Design of a wide field far-UV spectrometer for a mission to Mars

摘要

An imaging spectrometer for observations of the Martian corona and the Martian thermosphere is presented. The corona extends over 10 Martian radii and its measurement requires observations over a very wide field. The spectrometer covers the wavelength region 120-170 nm where this band includes coronal spectral lines of hydrogen Lyman alpha and oxygen, and thermospheric spectral lines from atomic oxygen and carbon and the 4th positive band of CO. Stellar occultation observations will provide atmospheric density measurements. These scientific requirements are fulfilled by an Offner-type spectrometer with a 110 degree instantaneous field of view and no moving mechanisms. Both the spectral and imaging resolution vary across the field, from higher resolution across the planet body, to lower resolution required at the diffuse outer parts of the corona. This Offner-type design has not been previously used in the FUV.