Sliding Mode Attitude Control For Flexible Spacecraft

With the continuous development of space technology, the latest generation spacecraft are tending to be developed in large-scale and lightweight of the structure, now more and more spacecraft came with various large flexible structure, such as large-size solar battery panels, mechanical arms, large-size radar aerial and etc. The dynamic characteristics of these flexible structure tend to be low-frequency, dense model and strong geometric nonlinearity, The flexible chattering can’t be avoid when the spacecraft is doing orbital maneuver and attitude maneuver, as well as when the flexible accessories are conducting the stretching movement under the affection of the special physical environment of out space. Such chattering will bring the spacecraft serious damage, a better situation is to cause the failure of spacecraft mission, and a serious one can threaten the safety of the spacecraft, leading to a disastrous consequence. Therefore, seeking a controlling method which can both control the attitude and reduce the robustness caused by the chattering of flexible structure has a very important meaning in both theoretical and engineer practical application.Aiming at the spacecraft attitude control issue, using quaternion to express the dynamic equation of spacecraft attitude to avoid the irregularity problem under the control space, take use of Lagrange’s equation as theory basis, establish the hub and complex spacecraft dynamic equation with flexible accessories, and show the reduced attitude dynamic equation of flexible spacecraft on the basis of mixed coordinates at last.As a comprehensive method of controlling system, the sliding model variable structure control is insensitive to the external disturbance which satisfied the match condition and the uncertainty of parameters, due to good robustness and other advantages, it has been paid a special attention and gets a widespread application on the spacecraft attitude control. Firstly, use the Lypauoy direct-approach designed the attitude controller of sliding model various structure and optimize the chattering problem in the control sliding model various structure; use “arc tangent” function to replace the original switch function item in the control of sliding model various structure, reduce the chattering in system; After bring the lag which can decrease the required large control torque when start maneuvering to reduce the chattering of flexible accessories.Finally, use MATLAB to conduct the numerical stimulation, and compare with the stimulation results in horizontal. The final result shows, compared to traditional control law, improved control law possess a better performance and the controller with a good robustness, which is suitable for the flexible spacecraft to conduct more effective attitude control and reduce the chattering of flexible accessories simultaneously.