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I'm sending a manned mission to Minmus and, as Minmus' orbit is inclined to Kerbal I need to perform a maneuver to align inclination. From one of Scott Manley's newbie career guide videos I hear that I should do that as early as possible, i.e. at some LKO as it will be more efficient, but its not obvious why and at which exact point on the orbit (Ap, Pe, An, Dn being just a few possible cases). Thus my questions are:

  • Why should the inclination matching maneuver is most efficient at low altitude?
  • When I'm in some stable elliptic LKO, at which point of the orbit should I perform that inclination-matching burn?
  • Going further, as I intend to go into a transfer orbit next, could it be more efficient to combine burns and perform inclination (normal) & transfer (prograde) burns at a single node?
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  • Scott Manley is the Chuck Norris of KSP - he's always right. If he's wrong, it's KSP that needs to change. But it sounds like he would be recommending a inclination change during Hohmann transfer from LKO. If you're using a maneuver node you can see that an inclination change at the same time as Hohmann transfer will add only a few meters of delta-v - free inclination change! If you perform a course correction halfway to Minmus you're looking at around 50 meters.
    – Coomie
    Commented Aug 19, 2015 at 1:33
  • He actually is doing this on his way to LKO, directing the rocket slightly south/north. But, for the newbies like me who risk spinning the craft out of control, inclination correction is suggested at the LKO.
    – Sergii Zaskaleta
    Commented Aug 19, 2015 at 8:59
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    Once you know what you're doing, I recommend using MechJeb to avoid the tedium of minor course corrections. I have 700+ hours of KSP under my belt and I use MechJeb to perform simple course corrections like fine tuning planetary (or satellitic) intercept. These are best done at high transition nodes (usually half way between LKO and Minmus).
    – Coomie
    Commented Aug 20, 2015 at 1:04

1 Answer 1

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Inclination matching can only be done on the ascending or descending node. At any other point of the orbit you can not achieve perfect inclination matching.

While most course corrections are done best when you are fast, i.e. near periapsis, it's the opposite with inclination. The slower you are, the less delta-v you need to change it. So when one node is on a higher altitude than the other, you should do inclination-matching at the An/Dn node that is higher above Kerbin than the other one.

When you want to minmax your delta-v budget, time your launch until the rotation of Kerbin turned the space center to be directly beneath the ascending or descending node of Minmus' orbit around Kerbin thus making perfect inclination matching (see above) possible. Then head for the inclination during the gravity turn, i.e. aim for heading 96° instead of 90° in regular lift-off. That way your low-Kerbin parking orbit will be already inclined to Minmus' orbit.

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  • Definitely the best answer. +1
    – Tim S.
    Commented Aug 18, 2015 at 19:04
  • Took me 5 times read to understand the 2nd paragraph. Could you kindly explain more on the 3rd one, with timing the launch to start right 'under' the node?
    – Sergii Zaskaleta
    Commented Aug 19, 2015 at 8:57
  • @SergiiZaskaleta I am not sure how I could explain it any better. Could you be more specific about what you don't understand about it?
    – Philipp
    Commented Aug 19, 2015 at 9:04
  • How planet rotation helps with 'starting' inclination?
    – Sergii Zaskaleta
    Commented Aug 19, 2015 at 9:06
  • @SergiiZaskaleta The idea is to wait until the space center is at the ascending node, so that when you launch, you enter orbit at the ascending node. When you already started with an inclination of 6°, you will already be on a perfectly inclined orbit for a Minmus transfer.
    – Philipp
    Commented Aug 19, 2015 at 9:09

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