The Design Of An Innovative Thermal Control Subsystem For Long Term Mars Missions: The Case Of GEP
- Paper number
IAC-07-C2.7.01
- Author
Mr. Gabriele Messina, Deutsches Zentrum fur Luft und Raumfahrt e.V. (DLR), Germany
- Coauthor
Mr. Riccardo Nadalini, Deutsches Zentrum fur Luft und Raumfahrt e.V. (DLR), Germany
- Year
2007
- Abstract
The thermal subsystem of most of the past and present long term Mars surface missions includes radioactive units to keep the temperature of the components within design limits.
The use of radioactive elements has, besides benefits, like mass saving and steadfast performance, also technical, practical and political drawbacks. Among other, the security risks connected with the use of hazardous materials and all the thermal problems caused by the unstoppable dissipation during the hot phases of the mission.
The objective of this study was to assess if an alternative thermal control without radioactive material is possible and which balance of advantages and disadvantages it has. The study focused on the Geophysics and Environment Package (GEP), a package of instruments dedicated to the long term geophysical analysis of Mars, to be on board the ESA’s ExoMars lander element.
Initial assessments and trade offs, by means of extensive numerical modelling, have been performed and have shown that the most promising substitute for a Radioactive Heating Unit (RHU) is the use of a thermal capacitor connected to the battery element. In such a solution, a quantity of a phase change material is used to store the excess electrical power produced during the day. During the night the stored latent heat is released to keep the equipment in the enclosure (battery and electronics) warm.
To increase performance, battery and electronics are mounted in a “nested configuration”: the battery is positioned in the innermost box, while the electronics are in the external one. The whole is then separated from the external environment by a further enclosure. Boxes are insulated and structurally connected to each other by means of low-conductivity stand-offs.
To minimize mass, the use of Martian atmosphere as insulator has been investigated and compared with solid insulation. Sensitivity analyses identified a hybrid insulation to be the best solution, in which solid insulation is used for the battery, whereas carbon dioxide insulates the electronics from the outside. This hybrid design requires, in the worst case, 34.1 Wh (123kJ) per sol to keep battery temperature within design limits and grants a mass reduction of over 15% if compared with an all-solid insulation.
Further work will concentrate on optimization of electronics insulation, including reduction of space between boxes, the possibility of start-up heaters and of dedicated insulations around the single boxes.
- Abstract document
- Manuscript document
IAC-07-C2.7.01.pdf (🔒 authorized access only).
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