- Email: [email protected]
EVA worksite analysis—Use of computer analysis for EVA operations development and execution
Acta Asrronaurica Vol. 44, Nos. 7-12, pp. 593-606, 1999 Astronautical Federation Published by ElsevierScience Ltd All rights reserved. Printed in Great Britain 0094.5765199 5 - see front mnkr SOO94-5765(99)00100-9 0 1998 International
Pergamon PII:
EVA WORKSITE ANALYSIS-USE OF COMPUTER ANALYSIS FOR EVA OPERATIONS DEVELOPMENT AND EXECUTION Dave Anderson The Boeing Company Huntington Beach, CA both a highly complex and sufficiently flexible environment for EVA operations. To respond to this challenge, NASA and its contractors have developed an effective set of simulation tools, both electronic and physical, for design of the station, development of operational techniques, training of the assembly and maintenance EVA crew, and execution of EVAs. Naturally, we have the most experience with the earlier stages of this process. The story of how these tools succeed during the thousands of EVA hours coming in the next decade is just beginning to be written.
ABSTRACT To sustain the rate of extravehicular activity (EVA) required to assemble and maintain the International Space Station, we must enhance our ability to plan, tin for, and execute EVAs. An underlying analysis capability has been developed to ensure EVA access to all external worksites as a starting point for ground training, to generate information needed for on-orbit training, and to react quickly to develop contingency EVA plans, techniques, and procedures. This paper describes the use of computer-based EVA worksite analysis techniques for EVA worksite &sign. EVA worksite analysis has been used to design 80% of EVA worksites on the U.S. portion of the International Space Station. With the launch of the first U.S. element of the station, EVA worksite analysis is being developed further to support real-time analysis of unplanned EVA operations. This paper describes this development and deployment of EVA worksite analysis for International Space Station (ISS) mission Support.0 1998 International
SPACE STATION INBOARD TRUSS EVA WORKSITES ISS is composed of four major portions, as shown in Figure 1: m Russian modules m U.S., European, and Japanese pressurized modules m Truss inboard of the solar array rotary joints (SARJs) m Truss outboard of the SAIUs. In this paper, we examine the inboard truss segments. The inboard truss is made up five segments as shown in Figure 2. Segment SO (starboard zero) is the nexus between the truss and the pressurized modules providing structural, electrical, avionics, fluid, and crew translation connections. Segments Sl and Pl (port one) are very similar to each other; their primary purpose is to provide active heat rejection for station waste heat. Segments S3 and P3 are also very similar, providing attach points for payloads and spares and the large SARJs that rotate the outboard solar arrays to follow the sun. Each of the five inboard truss segments is brought to the station separately and assembled from the middle out. EVA assembly tasks for a given segment are performed by the space shuttle crew that brings the segment up, and later completed by the ISS crew after the shuttle departs. From there on, EVA maintenance tasks are performed as needed to keep the external systems up and running. More than 2,700 EVA worksites are required to assemble and maintain the five inboard segments, as shown in Figure 3. An EVA worksite is defined as a single crewmember location from a single setup of
Astronautical Federation Published by Elsevier Science Ltd. All rights reserved.
INTRODUCTION The large number of ISS EVAs requires that the external mobility unit (EMU) function many more times between ground servicings than current shuttle operations, and at a rate that will quickly overshadow all previous EVAs. More than 1,700 EVA hours will be required for ISS tisembly and more than four times the shuttle EVA experience to date’. Over the lifetime of the station, 1.622 additional maintenance hours are predicted. To sustain this EVA rate, we must also enhance our ability to plan, train for, and execute EVAs. Despite the standardization of EVA interfaces and tools, the thousands of space station EVA worksites are all unique, requiring specific setup of EVA access and tools. Multiply these worksites by the range of crewmembers who may be called on to perform the tasks, ranging from 95th percentile American male to 50th percentile American female, and by the range of EVA worksite access methods (by crane, foot restraint, cart, free-float, or body restraint tether), and the result is 593
49th IAF Congress
Figure 1.1% Components 04142 REUI
mated. The SOanalyses have been hampered by a major change in the early station orientation which required nearly every previous EVA worksite to be covered by thermal shrouding. EVA WORKSITE DESIGN Worksite Restraint
PMA3 Figure 2.
Inboard ‘IYussSegments
restraints. Each worksite requires methods for the crewmember to react loads through his/her feet and hands, to be able to see the object being worked on, and to reach it with hands or tools. EVA aids for each worksite must be designed and verified, procedures developed, and training provided. The worksite quantities shown in Figure 3 are taken from Boeing EVA worksite analyses for each segment. The analyses for segments S 1, PI, P3, and S3 are nearly complete. SO analyses that are not complete were esti-
The first concern at an EVA worksite is finding a way to restrain the extra vehicular (EV) crewmember so that he/she can apply loads to the worksite without affecting body orientation. Several methods are available: 1. Free-float (Figure 4). When very low forces are needed for short durations (e.g., less than 10 lb for less than 1.4 set), the crewmember can work without foot restraints, reacting the forces applied by one hand with the other hand using one of the 540 handrails on the inboard truss or any other eligible structure. This is the simplest and fastest restraint method but requires the most crew skill to remain stable. Strict requirements have limited use of free-float for worksite restraint during ISS design, ensuring that we would have other options for the crewmember restraint at most worksites. Development testing and training runs liave shown that
49th IAF Congress nnn
600 .z? Z
500
8
400
2
300 200
S-0 Segment Figure 3. EVA worksites
s’l
s’3
are distributed more or less evenly across the inboard truss and spiit between assembly and maintenance uses
04124REU8.2
4. Free float enables a crew member to reach many simple work sites quickly. Here one crew member (EV29) works from the SSRMS while the other crew member releases straps at many different work sites crewmembers prefer to free-float when feasible to cut down on task time and fatigue. 2. Tethered restraint. Creative use of tethers can provide the crewmember with another limited method of load reaction. Strap or cable tethers attached to the crewmember’s wrist, waist, or chest can be used in tension to provide load reaction. The body restraint tether, which is made up a series of spherical bearings, can be locked down in a wide range of shapes to react around 10 lb of load for extended periods. 3. Structure-based foot restraint. The articulating portable foot restraint (AWR) (Figure 5) can be
installed into any of the 238 worksite interfaces (WIFs) on the inboard truss and used to restrain a crewmember’s feet at a worksite (Figure 6). The APFR, at 50 lb and roughly a 24 cube, is the maximum weight and size the crew are willing to have hanging off them while they translate around hand over hand. Once at a WIF, the crewmember can set up the AWR clock, pitch, roll, and yaw in one of more than 33,000 potential orientations to place his/her body at the worksite. Choosing
Figure
Figure 5. The APFR will provide restraint for must EVA worksites. The APFR can be articulated in clock, pitch, roll, and yaw to more than 33,000 dh’ferent rientations from a given worksite interface. P
49th IAF Congress
596 EVA Work&e Envelope (See Claimcation of Work&e Area) :g,,
,\
jp,,,
EVl Crew Member &.c%c&:g Launch
\ VIEWLOOKING FORWARD (FACE 3I4)
Figure 6. Typical APFR -restrained between
these positions for the full range of potential sixes of EVA crew is a key element in computer-based EVA worksite analysis. Working from the APPR, the crewmember can react much higher sustained worksite loads (up to 45 lb) through hisher legs or hands. A load alleviator in the APFR assures that the crewmember does not react so much load that it damages the structure to which the WIP is mounted. Despite the large number of WIFs and APFR orientations, structure-based WlFs
are
Grapple Fixture (Face 3)
Worksite
still limited, in reach and orientation, to a given work location. In addition to lugging the API% around, the crewmember must get out of the foot restraint to change pitch and clock settings. Ingress into the APFR is a difficult skill; a swift APPR ingress is usually a sign of an experienced crewmember. 4. CETA-based foot restraint. The crew and equipment translation aid (CETA) (Figure 7) is a hand-operated rail car that can be translated along a rail on the
49lh IAF Congress
work Station
Adjustable
Es;,“’
Stanchion
Stowage Device
Energy Absorber, CETA MXETAAclive
597
Coupl
Assembly 4 Places
Patmg Brake Handle Assembly
Figure 7. CETA Cart On-orbit‘IkanslationContlguration 5. SSRMS-based foot restraint. The Space Station forwardface of the truss. Since most of the more freremote manipulator system (SSRMS) arm provides the quent maintenance tasks are located on one of the forlarge-object manipulation that makes ISS assembly ward truss faces, the CETA ad& another level of possible, but it is also the most versatile method of EVA flexibility for EVA access while cutting the cargo a restraint. With an APm mounted to the end of the arm crewmember must carry around on his/her body to get (Figure 9), nearly infinite EVA orientations are availthe job done (Figure 8). The CETA has five WsFs. All able for inboard truss worksites limited only by physihave their own pitch/yaw articulation, and three are cal obstructions (Figure 10). While there is great time mounted to swing arms. The nadir swing arm WTFScan be set to any of 4,800 orientations. A single CETA cart savings to the crewmember, not having to translate, set up, and ingress AH% at each worksite, but an addilocation along the rail provides over 450 million potential foot plate locations. Still, these locations are limited tional crewmember is required inside the station to to providing access to the forward faces of the truss and operate the arm. The SSRMS also draws power, data, nearly all with the crewmenher’s head pointing away and scarce camera resources to operate. Ultimately, from the CETA. Adjusting the cart location requires there is only one arm for the minimum of two crewingress into special translation foot restraints and members on a given EVA, so we can’t count on everyreleasing and setting brakes. Finding the right combinathing being done from the SSRMS. tion of location and settings is dependent on EVA EVA Worksite Requirements worksite analysis. These settings will be refined for Ideally, EVA access to each worksite, along with the assembly tasks and limited maintenance tasks during EVA aids locations, would be verified using physical neutral buoyancy training.
491h IAF Congress
598
C;t I A
cian Locate01or
CETA Light Zero-G Connector Disconnect/connect
CETA Cart Socket 1 Used for
APFR Setting (P3) APFR Setting (S3) Clock = E 12:OO (0’) Clock = 12:00 (0’)
CETA Handrail (P3 HHTl191 B (S3 - Not Shown
ETA Cart Socket 3 Socket Setting: Pitch = 15O Yaw = 3:00 (90”)
Used for Ingress and Stabilization CETA Light
Analysis Position 2-l Zero-G Connector Disconnect/Connect View Looking Nadir and Inboard
Figure 8. ‘I)-picalCETA-based EVA Worksite
mock-ups in neutral buoyancy and evaluated with the full range of crewmembers who might perform each task. Since the cost and time to accomplish this for thousands of worksites is prohibitive, the KS program has developed a set of requirements that, if met, nearly assure that a worksite will be EVA compatible, if not EVA friendly. Naturally, these requirements are conservative. NASA expects a broad size range for EVA crewmembers from 5 ft 2 in. 50% American‘ female to 6 ft 3 in. 95% American male (Figure 11). This is not to say all EVA crewmembers will be American, just that easily available American anthropomorphic databases were used. Requirements establish the following: m How hardware of different sizes and masses must be restrained by EVA crew m How big the gaps between EVA handrails can be m The area a crewmember can reach from a given restraint location m What each worksite must provide for EVA handrails and other aids and where they must be placed
m How much force or torque a crewmember can be expected to supply in comparison with n How much force or torque a crewmember might apply, such as a kick m How much the crewmember can see from a given restraint location m How big a free-volume area a crewmember needs to translate through or work from There are numerous other requirements to define clearance required around hardware, and requirements for safety and labeling. These requirements have allowed us to proceed efficiently with the design of EVA-operated hardware, saving neutral buoyancy time for difficult worksites. EVA Worksite Analysis
To apply EVA requirements, Boeing has developed EVA worksite analysis. It is performed primarily in Unigraphics, which is the computer-aided design tool used to design inboard truss hardware. A custom module to Unigraphics provides EVA crewmembers, articu-
Figure 9. SSRMS-based Worksite 04
(Has Been Replaced
HHTll856
i1186D
.HHT1185G
View Looking Zenith Removal of Say 18 Shroud
Figure 10. Working from the SSRMS (not shown), the crew member can move between these two worksites without changing body orientation
600
49th IAF Congress 04lSBRElJ8.3
95th Percentile American Mate
Figure 11. While ISS requirements provide for EVA accessfor crew membersranging from 50th percentile Americanfemale to 95th percentileAmericanmale, the optimalrestraintsetups for individual crewmemberscan be quite different
lating APFRs and CETAs, tools, and requirement volumes for quick evaluation of options for EVA access
to a given worksite. Once the access to the worksite is provided, we bring in requirements volumes to verify that the requirements are met. EVA worksite analysis reports (EARS) have been certified as a valid method for documentation that we have met the ISS requirements. In the course of conducting the analysis, we develop the basic procedures the EVA crew will use to do the assembly or maintenance task, Table 1. For each step, all the information on how to set up the worksite is documented (Table 2) and a picture of the worksite is provided (Figures 4,6, 8. and 10). The procedures are the basis for OP-01 flight report assembly procedure inputs and LSAR (Logistic Support Analysis Record) maintenance procedures that Boeing delivers to the NASA for eventual development of flight EVA procedures. The bottom line in an EVA worksite analysis is the compliance matrix (Table 3) that documents whether a given worksite is compliant with applicable requirements. If the result is “C’ for compliant, we are through (for now). If the result is “‘N/C,”the job is just beginning.
Table 1. Excerpt from EVAworksite analysis procaduras for attach structure deployment Position 1-5
1-6
1-7
1-6
1-9
l-10
Procedure for attach structure deployment EVl-working from SSRMS Position EV2-free float/APFR From SSRMS or free Roat EVl accesses 2-5 From free float position EV2 accesses expandable expandable diameter pin at secondary longeron diameter pin at main longeron hinge furthest from fitting. This pin is released with less than 5 lb of force SARJ. Pin is released with less than 5 lb of force. (Layers 123,144, and 133) (Layers 124,143, and 134) From SSRMS EVl guides attach structure to EV2 may choose to assist with attach structure detente position and locks in place. (Layers 129, rotation through no necessary to meet requirements. 149, and 139) (Not shown in layout) From SSRMS EVl untethers diagonal and rotates EV2 ingresses APFR using work station stanchion 45 deg away from grapple fixture and 7 deg toward as ingress/egress aid. (Note: in UG file Layers 130, face to original location. (Layers 122,131, and 146) 136, and 147 show astronaut in APPR) From SSRMS EVl bolts diagonal with power tcol in 2-7 EV2 holds attach structure. Per safety, attach original location. See Pos. 4, Note 1. (Layers 121, structure must be held while EVl reattaches 131, and 146) diagonal and deploys SARJ brace joint. (Layers 130, 136, and 147) tFrom power tool from stowed location on diagonal. (Layers 126 and 136) From SSRMS EVl rotates SARI brace joint toward SARJ bulkhead and attaches SARJ brace joint to structure on SARJ bulkhead. (Layers 127 and 137) EV2 may choose to help rotate attach structure arm out of detente and toward face 5 and lock in place though not necessary to meet requirements (not shown). b rotates attach structure arm toward face and locks in diameter pin at main longeron hinge furthest from place. (Layers 129, 139, 149) SARJ (Layers 124,134, and 143) From free-float position EV2 secures expandable deployed position and secures at secondary diameter pin at main longeron hinge closest to longeron fitting with adjustable diameter pin. (Layer , SARJ. (Layers 125,135, and 142) 123,133, and 144) oooo838.1
601
49th IAF Congress Table 2. EVA worksite analysis documents each worksite, showing which WIF socket used, restraint setup, and all EVA aids used. Layout Title: Task Title:
lf71657, Layout, EVAanaiyrb S-3, ShkJ trundle bearing maint. Maint.afther remove and replace a trundle bearing, or rotate between primary and secondary mods Ansly+..; i:Fil~Jn’?~~~cell4n +glven row; Mark~?J/A”t If nonrpp~lqabt+‘,Use’thhenotea/commentr IirtJn #teohm
r&b I
:‘+ : to’&cu-t I
-L Pstn no.
Task
P4A con.
Access trundle bearing P4A (EW
Sheeff1 IEVA zone I:rew no. no.
Sht 10. zone R7
Socket no.
1
T1221A”
1I
Socket orientation (clockzero direction)
APFR setting
Top mount c = 9:OO (clock zero p = -451~(VU) zenith) r = +90” (A) y ii 1o:oo
,
I
I
translation from previous task to install aid
APFR installation aid
transietion from Install to ingress aids
egress aid(s) or freefloat stebiifzation aid
Primary path HHT1221B8 HHT1221A Ingress HHT1224B and HHT1224A stabilize: HHT1204A HHTl204A Longeron HHT1203B HHT1223B HHT1223A HRT1222B8 HHT122A HHTl221A’ 4 I
Table 3. End result of EVA worksite analysis is a Requirements Compliance Matrix. NCs must be dealt with by _ design - changes or exceptions. Layout Title: Taik Title:
y:,
anythin’#~i~oannot b’ii&ed on “$s’ma~~;~: ,:, ; >::,.,‘]i; T’:;F*i ‘y :f.,: j. 1&pi‘$‘V% 1.‘,. ,,~,I i.a_: I APFR 1CerA I I I I I I tort Aid(r) for Aid(s) for fngrere/
If71 666, iavo ut, EVA analysis-“S3/P3, Attach Structure Deployment” r&h structure on Face 3 and Face.6 _ Assembiv taa;ki 7
r.nonF
or PiJa”-forn
m’doc 627),fc
;‘.Attachmerit‘. &nb; Note:re ^,~‘:‘.,~, *: I’: ij ,, <;,.L’,>,<.
. :
2-11
C
C
C
N/A
C
C
2-12
c
c
c
N/A
C
C
loco-
lion and iocket :elting N/A
I_
49th IAF Congress
602
EVA Requirement Exceptions Inevitably, even a long list of black and white requirements cannot define what is preferable, acceptable, or even doable in all EVA situations. And in the push and pull of engineering the Space Station, the needs and desires of the crew are traded against cost and schedule. To deliver a cost-effective station on any reasonable schedule, Boeing and NASA have had to work together to quickly decide just what an EVA crewmember can be expected to do at a given worksite. An N/C on an EVA worksite analysis usually means that all the easy fixes have been ineffective. Usually the N/C means that bringing the worksite into compliance is expensive and we estimate that the task is doable by the EVA crew as is, or that bringing the worksite into compliance doesn’t make sense and would actually make the worksite less EVA friendly. In either case, we go forward to the EVA analysis and integration team (EVA AIT) to request an exception to the requirement. The EVA AIT gathers inputs from the astronauts, safety, mission operations directorate (MOD), and others to decide if the exception should be approved. Their inputs are based on tabIe-top review of the worksites, shop floor checks of flight or qualification hardware, or neutral buoyancy testing results. Even a C on an EVA worksite analysis does not always assure that a worksite is acceptable. NASA is conducting a series of neutral buoyancy laboratory (NBL) and human thermal vacuum (HTV) tests to check tasks that may comply with the requirements but may still be unacceptable for reasons beyond the reach of the requirements. Seven major NBL tests and seven HTV tests are planned, and more will likely be conducted to gain confidence that the EVA crew will be able to do the job on orbit. NBL tests include both compliant and noncompliant tasks that are either difficult, unusual or time consuming. HTV tests include tasks that involve hardware that may function differently in the wide-ranging thermal vacuum environment of ISS. In either case, worksites will be found that are unacceptable and modified until they are acceptable. These tests will also reduce, but far from eliminate, the tasks and worksites that will not be physically experienced until an EVA crewmember sees them on orbit.
that we have used to design the station can be transitioned into training and operations use. Custom Human Modeling Analysis The EVA worksite analysis and procedures produced in ISS design provide generalized worksites for the whole EVA population. Customized analysis of the chosen assembly operation could be conducted using Boeing McDonnell Douglas human modeling system (BMDHMS) software with accurate models of the individual crewmembers selected to conduct the EVA. Results would likely demonstrate performance improvement over station development analyses, which are conducted to account for the full astronaut population and include more EVA restraint setups than a given crewmember will need. Custom human modeling analysis benefits are derived from assuring that a particular crewmember can reach a worksite and by making the most of his or her reach to increase EVA performance. The accuracy of the BMDHMS models of the EMU have been verified by studies conducted by Boeing and Hamilton Standard*. This analysis could be used as a starting point for flight training, increasing performance of training resources. Real-time custom human modeling analysis could be conducted in support of ISS flights for quickresponse replanning of EVAs for any in-flight contingencies. Using BMDHMS, we can analyze an EVA worksite, using a suit model sized to a particular crewmember that will accurately predict his or her reach (Figure 12). BMDHMS analysis also simulates the crew member’s
TRANSITION INTO TRAINING Once the analysis and tests have determined the shape and function of the hardware, the EVA crew must be trained to perform the assembly and maintenance tasks. Due the huge quantity of worksites, new and efficient methods of training need to be developed. The following sections describe how the analysis techniques
Figure 12. BMBHMS uses a crewmember’s dimensions to develop a model of that crewmember in the EMU. The model includes accurate limits based on the kinematic reach of a suit sized for that crewmember
49th IAF Congress
visual access to the worksite (Figure 13). Visual access
must be ensured for status indicators and all points on a worksite that the crewmember must touch. The results of this simulation can also be used to familiarize the crewmember with the worksite and the procedures (Figure 14) through desk-top review or as part of virtual reality training. WZWREUB.
IQpre 13. BMDHMS locates the viewpoint of the crewmember’s eyes and the EMU heIrnet to accurately simulate crewmember field of view, asqing visual access to the worksite
Using Boeing flight design and MOD EVA mission planning as input, BMDHMS analysis would be customized to each of the EVA crewmembers to provide optimal procedure predictions for each. These procedures could then be used as an input to MOD for flight procedures and training, reducing the training time
603
required for trial-and-error worksite restraint development. The analysis should also be available for review by the EVA crewmembers as task orientation. EVA Assembly ‘Ikaining
Boeing development testing has shown a significant increase in neutral buoyancy test performance when EVA analysis is conducted prior to test. For the pressurized mating adapter development test in 1995, 100% of EVA restraint setups used b the crew in neutral buoyancy matched the analysis if. Starting out with fimctional EVA restraint setups allowed neutral buoyancy time to be used for evaluation of the EVA tasks tbemselves, rather than performing a tial-and-error search for a functional EVA restraint setup. Custom human modeling analysis could be substituted for early NBL runs needed to rough out a procedure. Conducted on a desktop, the analysis requires far fewer man-hours to perform. The flight crew could then begin virtual reality or neutral buoyancy training with a functional, kinematically optimal procedure, freeing them to concentrate on learning flight mechanism functionality and developing personal preferences for approaching each task. Analysis will not replace hands-on training such as in the NBL. Programming of body movements that the crewmember experiences by repeatedly performing a task is fundamental to NASA’s training philosophy and is essential if the tasks are to be accomplished in a timely manner. Quickly establishing the procedure and movements that will be used on orbit increases learning depth in a given training run. False starts and nonfunctional procedures may actually have to be unlearned, increasing training time requirements. In this way,
Figure 14. BMDHMS analysis results provide a starting point for crew neutral buoyancy training
604
49th IAF Congress
using custom human modeling analysis to start training with functional, near-optimal crew restraints at each worksite will maximize crew benefit from training time available. In application, it may be possible to reduce the amount of training planned. Desktop and virtual reality simulations currently used by MOD provide accurate simulations of shuttle and SSRMS kinematics. Integrating BMDHhIS capabilities into these simulations would add accurate anthropomctrics of a selected crewmember’s suit and assure that the simulations limit the crewmember’s simulated reach to what his or her suit could reach on orbit. Automation of noncritical functions will decrease the time required to perform these analyses. virtual reality has been used increasingly for EVA training. MOD has the capability to train an EVA subject, using a head-mounted stereo display, together with an SSRMS operator, both interacting with a computer simulation of flight hardware. This system relies on the EVA subject’s experience in the suit to predict the reach of the EMU on orbit and does not restrict him/her from making motions or reaching locations that would not be possible in an EMU. BMDHMS software capabilities could be added to allow the EVA subject to inhabit the simulated EMU and constrain the EVA subject’s simulated reach to that of a chosen crewmember’s EMU. When an EVA subject instructs the simulation to reach beyond the limits of the suit, the subject could be alerted through audio and/or visual indications, to the suit limits that had been exceeded. These limitations would ensure that crewmember training on EVA operations would be kinematically possible on orbit. It would also be possible to substitute different suit sizes into the simulation for engineering analyses before training begins or to train
RMS operators for differences between positioning different crewmembers. MOD has a functional and effective system of EVA simulations. The addition and integration of custom human modeling analysis into that system would fill the niche of modeling EVA suit-reach, with the potential of lowering risk through assured EVA access and lowering costs through more effective use of training resources. EVA Maintenance
Tratning
There are over 300 orbit replaceable units (ORUs) on the five segments of inboard truss (Figure 15) in 59 different types. ORUs are specifically designed to be replaceable. Any of these ORUs might be removed and replaced by any EVA astronaut. For each ORU, a procedure for the task must be developed and then adapted for the crewmember who would actually perform the maintenance. Many maintenance EVAs will be performed by space station-based crews without the benefit of NBL or other ground-based training immediately prior to the EVA. In some cases, the crew will have trained for general maintenance tasks only and have no prior training on the specific maintenance task at hand. In preparation for such an EVA, custom human modeling analysis could be conducted on the ground for the crew that will conduct the EVA. Images, restraint setups, and electronic-file-based movies could be uplinked to the station using the existing s-band uplink (6 to 7 kb/sec). The data could be used in training for the EVA as part of an on-orbit training system, such as the field-deployable training system, that was evaluated by Shannon Lucid on board Mir. Procedures and images from the analysis could be loaded onto an electronic EVA cuff checklist, such as 04130REU62
InboardTruss ORUs
Pl
SO Segment Figure 15. ORU Distribution Across Inboard ‘Buss
49th IAF Congress
the one currently under development by the JSC Crew and Thermal Systems division, and used by the crewmember during the EVA (Figure 16). The electronic EVA cuff checklist enables procedures to be customized and updated just before the EVA, if necessary. On-orbit Operations During an KS assembly flight, analysts could establish and provide real-time custom human modeling analysis support both to: m Provide real-time analysis to support unscheduled EVA contingencies m Evaluate analysis predictions in comparison with resulting flight experience In the case where an unscheduled EVA operation arises during the flight, MOD often conducts a neutral buoyancy simulation to develop or confirm procedures and restraint setups that can then be sent to the crew. Real-time BMDHMS analysis could provide a starting point for the NBL simulation. In situations where there is no time to conduct an NBL simulation, BMDHMS analysis could provide a workable restraint setup for transmission to the crew. While computer analyses, such as BMDHMS, cannot replace a crewmember’s self-awareness while working in a suit in neutral buoyancy, MOD may choose to conduct custom human modeling analysis instead of a quick NBL for less critical, unscheduled EVAs. When an NBL is conducted, BMDHMS analysis may indicate that fewer cases need to be evaluated. This would result in more efficient use of time-limited NBL resources and provide an opportunity to concentrate more NBL time on optimizing the specific EVA techniques and procedures rather than selecting from a number of restraint options for an unscheduled task. This approach can enhance the likelihood of mission success.
605
There are 13 planned, flight-specific contingency EVAs listed for the FYI-3 common berthing modules on flight 2A alone4. Once validated, real-time custom human modeling analysis could significantly reduce the risk of failed EVA access during a contingency. The EVA support team on the ground can have flight hardware models and custom models of each EVA crew member available for real-time analysis of unexpected situations. The EVA support team would be able to develop new procedures and EVA restraint setups with the assurance that they can predict what a particular crewmember will be able to reach from a selected restraint setup. The resulting restraint locations can be transmitted to the crew, allowing them to concentrate on the unplanned worksite rather than on how to get to it. The quick reactions possible from real-time analysis will reduce the risk and time requirements for contingency EVAs. CONCLUSIONS ISS success will depend heavily on the success of thousands of hours of EVA conducted at thousands of worksites. Custom human modeling analysis has the potential to reduce ISS EVA cost and risk through enhancement of EVA training, procedural planning, reduced maintenance time, and enhanced support of unplanned EVAs. GLOSSARY AIT Analysis and Integration Team APFR Articulated Portable Foot Restraint BMDHMS Boeing McDonnell Douglas Human Modeling System CETA Crew and Equipment Translation Aid EAR EVA Worksite Analysis Report EMU Extravehicular Mobility Unit 04129REu8.1
Figure 16. Images and procedures generated by custom human modeling analysis could be displayed directly on the EVA crewmember’s wrist during the EVA
606
EV EVA ISS JSC MOD NBL ORU Pl SO SARJ SSRMS WIF
49th IAF Congress
Extravehicular crewmember Extravehicular activity Human Thermal Vacuum International Space Station NASA Johnson Space Center Mission Operations Directorate Neutral Buoyancy Laboratory Orbit Replaceable Unit Port segment one Starboard segment zero Solar Array Rotary Joint Space Station Remote Manipulator System Worksite Interface
REFERENCES 1. G. Nenninger, “International Space Station Crew Loading Report,” NASA Johnson Space Center, 27 November 1995. 2. “Validation Analysis of PG-1 EMU and EVA Tools 3D Models,” ISS Design Analysis Cycle 2, TDS 3.1.14-3, August 1995. 3. “Pressurized Mating Adapter (PMA) NBL Test Report,” JSC-33250, July 1995. 4. “Assembly Contingency Operations Assessment, Plights 2A - 6A,” JSC-36130 Rev A, April 1996. 5. “EVA Standard Interface Control Drawing,” SSP 30256 Revision E, October 1994.
Pergamon PII:
EVA WORKSITE ANALYSIS-USE OF COMPUTER ANALYSIS FOR EVA OPERATIONS DEVELOPMENT AND EXECUTION Dave Anderson The Boeing Company Huntington Beach, CA both a highly complex and sufficiently flexible environment for EVA operations. To respond to this challenge, NASA and its contractors have developed an effective set of simulation tools, both electronic and physical, for design of the station, development of operational techniques, training of the assembly and maintenance EVA crew, and execution of EVAs. Naturally, we have the most experience with the earlier stages of this process. The story of how these tools succeed during the thousands of EVA hours coming in the next decade is just beginning to be written.
ABSTRACT To sustain the rate of extravehicular activity (EVA) required to assemble and maintain the International Space Station, we must enhance our ability to plan, tin for, and execute EVAs. An underlying analysis capability has been developed to ensure EVA access to all external worksites as a starting point for ground training, to generate information needed for on-orbit training, and to react quickly to develop contingency EVA plans, techniques, and procedures. This paper describes the use of computer-based EVA worksite analysis techniques for EVA worksite &sign. EVA worksite analysis has been used to design 80% of EVA worksites on the U.S. portion of the International Space Station. With the launch of the first U.S. element of the station, EVA worksite analysis is being developed further to support real-time analysis of unplanned EVA operations. This paper describes this development and deployment of EVA worksite analysis for International Space Station (ISS) mission Support.0 1998 International
SPACE STATION INBOARD TRUSS EVA WORKSITES ISS is composed of four major portions, as shown in Figure 1: m Russian modules m U.S., European, and Japanese pressurized modules m Truss inboard of the solar array rotary joints (SARJs) m Truss outboard of the SAIUs. In this paper, we examine the inboard truss segments. The inboard truss is made up five segments as shown in Figure 2. Segment SO (starboard zero) is the nexus between the truss and the pressurized modules providing structural, electrical, avionics, fluid, and crew translation connections. Segments Sl and Pl (port one) are very similar to each other; their primary purpose is to provide active heat rejection for station waste heat. Segments S3 and P3 are also very similar, providing attach points for payloads and spares and the large SARJs that rotate the outboard solar arrays to follow the sun. Each of the five inboard truss segments is brought to the station separately and assembled from the middle out. EVA assembly tasks for a given segment are performed by the space shuttle crew that brings the segment up, and later completed by the ISS crew after the shuttle departs. From there on, EVA maintenance tasks are performed as needed to keep the external systems up and running. More than 2,700 EVA worksites are required to assemble and maintain the five inboard segments, as shown in Figure 3. An EVA worksite is defined as a single crewmember location from a single setup of
Astronautical Federation Published by Elsevier Science Ltd. All rights reserved.
INTRODUCTION The large number of ISS EVAs requires that the external mobility unit (EMU) function many more times between ground servicings than current shuttle operations, and at a rate that will quickly overshadow all previous EVAs. More than 1,700 EVA hours will be required for ISS tisembly and more than four times the shuttle EVA experience to date’. Over the lifetime of the station, 1.622 additional maintenance hours are predicted. To sustain this EVA rate, we must also enhance our ability to plan, train for, and execute EVAs. Despite the standardization of EVA interfaces and tools, the thousands of space station EVA worksites are all unique, requiring specific setup of EVA access and tools. Multiply these worksites by the range of crewmembers who may be called on to perform the tasks, ranging from 95th percentile American male to 50th percentile American female, and by the range of EVA worksite access methods (by crane, foot restraint, cart, free-float, or body restraint tether), and the result is 593
49th IAF Congress
Figure 1.1% Components 04142 REUI
mated. The SOanalyses have been hampered by a major change in the early station orientation which required nearly every previous EVA worksite to be covered by thermal shrouding. EVA WORKSITE DESIGN Worksite Restraint
PMA3 Figure 2.
Inboard ‘IYussSegments
restraints. Each worksite requires methods for the crewmember to react loads through his/her feet and hands, to be able to see the object being worked on, and to reach it with hands or tools. EVA aids for each worksite must be designed and verified, procedures developed, and training provided. The worksite quantities shown in Figure 3 are taken from Boeing EVA worksite analyses for each segment. The analyses for segments S 1, PI, P3, and S3 are nearly complete. SO analyses that are not complete were esti-
The first concern at an EVA worksite is finding a way to restrain the extra vehicular (EV) crewmember so that he/she can apply loads to the worksite without affecting body orientation. Several methods are available: 1. Free-float (Figure 4). When very low forces are needed for short durations (e.g., less than 10 lb for less than 1.4 set), the crewmember can work without foot restraints, reacting the forces applied by one hand with the other hand using one of the 540 handrails on the inboard truss or any other eligible structure. This is the simplest and fastest restraint method but requires the most crew skill to remain stable. Strict requirements have limited use of free-float for worksite restraint during ISS design, ensuring that we would have other options for the crewmember restraint at most worksites. Development testing and training runs liave shown that
49th IAF Congress nnn
600 .z? Z
500
8
400
2
300 200
S-0 Segment Figure 3. EVA worksites
s’l
s’3
are distributed more or less evenly across the inboard truss and spiit between assembly and maintenance uses
04124REU8.2
4. Free float enables a crew member to reach many simple work sites quickly. Here one crew member (EV29) works from the SSRMS while the other crew member releases straps at many different work sites crewmembers prefer to free-float when feasible to cut down on task time and fatigue. 2. Tethered restraint. Creative use of tethers can provide the crewmember with another limited method of load reaction. Strap or cable tethers attached to the crewmember’s wrist, waist, or chest can be used in tension to provide load reaction. The body restraint tether, which is made up a series of spherical bearings, can be locked down in a wide range of shapes to react around 10 lb of load for extended periods. 3. Structure-based foot restraint. The articulating portable foot restraint (AWR) (Figure 5) can be
installed into any of the 238 worksite interfaces (WIFs) on the inboard truss and used to restrain a crewmember’s feet at a worksite (Figure 6). The APFR, at 50 lb and roughly a 24 cube, is the maximum weight and size the crew are willing to have hanging off them while they translate around hand over hand. Once at a WIF, the crewmember can set up the AWR clock, pitch, roll, and yaw in one of more than 33,000 potential orientations to place his/her body at the worksite. Choosing
Figure
Figure 5. The APFR will provide restraint for must EVA worksites. The APFR can be articulated in clock, pitch, roll, and yaw to more than 33,000 dh’ferent rientations from a given worksite interface. P
49th IAF Congress
596 EVA Work&e Envelope (See Claimcation of Work&e Area) :g,,
,\
jp,,,
EVl Crew Member &.c%c&:g Launch
\ VIEWLOOKING FORWARD (FACE 3I4)
Figure 6. Typical APFR -restrained between
these positions for the full range of potential sixes of EVA crew is a key element in computer-based EVA worksite analysis. Working from the APPR, the crewmember can react much higher sustained worksite loads (up to 45 lb) through hisher legs or hands. A load alleviator in the APFR assures that the crewmember does not react so much load that it damages the structure to which the WIP is mounted. Despite the large number of WIFs and APFR orientations, structure-based WlFs
are
Grapple Fixture (Face 3)
Worksite
still limited, in reach and orientation, to a given work location. In addition to lugging the API% around, the crewmember must get out of the foot restraint to change pitch and clock settings. Ingress into the APFR is a difficult skill; a swift APPR ingress is usually a sign of an experienced crewmember. 4. CETA-based foot restraint. The crew and equipment translation aid (CETA) (Figure 7) is a hand-operated rail car that can be translated along a rail on the
49lh IAF Congress
work Station
Adjustable
Es;,“’
Stanchion
Stowage Device
Energy Absorber, CETA MXETAAclive
597
Coupl
Assembly 4 Places
Patmg Brake Handle Assembly
Figure 7. CETA Cart On-orbit‘IkanslationContlguration 5. SSRMS-based foot restraint. The Space Station forwardface of the truss. Since most of the more freremote manipulator system (SSRMS) arm provides the quent maintenance tasks are located on one of the forlarge-object manipulation that makes ISS assembly ward truss faces, the CETA ad& another level of possible, but it is also the most versatile method of EVA flexibility for EVA access while cutting the cargo a restraint. With an APm mounted to the end of the arm crewmember must carry around on his/her body to get (Figure 9), nearly infinite EVA orientations are availthe job done (Figure 8). The CETA has five WsFs. All able for inboard truss worksites limited only by physihave their own pitch/yaw articulation, and three are cal obstructions (Figure 10). While there is great time mounted to swing arms. The nadir swing arm WTFScan be set to any of 4,800 orientations. A single CETA cart savings to the crewmember, not having to translate, set up, and ingress AH% at each worksite, but an addilocation along the rail provides over 450 million potential foot plate locations. Still, these locations are limited tional crewmember is required inside the station to to providing access to the forward faces of the truss and operate the arm. The SSRMS also draws power, data, nearly all with the crewmenher’s head pointing away and scarce camera resources to operate. Ultimately, from the CETA. Adjusting the cart location requires there is only one arm for the minimum of two crewingress into special translation foot restraints and members on a given EVA, so we can’t count on everyreleasing and setting brakes. Finding the right combinathing being done from the SSRMS. tion of location and settings is dependent on EVA EVA Worksite Requirements worksite analysis. These settings will be refined for Ideally, EVA access to each worksite, along with the assembly tasks and limited maintenance tasks during EVA aids locations, would be verified using physical neutral buoyancy training.
491h IAF Congress
598
C;t I A
cian Locate01or
CETA Light Zero-G Connector Disconnect/connect
CETA Cart Socket 1 Used for
APFR Setting (P3) APFR Setting (S3) Clock = E 12:OO (0’) Clock = 12:00 (0’)
CETA Handrail (P3 HHTl191 B (S3 - Not Shown
ETA Cart Socket 3 Socket Setting: Pitch = 15O Yaw = 3:00 (90”)
Used for Ingress and Stabilization CETA Light
Analysis Position 2-l Zero-G Connector Disconnect/Connect View Looking Nadir and Inboard
Figure 8. ‘I)-picalCETA-based EVA Worksite
mock-ups in neutral buoyancy and evaluated with the full range of crewmembers who might perform each task. Since the cost and time to accomplish this for thousands of worksites is prohibitive, the KS program has developed a set of requirements that, if met, nearly assure that a worksite will be EVA compatible, if not EVA friendly. Naturally, these requirements are conservative. NASA expects a broad size range for EVA crewmembers from 5 ft 2 in. 50% American‘ female to 6 ft 3 in. 95% American male (Figure 11). This is not to say all EVA crewmembers will be American, just that easily available American anthropomorphic databases were used. Requirements establish the following: m How hardware of different sizes and masses must be restrained by EVA crew m How big the gaps between EVA handrails can be m The area a crewmember can reach from a given restraint location m What each worksite must provide for EVA handrails and other aids and where they must be placed
m How much force or torque a crewmember can be expected to supply in comparison with n How much force or torque a crewmember might apply, such as a kick m How much the crewmember can see from a given restraint location m How big a free-volume area a crewmember needs to translate through or work from There are numerous other requirements to define clearance required around hardware, and requirements for safety and labeling. These requirements have allowed us to proceed efficiently with the design of EVA-operated hardware, saving neutral buoyancy time for difficult worksites. EVA Worksite Analysis
To apply EVA requirements, Boeing has developed EVA worksite analysis. It is performed primarily in Unigraphics, which is the computer-aided design tool used to design inboard truss hardware. A custom module to Unigraphics provides EVA crewmembers, articu-
Figure 9. SSRMS-based Worksite 04
(Has Been Replaced
HHTll856
i1186D
.HHT1185G
View Looking Zenith Removal of Say 18 Shroud
Figure 10. Working from the SSRMS (not shown), the crew member can move between these two worksites without changing body orientation
600
49th IAF Congress 04lSBRElJ8.3
95th Percentile American Mate
Figure 11. While ISS requirements provide for EVA accessfor crew membersranging from 50th percentile Americanfemale to 95th percentileAmericanmale, the optimalrestraintsetups for individual crewmemberscan be quite different
lating APFRs and CETAs, tools, and requirement volumes for quick evaluation of options for EVA access
to a given worksite. Once the access to the worksite is provided, we bring in requirements volumes to verify that the requirements are met. EVA worksite analysis reports (EARS) have been certified as a valid method for documentation that we have met the ISS requirements. In the course of conducting the analysis, we develop the basic procedures the EVA crew will use to do the assembly or maintenance task, Table 1. For each step, all the information on how to set up the worksite is documented (Table 2) and a picture of the worksite is provided (Figures 4,6, 8. and 10). The procedures are the basis for OP-01 flight report assembly procedure inputs and LSAR (Logistic Support Analysis Record) maintenance procedures that Boeing delivers to the NASA for eventual development of flight EVA procedures. The bottom line in an EVA worksite analysis is the compliance matrix (Table 3) that documents whether a given worksite is compliant with applicable requirements. If the result is “C’ for compliant, we are through (for now). If the result is “‘N/C,”the job is just beginning.
Table 1. Excerpt from EVAworksite analysis procaduras for attach structure deployment Position 1-5
1-6
1-7
1-6
1-9
l-10
Procedure for attach structure deployment EVl-working from SSRMS Position EV2-free float/APFR From SSRMS or free Roat EVl accesses 2-5 From free float position EV2 accesses expandable expandable diameter pin at secondary longeron diameter pin at main longeron hinge furthest from fitting. This pin is released with less than 5 lb of force SARJ. Pin is released with less than 5 lb of force. (Layers 123,144, and 133) (Layers 124,143, and 134) From SSRMS EVl guides attach structure to EV2 may choose to assist with attach structure detente position and locks in place. (Layers 129, rotation through no necessary to meet requirements. 149, and 139) (Not shown in layout) From SSRMS EVl untethers diagonal and rotates EV2 ingresses APFR using work station stanchion 45 deg away from grapple fixture and 7 deg toward as ingress/egress aid. (Note: in UG file Layers 130, face to original location. (Layers 122,131, and 146) 136, and 147 show astronaut in APPR) From SSRMS EVl bolts diagonal with power tcol in 2-7 EV2 holds attach structure. Per safety, attach original location. See Pos. 4, Note 1. (Layers 121, structure must be held while EVl reattaches 131, and 146) diagonal and deploys SARJ brace joint. (Layers 130, 136, and 147) tFrom power tool from stowed location on diagonal. (Layers 126 and 136) From SSRMS EVl rotates SARI brace joint toward SARJ bulkhead and attaches SARJ brace joint to structure on SARJ bulkhead. (Layers 127 and 137) EV2 may choose to help rotate attach structure arm out of detente and toward face 5 and lock in place though not necessary to meet requirements (not shown). b rotates attach structure arm toward face and locks in diameter pin at main longeron hinge furthest from place. (Layers 129, 139, 149) SARJ (Layers 124,134, and 143) From free-float position EV2 secures expandable deployed position and secures at secondary diameter pin at main longeron hinge closest to longeron fitting with adjustable diameter pin. (Layer , SARJ. (Layers 125,135, and 142) 123,133, and 144) oooo838.1
601
49th IAF Congress Table 2. EVA worksite analysis documents each worksite, showing which WIF socket used, restraint setup, and all EVA aids used. Layout Title: Task Title:
lf71657, Layout, EVAanaiyrb S-3, ShkJ trundle bearing maint. Maint.afther remove and replace a trundle bearing, or rotate between primary and secondary mods Ansly+..; i:Fil~Jn’?~~~cell4n +glven row; Mark~?J/A”t If nonrpp~lqabt+‘,Use’thhenotea/commentr IirtJn #teohm
r&b I
:‘+ : to’&cu-t I
-L Pstn no.
Task
P4A con.
Access trundle bearing P4A (EW
Sheeff1 IEVA zone I:rew no. no.
Sht 10. zone R7
Socket no.
1
T1221A”
1I
Socket orientation (clockzero direction)
APFR setting
Top mount c = 9:OO (clock zero p = -451~(VU) zenith) r = +90” (A) y ii 1o:oo
,
I
I
translation from previous task to install aid
APFR installation aid
transietion from Install to ingress aids
egress aid(s) or freefloat stebiifzation aid
Primary path HHT1221B8 HHT1221A Ingress HHT1224B and HHT1224A stabilize: HHT1204A HHTl204A Longeron HHT1203B HHT1223B HHT1223A HRT1222B8 HHT122A HHTl221A’ 4 I
Table 3. End result of EVA worksite analysis is a Requirements Compliance Matrix. NCs must be dealt with by _ design - changes or exceptions. Layout Title: Taik Title:
y:,
anythin’#~i~oannot b’ii&ed on “$s’ma~~;~: ,:, ; >::,.,‘]i; T’:;F*i ‘y :f.,: j. 1&pi‘$‘V% 1.‘,. ,,~,I i.a_: I APFR 1CerA I I I I I I tort Aid(r) for Aid(s) for fngrere/
If71 666, iavo ut, EVA analysis-“S3/P3, Attach Structure Deployment” r&h structure on Face 3 and Face.6 _ Assembiv taa;ki 7
r.nonF
or PiJa”-forn
m’doc 627),fc
;‘.Attachmerit‘. &nb; Note:re ^,~‘:‘.,~, *: I’: ij ,, <;,.L’,>,<.
. :
2-11
C
C
C
N/A
C
C
2-12
c
c
c
N/A
C
C
loco-
lion and iocket :elting N/A
I_
49th IAF Congress
602
EVA Requirement Exceptions Inevitably, even a long list of black and white requirements cannot define what is preferable, acceptable, or even doable in all EVA situations. And in the push and pull of engineering the Space Station, the needs and desires of the crew are traded against cost and schedule. To deliver a cost-effective station on any reasonable schedule, Boeing and NASA have had to work together to quickly decide just what an EVA crewmember can be expected to do at a given worksite. An N/C on an EVA worksite analysis usually means that all the easy fixes have been ineffective. Usually the N/C means that bringing the worksite into compliance is expensive and we estimate that the task is doable by the EVA crew as is, or that bringing the worksite into compliance doesn’t make sense and would actually make the worksite less EVA friendly. In either case, we go forward to the EVA analysis and integration team (EVA AIT) to request an exception to the requirement. The EVA AIT gathers inputs from the astronauts, safety, mission operations directorate (MOD), and others to decide if the exception should be approved. Their inputs are based on tabIe-top review of the worksites, shop floor checks of flight or qualification hardware, or neutral buoyancy testing results. Even a C on an EVA worksite analysis does not always assure that a worksite is acceptable. NASA is conducting a series of neutral buoyancy laboratory (NBL) and human thermal vacuum (HTV) tests to check tasks that may comply with the requirements but may still be unacceptable for reasons beyond the reach of the requirements. Seven major NBL tests and seven HTV tests are planned, and more will likely be conducted to gain confidence that the EVA crew will be able to do the job on orbit. NBL tests include both compliant and noncompliant tasks that are either difficult, unusual or time consuming. HTV tests include tasks that involve hardware that may function differently in the wide-ranging thermal vacuum environment of ISS. In either case, worksites will be found that are unacceptable and modified until they are acceptable. These tests will also reduce, but far from eliminate, the tasks and worksites that will not be physically experienced until an EVA crewmember sees them on orbit.
that we have used to design the station can be transitioned into training and operations use. Custom Human Modeling Analysis The EVA worksite analysis and procedures produced in ISS design provide generalized worksites for the whole EVA population. Customized analysis of the chosen assembly operation could be conducted using Boeing McDonnell Douglas human modeling system (BMDHMS) software with accurate models of the individual crewmembers selected to conduct the EVA. Results would likely demonstrate performance improvement over station development analyses, which are conducted to account for the full astronaut population and include more EVA restraint setups than a given crewmember will need. Custom human modeling analysis benefits are derived from assuring that a particular crewmember can reach a worksite and by making the most of his or her reach to increase EVA performance. The accuracy of the BMDHMS models of the EMU have been verified by studies conducted by Boeing and Hamilton Standard*. This analysis could be used as a starting point for flight training, increasing performance of training resources. Real-time custom human modeling analysis could be conducted in support of ISS flights for quickresponse replanning of EVAs for any in-flight contingencies. Using BMDHMS, we can analyze an EVA worksite, using a suit model sized to a particular crewmember that will accurately predict his or her reach (Figure 12). BMDHMS analysis also simulates the crew member’s
TRANSITION INTO TRAINING Once the analysis and tests have determined the shape and function of the hardware, the EVA crew must be trained to perform the assembly and maintenance tasks. Due the huge quantity of worksites, new and efficient methods of training need to be developed. The following sections describe how the analysis techniques
Figure 12. BMBHMS uses a crewmember’s dimensions to develop a model of that crewmember in the EMU. The model includes accurate limits based on the kinematic reach of a suit sized for that crewmember
49th IAF Congress
visual access to the worksite (Figure 13). Visual access
must be ensured for status indicators and all points on a worksite that the crewmember must touch. The results of this simulation can also be used to familiarize the crewmember with the worksite and the procedures (Figure 14) through desk-top review or as part of virtual reality training. WZWREUB.
IQpre 13. BMDHMS locates the viewpoint of the crewmember’s eyes and the EMU heIrnet to accurately simulate crewmember field of view, asqing visual access to the worksite
Using Boeing flight design and MOD EVA mission planning as input, BMDHMS analysis would be customized to each of the EVA crewmembers to provide optimal procedure predictions for each. These procedures could then be used as an input to MOD for flight procedures and training, reducing the training time
603
required for trial-and-error worksite restraint development. The analysis should also be available for review by the EVA crewmembers as task orientation. EVA Assembly ‘Ikaining
Boeing development testing has shown a significant increase in neutral buoyancy test performance when EVA analysis is conducted prior to test. For the pressurized mating adapter development test in 1995, 100% of EVA restraint setups used b the crew in neutral buoyancy matched the analysis if. Starting out with fimctional EVA restraint setups allowed neutral buoyancy time to be used for evaluation of the EVA tasks tbemselves, rather than performing a tial-and-error search for a functional EVA restraint setup. Custom human modeling analysis could be substituted for early NBL runs needed to rough out a procedure. Conducted on a desktop, the analysis requires far fewer man-hours to perform. The flight crew could then begin virtual reality or neutral buoyancy training with a functional, kinematically optimal procedure, freeing them to concentrate on learning flight mechanism functionality and developing personal preferences for approaching each task. Analysis will not replace hands-on training such as in the NBL. Programming of body movements that the crewmember experiences by repeatedly performing a task is fundamental to NASA’s training philosophy and is essential if the tasks are to be accomplished in a timely manner. Quickly establishing the procedure and movements that will be used on orbit increases learning depth in a given training run. False starts and nonfunctional procedures may actually have to be unlearned, increasing training time requirements. In this way,
Figure 14. BMDHMS analysis results provide a starting point for crew neutral buoyancy training
604
49th IAF Congress
using custom human modeling analysis to start training with functional, near-optimal crew restraints at each worksite will maximize crew benefit from training time available. In application, it may be possible to reduce the amount of training planned. Desktop and virtual reality simulations currently used by MOD provide accurate simulations of shuttle and SSRMS kinematics. Integrating BMDHhIS capabilities into these simulations would add accurate anthropomctrics of a selected crewmember’s suit and assure that the simulations limit the crewmember’s simulated reach to what his or her suit could reach on orbit. Automation of noncritical functions will decrease the time required to perform these analyses. virtual reality has been used increasingly for EVA training. MOD has the capability to train an EVA subject, using a head-mounted stereo display, together with an SSRMS operator, both interacting with a computer simulation of flight hardware. This system relies on the EVA subject’s experience in the suit to predict the reach of the EMU on orbit and does not restrict him/her from making motions or reaching locations that would not be possible in an EMU. BMDHMS software capabilities could be added to allow the EVA subject to inhabit the simulated EMU and constrain the EVA subject’s simulated reach to that of a chosen crewmember’s EMU. When an EVA subject instructs the simulation to reach beyond the limits of the suit, the subject could be alerted through audio and/or visual indications, to the suit limits that had been exceeded. These limitations would ensure that crewmember training on EVA operations would be kinematically possible on orbit. It would also be possible to substitute different suit sizes into the simulation for engineering analyses before training begins or to train
RMS operators for differences between positioning different crewmembers. MOD has a functional and effective system of EVA simulations. The addition and integration of custom human modeling analysis into that system would fill the niche of modeling EVA suit-reach, with the potential of lowering risk through assured EVA access and lowering costs through more effective use of training resources. EVA Maintenance
Tratning
There are over 300 orbit replaceable units (ORUs) on the five segments of inboard truss (Figure 15) in 59 different types. ORUs are specifically designed to be replaceable. Any of these ORUs might be removed and replaced by any EVA astronaut. For each ORU, a procedure for the task must be developed and then adapted for the crewmember who would actually perform the maintenance. Many maintenance EVAs will be performed by space station-based crews without the benefit of NBL or other ground-based training immediately prior to the EVA. In some cases, the crew will have trained for general maintenance tasks only and have no prior training on the specific maintenance task at hand. In preparation for such an EVA, custom human modeling analysis could be conducted on the ground for the crew that will conduct the EVA. Images, restraint setups, and electronic-file-based movies could be uplinked to the station using the existing s-band uplink (6 to 7 kb/sec). The data could be used in training for the EVA as part of an on-orbit training system, such as the field-deployable training system, that was evaluated by Shannon Lucid on board Mir. Procedures and images from the analysis could be loaded onto an electronic EVA cuff checklist, such as 04130REU62
InboardTruss ORUs
Pl
SO Segment Figure 15. ORU Distribution Across Inboard ‘Buss
49th IAF Congress
the one currently under development by the JSC Crew and Thermal Systems division, and used by the crewmember during the EVA (Figure 16). The electronic EVA cuff checklist enables procedures to be customized and updated just before the EVA, if necessary. On-orbit Operations During an KS assembly flight, analysts could establish and provide real-time custom human modeling analysis support both to: m Provide real-time analysis to support unscheduled EVA contingencies m Evaluate analysis predictions in comparison with resulting flight experience In the case where an unscheduled EVA operation arises during the flight, MOD often conducts a neutral buoyancy simulation to develop or confirm procedures and restraint setups that can then be sent to the crew. Real-time BMDHMS analysis could provide a starting point for the NBL simulation. In situations where there is no time to conduct an NBL simulation, BMDHMS analysis could provide a workable restraint setup for transmission to the crew. While computer analyses, such as BMDHMS, cannot replace a crewmember’s self-awareness while working in a suit in neutral buoyancy, MOD may choose to conduct custom human modeling analysis instead of a quick NBL for less critical, unscheduled EVAs. When an NBL is conducted, BMDHMS analysis may indicate that fewer cases need to be evaluated. This would result in more efficient use of time-limited NBL resources and provide an opportunity to concentrate more NBL time on optimizing the specific EVA techniques and procedures rather than selecting from a number of restraint options for an unscheduled task. This approach can enhance the likelihood of mission success.
605
There are 13 planned, flight-specific contingency EVAs listed for the FYI-3 common berthing modules on flight 2A alone4. Once validated, real-time custom human modeling analysis could significantly reduce the risk of failed EVA access during a contingency. The EVA support team on the ground can have flight hardware models and custom models of each EVA crew member available for real-time analysis of unexpected situations. The EVA support team would be able to develop new procedures and EVA restraint setups with the assurance that they can predict what a particular crewmember will be able to reach from a selected restraint setup. The resulting restraint locations can be transmitted to the crew, allowing them to concentrate on the unplanned worksite rather than on how to get to it. The quick reactions possible from real-time analysis will reduce the risk and time requirements for contingency EVAs. CONCLUSIONS ISS success will depend heavily on the success of thousands of hours of EVA conducted at thousands of worksites. Custom human modeling analysis has the potential to reduce ISS EVA cost and risk through enhancement of EVA training, procedural planning, reduced maintenance time, and enhanced support of unplanned EVAs. GLOSSARY AIT Analysis and Integration Team APFR Articulated Portable Foot Restraint BMDHMS Boeing McDonnell Douglas Human Modeling System CETA Crew and Equipment Translation Aid EAR EVA Worksite Analysis Report EMU Extravehicular Mobility Unit 04129REu8.1
Figure 16. Images and procedures generated by custom human modeling analysis could be displayed directly on the EVA crewmember’s wrist during the EVA
606
EV EVA ISS JSC MOD NBL ORU Pl SO SARJ SSRMS WIF
49th IAF Congress
Extravehicular crewmember Extravehicular activity Human Thermal Vacuum International Space Station NASA Johnson Space Center Mission Operations Directorate Neutral Buoyancy Laboratory Orbit Replaceable Unit Port segment one Starboard segment zero Solar Array Rotary Joint Space Station Remote Manipulator System Worksite Interface
REFERENCES 1. G. Nenninger, “International Space Station Crew Loading Report,” NASA Johnson Space Center, 27 November 1995. 2. “Validation Analysis of PG-1 EMU and EVA Tools 3D Models,” ISS Design Analysis Cycle 2, TDS 3.1.14-3, August 1995. 3. “Pressurized Mating Adapter (PMA) NBL Test Report,” JSC-33250, July 1995. 4. “Assembly Contingency Operations Assessment, Plights 2A - 6A,” JSC-36130 Rev A, April 1996. 5. “EVA Standard Interface Control Drawing,” SSP 30256 Revision E, October 1994.