The New X-Ray Spectrometer (XRS)- a Revamped Cryogenic Instrument for the Restructured AXAF-S Mission

Abstract

The Advanced X-Ray Astrophysics Facility (AXAF) program was restructured in 1992. The most significant change was placing the instruments on two separate spacecraft: AXAF-S devoted to high resolution spectroscopy and AXAF-I devoted primarily to x-ray imaging. The sole instrument on the AXAF-S spacecraft is the XRS, which achieves a resolution of ∼12 eV over the energy range of 0.3 to 10 ke V by using calorimeters cooled to less than 0.1 Kelvin. These low temperatures are produced by an adiabatic demagnetization refrigerator, which in turn is cooled by superfluid helium. Stirling-cycle mechanical refrigerators are used to cool the outermost vapor-cooled shield of the helium dewar, thus reducing the parasitic heat load on the cryogen. Work on this complex cryogenic system has been ongoing for over 6 years. As a result of the AXAF restructuring, interfaces are being redefined, new requirements have been levied, and an entirely new AXAF-S Project management structure has been created. This has produced an unusually dynamic environment for revising the design of the XRS instrument for flight on the new AXAF-S mission.