On-Orbit Thermal Performance of NASA's Ocean Color Instrument

NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, launched 2/6/24, will provide data continuity for the ocean color, aerosol and cloud measurements acquired by NASA’s on-orbit Earth Science observatories since the 1990s. The PACE Ocean Color Instrument (OCI) is an optical spectrometer developed for hyper-spectral measurements in the ultraviolet-to-near-infrared band between 340 nm and 2260 nm. OCI provides greater insight and resolution than its predecessors, requiring a more complex thermal control approach to address high heat dissipations, stringent temperature stabilities, and thermal zones that range in temperatures from +30C to –70C. The Ultra-Violet to Near Infra-red (UVNIR) comprises two separate detectors independently controlled to -35C via propylene charged Loop Heat Pipes (LHP). The Short-Wave Infrared (SWIR) subsystem detectors are temperature controlled to –70C through passive radiators and thermal straps while maintaining thermal isolation from its relatively-warm (-20C) electronics. The optical element has a mirror which spins at 6Hz to provide a wide field of view for 2-day Earth coverage and are temperature controlled between 15C and 20C. In addition, the OCI tilts ±20° twice per orbit to decrease glint, increasing orbital environmental variation. This paper focuses on on-orbit thermal performance as compared to flight predictions, including survival heater performance, initial power-on, Loop Heat Pipe operations, nominal science collection, and safe hold operations. Thermal responses to the unanticipated attitude changes that occurred during spacecraft commissioning are also evaluated.