How do I change from this orbit to this orbit?

[tufduck]

I am in a polar orbit around Kerbin. The blue one in the picture below. I want to rotate my orbit to the same plane as the green one. How do I setup a maneuver node for that?

I tried a maneuver node with a normal / anti-normal change (the purple icons) like this:

But as can be seen isn't what I want. So how do I change to the green plane?

Edited December 30, 2014 by tufduck

[benkh]

Short answer : you will have to set up a maneuver node where the two orbits cross each other. So in your case near the poles . However this will take much dv. If you have the fuel to do so, don't forget to change your orbit into the right direction

[MarvinKitFox]

Simple way...

At a point where the two orbits cross (north or south pole, in your case), apply one great stonkin big humungous lateral burn, with enough retro to prevent it from going nuts on you.

Did I mention this will be a **very** big burn?

Basically, look at your orbital velocity. Multiply by 1.45 at least

That is what you will need to do the change, if the two orbits are 90 degrees on each other.

It could be 2 * orbital velocity delta-v needed if the orbits are almost counter to each other.

The smarter, and in reality easier approach.

Where the two orbits cross, add a prograde burn out to almost infinity. This should be about 0.4 times your current orbital velocity.

float out to a very very high apogee, then when your orbits cross again apply the plane change. It should be a good approximation of free. Adjust your perigee to exactly match the wanted orbit in perigee.

Now float to perigee, and circularize to match the desired orbit. Again, expect to use 0.4 of the resultant orbital speed, or less.

Total delta-v needed is, at most, 0.8 of your starting orbital speed.

.

.

Profit!

[Reactordrone]

Simple way...

At a point where the two orbits cross (north or south pole, in your case), apply one great stonkin big humungous lateral burn, with enough retro to prevent it from going nuts on you.

Did I mention this will be a **very** big burn?

Basically, look at your orbital velocity. Multiply by 1.45 at least

That is what you will need to do the change, if the two orbits are 90 degrees on each other.

It could be 2 * orbital velocity delta-v needed if the orbits are almost counter to each other.

The smarter, and in reality easier approach.

Where the two orbits cross, add a prograde burn out to almost infinity. This should be about 0.4 times your current orbital velocity.

float out to a very very high apogee, then when your orbits cross again apply the plane change. It should be a good approximation of free. Adjust your perigee to exactly match the wanted orbit in perigee.

Now float to perigee, and circularize to match the desired orbit. Again, expect to use 0.4 of the resultant orbital speed, or less.

Total delta-v needed is, at most, 0.8 of your starting orbital speed.

.

.

Profit!

Or with a planet with an atmosphere you can bring the periapsis into the atmosphere and aerobrake your apoapsis back down before circularizing into the final orbit.

[Superfluous J]

Note that just pulling on the Normal vector will affect the periapsis and apoapsis. And after you go 10-15 degrees it gets worse. By 45 degrees, a "normal" maneuver node manipulation will do more to your apoapsis and periapsis than it does your normal angle!

To correct this, you have to manipulate both the prograde/retrograde, and normal/antinormal nodes in tandem. Do one, then the other. Then the one, then the other. Keep alternating.

It's not intuitive but after fiddling with it for a few minutes you should start to see how they interact.

[Empiro]

Two more points of general advice that might be useful to you in the future:

If you wanted to launch directly into the second orbit, then the trick is to timewarp at the launchpad until your desired orbit passes right over the KSC, and then launch into the polar orbit. This way, your resulting inclination change very small.

Second, in general, when you perform a maneuver, you affect your orbit at every point except where you are currently at. This is why your first maneuver didn't work out -- no matter what sort of maneuver you perform, one point in your orbit will always be at that maneuver node, which isn't anywhere near your target. To match orbits, you want to burn where the two orbits "overlap".

[Anquietas314]

If you wanted to launch directly into the second orbit, then the trick is to timewarp at the launchpad until your desired orbit passes right over the KSC, and then launch into the polar orbit.

Just to add: you should actually launch a little bit before KSC passes under the orbit to account for planet rotation during the first ~10km of your ascent; after that it doesn't really matter since you can quickly overcome the 200m/s or so from that.

[tufduck]

Thanks everybody for your explanations. I've got it now.

Second, in general, when you perform a maneuver, you affect your orbit at every point except where you are currently at. This is why your first maneuver didn't work out -- no matter what sort of maneuver you perform, one point in your orbit will always be at that maneuver node, which isn't anywhere near your target.

This tip was great! I'll try to remember that in the future.

[LethalDose]

To make the burn directly, you would need to burn above or below the poles.

I'm only saying this because I don't see that anyone actually gave that answer yet. Its going to cost, ballpark, about 3 km/s of dV, I think. You could do a bi-eliptical transfer and maybe get it down to around 2 km/s. Those numbers could be wrong, though. I'm just riffing off the top of my head.

Launching into the orbit directly is a vastly better option, like everyone else has pointed out.

[Anquietas314]

Its going to cost, ballpark, about 3 km/s of dV, I think. You could do a bi-eliptical transfer and maybe get it down to around 2 km/s.

Raising apoapsis to ~Minmus's orbit only takes about 1-1.2km/s, at which point the cost of the plane change is negligible. After that you can just aerobrake to establish the desired orbit. The direct plane change figure seems reasonable though

[Behemoth1702]

don't forget to change your orbit into the right directio

So... Important...

I perfectly aligned fine print orbits for 30min just to realize that I was going into the wrong direction. Outraged I enabled cheats and just burned retrograde until the orbits matched again, hahahaha.