Time to go home, what's the best way?

[SkippydaHippie]

I am proud to report the near success of my first interplanetary mission. I went to Duna, and landed there, and after heading back into orbit and docking I ran some calculations and was tickled to find I had just enough fuel to also land on Ike. That didn't go quite as smoothly.. but the craft and Kerbal were well enough to make it back to the command module and get all docked up, and the crew are ready to prepare for the trip home. So we come to my current situation. I'm in a fairly low orbit over Ike, roughly 30km parked and my question is this: Whats the best way to get home from here? Obviously I'll have to make sure I'm in a decent enough launch window but I'm talking more about what I do in Duna's sphere of influence. Should I wait until Ike is at the ejection angle and burn directly from there? Or would it be best to drop myself into a highly elliptical orbit around Duna and use the gravity assist to help me pick up velocity, again, obviously timing it to line up with the ejection angle. Or should I do a Hohmann transfer to a lower/higher parking orbit around Duna and go from there? I doubt that last one is a very smart choice... but I'm no expert.

Edited June 21, 2016 by SkippydaHippie

[bewing]

Congrats on being interplanetary!

As a physicist, my gut instinct is that choice #1 is best. Ike gives you a decent amount of free orbital velocity around Duna, and some Oberth.

For Option #2, to get to a low Pe around Duna, you would have to burn retrograde to Ike's orbital velocity -- so you'd have to waste 400m/s of deltaV (or so) from your engines to escape Ike and lower your orbital speed. And Duna isn't going to give you much of a slingshot, since you are only slingshotting with the deltaV you pick up falling from Ike's orbit and not at interplanetary speeds.

Option 3 is very bad, agreed. You'd waste all the Oberth from both Duna and Ike. If you burn to change your orbit just to gain some Oberth, you never come out ahead.

[N_Danger]

 I vote for #1 also. You already spent the fuel getting to Ike's orbit and would use more by dropping down any closer to Duna.

[Lunar Sea]

I was in the same situation just a short while back - also my first interplanetary conquest! There is nothing like those first times, eh? 

Option 1 is the way to go, I can vouch for it. It felt tricky, for a noob anyway, and I wasn't totally sure it would work. But it did, and will for you too. Like you said just wait until Ike is at the ejection angle and set your burn to send you off more or less (more, preferably) along Ike's prograde. You should be able to encounter Kerbin for about 600m/s. You got this!