The Advanced X-ray Astrophysics Facility (AXAF), for which NASA and industry are currently conducting Definition and Preliminary Design studies, will provide a major advance in performance and observing opportunities beyond its predecessor space missions in X-ray astronomy, including Uhuru, Einstein and Rosat. The performance advances come from larger, higher quality mirrors with longer focal length that will extend the useful energy range and provide improved image resolution. Corresponding improvements will be made in observatory aspect determination and pointing stability. Increased observing opportunities come from facility-class operation of the observatory, including on-orbit maintenance and repair to provide potentially unlimited mission lifetime and on-orbit installation of new scientific instruments to take advantage of future advances in sensor technology. A summary of characteristics contrasting AXAF with the Einstein mission will be presented. Developing a design concept for AXAF that takes advantage of recent advances in technology and Shuttle-era capability for operations and servicing in space is a challenging process, requiring evaluation of a number of interesting, diverse design options for the X-ray telescope, science instrument accommodation and the host spacecraft. Major options for each of the areas will be identified and key considerations in selecting among them will be discussed. Specific elements addressed will include "beam switching" among the focal plane instruments, on-orbit access to the science instruments and components, major system interfaces, and observatory servicing.