RESUMO
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 degrees of freedom two-way laser link between remote spacecraft succeeded on the first attempt. Active beam pointing based on differential wave front 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 nm/sqrt[Hz] at Fourier frequencies above 100 mHz.
RESUMO
The Ground-Based European Nulling Interferometry Experiment (GENIE) is intended as an Earth-based precursor for the European Darwin mission that will prepare the Darwin science program and demonstrate the required technology at system level. We propose a compact nulling interferometer design consisting of a two-telescope aperture configuration, an optional split-pupil add-on, and only four active control loops for counteracting environmentally induced disturbances. We show by simulation that the proposed instrument is able to detect, within a few minutes of observation time, exo-zodiacal dust clouds around Sunlike stars at 20 parsecs that are 20 times stronger than the local zodiacal dust cloud density.