American Institute of Aeronautics and Astronautics1

Quantifying EVA Task Efficiency

Christopher A. Looper* and Zane A. Ney†

United Space Alliance, LLC, Houston, Tx., 77058

Quantifying Extravehicular Activity (EVA) task efficiency is defined here as a means tounderstand in full detail all the events that occur while operating in a spacesuit outside of thehabitable volume of a space vehicle. The EVA data presented in this paper was collectedduring spacewalks occurring on the International Space Station during 2005. Thesespacewalks were performed to accomplish both assembly and maintenance type tasks. Eachof the individual activities performed during a spacewalk on ISS are dictated primarily bythe Operational Concept in place, (along with all the support equipment and techniquesassociated with such), and secondarily by the work objectives assigned to a given spacewalk.Ultimately, how efficiently these work objectives can be performed is dependent upon howmuch time has to be dedicated to overhead tasks such as translation, support equipmentoperation and worksite setup/cleanup. This paper presents a method for recording EVA taskdata and analyzing the data in various ways in order to better understand how EVA time isinvested on ISS. The analysis results presented facilitate a detailed examination of thevarious factors affecting work efficiency. The methods described here are a continuation andexpansion of work previously documented by the authors [1]. The EVA task data from ISScan ultimately be used to establish baselines for EVA task efficiency to target and quantifyimprovements during future ISS operations. The ability to do this will be pivotal for thesuccessful matching of the available EVA resources to the required tasks for continued longterm ISS operation. The ISS data, if fully utilized, also forms a baseline for the EVA systemdesign to occur for exploration. The results and methods presented here can be used insupport of the design of all aspects of the next EVA system. The data can also be used to helpidentify and refine concepts for optimizing EVA training.

I. IntroductionOTION and time study, as defined by Barnes1 is the systematic study of work systems with the purpose of (1)developing the preferred system and method; (2) standardizing this system and method; (3) determining the

time required by a qualified and properly trained person working at a normal pace to do a specific task; and (4)assisting in training the worker in the preferred method. The pursuit of these four objectives has been evolving eversince the industrial revolution in the mid to late nineteenth century. During the latter part of the twentieth century,motion study began to be thought of as “methods design” and time study as “work measurement”1. A systematictime study of the tasks associated with International Space Station (ISS) Extravehicular Activities (EVA) wasinitiated with the EVA performed in June 2003 by the ISS Increment 9 crew. Most of the spacewalks occurring onISS since then have been included in this study. Barnes points out that in the late 1960’s perhaps the most commonmethod of measuring work was the stop-watch time study. This simple methodology is precisely what has beenemployed to capture EVA task results and begin to attempt to understand why the ISS EVA system produces theresults it does. The data that has been collected is forming the basis for a task time database of tasks typical for ISSmaintenance. This information will be available to better plan future ISS spacewalks and to capture evidence of

* Engineer Staff VI, Flight Crew Engineering & Operations, JSC/CB† Group Manager, Mission Operations EVA Support, JSC/DX32

Copyright © 2006 by United Space Alliance, LLC. Published by the American Institute of Aeronautics andAstronautics with permission. These materials are sponsored by the National Aeronautics and Space Administrationunder contract NAS9-20000. The U.S. Government retains a paid-up, nonexclusive, irrevocable worldwide licensein such materials to reproduce, prepare derivative works, distribute copies to the public, and perform publicly anddisplay publicly, by or on behalf of the U.S. Government. All other rights are reserved by the copyright owner.

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SpaceOps 2006 Conference AIAA 2006-5766

Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc.The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes.All other rights are reserved by the copyright owner.

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EVA technique, training and process improvements. The information also effectively characterizes the overallefficiency of ISS spacewalks, both for the United States (US) and Russian (RS) EVA systems. The potentialefficiency level achievable during spacewalks is dictated by the framework of tools that are utilized (such as thespacesuit and support equipment), by the external architecture of the vehicle (which defines translation paths andworksites), and by the rules and guidelines imposed by the space agencies involved. In this regard, the ISS EVAsystem is no different than a factory floor tasked with producing desired results within certain time limitations. Therules and guidelines applicable to EVA take the operational form of flight rules, operational constraints, andaccepted practices and techniques. EVA task efficiency data from ISS was initially documented by Looper and Neyin 20052. Presented below is an overview of the task measurement results from several ISS spacewalks performedsince June 2003. Descriptions are provided of how data was collected and analyzed.

II. ISS Spacewalk Task Measurement ResultsThe following information describes the methods by which the authors have performed time studies for ISS

spacewalks. The summarized results are presented for each spacewalk individually along with a very briefdescription of any peculiarities of the spacewalk.

A. Data CollectionISS spacewalks are controlled from either Mission Control Center - Houston (MCC-H) at the Johnson Space

Center (JSC) or Mission Control Center – Moscow (MCC-M), located in Russia. The MCC actively controlling ISSoperations during EVA depends upon whether or not the activities will occur on the US or Russian segments. Taskoversight can shift between control centers as crewmembers translate across the Functional Cargo Block(FGB)/Pressurized Mating Adapter 1 (PMA1) interface, but spacesuit and life support oversight remains theresponsibility of MCC-H when using the Extravehicular Mobility Unit (EMU) and MCC-M when using the Orlanspacesuit. Audio communications are maintained with the EVA crewmembers throughout the spacewalk if possible.There are occasional instances of communication outages based on the ISS location relative to communicationsatellites and Russian ground sites. The audio transmissions, including Russian to English translations, are carriedon various audio loops within the MCC-H intercom system. Live video is transmitted to MCC-H via a Ku-bandtransmitter onboard ISS. The availability of satellite coverage for video transmission usually is approximately 50%of the EVA time. Video cameras are available outside ISS at several locations. There is also a helmet mounted videosystem available for operations with the EMU. The audio and video are broadcast real time over the JSC cabletelevision network.

The authors recorded the task time measurements by listening to the audio transmissions over the appropriateMCC-H intercom loop while watching the live video on the cable network, as available. This was done either froman available workstation in MCC-H or from one of the author’s offices. Onsite at JSC, MCC-H audio can beaccessed through an in-house internet connection. Access to the MCC audio was of prime importance for collectingthe data because the cable TV broadcast, while continuously airing the crewmember audio, contains frequent generalinformation interruptions by a Public Affairs announcer superimposed on the crew’s transmissions.

Planned EVA activities are defined very precisely in detailed task procedures generated by the EVA MissionOperations Group at JSC. These procedures generally include each and every step required of the crewmembers, butare only time-tagged (planned time) at the task level, not the individual step level. The Russian EVA procedures,generated by the analogous Mission Operations group in Russia and subsequently provided to MCC-H, are typicallydefined in less detail and in a uniquely different format; but planned task step times are provided in some instancesdown to the three to five minute level. These detailed task procedures were used as a reference for tracking the EVAevents as they unfolded. The standard data collection process used was to time-tag the start of the EVA on a papercopy of the task procedures and then record on those procedures the completion time, using local time from awristwatch, of each step. Any additional steps performed, or unplanned work such as troubleshooting, were noted onthe procedure between the planned steps where they occurred. Notes were also made as applicable if steps wereperformed serially or in parallel by the two crewmembers, or if the operation involved seemed to be off-nominal insome respect. Concurrent with data collection on paper, a laptop was used to generate a record of the results usingthe Microsoft Excel application. This allowed creation of a chronological record of the events as they actuallyoccurred, including any unplanned events. Simple spreadsheet data manipulation was used to produce the elapsedtime for each operation. Operations were also categorized according to how the time was being spent. This is bestdone real time as the tone of communications and the flow of operations helps to define how the time is truly beingspent.

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The data collection process was used just as described for the last EVA to be analyzed, Russian EVA 15. Thisprocess was an evolution of the data collection attempts during the previous spacewalks. The intent was andcontinues to be directed at developing a method that can be accurately repeated with relatively minimal effort. It islabor intensive in that it requires the full uninterrupted attention of a single person for the duration of the spacewalk,typically 6 hours of external tasks. The first spacewalk for STS-114 was an exception to the process in that it wasanalyzed several days after the actual event by reviewing DVD’s recording during the spacewalk. It was also uniquein that the analysis was performed by a summer intern with coaching from the authors. This example proved thefeasibility of obtaining consistent interpretations of results by different individuals with differing levels of expertisein EVA.

B. Data AnalysisThe task categories first defined by Looper and Ney2 constituted the initial set of categories used. These were

based solely on the data from the Increment 9 spacewalk’s activities. The Work time, W, is defined as the time spentperforming the specific subset of tasks that are directly related to accomplishing the desired objectives. For ISS, thistypically constitutes actuation of bolts, connectors and/or insulation material. Worksite preparation time, WS, is thetime required at or very near the worksite that is needed to gain access to the worksite or otherwise enable thedesired work to begin, independent of time devoted to support equipment operations. WS time also includes cleanupactivities required to return the worksite to a desired condition. Support equipment time, Se, is time explicitlydevoted to the operation or stowage of support equipment, such as hand tools or tool bags. Se is inherently imbeddedto some extent within the work tasks themselves. The data collection rule imposed was to not separate out this timeunless the time became more than approximately two minutes for a particular tool operation. This was a judgmentcall to some extent as any tool reconfiguration type event lasting longer than two to three minutes meant somethingwas not functioning as expected. Obviously, off nominal events of any kind were separated from the nominal Worktime. Translation time, Te, was the time spent moving from one point to the next. Pauses in translation to operate oradjust support equipment were only separated when more than approximately two minutes were required. A goodexample of this was the performance of a safety tether swap from one tether to another one in the middle of a longtranslation.

W = Time associated with work objectivesWS = Time associated with worksite preparationSe = Time associated with EVA support equipmentTe = Time associated with EVA translation

Four additional categories were developed to better accommodate events from subsequent spacewalks that did not fiteasily into the initial four. Russian EVA 13 included time dedicated to rest. It has been standard in Russian EVAplans for the crewmembers to have planned periods of inactivity during the night portion of each Earth orbit. Thisconstitutes approximately 30 minutes of each 90 minute orbit. These planned rest periods are due to a combinationof factors including a physical need for rest, poor lighting provided by the Orlan helmet lights, and external surfacescrowded with sensitive hardware which could easily be damaged by contact with the Orlan. The actual rest periodstaken by the crew are typically less than the planned durations due to much improved lighting conditions providedthrough incorporation of the EMU helmet lights onto the Orlan, and crew prerogative to continue with tasks oncethey feel sufficiently rested. Troubleshooting time constitutes time spent performing unplanned or contingencyactivities associated with one of the planned objectives. This is typically time not represented in EVA timelines,which are planned based on nominal success of each task. The Sr and Tr categories were created for STS-114spacewalks as a means to capture support equipment and translation times directly associated with roboticoperations. For the purposes of comparing spacewalks, Support Equipment and Translation times are the sum of thecomponent EVA and robotic times.

R = Time spent at restTS = Time associated with unplanned troubleshooting operationsSr = Time associated with robotic support equipmentTr = Time associated with robotic translation

The data collected to date is summarized in Table 1 starting with the most recent spacewalk occurring on ISS andgoing back in time. Three Russian spacewalks in the early fall and winter of 2004/2005 (Russian EVAs 10, 11, &12) have not been analyzed. Some data was taken during EVA 10, but was not reduced. That spacewalk included a

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~25 minute loss of communication with the crewmembers due to a commanding error from the ground. The Russianand ISS Stage spacewalks typically are choreographed such that the two crewmembers operate in the very nearproximity to each other on the same task. The STS-114 spacewalks frequently utilized the two crewmembers onindependent tasks. In that circumstance task time measurement was recorded for each crewmember independentlyand simply averaged to produce a single data point for each EVA. This was done because the time distributionsbetween crewmembers were within a few percentage points for each of the categories. The second spacewalk ofSTS-114 (EVA2) has not been analyzed due to difficulty obtaining the DVD recordings of the spacewalk.

One caveat should be provided with regards to the data presented for Russian EVA 9B. This spacewalk was uniquein that it originated in the Russian Docking Compartment 1 (DC1) airlock using Russian Orlan spacesuits, but wasperformed primarily to perform maintenance on the US segment. The time associated with DC1 egress, performanceof the US segment maintenance and return to the DC1 are included in the assessment values. There was anadditional hour of Russian “get ahead” tasks performed in proximity to the DC1 at the end of the spacewalk. Thetimes associated with these tasks were not recorded or included in the results. This fact skews the Work time slightlylower and the other times slightly higher than they would be for the full spacewalk.

Full explanation of the objectives for each of these spacewalks is not provided here. However, that information isrequired for full analysis of the results. Likewise, the detailed task measurement results are not included because ofthe volume of information that it constitutes. The information is available to any interested parties. Because thecollection method has been “improving”, the data is not all in the same format, or to the same level of detail, exceptfor the summary of results given above. The level of detail recorded has improved with each attempt, and canimprove more.

III. Discussion of ResultsThere are many potential uses for the information that has been gathered. This section is not a comprehensive

assessment of the results along those lines. Only a few important aspects of the information are presented here alongwith some examples of how the data can be used for EVA planning and training.

A. Projected Averages Based on DataThe spacewalks are grouped below in Tables 2 and 3 according to whether or not they were performed using the

US system or Russian system. The first row in each Table represents an estimate of the expected typical timedistributions that will result for each system in future spacewalks.

EVA Work Troubleshooting WorksitePrep

SupportEquipment

Translation Rest

Russian EVA 15 22% 9% 1% 20% 34% 15%US ISS 4 39% n/a 13% 33% 15% n/aRussian EVA 14 26% 13% 20% 23% 12% 6%STS-114 EVA3 24% 3% 12% 33% 28% n/aSTS-114 EVA1 45% 2% 8% 29% 16% n/aRussian EVA 13 36% n/a 26% 26% 12% n/aRussian EVA 9B 7% n/a 33% 34% 26% n/a

Table 1. Task Measurement Results for ISS Spacewalks

EVAWork Troubleshooting Worksite

PrepSupport

EquipmentTranslation Rest

Projected Averages 42% 5% 8% 30% 15% n/aUS ISS 4 39% n/a 13% 33% 15% n/aSTS-114 EVA 3 24% 3% 12% 33% 28% n/aSTS-114 EVA 1 45% 2% 8% 29% 16% n/a

Table 2. Projected Average Time Distribution for US Spacewalks

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Note that the Work time associated with STS-114 EVA 3 was non-typically low due to a specific task requiredof that spacewalk. This is discussed in more detail in Section B below. Over time the experiences gained during USEVA operations should enable a lowering of the support equipment and worksite prep times, perhaps to gain asmuch as 10% more time to devote to Work. However, it should be expected that an increasing amount of time willbe required for troubleshooting hardware, be it ISS mechanisms, ORUs or support equipment. It is very possible thatefficiency gained in the better utilization of support equipment and worksite prep type activities will be applied totroubleshooting activities. Note that there have been several ISS spacewalks (for which no task time data has beencollected) that have required numerous actions to deal with off-nominal tasks. Two examples from two differentspacewalks are a light mounting stanchion that had to be hammered out of its launch bracket (ISS EVA 3) and avalve that leaked ammonia onto one of the crewmember’s spacesuit (STS-98). The Translation time required canvary significantly depending upon the tasks assigned to an EVA. Hopefully, task scheduling priorities willaccommodate EVA planning to minimize the time spent translating between worksites that are inconvenient to oneanother. The rest obtained by crewmembers during a US EVAs will probably continue to be thoroughly dispersedand short enough in duration such that it doesn’t rate a separate category. It is an interesting consideration, however,that a few properly placed rest points could increase efficiency, lower the task times and improve the accuracy of thework performed during the balance of an EVA. This concept has certainly been proven in other industries wherework breaks are provided in order to keep employees mentally sharp in order to eliminate costly mistakes.

Russian EVA 9B is virtually in a class of its own being an Orlan EVA from the DC1 but with the primary workobjective being on the US elements. RS EVA 9B was also unique because it was short in duration and included onlyone primary work objective, which skewed the percent of time spent on Work significantly lower than typical. Asnoted above, there was also approximately an hour of additional Russian tasks that were not recorded. For all thesereasons, RS EVA 9B is not included in the summary below. Russian EVA 15 also spent a portion of the spacewalk

on the US segment to perform maintenance; a fact that shows in the higher translation time associated with thatEVA.

It was typically very challenging to differentiate distinctly between Worksite Prep and Support Equipmentoperations for the EVA activities on the Russian modules. Often times, the tasks were so intermingled that a blockof time, such as 8 minutes, was simply divided evenly into 4 minute blocks of each. It is also difficult to make directcomparisons between the US and Russian time distributions due to the differences in the tasks required, thearchitecture of the external surfaces, the different support equipment systems and the differences in spacesuits. Forinstance, the simpler RS support equipment system leads to lower support equipment time, but longer times requiredpreparing a worksite (and cleanup). There is no reason to expect the Troubleshooting time required to be any moreor less than on the US segment. Translation times on the Russian segment will consistently be less than the USsegment since there is less hardware to translate on. This is offset to some extent by the translation paths being morechallenging to negotiate due to antennas, experiments and such types of ancillary equipment attached to the outsideof the Russian modules. Translation times are also offset by the Russian technique for maintaining a safety tether tostructure, which slows down translation times slightly. This technique is also more tiring to crewmember’s hands,which contributes to the need for the Rest category. Rest periods are planned into Russian spacewalks for three mainreasons; 1) rest periods during critical activities is a real good idea; 2) Orlan helmet lights are too dim for effectiveoperations during eclipse periods; 3) the higher operating pressure of the Orlan can cause crewmember fatigue,predominantly in the hands/forearms. The incorporation of EMU helmet lights onto the Orlan has shortened the restperiods taken by ISS crewmembers during Russian spacewalks during period of eclipse. A special note should bemade about the data presented for Russian EVA 13. During this spacewalk, there were numerous periods of timewhere the crewmembers performed their assigned tasks without active communication with the MCC-M. This madeit very challenging to document precisely how time was spent. Notes made during the data collection state that there

EVA Work Troubleshooting WorksitePrep

SupportEquipment

Translation Rest

Projected Averages 32% 5% 19% 22% 12% 10%Russian EVA 15 22% 9% 1% 20% 34% 15%Russian EVA 14 26% 13% 20% 23% 12% 6%Russian EVA 13 36% n/a 26% 26% 12% n/a

Table 3. Projected Average Time Distribution for Russian Spacewalks

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were brief rest periods, but they were not explicitly voiced over the communications loop and therefore notdocumented as such.

B. STS-114 Data Showing Robotic SupportFigure 1 is a piechart from STS-114 EVA 3 that shows how the time associated with robotic operations

contributed to the overall time distribution for that spacewalk. That particular spacewalk required the robotic arm toposition a crewmember below the Space Shuttle in order to remove two dislodged gap filler items. It is evident fromthe time distribution that use of the robotic arm during an EVA adds extra overhead time for unique supportequipment utilization and robotic arm translation times. This example is probably a worst case in terms of theoverhead time costs for a single task due to the particulars of the task itself. There were special steps required of thecrewmembers to configure the EMU and ancillary equipment in order to protect the Space Shuttle thermal tiles fromequipment impact, as well as a long trajectory required for the robotic arm to fly in order to reach the underside ofthe Space Shuttle. There will be other tasks on ISS that simply can not be performed without robotic assistance dueto various factors such as worksite location or large mass translation. Interestingly, there are multiple other ISS ORUtasks for which robotic assistance may be desired, but is not required. In these cases, the determining factor may bean assessment of trading-off the overhead time costs associated with robotic assistance versus the amount of Work

tasks required of thatparticular EVA.

C. Specific OperationsTimes from Data

This section will presentsamples of the detailed dataavailable from the EVAsanalyzed. This level ofdetailed information wouldbe most useful to EVAplanning and training ifcaptured in a database thatfacilitates quick and easyaccess to the desired results.

1. Translation

There are several ways inwhich the translation time

data can be considered. Table 4 shows a list of multiple unique translation paths around the ISS. They are grouped toshow path times from the Airlock outward first, paths back to the Airlock next, and paths between non-Airlockdestinations last. The translation paths listed include the longest possible routes on the ISS segment in its currentconfiguration. As can be seen, most of these translations were performed by a crewmember with either an ORU orArticulated Portable Foot Restraint (APFR) on the Body Restraint Tether (BRT). The BRT is a dual purpose device

EVA Translation time18%

RMS Translation time10%

EVA Support Equipment time21%RMS Support Equipment time

12%

Work site prep time12%

Work time24%

Troubleshooting time3%

*Work time impacted by tile repair task

Figure 1. STS-114 EVA 3 Task Time Distribution

Translation Path EVA Performed On MinutesISS Airlock to P1 Bay 16 with ORU on BRT US ISS-4 7 ISS Airlock to S0 Bay 02 US ISS-4 2 ISS Airlock to MT on S0 Bay 01 with ORU on BRT US ISS-4 4 ISS Airlock to STS Airlock STS-114 EVA 3 5S1 Bay 13 to ISS Airlock with ORU on BRT US ISS-4 3 PMA2 to ISS Airlock STS-114 EVA 3 12S0 Bay 02 to ISS Airlock with ORU on BRT US ISS-4 1 S0 Bay 02 to zenith-most point on P6 with APFR on BRT US ISS-4 11P1 Bay 16 to S1 Bay 13 with ORU on BRT US ISS-4 8 STS Payload Bay to P1 Bay 12 STS-114 EVA 3 10

Table 4. Translation Times on the US Segment of ISS

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designed for use as body restraint at a worksite, but also to facilitate transport of an item without affecting acrewmember’s ability to translate using both hands. The data shows that encumbered translation can be slower asone would expect, but only marginally so. There are, of course, more details available than presented here, such aswhich particular ORU was being carried (i.e. large or small). This sample of data also shows that there is noconsistent difference between the translation times of the ISS Increment crew on US ISS-4 and the Space Shuttlecrew on STS-114.

The next three Figures represent translation times from two Russian spacewalks that each went from the RussianDocking Compartment 1 (DC1) airlock to the S0 truss on the US Segment. The path followed the Russian modulesforward to the first US element, which is the Pressurized Mating Adapter 1 (PMA1), and from there to the S0 truss.The tasks performed were different for each EVA, but the worksite locations were very close. Figure 2 shows thetranslation times between the PMA1 and the middle bay of S0, designated Bay 00. The times are quite consistent.There was not a comparable US EMU translation in the data. The closest would be to use half the time required totranslate from a similar S0 location (Bay 02) to the zenith-most portion of P6. PMA1 is approximately half-wayalong this route. The approximately six minutes it required the ISS-4 crew to make this translation demonstrates thefaster translation rates possible in the EMU using the US safety tether technique versus the Russian technique. Notethat the RS EVA 15 data shown in Figure 2 was produced by the same crewmembers who conducted US ISS-4. (RS

EVA 15 followed US ISS-4 by several weeks)Figure 3 shows the translation times between DC1

and PMA1. The paths followed were generally the samewith one significant difference. The Russian Strela cranewas setup for RS EVA 9B to provide a translation path,along the Strela boom, directly from DC1 to PMA1.Translation during RS EVA 15 was around the stowedStrela on DC1 and along the Russian Functional CargoBlock (FGB) to the PMA1; a less direct route. The lefthand graph in Figure 3 shows the translation timesindependent of the overhead time associated with setupand cleanup of the Strela. The right hand graph showsthe time comparison with this overhead time added in. Itis clear that time was saved by not using the Strela onRS EVA 15. It can also be seen that translation along theStrela is not necessarily quicker than along the FGB.One interesting aspect of RS EVA 15 that is not fairly

represented by these Figures is that there was some delay on the DC1, both leaving and returning, caused byconfusion during translation around the stowed Strela. These delays effectively negated the time saved by not usingthe Strela. There were several minutes of discussion each time about how to best get around the Strela, followed bytranslation around Strela without issue. Therefore, it appeared a viable translation path existed; it just wasn’t clear at

the time how best to access it. This delay should not occur in future spacewalks.

Translation Between PMA1 and S0 Bay 00

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Figure 2. Translation in Orlans on US Segment

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RS 9B RS 9B RS 15 RS 15

Figure 3. Translation Between DC1 & PMA1

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2. ORU Task TimesTable 5 contains task times associated with ORU installation and removals performed during the analyzed

spacewalks. Each entry reflects the Work time required as well as the associated Worksite Prep (which also includesworksite cleanup). These task times for the External Television Camera Group (ETVCG), Rotary Joint MotorController (RJMC), Mobile Transporter (MT) Remote Power Control Module (RPCM) and Global PositioningSystem (GPS) antenna have been used to update ISS maintenance projections produced by the ISS Program. Thepreviously estimated task times for these ORUs, as well as ORUs similar in size, shape and EVA interfaces, wereconsistently higher than the actual times proved to be, up to twice as high in some cases. This was due to there beinga premium within the Operations community on estimating conservatively for tasks which have never beenperformed. While conservatism is a good thing when properly applied, the ISS Program maintenance and logisticsplanning benefits more from accurate data. A natural side effect of knowing these task times is that planning forfuture spacewalks benefits from the knowledge of the level of difficulty involved with these ORU operations.

The Worksite Prep times shown are indicative of how well the worksites were designed for efficient EVAoperations. The one to seven minute time range is going to be typical of ISS worksites on the US segment. The 87minutes associated with the S0 RPCM illustrates a task that was not planned to occur at that location in theconfiguration existing on ISS at the time. In short, a deployable umbilical tray was (and still is) in its launch positiondue to Space Shuttle delays affecting ISS assembly. The ORUs underneath can only be accessed by removal of thistray. The umbilical tray then had to be reinstalled in the launch location since it can not be installed in its finallocation until after Node 2 is added to the ISS configuration. The GPS antenna worksite prep reflects the fact that themultilayer insulation around the antenna is not quite right and requires added EVA time to secure clear of theantenna. This was a known condition prior to launch. There are two additional points of interest that this data hintsat, but is not a large enough sample to confirm. First, is that the task times associated with ISS Increment crew ORUoperations is very similar to those of Space Shuttle trained crewmembers. This would be surprising because ISScrews are trained using a generic skills-based approach versus task-based training for Space Shuttle flights. EVAOperations have always assumed that task-based training produces more efficient task times across the board. Thatmay prove to be true for complex operations, but not true for the simpler types of operations such as RJMC orRPCM replacement. The second interesting point is that the RS EVA 9B RPCM task, which was performed inRussian Orlan spacesuits, was only marginally longer than similar ORU ops during US ISS-4 performed in EMU’s.Again, it may prove that only more complex tasks are impacted by the lower mobility of the Orlan.

3. Support Equipment OperationsThe time associated with support equipment operations is scattered throughout the spacewalks analyzed. As one

might expect, there is quite a lot of support equipment utilized during zero gravity spacewalks. Two examplespresented here are the times associated with APFR operations and the times required to perform an important safetytether operation. Figure 4 shows in the left hand graph the times from US ISS-4 and STS-114 to pick-up an APFRand attach it to the BRT; and in the right hand graph the time required to install an APFR in a worksite interface.The activities were consistently recorded with regards to starting and stopping points for time determination. Theaverage time expectation for either operation would be in the four to six minute range. Anything less (such as twominutes) is remarkably good, but realistically reflects a pace of operations that is not sustainable for six to seven

ORU Task EVA Performed on MinutesInstallation of ETVCG onto Stanchion US ISS-4 20Installation of Stanchion onto Camera Port US ISS-4 37- Worksite Prep Time 7RJMC Removal from S1 US ISS-4 15- Worksite Prep Time 5MT RPCM Change-out US ISS-4 18- Worksite Prep Time 1GPS Antenna Change-out STS-114 EVA 1 44- Worksite Prep Time 9S0 RPCM Change-out RS EVA 9B 20- Worksite Prep Time 87

Table 5. ORU Task Times

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continuous hours. APFR operation times larger than four to six minutes is indicative of something off-nominaloccurring. In the case of STS-114 EVA 3, represented in the right hand graph, the crewmember experienceddifficulty with the locking interface on the APFR that secures it into the standard worksite interface. There may alsohave been some unverbalized multitasking taking place during the 14 minute APFR installation, such asrearrangement of tool tethers and such. As already mentioned, this is a very limited data set, but again there is noclear indication of these tasks requiring more time for the ISS crew to perform. It may be that this type of task timeis more affected by the total personal EVA experience level of the crewmember than the time since last groundtraining. The ISS-4 times were produced by a crewmember with more past EVA experience than the STS-114crewmember.

A PFR A cquisit io n T imes ( in minut es)

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Figure 4. APFR Operations

Past crew experience levels may also be a factor in the safety tether operation times shown in Figure 5. Thesetimes reflect actions required to attach one safety tether reel to the spacesuit and release from the spacesuit and stowanother safety tether reel. This operation is required when a worksite requires a translation distance farther than thelength of the safety tether wire (either 55 or 85 feet). In a typical case, a crewmember’s original safety tether wirewould be anchored on a point near the airlock hatch. Once the required translation exceeds the length of that tether,a swap to a second tether reel (brought with you just for this purpose) is required. This operation occurs on the USsegment only, because this method of safety tethering is only utilized by the US EVA system. Safety tether swaps,as well as APFR operations, are standard skills trained by US EVA crewmembers continuously from initialfamiliarization events to final practice events prior to launch. Safety tether swap times of one to three minutes areexpected. This time can be affected by how much support equipment a crewmember is encumbered with as this cannegatively affect visibility and reach to the required interfaces. The time can also be affected by how well acrewmember maintains order among the various tethers and tools carried on the front of the spacesuit. Tangling and

confusion with regards to what is attached where occurseasily without due diligence.

The data shown in Figure 5 is interesting in that itreflects both EMU and Orlan operations, as well asexperienced and inexperienced crewmembers. TheRussian spacewalks that ventured onto the US segmentincluded US safety tether operations, as well as theRussian hand-over-hand safety tethering technique. Thelonger tether swap times produced by RS EVA 9Bprobably were indicative of crew inexperience whencompared to those of a more experienced crewmemberon RS EVA 15. Again, the Orlan operations in RS EVA15 reflect times consistent with the EMU operations inSTS-114. An additional fact not represented in the graphis that the safety tether swaps performed during RS EVA

9B were mostly done in series, first by one crewmember with the other watching and then the second crewmember.Therefore, the total elapsed time spent safety tether swapping during that spacewalk was double the value shown in

Safety Tether Swap Times (in minutes)

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Figure 5. Safety Tether Operations

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the graph. The swaps performed during RS EVA 15 and STS-114 were performed in parallel. Obviously, efficienttask planning prefers tether swaps performed in parallel, but real time situations can dictate otherwise.

4. Comparing Planned Times to Actual TimesOne of the more obvious uses of EVA task time data is to compare the actual time required to the planned time. Thestandard planning process in the US EVA system is to perform a series of neutral buoyancy simulations of theplanned EVA and record the time required to complete each major objective. This timeline recording is typicallyonly performed after a particular set of task objectives have been exercised together three times. This time is thenadjusted upward to create an on-orbit planned time. The standard for Space Shuttle based spacewalks is a 20%upward adjustment factor and the standard for ISS spacewalks is a 50% adjustment factor. The Shuttle EVAadjustment factor is based on operational history, but without specific rationale for what constitutes the added 20%.The ISS spacewalk adjustment factor is a conservative guess based on the differences in training (skills vs taskslevel) between ISS and Space Shuttle EVA crews. Figure 6 shows a comparison between the task times fromunderwater training, those planned for the spacewalk (which included the 50% factor) and the actual EVA tasktimes. It is apparent that the actual times were much closer to the training times than the planned times, suggesting alower adjustment factor would be in order. The most noticeable discrepancy between planned and actual occurredwith the ETVCG install task. Given that this task consisted of translations, tool operations, a safety tether swap,ORU bolting and electrical connector operations, it is not clear how it ever could have required, with nominal

hardware performance, three hours on-orbit versus the two hours required in training.

A more detailed comparison of exactly why and how the actual times differed from the training, or water, timeswould be very informative. This would simply require a time measurement study of the water timeline event just aswas done for the zero-g event followed by a side by side comparison. It may well be that certain activitiesconsistently require the same time to perform in zero-g as in neutral buoyancy, such as translation, and that othermore technique sensitive operations are candidates for more time in zero-g.

US ISS-4 Task Times

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Figure 6. US ISS-4 Task Times

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IV. Applications for ExplorationExploration efforts will be faced with the key resource utilization challenge of matching the EVA capability and

resources with the EVA requirements. This will be a more difficult challenge than ISS in that resupply of EVAresources will be much more difficult, if not effectively impossible, outside of in situ consumable production andregeneration. The EVA assembly and maintenance tasks associated with Exploration should, therefore, be of a muchnarrower scope consistent with the limitations of the EVA resources that will be present on a Moon or Mars mission;with the bulk of the EVA capability reserved for scientific endeavors. Those with recent ISS experience would notbe surprised when non-scientific EVA tasking inevitably requires time originally planned for science. It will also bevery easy for tasks associated with science to become cumulatively inefficient to the extent that desired scienceobjectives can no longer be addressed within the EVA capability. These reasons contribute to the logical need tomake methods design and work measurement a priority during the development of a new EVA system. It is veryimportant to note here that methods design and work measurement were also a priority during the development ofthe ISS US EVA system and were instituted in a manner unique to that process. The key improvement thatExploration activities can employ lies within a simple definition of work method design: a systematic way ofdeveloping an effective and economical utilization of the available resources1. The systematic aspect has to bedeveloped and employed to the absolute fullest extent possible.

V. ConclusionIt is generally agreed that Frederick W. Taylor originated the concept of time study in the machine shop of the

Midvale Steel Company in 18811. Taylor stated, “time study is the one element in scientific management beyond allothers making possible the transfer of skill from management to men.” Taylor’s real contribution to industry was hisscientific method, his substitution of fact-finding for rule-of-thumb procedure. He approached problems which hadbeen thought either not to exist or to be easily solved by common sense, in the spirit of scientific enquiry1. Thisapproach is very applicable to current day EVA Operations concerned with the examination of EVA task efficiency.In fact, some consider that within the NASA ISS community, EVA operations and planning are considered more ofan art than a science. The quantification, analysis and documentation of exactly what occurs during a spacewalk andwhy is necessary to remove as much guess work as possible from future EVA operations. As stated repeatedlyabove, the data set presented here is not large enough to make definitive conclusions regarding aspects of the ISSEVA systems. The data does suggest several points relating to EVA task efficiency that will merit further evaluationas more data becomes available.

• The US and Russian EVA systems and the ISS design allow approximately 42% and32%, respectively, of available EVA time to be devoted to the specific task objectiveinterfaces.

• Prior EVA experience may serve to lower task times more than recent training.• Basic skills that have been mastered, such as translation, APFR operations, tether swaps

(and others) may not be impacted by the duration of time since last training.• EVA skills training may be more cost-effective for non-complex tasks than task-based

training.• Russian Orlan spacesuit gloves and operating pressure only marginally affect efficiency

of operations for standard tasks during the first half of a standard length EVA.• A more thorough and detailed understanding of the differences between ground-based

neutral buoyancy training and on-orbit actuals may allow accurate planning without theneed for applying a time adjustment factor across an entire timeline.

• Data collection accuracy is tolerant of variations in how the data is collected. In otherwords, the meaning and usefulness of the results do not change if the category allocationschange by a few percentage points.

The final point above merits further explanation due to expected resistance encountered within the JSC EVAOperations community regarding the ability to capture data consistently. The data collection experience to date hasshown that it is not technically difficult to consistently capture the beginning and end of any activity, given goodcommunication skills by the crewmember (which is the expected norm). It is also apparent that there is no utility inattempting to quantify tasks, such as a safety tether swap, down to an exact minute. It is sufficient to understandwhat approximate time range represents the norm. The key is to employ a written standard for classifying events toassist with the categorization. A crewmembers voice and the passage of time take care of everything else.

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Additional information from Barnes provides a good concluding summary of the task ahead for ISS. “If a newproduct is to be manufactured or a new service is to be performed, then a fresh start can be made. There is evidenceto show that this same approach should be used even though an existing activity is being investigated with thepurpose of finding a better work method. Of course, consideration would be given to the present method, but theapproach would not be one of improving this current method, but rather designing an ideal method1.

References1Barnes, R. M., ME, PhD, Motion and Time Study – Design and Measurement of Work, 6th ed., John Wiley & Sons, New

York, 19682Looper, C. A., and Ney, Z. A., “Extravehicular Activity Task Work Efficiency, 35th International Conference on

Environmental Systems, SAE Aerospace, July 2005