The celestial-mechanics tag implies that planetary orbital mechanics are on-topic for space.SE. I would like to edit the description of the tag to clarify that it is intended for spacecraft only. However, I ask here first to be sure that it is the intention of both the tag and the site members that this be the case.
"Questions regarding the movements and interactions of astronomical bodies as it relates to spacecraft, their trajectories, and their maneuvers."
Feel free to edit.