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Executive Summary The International Space Station (ISS) is truly an inter- national undertaking. The project is being led by the United States, with the participation of Japan, the European Space Agency, Canada, Italy, Russia, and Brazil (see Figure ES-1~. Russia is participating in full partnership with the United States in the fabrication of ISS modules, the assembly of ISS elements on orbit, and, after assembly has been completed (so-called "Assembly Complete"), the day-to-day operation of the station. Construction of the ISS began with the launch of the Russian Zarya module in November 1998 followed by the launch of the U.S. Unity module in December 1998. The two modules were mated and interconnected by the crew of the Space Shuttle during the December flight, and the first assembled element of the ISS was in place. Construction will continue with the delivery of components and assembly on orbit through a series of 46 planned flights. During the study period, the Assembly Complete milestone was sched- uled for November 2004 with the final ISS construction flight delivering the U.S. Habitation Module. This study of the engineering challenges posed by long- term operation of the ISS shows that the National Aeronautics and Space Administration (NASA) and the ISS developers have focused almost totally on completing the design and development of the station and completing its assembly in orbit. After ISS Assembly Complete, the primary work on orbit will shift to scientific and engineering research, ISS operations, and the maintenance of ISS systems and experi- ments. Therefore, many of the issues and opportunities related to long-term operations have not yet been addressed thoroughly by NASA except as they apply to the more immediate tasks of ISS assembly. Despite this near-term focus, the committee found no major engineering problems with the design of the ISS that would adversely affect long-term operations. Most of the deficiencies can be corrected with procedural changes and equipment or software upgrades in time for incorporation at ISS Assembly Complete. Although funding for most of these changes has not been committed because of the higher 1 priority of current program issues, funds are likely to be available in the out years of the program as ISS assembly proceeds toward completion. In the first committee meeting in September 1998, the committee reviewed the report of the Cost Assessment and Validation (CAY) Task Force of the NASA Advisory Council, which had been released several months earlier (CAY, 1998~. The Terms of Reference for the CAV Task Force were compiled by NASA on October 14, 1997, con- current with, and in direct response to, the congressional interest expressed in the Appropriations Act of October 17, 1997, which also chartered this study. The CAV report was published in April 1998, just one month after the official start date of this study. The report examined in detail the cost and schedule risks in the ISS program, focusing on the assembly phase of the program and predicting a one to three year slip in schedule and a most likely date for Assembly Complete of December 2005. The committee found the CAV report to be a comprehen- sive and timely study of the ISS budget risks and decided that it need not be duplicated and that the study on the long term operation of the ISS should be complementary to it. Therefore, the committee decided to focus on the engineer- ing challenges of long-term ISS operations and delve into budget issues only if they were not covered in the CAV report. However, the CAV report covered the budget issues thoroughly and the recommendations in this report fit the CAY's budget assumptions for the operational phase. The committee made 36 recommendations, 17 of which are highlighted in this Executive Summary. All of the committee's recommendations are treated in detail in the body of the report. In the area of communications and data handling, the committee concluded that increases in communications up- link and downlink bandwidths, and an increase in the avail- ability of communications links through the tracking and data relay satellite system (i.e., increased antennae mutual visibility time) will be critical to the efficiency of long-term

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2 ENGINEERING CHALLENGES TO THE LONG-TERM OPERATION OF THE INTERNATIONAL SPACE STATION operation of the ISS. Enhanced communications will be an enabling innovation for long-term ISS missions by allowing time for on-orbit training and for the introduction of inter- active maintenance and repair tutorials that will facilitate making detailed equipment diagnoses and evaluations and will support direct interaction between the crew and the prin- cipal investigators (PIs) of the experiments. Thus, operating efficiency would be increased and the aggregate demands on crew time for long-term operations would be eased. These changes should be reflected in NASA's plans for the ISS. This subject is discussed further in Chapter 5. Recommendation. The National Aeronautics and Space Administration should make increasing the uplink bandwidth a high priority and should evaluate the importance of video communications. Recommendation. The International Space Station antennae should be relocated in a configuration that allows continuous communication through the tracking and data relay satellite system. NASA's control procedures for space flight operations have evolved over many years of diligent attention to detail, and they are excellent. These procedures are highly refined and have been highly successful since the very first sub- orbital Mercury flight some four decades ago. The challenges associated with the long-term operation of the ISS, however, will be very different from the challenges of the short-term human space flights of the past 40 years. The committee was concerned that the ISS operations and maintenance workload might leave ISS flight crews little time for research as happened in recent years on the Russian space station, Mir. NASA has not done sufficient analyses to alleviate this concern. The committee concluded that a rigorous analysis will be necessary to determine if the crews of the ISS will have enough time to conduct research. To that end, NASA should prepare a long-term "design refer- ence 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 nec- essary. This subject is discussed further in Chapter 3. 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. The time on orbit of three to four months for an ISS crew suggests a mode of operation different from the operational mode appropriate, for example, for the much shorter dura- tion Space Shuttle flights. This difference was noted by sev- eral of the U.S. astronauts who lived and worked on Mir in the Phase 1 program and who had had prior flight experience on several Space Shuttle flights. The observation is also included in the "Phase 1 Lessons Learned" documentation of August 26, 1998 (NASA, 1998a). The flight crews who will have months of accumulated experience with the equip- ment and experiments on board the ISS, will be extremely well qualified to participate in the planning of maintenance tasks and to implement changes to experiment protocols deemed necessary by the principal investigators (PIs). The resourcefulness of flight crews is legendary in NASA' s his- tory of space flight operations, and they should be delegated the responsibility for a great deal of the day-to-day planning of on-orbit operations. NASA should reassess its basic philosophy of space flight operations to take advantage of their expertise. This subject is discussed further in Chapter 3. 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 aboard the ISS should be maintained by mission control through peri- odic flight crew/ground controller progress reviews. 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 developed and communications systems upgraded to pro- vide real-time assessments of the data and the capability of responding to change. 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). 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.

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EXECUTIVE SUMMARY All of the information provided to the committee shows that the baseline extravehicular mobility unit (EMU) is a mature system that can be expected to support the ISS opera- tional phase. Nevertheless, many improvements could be made, including reducing prebreathing requirements, increasing the use of robotics for extravehicular activities (EVAs), and using more autonomous robotics that demand less crew time, skills, and training. Long-term operations will also afford a unique opportunity to use the ISS as a test bed for advances in EVA equipment and technology. This subject is discussed further in Chapter 4. Recommendation. The National Aeronautics and Space Administration and its international partners should develop a plan to incorporate improved control modes for the baseline robotic systems on the International Space Station (i.e., the space station remote manipulator system and the special purpose dexterous manipulator) that would simplify their operation and reduce astronaut training time (e.g., "flying the end pointy. The plan should address cost and safety considerations as well as teleoperation by ground-based operators. Recommendation. The National Aeronautics and Space Administration should assess the potential improvements in extravehicular activities from the introduction of new robotic technology into human-robot systems. This assessment should include a comparison of the cost for development and implementation and the potential cost savings and risk reduction associated with the use of these systems. Recommendation. The National Aeronautics and Space Administration should use the International Space Station (ISS) as a technology test bed for advanced extravehicular activity (EVA) systems, including robotic systems to sup- port long-term ISS operations and future space missions. Rather than introducing only incremental changes, revolu- tionary approaches should be pursued to developing new materials, achieving greater mobility, and incorporating new technologies for both EVA suits and robotics systems in sup- port of future exploration initiatives. The committee found that the requirements for logistics and resupply flights and for on-orbit maintenance could be refined and probably reduced by applying more practical, targeted failure analysis and logistics management techniques based on current NASA and Air Force space operations experience. The techniques NASA is currently using for failure prediction and logistics management are outdated. Overcompensating for the general nonspecific nature of the analyses will lead to excessively large and costly inventories of spare parts, maintenance depots, and ISS resupply flights (Butina, 1998; NASA, 1998b). With better planning, the ISS program could decrease logistics and maintenance costs and reduce the number of resupply 3 flights required, thereby reducing the frequency of disturbances to the ISS microgravity environment for critical experiments. This subject is discussed further in Chapter 3. 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 Several models exist for logistics planning. NASA has developed a computerized provision planning system for the EMU that tracks current inventory and projects future requirements based on a number of program parameters. This system could be used as a model for improving logis- tics planning. Lessons learned from the Hubble Space Tele- scope Program could also be used to improve planning. This subject is discussed further in Chapter 3. 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 asso- ciated costs. ISS management has expressed serious concerns about the ability of the Russian partners to deliver on their com- mitments. Nevertheless, NASA's options for reducing the dependency of the ISS Program on Russia are limited. NASA described three options: Option 1. Provide funding to Russia as necessary to complete and sustain all Russian contributions. Option 2. Provide funding to Russia for items neces- sary to continue the ISS Program in the near term while funding the U.S. capabilities (e.g., U.S. propulsion module) necessary to eliminate dependence on Rus- sian participation, thereby establishing U.S. autonomy, in the long term. Option 3. Provide no funding support to Russia and adjust the schedule of the ISS Program, as necessary, to accommodate late Russian deliveries.

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4 ENGINEERING CHALLENGES TO THE LONG-TERM OPERATION OF THE INTERNATIONAL SPACE STATION The committee believes that a more thorough analysis of these options is required, particularly as they apply to the long-term operation of the ISS after Assembly Complete. This subject is discussed further in Chapter 2. Recommendation. The National Aeronautics and Space Administration should develop a concise comparison of Options 1 and 2 to document the relative costs, as well as the program risks and benefits, associated with implementing Option 2 in order to reduce International Space Station (ISS) dependence on Russia and achieve autonomy for the ISS Program in the long term. The cost estimates should include the following items: the incremental cost of operating the Space Shuttle to replace Soyuz/Progress logistics flights the cost of developing a U.S. propulsion module and delivering it to the ISS the cost and risk associated with integrating a U.S. propulsion module with the ISS this late in the ISS program other costs that may accrue in establishing U.S. autonomy risks to the program schedule The committee reviewed NASA's plans for using the in- ternational launch vehicle fleet to ensure access to the ISS assuming that over the long-term operation of the ISS one or both of the primary launch vehicles supporting the ISS (i.e., the Space Shuttle and the Soyuz) would be in a stand-down. NASA has not yet seriously considered this aspect of contin- gency planning for operations in support of the ISS after Assembly Complete. NASA has been operating on the assumption that either the Space Shuttle or the Soyuz, or both, will be available for crew launches. If both the Space Shuttle and the Soyuz were concurrently in a stand-down mode, however, support of ISS crew opera- tions would no longer be possible. Other vehicles, particu- larly the autonomous transfer vehicle (ATV) (propellant logistics) launched by Ariane and the Japanese H-II transfer vehicle (HTV) launched by the H-II launch vehicle, are part of the ISS logistics support baseline and could be used for noncrew-related logistics operations in case of a concurrent stand-down of the two primary vehicles. In one scenario, the ISS would be moved to a higher altitude to prolong its life and reduce logistics flight requirements. The ISS can survive without a crew, and, like the Soyuz/Progress logis- tics resupply vehicle, the ATV can dock without a crew. In this scenario, the contingency plan for the concurrent stand- down mode, therefore, is to "mothball" the ISS by moving it to a higher orbit and replenishing propellant via the ATV in an automatic docking mode. The committee believes that NASA should look more carefully at its contingency plans for the operational phase of the ISS and assess other options for ensuring its survivability in case of a concurrent stand-down of the Space Shuttle and the Soyuz launch vehicles, and the Soyuz/ Progress logistics resupply vehicle. This subject is discussed further in Chapter 2. Recommendation. The National Aeronautics and Space Administration (NASA) should develop contingency plan- ning for personnel transport and resupply during the opera- tional phase of the International Space Station (ISS). The assessment should identify viable options other than moving the ISS into a high storage orbit in case of a concurrent stand- down of the Space Shuttle, the Soyuz, and the Soyuz/ Progress vehicles. NASA's plan should accommodate new launch vehicles that may become operational during the operational lifetime of the ISS for both crew transport and ISS resupply. The plan should address the relative costs of the various options for ensuring access to the ISS. NASA plans to deorbit the ISS with a controlled reentry at the end of its useful operating lifetime on orbit. The com- mittee believes that NASA should conduct a rigorous reassessment of entry probability criteria and the risks associated with ISS reentry to determine if the present decommissioning/deorbiting plan should be changed. NASA's plan should be consistent with the agency's objec- tives of maximizing the safety of the operation and minimiz- ing the potential risks associated with the reentry of such a large object. This subject is discussed further in Chapter 6. Recommendation. Because of the potential hazards asso- ciated with the reentry of relatively large objects, the safety requirement for International Space Station reentry should be more stringent than the requirement for other National Aeronautics and Space Administration operations (i.e., the chance of casualties should be much less than 1 in 10,000~. Recommendation. The National Aeronautics and Space Administration should undertake a thorough analysis of International Space Station reentry operations, including ranges of uncertainty associated with the multiple variables of reentry operations. The analysis could take the form of a Monte Carlo simulation of reentry operations and projected impact areas to characterize the hypothetical potential for property damage or casualties. The analysis should include the sequence of operations, possible failures, and conse- quences of failures, from the initiation of reentry operations to final impact. Uncertainty variables should include, but should not be limited to, reliability characteristics, duration of burn, atmospheric density, ballistic coefficients of frag- ments, population densities, and the characterization of acceptable impact areas. Finally, NASA has an important ongoing program to identify preplanned product improvements (P3I) for the ISS. Under this program, ~ ~~ ~ ~ the staff of the ISS Program Office, and

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EXECUTIVE SUMMARY the appropriate offices in the Engineering Directorate at the NASA Johnson Space Center, recommend candidate items for ISS system or component upgrades. Some of these up- grades could significantly reduce maintenance and resupply requirements for the long-term operation of the ISS thereby increasing crew efficiency. Although the P3I program is being conducted carefully and responsibly, its current funding is grossly inadequate. NASA should assign high priorities to the preplanned product improvements, and other specific items that will contribute to the efficient operation of the ISS after Assembly Complete and make the ISS less dependent on Russian supplied hardware. NASA should pre- pare a long-range budget plan for P3I to ensure that cost- effective and operations-effective upgrades are developed in time for ISS Assembly Complete. To ensure that NASA does not defer the long-term needs of the ISS until they become program critical, the committee recommends that NASA designate a senior ISS staff person to oversee imple- mentation plans for post-Assembly Complete ISS operations, including the upgrades identified in the P3I activity. This subject is discussed further in Chapter 5. Recommendation. The National Aeronautics and Space Administration should designate a senior member of the International Space Station (ISS) staff to assemble, review, and approve budgets and implementation plans for post Assembly Complete, to facilitate improvements in ISS systems, and ISS operations, and to maintain a high degree of management visibility for this important activity. The space station envisioned in the early 1960s could have been built with technology available at that time. As the committee noted in this report, the same is true of the ISS, which relies on existing technology and well established manufacturing techniques wherever possible. Therefore, the committee believes that the fundamental improvements cited in this report are well within the state of the art of cur- rent technology and should be introduced into the ISS Pro- gram as soon as possible. In the areas of communications and robotics, in fact, they have already been developed. With farsighted management and timely increases in fund- ing, these upgrades and enhancements would ensure that the ISS remains at the leading edge of long-term space research. REFERENCES Butina, T. 1998. Logistics and Maintenance Planning. Presentation by T. Butina, manager, Logistics and Maintenance, to the Committee on the Engineering Challenges to the Long-Term Operation of the International Space Station. NASA Johnson Space Center, Houston, Texas, Decem- ber 17, 1998. CAV (Cost Assessment and Validation Task Force). 1998. Report of the Cost Assessment and Validation Task Force on the International Space Station. Washington, D.C.: National Aeronautics and Space Adminis- tration. NASA(National Aeronautics and Space Administration). 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.