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On-Orbit Thermal Performance of the TES Instrument-Three Years in Space
Abstract:
The Tropospheric Emission Spectrometer (TES), launched on NASA's Earth Observing System Aura spacecraft on July 15, 2004 has successfully completed over three years in space and has captured a number of important lessons. The instrument primary science objective is the investigation and quantification of global climate change. TES measures the three-dimensional distribution of ozone and its precursors in the lower atmosphere on a global scale. It is an infrared (IR) high resolution, imaging Fourier Transform Spectrometer (FTS) with a 3.3 to 15.4 μm spectral coverage required for space-based measurements to profile essentially all infrared-active molecules present in the Earth's lower atmosphere. The nominal on-orbit mission lifetime is 5 years. The Aura spacecraft flies in a sun-synchronous near-circular polar orbit with 1:38 pm ascending node.
The instrument uses four focal plane arrays in two separate housings cooled to 65 K by a pair of Northrop Grumman Space Technology (NGST) pulse tube cryocoolers. It includes a two-stage passive cooler to cool the interferometer to 180 K. The electronics including the cryocooler compressors transport their waste heat via loop heat pipes (LHPs) and constant conductance heat pipes (CCHPs) to room temperature nadir facing radiators for rejection to space.
After cooling the optical bench and focal planes to their operating temperatures for the first time, a decontamination cycle was required only 14 days later due to ice contamination of the focal planes. The signal throughput from one of the eight channels decreased by 40%. The 2B1 channel with a 600-900 cm−1 filter showed strong evidence of the presence of water ice. Ice buildup of cryogenic surfaces also led to increased cryocooler heat loads.
After six months of successful science operations, plans were developed to increase the optics temperature to near 187 K to improve the interferometer optical alignment and obtain higher quality science data. The optics temperature was increased successfully on November 29, 2005 with results showing significant improvement in the science data quality. This paper provides a general overview of the thermal and cryogenic system design and reviews the on-orbit performance over the three years.