Here is the webpage for downloading the Orbiter Space Simulator. Also make sure that you visit the other links as well since they offer up free downloads that are simply a must to have for the Orbiter Simulator.

Of course, it's free of charge. Also note this has a steep learning curve...

Orbiter Simulator Website: orbit.medphys.ucl.ac.uk/index.html

Thank you LMUStats for reminding me of this Simulator.