Relative motion control for autonomous rendezvous based on classical orbit element differences

Relative motion control strategies for autonomous rendezvous operations in a near-circular orbit are presented in this paper. The relative motion equations described by classical orbit element differences are adopted and the periodic drift in along-track motion is deduced from the along-track motion equation. The control strategies in two different measurement cases are designed based on the periodic characteristics of relative motion. In the first case, the measurements of relative range and line-of-sight angles are available to estimate the relative position and velocity. The three-axis impulsive control strategies to adjust along-track, radial, and cross-track motions are designed using Gauss's perturbation equations. In the second case, only fine-of-sight angles are available. An iterative algorithm is presented to estimate the along-track motion using only the azimuth angle to obtain the impulsive changes to adjust the along-track motion. Numerical simulations are undertaken to verify the control strategies proposed. The results indicate that 1) three-axis motions can be controlled accurately when the relative range and line-of-sight angles are available and 2) the iterative algorithm is valid for along-track drift control when only line-of-sight angles are available.