Noncertainty-equivalence adaptive attitude control of satellite orbiting around an asteroid

Abstract

The development of an adaptive control system for the attitude control of spacecraft orbiting around uniformly rotating asteroids is the subject of this paper. It is assumed that inertia parameters of spacecraft, and zonal and sectorial harmonic coefficients associated with the gravitational field of asteroid are not known. The objective is to control the Euler (yaw, pitch, roll) angles of the spacecraft along prescribed reference attitude trajectories. Based on the immersion and invariance methodology, a noncertainty-equivalence adaptive (NCEA) control law for the trajectory control of the Euler angles is derived. The design is completed in two steps of a backstepping design process, and filtered signals are used for synthesis. Unlike traditional certainty-equivalence adaptive systems, the estimated parameters of this NCEA law consist of certain nonlinear algebraic functions as well as partial estimates, obtained by integral adaptation law. By the Lyapunov analysis, it is shown that in the closed-loop system, the yaw, pitch, and roll angles trajectory tracking errors asymptotically converge to zero. For the purpose of illustration, attitude control of a spacecraft orbiting around 433 Eros asteroid is considered. Simulation results confirm that this NCEA law can accomplish precise nadir pointing attitude of the spacecraft on elliptical prograde and retrograde orbits despite uncertainties in the spacecraft dynamics.