ESA GNC Conference Papers Repository
Robust Controller Design and Testing of an Active Isolation for a Payload-Launcher System
Payloads on top of launchers are subject to different sources of disturbances during the flight. The main critical loads are coming from the ignition of the solid rocket motors, the pressure oscillations inside the solid propellant booster and from the separation of the boosters. In order to reduce the dynamic loads acting on the payloads at minimum by a factor of 4, an active payload adapter is proposed to be integrated below the payload. The anticipated system is a conical truss structure consisting of up to 24 active struts, each driven by a piezo- electric actuator. Such a system has been designed for the ARIANE 5 launcher. The performance of the active payload adapter has been verified by analysis by integrating a mathematical model of the active payload adapter in the launcher dynamic model. The performance could be verified for harmonic as well as for transient load case. A prototype of one piezo-electric active strut has been developed, respecting ARIANE 5 launcher design requirements. For the performance verification of the active strut and the corresponding control law a breadboard has been designed and built. First tests demonstrated the performance active strut and the control law in an open loop, however, the performance of the closed loop could not be demonstrated. An improvement of the control law was necessary. The paper describes the system identification performed on test data coming from tests performed with the breadboard, the modeling of the breadboard in Simulink/SimMechanics and the design of the improved control algorithm. Three different control laws are analyzed. The first one is physically motivated and shows good nominal performance but lacked robustness. The H-infinity loop shaping based on normalized co-prime factorization is used to robustify the original law. A further step of improvement is achieved with a u-synthesis approach.