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

Hirofumi Noda, Kazuhisa Mitsuda, Atsushi Okamoto, Yuichiro Ezoe, Kumi Ishikawa, Ryuichi Fujimoto, Noriko Yamasaki, Yoh Takei, Takaya Ohashi, Yoshitaka Ishisaki, Ikuyuki Mitsuishi, Seiji Yoshida, Michel Dipirro, Peter Shirron

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


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.

Original languageEnglish
Article number011202
JournalJournal of Astronomical Telescopes, Instruments, and Systems
Issue number1
Publication statusPublished - 2018 Jan 1


  • Hitomi (ASTRO-H)
  • cryogenics
  • soft x-ray spectrometer
  • thermal mathematical model
  • thermal simulation
  • x-ray microcalorimeter

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Control and Systems Engineering
  • Instrumentation
  • Astronomy and Astrophysics
  • Mechanical Engineering
  • Space and Planetary Science


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