Drag-free control methods for space-basedgravitational-wave detection

Abstract

In order to meet the requirements of “high precision” for space-based gravitational-wave detection, the design of control systems for a drag-free satellite is researched from the point of view of dynamics and control theory. Based on the LISA Pathfinder mission, the drag-free satellite contains two test masses, and its control system includes an attitude control loop, a drag-free control loop, and an electrostatic-suspension control loop. Drag-free control technology is employed for the drag-free control loop, where a test mass is in a state of free fall, and the satellite platform is controlled to follow the test mass “strongly” in order to achieve a high-level microgravity of the satellite platform and the test mass. Active vibration-isolation control technology is applied in the electrostatic-suspension control loop, where the other test mass is controlled to follow the satellite platform “weakly” and is isolated from vibrations of the satellite platform, so as to achieve high-level microgravity of the test mass and avoid collisions between the test mass and the satellite platform. The frequency-domain characteristics of the two control technologies are analyzed, assuming them to be based on the PID control algorithm. A set of formulas for calculating the parameters for the PID controllers are established, so that the parameters can be determined quickly according to the performance requirements for these controllers. On this basis, a control strategy is proposed and the PID controllers are designed. The effectiveness of the control strategy and the accuracy of the controller parameters are verified through numerical simulations.