基于脉冲机动可达域的小行星探测器二维发射窗口研究

Launch opportunities Searching is a critical and essential problem to be solved in the mission planning of asteroid explorations. Nowadays, the Pork-Chop energy contour map is the most popular method to deal with this problem in practice, but it needs a large amount of computation, and can not consider some certain constraints in the searching process, which results in a very low search efficiency. Some intelligent algorithms improve the search efficiency in some extent, however they are apt to aging and sensitive to the initial value. What is more, these algorithms can only provide a local or global optimal solution, and fail to present the distribution of all the feasible solutions satisfying the given constraints. This reduces the flexibility of mission planning. The applicant found in the previous research that launch opportunities are closely related to the reachable domain of the asteroid detector. Thus, this research aims to put up a new and effective method based on the reachable domain of the asteroid detector to solve the problem of launch opportunities searching. First, put forward a brief and accurate computing method for the reachable domain of asteroid detector, and then applies it to the launch opportunities searching; second, put up the concept of 2-dimensional launch window which is able to present all the feasible solutions, and then study and build up an effective calculation method of the 2-dimensional launch window so as to show the distribution of all the feasible solutions in the whole search space; Finally, choose a set of performance parameters, and then compare the proposed 2-dimensional launch window method with the classical Pork-Chop method to prove the advantages of the former one. In all, the results of this research can serve as an important theoretical tool for the mission planning of interplanetary explorations.

发射机会搜索是小行星探测任务规划与设计中的关键问题。目前普遍采用的Pork-Chop图法计算量巨大，且无法将一些约束条件加入到搜索过程中以致搜索效率低下。一些智能方法在一定程度上提高了搜索效率，但算法易老化、对初值敏感，且只能给出最优解，无法给出满足各项约束条件的可行解在全局的分布情况，从而导致任务设计缺乏灵活性。申请者在前期研究中发现，发射机会与小行星探测器脉冲机动的可达域密切相关。因此，本项目以探测器脉冲机动的可达域为研究切入点，建立可达域的一种快速准确的计算方法，并将其应用于发射机会的搜索中；提出能够给出满足各项约束条件的所有可行解的二维发射窗口概念，重点设计二维发射窗口的计算方法，以精确、直观、全面地揭示发射机会在全局的分布情况；通过与Pork-Chop图法的特性对比分析，验证二维发射窗口法在科学与应用价值上的优越性。所得研究成果可为行星际探测任务规划和设计提供重要基础和理论依据。

准确、高效的发射机会搜索方法目前仍是行星际探测任务的设计师们所追求的目标。本项目以探测器脉冲机动的可达域为研究切入点，开展了行星际探测发射机会快速搜索问题的研究。通过对可达域问题的研究，确定了在发射能量约束条件下探测器在给定位置点处发射时所有可行日心转移轨道面的空间包络；探明了可达域在任意可行转移轨道面上的分布特性与分布规律；在此基础上，提出了一种基于特征椭圆的可达域快速计算方法，该方法只需计算６个特征椭圆即可获得转移轨道面上的可达域。该方法计算结果比较准确，且计算时间只有十几毫秒。项目进一步给出了三维可达域的快速计算方法。在突破可达域快速计算这一技术瓶颈之后，利用可达域的概念，本项目提出了一种快速准确的发射机会搜索方法——二维发射窗口法。在研究过程中，对于任意固定发射时刻，建立了一种转移飞行时间维度上的发射机会搜索方法，该方法可以获得此发射时刻对应的所有发射机会；在此基础上，提出了二维发射窗口法，该方法先后在发射时间和转移飞行时间两个维度上进行发射机会的搜索，并可快速获得满足各项约束条件的所有发射机会。本项目最后将所提出的二维发射窗口法与目前普遍采用的Pock-Chop图法进行了对比仿真，证实了该方法的快速性与准确性。与Pock-Chop图法相比，所提出的二维发射窗口法计算结果准确，并且在相同搜索精度条件下可使发射机会的搜索时间缩短约两个数量级。因此，该方法不仅适用于具体行星际探测任务发射窗口的确定，还特别适用于快速、高精度、大规模的发射机会搜索与评估。