Composite Adaptive Spacecraft's Orbit Control and Asteroid's Parameter Estimation by Integral Excitation

Abstract

This article develops a composite adaptive control system for spacecraft's orbit control around uniformly rotating asteroid and asteroid's parameter estimation. The mass and moment of inertia matrix of the asteroid are not known. First, a nonlinear adaptive law is designed for orbit control. Second, a state predictor is constructed and an adaptation law is derived for the parameter estimation. Third, two additional update laws are designed using (i) a static parametric model and (ii) a modified static parametric model of the spacecraft dynamics based on the gradient algorithm. Fourth, a composite identifier is developed by combining these three parameter estimation laws. Furthermore, it is shown that the closed-loop system is asymptotically stable by the Lyapunov stability analysis. The novelty of the composite identifier lies in inclusion of a regressor integral term in the parameter update law. Interestingly, this regressor integral component contributes a non-increasing negative semi-definite function of the parameter error in the derivative of the Lyapunov function. Therefore, the composite identifier achieves enhanced parameter excitation and parameter error convergence properties. Fifth, simulation results are presented for the orbit and hovering control in the vicinity of Ida. These results show precise trajectory control and parameter estimation.