Significant progress has been made towards increasing the operating temperature of cooled focal plane arrays to approximately 160K from the more common 77-120K temperature range. The coolers are still built upon existing open loop Joule-Thomson (JT) or Stirling cryocoolers driving size, weight and power (SWaP).
JT coolers are fed by a high pressure gas bottle limiting their duration of operation and thus the range of operation of the device on which they are installed. Increasing the focal plane temperature enables cooler dimensions to be decreased by a factor of between 5 and 10 and electrical consumption by a factor of 2 to 3 in addition to making persistence possible. A study of the candidate cooler technologies, led to the selection of the cascade JT cooler as a promising option. A cascade JT cooler has multiple thermodynamic cycles, each precooling the next stage to a lower temperature according to the saturation temperature of the gas used in the cycle, until the last cycle has a temperature close to the target temperature for the system. This allows to have cycle pressures reachable by conventional compressors. As a first goal, Absolut targets 5 cycles to operate between room temperature and 150K.
Relying on membrane technology for the compressor should allow for maximum miniaturization within a limited development cost. As a de-risking strategy, Absolut focus first on the compressor development. Micro-heat exchangers have already been demonstrated in the literature and will be tackled in the following.
Our goal is to produce a compact compressor, with a single actuator capable of transmitting motion to 5 compression cells in order to feed the 5 thermodynamic cycles with pressure ratios between 4 and 6. As a first step we have designed a single cell compressor using MEMS manufactured check valves, embedded in a larger structure machined with conventional methods. All parts have been manufactured and assembled; this compressor is now under test.
The technology has a very high potential for miniaturization as all the cycles can be integrated together. It will thus ease integration of such coolers for on-board systems. Distributed cooling is also eased by the miniaturization targeted, an envelope smaller or equal to 18cm3.
In this project, Absolut partnered with Inex Microtechnology Ltd. to develop and manufacture all the MEMS components.
Price of the most exploitable project at the MCM-ITP conference 2017
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