When a spacecraft flys past a planet eg. Jupiter , its heliocentric energy increases dramatically allowing it to go further away. How is this possible without using any more rocket fuel?

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    $\begingroup$ As Wikipedia says, the energy is taken from the planet's orbital energy. $\endgroup$ – PM 2Ring Feb 28 '19 at 14:23
  • $\begingroup$ Are you sure "heliocentric energy" has any meaning? Do you mean kinetic energy in the rest frame of the sun? $\endgroup$ – Carl Witthoft Feb 28 '19 at 20:23

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