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Executive Summary The Space Station Freedom program is the next major U.S. manned space initiative. It has as its objective the establishment of a permanently manned facility in low earth orbit. The facility is intended to be used for a range of activities and to accommodate a number of alternative evolutionary growth paths. The Space Station also is envisioned, by the National Aeronautics and Space Administration (NASA) and others, as an essential element in the recovery and maintenance of U.S. leadership in civil space activities and as an opportunity for increased international cooperation. In early 1987, the NASA Associate Administrator for Space Station indicated an interest in having the National Research Council (NRC) examine the Space Station program with a view toward identifying critical engineering issues related to the design and operation of the station. This activity was preempted by a 1987 NRC study of the Space Station program undertaken at the request of the Presidents Assistant for National Security Affairs, the Director of the Office of Management and Budget, the Presidents Science Advisor, and the Administrator of NASA. However, in early 1 98S, the Associate Administrator for Space Station submitted a formal request for an NRC workshop to identify and prioritize Space Station engineering issues. A week-long, intensive workshop was held on November 7-11, 198S, at the Arnold and Mabel Beckman Center of the National Academy of Sciences and the National Academy of Engineering in Irvine, California; this report summarizes the main findings and recommendations of that workshop, and reflects the vieurs and opinions of the workshop committee. The workshop was not a technical audit of the program. The report thus does not focus on identifying all the good features 1

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2 of the Space Station program, although the committee has noted some of these aspects at various points in the report. In addition, a number of areas of possible concern, such as the effect of the space environment on Space Station materials and structures, were not represented in the briefings to the committee or by its expertise. Consequently, the issues identified in this report should not be construed as an exhaustive set of concerns, but rather those that appeared most important to the committee based on its necessarily limited review of the Space Station in November 1988. Finally, the limited time available to the committee made it impossible to do a more detailed prioritization of the issues identified in this report, especially across subsystems. Major issues identified by the workshop committee were those related to general design, utilization and operations requirements, and specific Space Station systems and subsystems. The committee also raised a number of management issues that it believes could have an important impact on Space Station design and operation. GENERAL DESIGN ISSUES 1. The major issue of assuring the safe return of the Space Stations crew under emergency conditions has not been addressed in the Space Station concept presented to the committee; the committee believes a crew emergency rescue vehicle is required. 2. The allocation of verification activities and/or checkout of subsystems and assemblies (including software) between those activities that are ground-based and those that will be done on orbit is an important unresolved issue. 3. There is an extensive and perhaps excessive reliance on modeling of systems and software for verification in lieu of ground or flight testing. 4. The current schedule for the assembly of the Space Station on orbit appears incompatible with integration and verification requirements. 5. The committee believes NASA is to be commended for recognizing the criticality of software and data management to the Space Station program and for taking a proactive approach to addressing software issues through investments in a program-wide Software Support Environment (SSE) and Technical and Management Information System (TMIS). However, it is

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3 concerned that the SSE as mandated may be relatively inflexible and restrictive for some program purposes, such as real-time dynamic systems modeling. 6. The committee is concerned that there are inadequate margins and in some cases actual resource shortfalls (e.g., power, existing post-Challenger Shuttle payload weight margins for assembly flights) at this early stage of the Space Station program. 7. Preliminary design considerations for system alternatives to serve as ~insurance" for flight-critical systems (e.g., electrical power, thermal control, life support) are not yet being developed. 8. Questions of common measurement standards, commonality of tools and equipment, and so forth do not appear to have been resolved in a concrete fashion that is consistent with the planned long life of the Station. 9. Hardware and software provisions for future expansion or evolution of the Space Station are under study by the Space Station program. However, provisions for refurbishment, repair, and rebuilding over a multiyear time span do not appear to have received the same attention. ISSUES RELATED TO UTILIZATION AND OPERATIONS REQUIREMENTS 1. The committee believes that the general issue of the compatibility of all the planned/potential users of the Space Station is very important and needs to receive more attention. 2. The current Design Reference Missions, which show the Station resources to be more or less in balance, may not allow an accurate assessment of user and operator needs. Development of Design Reference Missions should be carried out with the intention of probing the design's weaknesses rather than demonstrating its strengths. 3. Further, it was evident to the committee that Shuttle airs Spacelab precedents were used in developing procedures for user experimentation on the Space Station. More innovative processes are needed to improve responsiveness to user needs consistent with safe and effective Station operations. 4. The committee is concerned that the Space Station's design, assembly, and operation may have become unduly constrained by such things as existing post-Challenger Shuttle

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4 performance limitations, certain congressional directives, and some user requirements. It is important that the justification for each constraint be firmly established and its impact on the program clearly understood. 5. A premature demonstration flight of the Flight Telerobotic Servicer (FTS) concept and early manifesting of the FTS in the Space Station assembly sequence is likely to have a contrary effect to the intended objective of advancing automation and robotics. 6. The current program plan, which does not accommodate the animal/plant centrifuge in the U.S. laboratory module, and which proposes to assemble and check out the life sciences facilities on orbit, does not appear to meet the requirements established by NASA and NRC advisory committees. 7. A particularly sensitive issue to the Space Station life science and materials science users is the production, transmission, and absorption of vibrations at frequencies that could damage the microgravity processes under study. Until the Space Station program tackles the vibration transmission issue squarely, such disturbances will have to be treated empirically, with a resulting awkwardness in layout and operations. S. The protection of the amount of crew time available for user activities is vulnerable to erosion as maintenance and operations requirements are better defined. 9. The committee is concerned that the Space Station program has no provision for unmanned resupply of the U.S. modules (e.g., facilities for unmanned rendezvous and docking). SELECTED ISSUES RELATED TO SYSTEM REQUIREMENTS AND DESIGN 1. The committee die! not find as ready an awareness of the impact of system interactions as it believes is desirable at this stage in the Space Station development program. Software and Data Management 2. No software risk management plan exists, although major software risk factors exist. 3. The current software schedule emphasizes early completion of software requirements documents, which then become baselined and more difficult to modify. The early

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s schedule should preferably emphasize execution of risk management plans and resolution of risk items before software requirements are "cast in concrete. 4. The coordination of the Space Station Information System (SSIS) with the other data distribution systems proposed by NASA user organizations does not appear to be well defined. Communications and Tracking 5. No end-to-end perspective in communications and tracking was evident or presented to the committee. 6. The committee is concerned that all communications to and from the Space Station will flow via the Tracking and Data Relay Satellite System. 7. The Space Station is dependent on many communication links for its successful operation; the vulnerability of these links to deliberate or inadvertent interference or access is a continuing concern. S. The relative inaccessibility of the Space Station and the relatively meager resources that will be available to the crew heighten the need for special attention to the potential problem of electromagnetic interference at the Station. Automation and Robotics 9. More emphasis is needed on advanced automation tools and capabilities to improve the efficiency of Space Station user operations. 10. There is no clear vision of the spectrum of applications to be supported by the FTS, particularly given the existence of the Canadian Mobile Servicing System. Electrical Power System 11. Power adequacy for the Phase 1 Space Station is of concern to the committee. 12. There is need for a management review of all utilities: electricity, heat, water, and so forth. Thermal Control System 13. More attention should be given to the analysis of thermal control system trade-offs.

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6 Environmental Control and Life SUDDOrt Svstem. Man Systems. Extravehicular Activity Svstem 14. Microbial and toxin control in the Space Station is a continuing area of concern. 15. The committee is concerned that sufficient in-space testing be done on the planned Space Station life support system. 16. The requirements for medical evacuation and its associated problems need to be addressed. 17. The committee believes that the issue of Space Station crew efficiency over time is an important one, with implications for operational timelines and crew schedules. Fluid Management Svstem 18. The control and handling of waste liquids and gases, as well as hazardous materials used in the laboratories, need to be addressed vigorously. MANAGEMENT ISSUES RELEVANT TO DESIGN 1. The committee believes that the Space Station management structure has complicated the Space Station development task. 2. Budgetary uncertainties, certain congressional directives, and operational limitations of the existing post-Challenger Shuttle have produced program instabilities that may have increased design complexity and reduced design conservatism. 3. The retention of the polar platform within the Space Station program has further complicated the programs management task. 4. The committee is concerned that a disciplined and contractually binding process for integration is not evident; one needs to be established early in the program. 5. A Space Station System Specification is needed to contractually define the system and provide a basis to effect change discipline and change control. 6. While there is considerable work under way, there does not appear to be a strong and crisp integration and verification management plan and architecture in place.

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7 7. The communications and data systems for the Space Station pass through elements that are developed by up to four separate NASA offices, with little evidence that adequate oversight is being provided by NASA. Thus, the potential exists for errors to be made (notably those of omission) even among well-intentioned, skilled organizations.

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