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小惑星探査は科学ミッションとして近年注目されている。数多く存在している小惑星の中から目標とする小惑星を選択するには、軌道設計結果を参考に最小燃料軌道で到達できる小惑星を選択することが多い。本稿は、最小燃料の基準で選択される小惑星の軌道要素の特徴を示すものである。小惑星軌道は地球軌道と同一平面内に存在し、インパルス近似を用いた最小ΔV問題を扱う。目標小惑星軌道の軌道長半径が同一であれば、最終のエネルギは同一である。しかし、離心率や初期条件により必要なΔV量が異なるので、本稿では離心率に注目して傾向を調べた。その結果、出発する地球軌道と接する小惑星軌道を与える離心率を境に、最小ΔV量や初期条件の依存性が異なる傾向が示された。, Exploration to asteroid in the solar system has been focused by space scientists because asteroids have different features from large planets. The target asteroid is usually not specified. Calculation of trajectory to an asteroid is also interest problem for space engineers because it is necessary to select a target asteroid and to design trajectory simultaneously. The purpose of this paper is to provide the technical information for the selection of a target from many asteroids. To simplify the problem, the following assumptions are used in this paper. The target asteroid's orbit is elliptic in the earth's orbital plane. The explorer is under influence of only the gravitational acceleration of the sun. Impulse approximation adopts the calculation in this paper. The minimum fuel trajectories are selected to minimize the summation of Delta Vs at the departure from the earth and at the arrival to the asteroid. Orbital energy is given as a function of semi-major axis, thus the relation between eccentricity and Delta V are shown numerically. The results show that 'critical eccentricity' is a significant parameter. Critical eccentricity, e(sub CR), is defined as an eccentricity when the elliptic orbit tangents the circular orbit. When the eccentricity is less than the critical eccentricity, two orbits do not across each other. The total Delta V also depends on the relative position of the earth and the target asteroid at the departure time of explorer. The minimum Delta V at the best departure time can be calculated for given eccentricity. While the eccentricity is less than e(sub CR), the value of minimum Delta V does not depend on eccentricity largely. The other hand, in the region of eccentricity is larger than e(sub CR), the value of minimum Delta V is increasing as the eccentricity is increasing. Thus it can be said that the better candidates for searching are asteroids whose eccentricities are less than e(sub CR). However, the value of minimum Delta V changes depending on the departure time in the case of small eccentricity. It means that large additional Delta V is necessary when the departure time is delayed by some reason. Finally, it is concluded that the best candidate is an asteroid whose eccentricity is e(sub CR)., 資料番号: AA0063480021

本稿は、多数ある小惑星の中から、目標惑星を選択する時に使用する情報を提供することを目的としている。電気推進などの低推力を用いた楕円軌道上の小惑星への最小燃料軌道に関して数値計算をもとにその特徴を示す。対象とする小惑星軌道は地球軌道と同一平面内の2次元問題とし、推力は太陽からの距離の2乗に反比例するモデルを使用する。出発時刻の変更が消費燃料の変化にどのように影響するかを中心にデータを示す。地球軌道の外側に小惑星軌道が存在する場合の結果を示す。離心率が高いと、消費燃料が少なく、出発時間の影響も少ないことが示される。, The purpose of this paper is to provide the information for selection of a target asteroid from many asteroids. The results of numerical calculation show the feature of trajectories to an asteroid on elliptic orbit with solar electric propulsion. It is assumed that the target orbit exists in the same plane of the earth's orbit and the maximum available thrust is inversely proportional to the square of distance from the sun. The results show how the minimum fuel is affected by the departure time. This paper shows the results of cases that orbits of asteroid are outside of the earth's orbit. It is concluded that orbits with higher eccentricity are less fuel and less affection of departure time., 資料番号: AA0047897054