# Applying secondary orbital perturbation effects

I read about secondary effects which influence on orbit propagation like solar radiation, moon, etc. (https://en.wikipedia.org/wiki/Orbit_modeling). First I calculate position vector Rpqw to object (artificial satellite) using 6 orbit elements with following formulas:

u = v + ω
r = a*(1-e*e)/(1+e*cos(v))
p = r * cos(v)
q = r * sin(v)
w = 0.0
RotationMatrix = R3(-Ω)R1(-i)R3(- ω)
Rijk = RotationMatrix * Rpqw
Where:
U – latitude argument
r – distance to object
Rijk – coordinates of object in 3D space in ECI coordinate system (a.k.a. IJK - axis)
a -  semimajor axis
i - inclination
Ω - right ascension of the ascending node
ω  - argument of perigee
v - true anomaly


I want to know when I must apply effects like solar radiation pressure or atmospheric drag and others, after I calculate Rijk or during the process? And does the applying order matter?

• +1 I'd never heard of Gauss' Planetary Equations before, but they seem quite useful! Great answer. – uhoh Feb 16 '18 at 23:28