Love this. I managed to get a pretty stable orbit by using the right angle and velocity (by chance). Highlighted in yellow: http://i.imgur.com/OOaTLMP.png
It ran for several hours like that and never deviated from the original "circular" path. Unlike the other attempts, which were all much more elliptical. I guess that's kind of how planets would stay in a stable orbit though, having the right distance and speed for their mass.
