The Voyagers made a grand tour using the gravity assist of each planet. But Jupiter, with a 12 year orbital period, doesn't always line up to be useful for spacecrafts destined to further planets. Venus is much quicker on its feet, but light.

What have been the altitudes of spacecrafts' perijove and perikrition (a look up word for periapsis at Venus) to date? What kind of delta-V change could one achieve by passing by Venus as close as possible, on the way to say Saturn or Uranus? Could aerobraking at Venus be helpful in optimizing the velocity vector?

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    $\begingroup$ While making these 'as low as safely possible' would yield the strongest gravity assist, it would also thoroughly randomize the ejection angle. The actual altitude choice prioritizes ejecting the probe in the desired direction over maximizing delta-V gains. $\endgroup$ – SF. Nov 29 '18 at 9:30
  • $\begingroup$ aerobraking is unlikely to help much with an outer planets mission, since it dissipates energy and you are going to need that energy to get out of the Suns gravity well. Could be useful for a Mercury or close solar mission though. $\endgroup$ – Steve Linton Nov 29 '18 at 12:39
  • $\begingroup$ @SF. I don't understand why a close flyby would fling of a probe randomly. The location of Saturn is said to be determined within one kilometer now. Fantastically. And the distance to a spacecraft within a radio wavelength or so. My impression is that this needle's can be thread. $\endgroup$ – LocalFluff Nov 29 '18 at 21:42
  • $\begingroup$ @SteveLinton I was thinking that a deflection of the velocity vector could be worth something in terms of delta-v. I wonder if at times a Venus flyby can give a better kick to the outer planets than an of Jupiter, or none. $\endgroup$ – LocalFluff Nov 29 '18 at 22:01
  • $\begingroup$ @LocalFluff: The periapsis altitude causes change in ejection angle. Yes, you can foresee exactly where the lowest possible periapsis will eject you. The problem is your calculation will most likely result in "in a completely useless direction." $\endgroup$ – SF. Nov 29 '18 at 22:19

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