An adaptive nonlinear control strategy is proposed for a pursue spacecraft in proximity operations on a non-cooperative target in space. The relative position vector between the pursuer and the target is required to direct towards the docking port of the target while the attitude of the two bodies must be synchronized. This formulation results in a highly nonlinear, highly coupled and uncertain system that poses a challenging control problem. The proposed relative pose model between the two spacecraft are expressed as the classical Euler-Lagrange equations to facilitate and simplify the relative pose controller design. An integrated controller of relative translation and relative rotation is formulated by using adaptive nonlinear state feedback control. The parametric uncertainties, unknown coupled dynamics and bounded external disturbances are compensated online with the norm-estimation-based adaptive update laws. It is proved via Lyapunov stability theory that the tracking errors of relative position and relative attitude are uniformly ultimately bounded. Numerical simulation demonstrates the effectiveness of the proposed controller.
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