Life in Extreme Environments: How Will ... - Semantic Scholar · provides. Unprotected by a spacecraft or spacesuit, anyoneBetween March 1995 and May 1998, NASA astronauts encountering

Gravitational and Space Biology Bulletin 13(2), June 2000 35

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

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.

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

capabilities relative to the effects of partial gravity on human locomotion will enhance the integration of humans and machines for future missions. THE SPACE SHUTTLE AND MIR SPACE STATION

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 Inter-

national 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.

ASTRONAUT PERFORMANCE FROM MIR TO MARS

Gravitational a nd Space Biology Bulletin 13(2), June 2000 36

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 astronaut-induced disturbances to the microgravity environment. The experiment was designed with two objectives:

1. Primarily, to assess nominal astronaut-

induced forces and torques during long-duration 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.

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;

a

b.



Table 1. Characteristic Astronaut Motions

Characteristic Motion

Description

Landing

Push off

Flexion/Extension

Single Support

Double Support

Twisting

Reorienting

Flying across module and landing

Pushing off and flying

Flexing or extending limb

Using one limb for support

Using two limbs for support

Twisting body motion

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.

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 lab-oratory in a novel environment; it is an international human experiment—an exciting city in space—and a place where we

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 approxi-mately 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 long-duration 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, well-being, and productivity for future exploration missions.

EXTRAVEHICULAR ACTIVITY (EVA)

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



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 ninety-fifth percentile males, a distinct advantage over the custom-fitted suits previously used. Further evolution will yield spacesuits

0

100

200

300

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

TOTA

L E

VA

DU

RA

TIO

N (C

lock

Hou

rs)

0

500

1000

1500

2000

2500RUSSIAN

SHUTTLE / HST /DTO / ISSAPOLLO / SKYLAB

GEMINI

MARS (Scale onthe right)

CALENDAR YEAR

Rev. E Assembly Sequence

With HST and Surface Exploration

Assumptions:12 US ISS Maintenance EVA/yr post assembly complete6 Russian ISS Maintenance EVA/yr post assembly complete8-Hour Lunar EVAs commencing in 2010

250 8-Hour Mars EVAs in 2015

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).



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 oxygen 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 components 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 bat-tery 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-vinyl-acetate 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 sunlight-reflecting 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)



Figure 3. The NASA Spacesuit, or Extravehicular Mobility Unit (EMU). (Courtesy of Hamilton Standard, rev. 2/95)



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 lithium-hydroxide 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

Skylab

Space Shuttle

1/6

microgravity

microgravity

microgravity

235 (suited)

151 (cabin)

238

197

The spacesuit has self-contained, integrated pressure and

O2 systems in a backpack-type PLSS that can be maintained on-orbit. 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



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 con-sumables. 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

• 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.

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.



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

• One adjustable size with axial restraint

system allowing on-orbit sizing • Two glove sizes

Construction of suit Assembly

• 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

• 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

Construction of Life-Support System

• Closed-loop, pure oxygen generative • 7 interchangeable subsystem modules • Expendables replaceable or rechargeable

on orbit

• 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



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

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 weight-bearing (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. 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-

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.

Figure 4. Pelvic Rotation during Walking . The pelvis is rotated from side-to-side about the longitudinal axis of the body.

Figure 5. Heel Strike and Heel-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.



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 (tc). The time for a single stride (tstride) 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 (ta—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.



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

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

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* Stone, R.W. , 1971* Stone, R.W. (1971) Man in Space.



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.

REFERENCES

Amir, A.R. and Newman, D.J. 2000. Research into the effects of astronaut motion on the spacecraft: A review. Acta Astronautica. In press. Asker, J. 1995. U.S., Russian suits serve diverse EVA goals. Aviation Week & Space Technology. 142(3):40-46. Bluth, B. J. and Helppie, M. 1987. Soviet Space Station Analogs (2nd Ed.). Report under National Aeronautics and Space Administration (NASA) Grant NAGW-659. Washington, DC: NASA. Farley, C. and McMahon, T. 1992. energetics of walking and running: insights from simulated reduced-gravity experiments. Journal of Applied Physiology 73(6): 2709-2712. Jones, E. and Schmitt, H. 1992. Pressure suit requirements for the moon and Mars EVA’s. Paper Number LA-UR-91-3083. Proceedings, Space ’92; May 1992. Denver, CO: American Society of Civil Engineers. Margaria, R. 1976. Biomechanics of human locomotion. In: Biomechanics and Energetics of Muscular Exercise. Cambridge, UK: Cambridge University Press, pp. 67-139. National Aeronautics and Space Administration. 1989. NASA Man Systems Integrated Standard (MSIS). Available from: NASA, Johnson Space Center, Houston, TX; NASA-STD-3000, Vol. 1, Revision A. Newman, D., Alexander, H. and Webbon, B. 1994. energetics and mechanics for partial gravity locomotion. Aviation Space and Environonmental Medicine 65:815-823. Newman, D. and Alexander, H. 1993. Human locomotion and workload for simulated lunar and martian environments. Acta Astronautica 29(8): 613-620. Severin, G. 1990. Spacesuits: concepts, analysis, and perspectives [lecture notes]. Moscow, USSR: Department of LSS/ERS, College of Cosmonautics, Moscow Aviation Institute. Stone, R.W. 1974. Man’s motor performance including acquisition of adaptation effects in reduced gravity environments. In: Chelovek B Kosmose. Moscow, USSR: International Symposium on Basic Environmental Problems of Man in Space, p. 351. Available from: UNIVELT, Inc., P.O. Box 28130, San Diego, CA 92128.

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. Wilde, R. 1984. EMU—a human spacecraft. Proceedings of the 14th International Symposium on Space Technology and Science. Tokyo, Japan: Hamilton Standard, pp. 1565-76.


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