Adaptive Control for Flexible Space Structures with Measurement Noise

This paper addresses the problem of measurement noise in the design of adaptive controllers for large space structures. It is shown by simulation that although the well known "fix" based on introducing leakage terms in the adaptive law is successful in eliminating drift in the adaptive gains, the overall control demand remains unrealistically high. In order to reduce the control demand, it is necessary to attenuate the noise by introducing filters at key positions in the adaptive configuration. However, arbitrary choice and placement of noise filters is dangerous since filter lags tend to cause instabilities in the adaptation loop. This phenomenon is verified by simulation. The main result of this paper is a general theory for introducing noise filters into the adaptive controller so as to effectively suppress measurement noise, while insuring global stability of the adaptive algorithm. This result utilizes the new concept of a "branch filter" which allows filtering of the output error without introducing phase lag into the adaptive loop. The effectiveness of the proposed methods are demonstrated by simulation on an adaptive payload articulation control for a Space Station model.