The Mercury sodium atmospheric spectral imager for the MMO spacecraft of Bepi-Colombo

摘要

The Mercury Sodium Atmosphere Spectral Imager (MSASI) on the Mercury Magnetospheric Orbiter (MMO) of the JAXA/ESA Bepi-Colombo (BC) Mission will address a range of fundamental scientific questions pertaining to Mercury's exosphere. The measurements will provide new information on regolith-exosphere-magnetosphere coupling as well as new understanding of the dynamics governing the exosphere bounded by the planetary surface, the solar wind and interplanetary space. MSASI is a high-dispersion visible spectrometer working in the spectral region near the sodium D_2 emission (589 nm), a major constituent of the Mercury exosphere. A single high-resolution Fabry-Perot etalon is used in combination with a narrow-band interference filter to achieve a compact and efficient instrument design. The etalon and filter are extremely stable with respect to long-term aging and temperature variations. Full-disk images of the planet are obtained by means of a single-axis scanning mirror in combination with the spin of the MMO spacecraft. This paper presents an overview of the MSASI and the design of the Fabry-Perot interferometer used as its spectral analyser.rnIt is concluded that:rn(1) The MSASI optical design is practical and can be implemented without new or critical technology developments.rn(2) The thermally stable etalon design is based on concepts, designs and materials that have a good space heritage.rn(3) The MSASI instrument will achieve a high signal-to-noise ratio (SNR) (＞ 10) in the range of 2K-10M Rayleigh.