Study On Control Methods During The Power Descent Period Of Probe

With the science technology rapidly developing, the deep space exploration have already became hot research field around the world. Especially the exploration mission to near-earth asteroids would be one of the most complex tasks in the future deep space exploration. This paper combines the fourth subtopic "the motion behavior analysis and the landing control of probe in the irregular weak gravitational field" of "973" programme to make a series of reaearch analysis about the tracking control during the power decline period. Research contents in this paper can be divided into three parts as follows:At first, the space kiematics and dynamics environment for the probe are analyzed. Because the asteriod has the tiny and irregular shape, it leads to the weak gravitation generated to the probe by the asteriod. Based on this reason, spherical harmonics is used to express the gravitational potential and build the gravitational model of the asteriod. Next, the probe dynamics model under the landing point coordinate is set up through the analysis of the probe dynamic characters.Secondly, As a result of complex environment in the deep space around the small bodies, the nominal landing trajectory is planned in advance to achieve soft landing security. Considering that the system has nonlinearity and multivariable coupling, so PID neural network controller is adopted to control the system. Simulation results show the real trajectories can track the nominal trajectories very rapidly and verify the feasibility of the proposed control law.Finally, in order to overcome the defect that inherent robustness of the sliding mode control algorithm isn’t enough to guarantee the actual trajectory to track the desired trajectory existing the larger disturbance, the neural network control algorithm based on PI observer is introduced. Deduce the dynamics equation of the probe under the landing site coordinate system and plan ahead the nominal trajectory meeting the constraints on the three axes. Then proportional integral observer is designed by using LMI technique to estimate the unknown fault. The estimation of disturbances is applied in the control law to guarantee the desired performance of the system and compensate the effects of the disturbance. At last, neural network control algorithm is used to realize double zero control of the probe and ensure that the probe can land safely.