NEW PULSE-MODULATION TECHNIQUE FOR GUIDANCE AND CONTROL OF AUTOMATED SPACECRAFT

A comprehensive approach to problems such as automated on-orbit rendez vous and soft landing on a planetary surface is presented for spacecra ft employing pulse-operated (on-off) propulsion systems. Using a techn ique derived from robust control theory, a new class of guidance algor ithms that modulate the duration and frequency of thruster firings Is developed. These algorithms allow analytical characterization of trans ient errors, limit cycle deadband, and the set of possible terminal co nditions in the design process, without the use of dynamic al approxim ations such as linearization. with this approach, the desired performa nce is ensured in the presence of dynamical modeling errors with known bounds; the effects of navigational errors can be minimized to the ex tent that they can be bounded, A realistic application is illustrated via computer simulation of a hypothetical mission scenario, in which a robotic spacecraft equipped with an aided-inertial guidance system so ft lands on the planet Mars.