Closed-loop dynamics and disturbance propagation mechanisms of a drag-free control ground-based validation system

In space-based gravitational wave detection missions and other space experiments utilizing the ultra-static and ultra-stable spacecraft, the drag-free control system (DFCS) plays a key role in maintaining the free-falling motion of the test masses (TMs). However, high-precision ground-based verification of DFCS faces a great challenge in suppressing and evaluating multiple disturbances and noises accurately. To this end, this article first proposes an active disturbance rejection controller for TM with a two-stage torsion pendulum. The dual-loop scheme with robust control approach is introduced for this underactuated pendulum system, which significantly reduces the impact of seismic noise on TM. Subsequently, on the basis of suspended TM and the controlled Stewart platform, the closed-loop dynamics of a ground-based DFCS validation system is conducted. The emulating capability of this system for in-orbit flight dynamics is analyzed. Furthermore, complex propagation mechanism models of multiple disturbances and noises are built, and residual acceleration and tracking performance are precisely evaluated.?Finally, numerical simulations are performed to validate the theoretical work. The presented work provides a design and analysis methodology for ground-based verification of DFCS.