If you want a slightly less time-sucky orbital mechanics game, then Space Flight Simulator (on Android and iPhone) is really good. It's limited to 2D, but you w

If you want a slightly less time-sucky orbital mechanics game, then Space Flight Simulator (on Android and iPhone) is really good. It's limited to 2D, but you will still learn a huge amount about orbital mechanics. And it is possible to build and launch a rocket to the moon and back in about ten minutes, once you know what you're doing.