Final Qualification and Early On-Orbit Performance of the RHESSI Cryocooler

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft was launched on February 5, 2002. It now observes the Sun with the finest angular and energy resolutions ever achieved from a few keV to hundreds of keV, using an array of nine germanium detectors operating at 75 K. The spacecraft was originally scheduled for launch in July 2000, but a vibration facility mishap damaged the primary structure of the spacecraft, along with the cryocooler. This paper describes issues in the qualification of a replacement for the original flight cooler, and describes early on-orbit performance.