The Gravity Recovery and Climate Experiment (GRACE) missions rely on inter-satellite interferometry to measure changes in the local gravity of the Earth. These measurements are compared over seasons and years, providing a critical tool for the understanding of large-scale mass transport, in particular the movement of water and ice. The next generation of GRACE-like gravity sensing missions are expected to rely on lasers as the primary instrument.

To enable the use of laser interferometry as the primary science measurement, a new technique will be required to provide long term laser frequency knowledge. This project has focused on the development of a technique based on a phase modulation scheme able to measure laser frequency change over long timescales using measurements of an optical cavity’s free spectral range, using hardware that is predominantly already baselined on the mission. 

This seminar will present the background and mission requirements, proof of concept work, and prototype development. Testing of the technique has shown promising results (see [1], [2]) and additional challenges. The technique has demonstrated performance exceeding the expected mission requirements as well as compatibility with existing flight hardware.

Implementation challenges and future work will also be discussed.