川勝 康弘

Discussed in this paper is a lunar approach strategy tolerant of a lunar orbit injection (LOI) failure. LOI is one of the most critical events for a lunar orbiting mission. If LOI is not performed, the spacecraft flies by the moon, and in the worst case, it escapes not only from the moon but also from the earth, which leads to mission failure. The proposed strategy is to design a trajectory so as to re-encounter the moon even when LOI is not performed. It provides an opportunity for mission recovery even in the case of an unexpected fly-by. A trajectory design procedure is introduced and an example of the designed trajectory is shown.

Analyzed in this paper are Near-Earth Asteroids sample return mission opportunities in early 2010s. The mission sequences supposed are Keplerian orbits connected with impulsive velocity changes including planetary gravity assists. The sequences are constructed by "trajectory parts connecting method", which is exploited by the author. The method enables to construct the possible sequences comprehensively under defined structure and given constraints. At the same time, it enables to assess the dynamical feasibility of the constructed sequences quantitatively by way of the total required velocity increment required to complete the sequences. Over 4000 Near-Earth Asteroids are taken into account as the candidates of the mission targets, and the mission sequences include not only the sample return from a single asteroid, but also the sample return from two asteroids. Lists of the asteroids (or their combinations) which have mission opportunities in early 2010s are provided and some example sequences are shown.

In this paper, the translunar trajectory of the simple sequence is investigated. The trajectory discussed in this paper is a two-burn ballistic trajectory from the low earth parking orbit to the low lunar orbit. The problem is practical in that the geometric relation from the launch site to the moon is fully considered. The paper includes three subjects. First is the structure of the problem and the solution space. The problems are defined and the solutions are grouped by the properties of the lunar transfer sequence. Second are the characteristics of optimal solutions. The topics discussed are the transition of the required velocity increment based on the launch date, and the difference according to the property of the lunar transfer sequence. Third is the sensitivity analysis of a number of items to the deviation of the parameters from the optimal solution.