This viewgraph presentation reviews NASA's extravehicular activity (EVA) procedures and the technological and biomedical issues surrounding EVA

Gernhardt, Michael L.

NASA Technical Reports Server

Diving in Space
Mik G h dte ern ar
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 1
https://ntrs.nasa.gov/search.jsp?R=20090002616 2019-08-30T06:05:29+00:00Z
Biomedical and Technological Challenges of EVA
• Decompression (denitrogenation required 
to work in low pressure suit (4.3 psi))
• Thermoregulation (-120oC to + 120oC)
• Nutrition (200 kcal/hr requirement)
• Hydration (1 liter/EVA)
• Waste Management
• Radiation
• Micrometeoroids and Orbital Debris
• Suit Trauma
• Mobility/Dexterity: current pressurized 
suits reduce mobility and dexterity 
Visibilit
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 2
• y
Type II DCS – Percentage of All DCS vs. Diving Methods
9 0
1 0 0
4 0
5 0
6 0
7 0
8 0
0
1 0
2 0
3 0
l l ic k s A
Co
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N 
Sa
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N 
Di
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 T
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B r
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• Character of Altitude DCS Different from Diving DCS
• Undersaturated Neurological Tissues
From DAN, 2005
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 3
  
• “Softer Bubbles” Metabolic Gases
Altitude DCS - Nitrogen Elimination during Oxygen Prebreathe
2500
V
'V60-90
Cumulative 
Nitrogen
Elimination
(ml)
N 2  e l im in a t io n  in  5  a n d  1 0  m in u t e  h a lf -
t im e  c o m p a r t m e n  ( ~ b r a in  a n d  s p in a l  
c o r d )
1 0
'V0-30
'30-60
4
6
8
0
30 60 90 120 1500
Time (min)
180
0
2
0 2 0 4 0 6 0 8 0
Time ( minutes)
- Over 50% of nitrogen eliminated in first 30 minutes
- Brain, spinal cord Halftime ~ 5-10 minutes, muscle and skin halftimes
- 15-25 minutes at resting conditions
  
     
- Resting prebreathe reaches point of diminishing return for reducing pain 
only DCS
- Type II DCS incidence higher on “Zero Prebreathe”
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 4
Gerth, W.A., R.D. Vann, N.E. Leatherman, and M.D. Feezor. 1987. Effects of microgravity on tissue perfusion and the
efficacy of astronaut denitrogenation for EVA. Aviat. Space Environ. Med. 58(9, Suppl.): A100-105
Shuttle Pre-breathe Ground Studies
Two Pre-breathe 
protocols approved 
• 4 hour in-suit 
resting oxygen pre-
for flight operation
breathe
• 12 hr 10.2 psi 
staged 
decompression 
procedure
• R value ( tissue 
( )/tension 360 suit 
pressure)= 1.65
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 5
Flight Experience Shuttle 10.2 psi Staged Protocol – Zero DCS 
120
Time at 10.2 psi prior to 60
80
100
Numbe r  of  
EVAs
shuttle EVA
0
20
40
12-16 16-20 20-24 24-144
Time (hours) 
25
d
e
x
12 hr*
Theoretical Tissue Bubble 
growth as a function of
10
15
20
l
e
 
G
r
o
w
t
h
 
I
n
d
0
 
m
i
n
 
T
i
s
s
u
e
 
16 hr*
20 hr*
     
10.2 exposure time
0
5
0 100 200 300 400
EVA Time (min)
B
u
b
b
l
4
8
0
24 hr*
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 6
  
Defining and Controlling Risk in Operational Research 
Programs – Example of Prebreathe Reduction Program (PRP)
ISS Overnight
Campout
Enabling  Counter 
Measure Research 
( NASA TRL 3/4)
Background
40
60
80
100
%
 
D
C
S
20/26 (77%)
11/26 (42%)
*Arm & leg work at 
75% VO2 max with
seated subjects
p=0.03
0
20
Rest                     0:10 Heavy Work*
1:00 O2 Prebreathe
USAF prebreathe exercise
Shuttle Prebreathe Ground 
Trials (~ 25% DCS, ~ 5% 
symptoms that would
Limitations
•Timeline, back to 40
60
80
C
S
10/20
Legs (p=0.0008)Arms (NS)
  
   
terminate an EVA.) Acceptable 
Risk?
- 4 hour prebreathe
- 10.2 psi staged protocol
back EVAs, 
•02 usage,ISS 02 
concentration
•crew isolation and 
0
20
Ambulatory Non-Amb.
%
 
D
2/20
3/21
1/21
95% CI
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 7
- 146 EVAs exposures with no 
reports of DCS
comfort
Duke, NASA micro-gravity 
simulation ( non ambulation)
Enabling Research
10 minutes 75% V02peak 88% lower
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 8
   ,   
body, 12% upper body
Prebreathe Reduction Program
• Start by defining 
acceptable DCS risk 
for ISS mission and 
developing
Prebreathe Reduction
Laboratory Studies
-5 Year Operational  
accept/reject limits 
for countermeasure 
trials
• Early development
  
Research Plan
Integrated Decompression
Stress Predictive Model
  
focused on 
delivering  
acceptable/effective 
counter measure
Acceptable
DCS Risk
Definition
2 Hr.
Prebreathe
Protocol
1.5 Hr.
Insuit
Prebreathe
Relationship 
between 
Micro-g sim. and
exercise
Break in
Prebreathe
Studies
Supporting
Studies
• Later development 
focused on 
increased efficiency 
and improved 
scientific
Phase 1 √
Phase 2 √
Phase 3 √
Phase 4 √
Phase 5.1 **
Phase 5.2
Phase 5.3
Phase 5.4
Brooks  
Studies *
adynamia 
cross over 
study
JSC        
Phase 6.1
Phase 6.XX
- Lactate measurements 
- Oxygen  Consumption *
- Cardiac Output
- Blood flow
- Nitrogen Elimination
 
understanding of  
counter measure 
mechanisms
Phase A **
EVA exercise 
simulations 
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 9
Accept: DCS < 15% and Grade IV VGE < 20% , @ 95% 
C.l
Reject:  DCS > 15%  or  Grade IV VGE > 20%  , @ 70% 
C.l
Multi-Center Study:  NASA, Duke, DCIEM, Hermann UT
2hr oxygen prebreathe
Exercise 10 mins @ 75% V02peak
And/or light exercise (160-253 Kcal/hr)
Micro-gravity simulation
( non-ambulation)
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 10
Simulated EVA exposure at
4.3 psi 4 hrs Use of “Suit Simulator” forEVA Exercise 
Prebreathe Trials
10 DCSPhase I
Phase II
Ph III
40 min
Light
Rest
Rest
Rest
min
75%
VO2 peak
4 hr
EVA
Simu-
19%
0%
22%ase 
Phase IV
Activity
Rest
95 min Light  Activity
lation
14%
PRP Phase I-IV 2 hr oxygen prebreathe exercise protocols
60
70
80
DCS
DCS
VGEn=47
n=9• High intensity exercise 
(75% peak oxygen
20
30
40
50or
Grade IV
VGE
(%)
n=56
n=45
   
consumption [VO2 
peak])
• Low intensity activity 
(5.8 mL·kg-1·min-1 VO2) 
0
10
I II III IV
Phase
• Neither High or low 
intensity exercise was 
acceptable
C li Hi h ith DCS and Grade IV VGE observations (shown with 95%
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 11
• oup ng g  w  
low intensity exercise 
was acceptable
        
upper confidence limit bars dashed lines indicating accept 
levels for DCS and VGE incidences)
Exercise and Inert Gas Kinetics
P1N2 = P0 + (1 - exp – k1t ) * (Pa - P0),  
k1 = [(1 / exp (-λ * mL*kg-1*min-1)) / 519 37]       . . 
Model Predictions vs Actual
20
25
30
35
0
5
10
15
%DCS
I II III IV V 1 V 3 V 4- - -
PRP Trials
Hosmer-Lemshow Goodness of fit  statistic = 2.188 with 5 degrees of 
freedom, p = 0.82 ( significance > .05)
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 12
Exercise Prebreathe Protocol:  Experience to Date
• Overview- The exercise prebreathe protocol has been used successfully  on 
34 EVAs from the International Space Station (ISS)- no DCS
• Five Shuttle assembly flights and two increment EVAs
• Starting in July 2001   
• These assembly missions would have been difficult or impossible to 
execute as base-lined, without the protocol
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 13
A United States Airlock:  Doorway to Space
U.S. “Quest” Airlock
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 14
The Challenge of Moving Past Apollo
A ll k bl h hi t• po o was a remar a e uman ac evemen
• Fewer than 20 EVAs, maximum of three per 
mission
• Constellation Program up to 2000 EVAs over ,       
the 10 year Lunar program
• Limited mobility, dexterity, center of gravity 
and other features of the suit required 
significant crew compensation to accomplish     
the objectives. It would not be feasible to 
perform the constellation EVAs using Apollo 
vintage designs
• The vision is to develop an EVA system that is          
low overhead and results in close to (or better 
than) one g shirt sleeve performance i.e. “ A 
suit that is a pleasure to work in, one that you 
would want to go out and explore in on your 
day off” 
• Lunar EVA will be very different from earth 
orbit EVA – a significant change in design and 
operational philosophies will be required to 
optimize suited human performance in lunar 
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 15
gravity
Challenges for EVA on the Moon
• Dealing with risk and consequences of a significant Solar Particle Event 
(SPE) 
• Long duration missions with three 8hr EVAs per person per week
– Apollo suits were used no more than 3 times
– Individual crewmembers might perform up to 76 EVAs in a 6-month mission           
– Suit-induced trauma currently occurs with even minimal EVA time
• With Apollo style un-pressurized rover (UPR), exploration range is limited by 
EVA sortie time and 10 km walkback constraint
– Science community input that optimal scientific return within this range could be             
accomplished within ~ 30 days of EVA
– Two UPRs could extend exploration range up to 15-20 km (crew-day limited)
• Apollo highlighted the importance of dust control for future long duration 
missions
• Increased Decompression Sickness (DCS) risk and prebreathe requirements 
associated with 8 psi 32% O2 cabin pressure versus Apollo with 5 psi 100% 
O2
• The high frequency EVA associated with the projected lunar architectures 
will require significant increases in EVA work efficiency (EVA prep time/EVA 
time)
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 16
“The Wall of EVA”
“The Wall”
250
ISS Construction 
(projected)
 
200
150
A
 
H
o
u
r
s
100E
V
A
Gemini
Apollo/Skylab
Pre-Challenger
Shuttle Shuttle
50
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 17
0
1
9
6
6
1
9
6
8
1
9
7
0
1
9
7
2
1
9
7
4
1
9
7
6
1
9
7
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1
9
8
0
1
9
8
2
1
9
8
4
1
9
8
6
1
9
8
8
1
9
9
0
1
9
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2
1
9
9
4
1
9
9
6
1
9
9
8
2
0
0
0
2
0
0
2
2
0
0
4
2
0
0
6
Year
“The Mountain of EVA”
5000
“The Mountain”
3500
4000
4500 Available Lunar EVA Hours 
(LAT-2 Option 2) – based on 
Three 8 hour EVAs per week 
using Unpressurized Rovers
2500
3000
A
 
H
o
u
r
s
Æ Need to extend range well 
beyond 10 km
1500
2000E
V
A
Gemini “The Wall”
500
1000
ISS Construction 
(projected)
Apollo/Skylab Pre-Challenger
Shuttle
Shuttle
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 18
0
1
9
6
6
1
9
6
8
1
9
7
0
1
9
7
2
1
9
7
4
1
9
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6
1
9
7
8
1
9
8
0
1
9
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2
1
9
8
4
1
9
8
6
1
9
8
8
1
9
9
0
1
9
9
2
1
9
9
4
1
9
9
6
1
9
9
8
2
0
0
0
2
0
0
2
2
0
0
4
2
0
0
6
2
0
0
8
2
0
1
0
2
0
1
2
2
0
1
4
2
0
1
6
2
0
1
8
2
0
2
0
2
0
2
2
2
0
2
4
2
0
2
6
2
0
2
8
2
0
3
0
Year
Intermittent Recompression - Background
C t l f l f• urren  p ans or unar sur ace 
exploration include Small 
Pressurized Rovers (SPRs) that 
are quickly ingressed and 
egressed with minimal  loss of 
consumables
• This capability enables crew 
members to perform multiple 
short extravehicular activities 
(EVAs) at different locations in a
9
Recompression      
single day versus a single 8-hr 
EVA
5
6
7
8
p
s
i
a
)
Cabin 
Pressure
• Previous modeling work and 
empirical human and animal data 
indicate that the intermittent 
recompressions may reduce
2
3
4
P
r
e
s
s
u
r
e
 
(
p
EVA EVA
Suit 
Pressure
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 19
   
decompression stress
0
1
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Time (hours)
Tissue Bubble Dynamics Model (TBDM)- Provides Significant 
Prediction and Fit of Diving and Altitude DCS Data
• Decompression stress index based on tissue bubble 
growth dynamics (Gernhardt, 1991)
• Diving: n=6437 laboratory (430 DCS cases)
– Logistic Regression Analysis: p <0.01
H L h G d f Fit 0 77– osmer- emes ow oo ness o    = .  
• Altitude: n=345 (57 DCS, 143 VGE)
– Logistic Regression Analysis (DCS): p <0.01 
– Logistic Regression Analysis (VGE): p <0.01 
– Hosmer-Lemeshow Goodness of Fit (DCS): p = 0.35        
– Hosmer-Lemeshow Goodness of Fit  (VGE): p = 0.55
r = Bubble Radius (cm)
t = Time (sec)    
a = Gas Solubility ((mL gas)/(mL tissue))
D = Diffusion Coefficient (cm2/sec)
h(r,t) = Bubble Film Thickness (cm)
Pa = Initial Ambient Pressure (dyne/cm2)
v = Ascent/Descent Rate (dyne/cm2⋅cm3)
g = Surface Tension (dyne/cm)
M = Tissue Modulus of Deformability (dyne/cm2⋅cm3)
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 20
      
PTotal = Total Inert Gas Tissue Tension (dyne/cm2)
Pmetabolic = Total Metabolic Gas Tissue Tension
Gernhardt M.L. Development and Evaluation of a Decompression Stress Index Based on Tissue  Bubble Dynamics. Ph.D dissertation, University of 
Pennsylvania, UMI #9211935, 1991.
Intermittent Recompression - Background
• Intermittent recompression during saturation decompression was previously proposed as a 
method for decreasing decompression stress and time (Gernhardt,1988)
– Gas bubbles respond to changes in hydrostatic pressure on a time scale much faster 
than the tissues
• Intermittent recompression (IR) has been shown to decrease decompression stress in 
humans and animals (Pilmanis et al. 2002, Møllerløkken et al. 2007)
6437 laboratory dives (430 DCS cases)
Gernhardt, M.L. Mathematical modeling of tissue bubble dynamics during decompression.  Advances in Underwater Technology, Ocean Science and Offshore 
E i i V l 14 S b ibl T h l S i t f U d t T h l 1988
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 21
ng neer ng, o ume : u mers e ec no ogy.  oc e y or n erwa er ec no ogy, .
Pilmanis A.A., Webb J.T., Kannan N., Balldin U. The effect of repeated altitude exposures on the incidence of decompression sickness. Aviat Space Environ Med; 
73: 525-531, 2002.
Møllerløkken A, Gutvik C, Berge VJ, Jørgensen A, Løset A, Brubakk AO. Recompression during decompression and effects on bubble formation in the pig. Aviat 
Space Environ Med; 78:557-560, 2007. 
Discussion
A
B
20
8
10
12
14
16
18
G
r
o
w
t
h
 
I
n
d
e
x
59% DCS
0
2
4
6
0 100 200 300 400
Time (min)
B
u
b
b
l
e
 
6% DCS
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 22
Pilmanis A.A., Webb J.T., Kannan N., Balldin U. The effect of repeated altitude exposures on the incidence of decompression 
sickness. Aviat Space Environ Med; 73: 525-531, 2002.
DCS Incidence TBDM Predictions
 
Intermittent Recompression - 3 x 2hr EVA at 4.3 psi
40
35
25
30
d
e
x
 
(
B
G
I
)
0 5hr between 2hr EVAs
6hr Continuous EVA
20
G
r
o
w
t
h
 
I
n
d
.    
1hr between 2hr EVAs
2hr between 2hr EVAs
10
15
B
u
b
b
l
e
 
G
3hr between 2hr EVAs
0
5
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 23
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Time (hours)
Floating Through the Terminator in the Sea Space Continuum
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 24
Slide Title
Diving in Space    |    National Aeronautics and Space Administration    |    Mike Gernhardt 25


Diving in Space

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