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There are a number of approaches to advanced guidance and control (

A problem of sliding mode control design for a SISO nonlinear system with unmodeled actuator of the 2 nd order is considered. A design methodology based on nonlinear dynamic sliding manifold (NDSM) is proposed to attenuate the chattering phenomenon affecting sliding-mode-controlled plants in presence of unmodeled dynamics. The controller utilizes the pass filter characteristics of the physical-actuating device to provide a smoothing effect on the discontinuous control signal. The methodology proposed allows for maintaining the sliding mode on the surface designed without actuator dynamics being taken into account. This goal is achieved via auxiliary dynamic sliding manifold design, the 2-sliding mode on the auxiliary NDSM provides for finite-time-convergence of the sliding surface quantity to zero. The proposed controller design is based on the relative degrees of the plant and the unmodeled actuator dynamics and the ranges of the uncertainties of the plant and actuator.

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Trajectory control for a reusable launch vehicle (RLV) is considered for two operational modes: reentry and launch modes are considered. Decentralized sliding mode controllers are designed to achieve the de-coupled asymptotic tracking of Euler angles' profiles upon plant uncertainties and externul disturbances. Two sliding mode control strategies are investigated: direct Euler angles' profiles tracking and angular rates tracking in combination with a coordinated turn inversion. Efectiveness of the sliding mode controllers is confirmed hy simulations of a trajectory tracking for the WBOOl RLV studied at NASA Marshall Space Flight Center. perturbations lead to the payload weight reduction launched to the orbit. From the control point of view it requires development of robust control algorithm that can automatically adjust to some changes in mission specifications and the operating environment. Various linear [3] and nonlinear guidance and trajectory control algorithms [4] were used. One of the effectme control strategies successfully applied in nonlinear systems is the Sliding Mode Control [S-71. The main advantage of the Sliding Mode Control is that the system's state response remains insensitive to parameter variaitions and disturbances in the sliding surface. The W13001 RLV trajectory tracking is addressed via the dle-coupling sliding mode control [S-91. Problem Formulation 1. IntroductionThe current research in developing a next generation launch vehicle is focused on reusable launch vehicles (RLV). The one-stage-to orbit RLV developing in X-33 project will replace the aging Space Shuttles at the beginning of the next century [l]. One proposed configuration for a RLV vehicle is a vertical-takeoff, horizontal-landing wing-body single-stage vehicle (WB001) [2]. The reentry control problem consists in automatic controlling the atmospheric entry trajectory which can be precalculated or generated in current time by guidance algorithms. The launch control problem consists of automatic tracking the given launch trajectory. For present launch systems the launch trajectory has to be remodeled for each mission, depending on the weight of the payload as well as the prescribed orbit and safety margins. Errors in optimal launch trajectory tracking caused by variousThe following model of a rigid RLV is taken. Orientation equations of a rigid RLV are given 1.in terms of Euler angles w, 0, cp (b = p + q tan0 sincp + r tan0 cos9The equations of an RLV rotational motion are q . 1 = -[-pr(J, -JU)-JX(p2 -r2)+ MI]