ADAPTIVE ATTITUDE-TRACKING CONTROL OF SPACECRAFT WITH UNCERTAIN TIME-VARYING INERTIA PARAMETERS

Adaptive control schemes for spacecraft attitude tracking are abundant in controls literature. However, very few are designed to guarantee consistent performance for a spacecraft with both rigid and non-rigid (time-varying) inertia components. Since inertia matrix changes are a common occurrence due to phenomena like fuel depletion or mass displacement in a deployable spacecraft, an adaptive control algorithm that takes explicit account of such information is of significant interest. In the present investigation, a certainty-equivalence based adaptive control scheme is proposed for the attitude control of a spacecraft characterized by a time-varying inertia matrix with known time-variation but unknown bounds. A smooth-projection scheme is implemented to ensure that parameter estimates stay bounded within a convex set. The variable inertia components may have time and/or state dependencies, or may be purely input dependent. Detailed derivations of the control law are provided along with a thorough analysis for the associated stability and error convergence properties. In addition, numerical simulations are presented for a spacecraft experiencing fuel depletion to highlight the performance benefits when compared with an adaptive control scheme that does not account for inertia variations.