# How can Sun-Jupiter Lagrangian points be used by flyby probes?

Sun-Jupiter L1 is 1/3 of an AU from Jupiter. Could it be used to slow down or redirect a spacecraft approaching Jupiter? And the same for Sun-Jupiter L4 and L5 for a spacecraft on the way to e.g. Saturn?

• A Lagrangian point does not have its own gravity. A restricted three-body problem can be exploited to give a "weak ballistic capture", reducing $\Delta V$ requirements somewhat. – Deer Hunter Aug 5 '15 at 9:41
• @DeerHunter Yes, AFAIK the reason one can orbit it has to do with the instability between Sun and Jupiter in this case. But is there no use of that instability for a fast flyby spacecraft? (A space telescope specialized on observing solar system planets is on NASA's wishlist. Maybe such a thing could be put at Sun-Jupiter L1 to study the Jupiter system fairly up close. But that's another topic.) – LocalFluff Aug 5 '15 at 9:46
• @DeerHunter According to this accepted answer a spacecraft can move .06 AU from Sun-Earth L2 with "a nudge". With only .3 AU left to Jupiter, I thought that a similar effect out there might substantially benefit an orbital insertion. – LocalFluff Aug 5 '15 at 9:56
• Like this (a trajectory of J002E3, aka Apollo 12 mission's Saturn V S-IVB third stage, from April 2002 to July 2003 as it was gravitationally captured into the Earth-Moon system from the heliocentric trajectory via SEL1 and then perturbed out of it again back into heliocentric regime). Yes, this actually happened "naturally" (no propulsion) and resulted in several Earth-Moon flybys of the object that was initially considered an Earth-crossing asteroid, until it was realized it's covered with titanium oxide paint. :) – TildalWave Aug 5 '15 at 13:30