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Supplementary Discussion The bulk of the issues and concerns discussed in this report resulted from the November 1988 Workshop at the Academies' Beckman Center. As already mentioned, the issues identified are not intended to be an exhaustive list. Neither has the report attempted to highlight all of the good features of the Space Station program--the committee's energies have been directed, at the request of the Office of Space Station, toward issue identification. The following paragraphs outline several additional potential issues identified or further elaborated since the workshop. As the committee has not had the benefit of detailed briefings on the topics, the committee's conclusions should be considered tentative. MATERIALS Time limitations did not allow the committee to address the area of Space Station materials in any depth. However, the committee has some concerns that it feels deserve additional consideration. One of the most important concerns is the planned use of aluminum-clad graphite-epoxy structural elements in at least three areas: (1) for truss segments, (2) for pressure vessels at 3000 psi, and (3) for structural walls of the Logistics Module. As is already understood by NASA designers, the use of this composite material has many benefits, but it also has the serious drawback of rapidly degrading in the presence of atomic oxygen after the aluminum cladding has been pinholed. Members of the committee have heard estimates from outside sources of as low as 3 years 61

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62 exposure to the space environment before truss elements might have to be replaced (for a facility with an intended life of 30 years). NASA is planning to shield critical areas to reduce the probability of pinholing, but the committee believes that the potential seriousness of the problem requires further analysis, especially in assessing its impact on the need for additional spare parts, maintenance time, and extravehicular activity. The potential impacts of outgassing from the materials also needs to be assessed. HEALTH MAINTENANCE As was noted earlier, the Space Station's health maintenance facility is in an early stage of development. The facility's mission and timing, as well as its relationship to facilities for health research and extended duration crew operations activities, still need to be clarified. Moreover, the committee is concerned that all of the precursor activities required to allow design of a viable health maintenance capability may not be being adequately pursued. For example, it is highly likely that some medical emergencies on board the Space Station would require the use of invasive techniques on humans (e.g., minor surgery, stabilization with IVs). However, U.S. experience to date in such techniques has largely been limited to drawing blood samples. One of the Spacelab flights in the early 1990s is planned to include some experimentation, mainly on animal subjects, but the committee is concerned that there will not be a sufficient data base of experience available prior to the design of the health maintenance facility and its associated operational concept. TOXIC MATERIALS HANDLING An issue that was touched on by the workshop committee during the NASA presentations on the Fluid Management System and the life support systems was the handling of toxic materials. The materials science research activities on board the Space Station will utilize very toxic substances. Hazardous materials handling, storage, and emergency isolation procedures developed for terrestrial laboratories are likely to

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. 63 be of limited applicability in the Space Station environment. This issue could be very significant, as its resolution is likely to have an impact on several Station system designs. The committee is aware that NASA is devoting some attention to the issue, but the committee did not have time during the workshop to assess NASA's activities in this area. POTENTIAL INCOMPATIBILITY OF USER REQUIREMENTS The committee is concerned about the potential incompatibilities of the requirements of different groups of users, notably between those in the materials sciences and life sciences disciplines. While NASA clearly is devoting attention to this area, the committee believes this will remain a ~ - slgal~lcant Issue. CREW SAFETY Various aspects of crew safety were discussed during the workshop and have been noted in this report. However, time limitations precluded a systematic examination of safety-related issues. Several matters of potential concern, e.g., toxic materials handling, have been identified in this Supplementary Discussions section. Other possible concerns include orbital debris, joint Shuttle-Space Station activities, and the overall state of emergency planning and its impact on the design process. While the committee has no reason to believe that NASA is not attaching a high degree of importance to the resolution of crew safety issues, it believes that crew safety is an area that will require continued diligence throughout the design, development, and operational phases of the Space Station program.

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