elements from state vector - Kerbalscript

orbit_vectors.ks

REBOOT.
CLEARSCREEN.

@LAZYGLOBAL OFF.

// Direct port of https://github.com/RazerM/orbital/blob/0.7.0/orbital/utilities.py#L252
FUNCTION elements_from_state_vector {
	PARAMETER r.	// Position vector.
	PARAMETER v.	// Velocity vector.
	PARAMETER mu.	// Body mu.
	LOCAL epsilon IS 1E-15.
	
	LOCAL h IS VCRS(r, v).	// Angular momentum.
	PRINT "h=" + h.
	// LOCAL n IS VCRS(V(0,0,1), h).  // Node vector right-hand
	LOCAL n IS VCRS(V(0,0,1), h).  // Node vector.
	PRINT "n=" + n.
	LOCAL ecc IS ((v:mag^2 - mu/r:mag) * r - (r*v)*v):mag / mu.	// Eccentricity.
	//LOCAL ecc IS  1 / mu * ((norm(v) ** 2 - mu / norm(r)) * r - dot(r, v) * v)
	PRINT "ecc="+ ecc.
	LOCAL e IS (v:mag^2)/2 - (mu/r:mag).	// Energy.
	PRINT "e="+e.
	// Not technically orbital parameters.
	// Will fail if e=1, but it's unlikely to be exactly that anyways.
	LOCAL a IS -mu/(2*e).	// Semi-major axis.
	PRINT "a="+a.
	LOCAL p IS a*(1-ecc^2).	// Parameter, semi-latus rectum
	PRINT "p="+p.
	//Inclination... if KSP was right-hand rule.
	//LOCAL i IS arccos(h:z/h:mag).	// Inclination.  0=polar, 90=equatorial.
	//PRINT "i="+i.	// 0 is polar, 90 equatorial
	LOCAL i IS arccos(-h:y/h:mag).	// Inclination.  0=polar, 90=equatorial.
	PRINT "iy="+i.	// KSP-normal(?)
}	
elements_from_state_vector(-body:position, ship:velocity:orbit, body:mu).