Getting Absolute Longitude (in same reference system as LAN)

[Luke321]

Hey guys,

I\'m currently working on a plane alignment module for MechJeb,

and my problem is that i can\'t get the absolute longitude in which the game calculates the LAN.

which is essential for precise burns especially in polar orbits.

if anyone has an idea on how to solve this, it would be a huge help

[lai]

LAN + LPE + true anomaly

[shimavak]

That isn\'t quite correct. It works perfectly at zero inclination, but fails otherwise due to mixing of angle mixing. What you really want is effectively the current sidereal time, as that is the coordinate system that LAN is measured against.

A more complete answer would be:

Local Sidereal Time = Current Orbital Longitude = LAN + Arctan[ tan( tA + APe ) * cos(i) ]

Where:

tA = True Anomaly

APe = Argument of Periapsis

i = Inclination

Of course, in KSP you have a lot easier ways to do this, as you always have the local latitude relative to the celestial body\'s surface, and the celestial body\'s surface relative position to the stars, so you can just do:

Local Sidereal Longitude = surface longitude + vessel.orbit.referenceBody.rotationAngle

Hope that helps with your orbital maneuvers!

[HarvesteR]

If you want to get coordinates relative to the 'universe', you can also use the Planetarium.up, Planetarium.right and Planetarium.forward unit vectors as a baseline. They define the coordinate system for the universal rotation.

Cheers