Laser metrology for a next generation gravimetric mission

Within the ESA technology research project "Laser Interferometer High Precision tracking for LEO", Thales Alenia Space Italia is developing a laser metrology system for a Next Generation Gravimetric Mission (NGGM) based on satellite-to-satellite tracking. This technique is based on the precise measurement of the displacement between two satellites flying in formation at low altitude for monitoring the variations of Earth’s gravity field at high resolution over a long time period. The laser metrology system that has been defined for this mission consists of the following elements: • an heterodyne Michelson interferometer for measuring the distance variation between retroreflectors positioned on the two satellites; • an angle metrology for measuring the orientation of the laser beam in the reference frames of the two satellites; • a lateral displacement metrology for measuring the deviations of the laser beam axis from the target retro-reflector. The laser interferometer makes use of a chopped measurement beam to avoid spurious signals and nonlinearity caused by the unbalance between the strong local beam and the weak return beam. The main results of the design, development and test activities performed on the breadboard of the metrology system are summarized in this paper.