Magnetospheric multiscale (Mms) mission: Surviving extended mission long eclipse

Abstract

The Magnetospheric Multiscale (MMS) mission is the fourth Solar Terrestrial Probe (STP) program of National Aeronautics and Space Administration (NASA). The MMS mission was launched on March 12, 2015. The mission consists of four identically instrumented spin-stabilized spacecraft flying in a tetrahedral formation to study the magnetosphere of the Earth. As the MMS formation moves in orbit during the different science observation phases, the apparent Sun position shifts such that MMS experiences variable eclipse durations. By the end of the primary science observation phase, September 2017, MMS completed 792 orbits and had experienced 683 eclipse events. Seventy-four percent of the eclipse events lasted for less than 1 hour long while fourteen percent lasted between 1 hour and 2 hours long, and the remaining twelve percent lasted between 2 hours and 3.5 hours long. MMS eclipse configuration rules, inherited from pre-launch test results and analyses, implement spacecraft suite and instrument suite power configurations as well as heater and temperature setting management for eclipse durations up to 4 hours long. In August 2019, as the mission progresses into extended science observation phases, MMS is predicted to experience eclipse durations of 3.7 hours, 5.2 hours, 4.4 hours, and 2.8 hours long on four consecutive orbits. The 4.4 hour and 5.2 hour long eclipse events are longer than any tested during pre-launch energy balance simulation and analyses. This paper discusses the energy balance analyses and results obtained for the four long August 2019 MMS eclipse orbits amending existing MMS eclipse configuration rule sets.