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Abstract
The soft x-ray spectrometer (SXS) was a cryogenic high-resolution x-ray spectrometer onboard the Hitomi (ASTRO-H) satellite that achieved energy resolution of 5 eV at 6 keV, by operating the detector array at 50 mK using an adiabatic demagnetization refrigerator (ADR). The cooling chain from room temperature to the ADR heat sink was composed of two-stage Stirling cryocoolers, a He4 Joule–Thomson cryocooler, and superfluid liquid helium and was installed in a dewar. It was designed to achieve a helium lifetime of more than 3 years with a minimum of 30 L. The satellite was launched on February 17, 2016, and the SXS worked perfectly in orbit, until March 26 when the satellite lost its function. It was demonstrated that the heat load on the helium tank was about 0.7 mW, which would have satisfied the lifetime requirement. This paper describes the design, results of ground performance tests, prelaunch operations, and initial operation and performance in orbit of the flight dewar and the cryocoolers.
Highlights
Hitomi, formerly known as ASTRO-H, was the sixth Japanese x-ray astronomy satellite and was developed under extensive international collaboration between Japan and the United States with European and Canadian participation.[1]
The cooling chain from room temperature to the adiabatic demagnetization refrigerator (ADR) heat sink consisted of two-stage Stirling-cycle (2ST) cryocoolers,[7] a 4He Joule–Thomson (JT) cryocooler,[7] and superfluid liquid helium (LHe)
We describe the design, pre- and postlaunch operations, and in-orbit performance of the cooling system from room temperature to the ADR heat sink
Summary
Formerly known as ASTRO-H, was the sixth Japanese x-ray astronomy satellite and was developed under extensive international collaboration between Japan and the United States with European and Canadian participation.[1]. The cooling chain from room temperature to the ADR heat sink consisted of two-stage Stirling-cycle (2ST) cryocoolers,[7] a 4He Joule–Thomson (JT) cryocooler,[7] and superfluid liquid helium (LHe). It became inoperative due to attitude control problems and subsequent loss of communication on March 26, the SXS cooling chain worked perfectly, the detector was cooled to 50 mK, and it achieved the energy resolution better than 5 eV at 5.9 keV (resolving power of about 1200) in orbit.[10,11] In this paper, we describe the design, pre- and postlaunch operations, and in-orbit performance of the cooling system from room temperature to the ADR heat sink. Fujimoto et al.: Performance of the helium dewar and the cryocoolers of the Hitomi soft x-ray spectrometer
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