Robust control of a booster vehicle using Hinfinity and SSV techniques

The authors consider three different versions of a candidate booster vehicle design. The vehicle is difficult to control due to an aerodynamic instability, lightly damped flex modes a decade beyond the aerodynamic instability, and lightly damped slosh modes near the instability. The latter are almost uncontrollable due to vehicle geometry. The task is to assess the degree of design difficulty associated with the presence or absence of propellant slosh baffles in the LOX and LH2 fuel tanks. An open loop analysis of the design difficulty is first performed, and then controllers are synthesized using the McFarlane-Glover (MFG) and the structured singular value (SSV) synthesis methodologies. Robustness is analyzed using SSV techniques for complex, real, and mixed uncertainty structures.