Drag-Free Control Design for the ST7 Disturbance Reduction System Flight Experiment

Abstract

* Senior Aerospace Engineer, Flight Dynamics Analysis Branch, Code 595, Senior Member AIAA. † Associate Branch Head, Flight Dynamics Analysis Branch, Code 595, Senior Member AIAA. ‡ Aerospace Engineer, Flight Dynamics Analysis Branch, Code 595, Member AIAA The ST7 Disturbance Reduction System (DRS) is tasked to maintain the spacecraft’s position with respect to two free-floating test masses (better than 10nm/√Hz along the sensitive axis) while limiting the residual accelerations of those test masses to below 3x10-14 (1 + [f/3 mHz]2) m/s2/√Hz over the frequency range of 1 to 30 mHz. This paper describes the design and analysis of control systems for the 18-DOF mode of the ST7-DRS. This mode is the dual drag-free mode (nominal mission mode) in which dragfree control is used to establish drag-free motion of both test masses in the measurement band. The designs for the spacecraft attitude control system (ACS), drag-free control system (DFCS), and suspension control system of the test masses are included. The nominal performance of the system is evaluated and presented in terms of frequency and time domain results. It is shown that the current design meets all requirements with margins.