Comparative Ergonomic Evaluation of Spacesuit and Space Vehicle

CHAPTER XX

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Comparative Ergonomic

Evaluation of Spacesuit and

Space Vehicle Design



Scott England

, Elizabeth Benson

, Matthew Cowley

, Lauren Harvill

Christopher Blackledge

, Esau Perez

, Sudhakar Rajulu



MEI Technologies Inc.

2525 Bay Area Blvd. Suite 300

Houston, TX 77058, USA

Lockheed Martin

1300 Hercules

Houston, TX 77058, USA

National Aeronautics Space Association (NASA)

Anthropometry and Biomechanics Facility

NASA, Johnson Space Center

Houston, TX 77058, USA

ABSTRACT

With the advent of the latest human spaceflight objectives, a series of prototype

architectures for a new launch and reentry spacesuit that would be suited to the new

mission goals. Four prototype suits were evaluated to compare their performance

and enable the selection of the preferred suit components and designs. A

consolidated approach to testing was taken: concurrently collecting suit mobility

data, seat-suit-vehicle interface clearances, and qualitative assessments of suit

performance within the volume of a Multi-Purpose Crew Vehicle mockup.

It was necessary to maintain high fidelity in a mockup and use advanced

motion-capture technologies in order to achieve the objectives of the study. These

seemingly mutually exclusive goals were accommodated with the construction of an

optically transparent and fully adjustable frame mockup. The construction of the

mockup was such that it could be dimensionally validated rapidly with the motion-

capture system. This paper describes the method used to create a space vehicle

mockup compatible with use of an optical motion-capture system, the consolidated

approach for evaluating spacesuits in action, and a way to use the complex data set

resulting from a limited number of test subjects to generate hardware requirements

for an entire population.

Kinematics, hardware clearance, anthropometry (suited and unsuited), and

subjective feedback data were recorded on 15 unsuited and 5 suited subjects.

Unsuited subjects were selected chiefly based on their anthropometry in an attempt

to find subjects who fell within predefined criteria for medium male, large male,

and small female subjects. The suited subjects were selected as a subset of the

unsuited medium male subjects and were tested in both unpressurized and

pressurized conditions. The prototype spacesuits were each fabricated in a single

size to accommodate an approximately average-sized male, so select findings from

the suit testing were systematically extrapolated to the extremes of the population to

anticipate likely problem areas. This extrapolation was achieved by first comparing

suited subjects’ performance with their unsuited performance, and then applying the

results to the entire range of the population.

The use of a transparent space vehicle mockup enabled the collection of large

amounts of data during human-in-the-loop testing. Mobility data revealed that most

of the tested spacesuits had sufficient ranges of motion for the selected tasks to be

performed successfully. A suited subject’s inability to perform a task most often

stemmed from a combination of poor field of view in a seated position, poor

dexterity of the pressurized gloves, or from suit/vehicle interface issues. Seat

ingress and egress testing showed that problems with anthropometric

accommodation did not exclusively occur with the largest or smallest subjects, but

also with specific combinations of measurements that led to narrower seat

ingress/egress clearance.

Keywords:

Spacesuits, Ergonomics, Biomechanics, Human System

Integration, NASA

1 INTRODUCTION

The next generation space vehicle being designed at the National Aeronautics

and Space Administration (NASA) is required to accommodate a large range of

crewmember anthropometry while enabling suited operations at a variety of

pressures and permitting all safety hardware to be used in all planned contingencies.

The Human-System Integration Requirements (CxP 70024) specify these various

human factors constraints including critical anthropometric dimensions that must be

accommodated by any spacesuits and space vehicles and the mobility and strength

required of crewmembers wearing spacesuits. These conflicting design objectives

necessitate a consolidated approach to testing and quantitative hardware evaluation,

bringing multiple groups together to investigate integration issues. However,

historically hardware testing has focused on qualitative evaluation of a single major

hardware system at a time. One such test, labeled Functional Mobility Testing

(England 2010), was conducted to determine the mobility requirements for the new

generation of spacesuits. This testing became the corner stone for MPCV suited

mobility requirements, despite relatively immature operational concepts and lack of

a high fidelity test environment. As vehicle, operations, and suit concepts became

more mature over several years, a consolidated test was envisioned to evaluate the

integrated performance of the resulting spacesuits and the latest vehicle design.

The primary goals of this study were to quantitatively evaluate the performance

of a series of prototype spacesuit architectures in the completion of a simulated

mission to the International Space Station (ISS) and to estimate this performance for

populations not currently accommodated by the prototype spacesuits. To accurately

simulate performance of the tasks, a high fidelity mockup of the Orion Multi-

Purpose Crew Vehicle (MPCV) was needed. However, quantitative analysis of

spacesuit performance required extensive visual access for the motion capture

cameras. These conflicting objectives were resolved with the construction of an

optically transparent and fully adjustable vehicle frame mockup.

2 METHOD

Once the objectives of this test were defined, personnel in NASA’s

Anthropometry and Biomechanics Facility (ABF) immediately began resolving

what operational concepts must be performed to evaluate the prototype spacesuits.

It quickly became obvious that, in order to accurately represent a mission-similar

environment, a high fidelity mockup of the MPCV would be required. The primary

challenge was that the internal volume of the MPCV is too small for an adequate

motion capture volume and existing vehicle mockups were fully enclosed. To

resolve these problems, ABF personnel began designing a fully adjustable mockup

of the vehicles critical work areas with as little solid structure as possible. The

adjustability of the mockup was critical as the MPCV’s design was still evolving. A

stress analysis of the resulting mockup was performed to verify that it was safe for

the ensuing test subjects. Commercially available bird netting wrapped around the

structure created a sense of the internal crew areas while permitting the use of an

optical motion capture system (Vicon, Oxford, UK). The ensuing mockup frame

(Figure 1) was constructed chiefly out of extruded aluminum beams (80/20 Inc.,

Columbia City, Indiana).

Figure 1: Modeled drawing of reconfigurable mockup

A Vicon capture volume was constructed around the perimeter of the mockup

such that subjects could be tracked while translating from the vehicle hatch to either

recumbent seat in either position shown in Figure 1. The Vicon system was also

used to validate the dimensions of the mockup against a computer aided design

(CAD) drawing of the relevant iteration of the MPCV by quickly enabling the

calculation of distances between key points.

Fifteen unsuited and five suited subjects participated in this study. Unsuited test

subjects were selected chiefly based on anthropometry, in an attempt to find

subjects who fit within defined categories for a medium male, large male and small

female. Suited test subjects were selected for their ability to adequately fit multiple

prototype suits and also were required to complete the test in the unsuited state.

Test subjects were fully instrumented with a set of retroreflective markers

positioned to enable the calculation of all major joint angles. Once instrumented

subjects completed an array of functional tasks representative of major tasks

performed in a mission to the International Space Station (ISS) as kinematic data

was recorded at 100 Hz (Figure 2). In addition to kinematic data; hardware

clearance, suited anthropometry and subjective feedback were recorded at key

instances throughout the test. Relevant operational tasks were performed while

with both seat positions and with suited subjects at each of three pressure states;

unpressurized, vent pressure, and nominal pressure. Suited anthropometry was

recorded for critical dimensions at each pressure. Hardware clearance was recorded

for hardware interference issues relevant to suited ingress and egress of the

recumbent seats (Figure 2).

Figure 2: Left – Suited anthropometry being collected in a suit at vent pressure, Right – Kinematic

data, hardware clearance and subjective feedback being recorded

Four prototype spacesuit concepts were evaluated in this study including the

Pathfinder 1, Pathfinder 2, Demonstrator Suit, and Zipper Entry ILC suit (ZEI).

These suits had multiple designs for helmets, mobility components and sizing

adjustments, and had varying pressurization strategies. Typically when fabricating

a new suit design concept, a single prototype is constructed for initial evaluation.

These prototypes are generally fabricated in a single size to accommodate an

approximately average sized male. Because the suits only accommodated a narrow

band of the potential population, findings from the suit testing were systematically

extrapolated to the extremes of the required anthropometry for crewmembers. This

analysis into accommodated populations was performed by first comparing the

suited test subjects’ performance with their unsuited performance and then applying

this relative performance ratio to the entire range of the population.

3 RESULTS

3.1 MockupforMotionCapture

The optically transparent mockup was a success in enabling the use of motion

capture technology while performing high fidelity tasks. Figure 3 shows an

unsuited test subject reaching for the Displays and Controls (D&C) panel in Vicon

and in video. Calculation of joint angles requires the reflective marker sets

comprising body segments on either side of a joint to be fully visible. Figure 3

illustrates that the upper body for the test subject was fully captured by the Vicon

cameras enabling calculation of all key joint angles for this task. Ranges of motion

(ROM) were then calculated for each joint by determining the maximum joint

mobility necessary for each task performed.

Figure 3: Large, unsuited test subject touching the Display and Controls Panel in Vicon (LEFT)

and on video (RIGHT)

The fidelity of the mockup was such that, for any critical dimension, the

reconfigurable mockup was never more than one inch from the dimensions in the

official CAD file and was often substantially less. This could rapidly be verified by

placing Vicon markers on key landmarks of the MPCV mockup and taking a short

data capture (Figure 4). Once landmarks of the physical mockup were recorded in

Vicon, they could be exported into a spreadsheet where distances between markers

were calculated and compared to the intended design of the vehicle.

Figure 4: Key landmarks from the reconfigurable mockup reconstructed in Vicon

3.2 SpacesuitEvaluation

The use of a transparent space vehicle mockup permitted large quantities of both

quantitative and qualitative data to be collected with human-in-the-loop testing.

While the intent of testing was to quantify the performance of the various spacesuit

prototypes, obviously qualitative evaluation was a simple but necessary data point

to paint a more comprehensive picture of how the suits performed. To that end, all

suits were largely successful in having sufficient mobility to complete tasks

required of them. Qualitatively, failures to complete a task were generally

attributed to problems with suit-vehicle integration, poor pressurized glove dexterity

and tactility, or field of view issues when seated rather than insufficient mobility

from the new spacesuits. All collected data was consolidated when determining

how to update the suit mobility requirements (Figure 5).



Figure 5: Pre and post-test mobility requirements for primary shoulder motions

3.3 PopulationAnalysis

Observational data and feedback from suited test subjects indicated few

challenges based on subject anthropometry within nominal operations of the suits.

For example, of the four inspected suits, only in the Demonstrator suit did subjects

indicate difficulty reaching any the upper-most controls on the D&C panel,

representing insufficient shoulder flexion. However, extrapolating this finding to

smaller subjects with shorter arms, it can be inferred that the suits would exacerbate

this problem, potentially requiring more mobility than they are currently capable.

For this reason, mobility requirements were buffered conservatively to produce

newer suits with greater mobility than was minimally necessary.

Ingress and egress of the recumbent seats provided the greatest opportunity for

problems to arise based on bulk of the suit and anthropometry of the test subjects.

Subjects often attempted multiple techniques unsuccessfully before finding an

approach that worked for them. These techniques included sliding into the seat

facing down, facing up, squeezing the helmet between the seat and D&C console

then laying down, hugging the strut, and more (Figure 6). Suited ingress of the

recumbent seat was easily the most challenging task encountered in this test and it

could potentially become more difficult with smaller test subjects. The smaller the

test subject, the closer the seat pan must be adjusted toward the D&C panel to

maintain proper eye alignment with the controls, which reduces the available

ingress window. Small unsuited test subjects were able to ingress the seat without

severe difficulty; however, comparison of suited anthropometry to unsuited

anthropometry indicates that this will not be the case for small suited crewmembers.



Figure 6: Multiple techniques were employed for ingressing/egressing the seat

4 DISCUSSION

The construction and use of a high fidelity mockup compatible with advanced

motion capture technology was quite successful. The mockup was validated to be

within acceptable tolerances of other high fidelity mockups of the Orion MPCV.

Additionally, the mockup enabled suited ROMs to be quantified for all suits in all

conditions as they completed the critical functional tasks. The update of mobility

requirements evident in Figure 5 reflect varying needs and capabilities of the new

prototype suits. For example, the requirements were updated to increase shoulder

flexion and adduction, which reflects a more mature series of operational concepts

in this round of tests and the need for greater arm mobility in a mission which now

is geared towards microgravity IVA while unpressurized or at a low vent pressure.

Previous mobility requirements included more significant operations for planetary

EVA operations including fall recoveries, geological exploration, and habitat

fabrication which all require much more significant lower body mobility.

Variation in subject anthropometry among unsuited subjects did not report any

serious design accommodation issues; however, analysis of suited anthropometry

and suited performance suggests that suited subject accommodation issues may

exist when prototype spacesuits are developed for other sized crewmembers. While

the seat ingress and egress evaluation of large and small unsuited test subjects did

not produce any outright failures, it did reveal some difficulties that may arise when

multiple circumstances coincide. The simplest example may be small subjects

failing due to the small clearance window, but that may be over simplifying the

issue. In practice, seated problems are more likely to occur for subjects with shorter

torsos and longer legs or wider shoulders, which results in larger body segments

needing to squeeze through smaller than normal access areas. Conditions may exist

where specific subject anthropometry merged with additional suit bulk exceed

hardware clearances. Care must be taken during crew selection and hardware

verification to avoid creating excessive rates of failure for nominal mission

operations.

5 CONCLUSION

Concurrent evaluation of prototype spacesuits in a vehicle mockup for multiple

test subject anthropometries is a difficult task yet necessary to provide meaningful

insight to hardware designers about spacesuit and space vehicle requirements

verification. The creation of an optically transparent, fully adjustable vehicle

mockup was challenging yet successful in practice. It enabled quantitative analysis

of the spacesuit prototypes while allowing inspection by all variety of stakeholders

in real time. This ability to observe the subjects in real time was secondary to the

three dimensional kinematic data in initial test priority yet ended up being very

useful for breaking down task completion beyond what is normally visible in a fully

enclosed vehicle mockup. While the test was successful in completing its

objectives, it must be acknowledged that this test had several key limitations

including all operations being performed at full gravity and a single test subject

completing tasks in an open mockup where at least two astronauts would be present

in actuality. Despite those acknowledged limitations, this series of consolidated

experiments still provided vast improvements in knowledge base for the data

collectors and stakeholders the involved hardware systems.

ACKNOWLEDGEMENTS

The authors would like to thank NASA’s EVA Systems group for providing

funding for this study. We appreciate Oceaneering International Inc., David Clark

Company Inc., and ILC Dover Inc., for providing spacesuits and relevant suit

hardware. We would also like to thank the test subjects for their time. Additionally

we would like to thank Lockheed Martin’s Orion Human Engineering group for

their assistance in validating the construction of the reconfigurable Orion mockup.

REFERENCES

England, S. A., Benson, E.A., and Rajulu, S.L. Functional Mobility Testing:

Quantification of Functionally Utilized Mobility among Unsuited and Suited

Subjects. (NASA/TP-2010-216122) NASA Johnson Space Center, Houston,

TX, May 2010

Human-Systems Integration Requirements (HSIR) Revision D (CxP 70024).

NASA Johnson Space Center, Houston, TX, December 2009

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