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.
Highlights
The soft x-ray spectrometer (SXS)[1] is an x-ray microcalorimeter array onboard the Japanese x-ray satellite Hitomi (ASTRO-H),[2] which was successfully launched on February 17, 2016, by an H2A rocket from Tanegashima Space Center
The performance is achieved by cooling the x-ray microcalorimeter array to 50 mK with a cooling system that utilizes a dewar cooled down by several mechanical coolers, adiabatic demagnetization refrigerators (ADRs), and superfluid liquid helium (LHe)
The LHe temperature did not start decreasing immediately after the start of the Shield Coolers (SCs) 25-W operations but reached a maximum 1 to 2 days after launch. This is because only the outer vapor-cooled shield (OVCS) and inner vapor-cooled shield (IVCS) are directly cooled by the SCs, and the He tank temperature responds after the shield temperatures decrease following their time constants
Summary
The soft x-ray spectrometer (SXS)[1] is an x-ray microcalorimeter array onboard the Japanese x-ray satellite Hitomi (ASTRO-H),[2] which was successfully launched on February 17, 2016, by an H2A rocket from Tanegashima Space Center. Two ADR stages operate to stabilize the temperature of the x-ray microcalorimeter array at 50 mK, requiring periodic recycles about once per two days. The following procedures are performed: (1) operation of the SCs continues without the JT cooling and vapor cooling of the shields, (2) during rocket roll-out and before the launch, all cryocoolers are powered off. (4) after a few orbits, the cryocoolers are powered on Until this last operation, the heat load on the liquid continues to rise along with the shield temperatures, but afterward, the heat loads decrease and the LHe temperature eventually peaks and starts decreasing. We employed the thermal analysis software SINDA/FLUINT version 5.8, which solves heat conduction equations by the finite difference/ element method
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Journal of Astronomical Telescopes, Instruments, and Systems
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
