Laythe to Kerbin

[mastiwawa]

A simple enough question, but one I have been unable to find the answer to. Is the most efficient way to get from an orbit around laythe to Kerbin's SOI to burn directly from Laythe, or to transfer to jool first and then burn from there?

[astropapi1]

I'd suggest to get out of laythe, and take your periapsis just above Jool's atmosphere, so you can take advantage of the oberth effect and do an efficent burn at kerbin.

[SlyReaper]

I don't have the maths right to hand, but burning to a jool orbit with low periapse is indeed the most efficient way because you get a much biger boost from the much vaunted oberth thingy-ma-bob.

But in practice, unless you've shaved your fuel allowance very finely indeed, it's often easier to just burn away from Laythe directly, because you don't have to wait until Laythe is in the correct position in its orbit around Jool.

[astropapi1]

But in practice, unless you've shaved your fuel allowance very finely indeed, it's often easier to just burn away from Laythe directly, because you don't have to wait until Laythe is in the correct position in its orbit around Jool.

Well, you'd only have to wait an in-game day or so. How long does laythe take to complete a Jool orbit?

[mastiwawa]

I would imagine you would imagine you would have to wait for laythe to get to the light side of jool so when your burn you go in the correct direction correct? or would it matter where laythe was in relation to jool as long as you burned from the correct side of laythe?

[GreenDragon]

Wait till your both on the sunny side of Lathe and Laythe is on the sunny side of Laythe, then burn for an escape from a ninety degree orbit, Jool should be about 90 degrees ahead of Kerbin in its orbit, this will give you the best shot of getting from Laythe to Kerbin in a single efficient burn, as for escaping Laythe and then dropping into a lower Jool orbit, at some point the gains from stuff like that just arent worth it, especialy since you have to escape from Laythe too, not just modify your orbit, also you are already deep enough in Laythes and Jools gravity well already.

[Brotoro]

I've wondered about the answer to this question myself.

Certainly when you are coming UP from the surface of a planet and want to escape, the most efficient way to use your fuel is to boost into a very low orbit and make your escape burn from there (instead of going to a higher orbit first).

BUT if you are already in a higher orbit, is it more efficient to expend energy to climb down into the planet's gravity well just so you can take advantage of the Oberth effect? Would you suggest that somebody in orbit around Pol drop way down to Jool to make their escape burn as well? Or is there a distance for which it is most efficient just to leave directly?

[GreenDragon]

We had a discussion on something like this a while back before the forum massacre and the idea was that it really depends on how high you are already and how far you're going, dropping to a lower altitude might make sense for a Kerbin-Jool transfer if you start from a high enough altitude, the case we were discussing involved refueling in various altitudes above kerbin before escaping the SOI and the consensus was that refueling in as high an orbit as possible and dropping down made sense for long range trips like Jool and Eeloo. Some people came up with the math. I would say that it might make sense with Pol but im not sure, certainly something you could experiment with to see how the Delta V works out.

[RoboRay]

Laythe is so close to Jool that lowering your Pe in respect to Jool prior to the burn will not produce enough gain from the Oberth effect to make the exercise worthwhile.

Just wait until Laythe is at the right ejection angle for the transfer and make your transfer burn directly from low orbit around Laythe.

Edited May 4, 2013 by RoboRay

[bsalis]

What Roboray said.

Also questions like these can usually be answered by playing around with maneuver nodes.