high-temperature, high-lift, microgravity, oil-less, lunar rover
In the extreme temperature environment of the moon, the regolith surface temperature can reach 100°C during the 354-hour lunar day. This often exceeds the maximum allowable temperature of critical electronics onboard small lunar rovers designed for long-term science missions. In environments with such high heat sink temperatures, active vapor compression cooling solutions allow greater mission flexibility than traditional passive spacecraft thermal control. The objective of this research was to design and experimentally evaluate a critical enabling technology for effective lunar rover class heat pumps: the high-lift, high-temperature, microgravity compressor. The main technical challenges in the design of a compressor for these conditions include operation in a microgravity environment, relatively high compression ratio requirements, extreme temperatures during transport and operation in space and on the moon, and the low equipment vibration requirements for small lunar rovers. A twin-piston oil-less reciprocating compressor was designed to meet these requirements. The oil-less design mitigates the challenges of oil distribution in microgravity environments. A twin-piston configuration was designed to balance the dynamic forces and lower the vibration of the compressor. Compressor components were sized to operate with new high-temperature, environmentally friendly refrigerants at compression ratios between 3 and 7. The compressor was designed for a cooling capacity on the order of 100 W. A prototype compressor was fabricated and experimentally evaluated. The total mass of the compressor was 2.86 kg. Maximum exported vibration was estimated to be 0.04 N at the base of the compressor based on kinematic calculations and measured motor torque. Experimental capacity and efficiency measurements were lower than predicted. This was likely due to manufacturing and tolerance deficiencies in the first prototype compressor resulting in blowback around the piston seal, higher friction than predicted, suboptimal bearing performance, suboptimal reed valve design, and tolerance stack up in the crankshaft and cylinders. These manufacturing issues can be overcome in next generation prototypes.