How do I efficiently do a sun flyby and return.

[CaptainKipard]

I don't want to stay in orbit around Kerbol, I'd just like to do a close flyby for science, and return to Kerbol.

I know that Kerbin will obviously not be at the apoapsis any more, so how do I efficiently change my orbit for a quick Kerbin encounter?

Edited April 22, 2014 by Cpt. Kipard

[Taki117]

You're best bet is with a Bi-elliptic Transfer. It ill increase mission time (On the order of years) but will be much more fuel efficient.

[Jouni]

The easiest way is to set your orbital period to 30 minutes less than 40% of Kerbin's orbital period as soon as you leave Kerbin's sphere of influence. Then you just drift around for five orbits, until you have a close encounter with Kerbin two Kerbin years later.

It's possible to cut the drifting down to around one year: just burn prograde at the periapsis until you get an encounter. I have no idea how much fuel you'll need for that.

[FREEFALL1984]

Yeah just make sure you're orbital period is in phase with kerbins, so for instance you could make your new orbital period 1/2 of kerbins and you would perform 2 orbits per kerbins 1, as long as you're pretty exact once in kerbols SOI, you should be able to easily perform a correction burn to finetune your approach,

[Kasuha]

About the most dv-effective approach is to burn for Jool intercept and get a powered slingshot to whatever Sun periapsis you desire. You need to raise your apoapsis above Jool orbit in order to be able to slingshot in any useful direction. Returning to Kerbin is then matter of fiddling with the orbit to get a Kerbin intercept after you have returned to apoapsis.

The most straighforward approach is exiting Kerbin SOI retrograde to its orbital motion fast enough to get the desired periapsis altitude, then again fiddling with the orbit from apoapsis after you return there to get another Kerbin intercept in reasonable time.

You can also save some dv compared with the second case if you burn for Eve intercept and use powered slingshot to get low Sun apoapsis (Eve Oberth effect is stronger than Kerbin's and you save some more dv by inverting your orbit by the slingshot). You need another Eve slingshot to return to Kerbin after that, though.

[FREEFALL1984]

Kasuha made a good point, if you're just aiming for a close kerbol approach you could try to slingshot your way down the planets, personally I would try and time it so the mun is 45 degrees to kerbins prograde and minmus is approaching almost 45 degrees past prograde (sorry my orbital terminology is slightly rust) then slingshot around the mun into a close encounter with minmus and burn at minmus peri to slow your kerbol orbital speed.

[Champ]

Kasuha made a good point, if you're just aiming for a close kerbol approach you could try to slingshot your way down the planets, personally I would try and time it so the mun is 45 degrees to kerbins prograde and minmus is approaching almost 45 degrees past prograde (sorry my orbital terminology is slightly rust) then slingshot around the mun into a close encounter with minmus and burn at minmus peri to slow your kerbol orbital speed.

I am pretty sure you are wrong. Minmus is too light for oberth effect (so, why would you burn at minmus peri ?), and even Mun is too light for gravity assist. I really think jool would be the best bet. Even if you can't encounter jool, you will have done a bi-elliptic transfer.