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Home , Alexei Leonov, Carrying the Fire, Charles Duke, David Leestma, Edward Gibson, Extravehicular activity

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Chapter 22

LIFE SUPPORT AND PERFORMANCE ISSUES FOR (EVA)

Dava Newman, Ph.D. and Michael Barratt, M.D.

22.1 Introduction

Defining the goals for future human space endeavors is a challenge now facing all spacefaring nations. Given the high costs and associated risks of sending humans into orbit or beyond – to lunar or Martian environments, the nature and extent of human participation in and habitation are key considerations. Adequate protection for humans in orbital space or planetary surface environments must be provided. The , , Salyut-, and programs have proven that humans can perform successful extravehicular activity (EVA) in microgravity and on the Lunar surface.

Since the beginning of human exploration above and below the surface of the Earth, the main challenge has been to provide the basic necessities for human life support that are normally provided by nature. A person subjected to the near of space would survive only a few minutes unprotected by a spacesuit. Body fluids would vaporize without a means to supply pressure, and expanded gas would quickly form in the lungs and other tissues, preventing circulation and respiratory movements. EVA is a key and enabling operational resource for long- duration missions which will establish human presence beyond the Earth into the solar system. In this chapter, EVA is used to describe space activities in which a crew member leaves the or base and is provided life support by the spacesuit. To meet the challenge of EVA, many factors including atmosphere composition and pressure, thermal control, radiation protection, human performance, and other areas must be addressed.

Compared to Earth-based capabilities, performance during in-space EVA is enhanced for some functions and degraded for others. EVA offers many advantages for accomplishing space missions. The is present at the worksite and has the following capabilities: flexibility, dexterous manipulation, human visual interpretation, human cognitive ability, and real time approaches to problems. The factors which may degrade performance include encumbrance, prebreathe requirements, insufficient working volume, limited duration, sensory deprivation, and poor task or tool design [34]. EVA, as well as robotics and automation, expand the scope of space operations. A thorough understanding of EVA capabilities will help bring about the integration of humans and machines for future missions. In addition to microgravity EVAs, the partial gravity environments of the and Mars require advanced EVA hardware and performance capabilities.

22.2 Historical Background - 2 -

In March of 1965, cosmonaut became the first human to walk in space (Figure 22.1). Attached to a 5-meter long umbilical which supplied him with air and communications, Leonov floated free of the spacecraft for over ten minutes. In June of the same year, Edward White became the first American astronaut to egress his spacecraft while in orbit. White performed his spectacular space walk during the third orbit of the Gemini – Titan 4 flight. Table 22.1 summarizes Russian and U. S. extravehicular activity to date.

Insert Figure 22.1 here

Although some of the early EVA efforts of both programs were plagued with problems, the feasibility of placing humans in free space was demonstrated. The Gemini EVAs showed the necessity of providing adequate body restraints to conduct EVA and demonstrated the value of neutral buoyancy simulation for extended duration training in . The second Russian EVA saw the partial transfer of a crew from one craft to another. An important anomaly was evident in photographs of the Soyuz 5 spacesuit design. Rather than wearing a large backpack-type primary life support system, the crew wore air supplies strapped to their legs. Locating the life support on the front part of the legs made it possible to solve the problem of crew transfer through the Soyuz "manholes with relatively small dimensions (66-cm diameter)" [49].

During the , 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, while collecting 2196 soil and rock samples. The Apollo EVAs were of unprecedented historical importance as and Edwin "Buzz" Aldrin became the first humans to set foot on another celestial body. Many successful scientific experiments were carried out during the Apollo EVAs. 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 p s i ) 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 p s i ). To counteract the risk of after this depressurization, the prebreathed 100% oxygen for three hours prior to launch (This will be discussed in greater detail subsequently). Despite these efforts, Michael Collins reported a suspicious pain upon orbital insertion that fortunately resolved spontaneously; this episode possibly represented joint pain associated with decompression sickness [9].

The potential benefits of EVA were nowhere more evident than in the missions. When the crew first entered Skylab, the internal temperature was up to 71°C (160°F), rendering the spacecraft nearly uninhabitable. The extreme temperatures resulted from the loss of a portion of the vehicle's outer skin as well as a lost solar panel. After failure of a second solar panel deployment and the consequent loss of power and cooling capability, astronauts Joseph Kerwin and Charles "Pete" Conrad salvaged the entire project by rigging a solar shade through the science and freeing the remaining solar panel during EVA. The paramount flexibility offered by EVA for accomplishing successful space missions, operations, and scientific endeavors was realized during Skylab. - 3 -

After a nine year lapse in Russian extravehicular activity, cosmonaut Georgi Grechko performed a critical EVA to examine the cone of the docking unit which was thought to be damaged. Additional EVAs were performed during Salyut 6 in order to replace equipment and to return experimental equipment to Earth which had been subjected to solar radiation for ten . The success of the Salyut 6 program during 1977–1981 brought about the space station program. Successful EVAs were performed to continue studying cosmic radiation and the methods and equipment for assembly of space structures. Ten EVAs were performed during the Salyut 7 – Soyuz missions; experience and expertise in space construction, telemetry, and materials science was gained. On 25 July 1984 during her second (Her first flight was in August 1982.), cosmonaut became the first woman to perform an EVA (Figure 22.2), during which she used a portable electron beam device to cut, weld, and solder metal plates.

Insert Figure 22.2 here

From 1983 through 1985, 13 two-person EVAs were performed during STS (Space Transportation System, commonly called Space Shuttle) missions. During these missions, trained crew members have responded in real time to both planned mission objectives and unplanned contingencies. Evaluation and demonstration of the Extravehicular Mobility Unit (EMU), a 29.6 kPa (4.3 psi) spacesuit; the (MMU); the Remote Manipulator System (RMS, commonly known as the Canadian Arm); and specialized tools have resulted in the repair of modules, the capture and berthing of , and the assembly of space structures. The STS EMU is self-contained; therefore, an umbilical for its life support and communications systems is unnecessary. 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.

Several firsts were accomplished during Space Shuttle EVAs, including the first American woman EVA performed by Kathryn Sullivan during mission 41–G. (In this nomenclature, 4 stands for the year 1984, 1 is for the launch site: , and the G is the order of the launch. This numbering system has been subsequently changed back to the more straight forward STS-XX sequential numbering system.) The EVA by Bruce McCandless in February 1984 was the first space trial of the MMU (Figure 22.3). The MMU is a completely separate space propulsion module which combines with the EMU to allow astronauts to maneuver up to 366 meters (1200 ft) away from the spacecraft. However, it is no longer manifested on Space Shuttle EVA missions due to the accuracy and success the astronaut pilots have had in bringing the EVA crew members to their desired orbital location by precise maneuvering of the orbiter.

The first American spacewalk in over five years took place on 14 April 1991. Astronauts Jerry Ross and Jay Apt performed an unscheduled EVA on STS-37 in order to shake loose the antenna of the Gamma Ray Observatory prior to deployment. The crew members' second EVA consisted of conducting the Crew and Equipment Translation Aid (CETA) flight experiment which investigated four modes of locomotion (a manual cart, a mechanical cart, an electrical cart, - 4 -

and a tether shuttle) for moving along the outside of the proposed space station truss. The manual cart was selected as the optimum translation aid. A second EVA Translation Experiment (ETE) on STS-37 provided the recommendation that non-rigid translation technologies should be considered for accessing areas of which do not require frequent service. The third STS-37 EVA experiment was the Crew Loads Instrumented Panel (CLIP) that measured loads exerted by crew members while they performed typical tasks, such as using an EVA tool or applying torque to an EVA knob. The results yielded loads greater than expected for many of the tasks [34, 39]. Also of note is that one crew member's palm bar wore all the way through his EMU glove. The value of human presence during spaceflight was re-emphasized during these EVAs.

The highly publicized STS-49 EVAs had two original objectives: retrieval, repair, and redeployment of the International Telecommunications VI ( VI) and a space construction technique experiment entitled Assembly of Station by EVA Methods (ASEM). The record for the longest U.S. EVA was set on this flight with an EVA lasting 8 hours and 29 minutes performed by astronauts Tom Akers, Rick Hieb, and Pierre Thout. STS-49 was also the first Shuttle mission with four EVAs. Due to difficulties with the INTELSAT VI retrieval, the ASEM activities were shortened, but the accomplishments included building the ASEM attachment fixture, evaluating the crew propulsive device, installing six of eight legs on the multipurpose experiments support structure, and attempting (unsuccessfully) to perform a three point pallet attachment [18]. Finally, the STS-49 EVAs yielded information regarding improving foot restraint installation at worksites.

EVAs were added to two Space Shuttle Missions (STS-54 and STS-57) in order for crew members to accumulate EVA experience and to carry out generic EVA tasks. These additional EVAs were added to accommodate future EVA requirements and experience, especially leading up to the Hubble Service Mission (HST SM-01) on STS-61. The primary focus of the STS-54 EVA was to assess astronaut abilities with special emphasis on the fidelity of training techniques. Astronauts Mario Runco and Gregory Harbaugh performed a 4 1/2 hour EVA on 17 January 1993. The EVA on STS-57 by astronauts G. David Low and Jeff Wisoff included stowing the EURECA satellite antenna and the handling of large masses [2]. NASA's Hubble Telescope Repair Mission (STS-61) was a major success. In a record setting five consecutive days of EVA, Astronauts F. (payload commander), Jeff Hoffman, , and Kathryn Thornton replaced failed rate sensors (containing gyroscopes used to point Hubble precisely), electronic control units, solar arrays, Hubble's Wide Field/Planetary Camera, and a second set of corrective . Akers now holds the U.S. record for the most total EVA time (29 hr. 40 min.), surpassing Eugene Cernan's 24 hr. 12 min. in Earth orbit and on the lunar surface, a record that stood for 21 years. The crewmembers' relied on extensive training, thoroughly prepared hardware, and efficient ground support to accomplish the nearly flawless mission. However, a screw that got loose and difficulty in hooking up computer connections during EVA 5 remind us of the ever-present difficulties of working in space. The usefulness of humans in space was highlighted by the Hubble EVA rescue mission.

Insert Figure 22.3 here - 5 -

During the last decade, EVA has been regularly performed by Russian cosmonauts. and Alexander Laveikin performed an unscheduled EVA on 12 April 1987 in order to solve a docking problem between the Mir and Kvant modules. Prior to the contingency EVA, a rehearsal by backup cosmonauts in the hydrotank facility in the Zvezdny Gorodok training center (better known as 'Star City') was performed. As a result, cosmonauts Romanenko and Laveikin were able to remove an obstruction (most likely a sheet) that was fouling the docking system. Docking between Kvant and Mir was accomplished and the mission was salvaged [12]. Five Russian EVAs were performed in January and February of 1990. On 1 February 1990, cosmonaut Alexander Serebrov became the first pilot of the Russian SPK (Sredstvo Peredvizheniy Kosmonavtov - "cosmonaut mobility equipment") in space. The Russian SPK is similar to the American MMU; it allows a cosmonaut to fly to any point on the exterior of a spacecraft [23].

An exciting EVA took place on 18 July 1990 when cosmonauts Alexander Balandin and Anatoly Solovyov exited the Mir space station and used a small ladder extended from the Kvant 2 module to the Soyuz TM-9 capsule in order to repair the shield-vacuum heat insulation blankets [52]. The ladder was employed rather than the SPK in order to allow for maximum stability during the repairs. Problems developed during reentry to the station due to an improperly closed airlock and emergency entry occurred through a small secondary hatch [Radio in Russian, 17 July 1990]. On 26 July 1990, the two cosmonauts performed a 3 hour 31 minute EVA and identified the faulty hatch feature and forced it closed [Moscow Television Service in Russian, 26 July 1990]. Gennadiy Manakov and Gennadiy Strekalov carried out a space walk on 30 October 1990 in order to completely repair the faulty one meter hatch, but the damage was more extensive then originally postulated [Moscow Television Service in Russian, 30 October 1990]. Cosmonauts Viktor Afanasyev and performed an EVA on 7 January 1991 which lasted for 5 hours and 18 minutes. The cosmonauts finally repaired the problematic exterior hatch and worked on the external surface of the Kvant 2 module of the Russian orbital complex Mir [Moscow TASS International Service in Russian, 8 January 1991]. Russian EVAs have been remarkable for their successful accomplishments near the end of long duration flights, when physiological deconditioning is expected to be significant.

The Orlan-DMA spacesuit, nominally operated at 40.6 kPa (5.88 psi) with the capability for short term operation at 27.6 kPa (4 p s i ), is used for EVA. During periods when increased hand/finger dexterity is required, spacesuit pressure may be decreased for short periods, but this has only been done twice and is generally not an option that is utilized. The pressure was lowered once to ingress an airlock during a tight fit and the second time the pressure was accidentally lowered.

Successful EVAs to date have been accomplished with crew members wearing a variety of spacesuits. These spacesuits have evolved from the umbilical models of the Voskhod and Gemini era into the self-contained, modular spacesuits currently used. Further spacesuit evolution will yield higher pressure spacesuits for microgravity, lunar, and Martian environments. Section 22.3 describes the American EMU, the current Russian Orlan-DMA spacesuit, and suggests some trade-offs for advanced spacesuit design. - 6 -

Table 22.1 Summary of Russian and American Extravehicular Activity (EVA). Edited from [35, 43].

Year Mission EVA Date Cosmonauts/Astronauts Duration 1965 Alexei Leonov 24 min June 6 Edward Whitea,b 23 min 1966 Gemini 9-A June 5 Eugene Cernana 2 hr 10 min July 19 Michael Collinsa 49 min July 20 Michael Collinsa 38 min Sep. 13 Richard Gordona 33 min Sep. 14 Richard Gordona,b 2 hr 8 min Nov. 12 Edwin "Buzz" Aldrina,b 2 hr 29 min Nov. 13 Edwin Aldrin 2 hr 6 min Nov. 14 Edwin Aldrina,b 55 min 1969 Soyuz 4/5 Jan. 16 Yevgeny Khrunovc 1 hr Alexei Yeliseyev March 6 Russell Schweickart 1 hr 7 min David Scottb 1 hr 1 min Apollo 11 July 21 Neil Armstrongd 2 hr 48 min Edwin Aldrin Nov. 19 Charles Conradd 4 hr Nov. 20 Charles Conradd 3 hr 46 min Alan Bean 1971 Feb. 5 Alan Shepardd 4 hr 48 min Feb. 6 Alan Shepardd 4 hr 35 min Edgar Mitchell July 30 David Scotte 33 min July 31 David Scottd 6 hr 33 min August 1 David Scottd 7 hr 12 min James Irwin August 2 David Scottd 4 hr 50 min James Irwin August 5 Alfred Wordenf 38 min James Irwinf,b 38 min 1972 John Youngd 7 hr 11 min April 22 John Youngd 7 hr 23 min Charles Duke April 23 John Youngd 5 hr 40 in Charles Duke April 25 Thomas Mattinglyf 1 hr 24 in Charles Dukef Dec. 11 Eugene Cernand 7 hr 12 min

a The duration for the Gemini EVAs is the time from hatch opening to hatch closing. For Apollo and Skylab, both space and lunar EVAs are computed from the time cabin pressure reached 3.0 psi during depressurization and repressurization. The durations presented for the two-person EVAs are the amount of time spent by each person. b Stand-up EVA. c Y. Khrunov and A. Yeliseyev were launched on Soyuz 5 and transferred to Soyuz 4 via EVA. d Lunar surface EVA. e Stand-up EVA from lunar module on lunar surface. f Cis-lunar or deep-space EVA. - 7 -

Table 22.1 (cont.): Summary of Russian and American Extravehicular Activity (EVA). Year Mission EVA Date Cosmonauts/Astronauts Duration 1972 Apollo 17 Dec. 12 Eugene Cernand,g 7 hr 37 min Harrison Schmittg Dec. 13 Eugene Cernand,h 7 hr 15 min Harrison Schmitt Dec. 17 Ronald Evansf 1 hr 6 min Harrison Schmittf 1 hr 6 min 1973 May 25 Paul Weitzb 35 min June 7 Charles "Pete" Conrad 3 hr 23 min Joseph Kerwin June 19 Charles Conrad 1 hr 36 min Paul Weitz August 6 6 hr 31 min August 24 Owen Garriott 4 hr 30 min Jack Lousma Sep. 22 Owen Garriott 2 hr 41 min Alan Bean Nov. 22 3 hr 29 min 6 hr 34 min Dec. 25 William Pogue 7 hr 3 min Dec. 29 Edward Gibson 3 hr 29 min Gerald Carr 1974 Skylab 4 Feb. 3 Edward Gibson 5 hr 19 min Gerald Carr 1977 Salyut 6- Dec. 20 Georgi Grechko 1 hr 28 min Yuri Romanenkoi 1978 Salyut 6- July 29 2 hr 5 min Alexander Ivanchenkov 1979 Salyut 6- August 15 1 hr 23 min (Soyuz 34 at station time of EVA) 1982 Salyut 7-Soyuz T-5 Anatoly Berezovoi 2 hr 33 min 1983 STS-6 April 7 F. Story Musgrave 4 hr 17 min Donald Peterson Salyut 7-Soyuz T-9 Nov. 1 Vladimir Lyakhov 2 hr 50 min Alexander Alexandrov Nov. 3 Vladimir Lyakhov 2 hr 55 min Alexander Alexandrov 1984 41-B Feb. 7 Bruce McCandlessj 5 hr 30 min Robert Stewart Feb. 9 Bruce McCandless 6 hr Robert Stewart 41-C April 8 George Nelson 3 hr April 11 George Nelson 6 hr James Van Hoften

g Longest EVA on the lunar surface. h Most hours logged EVA (U.S.A.), in orbit and lunar for a total of 24 hr 14 min. i Y. Romanenko stayed in the depressurized compartment during G. Grechko’s EVA. j First untethered EVA. - 8 -

Table 22.1 (cont.): Summary of Russian and American Extravehicular Activity (EVA). Year Mission EVA Date Cosmonauts/Astronauts Duration 1984 Salyut 7-Soyuz T-10 April 23 4 hr 15 min (Soyuz T-11 at station time of EVA) Vladimir Solovyov Salyut 7-Soyuz T-10 April 26 Leonid Kizim 5 hr (Soyuz T-11 at station time of EVA) Vladimir Solovyov Salyut 7-Soyuz T-10 April 29 Leonid Kizim 2 hr 45 min (Soyuz T-11 at station time of EVA) Vladimir Solovyov Salyut 7-Soyuz T-10 May 4 Leonid Kizim 2 hr 45 min (Soyuz T-11 at station time of EVA) Vladimir Solovyov Salyut 7-Soyuz T-10 May 18 Leonid Kizim 3 hr 5 min (Soyuz T-11 at station time of EVA) Vladimir Solovyov Salyut 7-Soyuz T-10 Svetlana Savitskayak 3 hr 35 min (Soyuz T-10/T-11 crew there also) Salyut 7-Soyuz T-10 August 8 Leonid Kizim 5 hr (Soyuz T-11 at station time of EVA) Vladimir Solovyov 41-G Oct. 11 Kathryn Sullivan 3 hr 29 min David Leestma 51-A Nov. 12 Joseph Allen 6 hr Nov. 14 Joseph Allen 5 hr 42 min Dale Gardner 1985 51-D April 12 Jeff Hoffman 3 hr 7 min David Griggs Salyut 7-Soyuz T-13 August 2 Vladimir Dzhanibekov 5 hr 51-I August 31 James Van Hoften 7 hr 8 min William Fisher Sep. 1 James Van Hoften 4 hr 32 min William Fisher 61-B Dec. 1 Jerry Ross 5 hr 32 min Sherwood Spring Dec. 3 Jerry Ross 5 hr 42 min Sherwood Spring 1986 Soyuz T-15 May 28 Leonid Kizim 3 hr 50 min (Transfer from Mir to Salyut 7) Vladimir Solovyov 1987 Soyuz TM-2 (Mir) April 12 Alexander Laveikin 3 hr 40 min Yuri Romanenko June 12 Alexander Laveikin 3 hr 15 min Yuri Romanenko June 16 Alexander Laveikin 1 hr 53 min Yuri Romanenko 1988 Soyuz TM-4 (Mir) Feb. 26 Vladimir Titov 4 hr 25 min Musa Manarov Mir Oct. 20 Vladimir Titov 4 hr Musa Manarov 1990 Mir Jan. 9 Alexander Serebrov 3 hr Alexander Viktorenko Mir Jan. 11 Alexander Serebrov 2 hr 54 min Alexander Viktorenko Mir Jan. 26 Alexander Serebrov 3 hr 2 min Alexander Viktorenko Mir Feb. 1 Alexander Serebrov 4 hr 59 min Alexander Viktorenko Mir Feb. 5 Alexander Viktorenko 3 hr 45 min Jean Carpe Chveteu Soyuz TM-9/Mir July 18 Anatoly Solovyov 6 hr Alexander Balandin

k First woman to perform EVA, first woman to make a second spaceflight. - 9 -

Table 22.1 (cont.): Summary of Russian and American Extravehicular Activity (EVA). 1990 Mir July 26 Anatoly Solovyov 3 hr 31 min Alexander Balandin Mir Oct. 30 Gennadiy Manakov 2 hr 45 min Gennadiy Strekalov 1991 Mir Jan. 7 Viktor Afanasyev 5 hr 18 min Musa Manarov Jan. 23 Viktor Afanasyev 5 hr 33 min Musa Manarov Jan. 26 Viktor Afanasyev 6 hr 20 min Musa Manarov STS-37 April 14 Jerry Ross 4 hr 38 min Jay Apt April 15 Jerry Ross 6 hr 11 min Jay Apt Mir April 26 Viktor Afanasyev 3 hr 34 min Musa Manarov 1992 STS-49 May Pierre Thout 17:42 total Rick Hieb 17:42 total Kathryn Thornton 7 hr 45 min Tom Akers 16:14 total May Pierre Thoutl 8 hr 29 min Rick Hiebl 8 hr 29 min Tom Akersl 8 hr 29 min Mir July 8 Alexander Viktorenko 2 hr 3 min Alexander Kaleriy 1993 STS-54 Jan. 17 Mario Runco 4 hr 27 min Gregory Harbaugh STS-57 June 25 G. David Low 5 hr 30 min Jeff Wisoff STS-61 Dec. 5 F. Story Musgrave 7 hr 54 min (HST SM-01) Jeff Hoffman Dec. 6 Kathryn Thornton 6 hr 36 min Tom Akers Dec. 7 F. Story Musgrave 6 hr 47 min Jeff Hoffman Dec. 8 Kathryn Thornton 6 hr 50 min Tom Akersm Dec. 9 F. Story Musgrave 7 hr 21 min Jeff Hoffman

22.3 Spacesuit Design 22.3.1 Space Shuttle Extravehicular Mobility Unit

The current STS Space Shuttle EVA system, known as the Extravehicular Mobility Unit or EMU, consists of a spacesuit assembly (SSA), an integrated life support system (LSS), and the EMU support equipment. The SSA is a 29.6 kPa (4.3 psi), 100% oxygen spacesuit made of multiple fabric layers attached to an aluminum/fiberglass unit (known as the HUT). The SSA retains the oxygen pressure required for breathing and ventilation and protects the crew member against bright sunlight and temperature extremes. 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 carbon dioxide, water vapor, and trace contaminants released by the crew member. The spacesuit and l Longest U.S. orbital EVA and the first three-person Space Shuttle EVA. m Most total hours logged in EVA (U.S.A.) at 29 hr 40 min. - 10 -

life support system weigh approximately 118 kg (260 lbm) when fully charged with consumables for EVA [64]. The EMU support equipment stays in the airlock during an EVA; primary functions are to replenish consumables and to assist the crew member with EMU donning and doffing (putting on and taking off). The EMU spacesuit components are discussed in more detail below and shown in Figure 22.4.

The HUT is the primary structural member of the EMU. The helmet, arms, lower torso assembly (LTA), and primary life support system (PLSS) all mount to the HUT. The HUT incorporates scye bearings to accommodate a wide range of shoulder motions. The spacesuit helmet is a transparent polycarbonate bubble that protects the crew member and directs ventilation flow over the head for cooling. The helmet neck ring disconnect mounts to the HUT. 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 "". The spacesuit arms are fabric components equipped with upper arm, elbow, and wrist bearings that allow for elbow extension and flexion as well as elbow and wrist rotations. The LTA includes the legs and boots and is equipped with a bearing that allows waist rotation while the fabric legs permit hip and knee flexion. The PLSS, or backpack, houses most of the LSS and a two-way AM radio for communications and bioinstrumentation monitoring. Typically, EVA is scheduled for up to 6 hours, but the PLSS is equipped with 7 hours of oxygen and carbon dioxide scrubbing capability for nominal metabolic rates. 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) in case of an emergency. A silver-zinc cell battery powers the LSS machinery and communications and is recharged in place between EVAs. All of the displays and controls for the crew member to activate and monitor 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. The spacesuit is equipped with a disposable urine collection device.

Insert Figure 22.4 here

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 liquid cooling and ventilation garment (LCVG) is the innermost layer of the spacesuit and provides thermal control by circulating air and water (cooled by a sublimator) over the crew member's body. The LCVG can handle peak loads of up to 500 kcal/hr (2000 Btu/hr) for 15 minutes, 400 kcal/hr (1600 Btu/hr) for up to 1 hour, or 250 kcal/hr (1000 Btu/hr) for up to 7 hours. Average metabolic rates for past missions have been [58, 59, 60]: Apollo - 1/6 g 235 kcal/hr (Apollo spacesuit) 0 g 151 kcal/hr Skylab - 0 g 238 kcal/hr (Apollo spacesuit) STS - 0 g 197 kcal/hr (Space Shuttle EMU) The reduction in workload seen during the STS missions is ascribable to the EMU itself, EVA support tools (i.e., foot restraints, handholds, and specialized tools), and EVA training. Most EVA training takes place underwater in the weightless environment training facility, or WETF, at - 11 -

NASA's in , . Crew members extensively practice scheduled EVAs in the neutral buoyancy setting to simulate weightlessness.

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. Electrocardiographic leads are worn to allow constant monitoring of heart rate and rhythm throughout the EVA. In order to provide sustenance for the crew member, a food bar and up to 21 ounces of water are provided in the EMU.

The spacesuit gloves are the crew member's interface to the equipment and tools that he/she uses. The EMU gloves connect to the arms at the wrist joint. The gloves have jointed fingers and palm. The EMU glove includes a pressure bladder, a restraint layer, and the protective thermal outer layer. The glove fingertips are made from silicone rubber caps to enhance tactility. The design of the gloves is the hardest problem in spacesuit design. A dexterous spacesuit glove that provides adequate finger motion and feedback has not yet been realized.

22.3.1.1 EMU spacesuit construction

This section briefly describes the EMU fabric, or softgoods, construction. The fabric components of the EMU are made from numerous layers. The crew member first puts on the LCVG, which is the innermost garment and resembles a pair of long underwear. The LCVG is made of nylon/spandex which is lined with tricot. Ethylene-vinyl-acetate plastic tubing is woven throughout the spandex to route the water close to the crew member's skin for body cooling. Next, the spacesuit has pressure garment modules to retain pressure over the arms, legs, and feet. These pressure garment modules are made of urethane coated nylon and are covered by a woven dacron restraint layer. Sizing strips are used to adjust the length of the restraint layer. 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. The next five layers are aluminized mylar thermal insulation which prevent radiant heat transfer [64]. The outer layer is the familiar white covering to the spacesuit and it 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 is coated with teflon to stay clean during training on Earth. Sunlight is reflected by the white color of this outer TMG layer. The TMG covers the entire EMU except the helmet, controls and 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 whose temperatures can range from -118oC (-180oF) on the shadow side of an orbit to +113oC (+235oF) on the light side of an orbit. The following section provides an analytical tutorial on the design of EMU fabric components.

22.3.1.2 EMU spacesuit design tutorial [edited from 48] - 12 -

This section analyzes design issues related to the cylindrical fabric components of the EMU (the limb components). Specifically, basic equations for volumetric, thermodynamic, and work requirements as they pertain to spacesuit design are presented. The calculations give the reader a feel for real numbers and may be useful for design projects.

Assume a simple cylindrical shape for the fabric EMU components. As the astronaut bends the suit joint, the fabric cylinder develops folds on the inner side of the bend and the outer side remains its initial length. This bending action causes the volume of the joint to decrease and the work required (W) is the force (F) required to bend the cylinder times the distance (d) through which the force acts (See Equation 22.1). The work can also be viewed as the work required to decrease the volume plus the work required to bend the fabric. From experience, the latter is a small force (e.g., not noticeable during a typical joint movement). W =Fd 22.1 From thermodynamics, in a constant pressure process the work required to change the volume of gas is given by Equation 22.2 (the EMU spacesuit is regulated to stay at a constant pressure of 29.6 kPa (4.3 psi)): 2 W =−pdV =−p(V −V ) =p(V −V ) 22.2 ∫ 2 1 1 2 1 where p is pressure and V is volume. The initial volume (V1) of the joint is the area of the cylinder cross-section (A) times the joint length (L): π V =AL = D2 L 22.3 1 4 where D is the cylinder diameter.

Assuming that the cross-section remains circular and the inner and outer edges can be approximated as circles, the final volume (V2) of the joint can be calculated as the area of the cross-section times the centerline length (¢) of the deformed joint as seen in Figure 22.5 and represented by Equation 22.4. πD2 D θ πD 2L πD 3θ V =A¢ = (L − ) = − 22.4 2 4 2 4 8 where q is the deformation joint angle. Substituting into Equation 22.2 yields:

πD2L πD2 L πD3θ pπD3θ W =p(V −V ) =p[( ) −( − )] = 22.5 1 2 4 4 8 8

The joint activation force can be calculated from this expression if an approximation for the length through which the activation force operates is made. Using a reasonably good pπD3θ L θ W pπD3 approximation for this distance, ( ) , leads to: F = = 8 = 22.6 2 d Lθ 4 L 2

Using Equation 22.6, the forces for the various joints in a spacesuit are calculated and tabulated in Table 22.2. These data reveal joint operation forces which are almost at the crew - 13 -

member's maximum capability, or in the case of the waist joint, show that waist bending would be impossible. That is why the Gemini spacesuit incorporated a block and tackle arrangement to allow for bending at the waist. The crew members would tire very rapidly abiding by the required forces in these calculations. Table 22.2 also reveals the design specification of the EMU. From the past discussion it is easy to see why the secret of spacesuit design lies in the ability to maintain constant volume. Obviously, the EMU designers do an excellent job at keeping constant volume in the suit.

Insert Figure 22.5 here.

Table 22.2 Calculated Forces for Spacesuit Joints

Joint Diameter, D Length, L cm Force Force design Human cm (in) (in) calculated, N spec. N (lb) Capability N (lb) (lb) Finger 2.54 (1) 5.08 (2) 7.57 (1.7) No data 31-71 (7-16) Wrist 10.16 (4) 12.70 (5) 192.24 (43.2) No data No data Elbow 12.70 (5) 20.32 (8) 234.96 (52.8) 6.68 (1.5) 155.75 (≈35) Knee 15.24 (6) 12.70 (5) 405.84 (91.2) 6.68 (1.5) No data Waist 45.72 (18) 30.48 (12) 7302 (1641) 17.80 (4) 890 (200)

There are several ways to accomplish the design of a constant volume fabric component. The EMU is constructed so that as the volume of the fabric component decreases in the inside, it increases by the same amount in the outside of the joint. This is accomplished by holding the centerline of the joint at constant length instead of the outside of the joint. An elbow joint designed on this principal looks like the diagram in Figure 22.6. The axial restraint lines, located across the diagonal of the fabric cylinder, take the pressure load that tries to elongate the joint. This prevents the fabric cylinder part of the joint from carrying that load and allows for excess fabric to be placed on the outside of the joint. Without the axial restraint line, the pressure would cause the joint to elongate until all of the excess fabric was placed in tension. As the joint is bent with use the inside of the joint folds up just as it did in the fabric cylinder. As that happens, the outside of the joint where the excess fabric has been placed expands to compensate for the lost volume. The flexed joint is depicted in Figure 22.6. If this figure is considered as a free body diagram of a spacesuit joint, careful observation shows that the forces are not balanced. In practice, a spacesuit joint does not bend so that the centerline is in the shape of a circle as shown in the figure, but rather, the centerline shifts slightly to the outside and compensates for the otherwise unbalanced forces. In addition, the axial restraint lines are not placed exactly at the joints' centerline, but they are slightly off-set so that the joint will be balanced and stable. If the placement of the axial restraint line is not done carefully, the joint is either very difficult to bend or it might actually bend itself over when pressurized. Therefore, well designed joints are stable and remain where they are placed with little restraining or springback force.

Insert Figure 22.6 here. - 14 -

22.3.2 Russian EVA Spacesuit

The current spacesuit used for Mir Space Station EVAs is a derivative of the semi-rigid suit used during the Salyut-Soyuz program. The spacesuit has undergone continuous modification and the fourth model, Orlan-DMA, is currently used for EVA operations. Similar to the American EMU, the Orlan-DMA spacesuit has an integrated life support system to enable EVA operations from Mir. As previously stated, the 100% oxygen spacesuit nominally operates at 40.6 kPa (5.88 psi). The spacesuit weighs approximately 70 kg (154 lb) [49], but the weight of the spacesuit with a fully charged PLSS can not be verified. It is an adjustable universally sized suit with a metal upper torso and fabric arms and legs. Metal ball bearings and sizing adjustments are notable suit features. An advancement and difference from the EMU is the entry into the Orlan-DMA which occurs through a rear hatch, with unassisted spacesuit entry requiring two to three minutes [5].

The spacesuit has self-contained integrated pressure and O2 systems in the PLSS. The suit has a backpack-type PLSS which 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 LCVG concept was initially used for thermal control by English fighter pilots and was later adopted by the Russian and American space programs. The cosmonaut wears a liquid cooled garment comprised of a network of plastic tubes. The temperature can 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 [49]. Materials and colors which reflect strong solar radiation are used, and the spacesuit has layers of protection against extreme temperatures. The non-hermetically sealed outside layer is a protective vacuum insulator. 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 7 attributes of the semi-rigid Orlan-DMA spacesuit [49]:

1. Minimal overall dimensions of suit torso in a pressurized state. 2. Ease of rapid donning/doffing. 3. Easy handling capabilities and improved reliability of lines connecting the life support system and suit. 4. Reliability of hatch sealing system. 5. Single spacesuit for crew members of different anthropometric dimensions. 6. Easy replacement of consumable elements. 7. Easy maintainability due to ease of access to units. - 15 -

Severin has stated that future Russian spacesuit research and development activities are aimed toward improving suit performance characteristics (specifically mobility), decreasing the payload weight delivered to orbit in order to replenish spacesuit consumables, extending the spacesuit operating life, and using microprocessors to control and monitor spacesuit systems. Ideas to decrease the necessarily delivered payload weight include regeneration of CO2 absorbers, heat removal without evaporative water loss, decreasing spacesuit O2 leak rates, and use of advanced O2 supplies [49].

22.3.3 Advanced Microgravity Spacesuits: Past Problems and Future Considerations

Realizing the benefits and limitations of existing spacesuits, future EVA suits should incorporate technologically advanced designs. Increased levels of EVA capability will be required for the extensive construction and maintenance of future space stations. Current Space Station Freedom requirements call for 50 2-person EVAs per year. To meet the challenge of providing frequent EVA support while lessening the risk of decompression sickness, high pressure zero prebreathe suits might be necessary. A high pressure suit of 55.2 kPa to 57.2 kPa (8 p s i to 8.3 psi) reduces the need for prebreathing and was established with the risks of decompression sickness and physiological considerations as guiding parameters.

There are numerous problems associated with past and current spacesuits. In addition to operating in the low pressure range (< 40.6 kPa (5.88 psi)), current spacesuits offer less than ideal mobility and require higher than ideal energy expenditures for movement [50]. Cosmonauts lose about 3 k g (6.6 lb) in body weight after several hours of EVA, (presumably from body fluid loss), and have reported great difficulty in using tools, especially the URI (universal hand-operated electron-beam power tool which is the most commonly used EVA tool) [8]. Damp undergarments may produce problematic cooling, and overheating has been noted when high workloads are experienced. As previously mentioned, the sharp contrast in temperature between the light side and dark side of an orbit can be as much as 231oC (448oF). Limited vision and hand dexterity are additional problem areas. For higher pressure suits, weight reduction and design of a dexterous glove remain the most challenging engineering problems.

Ideally, advanced spacesuits will provide the crew member with a mobile, protective, regenerable life support system for use in orbit, as well as on planetary surfaces. Parameters such as operating pressure, fabrication, joint mechanics, useful life, inventory, maintenance, and environmental protection are drivers in the design and acceptability of advanced spacesuits. These seven issues are considered, and trade-offs between spacesuit concepts are discussed below.

Operating Pressure When the human body is exposed to a sudden decrease in atmospheric pressure (for instance, from a 70.3 kPa (10.2 psi) cabin pressure to the 29.7 kPa (4.3 psi) of the suit) nitrogen traces in the bloodstream will expand during this decompression and can create tiny bubbles and the potential for the "bends" (See Section 22.5 for a detailed description of decompression sickness). In order to lessen this effect, the astronaut must "prebreathe" pure oxygen to help purge nitrogen from his/her bloodstream before entering the low-pressure pure oxygen environment of a spacesuit. Under the current NASA protocol, the EVA crew members don their - 16 -

oxygen masks and prebreathe pure oxygen for a prescribed amount of time to purge the nitrogen from their blood. In addition, cabin pressure is lowered from the normal 101.3 kPa (14.7 psi) to 70.3 kPa (10.2 psi) in order to minimize the rate of nitrogen return while they breathe cabin air - a nitrogen/oxygen mixture. This technique allows for a short 30-40 minute prebreathe time in the EMU just prior to starting EVA [35]. The Russian spacesuit prebreathe protocol followed during Salyut EVAs maintained a constant sea level equivalent station pressure and required a 30 minute prebreathe.

A high pressure 57.2 kPa (8.3 psi) spacesuit has many advantages over current lower pressure (29.6 kPa American suit, 26.2 kPa to 53.3 kPa Russian suit) spacesuits. Two advantages are reducing the need for prebreathe and eliminating the need to lower the spacecraft pressure. Prebreathing is reduced or eliminated because the possibility of nitrogen bubble formation, which can have detrimental effects (i.e., decompression sickness), is reduced to a minimum in a 57.2 kPa (8.3 psi) spacesuit. Section 22.4, Physiological and Medical Aspects of EVA, examines medically acceptable pressure limits and Section 22.5, Decompression Disorders in the Context of EVA, describes decompression sickness in detail. Also, altering the space station pressure is not desirable because laboratory experiments will be inadvertently disturbed when standard Earth atmospheric pressure (101.3 kPa) is not provided. As the overall pressure of the space station is reduced the oxygen concentration in the space station increases (maintaining a normoxic breathing atmosphere), and there is a subsequent increase in the risk of fire. Also, avionics cooling is less effective. The best space station operating pressure (i.e., 101.3 kPa or 70.3 kPa) is hard to define because there are advantages at both pressures, but in either case, there would likely be no need to prebreathe if a high pressure spacesuit was used for EVA.

Fabrication Past spacesuits were primarily constructed of fabric (soft), whereas hard components (metal, composite, etc.) have been introduced into the designs of current spacesuits. Future EVA spacesuits will most likely be hybrids of fabric and hard components. Fabric components offer advantages, such as being lower weight and enabling the crew member to have sensory feedback. Metal components are advantageous in that the analysis of metals is a well understood science and this ensures control over fabrication and reliability. Metal parts can be fabricated using state- of-the-art computer controlled machines. In contrast, it is extremely hard to obtain reproducible, reliable lifetime data from stitched fabric components.

Joint Mechanics The joint mechanics which govern suit mobility partially depend on the suit volume type. Fabric suits offer a slightly changing volume while prototypical metal suits (Figure 22.7) are constant volume. Flexing the joints of a changing volume suit reduces the volume (recall Section 22.3.1.2) which increases the pressure; therefore, greater work forces are required as compared with flexing a constant volume suit. The EVA crew member may experience fatigue due to the energy required to overcome springback forces in suits. A metal constant volume suit does not have springback characteristics (i.e., has no memory) in the joints, so no additional energy is required to maintain a joint's position once it is flexed. Under pressurization, changing volume fabric components can support part of their own weight, whereas hard components cannot support their own weight. This weight bearing capability is advantageous for planetary EVA spacesuits because it offers greater latitude in the design of the life support system and aids the crew member with standing and locomotion. - 17 -

Useful Life The usable lifetime of a spacesuit is an important issue, especially when considering permanent human presence on space stations and planetary bases. Cycle testing of metal spacesuit components suggests a 20-year lifetime for properly maintained bearings and an indefinite lifetime for other suit components [47]; in contrast, many Shuttle EMU spacesuit components have an 8-year lifetime and are currently inspected after every EVA and certified for 20 hours of EVA time, after which a major overhaul is undertaken. Some current fabric elements are certified for a shelf and cycle life of eight years [63]. There is currently noticeable wear on the inside of suit bladders. Recently, the palm bar wore through the EMU glove during an EVA on STS-37 (April 1991). Undesirable discrete point loading may occur at the joints in fabric suits from unpredictable folding of the material. It is desirable to have evenly distributed loads in joint components which may be realized through metal suits with radial ball bearings [13]. Useful life of spacesuit components and life support equipment is paramount for future microgravity (space station) and planetary EVAs.

Inventory and Stowability There is limited storage and inventory aboard a space station or planetary base, and neither can afford frequent resupply of spacesuit parts. The trade-offs are that fabric spacesuits can be telescoped and thus occupy less stowage space than prototypical metal spacesuits, but metal spacesuits require fewer spare parts than fabric spacesuits, due to their longevity. The mass of the spacesuits should also be considered, where fabric components have a distinct advantage over metal components (i.e., fabrics are much lighter).

Maintenance and Cleaning Ease of maintenance and cleaning are key requirements for advanced suit design. An effective way of cleaning and maintaining the inside of the suit while in orbit must be found. Fabric is much harder to clean and sanitize than wiping and rinsing metal components. This issue has not received enough recognition in current space station plans and may prove to be of significant cost to the entire program. For example, the current protocol for the Space Shuttle EMU returning from a mission entails some 1,500 person-hours of seam inspection, pressure leak checks, and backpack life support system refurbishment. Even an order of magnitude reduction in hours to inspect the spacesuit would not be adequate for on-orbit space station EVA.

Environmental Protection Crew members must be protected from the harshness of space and planetary environments. In order to provide the crew member protection from debris, , and radiation, additional layers are added to fabric suits. This has the undesirable effects of increasing bulk and reducing mobility. Ongoing research on the construction of double hulled metal components may enable hard spacesuit components to incorporate environmental protection and automatic thermal control within the suit components [50]. Ideally, no performance decrement would be realized in a double hulled suit. - 18 -

Radiation shielding is of the utmost importance for crew safety during EVA [45]. The Space Shuttle EMU provides shielding with an approximate aluminum equivalent of 0.5 g/cm2 [31] to the upper torso. Prior to Space Station Freedom restructuring, in which the construction requirements for EVA were much greater than for the current design, this was deemed inadequate protection for such a robust EVA schedule. Advanced prototypical metal spacesuits (See Figure 22.7) would provide approximately 1.5 gm/cm2 aluminum equivalent of shielding. It has been noted by Thompson et al. [53] that 1.62 gm/cm2 would be required for polar and Geostationary Earth Orbit (GEO), where less deflection of solar particles is afforded by geomagnetic fields. A practical aspect is that a more formidable radiation shielding capability than that provided in current suits will be required to support vigorous EVA efforts for high orbit, lunar surface, and trans-lunar or trans-planetary operations. These locations make the EVA crew member vulnerable to Solar Particle Events (SPE), which may reach a level sufficient to induce acute whole-body exposure syndrome, as well as background Galactic Cosmic Radiation (GCR). However, the amount of shielding material required for protection of an EVA crew member commensurate with terrestrial levels represents an unacceptable weight burden, and the mainstay of protection must focus on minimizing exposure.

In sum, advanced spacesuits should provide high working pressures and dexterous gloves, shirtsleeve mobility, longevity, ease of maintenance, and adequate environmental protection. Gloves should be certified for long duration use at high pressures. Mobile joint systems must allow for minimum energy expenditures during EVA tasks. Improved technology and materials should allow for durable spacesuit design. Advanced reliable 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 realized with the thermal control system [62]. A modular, evolvable design is advantageous. Technological advances should lead to real-time environmental monitoring systems and innovative display and vision systems.

Insert Figure 22.7 here

22.3.4 Planetary EVA

Microgravity EVA has been admirably demonstrated. While significant improvements are necessary for long-term space station EVA, quantum improvements are required for planetary EVA. Advanced concepts previously covered were primarily for 0 g spacesuits where the crew member uses his/her small musculature of the upper body rather than the large musculature of the lower body. Planetary EVA dictates a true locomotion spacesuit because the large muscles of the legs will be called upon for locomotion, and the upper body muscles will be relied upon for accomplishing EVA tasks other than self-locomotion. Apollo 17 EVA astronaut Harrison Schmitt praised the Apollo EMUs for working without a serious malfunction for up to 22 hours of exposure to the lunar environment, but his recommendations for future planetary spacesuits should be heeded. Jones and Schmitt [27] suggest that improvements in mobility and suit flexibility will have a significant impact on astronaut productivity. They also recount instances where "(lunar EVA) astronauts fell repeatedly" [27, pg. 2] and state that improvements in manual dexterity and reduction of muscle fatigue and abrasion-induced damage to the hands would have the greatest impacts. The fine dust particles of lunar regolith caused notable problems with the - 19 -

Apollo suits and dust will pose quite an obstacle when EVA is performed on a continuous, daily basis from lunar and Martian habitats. All of these comments suggest that the future design and development of planetary spacesuits will be challenging. The following discussion lists additional issues to consider in planetary spacesuit design which is followed by sections covering the mechanics of locomotion and experimental data for human performance in simulated partial gravity environments. Based on the preliminary information presented in this planetary EVA section, the reader is encouraged to come up with novel design concepts for future lunar and Martian spacesuits.

Try to imagine what 'a day in the life of a lunar astronaut/construction worker' might involve. One of the crew member's simplest tasks might be to set-up a telescope. The crew member would suit-up in the airlock, assemble the necessary tools (including only the hand tools that they can carry, but what about necessary standard construction equipment such as, bulldozers, loaders, cranes, etc.?), leave the lunar habitat through the airlock, and begin the day's task. The construction worker either drives or uses self-locomotion to arrive at the site. In either case, a light, mobile spacesuit and LSS is required. Once at the site the crew member surveys the lunar terrain which requires agility, traction, tools, and possibly illumination. The crew member probably has to move some lunar regolith and flatten the desired plot, and there is likely to be dust everywhere fouling the spacesuit bearings and hampering the rover's machinery. Next, the crew member starts assembling the platform for the telescope. Once assembled, the platform is leveled and the actual assembly of the telescope commences. The assembly of and adjustments to the telescope require extreme finger dexterity. It is evident that the simple task of deploying a telescope requires a rather involved EVA. Planetary EVAs for building habitats, laboratories, and facilities are orders of magnitude more complicated than the cited example and will require EVA systems and crew member skills that do not currently exist.

Whatever the EVA task may be, the crew member must be provided with adequate life support, protection from the environment, and appropriate tools and equipment. Most of the trade-offs mentioned in Section 22.3.3, Advanced Microgravity Spacesuits, are also applicable to planetary spacesuits. A few additional human factors considerations for our hypothetical lunar EVA include: providing adequate mobility; ensuring natural, efficient locomotion; allowing for crew member balance and orientation; quantifying the loads to be imparted on the crew member, the spacesuit, and the life support system; providing adequate lighting and power; and equipping the crew member with dexterous spacesuit gloves. These requirements will only be met through extensive research and design efforts. Perhaps a spacesuit that incorporates mechanical pressure rather than air pressure will provide the crew member with a light, form-fitting spacesuit. If an optimal locomotion spacesuit can not be realized, concepts like full-body enclosures with manipulators might prove to be successful. However, at this early stage the field is wide open and all designs and methodologies should be considered. The following Section, 22.3.4.1, Mechanics of Locomotion, provides a brief introduction to the 1 g mechanics of walking. This information is included to acquaint the reader with some characteristics associated with walking and to provide a 1 g biomechanics background for Section 22.3.4.2, Human Performance in Partial Gravity Environments. - 20 -

22.3.4.1 Mechanics of Locomotion

Locomotion is the most common activity of humans. Movement of the body is not only our most characteristic activity, but our relationships with the environment and other people are based on human movement. The essential characteristics of walking are described below in order to familiarize the reader with biomechanic requirements as future locomotion spacesuit designs must account for human physiology as well as advanced technology. For normal 1 g locomotion, humans primarily use two gaits: walking and running. During walking a person has at least one foot in contact with the ground, and both feet make ground contact during the mid- phase of a stride cycle. The center of mass is highest at mid-step when the hip of the stance leg is directly over the ankle [32]. The typical rhythm or cadence of walking is 60 to 70 strides per minute. A complete stride cycle consists of a stance (or support) phase which is initiated at heel strike and then a swing phase from heel off to the next heel contact of the same foot. During running there is foot contact with the ground before and after an aerial flight phase, but there is never ground contact by both feet at the same time and the center of mass is lowest at mid-step during foot contact. Loping, an extension of running, is not a characteristic 1 g gait, but is common in low gravity environments such as on the lunar surface. Loping includes a step length increase and an increase in aerial time during the stride cycle [42].

The notions of minimizing energy expenditure and forces are basic hypotheses behind human movement. The functional significance of the determinants of gait is to minimize vertical and lateral oscillations of the center of gravity (CoG) during walking, thus minimizing energy expenditures and perhaps minimizing muscular force generation. There are numerous descriptions of the motions of the limbs during locomotion, but Jenkins' [26] succinct presentation is reiterated herein. Six characteristics of walking to incorporate into the design of future locomotion spacesuits are presented.

The six characteristics of walking include: 1) Pelvic rotation 5) Trunk lateral flexion 2) Pelvic tilt 6) Trunk anteroposterior flexion 3) Knee flexion during the stance phase 4) Heel strike and Heel-off interactions with the knee

The first distinguishing characteristic, pelvic rotation, describes the pelvis rotating from side-to-side about the body's longitudinal (vertical) axis for normal walking. During the swing phase, medial rotation at the weight-bearing (stance) hip advances the contralateral (swing phase) hip (See Figure 22.8). The effective increased leg length from pelvic rotation lengthens the step and flattens out the arcuate trajectory of the CoG insuring a smoother ride as the radii of the arcs of the hip increase, thus, a reduction in energy expenditure occurs. The pelvis is tilted downward about 5o on the swing phase side. This occurs with pelvic adduction at the hip joint on the stance phase side (See Figure 22.9). Pelvic tilt further flattens the arcs of the hip allowing for a smooth ride during walking. The third determinant of gait is knee flexion during the stance (support) phase. At heel strike the knee is extended, 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 - 21 -

energy expenditure. Heel strike and heel-off interactions with the knee comprise the fourth characteristic of gait. At heel strike the foot plantar flexes (rotating downward about an axis formed at heel contact) thus lowering the ankle as the foot makes full contact with the ground (See Figure 22.10). A fused ankle joint (immobile) without plantar flexion would cause the CoG to rise as if the leg were a stilt. Ankle plantar flexion affects gait similarly to ankle flexion in that 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 about an axis formed at the ball of the foot. The trunk flexes both laterally and anteroposteriorly during walking to make up the final characteristics of walking. 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.

Insert Figures 22.8, 22.9, and 22.10 here

In sum, the characteristics of walking described above were 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 has the effect of reducing the force exerted on the ground. This equivalently reduces the reactionary force on the skeletal system and human body. As applied to locomotion spacesuit design, recommendations would be to provide a waist bearing that allows for both pelvic rotation and tilt; a knee joint to enable flexion; an ankle joint for plantar and dorsi-flexion; and a hip/waist/upper body capability that accommodates trunk flexion. The next section reveals data from partial gravity studies.

22.3.4.2 Human performance in partial gravity environments This section highlights some experimental studies and provides data on human performance in partial gravity. Quantifying partial gravity performance allows for efficient spacesuit and life support system designs. The three primary techniques to simulate partial gravity are: underwater immersion, parabolic flight, and suspension. During underwater immersion 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 unlimited duration and freedom of movement, but the hydrodynamic drag is disadvantageous for motion studies. In parabolic flight, the NASA KC-135 aircraft or the 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 affect true partial gravity on Earth, but experiments are expensive and limited in time. Many partial gravity suspension systems have been designed and used since the 1960s. 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 the degrees of freedom for movement. - 22 -

Biomechanics and energetics data from recent studies are detailed below. Analyzing force traces is helpful in quantifiying the peak force exerted by the crew member on the ground. These data pertain to spacesuit design as well as to the physiologic effects of musculoskeletal deconditioning. Stride frequency, contact time, and aerial time measurements yield quantitative data to incorporate into the capabilities of a locomotion spacesuit. Bioenergetics data are revealed for consideration in planetary EVA life support systems. The results show surprising information for partial gravity locomotion. There is a change in the mechanics from typical 1 g walking and running and the oxygen required to ambulate on the moon or Mars is significantly less than for similar activities on the Earth.

There is a significant reduction in peak force during locomotion in partial gravity. Figure 22.11 displays mean values of peak force for a total of eight subjects. Reductions in stride frequency (strides/minute) at partial gravity conditions indicate a trend toward loping as the gravity level decreases from 1 g. The general trend of a reduction in stride frequency is seen for both immersion and parabolic flight partial gravity simulation studies as seen in Figure 22.12. However, the superimposition of the data yields stride frequency results which are markedly higher for parabolic flight. This result makes sense in view of the two simulation environments. The decrease in stride frequency for the underwater locomotion experiments is attributable to the added ballast on the subjects' bodies and the additional inertial effect of added mass to move the water column during locomotion. The underwater running experiments can be characterized by damped oscillatory motion, whereas the experiments run on the KC-135 aircraft and the 1 g control experiments in air can be characterized by undamped harmonic motion. The natural frequency of a damped system is always less than that of an equivalent undamped system; therefore, the result of increased stride frequency for parabolic running and running in air compared to the underwater results was expected. Reducing the gravitational acceleration decreases stride frequency (or the corollary, increases stride length) and has no significant effect on the amount of time the support limb is in contact with the ground (contact time). Figure 22.13 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 because the 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 suggest an increase in aerial time for partial gravity 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 [41].

Insert Figures 22.11, 22.12, and 22.13 here

Recall that Section 22.3.4.1, Mechanics of Locomotion, claimed the functional significance of the characteristics of gait is to minimize energy expenditures. The minimum cost of locomotion (or cost of transport) per unit distance can be defined as the ratio of steady-state oxygen consumption over speed. Each subject requires a different metabolic expenditure to travel the same distance. Therefore, in order to compare across subjects, the energy expenditures - 23 -

are normalized by the mass of each subject. There exists a well documented optimal cost of transport for terrestrial walking at the speed of 1 m/s [30]. In terms of metabolic expenditure, it costs about half the amount of energy to walk 1.67 km (1 mile) as compared to running 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 cost of transport. Results from underwater immersion and suspension simulators indicate that above 1/2 g, walking requires a lower cost of transport than running, but from 1/4 g to 1/2 g running is cheaper than walking [16, 41] (See Figure 22.14).

Insert Figure 22.14 here

The successful design of future planetary spacesuits depends on providing improved mobility, improved glove performance, higher operating pressures, improved radiation shielding, mass reductions, regenerable life support systems, and improved human/machine interfaces. Locomotion spacesuits should incorporate suggestions from past Apollo experience and current research efforts keeping in mind the change in mechanics for locomotion in partial gravity environments. 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 being assisted by robotic machines. Medical risks to the crew members will also be a driving force in planetary spacesuit design. The next Section 22.4, Physiological and Medical Aspects of EVA, details biomedical EVA factors.

22.4 Physiological and Medical Aspects of EVA

In examining some of the normal physiological and potentially adverse or pathologic aspects of EVA, one need only peruse the list of human requirements given in the previous section and speculate on the effects of partial or complete system failures. In essence, these are generic to the spaceflight environment, but with a drastically reduced margin of failure tolerance in the small confines of the EVA suit. Close monitoring of suit function, use of consumables, and physiologic parameters is warranted during EVA to detect any adverse trends as early as possible. This necessitates a highly sensitive and rapidly responsive atmospheric monitoring and control system. NASA requirements call for real-time telemetry of suit pressure, temperature, O2 consumption, CO2 partial pressure (ppCO2), electrocardiogram (ECG) and heart rate, and radiation exposure, along with nominal voice communication during EVA. It must also be born in mind that in the event of a medical problem or emergency, the crew member does not have immediate access to medical treatment. He or she must translate to and ingress the airlock, possibly requiring the aid of a crew member, undergo the repressurization cycle, and finally have the bulky spacesuit removed to whatever degree is necessary to accommodate emergency treatment. Following are basic physiological principles which will afford an understanding of EVA biomedical factors.

22.4.1 Pulmonary Aspects and Oxygenation - 24 -

A simple but vital concept when discussing closed gas systems is that the biological responses of most gases are dependent on their partial pressures, rather than their overall concentrations. At sea level, with an O2 concentration of 21% and a partial pressure of O2 (ppO2) of 21 kPa (158 mmHg), the respirable atmosphere is said to be normoxic. The same 21% is hypoxic at altitude, where ppO2 diminishes in step with total pressure, and hyperoxic in hyperbaric atmospheres. Either of these conditions may be detrimental. Similarly, the toxic effects of CO2 are partial pressure dependent; thus, what may be an acceptable concentration at sea level (e.g., 3%) may be unacceptably toxic at hyperbaric pressures of a few atmospheres.

Another point of emphasis regarding EVA O2 is that it is the alveolar pO2 (pAO2) that equates more directly with biological supply, as opposed to the ambient ppO2. This is determined using the alveolar gas equation, and becomes more important as lower pressure atmospheres with correspondingly higher O2 concentrations are utilized. The calculation in a simplified form is:

pAO2 (mmHg) = FiO2 [Pambient - 47] - paCO2 / RQ

FiO2 = fraction of inspired O2 (e.g., 0.21 at sea level, essentially 1.0 for 29.6 kPa shuttle suit.)

Pambient = suit or cabin pressure

47 mmHg = vapor pressure of water at body temperature (37 deg C)

paCO2 = partial pressure of CO2, expired by body; nominally about 40 mmHg

RQ = Respiratory Quotient = CO2 production / O2 consumption; nominally 0.8

Usually, for calculating pAO2's resulting from nominal activity, one can substitute nominal values for paCO2 and RQ. At sea level, total pressure = 760 mmHg, and pO2 = .21 x 760 = 160 mmHg. pAO2 is thus:

pAO2 = .21[760 - 47] - 40/0.8 = 100 mmHg

A pAO2 of approximately 100 should be considered defining for normoxia. The effects of hypoxia are manifested early by such symptoms as loss of color vision and peripheral vision, followed by confusion and eventual loss of consciousness as the degree of hypoxia becomes more severe. A catastrophic pressure loss is not required to present the problem of hypoxia during EVA. A slow leak and partial depressurization, balanced by the contingency reserve feature of the PLSS, could result in the entire spectrum of hypoxic symptoms, from subtle confusion to death. Telemetry will of course alert a controller to such occurrences that might lead to hypoxia, such as supply limitations or leaks, but the on-site medical facility must be prepared to deal with the consequences. - 25 -

Hyperoxia can produce toxic effects after prolonged exposure. Central nervous system toxic effects can result from exposure to hyperbaric pressures, generally greater than 250 kPa (37 psi). At sea level, prolonged exposure to 100% O2 eventually leads to pulmonary O2 toxicity, manifested progressively by chest discomfort, cough, decrease in tidal volume, and eventual pulmonary edema and possibly adult respiratory distress syndrome (ARDS). Initial effects are generally seen after 12 to 24 hours, but a splay exists on either side. At intermediate pressures (e.g., between current EVA working pressures and sea level) less is known about prolonged exposure to O2. Studies have been done examining effects of repeated simulated EVA sorties at 65 kPa (9.5 psi), showing no evidence of O2 pulmonary toxicity [61], and it is generally believed that 55 kPa (8 psi) could be tolerated indefinitely without pulmonary toxicity [19, 20]. Hyperoxia is also known to induce a reactive decrease in red blood cell mass, however it is unclear to what degree this might occur with a vigorous EVA schedule over several to months using a higher pressure suit. This might be combined with the known 'baseline' decrease in red blood cell mass in response to the microgravity environment.

22.4.2 Carbon Dioxide

A partial failure of the PLSS impairing its ability to scrub metabolically produced CO2 might lead to levels of hypercapnea impairing performance. Effects of hypercapnea are well characterized, and in the acute phase include increased respiratory rate, increased minute volume, and headache. These are usually seen with CO2 partial pressures of 20 mmHg or greater, but may be seen at lower levels. An upper limit for NASA spacecraft cabin CO2 levels is 15 mmHg. (EMU ventilation is considered to have failed if CO2 partial pressure exceeds 8 mmHg [36]; following loss of suit ventilation, inspired CO2 would increase as a function of time and metabolic rate.) Between 20 and 40 mmHg some degree of discomfort is expected and prolonged exercise performance may begin to decline; above 40 mmHg, a gradual depression of cognitive and exercise ability is expected. Values in the 70 - 150 mmHg range would be unlikely in an EVA setting; accumulation of CO2 to these levels would be accompanied by more marked cognitive impairment, respiratory depression, and unconsciousness. As CO2 is a metabolic product under continuous monitoring, acute exposure scenarios are not expected; trends showing buildups to untoward levels would prompt termination of the EVA within acceptable margins. It is known that even low-level chronic exposures induce tolerance mechanisms and compensatory acid/base adjustments, but again these are not expected in the EVA setting.

22.4.3 Thermoregulation

As discussed in the previous section, thermoregulation had been problematic in the early days of EVA. Highly variable workloads made it difficult for the gas-cooled systems to compensate adequately to maintain thermal equilibrium. Peak performance of the gas cooling - 26 -

system utilized for the Gemini suits was approximately 250 kcal/hr [24], with short-term workrates occasionally exceeding this. This has been solved operationally by both the Russian and U.S. programs with the introduction of the Liquid Cooling and Ventilation Garment (LCVG). As described earlier, the LCVG circulates cooling water through a series of flexible tubes integrated into a pliable body suit. Metabolically produced heat is transferred to circulating water and passed to a heat exchanger to be rejected to space through the process of water sublimation. By controlling water inlet temperature, this system offers individual control to accommodate the wide variation in heat production during changing workload requirements. This effectively doubles the acceptable heat load compared with the Gemini suit. Early use of the LCG was associated with overcooling of the lower extremities, presumably due to the relative decrease in blood flow induced by microgravity exposure. This has been addressed in the Russian program by shifting positions of water cooling panels and augmenting thermal garments to the lower extremities [3, 4].

A well distributed and easily manipulated thermal control system allows the EVA crew member to make corrective as well as anticipatory adjustments as needed. For example, the crew member may turn up his cooling in advance of heavy work requiring force exertion or involving cyclic exposure. In addition, the experience of the individual crew member influences thermal control. Barer reported failures of LCG systems during EVA which were not problematic due to the experience of the cosmonaut and the ability to adapt and distribute workload efficiently [3]. In the event that thermal control cannot be maintained, it is assumed that an EVA sortie could be aborted by ground controllers before physiologically significant heat storage occurred.

22.4.4 Cardiac Conduction

A variety of dysrhythmias have occurred during microgravity exposure in general, with some episodes apparently related to specific EVA sorties. These have ranged from premature ventricular contractions (PVCs) to sustained ventricular bigeminy and atrial quadrageminy [7]. None of these have been considered malignant dysrhythmias leading to immediate EVA mission termination, and it is not conclusive that dysrhythmias occur with any greater frequency during spaceflight than terrestrially. However, the events mentioned are suggestive of apparent alterations in cardiac conduction not observed prior to spaceflight. Of note, a Soviet cosmonaut was returned from the Salyut 7 space station relatively early in his mission due to an intermittent cardiac dysrhythmia which originated in the course of a minor mishap during an EVA sortie [28, 40]. This rhythm alteration resolved completely upon return from microgravity. Potential contributing factors include alterations in fluid and electrolyte status (which characterize the normal physiologic response to microgravity), workload, and psychological stress. The latter may contribute heavily; EVA has been described by many authors and crew members as the most hazardous and stressful aspect of spaceflight.

Real-time electrocardiographic (ECG) monitoring with telemetry to ground has been utilized throughout both manned space programs as a necessary part of EVA. Along with alerting ground controllers to rhythm disturbances, it gives objective information regarding - 27 -

workload and possibly anxiety level (via heart rate). In addition, the ECG tracing is sensitive to certain metabolic abnormalities, with different wave forms affected specifically by such changes as hyperventilation and electrolyte disturbances.

22.4.5 Waste Collection

A means for collection of waste body fluids is essential. For urine, an absorbant incontinence device is utilized in the Shuttle EMU; for EVA sorties of four to seven hours in duration, this has proven successful and comfortable. Should a crew member vomit during an EVA sortie, free-floating emesis poses a risk of aspiration into the lungs and damage to the respirable gas circulation lines. Gastric contents are highly acidic and pulmonary aspiration may lead to a severe chemical pnuemonitis and pneumonia. Events and conditions which might lead to emesis are similar to those on Earth, with the addition of Space Motion Sickness (SMS). SMS is a highly prevalent condition among astronauts occurring during the first few hours of spaceflight. It is manifested by headache, nausea, and vomiting, and could conceivably occur during EVA. As SMS usually resolves within one to three days on-orbit, it is advisable to avoid any planned EVAs during this time period. If contingency or emergency EVA is required early in the mission, anti-SMS medication should be used even for mild symptoms, although this must be balanced against the mild central nervous system depression occasionally caused by such agents. This of course does not preclude emesis for any other reason. A mechanical one-way flow-controlled conduit within easy reach of the astronaut's mouth, attached to a reservoir to catch and contain gastric contents, may be a desirable feature of future advanced EVA systems.

22.4.6 Injuries

Injuries must be considered a real possibility during EVA. These would be expected to consist primarily of soft tissue insults, such as muscle and tendon strains associated with over- exertion. As orbital EVA involves primarily upper body work, these types of injuries would be most likely to involve the shoulders and arms, where the work is actually performed, and the ankles which hold the crew member in place in a foot restraint. Astronauts Jerry Ross and Sherwood Spring, during an EVA orbital construction feasibility demonstration, emphasized the progression of pain and fatigue in the hands and forearms due to maneuvering large beams into position [1]. Even in the reduced gravity of the Lunar surface, some loads could exceed human capability, and injuries might be incurred while exerting large forces such as to dislodge a sample from the surface.

Traumatic events which cause serious injury without compromising suit pressure integrity should be considered possible as well. An unexpected lateral force against a crew member working in a foot restraint, for example, might induce a debilitating injury to ankle or knee ligaments. In addition, crush injuries, such as might be sustained by a limb between a structural surface and a sufficiently massive moving object, may lead to fractures and local tissue injury while leaving the suit's pressure seal intact. Penetrating trauma may result from impalement, - 28 -

rupture of a pressurized vessel, or possibly from an orbital debris impact. While these events are less likely to be survivable, a small penetration within the overpressurization capability of the reserve O2 system might allow a crew member to be translated back to the pressurized airlock prior to complete loss of suit pressure.

22.4.7 Radiation

Specific sources and effects of radiation are covered elsewhere in this text. Regarding EVA, it is apparent that potential exposure will be highly orbit dependent. For (LEO) operations well below the Van Allen Belts, a considerable degree of shielding is afforded by the Earth's geomagnetic fields, and even major Solar Particle Events (SPE's) will have little noticeable effect at altitudes commonly flown by the Shuttle or Soyuz spacecraft. The exception is during the transit through the South Atlantic Anomaly (SAA), a region in which the Van Allen Belts extend to a much lower altitude than at corresponding latitudes elsewhere. For a platform in LEO, particularly in higher inclination orbits, passage through the SAA must be factored into EVA planning, with sorties timed to avoid SAA transits. At issue are the astronaut's career limits on radiation dose; acute whole-body exposure syndromes are not expected from natural sources in LEO at latitudes currently in use. Continuous radiation dosimetry is performed for shuttle EVA operations, with real-time telemetry to the ground.

SPE's cannot be predicted per se, but buildups of solar flare activity can be detected over a matter of hours and EVA's avoided or terminated during heavy activity. For trans-Lunar or trans-planetary EVA en route, the spacecraft could be oriented in such a way that the EVA is performed in the "shadow" of the structural bulk relative to the solar wind. Lunar surface EVA that might take a crew member far from a home structure might make use of strategically located "storm shelters" carved from the Lunar regolith to afford a shielded safe haven in the event of unanticipated SPE activity. Background GCR is difficult to shield against during EVA, and meticulous radiation dosimetry will remain vital to EVA operations for the foreseeable future.

22.4.8 Contamination

A final issue before discussing decompression disorders is that of contamination of the habitable volumes by toxic substances adhering to the EVA suit. Fuels such as hydrazine and oxidizers such as nitrogen tetroxide (N2O4) are unlikely to adhere in amounts causing significant contamination, but the possibility does exist. A venting fuel line or an inadvertent thruster firing might lead to this situation. However, any time an astronaut works in close proximity to vessels or lines containing these highly toxic substances, monitoring and detection equipment should be available. The means to detect these substances in the airlock is a desirable requirement prior to full pressurization. Detection of hydrazine would prompt the crew member to egress the airlock, brush off visible contamination, and "bake" in the sun for a period of time, allowing residual hydrazine to sublimate away. - 29 -

22.5 Decompression Disorders in the Context of EVA

Because decompression sickness (DCS), a major potential hazard of EVA, will have a profound influence on the development of any EVA system, and a detailed discussion is appropriate. Its prevention is among the foremost health maintenance challenges facing EVA operations for space station and orbital construction. DCS is caused by the evolution of nitrogen (N2) bubbles in the tissue, induced by a state of tissue N2 supersaturation relative to the ambient pressure. Conditions for this arise in the relatively low pressure environment of the EVA spacesuit compared to the shuttle or Mir space station pressure of 101.3 kPa (14.7 psi, or sea- level equivalent pressure). Current technology limits suit pressure to a level much lower than sea level-equivalent, primarily due to mobility constraints. It is during and after the transition to this lower pressure environment that the requirements for relative supersaturation are met. As there is a considerable lag before tissue N2 equilibrates with ambient pressure, initial tissue N2 tension can easily exceed ambient pressure. The greater this margin, the more likely is the development of some manifestation of DCS.

The N2 tissue ratio (TR) is defined as tissue N2 tension/ambient pressure post- decompression. Theoretically, when transitioning to a lower pressure, any time this ratio exceeds 1.0 a state of supersaturation exists, along with the potential to form bubbles. In practice, Haldane discovered empirically that symptoms of DCS were rarely seen unless this ratio exceeded 1.58 [22]. Symptoms resulting from the evolution of N2 bubbles in tissue include localized limb and joint pain, known as type I DCS or "the bends", and the less common but more severe neurologic and pulmonary damage, known as type II DCS. It has since been shown that many factors work to affect the TR at which DCS may occur.

Both the Gemini and Apollo spacecraft maintained a cabin pressure of 34.5 kPa (5.0 psi), with 100% O2 as the breathing gas [57]. Thus the main danger of DCS occurred at launch, whereupon with transition to the cabin atmosphere (258 mm Hg) from sea level (760 mm Hg, of which N2 comprises 600 mm Hg), the N2 tissue ratio becomes 600/258 =2.3. The unacceptably high risk of DCS resulting from this TR was circumvented by a three hour prebreathe of 100% O2, which afforded a substantial washout of body N2 stores. The resulting pN2, or partial pressure of N2, of 414 mm Hg yielded a launch-to-orbit TR of 414/258 = 1.6. This was considered an acceptable risk. (No symptoms of DCS were reported during this time period; however, many years following his Apollo 11 flight, Collins reported joint pain post-launch highly suggestive of type I DCS [9]). Suit pressure for EVA operations was 25.5 kPa (3.7 psi, or 191 mmHg), representing yet another depressurization step. However by the time orbital or lunar EVA's were undertaken, an essentially complete N2 washout had occurred, resulting in no significant risk of DCS. - 30 -

The Skylab cabin atmosphere was also maintained at 34.5 kPa , but contained a breathing mix of 70% O2, 30% N2. Transfer from the 34.5 kPa Apollo vehicle represented no ambient pressure change, and after several hours of breathing 100% O2, almost no risk of DCS remained.

The sea-level atmosphere of the shuttle and Soyuz spacecraft and the Mir and proposed Freedom space stations more closely approximates a terrestrial environment for the human occupants as well as the onboard biological experimentation packages. Fire hazard is not increased, as with increased O2 fractions at lower absolute cabin pressures, and equipment calibration and performance are simplified. However, the risk of DCS has been shifted from the time of launch to that of EVA. Although suit pressure for the shuttle has increased slightly to 29.6 kPa (4.3 psi), the margin between cabin and EVA environment pressures has increased significantly, and with it the potential for DCS. Decompressing from the shuttle to the suit environment is the equivalent of ascending from sea level to approximately 9144 meters (30,000 ft) altitude in an unpressurized aircraft [22].

Among other factors that contribute to the risk of DCS is duration of exposure to the lower pressure. It is well known that the greater the duration of exposure to lower relative pressure, the greater the likelihood of DCS. The mean duration of shuttle EVAs so far is approximately five hours, not unlike the Mir EVA experience, and EVAs in the six to eight hour range are envisioned for space station [19]. Similar EVA durations would be expected for most orbital construction endeavors. Accordingly, most ground based EVA simulations investigating DCS are of six to eight hours' duration [14, 15, 61].

The effect of physical exercise during and after exposure increasing the incidence of DCS is well recognized. Presumably, resulting muscular tensile forces and microvascular collapse provide a milieu more conducive to microbubble nuclei generation and subsequent bubble growth in tissue. EVA operations will primarily involve moderate exercise levels for extended periods, especially during space station construction. Of note, Conkin et al. studied 43 subjects undergoing upper body exercise simulating EVA at 29.6 kPa after a 3.5 to 4 hour O2 prebreathe at sea level. This prebreathe is generally thought to afford good protection against DCS with the given pressure difference [24]. Of these, however, 28 (65%) developed venous bubbles detectable via Doppler ultrasound, while 13 (30%) developed symptoms of type I DCS [10]. Obviously, the effect of physical exercise on DCS incidence continues to be of great concern.

Recent prior exposure to low relative pressure is also a risk factor for the development of DCS [22]. It is generally accepted that re-exposure to altitude within a few hours of a previous flight is associated with an increased incidence of DCS. The role of re-exposure on consecutive days, however, is less clear, and this is a pertinent question with regard to EVA. A vigorous construction and maintenance schedule might drive the requirement for several EVA sorties per . Determining the optimal interval between EVA's will be crucial, both for scheduled and unforeseen operations, and will vary with several factors. Waligora et al. demonstrated, using the currently accepted staged decompression protocol for shuttle EVA, that repeated EVA exposure after seventeen hours did not appreciably increase the risk of DCS . It should be kept in mind that the baseline incidence of type I DCS, or limb bends only, in these simulated EVA operations was considerable, being 26% [56]. Using a 65 kPa (9.5 psi) EVA simulation and breathing - 31 -

100% O2, Webb et al. demonstrated that subjects could undergo eight hours of EVA-level activity daily for five consecutive days, as noted above with no evidence of DCS or O2 toxicity [61]. This protocol would depend on development of a higher pressure suit than is now available.

Increasing age, obesity, female gender, and decreased ambient temperature are also thought to increase the risk of DCS [6, 15, 22], although their contribution to the incidence is minor compared with the previously discussed factors. The dehydrated state is generally held to predispose to DCS, both in aviators and scuba divers [22], but this, too is a comparatively soft risk factor. It must be considered, however, because fluid status changes predictably in the weightless environment. Generally, an astronaut will loose approximately three percent of his or her total body water within the first few days of orbital flight [43]. A cephalad fluid shift is known to occur, and this leads to decreased thirst and subsequently decreased fluid intake. A slight increase in fluid excretion, secondary to the central shift and relative or sensed "volume overload", is also a possible contributing factor. In the EVA setting, some crew members may wish to restrict fluid intake further to avoid in-suit voiding and the associated clean-up, possibly contributing further to a state of mild dehydration [19]. What role fluid status will play in DCS during EVA is yet unclear.

As noted above, a four hour prebreathe of 100% O2 was shown to provide consistent protection from DCS during simulated EVA from the shuttle cabin to the suit pressure of 29.6 kPa. However, maintaining a closed system during such a lengthy prebreathe proved problematic when going about activities such as donning suit and equipment, fulfilling pre-EVA checklists, etc. A transient breach in O2 prebreathe leads to a unequivalent setback in N2 washout. Current flight rules call for a two for one payback in event of prebreathe breach; that is, five minutes of exposure to cabin atmosphere requires ten minutes of O2 prebreathe to balance [36].

A staged decompression allows the EVA crew member to avoid the lengthy oxygen prebreathe, yielding more productive time. This entails decompressing the entire Space Shuttle cabin for several hours prior to EVA. A concomitant elevation of O2 fraction is required to maintain a normal pAO2. Thus the optimum staged pressure will afford adequate protection from DCS during the final transition to suit pressure, and at the same time avoid inordinately high O2 partial pressures and their increased risk of fire. The upper limit of cabin O2 concentration for the Shuttle and SSF programs has been fixed at 30% [57].

Waligora et al. carried out extensive testing of a 70.3 kPa (10.2 psi) intermediate pressure stage [56]. Using subjects representative of the astronaut population, 173 man tests were conducted. Subjects were decompressed without prebreathe from sea level to 70.3 kPa, where they remained for a 12 hour equilibration period. O2 fraction was increased to 26.5% (140 mmHg). They were then subjected to 29.6 kPa at 100% O2, where EVA simulating tasks were performed for a period of six hours. Theoretical N2 TR would have approximated 1.74. Using precordial Doppler measurements, venous gas emboli (VGE) were detected in 55% of subjects, and fully 25% developed symptoms of type I DCS. - 32 -

A modified 70.3 kPa protocol has been adopted which includes a one hour prebreathe with 100% O2 prior to initial depressurization to 70.3 kPa, along with a final in-suit prebreathe of duration dependent on total time at the intermediate pressure step just prior to final depressurization to 29.6 kPa. Table 22.3 shows the options for staged decompression to afford adequate nitrogen elimination, and Figure 22.15 graphically depicts a decompression profile to support EVA. This protocol still carries a theoretical 20 - 25% risk of mild DCS type I [11, 56].

Figure 22.16 depicts graphically the incidence of DCS and circulating venous gas emboli (VGE) detectable by Doppler ultrasound during ground-based simulations of shuttle-based EVA. These simulations include staged decompression, prebreathe, EVA-typical tasks, workloads, and durations among a population representative of the astronaut corps. (These data are based on a 360 minute tissue ratio, meaning TR for a tissue with a nitrogen elimination half-life of 360 minutes, which empirically offers the best data fit.) Note that with a TR reflective of shuttle EVA, incidence of symptomatic DCS is 25%, and incidence of DCS symptoms severe enough to terminate the test is 5% [60]. The majority of DCS symptoms acquired during EVA simulations resolved upon repressurization to sea level or shortly thereafter, with about two percent requiring hyperbaric treatment [10, 14, 15, 56, 61]. Should a more rapid EVA deployment become necessary, the option of a four hour O2 prebreathe still exists. This protocol carries about the same risk of type I DCS during EVA simulations [10]. An operational flight rule waives the initial prebreathe if the crew member remains at 70 kPa for a period of 36 hours or longer; this affords a time period sufficient to equilibrate to the lower N2 concentration, and only a 40 minute prebreathe immediately prior to EVA is required [36]. Average TR for shuttle EVAs, following the staged decompression protocol to the suit pressure of 29.6 kPa, has been 1.59. Although the Mir suit operates at the higher pressure of approximately 39 kPa, differences in prebreathe and decompression protocols yield an average TR of about 1.8 [55]. Table 22.4 shows TR values of representative EVA's from the U.S. and Russian programs, along with EVA duration and metabolic rate. Given that the current decompression protocol for shuttle EVA produces a 20 plus percent incidence of symptomatic type I DCS during simulation studies, it seems paradoxical that to date, no signs or symptoms of DCS have been reported during orbital flight in either active manned space program. Again, most of the EVA hours have involved the type of continuous low to moderate activity levels duplicated in the simulation studies.

Table 22.3 Four prebreathe and decompression protocols prior to final decompression to 29.6 kPa (4.3 psi). (Maximum acceptable TR value is 1.65.)

A. 4 Hr Sea Level (SL) Prebreathe (101.3 kPa, 14.7 psi)

B. 1 Hr SL Prebreathe 24 Hr at 70.3 kPa 40 Min Final Prebreathe

C. 1 Hr SL Prebreathe 12 Hr at 70.3 kPa 75 Min Final Prebreathe

D. 1 Hr SL Prebreathe 8 Hr at 70.3 kPa 100 Min Final Prebreathe - 33 -

Insert Figure 22.15 here.

Several factors may account for the seeming discrepancy. A statistical cluster phenomenon is possible but becomes less likely with increasing EVA experience. Powell et al. have estimated the chances of not observing severe joint pain (bends) during 37 U.S. EVA's as 17%; addition of the Russian EVA experience drops this probability to 2.2% [46]. Individual variability may also play a role, although most studies made use of subjects highly representative of the current astronaut population. Also, one cannot rule out under reporting, and it should be noted that symptoms of Type I DCS overlap considerably with many of the localized aches and pains incurred with the physical work of EVA. Additionally, it is possible that the microgravity environment itself exerts some protective effect when compared with ground-based simulations. Ventilation/perfusion changes in the lungs may lead to enhanced N2 elimination, although this would most influence the short half-time tissues not thought to be contributory to most DCS symptoms. Fluid shifts and changes in tissue perfusion might affect both the N2 elimination profile and the formation of microbubbles.

Insert Figure 22.16 here.

Perhaps of greatest importance is the fact that use of antigravity musculature is significantly diminished in the weightless environment. In Earth-normal gravity, muscular tensile forces in the lower extremities probably support the formation of micronuclei. It is noted that although the EVA simulations involve primarily upper body work, there is a preponderance of symptoms in the lower extremities [55]. Possible reduction in stress-assisted micronuclei in the weightless environment have been addressed by Powell et al. in the ARGO project [46]. In a random cross-over study, 20 individuals underwent decompression and simulated EVA as ambulatory subjects and after three days of bed rest at - 6 degrees head down tilt (HDT) to reproduce fluid shifts associated with microgravity and simulate the relative hypokinesia of spaceflight. Decompression was from sea level to 45 kPa (6.5 psi), with a TR of 1.78. Although neither group was free of DCS, in all 20 paired exposures Doppler-detectable gas phase was smaller in subjects' bed-rested vs. their ambulatory phase. While the study was too small to make valid inferences on incidence of symptomatic DCS, it does suggest that forces giving rise to DCS are diminished in the relative hypokinesia of spaceflight. - 34 -

Table 22.4 Representative Extravehicular Activity Sorties from the U.S. and Russian programs, showing Nitrogen Tissue Ratio, duration, and metabolic rate.

U.S. PROGRAM DATE OF EVA DURATION TR360* METABOLIC Hr:Min RATE kCal/H (EV1 / EV2) 10/11/84 3:29 1.65 242 / 164 11/12/84 6:13 1.55 154 / 229 11/14/84 6:01 1.59 176 / 212 04/16/85 3:10 1.64 224 / 182 08/31/85 7:20 1.65 205 / 198 09/01/85 4:31 1.43 274 / 200 11/29/85 5:34 1.67 269 / 198 12/01/85 6:46 1.6 232 / 173 04/07/91 4:00 1.3 231 / 242 04/08/91 5:30 1.55 185 / 245

RUSSIAN PROGRAM DATE OF EVA DURATION TR360* METABOLIC Hr:Min RATE kCal/H (EV1 / EV2) 01/26/90 3:02 1.9 232 / 236 02/01/90 4:59 1.8 185 / 146 02/05/90 3:45 1.8 150 / 215 07/17/90 7:00 1.8 / 1.85 206 / 275 07/26/90 3:31 1.8 / 1.9 215 / 258 10/30/90 2:45 1.8 352 / 185 01/07/91 5:18 1.9 206 / 249 01/23/91 5:33 1.8 266 / 249 01/26/91 6:20 1.7 275 / 266 04/25/91 3:34 1.9 249 / 309

* Tissue Ratio TR based on 360 minute half-time tissue, t1/2 = 360 (Data adapted from Barer and Filipenkov, 1991 and Waligora, 1991).

The paradox in observed vs. expected DCS associated with EVA remains unresolved. Although the relative akinesia associated with microgravity exposure appears to play a significant role, a combination of multiple factors seems likely, among which are decreased mobility of the lower extremities in the EMU and improved N2 washout during the prebreathe. Further research efforts will hopefully continue ground-based bed rest studies, and a flight experiment performing on-orbit Doppler monitoring during decompression is proposed. In the interim, a conservative approach which includes treatment options is warranted. - 35 -

The mainstay of DCS treatment on-orbit is commensurate with its Earth-bound requirements - fluids and hyperbaric oxygen, with degree and duration of pressurization dependent on severity of symptoms. Under current EVA protocols, DCS symptoms, should they occur on-orbit, would be treated by repressurizing to maximum cabin atmosphere (110 kPa / 16 psi) immediately and continuing on 100% oxygen. If symptoms do not resolve, maximal suit over-pressure (55 kPa / 8 psi) can be added to this if needed, for a total pressure of 165 kPa (24 psi) [37]. Incurring this overpressure cycle could potentially "ground" the EMU for further EVA operations. If refractory symptoms or type II DCS or aeroembolism occur, de-orbit and landing would be performed as soon as practical. For advanced phase space station operations, an onsite hyperbaric chamber is to be incorporated into a pressure node, capable of delivering 284 kPa, or 2.8 atmospheres [38]. This will facilitate standard DCS treatment protocols utilized in diving and aviation medicine.

The projected increase in EVA operations during construction and maintenance of the space station or any orbital or Lunar construction endeavor fuels an analysis of preventive measures for DCS. Needed is a method which would decrease the pressure differential (and hence N2 TR) while optimally avoiding lengthy O2 prebreathe or staged decompression. The former is impractical and diminishes productive crew time, while the latter prohibits concomitant pressure sensitive experiments. One alternative is to lower the station's cabin atmosphere, similar to the projected 70.3 kPa (10.2 psi) early phase of SSF. This would also necessitate increasing the O2 fraction and raising the fire hazard, but might be a viable plan for the construction phases. With current suit technology, this would still require some period of prebreathe.

The other obvious option is to increase suit pressure. As previously mentioned, Webb et al. showed that eight hour simulated EVA exposures at 65.5 kPa, without prebreathe or staged decompression, were not associated with DCS over five consecutive days [61]. Breathing gas was 100% O2. Current suit technology precludes such high pressures, but advanced development has produced prototypes for 57.2 kPa (8.3 psi) suits with highly specialized joints, which might afford acceptable mobility [17, 54]. From a standard sea level atmosphere, this should give rise to a N2 TR of approximately 1.4, with no prebreathe. The risk of DCS is still present but much diminished, and the suit is termed a "zero-prebreathe system", or ZPS. The combination of an 57.2 kPa suit and a slight decrease in cabin atmosphere might offer complete protection. Time- dependent mathematical models would also allow "staging" of the EMU pressure, thus affording more rapid egress and increased joint mobility at a later time.

Further efforts would be targeted toward diminishing other risk factors. Physical activity should be minimized by providing efficient tools, robotic assist devices, and translational aids for traveling from the EVA airlock to the worksite. Normal fluid/volume status should be ensured. In addition, the relatively common heart condition known as Patent Foramen Ovale (PFO), consisting of a non-closure of a normal communication between the left and right atria remaining from fetal circulation, should be evaluated in the context of EVA. PFO potentially allows transit of bubbles directly into the arterial circulation and has been shown to correlate with more severe symptoms of diving DCS [33]. It is doubtful that some of the 'softer' risk factors such as age and sex will have a role in EVA crew selection. However, orienting a series of EVA simulation studies toward selecting low risk individuals may be warranted. Also, integrating a - 36 -

vascular Doppler ultrasound probe to monitor for the presence of VGE into new generation EVA systems may aid in defining the risk of DCS in microgravity and possibly preventing progression to symptomatic DCS. This concept has been studied for microgravity and altitude chambers [21, 44] and may be implemented in the future as Doppler ultrasound technology matures. In a real sense, the internal pressure of any EVA system will be bounded by mobility on the upper end of the scale and risk of DCS on the lower end.

22.5.1 Ebullism

Ebullism refers to the manifestations of direct exposure of body tissue to a hard vacuum. The vapor pressure of water at body temperature is 47 mmHg, or 6.3 kPa. Fluid components of tissue exposed to ambient pressures at or less than this level can be expected to essentially "boil away". Other responses include bubble formation in blood, mucous membranes, and subcutaneous spaces. Pulmonary barotrauma leading to vascular air burden is caused by rupture of the pulmonary-vascular interface due to the pressure differential, introducing air into the circulatory system. The phenomenon of cerebral air embolism is expected, consisting of circulating gas bubbles traveling to the brain and becoming lodged in the capillary bed. Local effects of ischemia and thrombosis due to blockage of blood flow at the blood-bubble interface would severely compromise brain function. In addition, manifestations of DCS would also be anticipated accompanying such severe decompression events. Of note, ambient pressure of 47 mmHg occurs at an atmospheric altitude of 19,200 m (63,000 ft); this is known as "Armstrong's Line". Thus, loss of cabin pressure above this altitude would render the human occupant vulnerable to the above symptom complex.

Inadvertent exposure to a vacuum is always possible with , and EVA affords a particular risk (e.g., from traumatic loss of suit integrity induced by mechanical puncture). Although it has been popularly thought that exposure to a vacuum would automatically signify a fatal event, a small body of evidence suggests this may not be true. Non- human primate studies performed during the Apollo era involving exposure at 36,580 m (120,000 ft) for 2 1/2 minutes have demonstrated a high rate of survival (94%) and return to baseline function [51]. Human survival following decompressions to pressures well below 47 mmHg have also been documented, with successful outcomes and no resulting neurologic deficit ; one of these involved an exposure of 3-5 minutes [29, 51]. Thus, in the event of an EVA mishap leading to ebullism, every effort should be made to translate the victim to an airlock for repressurization as soon as possible.

Although treatment protocols are not specifically identified for ebullism, it is accepted that hyperbaric oxygen treatment will play a role and most likely contributed heavily to the successful outcome of the human exposure cases noted above. Compression of circulating and embolic gas bubbles will serve to relieve vascular compromise and treat accompanying DCS. Further animal studies will aid in outlining the medical approach to ebullism. In the mean time, it is apparent that hyperbaric capability is a logical expectation for inclusion in manned space ventures involving EVA, whether orbital or surface-based. Ebullism and DCS may be - 37 -

considered occupational hazards of EVA, and along with prevention, an onsite treatment approach must be in place in case of mishap.

22.6 Conclusions

Extravehicular activity in space has proven quite successful over the past four decades, highlighted by the EVA that saved the Skylab module and the numerous EVAs performed to maintain the Mir space station. Looking toward future EVAs, advanced spacesuits should realize the advantage of higher pressurization (57.2 kPa (8.3 psi) to reduce or eliminate prebreathe requirements); enhanced glove dexterity; enhanced reliability, maintainability, and life cycle; and should protect crew members from debris/ impact and radiation. Along with system safety enhancements, onsite medical facilities must be equipped to treat medical events which may result from EVA mishaps, such as DCS: this type of capability is under development for space station Freedom.

Several questions remain concerning EVA and the effects that microgravity and partial gravity have on human performance. Future research efforts should strive to answer the following questions: • How will EVA be utilized in the future for space construction? What will be the allocation of tasks between humans and machines? • W hat are the effects of microgravity and partial gravity on human workload and biomechanics? • Which advanced spacesuit designs will incorporate advanced materials, mobility and automation, in addition to being useful in weightlessness and partial gravity environments? • How can the human role in EVA be optimized? What aids or tools are necessary for future EVAs? • How will spacesuit function and operational demands be balanced with long-term risks of DCS and physiologic requirements? • How will continuous EVA work and exercise alter the risk of DCS? • What treatment profiles are necessary to treat EVA DCS and/or air embolism?

EVA has been an essential enabling capability for initial human exploration of the cosmos. By meeting basic requirements for life support, EVA extends human presence beyond the confines of the spacecraft. Although EVA has had remarkable success, space remains a hostile environment that will not suffer lassitude or indifference. EVA and human presence in space offer great rewards, but must be pursued in the most creative and safest manner possible. - 38 -

APPENDIX A

Outline of 26 separate Prebreathe Procedures used in 607 manned tests conducted at the Johnson Space Center and (1982 – 1986).

No. Prebreathe Procedure

1. 3.5 hours oxygen prebreathe at 14.7 psi prior to 3.0 hours exposure to 4.3 psi. Decompression was rapid. Exercise stressed lower body. N = 11.

2. 12.0 hours at 10.2 psi plus a 40 minute oxygen prebreathe prior to 3.0 hours exposure to 4.3 psi. Decompression was rapid. Exercise stressed lower body. Gas composition at 10.2 psi was 26.5% O2 – 73.5% N2. N = 16. 3. 12.0 hours at 10.2 psi plus a 90 minute oxygen prebreathe prior to 3.0 hours exposure to 4.3 psi. Decompression was rapid. Exercise stressed lower body. Gas composition at 10.2 psi was 26.5% O2 – 73.5% N2. N = 12.

4. 3.5 hours oxygen prebreathe at 14.7 psi prior to 4.0 hours exposure to 4.3 psi. Decompression was gradual and allowed 30 minutes of additional oxygen prebreathe prior to reaching 4.3 psi. Exercise stressed upper body. N = 23.

5. 12.0 hours at 10.2 psi plus a 40 minute oxygen prebreathe prior to 4.0 hours exposure to 4.3 psi. Decompression was gradual and allowed 25 minutes of additional oxygen prebreathe prior to reaching 4.3 psi. Exercise stressed upper body. Gas composition at 10.2 psi was 26.5% O2 – 73.5% N2. N = 23.

6. 4.0 hours oxygen prebreathe at 14.7 psi prior to 6.0 hours exposure to 4.3 psi. Decompression was gradual and allowed 30 minutes of additional oxygen prebreathe prior to reaching 4.3 psi. Exercise stressed upper body. N = 28.

7. Same procedure as No. 6, except crew returned to 14.7 psi for 17.0 hours. Second EVA began after 4.0 hours oxygen prebreathe at 14.7 psi prior to second 6.0-hour exposure to 4.3 psi. Decompression was gradual and allowed 30 minutes of additional oxygen prebreathe prior to reaching 4.3 psi. Exercise stressed upper body. N = 14.

8. 60 minute oxygen prebreathe at 14.7 psi followed by 12.0 hours at 10.2 psi plus an additional 40 minute oxygen prebreathe prior to 6.0 hours exposure to 4.3 psi. Decompression was gradual and allowed 25 minutes of additional oxygen prebreathe prior to reaching 4.3 psi. Exercise stressed upper body. Gas composition at 10.2 psi was 26.5% O2 – 73.5% N2. N = 35.

9. Same procedure as No. 8, except crew returned to 10.2 psi for 17.0 hours. Second EVA began after 40 minutes of oxygen prebreathe at 10.2 psi prior to second 6.0-hour exposure - 39 -

to 4.3 psi. Decompression was gradual and allowed 25 minutes of additional oxygen prebreathe prior to reaching 4.3 psi. Exercise stressed upper body. N = 12.

10. 60 minute oxygen prebreathe at 14.7 psi followed by 12.0 hours at 10.2 psi plus an additional 40 minute oxygen prebreathe prior to 3.0 hours exposure to 4.3 psi. This was the first of two exposures in the same day. Decompression was gradual and allowed 25 minutes of additional oxygen prebreathe prior to reaching 4.3 psi. Gas composition at 10.2 psi was 26.5% O2 – 73.5% N2. N = 12.

11. Same procedure as No. 10. Crew then returned to 10.2 psi for 80 minutes. A 40-minute oxygen prebreathe was then performed prior to a second 3.0-hour exposure to 4.3 psi in the same day. Decompression was gradual and allowed 25 minutes of additional oxygen prebreathe prior to reaching 4.3 psi. N = 12.

12. Same procedure as No. 10 plus No. 11, except crew returned to 10.2 psi for 14.0 hours. First EVA of second day began with a 40-minute oxygen prebreathe prior to a 3.0-hour exposure to 4.3 psi. Decompression was gradual and allowed 25 minutes of additional oxygen prebreathe prior to reaching 4.3 psi. N = 12.

13. Same procedure as No. 8 plus No. 11 plus No. 12. Crew then returned to 10.2 psi for 80 minutes. A 40-minute oxygen prebreathe was then performed prior to a second 3.0-hour exposure of the second day EVA to 4.3 psi. Decompression was gradual and allowed 25 minutes of additional oxygen prebreathe prior to reaching 4.3 psi. N = 12.

14. Same procedure as No. 10 plus No. 11 plus No. 12 plus No. 13, except crew returned to 10.2 psi for 14.0 hours. First EVA of third day began with a 40-minute oxygen prebreathe prior to a 3.0-hour exposure to 4.3 psi. Decompression was gradual and allowed 25 minutes of additional oxygen prebreathe prior to reaching 4.3 psi. N = 12.

15. Same procedure as No. 10 plus No. 11 plus No. 12 plus No. 13 plus No. 14. Crew then returned to 10.2 psi for 80 minutes. A 40-minute oxygen prebreathe was then performed prior to a second 3.0-hour exposure of the third day EVA to 4.3 psi. Decompression was gradual and allowed 25 minutes of additional oxygen prebreathe prior to reaching 4.3 psi. N = 12.

16. Exposure to 7.8 psi for 6.0 hours using 50% O2 – 50% N2 mixture without prior oxygen prebreathe. Decompression required 10 minutes. Exercise stressed upper body. This was the first of a multiple exposure series separated by 18.0 hours at sea level conditions. N = 32.

16a. Same as No. 16, except females were tested. N = 32.

17. Same as No. 16, except crew returned to 14.7 psi for 18.0 hours prior to their second 6.0-hour exposure to 7.8 psi. No prebreathe prior to the 10 minute decompression. N = 31.

17a. Same as No. 17, except females were tested. N = 31. - 40 -

18. Same as No. 16 plus No. 17, except crew returned to 14.7 psi for 18.0 hours prior to their third 6.0-hour exposure to 7.8 psi. N = 31.

18a. Same as No. 18, except females were tested. N = 29.

19. Exposure to 9.0 psi for 6.0 hours without prior oxygen prebreathe. Decompression required 10 minutes. Exercise stressed upper body and 50% O2 – 50% N2 was used. Pilot study using susceptible subjects. % VGE data in these tests were reduced by 1/2 since the tested group was selected for its susceptibility to develop VGE. A randomly selected group would probably have developed the listed % VGE with the given prebreathe procedure. N = 16.

20. Exposure to 20.0 psi for 6.0 hours without prior oxygen prebreathe. Decompression required 10 minutes. Exercise stressed upper body and 50% O2 – 50% N2 was used. Pilot study using susceptible subjects. % VGE data in these tests were reduced by 1/2 since the tested group was selected for its susceptibility to develop VGE. A randomly selected group would probably have developed the listed % VGE with the given prebreathe procedure. N = 8.

21. Exposure to 8.5 psi for 6.0 hours without prior oxygen prebreathe. Decompression required 10 minutes. Exercise stressed upper body. Pilot study using susceptible subjects. % VGE data in these tests were reduced by 1/2 since the tested group was selected for its susceptibility to develop VGE. A randomly selected group would probably have developed the listed % VGE with the given prebreathe procedure. N = 9.

22. Exposure to 9.5 psi for 6.0 hours using 50% O2 – 50% N2 mixture without prior oxygen prebreathe. Decompression required 10 minutes. Exercise stressed upper body. Pilot study using susceptible subjects. % VGE data in these tests were reduced by 1/2 since the tested group was selected for its susceptibility to develop VGE. A randomly selected group would probably have developed the listed % VGE with the given prebreathe procedure. N = 6.

22a. Same as No. 22, except females were tested. N = 1.

22b. Same as No. 22, except males were tested (extended test). N = 20.

23. 6.0 hours oxygen prebreathe at 14.7 psi prior to 6.0 hours exposure to 4.3 psi. Decompression required 10 minutes. Exercise stressed upper body. N = 19.

23a. Same as No. 23, except females were tested. N = 19.

24. 8.0 hours oxygen prebreathe at 14.7 psi prior to 6.0 hours exposure to 4.3 psi. Decompression required 10 minutes. Exercise stressed upper body. N = 8.

25. 2.0 hours oxygen prebreathe at 14.7 psi prior to 24.0 hours at 10.2 psi. 15-minute decompression from 14.7 psi to 10.2 psi was included as a portion of the 2.0-hour oxygen prebreathe. 10-minute decompression from 10.2 psi to 6.0 psi after 24.0 hours. Subjects - 41 -

exercised 6.0 hours while breathing 60% O2 – 40% N2 mixture. Exercise stressed upper body. Gas composition at 10.2 psi was 28% O2 – 28% N2. N = 15.

25a. Same as No. 25, except females were tested. N = 14.

26. Exposure to 8.3 psi for 6.0 hours without prior oxygen prebreathe. Decompression required 10 minutes. Exercise stressed upper body and 50% O2 – 50% N2 mixture was used. N = 20.

26a. Same as No. 26, except females were tested. N = 11. - 42 -

ACKNOWLEDGMENTS

Thanks to the Man-Vehicle Laboratory at the Institute of Technology (MIT) in Cambridge, MA, U. S. A. – specifically: Dr. Laurence Young, Dr. Dave Akin, Dr. Harold Alexander, Dr. Daniel Merfeld, and Sherwood Modestino. Research sponsorship from NASA Ames Research Center, Moffett Field, CA, U. S. A. – thanks to the Extravehicular Systems Branch. Additional research sponsorship from NASA Johnson Space Center is acknowledged. The edits and recommendations of Dr. James Waligora, Dr. Michael Powell, and Dr. William Norfleet from NASA Johnson Space Center are greatly appreciated. The suggestions of Richard Wilde of United Technologies Hamilton Standard are also acknowledged.

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17. C. Flugel, J. Kosmo, and J. Rayfield. Development of a Zero-Prebreathe . SAE 840981 Proceedings of the 14th Intersociety Conference on Environmental Systems. San Diego, CA. July 1984.

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20. P. Furr, C. Monson, W. Sears, F. Abeles. Physiological Aspects of EVA. SAE 860991. Proceedings of the 16th Intersociety Conference on Environmental Systems. San Diego, CA, July 1986.

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22. R. Heimbach and P. Sheffield. Decompression Sickness and Pulmonary Overpressure Accidents. In: Fundamentals of Aerospace Medicine. DeHart, ed. Lea and Febiger, Philadelphia, PA., pp. 132-161, 1985. - 44 -

23. C. Helmke. Soviet Manned Maneuvering Unit. US Air Force Foreign Technology Division (AFSC). FTD-2660P-127/58-90, 1990.

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25. D. Horrigan. Shuttle and Space Station EVA. Proceedings of the 1990 Hypobaric Decompression Workshop, Crew Technology Division, Brooks Air Force Base, TX. AL-SR- 1992-0005, June 1992.

26. Jenkins. Human Anatomy. Medical School Lecture, Fall term, 1991.

27. E. Jones and H. Schmitt. Pressure Suit Requirements for Moon and Mars EVA's. Paper Number LA-UR-91-3083. Proceedings, Space '92, American Society of Civil Engineers, , CO. May 1992.

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29. G. Kolesari and E. Kindwall. Survival Following Accidental Decompression to an Altitude Greater Than 74,000 Feet (22,555 m). Aviat. Space Environ. Med. 53(12):1211- 1214, 1982.

30. R. Margaria. Biomechanics of human locomotion. In: Biomechanics and Energetics of Muscular Exercise. Cambridge University Press, Cambridge, England, pp. 67-139, 1976.

31. P. McCormack and D. Natchwey. Radiation Exposure Issues. In: Space Physiology and Medicine (2nd Ed.). A. Nicogossian, C. Huntoon, and S. Pool, eds. Lea and Febiger, Philadelphia, PA, pp. 328-348, 1989.

32. S. Mochon and T. McMahon. Ballistic Walking: An Improved Model. Mathematical Biosciences. 52:241-260, 1981.

33. R. Moon, E. Camporesi, and J. Kisslo. Patent Foramen Ovale and Decompression Sickness in Divers. The Lancet, I:513-14, 1989.

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Figure Legends

Figure 22.1 The First Spacewalk: Voskhod 2 EVA Sequence.

Figure 22.2 On the Soyuz T-12 flight of July 1984, Svetlana Savitskaya became the first woman to be launched for a second time and the first to perform a spacewalk.

Figure 22.3 Astronaut Bruce McCandless Using the Man Maneuvering Unit for the First Time.

Figure 22.4 Extravehicular Mobility Unit (EMU) Spacesuit Components.

Figure 22.5 Cylindrical, fabric spacesuit component upright (left) and deformed joint (right).

Figure 22.6 Spacesuit elbow joint with constant centerline length and flexed spacesuit joint. The force trying to elongate joint due to spacesuit internal pressure, F=PA.

Figure 22.7 Advanced Prototypical High Pressure Spacesuit Design: The AX-5.

Figure 22.8 Pelvic rotation during walking. The pelvis is rotated from side-to-side about the longitudinal axis of the body.

Figure 22.9 Pelvic tilt during walking. A 5o downward tilt of the pelvis is seen on the swing phase side.

Figure 22.10 A) Heel strike. The foot plantar flexes which lowers the ankle as the foot contacts the ground. B) Heel-off interactions with the knee. Heel-off keeps the excursion of the center of gravity to a minimum.

Figure 22.11 Mean peak force versus gravity level for partial gravity simulation experiments for various treadmill velocities, V. Each point is the mean and the error bars are the standard deviations of the means. Peak force is significantly reduced as gravity level is decreased (p<0.05) for all speeds of locomotion (From Newman, 1992, pg. 114). - 49 -

Figure 22.12 Mean stride frequency versus gravity level for all partial gravity simulation experiments. Each point is the mean and the error bars are the standard deviations of the means. A reduction in stride frequency for lunar (1/6-g) and Martian (3/8-g) locomotion is seen from normal 1 g values. The reduction in stride frequency is associated with an increase in stride length at the partial gravity simulations (From Newman, 1992, pg. 114).

Figure 22.13 Stepping frequency for Apollo 11 data and simulated lunar gravity. This is some of the only biomechanics data obtained from the Apollo lunar missions. Stepping frequency for terrestrial locomotion is also plotted. The Apollo data and simulated lunar data show a reduction in stepping frequency as compared to the terrestrial data, especially for locomotion at velocities of 1.5 m/s and 2.3 m/s (From Newman, 1992, pg. 110).

Figure 22.14 Cost of Transport (CoT) versus gravity level. All data points have the resting metabolic cost subtracted out, thus the CoT results show the extra energy cost of locomotion for the various gravity levels. Running at 3 m/s is seen to be more economical at gravity levels below 1/2 g and walking at 1 m/s is the most economical gait from 1/2 g to 1 g (From Farley and McMahon, 1992).

Figure 22.15 Staged Decompression Protocol for Shuttle EVA (12 Hour Intermediate Pressure Stage Option).

Figure 22 16 Incidence of Venous Gas Emboli (bubbles) and DCS during simulated EVA based on TR. (From Waligora et al., 1987). - 50 -

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Figure 22.2 On the Soyuz T-12 flight of July 1984, Svetlana Savitskaya became the first woman to be launched for a second time and the first to perform a spacewalk. - 53 -

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Figure 22.3 Astronaut Bruce McCandless Using the Man Maneuvering Unit for the First Time. - 54 -

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Figure 22.4 Extravehicular Mobility Unit (EMU) Spacesuit Components. - 56 -

L

L

D Θ

Axial Restraint Line Excess Fabric F=PA Opening to Increase Volume

Inside Outside

Volume being lost as Joint Folds - 57 -

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Figure 22.7 Advanced Prototypical High Pressure Spacesuit Design: The AX-5. - 58 -

V = 0.5 m/s 2 V = 1.5 m/s V = 2.3 m/s KC-135, V = 2 m/s 1.6

1.2 Martian 0.8 Lunar rce, eak 0.4 o P F f (kN) max

0 0 0.2 0.4 0.6 0.8 1 Error bars are SD Gravity Level (g) Immersion n=6 Parabolic flight n=2

V = 0.5 m/s

in) V = 1.5 m/s 80 V = 2.3 m/s

s/m KC-135, V = 2 m/s 70

60 y (stride

nc 50

que 40 Fre 30

Stride 20 n

a 0 0.2 0.4 0.6 0.8 1 1.2

e Error bars are SD Gravity Level (g) Immersion n=6 M Parabolic flight n=2 - 59 -

Earth gravity 3 Apollo 11 lunar data* Simulated lunar gravity 2.5 1 g

2

1.5 Lunar g

1

0.5

Stepping Frequency (steps/sec) 0 0 0.5 1 1.5 2 2.5 Velocity (m/s) * Stone, R.W. (1971) Man in Space.

HFS, V = 1 m/s HFS, V = 3 m/s * 4

3

2

1

0

Mean Cost of Transport [J/(kg m)] 0 0.2 0.4 0.6 0.8 1 1.2 Gravity level (g) - 60 -

14.7 100% O2 101.3 80% N2 x 60 min 100% O2 20% O2

10.2 74% N2/26% O2 70.3 Shuttle cabin Don Suit Return to 10.2 psi if decompressed 75 min 100% further EVA to intermediate O2 prebreathe 4.3 pressure stage EVA expected 29.6 Suit Pressure

0 Time Hours 0 2 4 6 8 10 12 14 16 18 20 22 24 - 61 -

Data on DCS and VGE incidence from 49 tests with n=925 Data on Grade 3 DCS incidence from 42 tests with n=689 100

90 At TR = 1.65 80 VGE = 59.3% VGE DCS = 23.4% 70 Grade 3 DCS = 4.7% DCS 60 At TR = 1.40 VGE = 31.2% 50 DCS = 4.5% Grade 3 DCS = 1.1% 40

30

20 Grade 3 DCS 10

0 0.8 1 1.2 1.4 1.6 1.8 2 360 Minute Tissue Ratio