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Operations, Maintenance, and Reliability A major purpose of the ISS is to provide a platform for long-duration microgravity experiments in the life sciences and physical sciences. ISS operational principles, mainte- nance requirements, the reliability of hardware and software, and the ability of onboard crews to work efficiently will directly affect the achievement of this goal. This chapter provides suggestions to NASA for ensuring the success of long-term ISS operations. DAILY FLIGHT CREW SCHEDULING ISS crews will have full daily schedules on board the station: they will support the day-to-day operation of the station; they will perform maintenance of ISS systems and laboratory equipment, make repairs to ISS systems and labo- ratory equipment, and conduct scientific research and manage experiments; and they will need time for regular exercise and periods of rest. Careful planning will be neces- sary to ensure a balance so that one set of priorities, such as maintenance and repair, does not conflict with others, such as scientific research or experiment management. NASA's traditional methodology for scheduling the day-to-day activities of the flight crew was appropriate for short- duration space flights. However, experience with long- duration space flights on Skylab and Mir suggests that a dif- ferent approach would ease the pressure on the daily timeline and ensure that the crew has time for scientific research. To capitalize on the full potential of the new environment provided by the ISS (i.e., the ability to operate in space for extended periods of time), NASA should consider transfer- ring some control of day-to-day scheduling details to the crew on board the ISS. The idea is to capitalize on the crew' s unique experience with the on-orbit laboratory and to permit the crew to organize their tasks in the most time-efficient manner. For example, the mission control center could pro- vide the crew with objectives for the upcoming week, including a summary of the science and a proposed timeline. The crew could then make adjustments to the timeline, send 13 them to the ground, and the ground controllers would follow the crew's suggestions without requiring justifications for each change. This would rely on the crew' s extensive knowl- edge of their space laboratory to optimize the order in which activities were performed and adjust the time required to perform specific tasks. The detailed crew-developed timelines would be subject to periodic progress reviews with the ground controllers to ensure that the overall objectives for that crew' s increment aboard the ISS were being met (an "increment" is the duration of a particular crew' s stay aboard the ISS, the period between crew rotations). Ideally, this arrangement would leave more time for research by allow- ing the crew to optimize their daily schedule and recover time otherwise committed to standard blocks of time for maintenance and repair tasks and station operations. Recommendation. The National Aeronautics and Space Administration should allow the International Space Station (ISS) crew on orbit to contribute to the development and optimization of the daily timeline. The time saved would allow the crew to devote more time to scientific research. Oversight of the accomplishment of crew tasks ahoard the ISS should be maintained by mission control through peri- odic flight crew/ground controller progress reviews. ONBOARD MAINTENANCE In briefings to the committee, the committee learned that the crew would be trained both to work on experiments and to perform "routine" maintenance on the station. The crew would also be able to do some troubleshooting of hardware and make some minor repairs. Tasks that require extra- vehicular activity (EVA) will be performed by Space Shuttle crews as much as possible (Harbaugh and Poulos, 1999~. Plans call for ISS crews to spend some time conducting research on behalf of the principal investigators (PIs) and some time performing routine maintenance. However, the committee believes, based on Phase 1 Mir experience, that

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14 ENGINEERING CHALLENGES TO THE LONG-TERM OPERATION OF THE INTERNATIONAL SPACE STATION the crew may also have enough time to accomplish some of the day-to-day mission operations and thus reduce the aggregate requirement for ground personnel. A reassess- ment of the crew timelines might reveal that they could per- form some of the work now planned for mission controllers on the ground. To that end, NASA should prepare a long- term "design reference mission" showing projected clusters of crew activities against a timeline. It would be useful, for example, to show a typical 30-day timeline with the Space Shuttle docked either at the beginning or the end of the 30-day period. This would help determine if measures to increase onboard crew efficiency and conserve the crew's working time will be necessary. NASA did provide the committee with copies of the Concept of Operation and Utilization Mission Scenarios and Mission Profiles, which documents this type of timeline planning for Space Station Alpha (NASA, 1994~. That document, however, has not been updated since 1994 and the timeline scenarios are not being continued in the ISS Program. Recommendation. The National Aeronautics and Space Administration should reassess the crew's activities against a more realistic timeline based on the Phase 1 Mir experi- ence, as well as experience gained during assembly of the International Space Station. If the crew could take on more of the day-to-day mission operations, the aggregate require- ments for ground crew personnel would be reduced. Recommendation. Maintenance onboard the International Space Station (ISS) should be scheduled during resupply missions as much as possible. Resupply missions are also the preferred times for conducting extravehicular activities because the microgravity environment will already have been disturbed by the resupply vehicle docking with the ISS. If the Space Shuttle is the resupply vehicle, additional per- sonnel will also be available to help with maintenance tasks during docked operations. Cooperative tasks between the arriving crew and the departing crew will also facilitate the passing of detailed information to the arriving crew (the so- called "crew hangover". STAFFING OF THE OPERATIONS CONTROL CENTER Current flight and ground control operations are under- standably focused on the ISS assembly processes, planning for EVAs, training, testing flight hardware, and planning logistics. NASA personnel who briefed the committee expressed the concern that this intense activity could lead to burnout of ground support personnel. The Phase 1 Mir experience shows that work/rest cycles are important for ground personnel and for the productivity of the long- duration mission. Chronic fatigue from working long hours and extended work weeks result in an increase in incidence of illness, loss of performance, and team member attrition (NASA, 1998a). In support of Mir operations, the Russian practice has been to maintain only a small team in the mis- sion control center and have experts on call to support them whenever necessary. New information technologies could enable NASA to go one step further by establishing remote workstations, which would allow people to focus on solving problems and rely on support software to identify problems. Although problems can occur at any time, experts "on duty" at their homes or offices could have on-line access to the data and analysis tools necessary to enable them to work with the smaller mission control center staff to prioritize and resolve problems with the help of support software and on- line displays. NASA' s current plans for flight and ground control opera- tions are concentrated on the ISS assembly flights and are based on the fully staffed, "all-up" mission control center philosophy that has been used by the U.S. space flight pro- gram since the days of Mercury, Gemini, and Apollo and has been continued for the Space Shuttle program. Almost none of these operations, however, lasted more than two weeks. NASA has acknowledged that the new operational environ- ment of the ISS (i.e., continuous operations in support of a very long-duration mission) and the intense continuous activity might eventually cause burnout of ground support personnel (Harbaugh and Poulos, 1999~. The safe reduction in on-site mission control staff is also essential to the long- term fiscal soundness of the ISS program. NASA has not yet addressed the challenges associated with optimizing the long-term operation of the ISS. Recommendation. The National Aeronautics and Space Administration (NASA) should develop a new concept of operations for the long-term operation of the International Space Station that includes the integration of new informa- tion technologies into mission control center processes. NASA should consider adopting the Russian operational practice used for Mir (i.e., maintaining a small team in the mission control center and relying on experts on call with remote access to the data and personnel in the mission con- trol center). COMMUNICATION WITH PRINCIPAL INVESTIGATORS For the long-term operation of the ISS, NASA has an opportunity to reinstate some of the procedures that were used for Spacelab, when the crew was allowed to communi- cate directly with the PIs instead of having to coordinate responses through the ground support team. NASA's traditional practices worked well for short-duration space missions, but with new communication technologies and long-duration space flight, NASA could consider allowing crew members to communicate directly with PIs on ques- tions of science, experiment protocol and experiment status, and other subjects that do not affect the operation or safety of the ISS. Direct communication would be more efficient, would result in better science, would lead to significant time

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OPERATIONS, MAINTENANCE, AND RELIABILITY savings for both the crew and the ground support team, and would ease the pressure on the crew's daily timeline, giving them more time to perform research. During Phase 1 operations on Mir, the Russians were able to take advantage of direct communications between PIs and crew members. This approach saved the crew time and pro- vided them with answers directly from the experts. If a crew member had further questions, the PI could respond immedi- ately. For the long-term operation of the ISS, direct commu- nication would be efficient and would greatly enhance the crew' s ability to support experiment protocols and scientific objectives. Recommendation. The National Aeronautics and Space Administration should adopt the practice demonstrated dur- ing the Mir program of direct communications between the crew and principal investigators (PIs). Crew members and PIs should be able to exchange data and instructions to enable the crew to carry out experiments in the way that best fulfills the goals of the experiment. Computer links should be devel- oped and communications systems upgraded to provide real- time assessments of the data and the capability of responding to change. Recommendation. The National Aeronautics and Space Administration and the scientific community should explore ways to enable principal investigators to access their experi- mental data directly from ground locations at universities and research facilities to increase the direct involvement of the science community in ISS experiments. PAYLOAD SPECIALIST NASA's projected requirements for the ISS crew do not include a payload specialist. The payload specialist program worked very well on Spacelab missions on the Space Shuttle. The payload specialist was in a unique position to make significant contributions to the quality of science and the success of experiments. Because some very precise experimentation will be performed on the ISS, having a scientific expert onboard would increase the quality of support available to the PI. The payload specialist could make in situ adjustments to experiments that might otherwise require time on the ground to analyze results and, perhaps, require reflight of the experi- ment. The payload specialist would also be able to provide early warning of the need to change or upgrade experimental equipment. Recommendation. The National Aeronautics and Space Administration should reassess its crew requirements for the International Space Station and consider including a pay- load specialist in the seven-person crew. 15 CREW HANDOVER NASA has not developed a plan for on-orbit handover to ensure that efficiency is maintained and no errors are intro- duced that would result in costly reworking or increase operational risk. Every effort should be made to capitalize on the knowledge of the departing crew members. The value of a smooth, efficient handover is well documented by the Mir experience (NASA, 1998a). Mission planning could allow Space Shuttle crew mem- bers to perform many joint tasks during the handover period. Ideally, crew members would have all of the docked time for the handover. Although this may not always be possible, it should be established as a goal to help mission planners establish priorities. During the handover period, the new flight crew can become familiar with the protocols of ongoing experiments through actual operations under the guidance of the departing crew. Recommendation. The National Aeronautics and Space Administration (NASA) should develop a plan and process to ensure that crew members on board the International Space Station have as much time as possible for their on- orbit handover during docked operations. The handover should be formal and should include essential hard copy and/ or laptop computer files of historical records to ensure that arriving crew members have a complete understanding of activities in progress before returning crew members depart. In developing the handover plan and process, NASA should assess the desirability of performing critical maintenance tasks during Shuttle handover periods to take advantage of the availability of additional crew members. ONBOARD FAILURE DETECTION AND CORRECTIVE ACTION On-orbit maintenance includes the detection of an anomaly, the identification of the failed orbital replacement unit (ORU), and replacement of the ORU or creation of a work-around. The first two of these activities are very diffi- cult to plan and train for comprehensively because failures are often unpredictable. Localization of a failed component is essential for the efficient functioning of the ISS. The most successful way to localize failures is for each ORU to be responsible for its own failure monitoring, with backup monitoring at the system level. The starting point for the process is usually the failure modes and effects analysis (FMEA), which is generated as part of reliability assess- ments. The FMEA made available to the committee was focused on safety-critical items but did not address overall maintenance. The methodology supporting this approach is referred to as failure detection, isolation, and recovery (FDIR). In the ISS context, FDIR has two meanings: (1) software programs for the automated detection of failures

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16 ENGINEERING CHALLENGES TO THE LONG-TERM OPERATION OF THE INTERNATIONAL SPACE STATION and identification of the failed units and (2) the overall pro- cess of which the software programs are a part. Only one individual is presently responsible for manage- ment oversight of the FDIR software program at the NASA Johnson Space Center. Overall failure identification is being investigated by Boeing as part of the Launch Package and Stage Assistance Program (Wolf, 1999~. Neither of these is directly connected to the FMEA generated by the reliability and quality assurance organization, and neither addresses the need for training, providing spare parts, or other logistics. The committee could not determine if failures in monitoring circuits, which might lead to the unnecessary removal of an ORU, have been considered by the ISS Program. The stated goal of the FDIR is to achieve 90-percent identification to a single ORU; 95-percent to two ORUs; and 98-percent to three ORUs. This goal appears to be unrealis- tic in light of the limited efforts NASA has devoted to FDIR to date. No plans for verifying these levels of identification were provided to the committee. Considering the impor- tance of FDIR for the efficient long-term operation of the ISS, the lack of attention to this activity is an indication of NASA's focus on the assembly phase of the ISS to the exclusion of important operational considerations and con- tingency planning for its long-term operation. Recommendation. The National Aeronautics and Space Administration should greatly expand its focus on failure detection, isolation, and recovery (FDIR) in conjunction with the failure modes and effects analysis (FMEA). The follow- ing issues should be addressed specifically: allocation of responsibility to automated/nonautomated functions consistency of the FDIR with known failures integration with space and ground crew training and logistics SAFETY, RELIABILITY, AND MAINTAINABILITY PROGRAM The safety, reliability, and maintainability program (SR&M) follows policies established by the NASA Head- quarters Office of Safety and Mission Assurance (Code Q) and meets the conventional requirements of SR&M pro- grams. In examples furnished to the committee, areas that impact safety had been analyzed in depth. Nevertheless, the committee found no evidence that NASA had taken into account the aggregate of interfaces in the ISS and the heavy dependence on software. NASA' s approach is not proactive in that it has not identified early, small expenditures for im- provements in SR&M that could avoid the eventual high cost of failures. The SR&M program would benefit from more trend analyses of all data that could have a bearing on the long-term failure rate, maintenance capabilities, and spare parts requirements of the ISS. The Hubble Space Telescope (MST) program, for example, now considers "trending" as its primary SR&M analysis method. Trend analysis for the ISS could include the following elements: incoming inspection reports in-process test reports failure reports from on-orbit segments maintenance records for ground and on-orbit operations Recommendation. Analyses of the incoming inspection and in-process testing data should be used to establish a six- sigma environment in which failures will be extremely rare. Analyses of failure reports and maintenance records should be used to improve on-orbit procedures and the quality of replacement items. SPARE PARTS PHILOSOPHY NASA provided the committee with information on plans to provide spare parts and logistics for the ISS (NASA, 1998b). The committee also reviewed the same information for the HST, the only other long-duration U.S. space vehicle that has involved crew servicing. The opportunities for com- ponent replacement on the ISS and the HST differ four or five visits per year for the ISS and three or four years between visits for the HST. In terms of manufacturing lead-time for producing spare parts, however, the biggest difference is that significant lead-time is available between repair visits to the HST to secure replacement parts. For the HST, solar panels, mechanical relays, and rotat- ing devices (e.g., wheels, gyros, gimbals, and servos) were stockpiled, but in MST's nine years on orbit, the electro- mechanical devices and the purely electronic devices have had only moderate failure rates (Styczynski, 1999~. Experi- once with the HST project revealed that NASA could not afford to stock and maintain the extensive depot facilities and the large numbers of spare parts required for the HST based on the "old" measure of statistical mean time between failures of the hardware (Kelley, 1999~. Another method of providing spare parts would be to introduce upgrades during the operational life of the ISS to reduce failure rates and thereby reduce maintenance requirements (this concept is discussed further in Chapter 5~. NASA's current philosophy of providing spare parts for the ISS requires a very large contingent of personnel and extensive facilities. Because the ISS is expected to have a nominal operational lifetime of 15 to 20 years after Assembly Complete, the project would require repair and maintenance depots, as well as inventories of spare parts. As the HST experience has shown, however, predictions of the require- ments for spare parts are not accurate. The combination of inaccurate predictions and the possibility of technological

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OPERATIONS, MAINTENANCE, AND RELIABILITY advances and evolving requirements of ISS operations sug- gests that NASA could adopt a less conservative approach except for items essential for life support. Recommendation. The National Aeronautics and Space Administration should reassess its current philosophy for providing spare parts, as well as the depots and associated personnel required to maintain them for the operational Inter- national Space Station (ISS). The criticality of hardware, wear-out factors, and the potential for subsystem upgrades should be considered in the reassessment. The logistics, reliability, and mission assurance personnel for the ISS should establish an ongoing liaison with their counterparts in the Hubble Space Telescope program to evaluate a new philosophy for the ISS and the possibility of reducing associated costs. REFERENCES Harbaugh, G., and S. Poulos. 1999. EVA Status. Briefing by G. Harbaugh, Manager, EVA Projects Office, and S. Poulos, Deputy Manager, EVA Project Office, to the Committee on the Engineering Challenges to the 17 Long-Term Operation of the International Space Station, NASA Johnson Space Center, Houston, Texas, February 21, 1999. Kelley, J. 1999. Personal communication from J. Kelley, Lockheed Missiles and Space Systems, to B. Bulkin, member of the Committee on the Engineering Challenges to the Long-Term Operation of the International Space Station, January 7, 1999. NASA (National Aeronautics and Space Administration). 1994. Concept of Operations and Utilization Mission Scenarios and Mission Profiles. SSP 50011-01. Houston, Texas: NASA Johnson Space Center. NASA. 1998a. Phase 1 Lessons Learned. August 26,1998. Houston, Texas: NASA Johnson Space Center. NASA. 1998b. Current Manifest of Assembly Critical Spares: Working Paper. December 11, 1998. Houston, Texas: NASA Johnson Space Center. Styczynski, T. 1999. Personal communication from T. Styczynski, Lockheed-Martin Hubble Space Telescope Operations, to H. Hecht, member of the Committee on the Engineering Challenges to the Long- Term Operation of the International Space Station, January 20, 1999. Window, K. 1999. Presentation by K. Window, Avionics and Software Office, International Space Station Program Office, to the Committee on the Engineering Challenges to the Long-Term Operation of the Inter- national Space Station, NASA Johnson Space Center, Houston, Texas, March 24, 1999. Wolf, K. 1999. Launch Package and Stage Assistance Program. Presenta- tion by K. Wolf, the Boeing Company, to the Committee on the Engi- neering Challenges to the Long-Term Operation of the International Space Station, NASA Johnson Space Center, Houston, Texas, March 25, 1999.