Test deployment of a Galileo solar wing in Dutch Space’s cleanroom. The completed wings are suspended on specially weighted deployment rigs, to compensate for the presence of gravity the 29 kg wings are not designed to endure. Here alignment testing is performed, to check the wings will unfold in a straight line as planned. Alignment testing involves the use of reference mirrors and theodolites to check the arrays’ straightness, down to a scale of a tenth of a millimetre at wing tip. In orbit, any bad alignment would be felt by the satellite’s attitude control system, and might even reduce a satellite’s operational life.
In practice, these delicate solar wings are folded against the side of their host satellite during launch. Then, once the satellite reaches their target orbit, the solar wings’ hold-down cables are cut using ‘thermal knives’. They then gradually unfold over a few minutes due to springs in the hinges of the multi-panel wings.