Microsoft's Space Simulator
Having trouble running in 98, Extended Memory settings difficult to set. This
is was the first and best space simulator
before Orbiter.

One of the many mathematical formulas in Space
Simulator

A great resource for a dying game.
http://www.planetmic.com/orbit/spasim05.htm
Lot of games
http://www.the-underdogs.org/game.php?id=719
Keyboard layout from Handbook
http://www.geocities.com/SoHo/Atrium/9253/SpaSimm.html
Orbiter
The best space simulator
http://www.medphys.ucl.ac.uk/~martins/orbit/orbit.html
Celestial Astronomy
Program
Excellent program for studying the stars.
http://www.shatters.net/celestia/
Army
Free. Excellent simulation.
The Army's own game. You can download it but
even better is to go to your local recruiter and pick it up. There's no blood
and lots of honor. You do have to go through boot camp. If you kill to many brothers
you go to Leavenworth.
Here are the links:
http://www.americasarmy.com/downloads.php?sec=full
http://www.nvidia.com/view.asp?IO=army_download