Interferometry for ELITE

The purpose of the interferometry in the ELITE mission is to measure the differential displacement between the two inertial sensors mounted in the spacecraft. It will thus provide an independent verification of the performance of the inertial sensors. The interferometric system should function under all the likely operating modes of the inertial sensors. In one likely mode all the suspension forces in one of the sensors would be switched off and the sensor allowed to drift freely over perhaps 10s of microns. Here we present a system to achieve this measurement and give some of the constraints on the laser performance and spacecraft environment that must be satisfied in order to provide a useful measurement.