Visible and Infrared Imaging Spectrometer Applied in Small Solar System Body Exploration

Abstract

With the development of human society and advances in science and technology, the need of looking for extraterrestrial energy and expanding human living space is increasing. Spectrometer played an irreplaceable role in the deep space exploration in recent decades, which was very effective in the research on physical and chemical properties of substances. By combining image data and fine spectral information, imaging spectrometer can obtain the spectral characteristics and spatial distributions of material compositions at the same time. Required by the detailed determination in both spatial and spectral dimensions of target body, the study on the sensors with high spatial resolution, high spectral resolution, and high detection sensitivity becomes an important technical direction in deep space exploration field. This method can provide higher precision detection means and science data with richer information for the research on space science exploration. The application of hyperspectral imaging in deep space exploration is discussed. The spectrometers using filters, grating spectrometers, and Fourier transform spectrometers applied in previous deep space exploration missions are concluded. The advantages and disadvantages of different spectroscopic methods are discussed, and the development trend of spectrometers for deep space exploration is analyzed. Based on the characteristics of small solar system bodies’ exploration, the scientific objects of detection for near-earth asteroids (NEAs) and main belt comets (MBCs) are present. According to the mission requirements of NEA remote sensing, in situ analysis and sample return, and MBC investigation, and based on the requirements for composition studies of NEA and MBC, the main specifications of visible and infrared imaging spectrometer for small solar system bodies are designed. The spectral coverage of the spectrometer is from visible to medium wave infrared (0.4–5 μm). The spatial and spectral information can be obtained simultaneously with the spatial resolution of 0.5 m at 5 km observation distance. High spectral resolution of 5 nm in visible band and medium spectral resolution of 10 nm in infrared band are realized. The signal-to-noise ratio of the instrument can be better than 100. A convex grating with two different groove densities in different regions is used to realize the integration of visible and infrared bands in a single offner spectrometer. The optical system is very compact so that the volume and mass of the instrument can be lower. Considering the albedo and temperature of most target bodies are very low, cryo-refrigeration technique for detector is adapted to reduce the dark current and its noise, and the optical-mechanical system is cooled to reduce the noise produced by background radiation. Thus the detection sensitivity of the instrument can be guaranteed by all this measures. This instrument is devoted to material composition mapping in wide spectral coverage of small body and landing site choosing of the mission.