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This paper presents a strategy for the soft landing trajectory optimization on an asteroid. The interior gravity field model, a counterpart of the classical spherical harmonic model，is used to estimate the gravity acceleration near the target asteroid. This model has an advantage in computational efficiency and its convergence properties can be guaranteed within the constructed interior Brillouin sphere. The soft-landing optimization problem on an asteroid is converted into a successive second-order convex programming (SOCP) through constraints slack，linearization of dynamics and discretization which can be solved by the primal-dual interior-point methods. The numerical simulations shows that the lander arrives at the target site with zero velocity and all the constraints are satisfied. The fuel consumption is also optimal. Solving soft-landing optimization problem on an asteroid with convex programming has an advantage in computational effectiveness and can potentially be implemented in the future asteroid mission. [ABSTRACT FROM AUTHOR]

Based on the overview of past Mars exploration missions and the requirements for future Mars landing missions, the importance of the Mars entry trajectory optimization and guidance techniques is analyzed. The challenges for the Mars atmospheric entry trajectory optimization and guidance are analyzed and summarized，based on the analysis of the Mars landing environment and the aerodynamic characteristics of the entry vehicles. Key techniques corresponding to the trajectory optimization problems and guidance schemes are proposed. Present researches and the development trend of the key techniques are analyzed synthetically. Finally，the development direction of the key techniques for Mars entry guidance of future Mars precision landing missions are previewed. [ABSTRACT FROM AUTHOR]

Based on small body landing missions carried out so far and future development trends of small body landing techniques, the necessity and key techniques of small body autonomous landing are elaborated. Successful small body landing missions to date are reviewed firstly. Further, difficulties and challenges encountered in small body autonomous landing explorations are summarized, key techniques related to small body autonomous landing are outlined, and state-ofthe- art research progress of these techniques are surveyed. Finally, future research focuses and development trends of small body landing techniques are discussed. [ABSTRACT FROM AUTHOR]

The objective of this paper is to design an optimal attitude maneuver path for a rigid body spacecraft under complex constraints. Firstly，dynamics and kinematic constraints，bounded constraints and attitude pointing constraints are described and analyzed. Especially, the attitude pointing constraints are formulized as the nonconvex quadratic form； Secondly, the constrained attitude maneuver problem can be formulated as the nonconvex quadratically constrained quadratic programming with the target that the energy-cost is smallest ； Then the linear relaxation technique is introduced， and the problem is converted into a bilinear programming problem, in which convex envelope and concave envelope of one variable can be obtained. By this theory the complexity of solving is reduced and a linear relaxation of the original problem can be obtained. Meanwhile，in order to improve the solution accuracy，an iterative planning algorithm based on evaluation function is presented in this paper. This algorithm makes the solution of linear relaxation as the initial value, and an optimal solution can be achieved by iteration ultimately. Simulation results show that this method not only meets the complex attitude constraints to give an optimal attitude maneuver path，but also reduces energy consumption. [ABSTRACT FROM AUTHOR]

Since the dynamics parameters of the small bodies and the initial state of the lander are uncertain, an optimization method considering the closed-loop tracking guidance is presented. Firstly, the dynamics for landing on small bodies is constructed and the optimal problem is analyzed. Then, the feedback guidance law is designed by use of the Linear Quadratic Regulator. The closed-loop sensitivity matrix equations are derived, and the performance index with weighted fuel consumption and sensitivity is constructed. Then, the trajectory considering the closed-loop tracking guidance is obtained by solving the constructed optimal problem. The simulation results show that the presented method can reduce position and velocity errors and meet the requirements for precision landing on small bodies. [ABSTRACT FROM AUTHOR]