Analysis of GRACE Follow-On Laser Ranging Interferometer derived inter-satellite pointing angles

TL;DR

This paper analyzes inter-satellite pointing angles derived from the Laser Ranging Interferometer on GRACE-FO, comparing them with traditional attitude data, and explores their potential as a new attitude measurement source.

Contribution

It introduces a method to derive spacecraft attitude angles from LRI FSM commands and compares them with existing star camera and IMU data, highlighting their correlation and potential.

Findings

LRI derived angles correlate with star camera and IMU data.

Temperature variations influence laser-based attitude measurements.

LRI data offers a new potential attitude measurement source.

Abstract

Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) was launched on May 22, 2018. It carries the Laser Ranging Interferometer (LRI) as a technology demonstrator that measures the inter-satellite range with nanometer precision using a laser-link between satellites. To maintain the laser-link between satellites, the LRI uses the beam steering method: a Fast Steering Mirror (FSM) is actuated to correct for misalignment between the incoming and outgoing laser beams. From the FSM commands, we can compute the inter-satellite pitch and yaw angles. These angles provide information about the spacecraft's relative orientation with respect to line-of-sight (LOS). We analyze LRI derived inter-satellite pointing angles for 2019 and 2020. Further, we present its comparison with the pointing angles derived from GRACE-FO SCA1B data, which represents the spacecraft attitude computed from star cameras and Inertial Measurement Unit (IMU) data using a Kalman filter. We discuss the correlations seen between the laser based attitude data and the spacecraft temperature variations. This analysis serves as the basis to explore the potential of this new attitude product obtained from the Differential Wavefront Sensing (DWS) control of a FSM.