C null 01-17-2011

1This briefing is for status only and may not represent complete engineering information

How one Functional Human-Factors Requirement Influenced a Rocket

Dr. Cynthia H. Null, Technical FellowNASA Engineering and Safety Center


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


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


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.


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.


Examples of Requirement Categories

• Anthropometry, biomechanics, and strength• Environments• Safety• Architecture • Crew Functions (Food, Hygiene, Exercise, Medical)• Crew Interfaces• Maintenance• Information Management• EVA


Acceleration Limits (CxP 70024 -- SRR 2006)


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.


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 Exposure Duration Per 24-hr Period

Maximum Frequency-Weighted Acceleration

10 Minutes 0.4 g rms

1 Minute 0.6 g rms


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


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

Vib

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on

Lev

el

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“Health Risks Likely” —ISO 2631-1:1997

Possible Perceptual & Physiological Aftereffects Severe Performance Degradation

Historic Crew PerformanceVibration Limits (at “11 Hz”)

Shuttle crew (0.1 g)?

Gemini crew spec (0.25 g)

• Simple visual & manual tasks only; Performance Degradation

• Coarse visual & manual tasks; speech

• Fine visual & manual tasks

Achievable Performance (Vykukal & Dolkas, 1966)

1963 Gemini Centrifuge-Vibration Study (Vykukal & Dolkas, 1966)

3.5 Gx (Chest-in) Bias

0.14-1.65 gx vibration at 11 Hz***

Historical Data/Guidelines/Requirements

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13This briefing is for status only and may not represent complete engineering information 13

Crew Vibration Knowledge Gaps & RisksHSIR 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


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


Thrust Oscillation Focus TeamTeam 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


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


573681489681

“No”

• 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”

Number Reading Task


Vibration and Reading(Stationary, 12 Hz Gx vibration)


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

ARC 20-G Centrifuge Facility

vibration chair

Chair recliningat 15.3°(fixed)

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ARC 20-G Centrifuge Vibration Chair

Head Restraint

Head Rest

Vibration Actuator(1 of 4)400 lb capacity each1.5 in max stroke

2-button handheld input device

Display(raised)

Dual triaxialaccelerometer assembly

Egress Harness

5-point restraintEmergency switch

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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


1-D Graphical FeaturesCrew participants rated their ability to acquire information about thestate of system (e.g., valve state)while ignoring the text

Display Usability Rating Study (under 1-G and 3.8-G)


2-D Graphical FeaturesCrew participants rated their ability to use the PFD (while ignoring the text)

Display Usability Rating Study (under 1-G and 3.8-G)


Task 2: Manual Control Flight TaskImmediately 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

PLUSroll-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”)


SA & Manual Steering Questions


Centrifuge Study (3.8-G): Error Rates And Response Times During Vibration

Response Time (RT)Error Rate (ER)

• 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)


• ER and RT return to zero-vibration (last 5 trials) levels as soon as 145-s vibration stops

Vibration Study (3.8G) : Error Rates and Response Times After Vibration

Error Rate (ER) Response Time (RT)


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


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.


Study Team Scientists:ARC/TH: B. Adelstein, B. Beutter, M. Kaiser, R. McCann, L. StoneJSC/SK: W. PaloskiIn 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. PostARC Engineering and Hazard Analysis: O. Talavera, M. Ospring, R. PhillipsARC Chief Medical Officer & HRIRB Chair: R. PelligraJSC/CB: P. Root, T. Verborgh, M. Ivins, M. Kelly, L. MorinJSC/SF: K. HoldenJSC/ILSM-SIG: (TOMCAT) E. Rayos, M. SamirJSC Engineering: A. Sena, D. Gohmert, B. DanielJSC Medical Monitors: J. Jones, R. Scheuring, J. ClarkJSC Video: J. Blair, R. MarkowitzESMD-HRP: B. Woolford, J. Connolly, D. Russo, D. Grounds HSIG: J. Dory, J. RochlisNESC: C. NullOrion Project: J. Fox, J. Falker

Participants from ARC community & JSC Crew Office

Vibrations Studies


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

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