Update on the design and performance of the cryogenic subsystem for the AXAF X-ray spectrometer

Abstract

The cryogenic subsystem (CSS) for the AXAF X-ray spectrometer (XRS) uses state-of-the-art superfluid helium Dewar technology along with Stirling cycle coolers to achieve a five year orbital lifetime with minimum system mass and size. The Dewar provides a 1.5 K temperature environment for operation of the cryogenic instrument assembly, which includes an adiabatic demagnetization refrigerator for cooling the detectors to 0.1 K. As a result of the AXAF programme being split into two separate missions, the XRS is the sole instrument comprising the AXAF spectrometer (AXAF-S). Launch is planned in December 1999. Substantial configuration changes have been made to the CSS to meet the new AXAF-S requirements. Changes are primarily the result of the new spacecraft configuration, increased instrument duty cycle and increased mission lifetime requirement. The programme status, the newly baselined CSS design and its predicted performance are discussed.