The first major ASC project milestone was passed in December 1993 with the completion of the System Requirements Review. Three documents formed the core of the review: the Data System Requirements defining the requirements for the software and hardware that will support all ASC activities including ground and on-orbit calibration, proposal submission, long-range target scheduling, telemetry processing, data products, archive access, etc; the Science Mission Operations Plan describing step by step the processes that will be used to operate the ASC; and the Science Plan defining the areas to be covered by ASC science policies.
Prior to the formal review the ASC hosted a team of external experts in science operations and data system development to review the documents and provide advice based on their experience with other missions. In addition to providing valuable feedback on the review material, the team noted the importance of extending the science mission operations plan to include detailed science observation scenarios (e.g., a week of typical observations) in order to influence the design and check compatibility with elements of the AXAF ground system and spacecraft. The ASC has now developed scenarios of this kind, and we are using them as input to such decisions as the size of the on-board computer memory.
The next major ASC milestone is the Preliminary Design Review scheduled for September 1994. The focus of this review is the hardware and software design of the Data System, and a review by external experts is also planned. A final review (Critical Design Review) is scheduled for July 1995, and is followed by the first release of the ASC Data System in April 1996 to support the ground calibration of the flight mirrors and science instruments. Subsequent releases will support the interface test with the Operations Control Center (OCC) at Marshall Space Flight Center, the first NASA Research Announcement a year before launch, and AXAF operations beginning in September 1998.
While a great deal of effort has been devoted to the development of review documentation, many other activities are ongoing and should be of interest to the science community.
Software prototypes are being used to test requirements, refine our understanding of operations and explore software technologies. Scientific and programming staff have worked to develop `forward data flow' and `backward data flow' prototypes. The forward flow follows the path of an observation from the submission of a proposal by an observer, through the peer review process, through creation of a list of targets at the ASC, and onto their submission to the OCC. The OCC develops detailed schedules, generates the on-board commands, and performs the up-link to the spacecraft, thereby completing the forward flow. The backward flow refers to the receipt of telemetry from the spacecraft by the OCC, standard processing (e.g., aspect solution, source detection), archiving, and distribution of data products to the observer. The goal of the prototyping is to flow a set of realistic proposals from submission all the way to the receipt of data products. This effort is well underway and is providing excellent `bottom up' input to the design work.
In parallel with the data-flow work, certain critical design areas have also been targeted for prototyping. These include data structure access and definition; development of an `open' architecture allowing access to ASC algorithms from external software systems and use of external software as part of the ASC Data System; image display; and archive design. The use of prototyping is proving most effective and will continue through the critical design phase.
Excellent relations have been developed with the Science Instrument (SI) teams, spacecraft contractor and AXAF Mission Support Team. ASC staff are working with these teams to define the laboratory and ground calibrations, arrange for transfer of appropriate data to the ASC, perform joint studies and trades, and develop necessary models. The calibration reference database has been established and data have started to flow, including mirror metrology, ACIS and HRC laboratory test data, and model outputs. The database will ultimately contain all AXAF-I calibration data.
Other ASC highlights include the completion of the preliminary version of the AXAF-I Guide/Aspect Star catalog, the creation of the ASC WWW home page (see The ASC on the World Wide Web) and the hosting of a meeting with the Goddard Space Flight Center HEASARC to discuss approaches to analysis systems, data representation, calibration, mission planning and scheduling.
As momentum builds throughout the AXAF Project during the next year, the ASC will complete the preliminary and final design of the Data System and continue supporting all areas of the Project by working with the SI, spacecraft, and Mission Support teams, performing studies, developing models, planning calibration, and developing observation scenarios.