What's the most efficient method of getting from Ike to Jool?

[Jett_Quasar]

Here is the scenario - I have a spacecraft orbiting Ike that has just been refueled. I'd like to go to Jool and complete some contracts there,

Should I:

1) Drop my orbit close to Duna (~50KM periapsis) and use the Oberth effect to slingshot my craft toward Jool?

or

2) Stay in orbit of Ike and do a direct burn to Jool using the moons orbital velocity to get there efficiently?

JR

Edited July 27, 2015 by Jolly_Roger

[Kryxal]

I'd go with the direct burn ... Duna's gravity is much lower than Kerbin, so Oberth savings would be minimal.

[Superfluous J]

My gut is telling me that Kryxal is correct. However, you can test it yourself in half an Ike month by setting up the maneuver node for one journey, and then setting the maneuver node up for the other journey when Ike's on the other side. Note the total burn dV of each attempt and bammo, you'll know the answer.

Duna and Jool's orbits are circular enough that just getting your resultant Sun apoapsis up to Jool's orbit is enough. No waiting for transfer windows necessary.

[Sharpy]

Depends on how much delta-V you have and how much you need. The Oberth maneuver would probably be *somewhat* cheaper but at cost of seriously increasing difficulty of the maneuvers. IMHO simply dish out the extra 100 or so m/s and go directly (also, pick the right moment in Ike's orbit - when Ike is moving prograde relative to the Sun).

edit: forgot an important factor. I'm not sure what is the inclination difference between Duna and Jool, but plane adjustment can be costly when done "out in the open". By aiming your Duna flyby right you can do it nearly for free.

[Jouni]

I'm not sure whether the optimal transfer involves a direct burn from Ike or an Oberth maneuver at Duna, but it's definitely based on a Kerbin gravity assist.

[Jett_Quasar]

Yeah I was thinking that the direct burn would be simpler but if I could time the Duna fly-by right I may also be able to come back and slingshot around Ike again to pick up some more delta-V. I'm more of a seat-of-the-pants pilot I was just wondering if there was a general rule or maybe someone has a mod to calculate a Duna manouver.

JR

[Yasmy]

Roughly:

Ike -> Duna -> Jool: 1158 m/s

Ike -> Jool: 1266 m/s

Direct vs slingshot table.

[Jouni]

Roughly:

Ike -> Duna -> Jool: 1158 m/s

Ike -> Jool: 1266 m/s

Direct vs slingshot table.

So it's Ike -> Kerbin -> Jool: 421 m/s. Or probably a bit more, because optimal transfers usually don't give the best gravity assists.

[rofltehcat]

Wouldn't it be theoretically most efficient if you chose your departure time such that you fly right by Duna (Ike on the sun side of the Duna system? Slightly behind Duna? , though unsure about angle) and do a lot of that burn when close to Duna? The trick would probably be getting the angle right so that you don't need to establish an orbit around Duna.

Edited July 27, 2015 by rofltehcat

[cantab]

https://www.reddit.com/r/KerbalAcademy/comments/1qu5jv/deltav_charts/

These are the most comprehensive set of delta-V charts I have found, and allow you to answer questions like that, as the Reddit post explains. Though do note it does not have updated values for ascents from atmo bodies. For going from low Ike orbit to Jool we get

Direct transfer: 1270 m/s

Low-over-Duna: 1130 m/s

Not much in it. Unless I was looking to absolutely minimise mass I'd take whichever option is more convenient.

[Jett_Quasar]

Thanks cantab, that's exactly what I was looking for - I'll bookmark that page. I rarely do transfers from Kerbin any more, I need to get better at inter-planetary navigation and this will help.

JR