public void UpdateFromOrbitAtUT(Orbit orbit, double UT, CelestialBody toBody)
 {
     pos = (orbit.getTruePositionAtUT(UT) - toBody.getTruePositionAtUT(UT)).xzy;
     vel = orbit.getOrbitalVelocityAtUT(UT) + orbit.referenceBody.GetFrameVelAtUT(UT) - toBody.GetFrameVelAtUT(UT);
     UpdateFromStateVectors(pos, vel, toBody, UT);
 }