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Elroy Jetson

Mun and Mimnus Tour?

Question

Well, this one is Turing out to be much more difficult than I expected.  I am trying to complete a tourist contract taking 5 tourists around Mun and Mimnus.  I'm in orbit around the Mun but can't seem to create a transfer from the mun to .Mimnus.  I'm not sure if I'm trying to do this in a bad sequence or what.

I thought I had the Mun encounter lined up so that if I flew past the Mun without performing a retrograde burn to enter orbit that I would fly by and be headed to Mimnus.  But I decided to get into orbit of the Mun, then transfer from that orbit to Mimnus.  Maybe this is not the proper order?  Should I go back around kerbin then to Mimnus?  Or should I have skipped Mun and gone to Mimnus first and then catch the Mun on the way back?

this is the first time I have tried to perform a multi body route and I am not enjoying myself so far.  :(

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Going from the Mun to Minmus is a bit tricky. It is also extremely slow - you should count on about 8-10 days transit time.

In fact, it's very much like a small-scale version of what you'd do to go from Kerbin to Duna, Dres or Jool. You need to leave the Mun's SOI going prograde, while the Mun is about a quarter orbit or so behind Minmus.
You eject from the Mun into a broad orbit and catch Minmus on the other side of Kerbin. You'll almost certainly have to drag the manouvre node around the orbit a bit to get the right ejection angle.

The way to do it is:

  • Check that Minmus is ahead of the Mun. About a quarter turn should be fine, maybe a bit less, but you can compensate for error by accepting a less efficient trajectory. In any event you are unlikely to get the exact angle, since the Mun moves so much each time you complete an orbit around it, so both your ejection angle and the difference in positions between the Mun and Minmus will vary enormously from one orbit to the next.
  • Set Minmus as target.
  • Drop a node and set it up for a prograde ejection from the Mun to give a resulting orbit remaining within Kerbin's SOI (assuming a standard prograde low orbit, that probably means a node on the far side of the Mun, with roughly a 350m/s burn (pure guess for that number, don't count on it!)).
  • Drop a second node about halfway to Minmus so that you get intercept "close approach" markers. If you need a plane-change correction (and you probably will), add a bit of normal or antinormal to that second node to get a better approach, but don't try to do too much yet. You need to improve the ejection burn first.
  • Go back to your first node, add or subtract prograde and drag it around your orbit until you get a very close approach.
    • If your closest approach has Minmus relatively far ahead of you, you need to either wait an orbit or two around the Mun (since the Mun will be catching up) or you need to head more towards Kerbin so that you dip down and then rise back up to meet Minmus. In the latter case, your ejection burn and your capture burn at Minmus will be higher.
    • If your closest approach has Minmus relatively far behind you, you've left it a bit too late and you'll need to head out away from Kerbin (i.e. you need to drag the node back along the orbit around the Mun) with a significantly harder burn, and a significantly higher capture burn at Minmus. The only advantage is that it'll be a much quicker transfer.
  • Go back to your second node and fine-tune your intercept.
Edited by Plusck

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Yes, I think it's easier to do it in the other order (Minmus first then the Mun on the way back) , for several reasons.

First, getting to the Mun from Minmus is pretty trivial. You can leave any time you want and still get an intercept at the Mun for an extremely small deltaV cost.

Second, if you are returning directly to Kerbin from Minmus, you have an extra 100 m/s of velocity at Kerbin that you need to get rid of -- than if you go from Minmus to the Mun, then the Mun to Kerbin.

Third would be the timing to get to Minmus. If you are leaving from the Mun, you can only leave on one day out of six. If you leave from Kerbin, you can leave during any orbit.

 

 

 

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I'm setting up a Mun to Minmus transfer right now ... order was dictated by wanting to land on the Mun, and it being a good place to drop a stage to avoid clutter.  I'm looking at an ejection burn of about 210 m/s, and a plane change of 40 m/s, with Minmus being 60 degrees in front of the Mun on ejection.  Given that ejection is 3 hours after the burn, not quite 90 degrees in front seems like a pretty good call...

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