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This project aims to produce a space-qualified coated cover glass for telecoms use. Cover glasses are routinely used to protect photovoltaic cells from the space radiation environment, which prolongs the life of the spacecraft. Cover glasses also provide a performance enhancement, allowing optimal efficiency of the solar array.
In 2009 Qioptiq took over the manufacturing of glass material for cover glasses. This had previously been subcontracted to Pilkington Special Glass. In order to ensure that the Qioptiq manufacturing process maintains space qualification of the glass material, a series of tests have been devised in accordance with ECSS-E-ST-20-08C. These tests will ensure that the glass material from the first melt at Qioptiq is equivalent to previous Pilkington glass melts. Further testing will ensure that the final anti-reflection coated cover glass that is commonly used on telecom satellites retains its space qualified status.
This project addresses the need for protection from the space environment for the current and upcoming generations of solar cells. Two companies worldwide currently provide the majority of cover glasses for space use, so continuity of cover glass availability is critical for the space industry.
The principal benefit of this programme is the continued supply of space-qualified cover glass components, securing the ability to use photovoltaic cells on spacecraft.
Cover glasses typically range from 50 microns to 500 microns in thickness. The thickness is a trade-off between mass and protection against particulate radiation such as protons, and must be selected according to the particular space environment of the mission. Cover glasses are manufactured to the same shape as the underlying solar cell, but slightly oversized to protect against grazing-angle proton ingress to the cell.
The particular glass type manufactured by Qioptiq is formulated to be more stable under UV, with an absorption edge that prevents UV from reaching the solar cell. The glass has a coefficient of thermal expansion that allows it to behave similarly to the solar cells under thermal cycling.
A variety of thin film coatings are routinely applied to the cover glass, which are tailored to maximise available light over the active spectral range of the cell. Coatings can also be used to block non-useful radiation, thereby reducing solar absorption and consequently cell temperature.
Completed. Equivalence between old- and new-melt glass was successfully demonstrated. The coated cover glass was deemed by ESA to have achieved space qualification to ECSS-E-ST-20-08C, and also complies with the specifications of Qioptiq’s European customers.