30 Years of Thermally Controlled Imaging Spectrometers for Earth and Planetary Science
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Since its inception spectroscopy has been used to pursue science and applications based on the interaction of light with matter on Earth, throughout the solar system, and for diverse astronomical objectives. Spectroscopic signatures of interest extend from the ultraviolet to the thermal infrared. In the late 1970’s, with advances in detector, optical, and electronic technologies, instruments that measured spectra for each point in an image became feasible. In 1979 the first imaging spectrometer was proposed using a cryogenically cooled 32x32 HgCdTe detector array. The Airborne Imaging Spectrometer first few in 1982 and made scientific discoveries during its first flights. Imaging spectrometers have been developed and sent to Jupiter, Saturn, Mars, the Moon, Earth orbit, and other objects throughout the solar system. In almost every case these instrument require carefully designed thermal systems to assure detector operability, control for detector and instrument background noise, and measurement stability. These thermal requirements are exceptionally stringent for imaging spectrometer instruments that measure signals in very narrow continuous wavelength bands. From 1979 to present JPL has lead and contributed to more than 15 major imaging spectrometer instruments requiring a range of thermal control architectures. This paper reviews the instrument detector, noise, and stability factors that drive the thermal requirements and approaches taken to meet the requirements. Highlights of science discoveries are given as well as new architectures and missions expected for the class of thermally controlled science instrument going forward.