Thermal Control System of the Moon Mineralogy Mapper Instrument

The Moon Mineralogy Mapper (M3) instrument is one in a suite of twelve instruments which will fly onboard the Indian Chandrayaan-1 spacecraft scheduled for launch in 2008. Chandrayaan-1 is India's first mission to the Moon and is being managed by the Indian Space Research Organization (ISRO) in Bangalore, India. Chandrayaan-1 overall scientific objective is the photo-selenological and the chemical mapping of the Moon. The primary science objective of the M3 instrument is the characterization and mapping of the lunar surface composition in the context of its geologic evolution. Its primary exploration goal is to assess and map the Moon mineral resources at high spatial resolution to support future targeted missions. It is a “push-broom” near infrared (IR) imaging spectrometer with spectral coverage of 0.4 to 3.0 μm at 10 nm resolution with high signal to noise ratio, spatial and spectral uniformity. The nominal on-orbit mission lifetime for the instrument is 2 years with 2 months of primary science imaging every 6 months. The Chandrayann-1 spacecraft will be placed in a near-circular Moon polar orbit with an inclination of 90 degrees, mean altitude of 100 km, and 118 minute orbit period.

The thermal control system consists of passive elements to maintain the instrument within allowable flight temperature (AFT) limits. Passive thermal control includes multi-layer insulation blankets, thermal straps, and surface coatings to manage the transfer of waste energy from sources through structures and ultimately to radiators. The detector is cooled to 150 K by means of a three-stage passive cooler which also cools the optical bench and telescope to near 180 K. This paper describes the instrument thermal requirements, top-level thermal design and analysis approach, key design drivers and analysis results.