Ending of 2nd evaluation period: new propagator in parabolic region, J3 perturbation, continuous thrust

Hello everyone! The second period of GSoC is ending and there’s a lot to tell about what has been done.

New parabolic propagator

In the region where e ~ 1, orbit is called near-parabolic, i.e. very close to parabola. The existing methods of orbit propagator behave unstably and can fail. In order to fight this, we employed the paper written by the guy 6 years ago who is now working at NASA.

He proposed an approach with introduction of some sophisticated function in the near-parabolic region, that is the alternative to common definition of mean motion. With this new approach, we managed to achieve maximum of 3 iterations required for Newton method convergence when 0.99 < e < 1.01, that’s great! And what is most important, now the mean_motion propagator converges everywhere, which is super-important.

J3 perturbation

As I wanted some time ago, in addition to J2-perturbation (oblateness of Earth!) we added J3 perturbation. The J3 perturbation represents whether Earth looks like peach or not :) The effect of J3 perturbation is three orders of magnitude smaller than the one of J2, but still its account is important for high-precision satellite propagation.

Thrust

Finally, we started working on continuous thrust. The perturbations that we were doing before, are natural. Thrust is some artificial perturbation of the orbit that allows us to change its parameters in the way we want it. There are numerous known maneuvers aimed at changing large semi-axis, ecc, inclination et cetera. We work on these here.

The problem, though, is that these maneuvers take quite some time, and so tests do not pass because they take too much time. We are going to accelerate finally our integration with numba jit, and we will see what it will turn into :)