Flight Dewar Research Articles

Performance of the helium dewar and the cryocoolers of the Hitomi soft x-ray spectrometer

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.

Operating modes and cooling capabilities of the 3-stage ADR developed for the Soft-X-ray Spectrometer instrument on Astro-H

A 3-stage adiabatic demagnetization refrigerator (ADR) (Shirron et al., 2012) is used on the Soft X-ray Spectrometer instrument (Mitsuda et al., 2010) on Astro-H (Takahashi et al., 2010) [3] to cool a 6×6 array of X-ray microcalorimeters to 50mK. The ADR is supported by a cryogenic system (Fujimoto et al., 2010) consisting of a superfluid helium tank, a 4.5K Joule–Thomson (JT) cryocooler, and additional 2-stage Stirling cryocoolers that pre-cool the JT cooler and cool radiation shields within the cryostat. The ADR is configured so that it can use either the liquid helium or the JT cryocooler as its heat sink, giving the instrument an unusual degree of tolerance for component failures or degradation in the cryogenic system. The flight detector assembly, ADR and dewar were integrated into the flight dewar in early 2014, and have since been extensively characterized and calibrated. This paper summarizes the operation and performance of the ADR in all of its operating modes.

Performance Testing of the Astro-H Flight Model 3-stage ADR

The Soft X-ray Spectrometer (SXS) is one of four instruments that will be flown on the Japanese Astro-H satellite, planned for launch in late 2015/early 2016. The SXS will perform imaging spectroscopy in the soft x-ray band using a 6x6 array of silicon microcalorimeters operated at 50 mK, cooled by an adiabatic demagnetization refrigerator (ADR). NASA/GSFC is providing the detector array and ADR, and Sumitomo Heavy Industries, Inc. is providing the remainder of the cryogenic system (superfluid helium dewar (<1.3 K), Stirling cryocoolers and a 4.5 K Joule-Thomson (JT) cryocooler). The ADR is unique in that it is designed to use both the liquid helium and the JT cryocooler as it heat sink. The flight detector and ADR assembly have successfully undergone vibration and performance testing at GSFC, and have now undergone initial performance testing with the flight dewar at Sumitomo Heavy Industries, Inc. in Japan. This paper summaries the performance of the flight ADR in both cryogen-based and cryogen-free operating modes.

Performance of the relativity mission superfluid helium flight dewar

The world's largest capacity helium flight dewar has been assembled for use on the Relativity Mission, also known as Gravity Probe-B (GP-B). Acceptance tests performed include (1) weight, (2) proof pressure and leak checks, (3) vacuum bakeout, (4) main tank fill with He I, (5) parasitic heat rate tests, (6) well fill with He I from both the main tank and an external supply dewar, (7) well depletion, (8) conditioning the main tank to He II, (9) porous plug tests, (10) heat pulse meter tests, (11) transferring He II from the main tank to the well with a fountain-effect pump, (12) guard tank fill with He I with a nonvented He II main tank simulating launch pad hold, and (13) guard tank emptying. The measured performance is compared to the previously launched IRAS, COBE, and ISO cryostats. The Relativity Mission spacecraft will be launched in the time span 1999 to 2000.

Ultralow magnetic fields and Gravity Probe B gyroscope readout

We describe the generation of an ultralow magnetic field of < 10 −11 Tesla in the flight dewar of the Gravity Probe B Relativity Mission. The field was achieved using expanded-superconducting-shield techniques and is maintained with the aid of a magnetic materials control program. A high performance magnetic shield system is required for the proper function of gyroscope readout. The readout system employs a dc SQUID to measure the London moment generated by the superconducting gyro rotor in order to resolve sub-milliarcsecond changes in the gyro spin direction. In addition to a low residual dc magnetic field, attenuation of external field variation is required to be 10 12 at the gyro positions. We discuss the measurement of the dc magnetic field and ac attenuation factor and the performance of the readout system.

Status of the relativity mission superfluid helium flight dewar

The world's largest capacity helium flight dewar has been assembled for use on the Relativity Mission, also known as Gravity Probe-B (GP-B). Acceptance tests have been successfully performed and the dewar has been delivered to Stanford University. The science mission dewar (SMD) is the first piece of flight hardware delivered for GP-B. It will be used in testing to demonstrate payload functionality with a prototypical Science Instrument Assembly, the flight spare probe (Probe-B), and prototypical electronics. Since delivery to Stanford, the flight dewar has undergone preparations for integration of Probe-B with the dewar. This involved filling both the main tank and the well with liquid helium and installing a superconducting ultralow magnetic field shield. This shield consists of 63-μm-thick lead foil which lines the inside of the dewar well and provides an ambient magnetic field environment of <10 pT (0.1 μG) in the region of the science instrument assembly. The installation of the shield is an iterative process which will be described briefly. Once the shield is installed, the dewar and the shield must be kept cold through to the end of the science mission. The ambient field inside the shield that has just been installed has been measured to be 5 pT or less in the gyro region. After completion of testing with Probe-B, the flight probe (Probe-C) will be integrated in early 1998 in preparation for testing the flight payload. This paper reviews the key design features of the dewar, especially those driven by the ultralow magnetic field requirements. The measured mass, helium boil-off, and ground hold performance are compared to those of the previously launched superfluid helium cryostats (IRAS, COBE, and ISO).

Progress report on the Relativity Mission superfluid helium flight dewar

The world's largest-capacity helium flight dewar is being assembled for use on the Relativity Mission. The 2441-litre main tank and 99-litre guard tank have been fabricated, tested and installed. The main tank is supported off the vacuum shell with 12 PODS supports. The guard tank is mounted off a γ-alumina composite neck tube. Cold plumbing is mounted on the forward end of the main tank. The main tank has already been insulated and honeycomb vapour-cooled shields plus MLI are currently being installed. The status of the dewar assembly and the performance of selected components are discussed.

GP-B SFHe flight dewar concept : R.T. Parmley, E. Cavey and J. Goodman Lockheed Research Laboratories, Palo Alto, CA, USA

GP-B SFHe flight dewar concept : R.T. Parmley, E. Cavey and J. Goodman Lockheed Research Laboratories, Palo Alto, CA, USA