Change an orbit from horizontal to vertical without increasing Pe or Ap?

[MR4Y]

Title says everything.

[Fyrem]

MR4y, you can, but the math is a pain. also, if you try to change more than 45deg, things get weird.

if I want to change from a normal horizontal to a vertical orbit, I do it in 30ish deg steps. and let 1/2 an orbit go by between each step. this isn't nessaary but due to the way the maneuver nodes work, it sure makes things easyier.

change the Blue node, then pull BACK on the retro node to reset your AP back down where you want to go. again, the maneuver node system chokes if you try to go more than 30-45 deg in one step.

[Sol_Rokks_Teddy]

Make a maneuver node and pull on the retrograde icon as well as the normal/anti-normal icon.

[MR4Y]

I tried both suggestions, but it ends on a excetric orbit.

[ThePsuedoMonkey]

You have to keep your heading dead-center between your prograde and retrograde vectors: if you are pointing slightly toward prograde your orbit will increase (i.e. antipode will become higher), and slightly toward retrograde will make your orbit decrease. This will change throughout the burn and will never be perfect, so try and make the amount of time you burn on either side about the same.

[RoboRay]

The cheapest way is to transfer out to the Mun on a free-return trajectory and select the desired inclination on the way back down.

Trying to make a 90 degree plane change by burning on the Normal axis is going to take crazy amounts of fuel.

[Jason Patterson]

Depending on the body you're orbiting, it might be simplest just to burn normal to your velocity until you've made the adjustment you want. As your velocity changes direction, so does its normal, so you have to continuously change your ship's orientation. For a high velocity orbit it's going to take a fair amount of delta-v to do this though.

If you're on Kerbin, you're best off just launching the vessel anew and burning toward the north or south to begin with. Make your usual gravity turn, but instead of turning toward 90, turn toward 0 or 180. Depending on how particular you're feeling regarding your polar orbit you can burn slightly to the west to correct for the eastward velocity you begin with from Kerbin's rotation.

In general, if you're in a circular orbit then the minimum delta-v is given by:

delta-v = 2v sin(theta/2)

where v is the orbital speed and theta is the inclination change. Here that would be 90 degrees, so you're looking at 1.4 times the orbital speed to change from an eastward orbit to a north- or southward orbit. That's the ideal, not what I suggested above.

If you're set on altering an existing orbit, burn to change your orbit (which will probably wind up being eccentric) then fix the eccentricity.

[tek_604]

If I want to shift into a polar orbit (for mapping), then as soon as you hit the SOI of the body, this is the best time I find. OK, probably better earlier than this, but I find as soon as you hit SOI, is more manageable.

Usually, my order is (as soon as I hit SOI):

1) Set periapsis to my desired altitude

2) Switch to polar orbit (~88 degrees)

3) Circularize at periapsis

Of course, I also use MechJeb, so...

[Morzak]

If you use the node's they will not give accurate changes, because as you're inclination changes during the burn so does you're Normal/anti Normal position, that means on the node you have to either use the Retrograde or the prograde marker to adjust for that difference, else you would try to stay on the normal/anti normal the whole burn. Around kerbin it will probably need more then one correction burn, since it will take a lot of delta V (launch everything in the inclination you need it, changing it in LKO is just not a good Idea).

[numerobis]

If you burn normal an infinitesimal amount, you only change the inclination (infinitesimally). If you do a bunch of infinitesimal normal impulses, updating which way is normal each time, then you're burning an arc around a circle. You can do the same net burn in a single impulse burning the chord. That corresponds to one big impulse that's halfway between normal of your correct orbit and normal of your destination orbit.

Unfortunately, that's not what the maneuver node lets you plan: it lets you fire a big impulse normal to your current orbit, and you have to plan some retrograde (or prograde? I always forget) to balance out and get that average.

That said, if you're doing a 90-degree plane change, you are best off pushing your apoapsis way high and changing inclination up there. The cost of an inclination change depends on your speed.