LISA Drag-Free Attitude Control System: Robust Stability and Performance Analysis

This paper proposes a robust stability and performance verification of the Drag-Free and Attitude Control System (DFACS) for the Laser Interferometer Space Antenna (LISA) space mission. LISA is a space-based gravitational wave observatory, expected to be launched by the European Space Agency in 2034. LISA was formally adopted by ESA in January 2024 as the third large-class mission of the Cosmic Vision program, marking the transition from the mission conceptual design to hardware development. The mission features a constellation of three spacecraft exchanging bidirectional laser links to perform interferometry: they measure the relative distance variations between free-falling test masses located at far distances. Given the categorical need of obtaining precise measurements, the DFACS plays a key role, since it allows the test masses to move in free-fall conditions, rejecting at the nanoscopic level external disturbances and noises, which can compromise the quality of the scientific measurements. A fundamental issue in this context is to rigorously analyze robust stability and robust performance of the closed-loop system. Based on a previously designed DFACS, in this paper we address this issue by means of mu-analysis. The theoretical analyses are supported by an extensive Monte Carlo campaign, carried out employing a high-fidelity simulator. Both the theoretical analyses and simulations show that the designed DFACS guarantees the desired closed-loop robustness levels.