To develop, manufacture and test an Engineering Model of a "vibration-free" cooler that can provide active cooling for a temperature in the range of 40-80K and with a heat lift capacity in the range of 0.5 to 1 W

With the development of vibration-free AOCS technologies (magnetic bearing reaction wheels, microthrusters), cryocoolers (Stirling, Pulse Tube) will become the main source of microvibrations. To overcome this difficulty and cope with missions (Science and Earth Observation) that have more and more stringent pointing requirements, it is necessary to develop alternate cooling solution or to adapt current technologies to generate no mechanical disturbances. The Darwin development studies covered 15K and 4K class coolers, but a need also exists in the 40-80K range (IR detection).One possibility for such a system could be Sorption Coolers + Passive Radiators:- The cooling power is obtained by using the Joule-Thomson process/cycle. First, a gas is pressurized from a low pressure to a high pressure by a compressor. The gas reaches the Joule-Thomson restriction and expands adiabatically and isenthalpically. Due to the expansion, the gas cools down and becomes partly saturated liquid. The liquid fraction is evaporated by a heat load. Finally, the vapour flows back and the cycle is closed.- The compressor necessary to run this cycle is not a mechanical compressor but a sorption compressor, which uses the adsorbing-desorbing properties of e.g. charcoal cells to compress the fluid. Therefore no inherent vibration. The adsorbing is done by cooling down the charcoal cell using passive radiators, the desorbing by electrical heating.The advantages of such system are the following: no moving parts, hence vibration-free long life-time; easily scalable to different sizes and cooling powers; simple electronics (only management of electrical heaters); possibility of separating compressor and cold stage (linked only by small-diameter tubing) providing flexibility for accommodation layout.Drawbacks are: need for passive radiator, some temperatures are not reachable with this cooling cycle (typically between 45 and 60K), the figure of merit (Cooling Power)/(Total Radiator Area) is lower than for Pulse Tube/Stirling coolers.A first assessment shows that such a system for an Earth Observation mission could have the following features: cooling power: 0.5W@70K; mass less than 5kg (without radiator); electrical power less than 50W; passive radiator of about 1 m2 at 200K (depending on the mission).