ESA GNC Conference Papers Repository
Gain-Scheduled and LPV Control for Re-Entry Vehicle
Many in house researches have been performed, and are still under development, in ASTRIUM Space Transportation to develop 3 degrees of freedom attitude control law for lifting body re-entry vehicle during hypersonic flight phase. The objective of this paper is twofold; first, we briefly present research results based on adaptation of gain scheduled control law that was developed for ARD capsule to lifting body re-entry control; then, we present results of LPV theory applied to re-entry vehicle control. Main interest of this so-called ARD-like gain scheduled control law is that all control gains are computed using analytic relations based on simplified models that may be implemented on-board. Gain scheduling is reduced to 12 parameters and ARD-like control law is robust to flight conditions. However, despite its robustness, such a control law still needs iterative tuning process to respect all performance and stability objectives for re-entry vehicle which characteristics are both varying along the flight and present huge domain of uncertainties. Among promising control method, LPV seems perfectly suited for such kind of problem and studies are on going to improve re-entry control design. First step of this research work on LPV theory applied to re-entry vehicle control was based on control of the simplest case (longitudinal motion). We have focused on the analysis of existing LPV modelling, synthesis and analysis tools in order to select the best suited ones for re-entry vehicle control. Four longitudinal control laws using polytopic modelling and LPV control design criteria based on pole placement feasibility problem and/or H? optimization problem are presented and compared to ARD-like existing gain scheduled control law for European re-entry vehicle. As ARD-like gain scheduled controller has independent longitudinal and lateral/directional control it means that LPV design for longitudinal control part can be integrated into the existing controller for testing. Originality of this work is to develop, compare and validate various modelling and synthesis approaches in an environment going from simple test cases to real validation tools (time domain and frequency domain). Results are satisfactory and should be extended to lateral control design, couplings terms control and nonlinear compensation. Studies are also still on going to evaluate LFT LPV in discrete time design.