Abstract
Two closed-cycle cryogenic refrigerators were used to generate temperatures of ~18 K via evaporation of liquid hydrogen at the interfaces with radiofrequency and infrared sensors on an Earth-orbiting spacecraft that measured the anisotropy of the cosmic microwave background (CMB) during the European Space Agency (ESA) Planck Mission from June 2009 until October 2013. The liquid hydrogen phase was continuously generated in each Planck Sorption Cryocooler (PSC) by coupling a Joule–Thomson (J–T) expander to hydrogen gas initially pressurized to nominally 3000 kPa (i.e., ~30 bar) and subsequently discharged at pressure of 30 kPa (i.e., ~0.3 bar) by desorption and absorption using LaNi4.78Sn0.22Hx contained in six individual sorbent beds. The pressures were varied by alternately heating and cooling this hydride that included temperature modulation with an integrated Gas-Gap Heat Switch (GGHS). The novel GGHS used the low-pressure hydride ZrNiHx to vary thermal conductance between the bed containing the LaNi4.78Sn0.22Hx sorbent and the rest of the compressor system. The design features and development of these hydride components are described along with details of fabrication and assembly. The results obtained during extended laboratory testing are also summarized. The predictions from this preflight testing are compared to the performance observed while operating in orbit during the Planck Mission. This review ends with a summary of lessons learned and recommendations for improved systems.
Highlights
The temperature in deep outer space is ~3 K due to cosmic microwave background (CMB) radiation, the internal temperature of spacecraft in earth or near-earth orbits is about 280 K but temperatures fluctuate substantially as the satellites travel into and out of solar illumination
After functional verification tests of the sorbent bed and Gas-Gap Heat Switch (GGHS) performance were completed on each compressor element assembly, the connecting tube to the GGHS volume was permanently sealed using a “pinch-off” weld procedure that left a short extending tube, as shown in the bottom of Figure 4, which is indicated by the red arrow
When the Planck satellite was launched on 14 May 2009, the minimum requirement for mission success was defined with the spacecraft needing to complete two whole surveys of the sky
Summary
The temperature in deep outer space is ~3 K due to cosmic microwave background (CMB) radiation, the internal temperature of spacecraft in earth or near-earth orbits is about 280 K but temperatures fluctuate substantially as the satellites travel into and out of solar illumination. Among the diverse technologies that have been developed for space applications over the past 60+ years are closed-cycled cryogenic refrigerators operating on the Joule–Thomson (J–T) effect [3] arising from pressure drops of various gases. These systems are generically called Sorption Cryocoolers [3]. 1. Schematic (a) Schematic diagram of a single-stage sorption cryocooler metal hydride producing liquid hydrogen and (b) the idealized closed-loop cycle. The Low-Frequency Instrument with a single telescope were used to characterize the CMB radiation during five scans of the entire (LFI) used an array of 22 tuned radio receivers to cover the frequency range of 27 to 77 GHz [10] WasPlanck’s to produce data in the far infrared the far infrared and radio wave spectral regions than were available from previous measurements of and radio wave spectral regions than were available from previous measurements of the CMB to test the CMB to test more quantitatively various theoretical models of the early universe and the origins of more quantitatively various theoretical models of the early universe and the origins of cosmic cosmic structure structure [15]. [15]
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