Pulse-modulated control synthesis for a flexible spacecraft

The describing function method is employed for the nonlinear control analysis and design of a flexible spacecraft equipped with pulse-modulated reaction jets. The method provides a means of characterizing the pulse modulator in terms of its gain and phase for structural mode limit-cycle analysis. Although the describing function method is inherently inexact and is not widely used in practice, a new way of utilizing it for practical control design problems is presented. It is shown that the approximations inherent in the method can be accounted for as a modeling uncertainty for the nonlinear control robustness analysis. The pulse-modulated control system of the INTELSAT 5 spacecraft is used as an example to illustrate the concept and methodology developed in the paper.