No abstract

This paper addresses the capturing control problem of a plug-and-play modularized dragfree spacecraft system, including two spherical proof masses, where the performance constraints, collision risk, uncertain model parameters, unknown external disturbances, and limited communication are considered simultaneously. First, a nonlinear relative dynamics of spherical proof masses with respect to spacecraft is formulated for the capture process. Second, two different prescribed performance event-triggered robust collision-free capturing control strategies are developed to capture the free-floating proof masses successfully. Suppose only the performance metrics on the relative position are considered, and an event-triggered adaptive terminal sliding mode capturing controller is implemented to achieve the capture process within a finite time. Suppose more performance constraints, such as the user predefined capture duration and the performance bounds on both the relative position and the relative velocity, are taken into account, and an event-triggered appointed-time prescribed performance capturing controller is proposed to solve the above issues. In particular, an artificial potential function is utilized to avoid the collision, and a relative threshold event-triggered rule is employed to save the communication source between the controller and the actuator without any Zeno behaviour. The simulation results demonstrate the efficacy and superiority of the proposed method.

The drag-free satellites, being space-borne ultrahigh precise measurement platforms, have played irreplaceable roles in a great number of space science missions such as navigation, earth science, fundamental physics, and astrophysics. Most of these missions have to be performed based on the satellites placed with double cube test-masses, which makes the satellite layout and control strategy be more complex. This paper investigates the orbit keeping control problem of a class of low Earth orbit drag-free satellites with double cube test masses. A disturbance observer-based composite control method is proposed, which consists of an extended sliding mode observer and the tube-based robust model predictive control approach. In this design, the observer is proposed to estimate the relative position and velocity of the satellite and the external space disturbance force. A tube-based robust model predictive control scheme is then developed to stabilize the satellite orbit control systems in the presence of actuator saturation, state constraints, and additive stochastic noises. Finally, a simulation example is presented to demonstrate the efficacy and superiority of the proposed orbit control method.