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In astrodynamics the characteristic energy () is a measure of the excess specific energy over that required to just barely escape from a massive body. The units are length2time−2, i.e. energy per mass. Every object in a 2-body ballistic trajectory has a constant specific orbital energy equal to the sum of its kinetic and potential energy: : where is the standard gravitational parameter of the massive body with mass and is the radial distance from its center. As an object in an escape trajectory moves outward, its kinetic energy decreases as its potential energy (which is always negative) increases, maintaining a constant sum. Characteristic energy can be computed as: : where is the asymptotic velocity at infinite distance. Note that, since the kinetic energy is , C3 is twice the specific orbital energy () of the escaping object. ==Non-escape trajectory== A spacecraft with insufficient energy to escape will remain in a closed orbit (unless it intersects the central body) with: : 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「characteristic energy」の詳細全文を読む スポンサード リンク
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