Welcome to Gaia! ::

This is a completely free space simulation I've been using for some time now, and thought it might interest some of the people here. It's an ultra-realistic simulation of space flight, enabling you to visit all the major bodies of our solar system, and their moons, asteriods and so on. The learning curve is steeper that a cliff, but it's WELL worth the effort.

I could go on endlessly about how much I love this program, but Wikipedia does a better job at summing it up: http://en.wikipedia.org/wiki/Orbiter_(sim)

And here is the actual site for Orbiter... I would highly recommend downloading the planetary extension package too, as it improves the planet-textures/weather-patterns: http://orbit.medphys.ucl.ac.uk/orbit.html

The modding community for this game is massive as well, There are endless craft to download, from historic to purely sci-fi.. theres also been rumors of someone designing a whole new system based around alpha centauri.. though I've yet to see any hard evidence of this.