S.R. Breon, J.A. Gibbon, R.F. Boyle, M.M. DiPirro, B.A. Warner
NASA/Goddard Space Flight Center, Greenbelt MD 20771
J.G. Tuttle
Hughes STX, Lanham MD 20706
The required lifetime fo the Astro-E X-Ray Spectrometer (XRS) is 2 years, with a goal of 2.5 years. To meet this requirement, significant advances in state-of-the-art long-life cryogenic systems are required. The XRS system is a hybrid neon/helium system with a final stage of cooling provided by an adiabatic demagnetization refrigerator. The thermal design of the helium cryostat is described in this paper. To achieve a lifetime of 2.5 years with a helium volume of approximately 20 liters, the heat load on the helium must be of the order of 800 microwatts or less. The expected lifetime and sensitivity of the lifetime to changes in the design or in the external heat loads is modelled. Results of preliminary thermal conductivity measurements are presented and future tests are identified. A study of heat loads that were small enough to be neglected in previous designs of long-life cryogenic systems was undertaken. A summary of the findings is presented.
Cryogenics 36 #10, 773 (1996).