1. How one Functional Human-Factors
Requirement Influenced a Rocket
Dr. Cynthia H. Null, Technical Fellow
NASA Engineering and Safety Center
This briefing is for status only and may not represent complete engineering information 1

2. Outline
• Development of CxP Human System Requirements
• Human Tolerance to Acceleration and Vibration
• Thrust Oscillation
• Developing a performance criterion for vibration
• Validation of a countermeasure
• Lessons Learned
This briefing is for status only and may not represent complete engineering information 2

3. Development of CxP
Human System Requirements
• Derived from NASA-STD 3000 (now 3001)
• Focus on crew health and safety
• Focus on performance issues during a
mission, specifically
– The human and system must function together
– Within the environment(s) and habitat(s)
– To accomplish tasks for mission success
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4. Example: High Level Functional
Performance Requirement
• Design system is to allow for all crewmembers to perform any of
the required tasks efficiently and effectively, for nominal, off-
nominal and emergency operations, thus ensuring crew health,
safety, and mission success.
• System means vehicle, habitat, operations
• Efficiently, so that all mission goals are met
• Effectively = low probability of error
= within the time required
 Human performance is affected by nearly all aspects of the
mission and system design: vehicle design, subsystem design,
environments, ConOps, interfaces, tasks, procedures, etc.
This briefing is for status only and may not represent complete engineering information 4

5. Examples of Specific Requirements
• The system shall provide potable water at or below the
physiochemical limits [from] table Potable Water
Physiochemical Limits at the point of crew consumption.
• The system shall provide a portable fire suppression system.
• The system shall provide a translation path for assisted
ground egress of an incapacitated suited crewmember.
• Hatches shall be operable without the use of tools.
• Connectors shall have physical features that preclude mis-
mating and misalignment.
• Controls shall be designed such that the input direction is
compatible with the resulting control response.
This briefing is for status only and may not represent complete engineering information 5

6. Examples of Requirement Categories
• Anthropometry, biomechanics, and strength
• Environments
• Safety
• Architecture
• Crew Functions (Food, Hygiene, Exercise, Medical)
• Crew Interfaces
• Maintenance
• Information Management
• EVA
This briefing is for status only and may not represent complete engineering information 6

7. Acceleration Limits
(CxP 70024 -- SRR 2006)
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8. Occupant Protection:
Crew Injury Risk Limits
• The Constellation Architecture shall limit the injury
risk criterion, β, to no greater than 1.0 according to
the Brinkley Dynamic Response model in Appendix
N, table Dynamic Response Limits.
This briefing is for status only and may not represent complete engineering information 8

9. Vibration Health Limit
• The Constellation Architecture shall limit vibration
to the crew such that the vectorial sum of the X, Y,
and Z frequency-weighted [using ISO 2631-1]
accelerations between 0.5 and 80 Hz is less than or
equal to the levels and durations in [the] table
during dynamic phases of flight.
Maximum Vibration Maximum Frequency-
Exposure Duration Per Weighted Acceleration
24-hr Period
10 Minutes 0.4 g rms
1 Minute 0.6 g rms
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10. But what about performance during or
after vibration?
• Members of the Human Systems Special Interest
Group (HSIG) wanted to develop additional
requirements in Fall 2006, SRR time frame.
• Not viewed as an issue (POGO for
Gemini/Apollo, vibration low for shuttle)
• Expectation that DOD had the necessary data
and experience, if such a requirement would be
needed
This briefing is for status only and may not represent complete engineering information 10

11. NESC AGILE Project (Oct 2007)
(Assessment of Gravito-Inertial Loads and Environments )
• Literature Search
• Workshop of Experts
– NASA
• Scientists (Human Performance, Medical)
• Engineers (Propulsion, Seats, Suits, etc)
• Astronauts (Apollo, Shuttle)
• CxP Projects
– DOD
– Industry
– University
• Gap Analysis
Lead: Dr. Bernard Adelstein
This briefing is for status only and may not represent complete engineering information 11

12. Vibration Level
g (0-peak)
Historical Data/Guidelines/Requirements
“Health Risks Likely”
—ISO 2631-1:1997
Historic Crew Performance
Vibration Limits (at “11 Hz”)
Possible Perceptual &
Physiological Aftereffects
Severe Performance
1963 Gemini Centrifuge-Vibration Study
Degradation
(Vykukal & Dolkas, 1966)
3.5 Gx (Chest-in) Bias
0.14-1.65 gx vibration at 11 Hz***
Achievable Performance (Vykukal & Dolkas, 1966)
•Simple visual & manual tasks only; Performance Degradation
Gemini crew spec (0.25 g) •Coarse visual & manual tasks; speech
Shuttle crew (0.1 g)? •Fine visual & manual tasks 12

13. Crew Vibration Knowledge Gaps & Risks
HSIR Vibration Health Limits based on ISO 2631-1 health-risk boundary
•ISO health boundaries derived for upright body posture (1-Gz bias, i.e., head-down)
and gz vibration for short-duration 1-, 3-minute exposure.
•Validated for semi-supine posture (1-Gx bias, i.e., chest-in) for short duration only (Temple et al,1964),
but NOT for 1-, 3-minute exposure.
•Vibration tolerance differs between seat designs and seat-suit coupling (Temple et a., 1964)
•ISO frequency-dependent vibration tolerance were derived for 1-Gz bias. Hyper-Gx alters human body
and internal organ impedance; may require revised frequency-dependent weighting functions.
Vibration Visual and Manual Performance
•Bulk of performance literature is for upright body posture and gz vibration.
•Vykukal & Dolkas (1966) for self-rated critical crew task performance at 3.5 Gx and Clarke et al (1965)
for dial reading at 3.85 Gx are the only reported vibration studies for hyper-G bias. These two
studies were conducted for Gemini vintage displays (and ConOps), only for gx vibration,
and only at 11 Hz vibration (i.e., Titan-II POGO).
•Orion will be commanded through electronic interfaces, i.e., virtual (soft) switch panels;
procedures will be displayed electronically; computer-stored checklists will be located and navigated
via an electronic procedure viewer.
•Orion analyses indicate crew-seat vibration transfer in x-, y-, and z-axes.
•Orion thrust oscillation response, currently 12 Hz, may change with seat, suit and display mitigations.
Vibration Aftereffects
•No systematic study (only anecdotal report by Faubert et al. (1963)) of perceptual and performance
aftereffects for gx vibration at levels below the health limit
This briefing is for status only and may not represent complete engineering information 13

14. Thrust Oscillation (Nov 2007)
• Issue raised at CxP Integrated Stack TIM
• Thrust Oscillation Focus Team (TOFT) established
Experts from several centers, many disciplines, industry
– 1. Review the forcing functions, models and analysis results to
verify the current predicted dynamic responses of the
integrated stack
– 2. Identify and assess options to reduce predicted responses
– 3. Validate and quantify the risk to the Ares I vehicle, Orion
spacecraft, crew, and other sensitive subsystems and
components to the extent allowed by the Ares I/Orion design
maturity
– 4. Establish and prioritize mitigation strategies and establish
mitigation plans consistent with the CxP integrated schedule
This briefing is for status only and may not represent complete engineering information 14

15. Thrust Oscillation Focus Team
Team Membership
• Leads - Garry Lyles / Eli Rayos (ILSM SIG)
• Chief Engineer’s Office - Leslie Curtis
• Vehicle Loads Analysis- Jeff Peck / Isam Yunis / Pravin Aggarwal
• Vehicle Controls Analysis - Steve Ryan
• Motor Analysis - Tom Nesman / Jonathan Jones / Dan Dorney / Jeremy Kenny / ATK
Engineering (Tyler Nester / Terry Boardman)
• Ares Vehicle Systems Integration - Rob Berry (Element Integration Lead)/ Bob Werka (Global
Mitigation Lead)/ Belinda Wright / James Sherrard
• Orion Systems Engineering - Chuck Dingle / Corey Brooker / Thomas Cressman (SM) / John
Stadler (LAS) / Tom Goodnight (SM) / Keith Schlagel (LM)
• Ares Systems Engineering - Joe Matus (US) / Rick Ballard (USE) / Wendy Cruit (FS)
• Safety and Mission Assurance - Ho Jun Lee / Chris Cianciola
• Crew and Human Factors - Phil Root / Bernard Adelstein
• NESC Structures and Dynamics Team - Curt Larsen / Alden Mackey
• NESC Consultants - Scott Horowitz / Gloyer-Taylor Labs (Paul Gloyer, Tim Lewis, Gary
Flandro, Fred Culick, Vigor Yang)
• Independent Structural Dynamics Discipline Experts - Hal Doiron / Bob Ryan / Luke
Schutzenhofer / George Zupp / Ken Smith / Jim Kaminski / Jim Blair / George James
• Boeing - Ted Bartkowicz / Steve Tomkies
• Shuttle Booster Project Engineering - Mike Murphy / Steve Ricks / Sam Ortega
• Aerospace Corporation - John Skratt / Kirk Dotson , et al
• Pratt and Whitney Rocketdyne - Tom Kmiec / Steve Mercer
This briefing is for status only and may not represent complete engineering information 15

16. Why was more data necessary?
• Modern displays are complex, crowded, small fonts and
have different task and demands from historical experience
• Understand impacts of vibration on crew performance
• Exposure levels may exceed the ~0.1 g (0-to-peak)
experience of Gemini-Apollo-Shuttle and maybe the
previous 0.25 g limit
• Previous results were at 11 Hz, CxP expected to be at 12 Hz
• Quantify risk
This briefing is for status only and may not represent complete engineering information 16

17. Number Reading Task
• Begin at central fixation
• Locate magenta block
• Read middle row
• 5-s maximum viewing time
•Is 3-digit string a monotonic (ascending/
descending) sequence?
•50/50 “yes” / “no”
573
681
489
“No” 17
This briefing is for status only and may not represent complete engineering information

18. Vibration and Reading
(Stationary, 12 Hz Gx vibration)
This briefing is for status only and may not represent complete engineering information 18

19. Expected G-loading effects on
human performance
• Impaired accommodation and decrease static visual
acuity
• Decreased visual sensitivity
• Increased response time
• Decreased field of view
• Increased workload
This briefing is for status only and may not represent complete engineering information 19

20. ARC 20-G Centrifuge Facility
Chair
reclining
at 15.3
vibration chair (fixed)
20

21. ARC 20-G Centrifuge Vibration Chair
Display
(raised)
Head Restraint Dual triaxial
Head Rest accelerometer
assembly
Vibration Egress Harness
Actuator
(1 of 4) 5-point restraint
400 lb capacity each
Emergency
1.5 in max stroke
switch
2-button handheld
input device
21

22. Critical Crew Capabilities
• Two Critical Capabilities identified by Crew Office for thrust
oscillation period:
1. Maintain situation awareness (SA) of vehicle state and
vehicle status through processing Primary Flight Display
(PFD) symbology
2. Manually steer (hand-fly) the vehicle immediately
following exposure to vibration
This briefing is for status only and may not represent complete engineering information 22

23. Display Usability Rating Study
(under 1-G and 3.8-G)
1-D Graphical Features
Crew participants rated their ability
to acquire information about the
state of system (e.g., valve state)
while ignoring the text
This briefing is for status only and may not represent complete engineering information 23

24. Display Usability Rating Study
(under 1-G and 3.8-G)
2-D Graphical Features
Crew participants rated their
ability to use the PFD
(while ignoring the text)
This briefing is for status only and may not represent complete engineering information 24

25. Task 2: Manual Control Flight Task
Immediately after TO vibration stops:
•PFD disappeared
•Screen remained blank for 2 s
•PFD reappeared with pre-inserted four-
quadrant pitch & roll offset:
pitch-up or -down
PLUS
roll-left or -right
•Participant instructed to make immediate
initial joystick input to null the error in
both axes
For full 30 s trial:
•Superimposed continuous
0.05 Hz sinusoidal pitch & roll error
•Participants made continuous joystick inputs
to null errors (i.e., they “flew the needles”)
This briefing is for status only and may not represent complete engineering information 25

26. SA & Manual Steering Questions
This briefing is for status only and may not represent complete engineering information 26

27. Centrifuge Study (3.8-G): Error Rates
And Response Times During Vibration
Error Rate (ER) Response Time (RT)
• Up to 7-fold increase in mean ER under some conditions (0.5 g for 10-pt)
• Up to 450-ms increase in mean RT under some conditions (0.5 g for 10-pt)
This briefing is for status only and may not represent complete engineering information 27

28. Vibration Study (3.8G) : Error Rates and
Response Times After Vibration
Error Rate (ER) Response Time (RT)
•ER and RT return to zero-vibration (last 5 trials) levels as soon as
145-s vibration stops
This briefing is for status only and may not represent complete engineering information 28

29. Countermeasure Validation
• Inspired from stroboscopic techniques commonly employed for
visual inspection of oscillating and/or vibrating machinery
• Developed an LCD monitor backlit by an array of LEDs, which
could strobe synchronizely with respect to the vibration pattern,
adjusting its phase and duty cycle
This briefing is for status only and may not represent complete engineering information 29

30. Display Strobe / Vibration Results
(Stationary, 0.7-gx 12 Hz vibration)
I. In the non-strobe condition, errors quadrupled (3.5% to 16.4%) and response
times slowed by 325 ms with vibration, consistent with 0.7-g condition in
previous studies. Lower constant luminance (EL) slowed response times by 110
ms.
II. In the zero-vibration condition, display strobing slowed response times by 110
ms versus a display with comparable constant luminance (EL).
III. Under 0.7-g vibration, display strobing at 5% duty cycle reduced error rates to
~5%, a level not significantly different than for zero vibration, and sped response
times by 240 ms. This briefing is for status only and may not represent complete engineering information 30

31. Vibrations Studies
Study Team Scientists:
ARC/TH: B. Adelstein, B. Beutter, M. Kaiser, R. McCann, L. Stone
JSC/SK: W. Paloski
In Collaboration with:
ARC/TH: M. Anderson, F. Renema, B. Spence, M. Godfroy,
G. Flores, D. Munoz
ARC 20-G Centrifuge Facility: C. Wigley, N. Rayl, T. Purcell, J. Dwyer,
R. Ryzinga, P. Brown, T. Luzod, R. Westbrook, M. Steele, V. Post
ARC Engineering and Hazard Analysis: O. Talavera, M. Ospring, R. Phillips
ARC Chief Medical Officer & HRIRB Chair: R. Pelligra
JSC/CB: P. Root, T. Verborgh, M. Ivins, M. Kelly, L. Morin
JSC/SF: K. Holden
JSC/ILSM-SIG: (TOMCAT) E. Rayos, M. Samir
JSC Engineering: A. Sena, D. Gohmert, B. Daniel
JSC Medical Monitors: J. Jones, R. Scheuring, J. Clark
JSC Video: J. Blair, R. Markowitz
ESMD-HRP: B. Woolford, J. Connolly, D. Russo, D. Grounds
HSIG: J. Dory, J. Rochlis
NESC: C. Null
Orion Project: J. Fox, J. Falker
Participants from ARC community & JSC Crew Office
This briefing is for status only and may not represent complete engineering information 31

32. Lessons Learned
• Expertise is critical. Don’t confuse intelligence with expertise
• System issues are solved though inclusion
– Cast a wide net
– Do not assume from where the solution will come
• Archive data
• Write up findings
• Beware of solutions for a single condition
• Systems management and systems engineering are NOT
synonyms
• Interconnections may not be obvious
• Not everything that is critical for design (or operations) can be
found in the requirement or interface documents
This briefing is for status only and may not represent complete engineering information 32