permitting daily manned access from earth. However duty periods of several weeks would normally be planned, limited by crew well-being limits without artificial gravity. Considerable knowledge & technology is known for such activities. However, the approaches for the specific functions are not known, therefore the appropriate risk rating is 4-. It would continue to be 4 in some respects on into the late 70's to early 80's, but it would be highly desirable if not mandatory to have the development proceed so that it is in use, risk rating l^in the mid 80's. Detail orbital assembly operations definition will proceed in parallel, but somewhat lag, operational system design and technology development. It will precede maintenance operations definition, however, in that maintenance operations will be in large part disassembly and assembly activities as discussed under "Support Modules". The definition and technology developments of both assembly and maintenance operations will be highly interactive. Development risk rating should be 4-. Standard considerations for reliability having to do with functional performance, safety and fail-safe operation apply to each of the equipments. The technologies for reliable operation for 30 years or more of the millions of DC to RF generators on orbit and the billions of diodes on the ground, as examples, are not known even though design approaches may be put forth which appear to have no known failure mechanisms and the guideline for design would be to have no known life limit. The effects associated with the coupling of Reliability and Maintainability requirements for such large numbers of components in the operational environment and location to achieve required safety and good economy are not known. The impact of reliability to the concept as well as detail for Operations & Maintenance is not known and should become known early in the program to guide development of technology as well as design and development of functional equipment, manufacturing modules, remote manipulators and support modules. A risk rating of 4 should apply at this time. ___
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