MASCOT Thermal subsystem design

MASCOT is a lander built by DLR, embarked on JAXA’s Hayabusa-2, a scientific mission to study the asteroid 162173 1999 JU3. It is a small lander, less than 300x300x200mm?, with onboard payloads (camera, magnetometer, radiometer and IR spectrometer), developed in collaboration by DLR and CNES. MASCOT lands on the asteroid surface, after being released by Hayabusa-2 from a very close position above the asteroid surface, and investigates the asteroid surface. The thermal design of the lander represents one of the main challenges in the whole project because of multiple constraints, depending on the mission phase, mass, power and free space available. MASCOT, notwithstanding its small size, is equipped with redundant heat-pipe system, MLI blanket, heaters. The thermal design of the lander has been chosen after a trade-off phase concerning the technology which could suit better the opposing requirements of the mission: low heat exchange between the lander and the exterior (including the main spacecraft) in cruise, possibility to transfer all the heat dissipated by the internal paylaods and electronic boards during operations on asteroid surface. After selecting the heat-pipe technology as baseline, a development phase was undertaken by the partners both in terms of manufacturing, testing, thermal characterization phase and analitical modelling in order to match the thermal requirements. Heaters are used to assure the survival of the most delicated parts of the lander during cold cruise phases: the battery cells (only primary battery on-board), the electronic boards and the main payload. Strict requirements are given by the main spacecraft in terms of maximum power available to heat the lander during cruise. MLI blankets are used where the available space allows it, e.g. to extra insulate the Ebox from the rest of the lander creating a „hot compartment" and between the lander and the main spacecraft to reduce the heat exchange with it during cruise below the given limits. The whole thermal concept in all its parts undertook a detailed modelling phase in parallel to an experimental phase in vacuum chamber to improve the model and to qualify the system