IN-ORBIT MONITORING AND READJUSTMENT OF SATELLITE STRUCTURES

Monitoring of satellites and its instruments means measurement of temperatures, displacements and displacement fields and also strain. Interesting sensors are Bragg grating sensors implemented in optical fibres, which can be mounted and integrated onto or into materials, respectively. Their advantages are the relatively high number of sensors which can be multiplexed within a single fibre, their electromagnetic insensitivity and low drift. Once integrated, these sensors might also be used for monitoring the curing of fibre composite structures, as well as during structural testing. On the other side, special effort has to be taken to generate and evaluate the emitted and received light, and transfer it to electrical signals. Some examples, such as temperature sensing in panels and reflectors will be discussed. For the latter, special emphasis is put also on determination of displacement fields from a set of measured strain data. This process relies on a combination of analytical and measured data such as eigenvectors and other types of vectors approximating the displacement field to be determined via proper strain-displacement transfer matrices. In addition to monitoring, in some cases re-adjustment of components is also in order. This for example holds for shape control and possibly also reshaping of reflectors. This leads to a highly coupled design task where structural and control designs highly interact with number and positioning of actuators. This will be shown for a refocusing problem for an antenna subreflector, where radially varying reflector thickness distribution leads to significantly higher shape accuracy after reforming as compared to constant thickness distribution