Design and preliminary verification of asteroid thermal emission spectrometer for Tianwen-2
Abstract
The Tianwen-2 mission will sample a near-Earth asteroid named 2016 HO<sub>3</sub>, return to Earth, and then proceed to a main-belt comet 311P. The asteroid thermal emission spectrometer (ATES) is one of the scientific payloads. ATES will provide remote measurements of the surface thermal emission spectrum of these two solar small bodies, to investigate their mineralogy and thermophysical properties, as well as to aid in the selection of the sampling site. ATES is a Fourier transform spectrometer covering the spectral range of 5–<sc>50 μm</sc> (200–<sc>2000 cm<sup>−1</sup>)</sc> with a spectral resolution of less than <sc>10 cm<sup>−1</sup></sc> and a field of view of 3.28 mrad×3.29 mrad. The signal to noise ratio is more than 326 (7.5–<sc>35 μm</sc>@<sc>325 K).</sc> ATES observes different positions on the bodies’ surfaces using its one-dimension pointing capability combining the rotation of the small body itself. The core subsystem is a time-modulated interferometer with two cube corners and four ports, which enables optical subtraction between the input energy of the scene observation port and the reference port. This design improves sensitivity and dynamic range to detect the bodies with surface temperature ranging from <sc>100</sc> to 422.5 K. The interferometer mechanism, featuring two-times optical path magnification, achieves a high-speed stability of 99% at slow scanning speed. Two thin LiTaO<sub>3</sub> detectors are used to detect interference signals at two output ports, respectively. The total mass of ATES is less than <sc>10 kg,</sc> owing to its highly integrated and lightweight design. The power consumption of the electronics is below <sc>50 W.</sc> The spectral and radiometric calibrations of the flight module are completed on the ground. The temperature and spectral feature detection capabilities are verified using the qualified module in vacuum chamber. The operational principle, technical characteristics, testing, calibration and verification of ATES on the ground are summarized. It can provide a reference for the development of similar instruments.
