Design And Development Of A 4k Mechanical Cooler

This paper describes the design and development of a closed cycle Joule-Thomson 4K Cooler aimed at the ESA Far Infra-Red Space Telescope (FIRST) and PLANCK astronomy missions.A cooler of this type has previously been developed by the Rutherford Appleton Laboratory (RAL) under ESA contract, but the criticality of the cryogenic cooling sub-system to the mission is such that ESA identified the need to prove and qualify the cooler against project specific requirements before the start of the spacecraft development.The environmental and performance requirements (>9mW heat lift at 4.2K) of the cooler are challenging and the FIRST 4K Cooler includes many features to enhance performance over previous designs. In making these changes the heritage gained on other MMS coolers has been retained and the cooler has been designed with a high degree of modularity with respect to MMS Stirling coolers that are in batch manufacture.One key area of the design has been the ruggedisation of the Joule Thomson stage to meet the Ariane 5 launch environment. This ruggedisation, which has to meet the conflicting thermal and structural requirements, uses pre-tensioned Kevlar threads and snubbers to achieve launch survivability.