Development of metal hydride beds for sorption cryocoolers in space applications

The development of hydrogen sorption cryocoolers over the past 30 years is briefly reviewed. The behavior of the metal hydride sorbent beds used in the sorption compressors dominates both the performance and reliability of these closed-cycle Joule-Thomson cryocoolers. Improved compressor elements have been recently designed to minimize their input power requirements and to enhance hydride durability during extended temperature cycling while in operation. ZrNi hydride is used to provide variable gas pressure in the gas-gap heat switches for each compressor element. Characterization tests have been performed on the compressor elements built for an engineering breadboard (EBB) cryocooler to evaluate the behavior of both the sorbent bed and gas-gap switches under conditions simulating flight operation for the future Planck mission of the European Space Agency (ESA). Operation of the Planck EBB sorption cryocooler has produced a cooling capacity of 1.0-1.7 W at a temperature of 17.7 K during initial laboratory tests. (C) 2003 Elsevier B.V. All rights reserved.