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Is matching planes neccessary?


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Hello everybody,

sooooo if you want to rondevouz with a target, the standard operating procedure is matching orbits, eyeball-rondevouz, fine-tune rondevouz.

Now my question: is matching planes realy neccessary?

I mean if I am in an 85° orbit and wanting to rondevouz with a 90° Orbit I just could wait a little bit and then make a homan transfere, come close and kill all relative velocity. Wouldn't that do the trick?

And would it be more efficient?

Quistions over Quesitons! What do you think?

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Well, what I do in that situation is correct my orbit when rendezvousing, I might overshoot a bit but it's usually not that bad.

Just get your closest approach as close as you can with the nodes, and be ready to burn that much extra to align yourself with your targets orbit when you get close :)

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Hello everybody,

sooooo if you want to rondevouz with a target, the standard operating procedure is matching orbits, eyeball-rondevouz, fine-tune rondevouz.

Now my question: is matching planes realy neccessary?

I mean if I am in an 85° orbit and wanting to rondevouz with a 90° Orbit I just could wait a little bit and then make a homan transfere, come close and kill all relative velocity. Wouldn't that do the trick?

And would it be more efficient?

Quistions over Quesitons! What do you think?

Not completely necessary, but you may end up waiting much longer for things to be aligned right, and you'll probably burn more fuel matching velocity because you won't be changing inclincation at the best time.

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if you are off be a degree or so matching planes isn't going to be all that necessary, any dV used to align planes is negligible in the grand scheme of things. Anything over about 3 degrees I align just to make my life easier.

Plus ... when you're killing your final relative velocity you ARE matching planes. Doing it sooner rather than later just makes the entire rendezvous a lot easier.

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if it's a matter of interception, like you're shooting for a planet or docking with a station, matching planes gives you far more and far longer opportunities for rendezvous. think about the odds of two objects meeting with orbits 90 degrees to one another as compared to those on an equal plane. and while i don't have the math on hand, the amount of delta-v required to rendezvous with and match speeds/correct motion with something going in a different direction is bound to be more than the delta-v required to match planes and then simply matching speed.

edit: basically what tex said. you have to match planes with whatever you're transferring to, so whether you do it in advance, or at the exact moment you intercept the target is basically the question. i imagine doing it at the moment of interception would also require far more TWR

Edited by Franklin
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Your question is a matter of perception. :) To bring ships together at rest with respect to each other for docking necessitates matching orbits. You WILL expend the same delta-V whether you do it as one burn or several. It's just often easier to match orbital parameters one step at time.

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No and Yes.

You don't have to do it outright; but by eliminating your relative velocity when near the target actually puts you into (essentially) the same plane. So it is something you will be doing; even if you don't do it as a first step before establishing an intercept.

Regarding efficiency.... it is more efficient to modify your plane at lower velocity (apoapsis). In a recent Jool intercept orbit trying to match the plane of a target at periapsis it would have requires over 9000 deltaV; but by doing it many million of meters higher at apoapsis I was able to do it for less than 1000. Whether it is more efficient to intentionally raise your apoapsis; modify your plane; then lower it back again depends primarily on how different the planes are with eachother.

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Try rendezvous from an equatorial orbit with a polar orbit and let me know how well that worked out :)

Really, the lame answer "it depends" is really the correct one. If they're nearly the same it doesn't matter. If they differ more you want to adjust your inclination and if you need to change your inclination significantly you might want to consider raising your apoapsis (and moving it to the ascent/descent node, obviously) before doing that.

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Alternatively you can use small taps of RCS to be lined up for aerocapture before you even leave Kerbin SOI

It's what Jeb would do (Stacking tons of heat shields on one side of the pod and filling it with pillows to absorb massive G forces as you enter Eve's lower atmosphere at 8000 M/s is recommended)

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