The Light Ion Analyzer (LIA) for the SMILE Mission

The Light Ion Analyzer (LIA) instrument, part of the Solar-wind-Magnetosphere–Ionosphere-link- Explorer (SMILE) mission, is designed to measure the ion velocity distribution function within an energy range of 5 eV up to 25 keV. LIA provides in-situ measurements of the ion velocity distribution functions of the solar wind and magnetosheath, from which the moments can be derived on the ground, serving as an upstream input for the magnetosphere-ionosphere downstream responses. Two identical 2π sr field-of-view LIA instruments are mounted on two opposite sides of the spacecraft platform, offering a combined 4π sr instantaneous field-of-view. Each LIA consists of a top-hat electrostatic analyzer, electrostatic aperture deflectors, and a microchannel plate detector for analyzing the energy, direction, and flux of ions. Depending on the operation mode, the angular resolution ranges from 5.625° to 22.5° in elevation and from 7.5° to 30° in azimuth, and the time resolution spans from 0.25 to 2 seconds. This paper describes the design of the LIA, its performance, ground calibration, operation procedures, and resultant data products.