Experimental Demonstration of an On-Axis Laser Ranging Interferometer for Future Gravity Missions

TL;DR

This paper demonstrates a novel on-axis laser ranging interferometer with active beam steering, achieving nanometer accuracy under simulated spacecraft jitter, suitable for future gravity missions.

Contribution

It introduces an on-axis LRI architecture with active beam steering and demonstrates its stability and accuracy in a laboratory setting for gravity applications.

Findings

Pointing stability below 10 urad/√Hz achieved

Carrier-to-noise-density ratio reduced by only 0.14% over 15 hours

Nanometer accuracy in inter-spacecraft ranging demonstrated

Abstract

We experimentally demonstrate a novel interferometric architecture for next-generation gravity missions, featuring a laser ranging interferometer (LRI) that enables monoaxial transmission and reception of laser beams between two optical benches with a heterodyne frequency of 7.3 MHz. Active beam steering loops, utilizing differential wavefront sensing (DWS) signals, ensure co-alignment between the receiving (RX) beam and the transmitting (TX) beam. With spacecraft attitude jitter simulated by hexapod-driven rotations, the interferometric link achieves a pointing stability below 10 urad/$\mathrm{\sqrt{Hz}}$ in the frequency range between 0.2 mHz and 0.5 Hz, and the fluctuation of the TX beam's polarization state results in a reduction of 0.14\% in the carrier-to-noise-density ratio over a 15-hour continuous measurement. Additionally, tilt-to-length (TTL) coupling is experimentally investigated using the periodic scanning of the hexapod. Experimental results show that the on-axis LRI enables the inter-spacecraft ranging measurements with nanometer accuracy, making it a potential candidate for future GRACE-like missions.