From RHESSI Wiki
The Germanium detectors are cooled through a single mechanical Stirling cycle pump. The cryocooler is one of only two essential mechanical subsystems onboard RHESSI. Through its single-state cycle, the cryocooler creates some vibrations which are monitored. Excessive vibration would feed noise into the sensitive detectors, and in fact this routinely happens during shutter motions. The cooler operating voltage can be adjusted in order to control the temperature, and there is also a heater within the cryostat for further control.
The GeDs are cooled on-orbit by a single electro-mechanical cryocooler. Recently, under contract to NASA/GSFC, Sunpower Inc. has developed an inexpensive single stage, integral (counterbalanced) Stirling cycle cooler which can provide up to 4W of cooling at 77 K, with an input of 100W. This M77 cryocooler has been designed for operational lifetimes greater than 50,000 hours, using a gas bearing/flexure system to prevent contact of moving parts. In extensive studies over the past two years at GSFC, M77 coolers have been vibrated to the GEVS mandated 14.1 Grms, run under thermal vacuum conditions from -25C to +30C, and life-tested already (continuing) for ~>10,000 hrs. Monitoring during these tests showed no internal contamination of the working gas. Units already tested at GSFC are fully qualified for flight, and will be used for HESSI.