John A. Spina

Design, Fabrication & Assembly Of The High Resolution Mirror Assembly For Nasa's Advanced X-Ray Astrophysics Facility

The new and powerful NASA Advanced X-ray Astrophysics Facility (AXAF) has entered the design and development stage and is currently scheduled for launch in the mid-1990s. AXAF will be 100 times more powerful in detecting x-rays, will double the spectral wavelength coverage, and provide ten times the resolution over its highly successful predecessor, the Einstein Observatory. To achieve these goals, AXAF will be equipped with a high resolution mirror assembly (HRMA) consisting of a nested set of six Wolter Type I, x-ray telescopes with outer diameters varying from 0.68m to 1.2m, and parfocalized at a common 10.0m focal length. The mirror mounting, assembly alignment, and orbital thermal stability requirements are nearly an order of magnitude more stringent than those of the HRMA developed for the Einstein Observatory. This paper summarizes the key design features and assembly alignment approach planned to meet these very stringent requirements.

Modeling the astrometric performance of the Space Interferometry Mission

The Space Interferometer Mission (SIM) will achieve important science objectives of NASAs Origins program by performing astrometric measurements of targets within and beyond our galaxy with a precision of the order of a few microarcseconds. This accuracy can only be attained by carefully balancing sources of astrometric error arising from the systematic accuracy of the interferometer, thermal distortions, vibration caused by spacecraft systems, and errors in knowledge of the spacecrafts altitude and velocity. A rigorous systems engineering approach must be applied to the conduct of trades between these different sources of error and the TRW SIM Study Team has developed a mathematical model of the performance of SIM to support these trades. This paper shows how the model is constructed using simple analytical relationships and then employed to determine the dependence of system performance on a wide range of configuration parameters, such as baseline length, aperture size, and attitude knowledge. These studies indicate where subsystem performance requirements are critical and where requirements may be relaxed with little degradation of overall astrometric accuracy.