PurposeThe purpose of this paper is to present a solution space searching method to study the initial design of interplanetary low thrust gravity assist trajectory.Design/methodology/approachFor reducing the complexity and nonlinearity of the initial design problem, a sixth degree inverse polynomial shape based approach is brought. Then some improvements are provided for solving the parameters in the shape function and a quasi‐lambert solver is brought through the shape based method, the thrust profile can be generated under the given time of flight, boundary states including positions and velocities for low thrust phase. Combining gravity assist model, the problem is summarized and an improved pruning technique is used for searching the feasible solution space for low thrust gravity assist trajectory.FindingsUsing the solution space searching method, the feasible solution region would be generated under the given mission condition. The treatment about gravity assist demonstrates more accurate than previous method. Also another advantage is that the searching method can be used to design different types of mission trajectory, including flyby and rendezvous trajectories.Practical implicationsThe method can be used as an efficient approach to search the feasible region for the complex low thrust gravity assist trajectory, and it can provide appropriate initial guesses for the low thrust gravity assist trajectory in mission design phase.Originality/valueFeasible solution space would be obtained through the searching method. The quasi‐Lambert solver in the paper is found under the shape‐based method and relative improvement, and it shows its availability during the searching process. Through mission trajectory design, the effectiveness of the method is shown.

Low thrust trajectory design and optimization is a challengeable work in interplanetary exploration. The launch opportunity of low thrust trajectory is studied in the paper. Based on a hybrid method, the low thrust optimal control problem is converted to a parameters optimization problem. An adjoint control transformation is proposed for decreasing the difficulty of initial values guess. And the solution searching scope can be reduced effectively through the introduction of adjoint control transformation, which converts costate state to other variables which possess actual range and meaning partially. Finally, a global-local searching procedure is proposed for obtaining the low thrust trajectory launch opportunities. Differential evolution algorithm is used to generate initial values for the nonlinear programming problem, and sequential quadratic programming algorithm is used for improving the accurate of solutions. The effectiveness of proposed method is validated through three Earth-Mars missions low thrust trajectory design.

The invention relates to a planet gravity-assist low-thrust trajectory optimization method based on a decomposition and coordination strategy and belongs to the technical field of aerospace technologies. The planet gravity-assist low-thrust trajectory optimization method based on the decomposition and coordination strategy comprises firstly decomposing a planet gravity-assist low-thrust transfer trajectory optimization problem into a system-level optimization problem and two second-level optimization sub-problems with planet gravity-assist positions serving as nodes; and then utilizing the system-level optimization problem solving as a main iteration for coordinating status matching of the planet gravity-assist positions of the optimization sub-problems, and utilizing the second-level optimization sub-problem solving as an auxiliary iteration for determining thrust control laws of every subsection trajectory until the main iteration and the auxiliary iteration are both converged. The planet gravity-assist low-thrust trajectory optimization method based on the decomposition and coordination strategy reduces the complexity of an optimization model and the sensitivity of the trajectory constraint to optimized parameters, and improves the convergence efficiency of the transfer trajectory optimization problem.

The application and advantage of low thrust propulsion system has been validated in practical mission launch even though the trajectory design difficulty is increased. The trajectory optimization problem brought by the use of low thrust propulsion in conjunction with gravity assist is researched. This paper proposes a hybrid technique for solving the strong nonlinear and multiple constraints optimal control problem using a hybrid technique. First, a nonlinear programming problem is proposed by abandoning the terminal constraints brought by Pontryagin maximum principle and treating costates as optimization variables; Then an adjoint control transformation is used for converting costate variables to other variables partially which possess actual bounds and physical meaning; Finally, differential evolution algorithm is employed for searching the initial values of nonlinear programming problem for local accurate optimization. Related low thrust gravity assist trajectories to outer planets by various gravity assists are designed for demonstrating the effectiveness of the proposed hybrid technique.

针对行星际小推力借力转移轨道初始设计问题，提出一种结合形状逼近策略与解空间剪切技术的的初始设计方法。该方法采用改进的逆六次多项式策略计算小推力弧段，通过引入B平面模型来描述行星借力机动以拼接小推力轨道。通过建立相应的约束条件来引入小推力借力轨道解空间的剪切准则，依据解空间剪切准则，对解空间进行剖析，并剔除解空间中的不可行域，进而搜索初始转移轨道的可行解。数值结果表明：本文方法可以有效对交会型转移轨道进行设计，并且可以消除由借力机动带来的速度匹配误差。