Rendezvous Trajectory Planning And Mission Trajectory Design In Proximity To Asteroid

As a focus of future deep space exploration,asteroid exploration has important scientific value and engineering significance.The design of trajectory is one of the key elements of close range asteroid exploration.Due to the irregular shape,the heterogeneous mass distribution and the complex mechanical environments which asteroids lie in,the trajectory design for the close range exploration faces numerous challenges.This dissertation studies the trajectory design of asteroid exploration mission,focusing on the orbit design of approach,hover and fly-around.Firstly,the approach trajectory of asteroids at close range under the impact of perturbations is explored.Based on the glideslope strategy,the multipulse approach orbits are adopted to divide it into several sections and the pulse conditions required for each of the phases are derived through the relative motion equations so as to realize a close range approximation process in any positions and directions.What is more,two orbit correction methods: segmental two-impulse correction and integrative reconstruction correction,are applied to rectify any potential position errors resulting from perturbation,and the optimal design of multipulse approach orbits is applied based on Primal-dual Interior Point Method.Furthermore,given the complicated dynamic environment which asteroids are in,the approach strategy for optimal fuel consumption is put forward,which helps increase the accuracy of approximation process.Secondly,the design method for spot hover and regional hover of asteroids in relative coordinate system and body fixed system are investigated.The control strategy for spot hover is designed through a closed-loop continuous control method by considering the thrust saturation constraint.The control strategy for any positions under body fixed system is devised on the basis of high-order sliding-mode control methods.For the regional hover,the control strategy based on the shooting method is proposed,that is,to maintain the desired performance of asteroids by applying finite times of impulses in the boundary area.Thirdly,the fly around orbits both within and beyond the gravitational field is examined.For the former,the nature-periodic-relative rotating orbits are used as the mission orbit and the stability of remote fly around orbits under perturbation are analysed.Two orbit keeping strategies based on the closed-loop continuous control and impulse control method are proposed.In terms of close range fly-round within the gravitational field,the necessary condition for the frozen orbits are revised based on the spherical harmonic coefficients of the gravitational field determined by polyhedral models and its stability under shape perturbation are also investigated.Finally,a whole process simulation analysis of asteroid exploration mission is done by taking the asteroid 1998 ML as a target.The dissertation presents the earth-asteroid transfer trajectory,approach trajectory,fly around trajectory and hover trajectory,then integrate them into a whole mission.The feasibility of orbit design methods adopted for close range asteroid detection in this study was verified by simulation.