# Solar drag and robust Kepler equation solution

Hello everyone! During the last two weeks, I’ve been finishing primary perturbation goals and was studying the robust Kepler equation solution proposed in the paper *“Robust resolution of Kepler’s equation in all eccentricity regimes”, Davide Farnocchia et al. *The guy now works in NASA, actually :)

**Solar pressure**

So, first of all, I finished the solar drag perturbation force. Unlike 3rd-body perturbation, which is also time-dependent, validation for solar drag went smoothly. The computation includes calculation of so-called shadow function, that allows to conclude whether the body is in the shadow of Earth (or some other planed) or not. We finally merged in in this PR.

**Robust Kepler propagation**

The paper, mentioned in the beginning of this post, proposed the way to solve the Kepler equation (to propagate orbit in time) more robust without Newton divergences) and faster (with less iterations). We (me and Juan) first tried to reproduce the results of this paper in a separate repository. After some work, we finally reproduced all the histograms from the paper, and now I am trying to make that work inside Poliastro :) Wait for the new PR!