A compact thermal heat switch for cryogenic space applications operating near 100 K

• A passive CTE-based heat switch for cryogenic space applications was built and tested.
• The heat switch is a proof of concept for a redundant cryocooler application.
• The construction demonstrated reliable switching behaviour over several switch cycles.
• An on-state conductance of 1 W/K and an off-state conductance of 3 mW/K was realised.
• The creep of the used CTE material at cryogenics temperatures was analysed.

A thermal heat switch has been developed intended for cryogenic space applications operating around 100 K. The switch was designed to separate two pulse tube cold heads that cool a common focal plane array. Two cold heads are used for redundancy reasons, while the switch is used to reduce the thermal heat loss of the stand-by cold head, thus limiting the required input power, weight and dimensions of the cooler assembly. After initial evaluation of possible switching technologies, a construction based on the difference in the linear thermal expansion coefficients (CTE) of different materials was chosen. A simple design is proposed based on thermoplastics which have one of the highest CTE known permitting a relative large gap width in the open state. Furthermore, the switch requires no power neither during normal operation nor for switching. This enhances reliability and allows for a simple mechanical design. After a single switch was successfully built, a second double-switch configuration was designed and tested. The long term performance of the chosen thermoplastic (ultra-high molecular weight polyethylene) under cryogenic load is also analysed.