BepiColombo/MMO Thermal Control System

Abstract

The thermal control system (TCS) of BepiColombo/MMO (Mercury Magnetospheric Orbiter) is presented. MMO is a spin-stabilized spacecraft due to the scientific requirements. The spin axis is pointed nearly perpendicular to the Mercury revolution plane. The harsh environment near Mercury (0.31AU from the Sun at perihelion) imposes 11 solar constant irradiation on MMO spacecraft, while its thermal control system is required to maintain the onboard equipment and the spacecraft structure in proper temperature range during the entire mission phases. The MMO is controlled by means of passive thermal design technique and some components are controlled by means of combined method of passive and active techniques. The passive thermal control elements are Optical Solar Reflector (OSR), thermal shield, paints, films, and Multi Layer Insulation blankets (MLI). All external surfaces should be electrical conductive due to scientific requirement. Although we have adopted conventional thermal control devices as much as possible, we have been obliged to develop a new component and new devices intended for high temperature environment : High Gain Antenna (HGA), High Temperature MLI (HT-MLI), High Temperature Conductive White Paint, and so on. The developments and tests of newly developed components and devices are presented as well as the selection of conventional thermal control materials and devices. MMO Thermal Test Model (TTM) will be tested three times elaborately; the thermal balance test (TBT) with 1 solar constant solar simulator at the Tsukuba Space Center (TKSC) in November-December 2009, the TBT with IR panels at ISAS (Institute of Space and Astronautical Science) in February 2010, and the TBT at ESTEC in September-October 2010.