economical high-orbit return from jool

[thiosk]

Simple question about economical ways to return from jool. I've noticed large increases to requisite dV after leaving planetary SOI, a function i assume of the oberth effect.

So heres my question. Lets say I leave vall orbit and slingshot off tylo for a nice kick to high jool orbit. Now I wait. and wait, and wait, and pop heres the return window. Unfortunately, as luck would have it, I've ended up 50 days from the correct point in orbit for an ideal ejection angle. Last time this happened, I overbuilt the mission so I had 4k dV I was returning with. This time its going to be a nail biter.

What does one really want to do in this situation? Go ahead and go solar orbit and then hohmann down to kerbin? Set up a return from the complete wrong side of the orbit? I've heard of people parking beyond pol for cheap returns, but I imagine this happening every time. Suggestions?

Edited February 5, 2014 by thiosk

[Kasuha]

The question is whether you do or don't use deadly reentry.

If you can freely aerobrake in Kerbin's atmosphere then there's little point in waiting for return window as it costs very little additional dv to set up Kerbin intercept from just about anywhere.

So the best approach IMO is to use gravity slingshot off Tylo or Laythe to get right on a return trajectory. Even if you need to burn a bit near the periapsis you're still getting home almost for free.

[arq]

Do a burn to intersect Kerbin's orbit (Kerbin doesn't necessarily need to be there when you arrive). When you cross Kerbin's orbit, burn pro- or retrograde to get a Kerbin encounter after one orbit (or a few orbits later, if you need to wait to bring it around). This maneuver can be done at any time and is only more expensive than a direct transfer by the adjustment you need to do to get intercept, which can be very little if you have the patience to wait several orbits. Because Jool's orbital period is so long compared to Kerbin's (about 12x longer), you should be able to get the intercept in just one or two orbits with only a small adjustment.

But a gravity assist could get you lined up to return at an actual transfer window and that will be faster in most cases. If you can do that, I would recommend it.

[thiosk]

This was the method I stumbled upon quite by accident. It was astonishingly cheap, once I corrected inclination problems.