ABSTRACT

Performance of new space suit designs is typicallytested quantitatively in laboratory tests, at both thecomponent and integrated systems levels. As the suitmoves into neutral buoyancy testing, it is evaluatedqualitatively by experienced subjects, and used toperform tasks with known times in earlier generationsuits. This paper details the equipment design and testmethodology for extended space suit performancemetrics which might be achieved by appropriateinstrumentation during operational testing. This paperpresents a candidate taxonomy of testing categoriesapplicable to EVA systems, such as reach, mobility,workload, and so forth. In each category, usefultechnologies are identified which will enable thenecessary measurements to be made. In the subsequentsection, each of these technologies are examined forfeasibility, including examples of existing technologieswhere available. All of these measurements systemstaken together can provide a much more detailed andquantitative evaluation of a pressure suit in realisticsimulations of its operating environment.

INTRODUCTION

Space suit design is a field of continual developmentwhich works to further the capabilities of astronautsworking in space or on a planetary surface. Thetremendous increase in extravehicular activities (EVA)associated with the International Space Station (ISS)provides a continual impetus to improve the Shuttleextravehicular mobility unit (EMU) as well as the Russian

Orlan suit. Similarly, focus on manned missions to Marsand return to the Lunar surface provide the drive todevelop advance space suit systems for theseendeavors.

The development of new, or improved, suit componentstypically culminates in laboratory tests whichquantitatively measure the performance characteristicsof the new component. Tests at this level may includebench-top measurements of joint torque, range ofmotion, strength and/or durability. Next, improvedcomponents are integrated into the suit system andtested at the systems level; again, typically throughstandard joint torque, range of motion and strength/durability tests [1] [2].

At this point, further performance data is typicallycollected qualitatively by experienced test subjects whocan compare new suit performance with that of earliergeneration suits. Facilities like NASA’s Neutral BuoyancyLaboratory (NBL) at the Johnson Space Center are thetypical sites for this level of testing for EVA suits.Planetary suits typically find performance evaluation insimulated Martian environments like the simulated Lunar/Mars terrain area at the NASA Johnson Space Center,or in field trials such as those of recent years at SilverLake, Meteor Crater, or the Mars Society testing groundsat Devon Island [3] [4]. These simulations can, and are,being improved by testing under the reduced gravityconditions achieved during parabolic flight aboard theKC-135.

All of these methods have contributed to substantialimprovements in space suit design, and each hasproven useful over the years. However, each method

2003-01-2415

Neutral Buoyancy Technologies for Extended Performance Testing of Advanced Space Suits

David L. Akin and Jeffrey R. Braden Space Systems Laboratory, University of Maryland

Copyright © 2003 SAE International

of system level testing is not without its drawbacks.Terrestrial testing of planetary suits provides a wealth ofdata on suit design; however, the reduced gravity ofboth Mars and the Moon will have significant effects onsuit performance which are not being captured in suchtesting. KC-135 flights, while they do capture reducedgravity conditions, are prohibitively expensive and shortin duration. And across the board, including the neutralbuoyancy tests for EVA suit evaluation, the largestproblem with current performance testing is a lack ofquantitative data collection.

To achieve revolutionary advances in pressure suitdesign, testing methodologies need to be furtherdeveloped to allow quantitative testing of performanceduring suit operations testing, which may bedevelopment, training, or even in-flight operations. Thispaper proposes an integrated approach to advancedsuit instrumentation and testing which applies at anumber of levels, ranging from simple methodologies toobtain quantitative comparison data, to unobtrusivesensor systems which will provide information on crewsensorimotor adaptation, metabolic workload, and othersignificant metrics of performance for the integratedhuman/suit system.

In a sense, this paper really presents a vision of anintegrated system for suit instrumentation, testing, andevaluation that is compatible with neutral byoyancy,field trials, and even flight evaluations of advancedsuits. In many cases, examples will be drawn from pastand present research projects of the University ofMaryland Space Systems Laboratory. These samplesystems presented range from concepts, tobreadboarded systems used for proof-of-concept testing,to highly developed systems already used for advancedresearch. In no case will this paper go into the detailedresults of any of these individual componenttechnologies; rather, this paper will focus on developinga set of useful components for an integrated suitevaluation system, and will describe how all thecomponents may be brought together to create a usefulsynthesis of performance metrics.

DESIRABLE EVALUATION METRICS FORSUIT OPERATIONS

When a current space suit reaches integrated teststatus, the primary focus is on getting experiencedsubjects into the suit, and having them perform testswhich correlate to prior experience. This approach isadequate for qualitative evaluation of design changes,but does not provide a full quantitative insight into theeffects of suit design modifications. What, then, are themetrics which need to be included to provide a more

complete picture of human/suit performance? Withineach metric, what technologies are required to provideuseful quantiative measures of performance? Somebeneficial candidates can be summarized under thefollowing categories.

DEXTERITY AND REACH METRICS

The vast majority of EVA development consists ofanswering two questions: Can you reach it? And whenyou do, can you operate it? A greater degree of rigor inthe quantification of reach and dexterity metrics wouldprovide hard metrics on critical suit capabilities, as wellas provide the necessary data base for advancedsimulations of pressure suit operations.

In this category, the objective is to quantify the reach ofthe suit with respect to some fiducial point on the suititself. Often this has been the suit upper torso; thisprovides a reach envelope of the arms alone. This datamay be reconstructed by forward transformation of armjoint angles without external measurements. In othercases, it has been a reference point between the feet,which allows the incorporation of suit flexibility in reducedor microgravity. These test traditionally involve the useof neutral buoyancy or parabolic flight, and are thereforeindicative of microgravity. There are no known full-bodyreach envelopes for partial gravity, such as lunar orMars conditions.

Traditional reach envelope testing of pressure suits hasbeen performed in the laboratory (1 g) environment.This was traditionally performed with manualphotogrammetry or goniometers, but has lately beenupgraded to automatic photogrammetric analysis.Electromagnetic position sensors also function well inthis controlled environment.

Technologies applicable to this category of metricsinclude:

• Accurate automatic position sensing• Whole-body partial gravity simulation• Limb pose measurement• Standardized dexterity tests

MOBILITY METRICS

While reach envelopes measure the crew's capability tospan distances from a fixed point, overall work stationdesign relies on the ability to translate from task locationto location. This translation task frequently is the largest"mass handling" task of the EVA, and suits whichfacilitate this type of motion convey an advantage forthe wearer. Looking at the problem in the other direction,

EVA timelines which reduce the requirement for thecrew to manipulate their own body positions free uptime to perform the required tasks. However, there hasbeen little means of measuring body motion other thancoarse inference from the work station design.

A system which can monitor the subjects body motionin all six dimensions (three translational and threerotational) could provide much finer-scale data onmobility as a component of operational tasks. Thiswould aid in refining work site design protocols. It wouldalso provide sufficient data for direct calculation of crewenergy which is expended in body motions, which willhelp to obtain more accurate energy estimates of theactual task operations.

Technologies applicable to this metric include:

• Automated six-axis state measurements

FORCE/MOMENT CAPABILITIES

Forces and moments are critical to EVA operations, andto the safe design and operation of EVA systems. Crewloads are often the driving factor in the design ofadvanced pressure suit components, and are of primaryconcern in the safe design of tools and interfaces for theEVA worksite. However, forces and moments are notgenerally well understood from a "first principles" pointof view. Suit joint torques are generally measured bysimple scales applying external forces on suitcomponents [5]; few opportunities for direct internalforce measurement exist in harmony with the space suitwearer.

However, significant types of data can be learned withwell-placed six-axis force/torque sensors. For instance,applied forces to a handrail can be directly measured byforce-torque sensors under the handrail, and substantialinformation can be further gleaned from six-axis force-torque measurements in the foot restraint mountingmechanism. To obtain this data from ground-basedsimulations, however, these sensors have to bepackaged to be compatible with the simulationenvironment.

Some hope still exists that direct force or torquemeasurements may be obtained from occupied pressuresuits. Force or pressure transducers mounted betweenthe wearer's limbs and the pressure suit garment maygive readings related to the relative force betweenthem, and therefore capable of providing estimatedforces and torques applied through the pressure suit.

Technologies applicable to this category of metricsinclude:

• Environmentally compatible force-torque sensors• Suit-compatible low-profile wearable pressure or

force sensors

PHYSIOLOGICAL WORKLOADMEASUREMENTS

Ultimately, the true measure of any pressure suit is thephysiological stress it places on its wearer; that is, theextent to which the EVA crew expends energy in movingthe suit rather than performing the assigned task. Acommon tool in physiology laboratories aremeasurement systems for metabolic workload,particularly oxygen uptake (VO2) systems. Thiscapability has been incorporated into pressure suits forflight EVA measurements, but has never been routinelyavailable for neutral buoyancy or other ground-basedsimulations.

This type of measurement is uniquely valuable forunderstanding to overall issue of pressure suit limitationson the wearer. For example, metabolic workloadmeasurements were available for the ExtravehicularAssembly of Structures in EVA (EASE) activities onSTS 61-C. The measured metabolic workload, basedprimarily on oxygen consumption, could be correctedfor basal metabolic workload to find the physiologicaldemands on the test subject. Photogrammetric meanswere used to calculate the energy going into the EVAtasks. Comparison of the results indicated that only25% of the physical activity of the EVA crew was beingapplied to the task elements, implying that the remaining75% of the crew's energy was being applied to operatingthe pressure suit. [6] This process provided a uniqueand graphic example of the limitations of conventionalpressure suits, and illustrates the utility of routinelyavailable physiological workload measurements.

Technologies applicable to this category of measurementinclude

• Pulmonary function metabolism measurements• Thermal balance monitors

NEUROMUSCULAR ACTIVITY MONITORING

While proposed sensor systems to this point havefocused on what the EVA crew is doing and whatphysiological exertion is required, there has not yetbeen any attempt to understand how the actual motionsare produced. One of the common comments followingan EVA is that specific locations of the subject areheavily fatigued by the end of the operation. Frequently,this occurs in the hand and wrist, which are heavily

crew performance, particularly later in an EVA, and is apotential safety hazard if fatigue is allowed to progressto the point where manual tasks required for close-outand ingress become difficult to perform.

Ideally, the degree of muscular fatigue should bemonitored in a noninvasive manner. Such a systemwould allow direct measurement of fatigue onset rates;this would provide an ideal quantitative metric forevaluating new designs for suit gloves or other suitarticulations.

Technologies applicable to this category ofmeasurement:

• Electromyographic Monitoring System

SENSORIMOTOR ADAPTATION

One of the purposes of repeated training is to inducesensorimotor adaptation to the required tasks. This"muscle memory" produces instinctive response tostimuli, and thereby uses natural body control loops toprovide near-optimal responses.

A good example of this is the use of rotary bearings insuit components, such as the shoulders of the ShuttleExtravehicular Mobility Unit (EMU). Direct shoulderextension/flexion can frequently results in forcesperpendicular to the bearing rotation direction, whichrequires high loads to overcome bearing friction. Bringingthe arms forward therefore is best done my moving theshoulders through a rotation pattern which more nearlymatches the rotation directions of the bearings. Untilthis "patterning" becomes instinctive to the wearer,much energy may be expended on trying to force theshoulder bearings to move in directions of poormechanical advantage.[7]

Understanding and documenting this sort ofsensorimotor adaptation has been difficult in the past,and has relied upon qualitative anecdotal information.By directly measuring body joint angles, however, arunning record may be kept on body motions inside thesuit. This record would document when and wherepatterning adaptations take place, and would serve asa quantitative metric on crew training and flight readiness.

Technologies applicable to this category of metricsinclude:

• Joint angle measurements

TECHNOLOGIES FOR ADVANCED SUITINSTRUMENTATION

Each of the measurement categories from thepreceeding section will be briefly examined to identifyfeasible approaches to the creation of suitable EVA-compatible instrumentation. Where appropriate, priorart will be identified and discussed.

AUTOMATED POSITION SENSING/AUTOMATED SIX-AXIS STATEMEASUREMENTS

The requirement for this sensor system is to provideunobtrusive measurements of more or more positionsat regular time intevals. Based on potential motionvelocities, data collection rates need to be on the orderof several times per second in order to facilitate accurateestimates of velocities. This should be capable of beingtime-tagged and automatically logged, for correlationagainst activities or workload measurements.

The University of Maryland Space Systems Laboratoryoriginally developed the Three-Dimensional AcousticPositioning System (3DAPS) as a means to collectaccurate position and attitude data for feedback controlof robots in a neutral buoyancy environment. Like theGlobal Positioning Satellite system, 3DAPS uses theranges from known locations to receivers on the vehicleto produce a three-dimensional position estimate. Dueto the physics of the underwater environment, theapproach used was the time of transmission of ultrasonicacoustic pulses from multiple emitters at known locationsaround the periphery of the water tank to hydrophoneslocated on the vehicle. A single hydrophone producesa three-dimensional position estimate with demonstratestatic accuracies below one centimeter. By using fourhydrophones fixed in relative locations to each other, afull six-axis position and attitude estimate can beobtained. This system currently uses sequential pulsesfrom eight emitters, allowing position updates atapproximately two Hertz. An upgraded system usingmultiple frequencies is currently under development,which should improve the update rate to approach thetheoretical maximum of 10 Hz. [8]

Early tests confirmed the usefulness of such a systemfor suit testing. Test subjects in EMUs were placed infoot restraints and given a "wand" containing fourhydrophones in a fixed pattern. The 3DAPS systemallowed the direct measurement of the position andattitude of the handle of the wand, which was inside thegrip of the EVA glove. The subjects moved the wandthroughout the extremes of their range of motion, forconditions including right hand, left hand, and two-handed operations. This included full body motions

tasked and working at considerable mechanicaldisadvantage in pressurized gloves. This fatigue limits

environment, and which much more accurately replicatesmicrogravity reach envelopes [Figure 1].

Such a system could be used for a variety of othertesting purposes. 3DAPS hydrophones mounted to thebackpack of the EVA subject could be used to provideaccurate continual measurement of body positionthroughout an EVA, which would allow directmeasurement of all body translations and attitudereconfigurations required for any given task. Use inconjunction with the ballasted partial-gravity simulationtechnique described below would provide similar reachand mobility measurements for planetary surface EVAsimulations.

debilitated by the cyclical g loading of parabolas andpull-outs. In addition, this test mode is prohibitivelyexpensive, in excess of $5000 per hour.

Counterbalance harnesses work adequately for whole-body activities such as walking, but do not attempt toprovide partial gravity simulation for body componentssuch as limbs. The complexity of overhead harnessescreates the need for considerable infrastructure, whichgenerally limits testing to specific small areas inside alaboratory. For these reasons, the vast majority ofsurface EVA training for Apollo was performed in 1 gwithout attempting to offset gravity conditions, otherthan the use of lightweight backpacks and mockups. [9]

The underwater environment, so familiar from neutralbuoyancy simulations, offers a opportunity for partialgravity simulations as well. By ballasting individualbody components proportionally to their relative masses,practical underwater simulations of lunar and Marsgravity can be achieved. This has been used in the pastat NASA Ames for studies of partial gravity walkinggaits, using a treadmill to reduce water drag effects onthe test subject. [10] While this approach is limitedbecause of the dynamic effects of water, it is more thanadequate for a wide range of static or quasistaticactivities, such as reach envelopes. In fact, tests recentlyconducted in the KC-135 aircraft on planetary roveringress and seating, and on effects of backpack centerof gravity on posture and stance stability [11], could bebeneficially conducted underwater using this technique.

LIMB POSE/JOINT ANGLE MEASUREMENTS

To truly understand what the EVA crew is doing, theideal situation would be to fully document all of themotions of the body. One approach would be to buildthis capability into the pressure suit itself; this wouldkeep the instrumentation transparent to the wearer, andwould provide direct measurements of suit motion.However, to really understand the human element, itwould be more beneficial to mount the joint anglesensors directly onto the suit wearer. This could beaccomplished for most of the major body joints byenbedding bend sensors (such as fiber optic or variableresistance strips) into the liquid cooling garment, whichideally fits conformally to the skin of the suit wearer. Thiswould provide the transparency to the EVA crew (i.e.,no additional overhead in donning or operations), whichproviding useful data to the researchers.

Perhaps the most important portion of the body toinstrument are the hands. The hands are the criticalreason for performing an EVA, and therefore are themost likely to fatigue and reach states of degraded

Figure 1EMU Reach Envelope Measurement using 3DAPS

WHOLE-BODY PARTIAL GRAVITYSIMULATION

Traditionally, partial gravity EVA simulation has involvedeither parabolic flights at reduced g, or counterbalanceharnesses to offset body weight. While the parabolicflight approach produces excellent simulations of partial

gravity, test times are limited to approximately 30seconds at a time, and test subjects are frequently

from the foot restraint, which produced a much widerrange of motion than would be attainable in a laboratory

performance. The University of Maryland has developedseveral generations of instrumented comfort gloves[Figure 2],[Figure 3] to continually measure finger jointpositions, compatible with use inside of standard andexperimental pressure gloves [12], [13] Theseinstrumented gloves were used with a self-containeddata collection system inside NASA EMUs for datacollection on hand motions and wrist fatigue[ref]. Theywere also used to document hand motions in theperformance of standardized dexterity tests; data fromthe gloves was used to determine finger motions inpressure suit gloves, which was then used to select thestandard dexterity tests most appropriate for use as astandard fiducial test in comparative testing of advancedglove concepts. [14]

results which carry over if the task changes, or if the nextstudy is performed at a location without the same high-fidelity training mockups.

An alternative approach is to investigate standarddexterity or body kinematics performance tests from thekinesiology and rehabilitation communities forapplicability to space suit operations. This approachleverages a large body of data on standard performancemetrics, and provides standardized test protocolsavailable at any participating research center.

In looking for a small number of dexterity tests whichwould exercise pressure suit glove mobility and allowquantitative comparisons between competing glovedesigns, the SSL examined a large number of manualdexterity tasks commonly used in rehabilitationassessment and therapy. The four tests most likely tobe applicable to EVA glove dexterity testing wereevaluated, and a single modified Purdue pegboard test[Figure 4] was selected as a simple test apparatus andprotocol which provided ideal data on EVA gloveperformance. [13],[14]

Figure 2Prototype Fiber Optic Sensor for Finger Flexion

Figure 3Instrumented EVA Comfort Glove

STANDARDIZED DEXTERITY TESTS

The tendency to adopt operational tasks for qualitativeevaluation of suit performance reduces the ability totransfer results between different studies at differentlocations. Performance of an International Space Stationservicing task, while informative, does not produce

Figure 4Modified Purdue Pegboard Test for EVA Dexterity

Similarly, it would be desirable to find a test which wouldexercise and measure suit performance over largerbody components, such as arm and waist mobility. Oneprotocol adapted to many such tests is the Fitts' TappingProtocol. Fitts' Law states that the index of difficulty ofa precision pointing task is a function of the ratiobetween the required precision (size of the target) andthe necessary motion distance (distance betweentargets). Using this approach, the SSL developed anunderwater Fitts' Law task board with variable sizedtargets and selectable intertarget distances. The subject(suited and unsuited) used a pointer to cyclically touchpairs of targets, with times and accuracies recordedautomatically by computer. This setup [Figure 5] hasbeen used to assess the effect of various design

decisions, such as position of foot restraints, on suitmobility.

ENVIRONMENTALLY COMPATIBLE FORCE-TORQUE SENSORS

Six-axis force-torque sensors may be bought off-the-shelf from several reputable companies for researchpurposes. At least two of these (JR3 and ATI) sellwaterproofed force-torque sensors applicable to neutralbuoyancy research. The SSL has used sensors fromboth these companies to instrument various EVA testsetups, including foot restraints, hand rails, and forcemeasurement plates.

However, many of the tests which might be done do notnecessarily map well into a test sensor fixed in onelocation. For example, it would be highly desirable toproduce a three-dimensional map of how the EVA forceand torque limits change throughout the suit's reachenvelope. Past testing in support of this mapping at theSSL [Figure 6] required a support diver to physicallymove the foot restraints and force plates between datapoints, a difficult and demanding task that limited theamount of data which could be collected to a sparselyposulated set of widely distributed points. [15]

Tests using SSL robotic manipulators havedemonstrated the potential for a robotic EVA test cell toprovide much more useful and adaptable data collectionopportunities. For example, by incorporating the forceplate into the end effector of a robot arm, the force datacollection throughout the EVA reach envelope could beautomated, and the grid size changed to get maximumdata discrimination in regions of primary interest. Thissystem could also be used to move beyond static forceapplications, and investigate pressure suited control

bandwidth as a function of various design parameterssuch as restraint type and location.[16]

SUIT-COMPATIBLE LOW-PROFILEWEARABLE PRESSURE OR FORCESENSORS

As described above, low-profile pressure/force sensorscould be beneficially placed on the pressure suit wearer'sbody to directly measure applied forces, or to monitorpressure points as a function of suit design. Conceptually,these sensors might be mounted at significant locationsof the liquid cooling garment, to simplify the interfacesto the wearer.

Although the SSL has never attempted to integrate thistype of sensor into a pressure suit, they have been usedeffectively with a robotic hand model to assess pressureloads in space suit gloves. This test apparatus, originallydesigned to test mechanical counterpressure gloves,has demonstrated the utility of this type of sensor, andshown that integration into an actual pressure suitwould not be a difficult task.[17]

Figure 5EVA Subject Performing Fitts' Law Test

Figure 6Instrumented Work Station for Force Mapping

PULMONARY FUNCTION METABOLISMMEASUREMENTS

In laboratories around the world, metabolic workloadmeasurements are routinely made using VO2instrumentation. These systems measure pulmonarytidal volume, and monitor partial pressures of oxygenand carbon dioxide in the inhaled and exhaled airstreams. Using this information, physiological workloadcan be calculated.

Since parallels to these measurements are available inpressure suit portable life support systems, metabolicworkload measurements have been available post-flight in some operational EVAs.[6] However, sincesurface-supplied breathing gases are used in neutralbuoyancy facilities, no corresponding underwatermetabolic workload measurement is available. This isseverely limiting, as this data would be invaluable forcorrelation of neutral buoyancy simulations to flightEVAs.

The problem with simply purchasing and integrating aVO2 instrumentation system into a neutral buoyancylife support system is the fact that suits are provided witha constant air flow (typically at six cubic feet per minute);there is therefore no way to directly measure tidalvolume. However, in the development of the MX-2underwater suit simulator [Figure 7], the SSL hasintegrated a set of air constituent sensors into the suitlife support systems at appropriate places to providesufficient information to infer tidal volume, and therebyobtain a metabolic workload measurement in thepressure suit. Initial tests of this system should occur inthe summer of 2003.

THERMAL BALANCE MONITORS

An alternative means of measuring metabolic workloadis to directly monitor the heat exchange rates of thehuman body. Because of the thickness and multiplelayers of a pressure suit, the heat transfer rate throughthe suit itself is quite low, and subject to experimentalmeasurement. Body cooling is effected by a liquidcooling garment, which circulates cold water throughtubes held against the surface of the subject's skin. Bymeasureing inlet and outlet water temperatures, as wellas water flow rates, an estimate may be obtained of totalmetabolic workload; the accuracy of this is enhanced byincluding data on air cooling (measuring inlet and outletair temperature and humidity, along with air flow rate).Ideally such as system should be used in conjunctionwith the pulmonary metabolic sensor system describedabove.

ELECTROMYOGRAPHIC MONITORINGSYSTEM

Critical muscle groups, such as the hands and forearms,control how much useful work an EVA crew may perform,and even limit the extent of safe EVA operations.Laboratories have been able for decades to directlymeasure muscle involvement and the rate of fatigueonset through the use of electromyographic (EMG)sensors. These surface-mounted electrodes pick upthe muscle activation signals of nearby muscle groups,and can be used to measure the fatigue and estimatethe remaining work limitations of the muscles.

The SSL as part of its Joint Angle and Muscle Signature(JAMS) experiment, developed and operated a self-contained EMG sensor system inside NASA EMUs inneutral buoyancy simulations. [Figure 8] Techniqueswere developed for this testing which allowed directinference of muscle state at arbitrary times, as opposedto common laboratory protocols in which the muscleunder study had to be relaxed and static to take an EMGreading.[18] This system has been demonstrated inneutral buoyancy operations at repeated intervals, and

Figure 7Maryland Advanced Research/Simulation (MARS)

Suit MX-2

is ready for incorporation today into advanced EVAtestbeds.

CONCLUSIONS AND RECOMMENDATIONS

The listed measurement systems have been developedby the University of Maryland Space Systems Laboratoryover the past 25 years of research. Taken individually,they have allowed a wealth of experimental investigationof EVA capabilties, and the effects of technologyupgrades on pressure suit design.

However, there has never been an occasion wherein allof these component instrumentation systems werebrought together into a single testbed setup. This wouldallow a wealth of data on EVA capabilities and pressuresuit desigh to be obtained. For example, reach andforce capabilities could be obtained in three-dimensionalspace throughout the reach envelope, as a function oflocal gravity and various competing suit component.Tasks which in the past were only used to generatetime-based performance metrics could providecorrelated numerical data on physiological workload,applied forces and moments, muscular activation andfatigue, and body motions. Data would be available tosort out exactly how much energy the test subject wasusing to perform the task, and how much goes into thesuit. Since all of these instrumentation systems arecompatible with neutral buoyancy testing, a much largerdata base can be accumulated than would be availableif limited to flight data. And, since the systems are(generally) EMU compatable and flight qualifiable, flightdata could be obtained from operational EVAs withoutadditional work load on the flight crew which would

produce a wealth of data for correlation of neutralbuoyancy (or other ground-based) simulation to actualflight data.

The intersection of all of these sensor systems, with theinclusion of modern technologies in scene generationand immersive virtual reality, offer the tantalizingpossibility of high fidelity dynamic VR training. An EVAcrew might train in the neutral buoyancy environment toobtain the benefit of realistic body motions in themicrogravity environment. Rather than produce anexpensive and high-maintenance high fidelity mockupof the entire spacecraft, however, the only pnysicalhardware would be a series of human interfaces (suchas hand rails) positioned and manipulated by roboticactuators. Position sensors (such as 3DAPS) and bodyjoint sensors would be combined to produce a model ofhow the subject is moving; force-torque sensors wouldrecord external forces and provide the input to referencemodels on how the subject and pressure suit would beresponding in actual microgravity. An immersive head-mounted display would show the subject not theunderwater pool environment, but a three-dimensionalimage of whatever space environment to which thetraining task is applicable. Actively controlled interfaceswould produce high-fidelity motion for any componentplanned for manipulation in space, from small orbitalreplacement units to large modules or truss segments.This underwater immersive reality would provide muchhigher fidelity training than is currently available inneutral buoyancy and virtual reality laboratories, andwould minimize "negative training" artifacts of theenvironment.

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Figure 8Final Installation of Joint Angle and MuscleSignature (JAMS) Data Recorder inside EMU

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11. Ross, Amy, "Lunar Rover Vehicle Mock-upAdvanced Space Suit Ingress/Egress Test" JSC39922, NASA Johnson Space Center, May 2000.

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13. Pelton, Melissa H., "The Effects of ExtravehicularActivity Gloves on Human Hand Performance" M.S.Thesis, University of Maryland, 2000.

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15. Chakraborty, Sayan, "Experimental Modeling ofEVA Tasks and Workload Using Force-TorqueSensing Apparatus" S. M. Thesis, MassachusettsInstitute of Technology, 1990.

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18. Claudia Ranniger, Beth Sorenson, David Akin,"Development and Applications of a Self-Contained,Non-Invasive, EVA Joint Angle and Muscle FatigueSensor System" NASA/AIAA Life Sciences andSpace Medicine Conference, Houston, TX, April1995.

CONTACT

For more information, please contact Dr. David Akin(dakin@ssl.umd.edu) or Jeff Braden(jeffbraden@ssl.umd.edu) at the Space SystemsLaboratory, Bldg. 382, University of Maryland, CollegePark, 20742.

The URL for the Space Systems Lab is: http://www.ssl.umd.edu.

5. Braden, Jeffrey R., and Akin, David L., “Developmentand Testing of a Space Suit Analogue for Neutral