Short presentations on calibration were given by M. Weisskopf and H. Marshall. The committee was told that the calibration was driven by spectroscopy and was more sophisticated than anything yet attempted in X-ray astronomy. There was a brief overview of plans for sub-assembly (individual instruments) calibration, of plans for work at the X-ray Calibration Facility (XRCF) at MSFC, and of on-orbit calibrations.
The Users' Committee raised the concern that there might be areas-of-uncertainty that were not being covered. They would like to understand how the calibration will help an observer who has something in an observation which is not understood. Although there are documents which cover ground calibration plans in great detail, the Users' Committee requested that the on-orbit calibration plan be presented at the next meeting. This should monitor loss of effective area, and contamination. On-orbit calibration data should be analyzed right away and tracked so that total calibration time will be kept to a minimum.
In view of complexities with Einstein, EXOSAT, and EUVE transmission-grating calibration, the Users' Committee would like to be assured that they and the community understand uncertainties and limitations in the AXAF calibration. The Users' Committee recommends having a `user'-level review where technical issues are presented and the connections between science objectives and the actual calibrations are spelled out. This should include how calibration results are going to be made available to the users.