Class BrouwerLyddanePropagator vs. analytical computation

Dear all,

I want to find satellites with repetitive ground tracks, so find the inclination and semi-major axis that would create the correct drift of the ascending node.
Analytically, it can be computed using the orbital period and the RAAN drift due to J2, as explained here: Ground track - Wikipedia.

However, when I use BrouwerLyddanePropagator (with mean elements), I do not find the same relation between inclination and semi-major axis. As a positive point, I find the same with BrouwerLyddanePropagator than with STK J2 propagator.

Why is there a difference between a simple analytical computation and BrouwerLyddanePropagator taking into account J2?

Thank you !

Hi @echarlie

You may want to see this recent discussion. It is not about the same theory (we are talking about osculating parameters), but it is related. The main point is that depending on the dynamics considered, the orbit changes slightly. The Brouwer Lyddane model is not J₂ only, it includes up to J₅ so it may explain the differences you observe.