How to calculate or plan interplanetary rendezvous after moon slingshot, the Ike 4rally mission

[davidpsummers]

I'm doing the Ike 4rally mission. I would like to enter they Duna system, slingshot off Ike, and then go on the Eve. So I need a trajectory out of Duna/Ike that will get me to Eve.

However, Alex Moon's planner only covers a burn to escape a planetary orbit. And I find the game doesn't give the distance of the closest intercept unless thing are already kinda lined up. So I doubt just moving things around will let me find a rendezvous.

Any help?

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Note: Of course it doesn't have to be specifically Duna to Eve. If one knows how to slingshot past the Mun to any planet, that is the same thing.

[tbarcello]

I'm doing the Ike 4rally mission. I would like to enter they Duna system, slingshot off Ike, and then go on the Eve. So I need a trajectory out of Duna/Ike that will get me to Eve.

However, Alex Moon's planner only covers a burn to escape a planetary orbit. And I find the game doesn't give the distance of the closest intercept unless thing are already kinda lined up. So I doubt just moving things around will let me find a rendezvous.

Any help?

- - - Updated - - -

Note: Of course it doesn't have to be specifically Duna to Eve. If one knows how to slingshot past the Mun to any planet, that is the same thing.

Slingshots are Fun is the newest episode in my Let's Play KSP series, but it's still unlisted, so for now your eyes only. I'm making a slingshot off the Mun to change trajectory to reenter kerbin along equator, but that slingshot isn't efficient at all, because I didn't care about fuel.

But the point you have to understand is slingshot doesn't give you new energy, but it does change your vector. So you can create a comfortable situation to make a necessary burn, when without slingshot you'd have to create such situation with your engines, wasting fuel.

In general, the slingshot better be planned before entering Duna SoI. Play with maneuver editor until you get an encounter with Ike, then adjust your encounter so your escape trajectory would create an intercept of your target planet. Your phase around the Kerbol in respect to target will matter how efficient your approach will be, but it'll be up to you to decide efficiency againt time. Even in bad current situation you can slingshot burn to a trajectory, that will intercept target not on this, but next orbit around Kerbol.

It's not for rookies, but I assume you aren't one.

Good luck and have fun. Setting up those trajectories takes time, so if you don't enjoy it, it's gonna be a chore.

[davidpsummers]

then adjust your encounter so your escape trajectory would create an intercept of your target planet..

That's the tricky part I was looking for help on. The game is stingy one showing closest approach info, esp. if you aren't in a position to align the orbits before hand. It is hard (and can require non-trivial luck) to get an intercept by just trying trajectories.

[mhoram]

So you want to know when to reach duna so that a gravitational assist to Eve is possible.

Have a look at the flyby finder

http://forum.kerbalspaceprogram.com/threads/80978-Flyby-Finder-for-KSP-V0-40

[tbarcello]

That's the tricky part I was looking for help on. The game is stingy one showing closest approach info, esp. if you aren't in a position to align the orbits before hand. It is hard (and can require non-trivial luck) to get an intercept by just trying trajectories.

[PLAD]

I'm assuming that you want to start in a Kerbin orbit, coast to a flyby of Duna and Ike, and coast from there to Eve. This is tricky because Duna is not massive enough to alter your path much. To go Kerbin-Duna-Eve you will need to leave Kerbin and get into a Solar orbit that already has a perihelion close to Eve's orbit and an aphelion close to Duna's orbit. An orbit like that will cross Kerbin's orbit at a sharp angle, and as such when you leave Kerbin you will be at a high angle to Kerbin's direction of motion around the Sun, which means it will take a lot of dV to leave Kerbin and get into this orbit.

But it is possible! Here is the first window I could find (Using Flyby Finder, Earth time):

Leave Kerbin Y1 day 97 12H (Earth time, From a 75x75km orbit an 1883m/s boost will be required, start orbit inclination is 0.1 degrees).

Flyby Duna Y1 day 193 at about a 45 km periapsis.

Arrive Eve Y1 day 242. (It would cost about 1950m/s to brake into a circular 100km orbit at Eve).

The windows are pretty tight. Arriving at Duna even 6 hours after the target time will cost about 50m/s, increasing rapidly after that. You can't leave Kerbin before day 97, 6H, or after day 100. If you search this using FF, raise the V at SOI max to at least 3000m/s.

Note that the start boost is almost what it would take to get to Jool. You could knock maybe 40m/s off of this by using a flyby of Mun at the start, but it would be nasty tricky. Since you fly by Duna lower than Ike's orbit, and your window is more than 1 Ike day wide, you can work an Ike flyby into the Duna flyby by adjusting your start time a bit. Note that tiny Ike will add almost nothing to your energy since you will be flying by it very fast. Flying a Kerbin-Mun-Duna-Ike-Eve path would be quite cool, though.

If you go the other way, Kerbin-Eve-Duna, you can start with a much smaller start boost because heavy Eve can alter you orbit a lot.

I should have a version of FF that uses both Earth and Kerbin time released in about 2 weeks if you prefer to work in Kerbin time. I'm debugging it now, this problem was a fine test case!