Sub-Kelvin Sorption Coolers for Space Application

Abstract

The European Space Agency’s FIRST satellite will be a multi-user observatory looking at the universe in the infrared and submillimeter wavelength range from 80 to 670 μm. It accommodates three instruments, all of which have detectors or mixers operating in the range 0.3 K – 2 K. A large superfluid helium (He II) dewar provides a cold heat sink at around 1.8 K, with the last cooling stage, down to 0.3 K, effected inside the instruments using a recyclable ³He sorption cooler developed at CEA-SBT.

Although these hardware developments are expected to begin in fall 2000, CEA-SBT, in collaboration with CSL, was awarded in September 1998 an ESA Technological Research Program (TRP) contract whose objective is to design, manufacture, test and qualify for space an engineering model of a sorption cooler. In this framework, two prototype coolers, one ³He and one ⁴He have been designed and fabricated. To benefit the future development of the FIRST coolers, the ³He prototype was sized according to the main specifications of the SPIRE instrument. These two prototypes have been assembled, and the test plan, which shall lead to the qualification of the coolers, is currently being performed. Preliminary results are presented.

In parallel with these projects and prior to the detailed design of the engineering models, a laboratory sorption cooler prototype which can be run with ³He or ⁴He was developed to further study specific aspects and answer various questions. For instance, convective effects that could severely impact the performance during ground test operation, and superfluid film behavior were both investigated. In addition, various measurements were performed on the titanium alloy Ta6V and Kevlar 29. These results are presented as well.