Development status of the mechanical cryocoolers for the Soft X-ray Spectrometer on board Astro-H

The soft x-ray spectrometer (SXS) instrument that flew on the Astro-H observatory was designed to perform imaging and spectroscopy of x-rays in the energy range of 0.2 to 13 keV with a resolution requirement of 7 eV or better. This was accomplished using a 6 × 6 array of x-ray microcalorimeters cooled to an operating temperature of 50 mK by an adiabatic demagnetization refrigerator (ADR). The ADR consisted of three stages to operate using either a 1.2 K superfluid helium bath or a 4.5 K Joule-Thomson (JT) cryocooler as its heat sink. The design was based on the following operating strategy. After launch, while liquid helium was present (cryogen mode), two of the ADR's stages would be used to single-shot cool the detectors, using the helium as a heat sink. When the helium was eventually depleted (cryogen-free mode), all three ADR stages would be used to continuously cool the helium tank to about 1.5 K and to single-shot cool the detectors (to 50 mK), using the JT cryocooler as a heat sink. The Astro-H observatory, renamed Hitomi after its successful launch in February 2016, carried ∼36 L of helium into orbit. Based on measurements during ground testing, the average heat load on the helium was projected to be 0.66 mW, giving a lifetime of more than 4 years. On day 5, the helium had cooled to <1.4 K and ADR operation began, successfully cooling the detector array to 50 mK. The ADR's hold time steadily increased to 48 h as the helium cooled to a temperature of 1.12 K. As the commissioning phase progressed, the ADR was recycled (requiring ∼45 min) periodically, either in preparation for science observations or whenever the 50 mK stage approached the end of its hold time. In total, 18 cycles were completed by the time an attitude control anomaly led to an unrecoverable failure of the satellite on day 38. This paper presents the design, operation, and on-orbit performance of the ADR in cryogen mode as the foreshortened mission did not provide an opportunity to test cryogen-free mode.

Section: Introductionmentioning

confidence: 99%

Design and on-orbit operation of the soft x-ray spectrometer adiabatic demagnetization refrigerator on the Hitomi observatory

Shirron

Kimball

James

et al. 2018

“…Figure 2 shows this cooling system and its complex arrangement of both active and passive cooling elements, including four 20-K 2-stage Stirling cryocoolers (2ST), 19 a 4.5-K Joule-Thomson (JT) cryocooler, 19 a 40-L superfluid helium tank, and 3-stage adiabatic demagnetization refrigerator (ADR). 9 When integrated, these elements are nested within a multistage dewar featuring four helium vapor cooled shields: outer, middle, and inner (OVCS, MVCS, and IVCS), and the innermost JT shield surrounding the helium tank.…”

Section: Cooling System Overviewmentioning

confidence: 99%

Cryogen-free operation of the Soft X-ray Spectrometer instrument

Sneiderman

Shirron

Fujimoto

et al. 2018

Abstract. The Soft X-ray Spectrometer (SXS) is the first space-based instrument to implement operational redundancy of a sub-Kelvin cooling system. Its cooling system includes a superfluid helium cryostat and five cryocoolers, provided by Japan Aerospace Exploration Agency, and three adiabatic demagnetization refrigerators (ADRs) with four active heat switches, provided by NASA. These elements are configured in one of two ways to control the heat sink of the x-ray microcalorimeter detectors at 50 mK. The "helium mode," the simpler of the two modes, is used while liquid helium is present and uses all five cryocoolers and two ADRs. The first two ADR stages operate together and reject their heat directly to the liquid at ∼1.1 K. In the "cryogen-free mode," for operation after the helium is depleted, the first stage ADR operation is unchanged, the second stage is repurposed to control the empty helium tank at ∼1.5 K, and the third stage transfers heat from the 1.5-K stage to the 4.5-K interface of the Joule-Thomson cooler. The development and verification details of this capability are presented within this paper and offer valuable insights into the challenges, successes, and lessons that can benefit other missions, particularly those employing cryogen-free or hybrid cooling systems. © 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.

“…In addition, the spectrum of the 2ST compressor contains a continuum feature above ∼200 Hz, caused by frictional motion, of the level of ∼2 N rms integrated in 0 to 500 Hz for each axis. 11 The vibrational heating occurs because of the coincidence of vibration spectrum and the sensitive frequency.…”

Section: Mechanism Of How Energy Resolution Was Degradedmentioning

confidence: 99%

“…Both the 2STs and the JT are mounted on the outer surface of DMS. 7,11 When the cryocoolers are in operation, the compressors and cold heads warm up because of the electrical power applied. The dissipated heat is transported to either the dewar surface or radiator panels and radiated to deep space.…”

Section: Overview Of the Sxs Cooling Systemmentioning

confidence: 99%

Vibration isolation system for cryocoolers of soft x-ray spectrometer on-board ASTRO-H (Hitomi)

Takei

Yasuda

Ishimura

et al. 2018

Self Cite

Abstract. The soft x-ray spectrometer (SXS) onboard ASTRO-H (named Hitomi after launch) is a microcalorimeter-type spectrometer, installed in a dewar to be cooled at 50 mK. The energy resolution of the SXS engineering model suffered from microvibration from cryocoolers mounted on the dewar. This is mitigated for the flight model (FM) by introducing vibration isolation systems between the cryocoolers and the dewar. The detector performance of the FM was verified before launch of the spacecraft in both ambient condition and thermal-vacuum condition, showing no detectable degradation in energy resolution. The in-orbit detector spectral performance and cryocooler cooling performance were also consistent with that on ground, indicating that the cryocoolers were not damaged by launch environment. The design and performance of the vibration isolation system along with the mechanism of how the microvibration could degrade the cryogenic detector is shown. Lessons learned from the development to mitigate unexpected issues are also described.