The Challenges of the Thermal Design of BepiColombo Mercury Planetary Orbiter
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BepiColombo is the first European mission to Mercury. It mainly consists of two separate spacecraft which will orbit the planet: Mercury Magnetosphaeric Orbiter (MMO), provided by the Japanese Space Agency, and Mercury Planetary Orbiter (MPO), provided by the European Space Agency, plus a dedicated module, Mercury Transport Module (MTM), which will provide the transfer from Earth to Mercury. MPO, the subject of this paper, is the European scientific contribution to the BepiColombo mission. Its orbit around Mercury will be 3-axis stabilized, planet oriented, with a planned lifetime of 1 year, and a possible 1-year extension. The mission will perform a comprehensive study on Mercury, by means of several instruments, including a laser altimeter, different types of spectrometers, a magnetometer and radio science experiments. The subject of this paper are the complex challenged faced by the thermal design of MPO. The very harsh thermal environment experienced by the Module changes from a relatively cold condition after the launch (1.15AU distance from Sun) to a very hot condition orbiting Mercury (0.3AU distance from Sun at aphelion plus the infrared heat load from the Planet). The TCS is based on the shielding effect of a High Temperature High Performance MLI and on the particular radiator design, capable of reflecting most of the infrared flux coming from the Planet. The equipment are mounted on the internal structural panels which are connected to the radiator by a complex network of Heat Pipes. The Payloads typically have a dedicated thermal control, based on low temperature sub-radiators, which have to be highly decoupled from the internal spacecraft environment. Pointing stability requirements are satisfied mounting the instrument on dedicated Optical Bench.