Miniature Thermal Emission Spectrometer for the Mars Exploration Rovers

Abstract

The Miniature Thermal Emission Spectrometer (Mini‐TES) will provide remote measurements of mineralogy and thermophysical properties of the scene surrounding the Mars Exploration Rovers and guide the rovers to key targets for detailed in situ measurements by other rover experiments. The specific scientific objectives of the Mini‐TES investigation are to (1) determine the mineralogy of rocks and soils, (2) determine the thermophysical properties of selected soil patches, and (3) determine the temperature profile, dust and water‐ice opacity, and water vapor abundance in the lower atmospheric boundary layer. The Mini‐TES is a Fourier Transform Spectrometer covering the spectral range 5–29 μm (339.50 to 1997.06 cm−1) with a spectral sample interval of 9.99 cm−1. The Mini‐TES telescope is a 6.35‐cm‐diameter Cassegrain telescope that feeds a flat‐plate Michelson moving mirror mounted on a voice‐coil motor assembly. A single deuterated triglycine sulfate (DTGS) uncooled pyroelectric detector with proven space heritage gives a spatial resolution of 20 mrad; an actuated field stop can reduce the field of view to 8 mrad. Mini‐TES is mounted within the rover's Warm Electronics Box and views the terrain using its internal telescope looking up the hollow shaft of the Pancam Mast Assembly (PMA) to the fixed fold mirror and rotating elevation scan mirror in the PMA head located ∼1.5 m above the ground. The PMA provides a full 360°of azimuth travel and views from 30° above the nominal horizon to 50° below. An interferogram is collected every two seconds and transmitted to the Rover computer, where the Fast Fourier Transform, spectral summing, lossless compression, and data formatting are performed prior to transmission to Earth. Radiometric calibration is provided by two calibration V‐groove blackbody targets instrumented with platinum thermistor temperature sensors with absolute temperature calibration of ±0.1°C. One calibration target is located inside the PMA head; the second is on the Rover deck. The Mini‐TES temperature is expected to vary diurnally from −10 to +30°C, with most surface composition data collected at scene temperatures >270 K. For these conditions the radiometric precision for two‐spectra summing is ±1.8 × 10−8 W cm−2 sr−1/cm−1 between 450 and 1500 cm−1, increasing to ∼4.2 × 10−8 W cm−2 sr−1/cm−1 at shorter (300 cm−1) and longer (1800 cm−1) wave numbers. The absolute radiance error will be <5 × 10−8 W cm−2 sr−1/cm−1, decreasing to ∼1 × 10−8 W cm−2 sr−1/cm−1 over the wave number range where the scene temperature will be determined (1200–1600 cm−1). The worst‐case sum of these random and systematic radiance errors corresponds to an absolute temperature error of ∼0.4 K for a true surface temperature of 270 K and ∼1.5 K for a surface at 180 K. The Mini‐TES will be operated in a 20‐mrad panorama mode and an 8‐mrad targeted mode, producing two‐dimensional rasters and three‐dimensional hyperspectral image cubes of varying sizes. The overall Mini‐TES envelope size is 23.5 × 16.3 × 15.5 cm, and the mass is 2.40 kg. The power consumption is 5.6 W average. The Mini‐TES was developed by Arizona State University and Raytheon Santa Barbara Remote Sensing.