The Design and Development of an Oil-Free Compressor for Spacelab Refrigerator/Freezer

A Compressor has been developed for Spacelab Refrigerator/Freezer to work in zero-gravity in Spacelab mission-4 and afterwards to conduct life science experiments. It has four identical pistons each arranged at 90° in four radial directions at different levels. Each piston is moved by a common eccentric shaft operated by a brushless DC motor using spacelab power at +28 VDC. Each piston moves its own diaphragm to pump freon R502 across its suction and discharge valves. The shaft has four needle bearings (sealed) staggered along its axis so that each bearing will move only its own piston. There is no relative motion between the outer surface of the bearing and the piston end. So no oil is necessary for the compressor which eliminates the problem of lubrication in zero-gravity. Three heads are connected in parallel to each other while the fourth head is connected in series to the outlets of the three heads. The stroke of each piston is 0.28 cm. The rotational speed of the shaft is around 1300 RPM. Tests results show that the compressor can deliver the cooling requirements of the Spacelab Refrigerator/Freezer.