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Chapter 22
LIFE SUPPORT AND PERFORMANCE ISSUES FOR
EXTRAVEHICULAR ACTIVITY (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 Earth orbit
or beyond – to lunar or Martian environments, the nature and extent of human participation in
space exploration and habitation are key considerations. Adequate protection for humans in
orbital space or planetary surface environments must be provided. The Space Shuttle, Mir Space
Station, Salyut-Soyuz, and Apollo 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 vacuum 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 longduration 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
spacecraft 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 astronaut 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 pressure suit
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 Moon and Mars require advanced EVA hardware
and performance capabilities.
22.2
Historical Background
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In March of 1965, cosmonaut Alexei Leonov 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 Voskhod 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 weightlessness. 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 Apollo program, EVA became a useful mode of functioning in space, rather
than just an experimental activity. Twelve crew members spent a total of 160 hours in spacesuits
on the moon, covering 100 kilometers (60 miles) on foot and with the lunar rover, while
collecting
2196 soil and rock samples. The Apollo EVAs were of unprecedented historical importance as
Neil Armstrong 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 decompression sickness after this depressurization, the astronauts
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 Apollo 11
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 Skylab 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 airlock 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.
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After a nine year lapse in Russian extravehicular activity, cosmonaut Georgi Grechko
performed a critical EVA to examine the cone of the Salyut 6 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 months. The success of the Salyut 6 program during 1977–1981 brought about the Salyut 7
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 spaceflight (Her first flight
was in August 1982.), cosmonaut Svetlana Savitskaya 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 Manned Maneuvering Unit (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 satellites, 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 selfcontained 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: Kennedy Space Center, 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,
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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 Space Station Freedom 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 Satellite VI (INTELSAT 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 Space Telescope 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. Story Musgrave (payload commander), Jeff Hoffman,
Thomas Akers, 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 optics. 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
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During the last decade, EVA has been regularly performed by Russian cosmonauts. Yuri
Romanenko 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
Moscow 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 Musa Manarov 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.
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Table 22.1
Summary of Russian and American Extravehicular Activity (EVA). Edited from [35, 43].
Year
Mission
EVA Date
Cosmonauts/Astronauts
Duration
1965
Voskhod 2
Gemini 4
Gemini 9-A
Gemini 10
Soyuz 4/5
March 18
June 6
June 5
July 19
July 20
Sep. 13
Sep. 14
Nov. 12
Nov. 13
Nov. 14
Jan. 16
24 min
23 min
2 hr 10 min
49 min
38 min
33 min
2 hr 8 min
2 hr 29 min
2 hr 6 min
55 min
1 hr
Apollo 9
March 6
Apollo 11
July 21
Apollo 12
Nov. 19
Alexei Leonov
Edward Whitea,b
Eugene Cernana
Michael Collinsa
Michael Collinsa
Richard Gordona
Richard Gordona,b
Edwin "Buzz" Aldrina,b
Edwin Aldrin
Edwin Aldrina,b
Yevgeny Khrunovc
Alexei Yeliseyev
Russell Schweickart
David Scottb
Neil Armstrongd
Edwin Aldrin
Charles Conradd
Alan Bean
Charles Conradd
Alan Bean
Alan Shepardd
Edgar Mitchell
Alan Shepardd
Edgar Mitchell
David Scotte
David Scottd
James Irwin
David Scottd
James Irwin
David Scottd
James Irwin
Alfred Wordenf
James Irwinf,b
John Youngd
Charles Duke
John Youngd
Charles Duke
John Youngd
Charles Duke
Thomas Mattinglyf
Charles Dukef
Eugene Cernand
Harrison Schmitt
1966
Gemini 11
Gemini 12 1969
Nov. 20
1971
Apollo 14
Feb. 5
Feb. 6
Apollo 15
July 30
July 31
August 1
August 2
August 5
1972
Apollo 16
April 21
April 22
April 23
April 25
Apollo 17
Dec. 11
1 hr 7 min
1 hr 1 min
2 hr 48 min
4 hr
3 hr 46 min
4 hr 48 min
4 hr 35 min
33 min
6 hr 33 min
7 hr 12 min
4 hr 50 min
38 min
38 min
7 hr 11 min
7 hr 23 min
5 hr 40 in
1 hr 24 in
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.
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Table 22.1 (cont.): Summary of Russian and American Extravehicular Activity (EVA).
Year
Mission
EVA Date
1972
Apollo 17
Dec. 12
Dec. 13
Dec. 17
1973
Skylab 2
May 25
June 7
June 19
Skylab 3
August 6
August 24
Sep. 22
Skylab 4
Nov. 22
Dec. 25
Dec. 29
1974
Skylab 4
Feb. 3
1977
Salyut 6-Soyuz 26
Dec. 20
1978
Salyut 6-Soyuz 29
July 29
1979
1982
Salyut 6-Soyuz 32
August 15
(Soyuz 34 at station time of EVA)
Salyut 7-Soyuz T-5
1983
STS-6
April 7
Salyut 7-Soyuz T-9
Nov. 1
Nov. 3
1984
41-B
Feb. 7
Feb. 9
41-C
April 8
April 11
Cosmonauts/Astronauts
Eugene Cernand,g
Harrison Schmittg
Eugene Cernand,h
Harrison Schmitt
Ronald Evansf
Harrison Schmittf
Paul Weitzb
Charles "Pete" Conrad
Joseph Kerwin
Charles Conrad
Paul Weitz
Owen Garriott
Jack Lousma
Owen Garriott
Jack Lousma
Owen Garriott
Alan Bean
Edward Gibson
William Pogue
Gerald Carr
William Pogue
Edward Gibson
Gerald Carr
Edward Gibson
Gerald Carr
Georgi Grechko
Yuri Romanenkoi
Vladimir Kovalyonok
Alexander Ivanchenkov
Vladimir Lyakhov
Valery Ryumin
Anatoly Berezovoi
Valentin Lebedev
F. Story Musgrave
Donald Peterson
Vladimir Lyakhov
Alexander Alexandrov
Vladimir Lyakhov
Alexander Alexandrov
Bruce McCandlessj
Robert Stewart
Bruce McCandless
Robert Stewart
George Nelson
James Van Hoften
George Nelson
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.
Duration
7 hr 37 min
7 hr 15 min
1 hr 6 min
1 hr 6 min
35 min
3 hr 23 min
1 hr 36 min
6 hr 31 min
4 hr 30 min
2 hr 41 min
3 hr 29 min
6 hr 34 min
7 hr 3 min
3 hr 29 min
5 hr 19 min
1 hr 28 min
2 hr 5 min
1 hr 23 min
2 hr 33 min
4 hr 17 min
2 hr 50 min
2 hr 55 min
5 hr 30 min
6 hr
3 hr
6 hr
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Table 22.1 (cont.): Summary of Russian and American Extravehicular Activity (EVA).
Year
Mission
1984 Salyut 7-Soyuz T-10
April 23
(Soyuz T-11 at station time of EVA)
Salyut 7-Soyuz T-10
April 26
(Soyuz T-11 at station time of EVA)
Salyut 7-Soyuz T-10
April 29
(Soyuz T-11 at station time of EVA)
Salyut 7-Soyuz T-10
May 4
(Soyuz T-11 at station time of EVA)
Salyut 7-Soyuz T-10
May 18
(Soyuz T-11 at station time of EVA)
Salyut 7-Soyuz T-10
July 25
(Soyuz T-10/T-11 crew there also)
Salyut 7-Soyuz T-10
August 8
(Soyuz T-11 at station time of EVA)
41-G
Oct. 11
51-A
EVA Date
Nov. 12
Nov. 14
1985
51-D
April 12
Salyut 7-Soyuz T-13
August 2
51-I
August 31
Sep. 1
61-B
Dec. 1
Dec. 3
1986 1987
Soyuz T-15
May 28
(Transfer from Mir to Salyut 7)
Soyuz TM-2 (Mir)
April 12
June 12
June 16
1988
1990
Soyuz TM-4 (Mir)
Feb. 26
Mir
Oct. 20
Mir
Jan. 9
Mir
Jan. 11
Mir
Jan. 26
Mir
Feb. 1
Mir
Feb. 5
Soyuz TM-9/Mir
July 18
Cosmonauts/Astronauts
Duration
Leonid Kizim
Vladimir Solovyov
Leonid Kizim
Vladimir Solovyov
Leonid Kizim
Vladimir Solovyov
Leonid Kizim
Vladimir Solovyov
Leonid Kizim
Vladimir Solovyov
Svetlana Savitskayak
Vladimir Dzhanibekov
Leonid Kizim
Vladimir Solovyov
Kathryn Sullivan
David Leestma
Joseph Allen
Dale Gardner
Joseph Allen
Dale Gardner
Jeff Hoffman
David Griggs
Vladimir Dzhanibekov
Viktor Savinykh
James Van Hoften
William Fisher
James Van Hoften
William Fisher
Jerry Ross
Sherwood Spring
Jerry Ross
Sherwood Spring
Leonid Kizim
Vladimir Solovyov
Alexander Laveikin
Yuri Romanenko
Alexander Laveikin
Yuri Romanenko
Alexander Laveikin
Yuri Romanenko
Vladimir Titov
Musa Manarov
Vladimir Titov
Musa Manarov
Alexander Serebrov
Alexander Viktorenko
Alexander Serebrov
Alexander Viktorenko
Alexander Serebrov
Alexander Viktorenko
Alexander Serebrov
Alexander Viktorenko
Alexander Viktorenko
Jean Carpe Chveteu
Anatoly Solovyov
Alexander Balandin
4 hr 15 min k First woman to perform EVA, first woman to make a second spaceflight.
5 hr
2 hr 45 min 2 hr 45 min 3 hr 5 min 3 hr 35 min 5 hr
3 hr 29 min 6 hr
5 hr 42 min 3 hr 7 min 5 hr
7 hr 8 min 4 hr 32 min 5 hr 32 min 5 hr 42 min 3 hr 50 min 3 hr 40 min 3 hr 15 min 1 hr 53 min 4 hr 25 min 4 hr 3 hr
2 hr 54 min 3 hr 2 min 4 hr 59 min 3 hr 45 min 6 hr
- 9 -
Table 22.1 (cont.): Summary of Russian and American Extravehicular Activity (EVA).
1990
1991
Mir
July 26
Mir
Oct. 30
Mir
Jan. 7
Jan. 23
Jan. 26
STS-37
April 14
April 15
1992
Mir
April 26
STS-49
May
May
1993
Mir
July 8
STS-54
Jan. 17
STS-57
June 25
STS-61
(HST SM-01)
Dec. 5
Dec. 6
Dec. 7
Dec. 8
Dec. 9
22.3
22.3.1
Anatoly Solovyov
Alexander Balandin
Gennadiy Manakov
Gennadiy Strekalov
Viktor Afanasyev
Musa Manarov
Viktor Afanasyev
Musa Manarov
Viktor Afanasyev
Musa Manarov
Jerry Ross
Jay Apt
Jerry Ross
Jay Apt
Viktor Afanasyev
Musa Manarov
Pierre Thout
Rick Hieb
Kathryn Thornton
Tom Akers
Pierre Thoutl
Rick Hiebl
Tom Akersl
Alexander Viktorenko
Alexander Kaleriy
Mario Runco
Gregory Harbaugh
G. David Low
Jeff Wisoff
F. Story Musgrave
Jeff Hoffman
Kathryn Thornton
Tom Akers
F. Story Musgrave
Jeff Hoffman
Kathryn Thornton
Tom Akersm
F. Story Musgrave
Jeff Hoffman
3 hr 31 min 2 hr 45 min 5 hr 18 min 5 hr 33 min 6 hr 20 min 4 hr 38 min 6 hr 11 min 3 hr 34 min 17:42 total 17:42 total 7 hr 45 min 16:14 total 8 hr 29 min 8 hr 29 min 8 hr 29 min 2 hr 3 min 4 hr 27 min 5 hr 30 min 7 hr 54 min 6 hr 36 min 6 hr 47 min 6 hr 50 min 7 hr 21 min Spacesuit Design
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 hard upper torso 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 "Snoopy cap". 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)
0g
151 kcal/hr
Skylab 0g
238 kcal/hr (Apollo spacesuit)
STS 0g
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 Johnson Space Center in Houston, Texas. 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 engineering 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(V2 − V1 ) = p(V1 − V 2 )
22.2
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
V1 = AL = D2 L
22.3
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.
Dθ
πD2
πD2 L π D3θ
V 2 = A¢ =
(L −
)=
−
22.4
4
4
2
8
where q is the deformation joint angle. Substituting into Equation 22.2 yields:
W = p(V1 − V2 ) = p[(
pπ D3θ
πD2 L
πD2 L πD3θ
)−(
−
)] =
4
4
8
8
22.5
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
pπ D3 θ
W
pπ D 3
Lθ
8
approximation for this distance, ( ) , leads to: F =
=
=
22.6
Lθ
d
4L
2
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
Finger
Wrist
Elbow
Knee
Waist
Diameter, D
cm (in)
Length, L cm
Force
Force design
Human
(in)
calculated, N spec. N (lb) Capability N
(lb)
(lb)
2.54 (1)
5.08 (2)
7.57 (1.7)
No data
31-71 (7-16)
10.16 (4)
12.70 (5)
192.24 (43.2)
No data
No data
12.70 (5)
20.32 (8)
234.96 (52.8)
6.68 (1.5) 155.75 (≈35)
15.24 (6)
12.70 (5)
405.84 (91.2)
6.68 (1.5)
No data
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 stateof-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, micrometeorites, 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 midphase 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 general 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 fellow 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
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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 weeks 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 sun 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 overexertion. 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 Low Earth Orbit
(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 sealevel 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 postdecompression. 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
week. 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.
DATE OF EVA
U.S. PROGRAM
DURATION
TR360*
Hr:Min
10/11/84
11/12/84
11/14/84
04/16/85
08/31/85
09/01/85
11/29/85
12/01/85
04/07/91
04/08/91
3:29
6:13
6:01
3:10
7:20
4:31
5:34
6:46
4:00
5:30
DATE OF EVA
RUSSIAN PROGRAM
DURATION
TR360*
Hr:Min
01/26/90
02/01/90
02/05/90
07/17/90
07/26/90
10/30/90
01/07/91
01/23/91
01/26/91
04/25/91
3:02
4:59
3:45
7:00
3:31
2:45
5:18
5:33
6:20
3:34
1.65
1.55
1.59
1.64
1.65
1.43
1.67
1.6
1.3
1.55
1.9
1.8
1.8
1.8 / 1.85
1.8 / 1.9
1.8
1.9
1.8
1.7
1.9
METABOLIC
RATE
kCal/H
(EV1 / EV2)
242 / 164
154 / 229
176 / 212
224 / 182
205 / 198
274 / 200
269 / 198
232 / 173
231 / 242
185 / 245
METABOLIC
RATE
kCal/H
(EV1 / EV2)
232 / 236
185 / 146
150 / 215
206 / 275
215 / 258
352 / 185
206 / 249
266 / 249
275 / 266
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. Timedependent 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 human presence in space, 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. Nonhuman 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/micrometeorite 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 Brooks Air Force Base (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 Massachusetts 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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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 -
Reduce Original Figure by 25% (figure on this page is 75% of original size)
Figure is from The Soviet Manned Program by P. Clark
ISBN 0-517-56954-X / p. 30
- 51 -
- 52 -
Reduce Original Figure by 15% (figure on this page is 85% of original size)
Figure is from The Soviet Manned Program by P.Clark ISBN 0-517-56954-X / p. 141 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 -
Reduce Original Figure by 50%
(figure on this page is 85% original size)
Photo is NASA registered.
Figure 22.3 Astronaut Bruce McCandless Using the Man Maneuvering Unit for the First Time. - 54 -
Reduce Original Figure by 15%
(figure on this page is 85% original size)
- 55 -
Figure 22.4 Extravehicular Mobility Unit (EMU) Spacesuit Components.
- 56 -
L
L
Θ
D
F=PA
Inside
Axial Restraint Line
Outside
Volume being lost
as Joint Folds
Excess Fabric
Opening to Increase
Volume
- 57 -
Reduce Original Figure by 15%
(figure on this page is 85% of original size)
Photo is NASA registered.
Figure 22.7 Advanced Prototypical High Pressure Spacesuit Design: The AX-5.
- 58 -
V = 0.5 m/s
V = 1.5 m/s
V = 2.3 m/s
KC-135, V = 2 m/s
2
1.6
1.2
Lunar
f
0.4
max
Force,
Peak
0.8
(kN)
Martian
0
Mean Stride Frequency (strides/min)
0
0.2
0.4
0.6
0.8
Gravity Level (g)
1
Error bars are SD
Immersion n=6
Parabolic flight n=2
V = 0.5 m/s
V = 1.5 m/s
V = 2.3 m/s
KC-135, V = 2 m/s
80
70
60
50
40
30
20
0
0.2
0.4
0.6
0.8
Gravity Level (g)
1
1.2
Error bars are SD
Immersion n=6
Parabolic flight n=2
- 59 -
Stepping Frequency (steps/sec)
Earth gravity
Apollo 11 lunar data*
3
Simulated lunar gravity
2.5
1g
2
Lunar g
1.5
1
0.5
0
0
0.5
1
1.5
Velocity (m/s)
2
2.5
Mean Cost of Transport [J/(kg* m)]
* Stone, R.W. (1971) Man in Space.
HFS, V = 1 m/s
HFS, V = 3 m/s
4
3
2
1
0
0
0.2
0.4
0.6
0.8
Gravity level (g)
1
1.2
- 60 -
14.7
101.3
100% O2
x 60 min
80% N2
20% O2
74% N2/26% O2
10.2
70.3
4.3
29.6
0
100% O2
Return to
10.2 psi if
further EVA
expected
Don Suit
Shuttle cabin
decompressed
to intermediate
pressure stage
75 min 100%
O2 prebreathe
EVA
Suit Pressure
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
VGE = 59.3%
DCS = 23.4%
Grade 3 DCS = 4.7%
80
70
60
VGE
DCS
At TR = 1.40
VGE = 31.2%
DCS = 4.5%
Grade 3 DCS = 1.1%
50
40
30
20
Grade 3 DCS
10
0
0.8
1
1.2
1.4
360 Minute Tissue Ratio
1.6
1.8
2