Robust Nonlinear Adaptive Relative Pose Control for Cooperative Spacecraft during Rendezvous and Proximity Operations

This brief addresses the relative pose control for cooperative spacecraft during rendezvous and proximity operations with parametric uncertainties based on the noncertainty equivalence approach. The relative position dynamics modeled in the target's line-of-sight coordinate frame and attitude synchronized dynamics described by modified Rodrigues parameters are formulated as the typical Euler-Lagrange form to facilitate six-degrees-of-freedom relative pose control design. Due to the immersion and invariance adaptive control approach, unknown parametric uncertainties are compensated online and the transient performance of closed-loop states can be regulated by both controller and estimator parameters. Asymptotic convergence of the relative position and relative attitude is proved rigorously in the Lyapunov framework. Numerical simulation of the nonlinear adaptive control scheme for spacecraft line-of-sight rendezvous and proximity operations is also presented to highlight potential closed-loop performance improvements compared with the application of classical certainty equivalence-based adaptive controllers.