Scientific Objectives and Design Concepts of Onboard Spectrometers for Main Belt Comets Exploration

Abstract

The discoveries of main belt comets (MBC) in early twentieth century have attracted great interests of the planetary society, as the water ice and other volatile rich MBCs are located in the main belt and thus may have played a fundamental role in supplying water to the early Earth. Therefore, MBCs are very interesting and important candidate objects for the near future space missions. The scientific objectives of optical and infrared spectrometers for a flyby mission are summarized. Then the major technical specifications for the spectrometers are proposed based on the optical and thermal properties of the main belt comet 133P/Elst-Pizarro, one of the major targets. The spectral coverage of the proposed spectrometeris from 0. 4 to 50 μm, which is realized by two spectrometers covering 0. 4~5 μm and 5~50 μm, respectively. The visible and infrared imaging spectrometer (VIIS) is a very compact grating spectrometer covering 0. 4 to 5 μm with a spectral resolution of 5 nm in the visible and 10nm in the infrared. The spatial resolution of the VIIS is 0. 5 m at an observational distance of 5km. The signal to noise ratio of the spectrometer is better than 100 using cryogenic optics technology. Thermal emission spectrometer (TES) is a time modulated Fourier transform spectrometer. The core component of TES is one interferometer with two cube corners and swing arms which covers 5~50 μm. The spectral resolution of TES is 8 cm-1. The spatial resolution of TES is 10 m at an observational distance of 5 km. A pyro-electric detector is used for the TES, working at ambient temperature. The key technologies and specifications for the two instruments are described and analyzed. The current results provide important information for engineering development in the future.

Keywords

Main Belt Comets / reflectance and emittance spectroscopy / grating spectrometer / Fourier transform spectrometer