A low-energy spectrometer with a 2pi field of view for planetary missions

We present a novel ion mass spectrometer designed to measure thermal and low-energy suprathermal ion populations of planetary and cometary environments on board a three-axis-stabilized spacecraft. It consists of three main parts: an electrostatic analyser to perform the angular and energy scans, a magnetic analyser to provide the mass separation and a position-sensitive detector in the focal plane of the magnet. The instrument has a 2 field of view divided into 16 azimuthal sectors with continuous-elevation scanning between 0 and 90°. A high-resolution cylindrical energy analyser with adjustable energy resolution allows measurement of the temperature and velocity of thermal ions and the energy spectrum of suprathermal ions. The mass range extends from 1 to 45 amu/q . Comparisons between numerical simulation and laboratory tests of a prototype are presented.