Attitude Control Of Mars Probe Based On Sliding Mode Variable Structure

Mars probing is an important part of human universe exploration, having important scientific value. A major mean to explore Mars is to observe Mars close using Mars probe. In the Mars probe control system, the attitude control subsystem plays a significant role. Based on the Mars probe, this thesis mainly researches the attitude control problem of the probe.The Mars probe in the steady-state flight needs to complete sun-pointing, nadir-pointing and Mars-pointing missions including attitude maneuvering and attitude tracking. The thesis first narrates attitude description methods like Euler angles, quaternion and MRP, then gives the attitude dynamics equation and the attitude kinematics equation of the Mars probe. It also contains frequently-used time systems and simplified two-body orbit model.Then, the traditional linear PD control law is improved. A nonlinear PD control law is designed. The proportion parameter of the nonlinear PD controller is changeable for the purpose of shortening the accommodation time and reducing the overshoot. The proportion parameter is larger when the attitude deviation is larger and less when the attitude deviation is less.For the Mars probe attitude maneuvering problem and attitude tracing problem with uncertain rotational inertia coefficients, sliding mode variable controllers are designed. A time-variable sliding mode surface is used in order to take full advantage of the robustness of sliding mode movement. The initial states of the system are on the sliding surface by adjusting the parameters of the time-variable sliding surface. Rotating or translating the sliding surface on the basis of the initial states of the system, the time-variable sliding mode surface approaches a linear sliding mode surface to guarantee the convergence rate of the system. The adaptive law for the rotational inertia coefficients is designed to make sure that the close-loop system with uncertain rotational inertia coefficients is stable.Finally, the Mars probe output feedback attitude control problems with uncertain rotational inertia coefficients are researched, and an attitude maneuvering controller and an attitude tracking controller with no need for angular velocity feedback are designed. Using the attitude filter, pseudo angular velocity information can be got from the attitude information. Sliding mode surface is structured by attitude MRP and pseudo angular velocity. The attitude maneuvering controller and the attitude tracking controller are designed in the sliding mode variable structure control method. In the attitude tracking problem, an adaptive law for the rotational inertia coefficients is put forward. Simulation analysis for the control algorithms makes it clear that the controllers can meet the attitude control task demands of the Mars probe close-loop system.