I have a question on TLE propagation and specifically the A value.
Taking the TLEPropagatorTest as an example with the GPS satellite data (from the Orekit unittests).
The orbital period there is defined as
period = 717.97 * 60.0 (43078.2 sec) or
2.00565440 in the TLE field.
If I do the A calculation myself using Mu = 3.986004418e14 and the defined period I get A = 2.656018572623494E7
When I use the TLEPropagator as
TLEPropagator propagator = TLEPropagator.selectExtrapolator(tle); SpacecraftState initialState = propagator.getInitialState(); then
initialState.getA() returns 2.6561853901682895E7 (~1.7km more) and subsequently the orbital period via
initialState.getKeplerianMeanMotion() converted to seconds is 43082.248 (+4 seconds compared to the original TLE value).
And this is even without any propagation just the initial state.
Maybe I miss something but it looks pretty strange/inconsistent. Could you please advise me how to deal with this to get consistent results comparable to the original raw TLE data (if it’s possible)?