Thermal analyses for initial operations of the soft x-ray spectrometer onboard the Hitomi satellite

Abstract

Abstract. The soft x-ray spectrometer (SXS) onboard the Hitomi satellite achieved a high-energy resolution of ∼4.9 eV at 6 keV with an x-ray microcalorimeter array cooled to 50 mK. The cooling system utilizes liquid helium, confined in zero gravity by means of a porous plug (PP) phase separator. For the PP to function, the helium temperature must be kept lower than the λ point of 2.17 K in orbit. To determine the maximum allowable helium temperature at launch, taking into account the uncertainties in both the final ground operations and initial operation in orbit, we constructed a thermal mathematical model of the SXS dewar and PP vent and carried out time-series thermal simulations. Based on the results, the maximum allowable helium temperature at launch was set at 1.7 K. We also conducted a transient thermal calculation using the actual temperatures at launch as initial conditions to determine flow and cooling rates in orbit. From this, the equilibrium helium mass flow rate was estimated to be ∼34 to 42 μg∕s, and the lifetime of the helium mode was predicted to be ∼3.9 to 4.7 years. This paper describes the thermal model and presents simulation results and comparisons with temperatures measured in the orbit. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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“…On top of that, internal heat loads will also appear due to the operation of different systems onboard the satellite, such as Joule dissipation in circuits, the propulsion system, 58 the laser source, 59 or the cryocooler 60 . Optical amplifiers used onboard satellite to amplify the power of the beam coming from the source can also be an important source of heat 61 .…”

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