Abstract: A universal improved nonlinear longitudinal model of a hypersonic vehicle developed by the Langley lab is adopted. For its I/O linearized model, a sliding mode controller is designed. This method can solve the uncertainty problem and it is insensitive to disturbances. The index approach law used to drive the sliding mode to reach the sliding surface is adopted to eliminate the quiver. The simulation results for tracking the height step and velocity step order at cruise condition show that the sliding mode controller with index approach law acquires satisfying tracking ability and strong robustness. The controller can not only track the single height step order or velocity step order accurately, but track the height step order and velocity step order together fleetly with zero error. In addition, the sliding controller with index law is better than the one with sign function in tracking speed and precision. Another result is also proved that the index approach law can eliminate the quiver perfectly.

Key words: hypersonic vehicle, sliding mode control, approach law, robustness