How to Rendezvous with a Vessel on Escape/Ballistic Tragectory

[worir4]

I have, in all my KSP time, never managed to rendezvous with a vessel that is not in a stable orbit. I can do it easily as long as it has a periapsis and apoapsis but i struggle when there is a limited time to achieve rendezous.

My questions are

1. Assuming the target is not inclined, when should i launch? (Location of KSC relative to target)

2. Should i make a stable orbit? If so , how should i burn to get an approach?

3. For vessels returning from other planets, where on it's orbit is the best place to aim to meet at? The periapsis? This will have the highest velocity so i will require more delta-v to circularize. High in it's orbit? This will mean i will have to burn more on launch.

I would be grateful if any one could point me towards a tutorial for this kind of rendezvous.

Thanks for the Help.

[Empiro]

For meeting something on a hyperbolic trajectory, you should launch early into a circular orbit at the same inclination while having your altitude be equal to your target's PE.

Once your target enter's your SOI, place a maneuver node at intersection point between your orbit and the target's. Press the "next orbit" a bunch of times until you see close approach markers. Then, pull the prograde handle, which should move the markers closer together until they meet up at the PE.

Essentially what you're doing is finding a point where your ship is at PE and your target will reach PE in 1 orbital period (of your orbit) plus a bit. Then you increase your orbital period by burning prograde so you'll arrive at PE at exactly the same time. You'll then match velocity the next time you come around.

You actually save fuel doing this, because you're matching your target's orbital energy (which is much higher than yours since they're coming in at interplanetary speeds), so it's best do perform your burn at PE, when you're going the fastest in order to take maximum advantage of the Oberth effect. However, if after rendezvous, your next goal is to slow back down, then you might want to make your rendezvous earlier so you can maneuver yourself into an aerobraking trajectory (though your target should could potentially do the same at very low fuel cost too). Performing a solar rendezvous is easier in this case.

[Zargg]

Great pointers, thanks Empiro. This is something that also has me stumped for some reason. Randomly seeing an asteroid coming by Kerbin, I'll put something in orbit, but then for some reason I could never figure out how to match it's speed and path in an easy way...

[Semmel]

I d it similar to Empiro but slightly differently. Usually, I launch ahead and make an efford to launch in the same inclination by timing the launch properly. Any inclination errror, I fix in orbit. Then, I put my spacecraft into a highly elliptical orbit with the apoapsis intersecting the incoming trajectory. Then hit next orbit until my spacecraft and the asteroid are at roughly the same place at spacectraft apoapsis. Once they are there, I perform a normal docking maneuver: kill velocity and then dock. That way, its possible to adjust inclination and periapsis prior to the encounter. Slightly more complex for mission planing but usually saves a lot of delta v because the docking procedure is much easier. And it allowes to divert the asteroid in case it would hit the surface.