Materials Testing Activities within ESA in Support of Future Inner Solar System Missions
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Materials Testing Activities within ESA in Support of Future Inner Solar System Missions Christopher O. A. Semprimoschnig, Stan Heltzel, Marc van Eesbeek Materials Physics and Chemistry Section European Space Research and Technology Centre (ESTEC), European Space Agency (ESA), Keplerlaan 1, PO Box 299, NL-2200 AG Noordwijk, The Netherlands Correspondence Email: [email protected]
ABSTRACT In this paper the ESA internal approach regarding the assessment of materials for inner solar system missions is presented. A main part of the work is devoted to the assessment of thermal control materials and space environmental testing at elevated temperature. As these materials are the most exposed it is important to understand how they will interact with the relevant space environment at elevated temperature. Driving parameters for materials degradation are discussed and on-going testing efforts are described. An important input parameter for thermal models is the knowledge of the end of life values for the thermooptical properties as these determine the equilibrium temperatures. In certain cases end of life testing needs to be done when the uncertainty of extrapolation is too high. 1. Introduction Several ambitious science missions of ESA (European Space Agency) plan to reach the inner solar system. Venus Express aims to explore Venus, BepiColombo Mercury and Solar Orbiter shall investigate the sun at an unprecedented small distance. This environment poses severe challenges to materials. Beside the environment, schedule is an additional driver for materials assessment as in the case for the Venus Express mission. The launch date of 2005 for this mission makes it clear that only readily available materials can conceived to be used and that looking into materials that are in the development phase is prohibitive. The other two missions are planned to launch after 2010 and therefore some materials developments can be considered. For all three missions however it is paramount to perform a comprehensive and as realistic as possible space environmental testing activity. This includes knowledge of the relevant space environment, understanding its effects on materials properties and finally its simulation. The latter is often hampered by the fact that not all environmental effects can be simulated in one facility and it is therefore important to know what drives materials properties degradation. In this paper our approach regarding the challenges for the assessment of materials for inner solar system missions will be described. As mentioned before temperature is one driver for testing and its complex influence on space materials is schematically shown in Fig. 1. The second important driver for inner planetary missions is the increased radiation intensity. High temperature (in particular in combination with radiation) can lead to several physicochemical degradation of materials which can lead to a degradation of the functional properties of materials. Examples are for instance the stability of thermo-optical pr
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