The purpose was to investigate efficiency as related to the work transmission and the metabolic cost of various extravehicular activity (EVA) tasks during simulated microgravity (whole body water immersion) using three space suits. Two new prototype space station suits, AX-5 and MKIII, are pressurized at 57.2 kPa and were tested concurrently with the operationally used 29.6 kPa shuttle suit. Four male astronauts were asked to perform a fatigue trial on four upper extremity exercises during which metabolic rate and work output were measured and efficiency was calculated in each suit. The activities were selected to simulate actual EVA tasks. The test article was an underwater dynamometry system to which the astronauts were secured by foot restraints. All metabolic data was acquired, calculated, and stored using a computerized indirect calorimetry system connected to the suit ventilation/gas supply control console. During the efficiency testing, steady state metabolic rate could be evaluated as well as work transmitted to the dynamometer. Mechanical efficiency could then be calculated for each astronaut in each suit performing each movement

Gilbert, John H.

Greenisen, Michael C.

Newton, Frederick K.

Squires, William G.

West, Phillip

English

NASA Technical Reports Server

NASA
Technical
Paper
3153
1991
National Aeronautics and
Space Administration
Office of Management
Scientific and Technical
Information Program
A Method of Evaluating
Efficiency During Space-
Suited Work in a Neutral
Buoyancy Environment
Michael C. Greenisen,
Phillip West,
and Frederick K. Newton
Lyndon B. Johnson Space Center
Houston, Texas
John H. Gilbert
KRUG International
Houston, Texas
William G. Squires
Texas Lutheran College
Seguin, Texas
https://ntrs.nasa.gov/search.jsp?R=19920010530 2020-03-17T13:25:34+00:00Z
111Ii
CONTENTS
ABSTRACT ....................................................
INTRODUCTION ................................................
METHODS ....................................................
DISCUSSION ..................................................
RESULTS .....................................................
REFERENCES .................................................
Page
1
1
1
2
3
5
FIGURES
Efficiency Test Protocol (WETF Neutral Buoyancy Environment) ......
Average Dynamic Force Production During the Ratchet
Wrench Push ..........................................
Ratchet Wrench Push: Mean Metabolic Rate and Mean Force
Production During Fatigue Trial ............................
Mean Mechanical Efficiencies Achieved in Each Suit ..............
6
6
7
7
• !
Ill PRECEDING PAGE BLANK NOT FILMED
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ABSTRACT
The purpose of this study was to investigate efficiency as related to the work transmission
and the metabolic cost of various extravehicular activity (EVA) tasks during simulated
microgravity (whole body water immersion) using three space suits. Two new prototype
space station suits, the AX-5 and MKIII, are pressurized at 57.2 kPa (8.3 psi) and were
tested concurrently with the operationally used 29.6 kPa (4.3 psi) shuttle suit. Subjects
were four male astronauts who were asked to perform a fatigue trial on four upper-
extremity exercises during which metabolic rate and work output were measured and
efficiency was calculated in each of the suits. The activities were selected to simulate
actual EVA tasks. The test article was an underwater dynamometry system to which the
astronauts were secured by foot restraints. All metabolic data was acquired, calculated,
and stored using a computerized indirect calorimetry system connected to the suit
ventilation/gas supply control console. During the efficiency testing, steady-state
metabolic rate could be evaluated as well as work transmitted to the dynamometer.
Mechanical efficiency could then be calculated for each astronaut in each suit performing
each movement.
INTRODUCTION
Performing productive work in space has been a proven concept for over two decades.
As early as Gemini GT-12 in November 1966, astronaut Edwin "Buzz" Aldrin established
the capacity of man to work productively outside the protective spacecraft environment by
performing EVA experiments and useful work for more than 5.5 hours (Mallan, 1971).
Given the necessity of working in space and the high monetary cost of on-orbit time,
optimizing performance and increasing efficiency are important tasks for future space
flights. The current space shuttle suit has been successfully used to perform various
EVAs ranging from satellite recovery to simulations of space station construction. While
the shuttle suit maintains adequate joint flexibility and force transmission capabilities, the
29.6 kPa (4.3 psi) pressurization forces the astronaut to perform a 3.5 hour nitrogen
washout or 100-percent oxygen prebreathing procedure prior to an "emergency" EVA to
eliminate the risk of decompression sickness when depressing from the shuttle's earth-
like 101.3 kPa (14.7 psi) ambient pressure (Horrigan, et al., 1989). Prebreathing is not
only time-consuming and physically difficult to accomplish, but also decreases mission
safety by hindering any attempt at an emergency or contingency EVA. The development
of a space suit pressurized in the range of 55.2 to 69 kPa (7.8 to 9.7 psi) (decompression
of ca. 12,000 feet from sea level) with comparable joint flexibility and low resistance to
motion would not only eliminate the prebreathe period but would also optimize EVA
performance (Horrigan, et al., 1989). The purpose of this study was to develop a method
for evaluating the mechanical efficiency of space-suited work using three pressurized
space suits during various EVA tasks under simulated microgravity conditions (whole body
water immersion). Two new prototype space station suits, the AX-5 and MKIII, are
pressurized at 57.2 kPa and were tested concurrently with the 29.6 kPa shuttle suit.
METHODS
Four male astronauts were asked to perform a fatigue trial on each of four exercises
during which metabolic rate and torque input was measured. The protocol (figure 1) was
performed while suited, in foot restraints, and during whole body water immersion in the
Johnson Space Center Weightless Environment Training Facility (WETF). The activities
were selected to simulate actual EVA tasks and were performed in random order. Before
any performed movements, the resting metabolic rate of each astronaut was established
during the weigh-out period (the astronaut was held motionless and weighted to achieve
neutral buoyancy). During all testing phases, investigators, test directors, and suit
technicians were in voice contact with each astronaut. Suit environmental control was
managed and performed by space suit technicians.
To collect the torque transmission data, the test article consisted of an underwater
dynamometry system to which the astronauts were secured by foot restraints. The
dynamometer test apparatus consisted of an isokinetic dynamometer (Cybex II + )
contained in a pressurized (N2 charged) housing and mated to a height-adjustable stand
with a gridded base platform. Repeatable placement of the astronauts and foot restraints
was achieved by using the grid pattern on the base platform and the ruled height
adjustments on the test stand. A stripchart recorder (Cybex) and an analog tape-recorder
(TEAC) at the surface were used to collect and store data. Peak and mean torque values
attained at a constant angular velocity or 60 deg/sec were collected for each movement,
each suit, and each astronaut.
The custom indirect calorimetry system consisted of a mass spectrometer, portable
computer/data acquisition system and flowmeter. Gas concentrations were measured by
a Perkin-Elmer Medical Gas Analyzer/Mass Spectrometer (Model 1100). With the
spectrometer connected to a sample catheter placed in the output port of the suit
ventilation/gas supply control console, suit output 02 and CO2 concentrations were
continuously monitored. By using a Data Translation DT-707/DT-2801 analog to digital
conversion system, the analog voltage output from the mass spectrometer was interfaced
to a portable computer (Toshiba T1200).
Using data a'cquisition software (Laboratory Technologies Corporation LABTECH
NOTEBOOK), data was sampled, manipulated, stored on a hard disk, and displayed real-
time on an EGA color computer monitor. In addition, the software was programmed to
correct for standard temperature and pressure dry conditions and continuously compute,
display, and store the metabolic rate of each astronaut.
During the efficiency testing, steady-state metabolic rates were reached and could be
compared across suits and within astronauts. When an astronaut reached a plateau and
then reached either a 65 percent of peak VO2 value or a test bout duration of 10 minutes,
the fatigue trial was halted. Elimination of the transitory first and last minute from the
metabolic rate charts provided an interval of steady-state work that ranged from 3 to 8
minutes. Peak and mean metabolic rate values were then collected from this interval.
DISCUSSION
As illustrated by a resulting maximum achieved mechanical efficiency of 3 percent, space-
suited work during whole body water immersion is very inefficient. Any factor which
limited torque input or elevated metabolic rate decreased the mechanical efficiency of
performing the movement. While some of the energy consuming components of neutral
buoyancy suited work (such as body stabilization, resisting suit inertial forces, and an
increased level of anxiety) exist in the space environment, the work done against an
induced drag force has no counterpart. The drag force on a moving body through a
medium is proportional to one-half the density of the medium multiplied by the square of
the velocity multiplied by the projected area of the body. As a result of the medium being
water (1.0 kg/m3), the angular velocity (60 deg/sec), and the large circumference of the
suit's arm segments, the induced drag force generates considerable resistance to
movement and can, therefore, explain in large part the very low observed mechanical
efficiencies. The effect of the drag force both limits torque production and raises the
metabolic output as compared to working in a vacuum. It should also be noted that torque
il |i
production measurements from this study were of the same magnitude and range as
those in previous torque measurement studies using the same underwater dynamometry
system.
Also, error in measuring the metabolic rate as well as creating an EVA work simulation
that required higher than actual EVA work rates could contribute to a low observed
mechanical efficiency. However, several studies made to evaluate metabolic rate during
actual EVA show evidence that the average metabolic rated collected during the simulated
EVA fatigue trial were higher, but the range of collected rates correlated well with actual
EVA ranges. For example, the range of metabolic rates achieved in the shuttle suit (29.6
kPa) covering the four simulated EVA movements were 245 Kcal/Hr (.85 D'min) to 597
Kcal/Hr (2.06 L/min) with an average rate of 386 (+/- 25.4 SE) Kcal/Hr (1.34 L/min +/-
.089 SE). The average metabolic rate reported by Waligora and Horrigan, 1975, during
Apollo EVAs was 235 Kcal/Hr (ca..81 L/rain). Waligora and Horrigan, 1977, reported that
Skylab EVAs averaged 238 Kcal/Hr (ca..82 L/min). However, more recent reports
(Horrigan, et al., 1985) show that Shuttle EVAs average a somewhat lower 197 Kcal/Hr
(ca..68 L/min). Interestingly, the Soviets report comparable EVA metabolic rates
averaging 232 Kcal/min (ca..80 L/min) with a suit that has a main operational pressure of
40 kPa (Barer, 1989). The metabolic rates recorded throughout these Apollo, Skylab,
Shuttle, and Soviet EVAs range from a benign 60 Kcal/Hr (.21 L/min) to a vigorous 720
Kcal/Hr (2.5 L/min). The method developed for measuring the metabolic rates of subjects
during space-suited whole body water immersion and the work requirement of the EVA
fatigue simulation produce metabolic rates that fall within the range of actual reported EVA
rates.
Future studies should address and examine the contribution of the drag force on energy
expenditure and measure peak VO2 consumption and mechanical efficiency while
performing specific arm-dynamometry work tasks unsuited. By obtaining a measure of the
suit's operational mechanical efficiency, a transfer function for better describing the work
capabilities of the astronaut in the suit could be defined. Horrigan, et al., 1986 shows that
when metabolic rates measured during the specific space construction tasks of the
EASE/ACCESS flight experiment (Flight 61-B) were corrected for body weight, they were
almost identical for the two crewmembers. During the ACCESS activity, Crewmember
EV1 had a rate of 6.0 BTU/Ib/Hr (11 ml/kg/min) and Crewmember EV2 had a rate of 6.5
BTU/Ib/Hr (12 ml/kg/min). As mechanical efficiency normalizes work capability, future
studies involving a larger number of subjects could easily address intrasubject and
between measures variability.
Also, in calculating the net metabolic rate for the fatigue simulation, the resting rate was
established while the astronauts were suited and in the pool. This resting rate parameter
could be erroneously high due to the possible anxiety of being underwater and dependent
on divers for control and stability. Therefore, our efficiency results could actually be
inflated because a lower resting rate would increase the net metabolic rate and lower the
observed mechanical efficiency. Another addressable question should be the contribution
of anaerobic metabolism to periods of steady-state work. This unaccounted for energy
also lowers the observed mechanical efficiency. With the effects of drag and other non-
operational energy consuming components accounted for, evaluating the mechanical
efficiency of work in a neutral buoyancy environment provides a convenient method for
comparing space suits, or other pressure suits, and specific work tasks or movements.
RESULTS
Average torque transmission, T{N-m}(figure 2), was collected along with peak and
average metabolic rate, MR {L/min} (figure 3), for each astronaut in each suit and during
3
each movement. Mechanical efficiency was calculated by startingwith the general
definitionof power outputdivided by power input. However,a calculation of net
mechanical efficiency was actually made as a better representation of performance above
a resting metabolic rate. The net mechanical efficiency therefore became the power
output divided by the metabolic rate above a resting state. The power output was the
torque measured on the dynamometer multiplied by the constant angular velocity of 60
deg" sec-1 {rd3 rad.sec-1}. The metabolic rate above rest was the difference in testing
and resting metabolic rates (MR minus MRrest). Therefore, mechanical efficiency was
calculated and graphs were plotted for each astronaut in each suit and during each
movement. Figure 4 illustrates the mean mechanical efficiency achieved by the
astronauts in each of the three suits during the EVA ratchet wrench crank and push
movements.
4
fit J|i
REFERENCES
Barer, A.S.: Extravehicular Activity Medical Support. JAA-t-71, Paper delivered at the 8th
IAA Symposium "Man in Space," Tashkent, Uzbekistan, USSR, September 29 - October
4, 1989.
Greenisen, MC.: Data Collection for Human Work Performance In Space. Three
Decades of Life Science Research In Space. Washington, D.C., June 1987, pp. 287-288.
Horrigan, D.J.; Waligora, J.M.; and Bredt, J.H.: Extravehicular Activities. In:
Nicogossian, A.E.; Huntoon, C.L.; and Pool, S.L. (eds) Space Physiology and Medicine, 2
ed. NASA-SP 447, 1989, pp. 122-134.
Horrigan, D.J.; Waligora, J.M.; and Nachtwey, D. S.: Physiological Considerations for EVA
in the Space Station Era. Intersociety Conference on Environmental Systems, July 1985.
Horrigan, D.J.; Waligora, J.M.; Stanford, J.; and Edwards, B.F.: Overview of Crewmember
Energy Expenditure During Shuttle Flight 61-B EASE/ACCESS Task Performance. NASA
Conference Publication 2490: Space Construction, pp. 228-235, August 6-7, 1986.
Mallan, L.: Suiting Up for Space: An Evolution of the Spacesuit. The John Day Company,
New York, 1971, p. 155.
Waligora, J.M. and Horrigan, D.J.: Metabolism and Heat Dissipation During Apollo EVA
Periods. In Biomedical Results of Apollo. NASA-SP 368, 1975.
Waligora, J.M. and Horrigan, D.J.: Metabolic Cost of Extravehicular Activities. In:
Johnson, R.S. and Dietlein, L.F. (eds) Biomedical Results from Skylab, NASA-SP 377,
1977, pp. 395-399.
Astronauts SPace Suit Assemblies
A1
A2
A3
A4
Shuttle Suit
MKIII
AX5
Phase 1
Resting metabolic data
taken during weigh-out
period
Phase2
Fatigue Trial/Efficiency Test
Test duration: 10 min. or
65% fatigue
Movements
(randomized)
EVA Ratchet Wrench Crank
Elbow Flexion
Shoulder Rotation Med-lnt
EVA Ratchet Wrench Push
Figure 1. Efficiency Test Protocol (WETF Neutral Buoyancy Environment)
350
300
250
200
!
100
Figure 2.
50
SS MKIII AX5
Average Dynamic Force Production During the Ratchet Wrench Push
c
.m
E
O_
m
E
60
5O
40
3O
20
10
6O
5O
4O
2O
Z
10
0
0 [] Mean Metabolic Rate
SHU'I-I'LE SUIT MKIII AX5
[] Mean Dynamic Force
Figure 3. Ratchet Wrench Push:
Mean Metabolic Rate and Mean Force Production During Fatigue Trial
Ratchet Wrench Crank Ratchet Wrench Push
o 1
Shuttle MKIII AX5 Shuttle MKIII AXS
Figure 4. Mean Mechanical Efficiencies Achieved in Each Suit
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A Method of Evaluating Efficiency During Space-Suited Work in
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Michael C. Greenisen, Phillip West, Frederick K. Newton, John
H. Gilbert, and William G. Squires
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Medical Sciences Division
Space Biomedical Research Institute
National Aeronautics and Space Administration
Johnson Space Center
Houston, Texas 77058
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11.SUPPLEMENTARYNOTES
M. C. Greenisen, P. West, F. K. Newton: Johnson Space Center,
J. H. Gilbert: KRUG International, Houston, Texas
W. G. Squires: Texas Lutheran College, Seguin, Texas
Houston, Texas
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1Zb. DISTRIBUTION CODE
The purpose of this study was to investigate efficiency as related to the work
transmission and the metabolic cost of various EVA tasks during simulated microgravity
(whole body water immersion) using three space suits. Two new prototype space station
suits, AX-5 and MKIII, are pressurized at 57.2 kPa and were tested concurrently with the
operationally used 29.6 kPa shuttle suit. Four male astronauts were asked to perform a
fatigue trial on four upper-extremity exercises during which metabolic rate and work
output were measured and efficiency was calculated in each suit. The activities were
selected to simulate actual EVA tasks. The test article was an underwater dynamometry
system to which the astronauts were secured by foot restraints. All metabolic data was
acquired, calculated and stored using a computerized indirect calorimetry system
connected to the suit ventilation/gas supply control console. During the efficiency
testing, steady-state metabolic rate could be evaluated as well as work transmitted to
the dynamometer. Mechanical efficiency could then be calculated for each astronaut in
each suit performing each movement.
14 $USJE_TERMS
steady-state metabolic rate, fatigue trial, dynamometer
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A method of evaluating efficiency during space-suited work in a neutral buoyancy environment

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