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Astrophysics, Instrumentation and Methods for Astrophysics, astro-ph.IM, Physics, Geophysics, physics.geo-ph
Abstract:
The Laser Ranging Interferometer (LRI) instrument on the Gravity Recovery and
Climate Experiment (GRACE) Follow-On mission has provided the first laser
interferometric range measurements between remote spacecraft, separated by
approximately 220 km. Autonomous controls that lock the laser frequency to a
cavity reference and establish the 5 degree of freedom two-way laser link
between remote spacecraft succeeded on the first attempt. Active beam pointing
based on differential wavefront sensing compensates spacecraft attitude
fluctuations. The LRI has operated continuously without breaks in phase
tracking for more than 50 days, and has shown biased range measurements similar
to the primary ranging instrument based on microwaves, but with much less noise
at a level of $1\,{\rm nm}/\sqrt{\rm Hz}$ at Fourier frequencies above 100 mHz.