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If a spacecraft enters flat enough into the Earth's (or another planet's) atmosphere it will "bounce off" the Earth at a higher speed. That method can be used if a spacecraft has not enough fuel to reach orbital or escape velocity by itself. Has any (manned or unmanned) spacecraft ever used that technique? If so, which one on what planet or moon?

Perhaps I should tell that of course you need to have the engines on. If you enter an atmosphere by gliding it will bounce you off but you won't reach a higher speed, don't you?

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    $\begingroup$ Really. Do you have references for any of this? $\endgroup$
    – user20636
    Commented Mar 28, 2020 at 15:44
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    $\begingroup$ You don't gain speed when aerobraking or "skipping" off the atmosphere. $\endgroup$
    – Star Man
    Commented Mar 28, 2020 at 15:45
  • $\begingroup$ You can bounce yourself off the planet if you enter its atmosphere flat enough. $\endgroup$
    – user35272
    Commented Mar 28, 2020 at 15:46
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    $\begingroup$ While an incorrect trajectory can prevent aerocapture, that's not the same thing as you're imagining. $\endgroup$
    – user20636
    Commented Mar 28, 2020 at 15:49
  • $\begingroup$ If you enter the Earth atmosphere flat enough, you don't bounce off, you just leave the atmosphere a short time later following your initial trajectory. The speed reduction is too small to stay in the atmosphere. $\endgroup$
    – Uwe
    Commented Mar 28, 2020 at 16:16

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Entering the atmosphere introduces drag, which could only reduce your energy. That is, reduce your speed relative to the planet. If you hit the atmosphere at 18,000 mph at too shallow an angle you could bounce off, but not with more energy than you had on approach. You'll fall back, but your landing point may then be outside of your control.

You may be thinking of gravitational slingshots (gravity assist, swing-by maneuver). In that, the planet is approached in a way that lets you steal some momentum from it. That's a common way to get space probes to the outer planets. You can also do the reverse, losing momentum, which helps space probes get to Venus, Mercury, and the sun. The atmosphere is not entered.

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Your premise is incorrect. In no case does "skipping off the atmosphere" leave you going faster than you arrived, engines on or not.

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