Thermal Design and On-Orbit Performance of the Multi-Angle Imaging SpectroRadiometer 2001-01-2262
The Multi-angle Imaging SpectroRadiometer (MISR) instrument was launched aboard NASA’s Earth Observing System (EOS) Terra spacecraft on December 18, 1999. The overall mission design lifetime for the instrument is 6 years. The EOS Terra spacecraft was placed in a sun-synchronous near-circular polar orbit with an inclination of 98.3 degrees and a mean altitude of 705 km. The overall objective of MISR is to provide a means to study the ecology and climate of Earth through the acquisition of global multiangle imagery on the daylit side of Earth. MISR views the sunlit Earth simultaneously at nine widely spaced angles, collects global images with high spatial detail in four colors at every angle. The images acquired, once calibrated, provide accurate measurements of brightness, contrast and color of reflected sunlight. Changes in the reflection at different view angles provides a means to distinguish between different types of atmospheric particles (aerosols), cloud forms and land surface covers. Using stereoscopic techniques, MISR data enables construction of 3-dimensional models and more accurate estimates of the total amount of sunlight reflected by Earth’s diverse environments.
The thermal design provides three temperature zones required by the instrument, namely −5°C, 5°C and 20°C. The charged-couple device (CCD) detectors are cooled by solid state single-stage thermoelectric coolers (TECs) which dump their waste heat to nadir radiators. Nadir radiators provide cooling for the optical bench and all nine cameras with camera head electronics. The remaining electronics are cooled to ambient temperatures near 20°C with separate nadir radiators.
The thermal control system (TCS) consists of passive and active elements to maintain the instrument within allowable flight temperature limits (AFTs). Passive thermal control includes multi-layer insulation (MLI) blankets, thermal straps, and surface coatings to manage the transfer of waste energy from sources through structures and ultimately to nadir radiators. Active thermal control employs TECs and close-loop heater control systems for the detectors and optical bench. Operational and replacement heaters are used in the instrument science and safe modes and survival heaters are used in the survival mode. This paper describes the instrument thermal requirements, thermal design, key drivers for the design process and analysis results. The on-orbit performance to date is also presented.