Space Flight Sim for PC
Check out :
Orbiter:Space Flight Simulator.
They have a space flight simulator called Orbiter that you can download onto your computer.
Try get into orbit around or even land on the Moon. (You can use time compression to shorten the transit time from days to minutes.)
You could even try a trip to Mars. (Though even at the highest time compression the program allows, this would take Hrs. But if you have the time to kill ....)
Fun and educational at the same time.
Janus