Abstract
BepiColombo is the joint mission of the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA) to explore the planet mercury. The European contributions, namely the mercury transfer module (MTM) and the mercury planetary orbiter (MPO), are both powered by deployable solar arrays. Many materials and technologies are at their limit under the harsh high-intensity, high-temperature (HIHT) conditions of the mission. Synergistic effects like photo fixation and photo enhanced contamination by ultra violet and vacuum ultra violet radiation (UV/VUV) on sunlit surfaces are considered to play an important role in the HIHT environment of the BepiColombo mission.A design verification test under UV/VUV conditions of sun exposed materials and technologies on component level is presented which forms part of the overall verification and qualification of the solar array design of the MTM and MPO. The test concentrates on the self-contamination aspects and the resulting performance losses of the solar array under high intensity and elevated temperature environment representative for the photovoltaic assembly (PVA).
Highlights
A classical approach to predict contamination levels is based on the surface temperature in comparison to the temperature of the outgassing source
On the optical solar reflectors (OSRs) no obvious contamination layer was observed as can be seen in Fig. 5 d
A novel test approach was included in the qualification of solar array materials for the high temperature and high intensity mission BepiColombo
Summary
A classical approach to predict contamination levels is based on the surface temperature in comparison to the temperature of the outgassing source. One explanation for the formation of non-volatile contamination layers is that the adsorbed molecules polymerize to species with longer residence times (= photo fixation). Another mechanism discussed is the photochemical modification of a molecule immediately before it is sticking to the surface leading to a different sticking behaviour (= photo enhanced deposition). One important consequence of this behaviour for solar arrays is the decrease of transmission of the cover glasses which translates into solar cell performance loss Another important consequence is the higher absorbance of thermal control materials e.g. OSRs which has an impact on the overall solar array temperature. The test plan tried to mimic the environmental conditions as far as possible in an on-ground based simulation, and the most relevant material constellations and solar array outgassing sources
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