Hi,

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.getKeplerianPeriod()`

or `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)?

Thank you!