On-Axis Optical Bench for Laser Ranging Instruments in Future Gravity Missions.

Yichao Yang,Jianjun Jia,Juan José Esteban Delgado,Daikang Wei,Miguel Dovale Álvarez,Kohei Yamamoto,Gerhard Heinzel,Vitali Müller

doi:10.3390/s22052070

Abstract

The laser ranging interferometer onboard the Gravity Recovery and Climate Experiment Follow-On mission proved the feasibility of an interferometric sensor for inter-satellite length tracking with sub-nanometer precision, establishing an important milestone for space laser interferometry and the general expectation that future gravity missions will employ heterodyne laser interferometry for satellite-to-satellite ranging. In this paper, we present the design of an on-axis optical bench for next-generation laser ranging which enhances the received optical power and the transmit beam divergence, enabling longer interferometer arms and relaxing the optical power requirement of the laser assembly. All design functionalities and requirements are verified by means of computer simulations. A thermal analysis is carried out to investigate the robustness of the proposed optical bench to the temperature fluctuations found in orbit.

Highlights

The Gravity Recovery and Climate Experiment (GRACE) mission [1], in orbit fromMarch 2002 to the end of its science mission in October 2017, was a joint mission of the National Aeronautics and Space Administration (NASA) and the German AerospaceCenter (DLR)
Earth’s varying gravity field, the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission [2] was launched in May 2018, again as a US–Germany collaboration
This beam is tilted in the pitch and yaw degrees of freedom to simulate angular motion of the S/C around its c.m.; The RX beam is propagated through the setup, and it is interfered with the locally generated reference beam (LO) beam whilst the fast steering mirror (FSM) is being actively controlled using differential wavefront sensing (DWS) loops to obtain optimal RX-LO overlap at the detectors

Summary

Introduction

March 2002 to the end of its science mission in October 2017, was a joint mission of the National Aeronautics and Space Administration (NASA) and the German Aerospace. This allows inference of the misalignment of the receiver S/C relative to the inter-satellite line-of-sight This information is used in the LRI to actuate on the pointing of the transmitted beam to the remote S/C, and can be used in future missions to actuate in the attitude of the local S/C, in order to enhance the optical link power, keep the link stable, and minimize secondary noise sources. In the GRACE-FO mission, the LRI OB followed an “off-axis” design [13], where the receiving (RX) light and the transmitting (TX) light propagate into and out of the OB through separate apertures, namely the RX and TX apertures, and follow different paths along the OB This type of design can lead to instruments with fewer optical components compared to the “on-axis” topology, where the RX and TX beam paths coincide, and the OB features a single aperture (Figure 1).

On-Axis LRI Optical Bench Design

Optical Simulations

Summary and Outlook