In-Flight Thermal Performance of the OCO-2 Instrument

The Orbiting Carbon Observatory-2 (OCO-2), launched on July 2, 2014, continues to operate nominally after successfully completing its primary mission of two years in space. It is hoped that, following a Senior Review and proposal phase, NASA will fund a two year extended mission, which would start in June 2017. The thermal design provides three temperature zones required by the instrument, specifically at 120 K, 267 K and 297 K. A single-stage pulse tube cryocooler provides refrigeration to three focal plane arrays to 120 K, via a high conductance flexible thermal strap. A variable conductance heat pipe (VCHP) based heat rejection system transports waste heat from the instrument, located inside the spacecraft, to the space-viewing radiators, providing tight temperature control of the spectrometer optics to 267 K, and maintains the electronics and cryocooler at 297 K. Soon after entering the A-Train on August 3, 2014, the optics and focal planes were cooled to their operating temperatures. Ice contamination of the cryogenic surfaces led to increased cryocooler loads and drove the need for two focal plane decontamination cycles between September 2014 and October 2014. A decrease in the radiometric gain of the O2 A-Band channel led to five additional focal plane decontamination cycles, between January 2015 and February 2017, and is now the primary driver of decontamination cycles. This paper provides a general overview of the thermal and cryogenic system design and reviews the inflight thermal performance for the mission.