Position Based Impedance Control on Space Docking

In this paper, a Force Control Solution on Space Docking is proposed providing low impact and safe connection between space modules in different missions. In this solution, the force control concept has been employed along with traditional position control in space docking process  because the interaction forces between those parties involved (the chaser spacecraft and the target) in this phase are quite significant. Among the available methods in the force control field, Position Based Impedance Control strategy has been used as this strategy controls neither position nor force but the dynamic relationship between relative positions and interaction forces which is used widely in robotic science; however, other methods exhibit instability problems at the connection stage due to change between the position controller and the force controller. As we know, there are different kinds of space vehicles with particular connection scenarios and various connection latches; in order that, each vehicle demands specific interaction force in the connection phase; therefore, Position Based Impedance Control combined with Hill's Equations, which is used for space docking in circular orbit as relative position, is presented to be applied to different docking strategies and mechanisms. For the position controller that lies into Position Based Impedance Control structure, a nonlinear-PID Controller has been utilized possessing an anti-windup property and good capability to track the reference signal. The results show that we can ensure low impact connection by modifying target impedance coefficients in addition to precise position control.