The Tropospheric Emission Spectrometer (TES) is a cryogenic instrument which will be launched on NASA's Earth Observation System (EOS) Chemistry Platform in the year 2003. The overall mission lifetime for the instrument is 5 years with an additional period of 2 years required for ground test and calibration. The EOS Chemistry Platform will be placed in a sun-synchronous near-circular polar orbit with an inclination of 98.2 degrees and a mean altitude of 705 km. The overall objective of TES is the investigation and quantification of global climate change, both natural and anthropogenic. It is a high resolution infrared imaging (1×16 pixels) Fourier Transform Spectrometer with spectral coverage of 3.3-15.4 μm at a spectral resolution of 0.10 cm−1 or 0.025 cm−1 intended for the measurement and profiling of essentially all infrared-active molecules present in the Earth's lower atmosphere (0-30+ km).The thermal design provides four temperature zones required by the instrument, namely 65 K, 180 K, 230 K and 300 K. The detectors are cooled by mechanical pulse-tube coolers to 65 K and a two-stage passive cooler provides cooling for the interferometer optics at 180 K. Detector pre-amplifier electronics requires 230 K as well as the optics filter wheel actuators. The remaining electronics including the mechanical cooler compressor requires ambient temperatures near 300 K.The thermal control system consists of passive and active elements to maintain the instrument within allowable flight temperature limits. 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 radiators. Active thermal control employs constant conductance heat pipes (CCHPs), loop heat pipes (LHPs) and both open-loop and close-loop heater control systems. Operational and replacement heaters are used in the instrument science mode and survival heaters are used in the safe and survival modes. LHPs are used to transport waste heat from components to the heat rejecting radiator surfaces. Detailed description of LHPs can be found elsewhere [1,2,3,4,5,6,7,8]. Steady state and transient performance test results of a propylene LHP of similar design to the TES LHPs is presented in Refs. 9 and 10. This paper describes the instrument thermal requirements, thermal design and analysis approach, key drivers for the design process and analysis results.