Hello everyone,
I’ve seen a strange behaviour in Brouwer Lyddane propagation that may be a bug.
There are some jumps in RAAN and Arg. of Perigee at perigee and apogee.

I’ve done a small piece of code to show the problem. It is a simple comparison between Brouwer-Lyddane propagator and a numerical propagator using only 6x6 Earth potential. BrouwerLyddaneBug.java (4.4 KB)
Here is the orbital parameters plot (blue=numerical, red=BrouwerLyddane)

That’s a strange behavior we must investigate. Thank you for the code allowing to reproduce the problem.

I remember that Lyddane contribution to the Brouwer propagation model is to sum the argument of perigee with the true anomaly in order to avoid the singularity of the Brouwer’s model. Therefore if an equation is wrong in the arg. of perigee, I would expect something wrong also in the true anomaly. But not…

I just have one question, did you try the comparison with 5x0 Earth potential?
It is the dynamical model of Brouwer-Lyddane propagator. Maybe the problem will still be here, but I find interesting to test at iso-model.

Hi Bryan,
The comparison with5x0 Earth Potential 5x0 gives the same problem.
For better analysis, I have also plotted the orbital parameters differences.
Regards,
Sébastien

Thank you Sébastien for reporting this.
That actually brings up a question I had (more for @bcazabonne I guess): does the B-L model consider that inertial and Earth-fixed frames have the same Z-axis, or is a tilt included?