When to Accurately Know When to Launch to Intercept an Orbiting Vessel?

[SirSnuggles]

Recently, I've been taking KSP more seriously, making efficient rockets & mathematical equations, etc. I'm wondering if there is a way I can more efficiently intercept an orbiting vessel other than just guessing the launch window. I would imagine it's the same concept as phase angles for planets, but I don't know how it would work if, for example, I want a Duna lander to intercept the return stage.

Edited October 31, 2013 by SirSnuggles

[Superfluous J]

Experience, mostly. Just do it a few times and you'll see when to launch. Mostly, though, I just launch aiming to get behind what I need to dock to, so I can orbit a few times below it waiting for it to catch up to me. If you get in front of it you have to raise your orbit higher, wasting fuel.

The problem is that the exact time to orbit is variable based on your ship, your boosters, what you're carrying, how well you perform your gravity turn, etc. Even if you use MechJeb the varying thrusters and weights will cause deviations.

[merlinux]

It is different for all planetary bodies and also relative to the altitude of your target. As the previous poster said your goal is to be slightly below and behind your target.

[Vanamonde]

An effective if not fancy way of doing it is to save the game, launch and fly to the target's orbital height, and note how far the target has moved in that time. Then load your save and launch when the target is that far behind you in its orbit.

[Unit327]

Somewhere on reddit I learned a good rule of thumb - if you are in a lower orbit than your target, thrust when the tangent of your orbit at your current position intersects the current position of the body you are catching. Or to put it simply, draw a line between yourself and your target; when that line is tangential to your orbit, hit the throttle.

Apparently works if you are in a higher orbit as well, the line just has to be tangential to your target's orbit instead of yours.