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The advanced X-ray Astrophysics Facility (AXAF) is planned as a major space-born stellar x-ray observatory. It will be in the Space Telescope class, i.e., fifteen year lifetime maintainable in orbit, with orbitally replaceable instruments, all sky viewing capability, and with state-of-the-art high resolution x-ray imaging optics. The AXAF, along with the Hubble Space Telescope and the Very Large Array comprise the corner stone of U . S . astronomy capabilities through the end of this century . AXAF will weigh on the order of 20,000 to 25,000 pounds, will be launched by Space Shuttle on a dedicated mission, and will be serviced and reboosted on subsequent Shuttle missions. AXAF has undergone a Phase A conceptual definition at the Marshall Space Flight Center with assistance by the Smithsonian Astrophysical Observatory. It is now undergoing a two year long competitive Phase B effort by industry to provide a preliminary design and an overall project definition. TRW and Lockheed are conducting the definition activities. A parallel instrument definition activity will take place by the x-ray astronomy community as a result of an Announcement of Opportunity released in August of 1983. The observatory will accommodate several focal plane instruments and a smaller number of supporting non-focal plane instruments. This paper will describe the general configuration of the observatory based on the Phase A study results, and will describe the conceptual approach to instrument accommodation by means of a focal plane assembly. The instruments are viewed conceptually as being modular in design so that they may be orbitally replaceable with standard interfaces. Many issues need to be resolved with respect to standard instrument interfaces and modularity. As such, this area will constitute a major challenge during the Phase B definition, and will require significant and iterative information exchange and design activities among the industrial, government and astronomy community participants.
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