@MLB: The idea that you are shooting from a planet (and so you are not able to control the movement of the planet), however you can change planet (only between the green ones) by clicking on it.
For the moment the player starting planet is the center of the system (as is the more heavy) however in the next update I will add some sort of menus to choose the planetary system settings and as well the rocket to rocket collision (great idea). See you tomorrow!