# Can a trajectory between planets accelerate a space craft?

I read that if some spacecraft's trajectory is carefully planned, i.e. if it can slingshot (at loss of a better word) a massive body like a planet, it can gain speed. Is that correct ?

Does solar system actually lose some energy to such a space craft in this way ?

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"Slingshot" is in fact the proper technical term for this maneuver. –  David Z Oct 18 '12 at 17:42