Mass Change Technology Developments for Next Generation Laser Ranging Interferometry

The Laser Ranging Interferometer (LRI) on the Gravity Recovery and Climate Experiment - Follow-On (GRACE-FO) mission has exceeded all expectations and proven to be a hugely successful technology demonstration (Abich, 2019), providing reliable and highly precise ranging measurements (~100x better than the microwave ranging system). Based on this performance, LRI has been recommended by the Mass Change study team to replace the microwave ranger as the primary instrument on the anticipated Mass Change Designated Observable (MCDO) mission to continue the data legacy of GRACE and GRACE-FO. To support LRI readiness as primary instrument for MCDO, NASA is funding technology development studies investigating three areas that could improve the quality and/or reliability of LRI measurements: (1) Laser frequency combs for enhanced LRI, (2) redundancy concepts, and (3) cavity improvements. Each study is described below; we will present the results of these technology study areas and recommendations to future gravity missions.

Laser Frequency Combs for Enhanced LRI (1): We investigated the application of frequency combs to enhancing the dynamic range of the intersatellite distance rate of change measurement, as well as a proposed solution to resolve the scale factor ambiguity of optical interferometry with a single wavelength laser.

Redundancy Concepts (2): We considered the critical components in the optical path of the LRI and proposed ideas for improving redundancy and reliability for the optical bench assembly and triple mirror assembly.

Cavity Improvements (3): We evaluated the possibility of a vacuum tight inner can for the laser reference cavity assembly and completed an assessment of both implemented changes and recommended improvements to the optical cavity design.