Distributed Joule-Thomson microcooling for optical detectors in space

The utilization of micromachined Joule‐Thomson (JT) coolers for future space missions in cooling small optical detectors operating in the temperature range 80 ‐ 300 K is investigated. The scope is to obtain a distributed cooling system in which multiple miniature coolers, each cooling a small detector, are driven by a single compressor. A literature survey was done to identify the detectors used in space, and detectors suitable for cooling with a miniature JT cooler were selected. A conceptual design of a miniature cooler ‐ detector system was made that focuses on the interface between a JT cooler and a detector and on the wiring of the detector. Various bonding and wiring techniques were discussed and the most suitable ones were selected. The optimum working fluid for a JT cold stage operating at a specific temperature in the range 80 ‐300 K was selected on basis of fluid properties only. A theoretical analysis was developed to investigate whether existing JT coolers can be operated with different working fluids. It was shown that JT cold stages optimized for operating with nitrogen can be driven by various other fluids. A new generation of JT coolers was developed and characterized. The temperature profiles along the length of the counter‐flow heat exchangers and the cooling powers of the JT coolers operating with nitrogen and methane were measured. Cooling powers up to 130 mW at 100 K were obtained. Also, the performance of the coolers while cooling a dummy detector array was mapped. To obtain closed‐cycle JT cooling, a miniature JT cooler was combined with a linear compressor. A gas mixture of 39 mol% methane, 20 mol% ethane and 41 mol% isobutene was used as refrigerant and the performance of this cooling system was measured.