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1 Introduction The Space Station Freedom program 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. Table 1 lists the major intended attributes of the Space Station Freedom manned base (the program also includes polar orbiting platforms and a co-orbiting man-tended free-flyer). The Phase 1 Space Station is planned to be a facility with the potential to support activities in microgravity materials research, fluid physics, crystal growth, biomedical studies, human habituation studies, and astrophysical and earth observations. The station would also support in-space technology experiments and development efforts. BACKGROUND There have been a number of external reviews of the Space Station Freedom program. The National Research Council (NRC), at the request of the President's Assistant for National Security Affairs, the Director of the Office of Management and Budget, the President's Science Advisor, and the Administrator of the National Aeronautics ant! Space Administration, undertook a study of the Space Station program in 1987. Prior to that 9

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10 Table 1 Intended Attributes of Space Station Freedom Manned Base A Permanently Occupied Spacecraft A Research Laboratonr An Observational Platform Verv High User Power (45 kW) Very Low Quasi-Stead~r Micro~ra~ritv Accelerations An Ontimized Spacecraft Attitude High Data Rate f300 MbPs) Weeklv Extravehicular Acti~ritv (6 hours/week, An Internal Environment of One Standard Atmosphere Clean External Environment (Gases. Condensibles. EMI) A Payload Pointing Svstem Large Annual Unmass Capability {50.000 k~r/`rr) Accommodations for Suace Station Evolution The spacecraft would have 8 crew of eight and a facility lifetime of 30 years; it is designed to conduct the operational and medical research required to support long-term manned space exploration objectives. More than 120 standard equipment racks would be available to hold scientific research equipment. The platfo...` could hold four ~ fi're large experiment footprints of 10 m for long (up to 30 yeare) aberration times. Such pourer levels are required to operate experiments; they are especially necessary to pourer furnaces, and so forth, for materials research. Accelerations of 1 x 10 6 g (at f < 0.1 Hs) are critical for materials research in order to force diffusion-dominated process. Designed to benefit both laboratory and observational experiments (LVLH = +/- 5~; +/- 2.5 stability; < .02 /see stabilization rate), this attitude keeps the residual microgra~rity acceleration Rector in a near-constant direction for materials rceearch. It also provides sufficient pointing orientation for many obeenring nstn~mente. It is accomplished without disturbing thruster firings, by using control moment gyros. This rate will support modern research needs for high resolution and high-speed image transfer. EVA would be available to users for external, obeer~rational experiment resupply (cryogens, film, etc.) as well as for servicing and repair. This internal environment is critical, since it allocate researchers to draw on decades of ground-based life science data. A clean environment is necessary for the conduct of optical and plasma obeer~ratione. It will handle large payloads (3 m in diameter by m long, 6,000 kg mass), providing 30 arc set of inertial pointing for precision obeenratione. A large upmass capability is needed to provide resupply and experiment change-out for research. The Station is designed to allow more power, crew, laboratory space, and attached payload space to be added.

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11 activity, the Aeronautics and Space Engineering Board of the NRC conducted examinations of various aspects of the Space Station program during 1984 and 1985, including its maintainability, program performance, onboard command and control, solar thermodynamics research and technology, and research and technology in space. In early 1987, the NASA Associate Administrator for Space Station indicated an interest in having the NRC examine the Space Station program with a view toward identifying critical engineering issues related to the stationts design and operation. This activity was preempted by the aforementioned study for the White House, et al. However, in early 1988 the NASA Office Space Station submitted a formal request for an NRC workshop to identify and prioritize Space Station engineering issues. (See Appendix A) The workshop was held on November 7-11, 198S, at the Beckman Center in Irvine, California; this report summarizes the main findings of that event, and reflects the views and opinions of the workshop committee. APPROACH Following formal acceptance of NASA's request by the NRC's Governing Board, an ad hoc committee was formed by the Aeronautics and Space Engineering Board to conduct the workshop. The members of the committee were chosen for their expertise in the areas of space systems, space structures, guidance and control, operations and management, space transportation, power, communications, space medicine and life sciences, robotics, software development and management, utilization, and space applications. Prior to the workshop, the committee was supplied with extensive background materials. The workshop itself was an intensive, four-and-a-half clay review of the engineering and operational aspects of the planned Space Station, with some sessions lasting until nearly midnight. Nonetheless, the magnitude of the program under review coupled with the limited time available to conduct the review, make several caveats necessary: The workshop was not a technical audit. Most of the committee's information was based on views of the Space Station program and design plans as of November 198S, derived primarily

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12 from briefings presented at the workshop by Level I and Level II personnel of the NASA Space Station program. Some areas of possible concern, such as materials and the effect of the space environment thereon, were not represented in the briefings or by the expertise of the committee. Some thoughts of the committee concerning these areas are included in the Supplementary Discussion section of this report. The workshop report has not attempted to identify all the good features of the Space Station program. The committee has noted some of these aspects at various points in the report, but most of its energies have been directed--in accordance with its task statement (see Appendix B)--toward the identification of issues. 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. However, the committee does believe that all of the issues identified in this report will require resolution for the Space Station program to be successful. 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 program. Furthermore, the committee was not asked to address the desirability of developing a Space Station; President Reagan's 1984 decision was taken as the committee's point of departure. In its deliberations the committee has searched for the inconsistent, the overly optimistic, and for those areas that, if they continue in the direction they are currently headed, are likely to be troublesome later. The committee used two basic principles in its evaluation: (1) early recognition and correction of potential problems is the most efficient and least costly approach, and (2) flexibility in design and Insurance provided by alternative approaches can yield major downstream dividends, especially when coping with unexpected or unanticipated events. The following sections of the report present the workshop committee's major findings and recommendations. A number of general design issues are discussed first. Next, issues related to Space Station utilization and operations requirements are identified' followed by issues concerning specific Space Station systems and subsystems. Finally, a

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13 number of management issues that the committee believes could have an important impact on Space Station design and operation are discussed.

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