On-orbit performance of the RHESSI cryocooler

The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft was launched on February 5, 2002. With more than a year of operation on-orbit, its Sunpower M77 cryocooler continues to maintain the array of nine germanium detectors below 80 K. Trends have begun to emerge in cryocooler power and vibration, suggesting that the cooler's operating point is slowly changing. Possible causes are identified and discussed.