KSP Perfect Inclination Change

[CorMazz]

Hey guys, I was wondering if it is possible to do a ~perfect inclination change. By perfect I mean that your apoapsis and periapsis almost do not move. I know that with the default nav ball you cannot do it because the nav ball doesn't account for the fact that normal and anti-normal moves as you burn. If there was a way to mod it or just eyeball it and you guys know, I would appreciate it.

[Ravenchant]

Depends on how you define "perfect" You can easily get to NaN° with a bit of maneuver node fumbling (NaN° because of a programming limitation, AFAIK. I assume it means less than 0.05°, since 0.1° is the usual accuracy of the marker).

[Alistone]

Use ion engines. Any movement will be minimal.

The difficulty you run into trying to make it "perfect" is that the way to do this is to thrust perpendicular to the plane. But as you are thrusting the plane is changing and you would have to turn your craft to keep it's perpendicular orientation to the orbital plane of your vehicle.

Most people like to set up a maneuver node and keep the ship pointed in the same direction during a burn rather than turning along with your orientation. But to accomplish this you must change your orientation while you are changing your plane.

[Captain Sierra]

Use ion engines. Any movement will be minimal.

The difficulty you run into trying to make it "perfect" is that the way to do this is to thrust perpendicular to the plane. But as you are thrusting the plane is changing and you would have to turn your craft to keep it's perpendicular orientation to the orbital plane of your vehicle.

Most people like to set up a maneuver node and keep the ship pointed in the same direction during a burn rather than turning along with your orientation. But to accomplish this you must change your orientation while you are changing your plane.

What this translates to is you must constantly stay aligned with the normal/antinormal vector, which is constantly shifting with your orbit. You can accomplish this manually if you have Enhanced NavBall or automatically with MechJeb Smart ASS.

EDIT: IN better response to the OP, there is Enhanced NavBall which adds radial and normal vectors to the navball. There is also MechJeb Smart ASS which can hold you to any of the orbital vectors with computer accuracy.

[purpletarget]

You can check this video here, which eventually gets to doing inclination changes, either by eye & math, or by modifications with the nodes.

Basically,

• take your perpendicular heading (eg: Prograde vector on 090, look at 000),
  
• run back towards the retrograde 1/2 the degrees you want to change. (30 degree change, go from 000 back 15 to hdg 345).
  
• Note your speed.
  
• Burn quick and hot, your speed will drop (you may want to point a bit above horizon to compensate) and eventually start to climb again.
  
• Burn until you've got back to your original velocity.
  

With the nodes, adjust your inclination until you're happy, and then pull the retro marker until your Ap goes back close to where it is. (You'll find the Manuever node in pretty much the same place as method 1)

[Traches]

I do them all the time-- there's a mod called enhanced nav ball that adds normal and radial markers. For a small change or when your orbital velocity is low, just burn at very low thrust and track the normal marker as it moves. (It's not the most efficient way though, as you're burning in a curve.)

Otherwise, just tweak your maneuver node until you get the orbit you want.

[Flixxbeatz]

EDIT: Got it now. But it's nearly impossible to do a perfect one (there's still little excess).

[match]

If what you are asking is if you can maintain Ap and Pe altitude during the maneuver, as was pointed out is very difficult and amounts to a sliding vector change. For minor changes, the change in altitudes is negligible. On larger changes, you experience the "dip and recover" (plane changes as was mentioned earlier). The "perfect" maneuver would deliver the dV in an instant. Since this is not practical, we calculate the midpoint of the burn and extend the beginning and end from there. (If nothing else, KSP has taught me to divide time in half very well!)

This phenomena can best be experienced by attempting such a maneuver with differing propulsion systems. Let's say I... I mean this Kerbal was orbiting the Mun equator. This Kerbal wants to change to a 45 degree inclination but only has about 100 dV left on my rocket engine. No problem, the mission plan included a large amount of RCS. Once the motor quits, it is ejected and we finish the maneuver with RCS. Great plan, right?

Once the engine quits and is ejected, we are far into the "dip". As we continue the maneuver and adjust our trajectory to match our intended orbit, the trajectory passes through the Mun. While theoretically we have enough dV from the RCS to complete the maneuver, we lack the time to apply it and recover.

Result: Lithobraking on the Mun

This is completely based on a hypothetical situation; At no time did I... I mean this Kerbal think that this plan was ever going to work

So the "perfect" inclination change would require the vector change in an instant. Barring that, faster delivery of the needed thrust will make the "dip and recover" less pronounced, but still there.

[thereaverofdarkness]

The easiest way I can think of is to tweak a nav point in the map until it's just right, and use that blue mark on your nav ball. Once you get the hang of how far it is from the standard marker on the navball, you can learn to eyeball it.