiments in
the unique environment of space. The ISS’s invaluable assets
include opportunities for prolonged exposure to microgravity
and the presence of human experimenters in the research
process. Yet the ISS is much more than a state-of-the-art laboratory in a novel environment; it is an international human
experiment—an exciting city in space—and a place where we
Human space exploration is epitomized by extravehicular
activity (EVA)—that is, space walks. In March of 1965,
cosmonaut Alexei Leonov became the first human to walk in
space. Attached to a 5-meter long umbilical that supplied him
with air and communications, Leonov floated free of the
Voskhod spacecraft for over ten minutes. In June of the same
year, Edward White became the first American astronaut to leave
a spacecraft while in orbit. White performed his spectacular
space walk during the third orbit of the Gemini-Titan 4 flight.
Figure 2 summarizes Russian and U. S. EVA to date, as a
Gravitational and Space Biology Bulletin 13(2), June 2000
37
ASTRONAUT PERFORMANCE FROM MIR TO MARS
TOTAL EVA DURATION (Clock Hours)
baseline for comparison to future EVA entailed by the ISS
assembly and Mars exploration (to be discussed later).
Although some early EVA efforts were plagued with
problems, the feasibility of placing humans in free space was
demonstrated. The Gemini EVAs revealed the need for adequate
body restraints and the value of neutral buoyancy simulation for
extended-duration training in weightlessness. During the Apollo
program, EVA became a useful mode of functioning in space,
rather than just an experimental activity. Twelve crew members
spent a total of 160 hours in spacesuits on the moon, covering
100 kilometers (60 miles) on foot and with the lunar rover as
they collected 2196 soil and rock samples. The EVA spacesuits
were pressurized to 26.2 kPa (3.9 psi) with 100% oxygen, and
the Apollo cabin pressure was 34.4 kPa (5 psi) with 100%
oxygen. During pre-launch, the Apollo cabin was maintained at
101.3 kPa (14.7 psi) with a normal air (21% oxygen and 79%
nitrogen) composition. Just before liftoff, the cabin was
depressurized to 34.4 kPa (5 psi). To counteract the risk of
decompression sickness after this depressurization, the
astronauts prebreathed 100% oxygen for three hours prior to
launch.
The potential benefits of EVA were nowhere more evident
than in the Skylab missions. When the crew first entered Skylab,
the internal temperature was up to 71oC (160oF), rendering the
spacecraft nearly uninhabitable. The extreme temperatures
resulted from the loss of a solar panel and a portion of the
vehicle’s outer skin. After the failure of a second solar panel
deployment and a consequent loss of power and cooling
capability, astronauts salvaged the entire project by rigging a
solar shade through the science airlock and freeing the remaining
solar panel during EVA. The Skylab experience demonstrated the
paramount flexibility that humans performing EVA offer toward
the success of space mission operations and scientific endeavors.
Cosmonauts performed critical EVAs on Salyut to examine and
replace a docking unit and returned experimental equipment to
Earth that had been subjected to solar radiation for ten months.
The Salyut 7 space station program saw successful astronaut
EVAs to study cosmic radiation and the methods and equipment
for assembly of space structures. On 25 July 1984, during her
second spaceflight (her first was in August 1982), cosmonaut
Svetlana Savitskaya became the first woman to perform an EVA,
during which she used a portable electron beam device to cut,
weld, and solder metal plates.
EVAs performed during Space Shuttle missions and Mir
long-duration missions have accomplished many significant
tasks. During these missions, trained crew members have
responded in real time to both planned mission objectives and
unplanned contingencies.
SPACESUITS
To date, crew members have accomplished successful
EVAs wearing a variety of spacesuits that have evolved from the
umbilical models of the Voskhod and Gemini era into today’s
self-contained, modular designs. Advanced spacesuit concepts
incorporate self-contained life-support systems (both the
American and Russian spacesuits) and modular components (the
American spacesuit). Modularity allows for ease of resizing to
fit humans ranging in size from fifth percentile females to ninetyfifth percentile males, a distinct advantage over the custom-fitted
suits previously used. Further evolution will yield spacesuits
300
RUSSIAN
Rev. E Assembly Sequence
With HST and Surface Exploration
SHUTTLE / HST /
DTO / ISS
APOLLO / SKYLAB
2500
2000
GEMINI
200
Assumptions:
12 US ISS Maintenance EVA/yr post assembly complete
6 Russian ISS Maintenance EVA/yr post assembly complete
8-Hour Lunar EVAs commencing in 2010
MARS (Scale on
the right)
1500
1000
250 8-Hour Mars EVAs in 2015
100
500
0
0
65 67 69 71 73 75 77 79 81 83 85 87 89 91 93 95 97 99 01 03 05 07 09 11 13 15
CALENDAR YEAR
Figure 2. The “Wall of EVA.” Illustrating the history of EVA, the three-fold anticipated increase in EVAs for ISS assembly,
and the possible 40-fold increase for planetary EVA. HST=Hubble Space Telescope; DTO=detailed test objective
(additional EVA opportunities).
38
Gravitational and Space Biology Bulletin 13(2), June 2000
ASTRONAUT PERFORMANCE FROM MIR TO MARS
for microgravity, lunar, and Martian environments.
The Space Shuttle Extravehicular Mobility Unit (EMU)
The current Space Shuttle EVA system, known as the
Extravehicular Mobility Unit (EMU), consists of a spacesuit
assembly (SSA), an integrated life-support system (LSS), and
the EMU support equipment.
• Space Suit Assembly. The SSA is a 29.6 kPa (4.3 psi),
100% oxygen spacesuit made of multiple fabric layers
attached to an aluminum-fiberglass hard upper torso unit
(HUT). The SSA retains the oxygen pressure required for
breathing and ventilation and protects against bright
sunlight and temperature extremes.
• Life Support System. The LSS controls the internal
oxygen pressure, makes up oxy gen losses due to leakage
and metabolism, and circulates ventilation gas flow and
cooling water to the crew member. The LSS also removes
the crew member’s released carbon dioxide, water vapor,
and trace contaminants. The spacesuit and its life-support
system weigh approximately 117 kg (258 lbm ) when fully
charged with consumables for EVA (Wilde, 1984). The
spacesuit is equipped with a disposable urine collection
device.
• Support Equipment. The EMU support equipment,
which stays in the airlock during an EVA, functions
mainly to replenish consumables and assist the crew
member with EMU donning and doffing.
The SSA’s Hard Upper Torso Unit (HUT) is the primary
structural member of the EMU. The helmet, arms, lower torso
assembly (LTA), and the primary life-support system (PLSS)
both mount to the HUT, which incorporates scye bearings to
accommodate a wide range of shoulder motions.
• Helmet.
The spacesuit helmet is a transparent
polycarbonate bubble that protects the crew member and
directs ventilation flow over the head for cooling. The
neck-ring disconnect of the helmet mounts to the HUT,
and the helmet is equipped with a visor that has a
moveable sunshade as well as camera and light mounts.
The crew member’s earphones and microphones are held
in place by a fabric head cover, known as the “Snoopy
cap.”
• Arms . The spacesuit arms are fabric comp onents
equipped with wrist-, elbow-, and upper-arm bearings that
allow for elbow extension and flexion in addition to elbow
and wrist rotation.
• Lower Torso Assembly. The LTA, which includes
boots and fabric legs that permit hip and knee flexion, is
equipped with a bearing that allows waist rotation.
• Primary Life Support System. The PLSS, or backpack,
houses most of the LSS and a two-way AM radio for
communications and bioinstrumenta-tion monitoring.
Typically, EVA is scheduled for up to six hours, but the
PLSS is equipped with a seven hour oxygen and carbon-
dioxide-scrubbing capability for nominal metabolic rates.
In case of an emergency, a secondary oxygen pack, located
at the bottom of the PLSS, provides an additional 30
minutes, minimum, of oxygen at a reduced pressure of
26.9 kPa (3.9 psi). Between EVAs, the silver-zinc cell battery that powers the LSS machinery and communications
is recharged in place.
• Displays and Controls. All of the displays and controls
that a crew member activates and monitors are mounted on
the front of the HUT. The temperature control valve is on
the crew member’s upper left, and the oxygen control
actuator is on the lower right. The large controls are
designed to be simple to operate, even by a crew member
wearing pressurized spacesuit gloves.
There are numerous fabric layers in the EMU:
1. The liquid cooling and ventilation garment (LCVG)
is innermost. It is made of nylon/spandex lined with tricot
and resembles a pair of long underwear. Ethylene-vinylacetate plastic tubing is woven throughout the spandex to
route water close to the crew member’s skin for body
cooling.
2. The spacesuit’s pressure-garment modules come next.
These retain pressure over the arms, legs, and feet. They
are made of urethane-coated nylon, covered by a woven
dacron restraint layer. Sizing strips are used to adjust the
length of the restraint layer.
3. The thermal meteoroid protection garment (TMG)
comprises the final layers of the EMU’s fabric
components. The TMG liner is neoprene-coated ripstop
nylon, and it provides puncture, abrasion, and tear
protection.
4. Aluminized mylar thermal insulation, designed to
prevent radiant heat transfer, make up the spacesuit’s next
five layers (Wilde, 1984).
5. The familiar white covering comes last. This sunlightreflecting outer layer is made of ortho fabric, which
consists of a woven blend of kevlar and nomex synthetic
fibers. The ortho fabric itself is very strong and resistant
to puncture, abrasion, and tearing, and it is coated with
teflon to stay clean during training on Earth.
Metabolic expenditures and crew performance during EVA
are integrally tied to the mobility of the spacesuit and the
capabilities of the life-support system. The LCVG, the
innermost layer of the spacesuit, provides thermal control by
circulating air and water, cooled by a sublimator, over the crew
member’s body. (This concept was initially used by English
fighter pilots and later adopted by the Russian and American
space programs.) The LCVG can handle peak loads of up to 500
kcal/hr (2000 Btu/hr) for 15 minutes, 400 kcal/hr (1600 Btu/hr)
Gravitational and Space Biology Bulletin 13(2), June 2000
39
ASTRONAUT PERFORMANCE FROM MIR TO MARS
Figure 3. The NASA Spacesuit, or Extravehicular Mobility Unit (EMU). (Courtesy of Hamilton Standard, rev. 2/95)
40
Gravitational and Space Biology Bulletin 13(2), June 2000
ASTRONAUT PERFORMANCE FROM MIR TO MARS
for up to one hour, or 250 kcal/hr (1000 Btu/hr) for up to seven
hours. (See Table 2)
The TMG covers the entire EMU, except for the helmet,
controls, displays, and glove fingertips. The TMG and LSS
cooling system limit skin-contact temperature to the range of
10oC to 45oC (50oF to 113oF), and additional thermal mittens are
used for grasping objects with temperatures that can range from 118oC (-180oF) on the shadow side of an orbit to +113oC
(+235oF) on the light side of an orbit.
Gloves are the crew member’s interface with the equipment
and tools he or she uses. The EMU gloves, which connect to the
arms at the wrist joints, have jointed fingers and jointed palms.
Each glove also includes a pressure bladder, a restraint layer, and
a protective thermal outer layer. To enhance tactility, fingertips
are made from silicone rubber caps. The gloves present the most
difficult engineering problem in spacesuit design. A dexterous
spacesuit glove that provides ideal finger motion and feedback
has not yet been realized.
Throughout the EVA, monitoring of carbon-dioxide
concentration and other suit parameters occurs via telemetry to
the ground, with updates every two minutes. Carbon dioxide is
kept below 0.99 kPa (0.15 psi) and is absorbed by lithiumhydroxide canisters. Electrocar-diographic leads are worn to also
allow constant monitoring of heart rate and rhythm. For
sustenance, the crew member is provided with a food bar and up
to 21 ounces of water in the EMU.
The EMU, EVA support tools (i.e., foot restraints,
handholds, and specialized tools), and EVA training are credited
with the reduction that has occurred in Shuttle mission workload
over the course of time. Most EVA training takes place
underwater in the neutral buoyancy laboratory (NBL) at
NASA’s Johnson Space Center in Houston, Texas. Training crew
members extensively practice scheduled EVAs in the neutral
buoyancy setting to simulate weightlessness.
The Russian Spacesuit
The current spacesuit used for Mir Space Station EVAs is a
derivative of the semi-rigid suit used in the Salyut-Soyuz
program. The Orlan suit has undergone continuous modification,
and a fifth-generation model is currently used for EVA
operations. Similar to the American EMU, the Orlan spacesuit
has an integrated life-support system to enable EVA operations
from Mir. As stated, the 100% oxygen spacesuit nominally
operates at 40.6 kPa (5.88 psi). Weighing ~105 kg (231 lbm )—
which does not include a fully charged PLSS—this is an
adjustable, universally sized suit with a metal upper torso and
fabric arms and legs. Metal ball bearings and sizing adjustments
are notable features. An advancement and difference from the
EMU is found in the Orlan’s rear hatch entry, which allows an
unassisted spacesuit entry that requires only two to three
minutes (Bluth and Helppie, 1987).
Table 2. Average Metabolic Rates for Past Space
Missions (Waligora et al., 1991)
Spacesuit
Gravity (G)
Metabolic Rate
(kcal/hr)
Apollo
1/6
235 (suited)
microgravity
151 (cabin)
Skylab
microgravity
238
Space Shuttle
microgravity
197
The spacesuit has self-contained, integrated pressure and
O2 systems in a backpack-type PLSS that can be maintained onorbit. The oxygen supply system includes reserve oxygen storage
and equipment for controlling and maintaining the pressure. The
ventilation system and environmental gas-composition control
system include CO2 and contaminant-removal units along with
gas circulation control equipment. The spacesuit has no umbilical
lines. Oxygen, water supplies, pumps, and blowers are located in
the cover of the rear hatch.
Adequate microclimate conditions in the suit are provided
by a closed-loop, regenerative life-support system. The suit’s
thermal control system maintains the cosmonaut’s body
temperature and humidity level within acceptable limits and
utilizes an efficient sublimating heat exchanger. The cosmonaut
wears the liquid-cooled garment described earlier (LCVG),
comprised of a network of plastic tubes, that allows the
temperature to be maintained manually on a comfort basis or
automatically by the spacecraft temperature-regulation system.
The heat exchanger and LCVG provide a nominal thermal mode
for sustained operation at practically any metabolic workload.
Materials and colors which reflect strong solar radiation are used,
and the spacesuit has layers of protection against extreme
temperatures. The nonhermetically sealed outside layer is a
protective vacuum insulator, while the hermetically sealed inside
layer is a special rubber suit that retains the pressure.
In summary, the spacesuit’s designer, Guy Severin of
Svezda, lists the following seven attributes of the semi-rigid
Orlan spacesuit (Severin, 1990):
•
•
•
•
•
•
•
Minimal overall dimensions of suit torso in a
pressurized state
Rapid donning and doffing
Easy handling capabilities and improved reliability of
lines connecting the life-support system
Reliability of the hatch sealing system
Suitability for crew members of different
anthropometric dimensions
Easy replacement of consumable elements
Easy maintainability through convenient access to units
Gravitational and Space Biology Bulletin 13(2), June 2000
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ASTRONAUT PERFORMANCE FROM MIR TO MARS
Future Russian spacesuit research and development
activities are aimed toward improving suit performance
characteristics (specifically mobility), extending spacesuit
operating life, using microprocessors to control and monitor
spacesuit systems, and decreasing the payload weight that is
delivered to orbit in the process of replenishing spacesuit consumables. Ideas to decrease payload weight include regenerating
CO2 absorbers, removing heat without evaporative water loss,
decreasing spacesuit O2 leak rates, and using advanced O2
supplies.
PHILOSOPHICAL DIFFFERENCES UNDERLYING
DESIGN CHOICES
Many instructive design lessons emerge from comparing
U.S. and Russian spacesuits. NASA has used a different
spacesuit design for each of its main human spaceflight programs
(except Apollo/Skylab and Shuttle/ ISS), whereas the Russians
have used essentially one spacesuit design that has evolved
throughout their program history. This difference is a matter of
design choice—there is no right or wrong—and the U.S. and
Russian approaches to spacesuit design selection may reflect
underlying philosophical differences.
In NASA’s case, each human spaceflight program has
offered many different industrial and academic partners new
opportunities to influence spacesuit design. In Russia, on the
other hand, one spacesuit designer provided the spacesuit,
which, once adopted, has been enhanced for various programs.
NASA’s approach promotes creativity and cost savings, as, with
each new program, designers with the most unique designs and
the lowest bids compete for a contract. The Russians have
pursued their goal—to create a robust, reliable system—by
relying on the master designer’s original design, which has been
tested over time and altered very little. (The NASA and Russian
space programs have followed similar design philosophies for
space vehicles, where NASA typically designs and builds a
new craft for each major program and the Russians rely
more on mass production of similarly designed,
evolutionary spacecraft.)
The need always drives the design requirement; and design
requirements are met by a successful design. Both the EMU and
Orlan spacesuits meet the crew member’s need for life support
during EVA. Among the design requirements for a spacesuit are
42
•
life support for the extravehicular crew
member, including pressure, oxygen supply,
carbon dioxide and trace gas removal,
humidity and temperature control, and
environmental protection;
•
mobility and dexterity—especially in the
gloves—for successfully accomplishing EVA
tasks;
•
a system that is as light as possible;
•
continuous operation during of the EVA
excursion.
Gravitational and Space Biology Bulletin 13(2), June 2000
Both the EMU and the Orlan spacesuits meet these design
requirements, although there is room for much improvement in
glove design and the matter of weight. Each suit has its own
strengths and limitations (see Table 3). For example, the EMU
provides better mobility than the Orlan, primarily because its
lower operating pressure permits more joint and glove motion.
The incorporation of advanced materials into the EMU’s design
also extends its design life. However, when it comes to donning
and doffing, the Orlan design is clearly superior. Its rear hatch
entry allows the crew member to don and doff the spacesuit
unassisted. (Only in theory is this possible with the two-piece
EMU.) The lower mass, hence lower weight, of the Orlan system
also offers a distinct advantage over the EMU. For space station
operations in a weightless environment, designers tend to discard
mass as a critical spacesuit design requirement, but for a future
planetary spacesuit, a suit with low mass will most likely offer
the most promising design.
SPACESUITS FOR FUTURE MISSIONS
Planetary EVA and the extensive construction and
maintenance of future space stations will require increased levels
of EVA capability. To meet a three-fold increase in the number of
EVAs needed for ISS assembly and a possible forty-fold increase
for planetary EVA (Figure 2) revolutionary spacesuit design
concepts should be considered. An advanced spacesuit might be
more like everyday clothing or something radically different, such
as a pod with robotic actuators. No design rule dictates that
future spacesuits must look like current ones, only that spacesuit
requirements be met through innovative design. Ideally,
advanced spacesuits will provide the crew member with a
protective, mobile, regenerable life-support system for use in
orbit and on planetary surfaces. Advanced spacesuits should
provide:
•
Working pressures for shirtsleeve mobility
•
Dexterous gloves or actuators
•
Longevity
•
Easy maintenance
•
Adequate environmental protection
Mobile joint systems must allow for minimum energy
expenditures during EVA tasks; gloves should be certified for
long-duration use at high pressures; and improved technology and
materials should insure spacesuit durablity. Primary life-support
systems should be regenerable, low-mass, and modular. A broad
metabolic loading range between 63-625 kcal/hr (250-2500
Btu/hr) should be achieved with automatic thermal control
systems; a modular, evolvable design is advantageous.
Technological advances should lead to real-time environmental
monitoring and innovative display and vision systems. It is clear
that a radical new approach to spacesuit design will best meet
such future challenges as Martian EVAs likely to entail repelling
down shear cliffs and traversing monumental canyons.
ASTRONAUT PERFORMANCE FROM MIR TO MARS
Future Space Walks
Microgravity EVA has been admirably demon-strated.
While significant improvements are necessary for long-term space
station EVA, quantum improvements are required for planetary
EVA. To move about in microgravity, the crew member primarily
uses the small musculature of the upper body, rather than the
large musculature of the lower body. Planetary EVA, however,
will dictate a true locomotion spacesuit, because the large muscles
of the legs will be used for locomotion in the 3/8-g environment,
and the upper body muscles will be called upon for EVA tasks
other than self-locomotion. Apollo 17 EVA astronaut Harrison
Schmitt praised the Apollo spacesuits for working without a
serious malfunction for up to 22 hours of exposure to the lunar
environment, but he also made recommendations for future
planetary space-
suits that should be heeded. Recounting lunar astronauts’
frequent falls, Jones and Schmitt (1992) suggested that
improvements in mobility and suit flexibility would have a
significant impact on astronaut productivity. They emphasized,
however, that the greatest impact would come from
improvements both for increased manual dexterity and for
reduced muscle fatigue and abrasion-induced damage to the hands.
Noting that the fine dust particles of lunar regolith caused
problems with the Apollo suits, Jones and Schmitt (1992) also
predicted that dust from lunar and Martian habitats would
present an obstacle to EVA performance on a continuous, daily
basis. It is clear from these comments that the design and
development of future planetary spacesuits will be challenging.
Table 3. Comparisons between the U.S. and Russian Space Suits (Asker, 1995)
NASA Space Shuttle Extravehicular Mobility
Unit (EMU)
Orlan-DMA Space Suit
Manufacturer
United Technologies, HamiltonSundstrand,
Windsor Locks, CT
Zvezda Research, Development, and
Production Enterprise Tomilio, Russia
Suit Operating Pressure
30 kPa (4.3 psi) differential
40 and 26 kPa (5.8 and 3.8 psi) differential
Nominal Maximum
Mission Duration
7 hours
6 hours
Emergency Life Support
Useful Life
30 minutes
30 minutes
Sizing
•
Modular assembly to 5 percentile female
to 95 percentile male
11 suit assembly items
•
•
•
•
•
•
•
Urethane-coated nylon pressure bladder
Polycarbonate helmet and visors
Ball-bearing joints
Liquid cooling/ventilation undergarment
Fiberglass hard upper torso
Ortho fabric and aluminized mylar
thermal/meteoroid garment
•
•
•
•
Clos ed-loop, pure oxygen generative
7 interchangeable subsystem modules
Expendables replaceable or rechargeable
on orbit
•
•
•
Construction of suit
Assembly
Construction of LifeSupport System
•
•
•
•
•
•
•
One adjustable size with axial restraint
system allowing on-orbit sizing
Two glove sizes
Semi-rigid with latex rubber dual
pressure bladder in arms and legs
Dual-layer helmet
Dual-seal bearings in shoulder and
wrist
Liquid cooling undergarment
Rear-entry suit design
On-orbit limb sizing
Closed-loop, pure oxygen generative
On-orbit servicing through rear entry
door
Redundant life-critical features
Donning
15 minutes (typically with assistance)
Self-donning, rapid
Weight
117 kg (258 lbm)
105 kg (231 lbm)
Design Life
Up to 30 years with maintenance
4 years/10 missions
Gravitational and Space Biology Bulletin 13(2), June 2000
43
ASTRONAUT PERFORMANCE FROM MIR TO MARS
LOCOMOTION IN PARTIAL GRAVITY
Some Characteristics Associated with Walking
Basic hypotheses relating to human movement involve
notions about minimizing energy expenditure and forces. The
functional significance of the determinants of gait is to minimize
vertical and lateral oscillations of the center of gravity (CoG)
during walking, thus to minimize both energy expenditure and,
perhaps, the generation of muscular force. The design of future
locomotion spacesuits ideally will incorporate what we know
about the following six desirable characteristics of walking:
•
•
•
•
•
•
Pelvic rotation
Pelvic tilt
Knee flexion during the stance phase
Heel strike and heel-off interactions with the knee
Trunk lateral flexion
Trunk anteroposterior flexion
cm displacement. The anteroposterior flexion of the trunk
reveals maximum backward flexion at the beginning of the
support phase and maximum forward flexion toward the end of
the support phase, resulting in small 1- to 2-cm deflections.
In sum, the characteristics of walking described above are
seen to minimize oscillations of the CoG and optimize efficiency
during locomotion, due to minimum energy expenditure. Many
of the characteristics of gait absorb shock during a stride cycle,
which effectively reduces the force exerted on the ground and,
equally, the reactionary force on the skeletal system and the
whole human body. Recommendations based on the
understanding of gait determinants suggest that spacesuit design
should provide a waist bearing that permits pelvic rotation and
tilt; a knee joint that enables flexion; an ankle joint for plantar
and dorsi-flexion; and a hip/waist/upper-body capability that
accommodates trunk flexion.
Pelvic rotation describes the pelvis rotating from side-to-side
around the body’s longitudinal (vertical) axis for normal walking.
During the leg’s swing phase, medial rotation at the weightbearing (stance) hip advances the contralateral (swing-phase) hip
(Figure 4). Pelvic rotation effectively increases leg length,
thereby step length, and flattens out the arcuate trajectory of the
CoG, reducing energy expenditure by insuring a smoother ride as
the radii of the arcs of the hip increase. The pelvis is tilted
downward about five degrees on the swing phase side. This
occurs with pelvic adduction at the hip joint on the stance phase
side.
Pelvic tilt further flattens the arcs of the hip, allowing for a
smooth ride during walking.
Knee flexion occurs during the stance (support) phase of
walking. The knee is extended at heel strike, but then begins to
flex. At heel-off, just prior to the middle of the support phase,
the knee extends again. This extension-flexion-extension
sequence reduces the excursion of the CoG’s arcuate trajectory
and absorbs shock during a stride cycle. If the knee joint is
absent, the travel of the CoG is not reduced, which is very
costly in terms of energy expenditure.
Figure 4. Pelvic Rotation during Walking . The pelvis is
rotated from side-to-side about the longitudinal axis of
the body.
Heel strike and heel-off interactions with the knee
comprise the fourth characteristic of gait. At heel strike, the foot
plantar flexes (rotates downward around an axis formed at heel
contact), thus lowering the ankle as the foot makes full contact
with the ground (Figure 5). A fused (immobile) ankle joint
without plantar flexion would cause the CoG to rise as if the leg
were a stilt. Ankle plantar flexion affects gait in a manner similar
to ankle flexion—i.e., the trajectory of the CoG is reduced and
shock absorption is noted at heel strike. The heel-off phase
provides a horizontal CoG trajectory as the ankle rotates
upwards around an axis formed at the ball of the foot.
Trunk lateral and anteroposterior flexion make up the final
characteristics under discussion. The ipsilateral flexion of the
vertebral column toward the stance phase side causes a 1- to 2-
44
Figure 5. Heel Strike and He el-off. Top: Heel strike. The
foot plantar flexes which lowers the ankle as the foot
contacts the ground. Bottom: Heel-off interactions with
the knee. Heel-off keeps the excursion of the center of
gravity to a minimum.
Gravitational and Space Biology Bulletin 13(2), June 2000
ASTRONAUT PERFORMANCE FROM MIR TO MARS
Human Performance in Partial-Gravity Environments
Quantifying partial-gravity performance allows for
efficient spacesuit and life-support system designs. The three
primary techniques to simulate partial gravity (before we make it
back to the moon or Mars) are
•
underwater immersion,
•
parabolic flight,
•
suspension.
Underwater Immersion. During tests, a neutrally buoyant
subject is ballasted to simulate the desired partial gravity loading.
For example, one-sixth of the subject’s body mass is added in
ballast if a lunar simulation is desired. Water immersion offers
the subject freedom from time constraints and freedom of
movement, but the hydrodynamic drag is disadvantageous for
movement studies.
Parabolic Flight. NASA KC-135 aircraft or Russian IL-76
aircraft are typically used to simulate partial gravity by flying
Keplerian trajectories through the sky. This technique provides
approximately 20, 30, and 40 seconds for microgravity, lunar
gravity, and Martian gravity tests, respectively. Parabolic flight
is the only way to effect true partial gravity on Earth, but
experiments are expensive and of limited duration.
Suspension. Many partial-gravity suspension systems have
been designed and used since the Apollo program. The cable
suspension method typically uses vertical cables to suspend the
major segments of the body and relieve some of the weight
exerted by the subject on the ground, thus simulating partial
gravity. Suspension systems often afford the most economical
partial-gravity simulation technique, but limit freedom of
movement.
Force traces help quantify the peak force exerted by a
crew member during locomotion. These data pertain to spacesuit
design, as well as to the human physiologic effects of
musculoskeletal deconditioning during long-duration spaceflight.
There is a significant reduction in peak force during locomotion
in partial gravity and a general trend toward loping (between
running and skipping) as gravity decreases from 1 g (Figure 6).
Figure 7 shows actual data from the Apollo 11 lunar mission.
Stepping frequency is displayed for the Apollo 11 data,
underwater-simulated lunar gravity data, and 1-g data. There is
scatter in the Apollo data, but the simulated lunar stepping rates
are seen to correlate well with the actual Apollo data. The
stepping frequencies at 1 g are significantly higher than the lunar
stepping frequencies (P<0.05). Since the time available to apply
muscular force to the ground during locomotion is constant
across gravity levels, a reduction in metabolic costs for low
gravity levels is anticipated (peak-force results reveal that less
muscular force is required for locomotion at reduced gravity
levels). The combination of decreases in stride frequency and
constant values of contact time also
Figure 6: A Comparison of Partial Gravity Locomotion
with Earth Gravity. The data reveal a significant
reduction of (P<0.001) in peak force, fmax, for a
decrease in gravity level. There is a 50% reduction from
1 g to Martian gravity (3/8 g) and a 74% reduction in
peak force from 1 g to lunar gravity (1/6 g). The contact
time is the duration of the support foot’s contact with the
ground (t c ). The time for a single stride (t stride) increases
as the gravity level decreases; thus, a decrease in stride
frequency (strides/min) is seen for a reduction in gravity
level. A significant aerial time (t a—time between toe-off
and ground contact of the opposite foot), exists for
partial
gravity
locomotion,
whereas
terrestrial
locomotion elicits no significant aerial phase at this
velocity.
Gravitational and Space Biology Bulletin 13(2), June 2000
45
ASTRONAUT PERFORMANCE FROM MIR TO MARS
Stepping Frequency (steps/sec)
Earth gravity
Apollo 11 lunar data*
3
Simulated lunar gravity
2.5
1g
2
Lunar g
1.5
1
0.5
0
0
0.5
1
1.5
2
2.5
Velocity (m/s)
Stone, R.W. Celobeka b Kosmos , 1971
**Stone,
R.W. (1971) Man in Space.
Firgure 7. Stepping Frequency for Apollo 11 and
Simulated Lunar Gravity. Stepping frequency for
terrestrial locomotion is also plotted. The Apollo data
and simulated lunar data show a reduction in stepping
frequency as compared to 1 g, especially for locomotion
at velocities of 1.5 m/s a nd 2.3 m/s. (Stone, 1971)
suggest an increase in aerial time for partial-gravity locomotion
locomotion. A significantly extended aerial phase typifies loping,
in which subjects essentially propel themselves into an aerial
trajectory for a few hundred milliseconds during the stride
(Newman et al., 1994).
Since the functional significance of the characteristics of
gait is to minimize energy expenditures, bioenergetics (oxygen
consumption) data drive the design requirements for planetary
EVA life-support systems. Results show surprising information
for partial-gravity locomotion. There is a well-documented
optimal cost of transport for terrestrial walking at the speed of 1
m/s (Margaria, 1976). In terms of metabolic expenditure, it costs
about half of the amount of energy to walk 1.67 km (1 mile) that
it costs to run 1.67 km. However, walking at 1 m/s is not the
optimal method of transporting one kg of body mass over one
meter in partial gravity. Cost of transport for the lunar (1/6 g)
and Martian (3/8 g) environments decreases as speed increases,
suggesting that quicker locomotion is cheaper in terms of the
cost of transport. Results from underwater immersion and
suspension simulators indicate that above 1/2 g, walking has a
lower cost of transport than running, but running is cheaper than
walking from 1/4 g to 1/2 g (Farley and McMahon, 1992;
Newman and Alexander, 1993).
A DAY IN THE LIFE OF A LUNAR CONSTRUC-TION
WORKER
Try to imagine what a day in the life of a lunar
astronaut/construction worker might involve. One of the
simplest tasks confronting a crew member might be to set up a
46
telescope. He or she suits up in the airlock, assembles the
necessary hand tools to carry by hand to the worksite (at this
point you may well ask, “What about construction equipment—
bulldozers, loaders, cranes, etc.?”), leaves the lunar habitat
through the airlock, and begins the day’s task. Whether driving
or using self-locomotion to get to the site, the crew member
needs a light, mobile spacesuit and LSS. Once at the site, an
initial survey of the lunar terrain requires agility, traction, tools,
and possibly illumination. Before starting to assemble the
telescope platform, the crew member probably has to move
some lunar regolith and flatten the desired plot. No doubt there
is dust everywhere, fouling the spacesuit bearings and hampering
the rover’s machinery. Once the platform is assembled and
leveled, work on the telescope begins. The telescope’s assembly
and adjustments require extreme finger dexterity.
Clearly, the simple task of deploying a telescope requires
an involved EVA. Planetary EVAs for building habitats, setting
up laboratories, and conducting field science will be a great deal
more complicated, demanding EVA systems and crew member
skills that do not currently exist.
Whatever the EVA task may be, the crew member must
have adequate life support, protection from the environment,
and appropriate tools and equipment. In addition to meeting the
design requirements already mentioned, spacesuit design for our
hypothetical planetary EVA must assure
•
adequate mobility;
•
natural, efficient locomotion;
•
correct balance and orientation;
•
reasonable physical loads on the crew member, the
spacesuit, and the life-support system;
•
adequate lighting;
•
adequate power;
•
gloves that support maximum manual dexterity.
Again, such requirements will be met only through extensive
research and design efforts. Perhaps a model that incorporates
mechanical pressure rather than air pressure will provide the
crew member with a light, form-fitting spacesuit. On the other
hand, if an optimal-locomotion spacesuit cannot be realized, the
concept of a full-body enclosure with manipulators may prove
successful. At this early stage in the conceptual design of future
spacesuits, the field is wide open and all designs and
methodologies should be considered.
CONCLUSION
The successful design of future planetary spacesuits
depends on providing improved mobility, improved glove
performance, adequate operating pressures, improved radiation
shielding, mass reductions, regenerable life-support systems, and
improved human/machine interfaces. Locomotion spacesuits
should incorporate current research efforts, findings that pertain
to the altered mechanics for locomotion in partial gravity, and
Gravitational and Space Biology Bulletin 13(2), June 2000
ASTRONAUT PERFORMANCE FROM MIR TO MARS
suggestions from past Apollo experience. Medical risks to crew
members will be another driving force in planetary spacesuit
design. Finally, the relationship between humans and machines is
still undefined in EVA operations, and further research could
lead to optimal mission planning with EVA crew members
assisted by robotics.
Waligora, J., Horrigan, D. and Nicogossian, A. 1991. The
physiology of spacecraft and spacesuit atmosphere selection.
8th IAA Man in Space Symposium. Acta Astronautica 23:
171-77.
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Gravitational and Space Biology Bulletin 13(2), June 2000