http://orbit.medphys.ucl.ac.uk/ I have been playing around with this program for about a week, it's a bit technical (read the documentation) but once you get into it it's a lot of fun. Basically, it's a flight simulator, but the entire solar system is in there, you can fly anywhere on the planet and several spaceports are present, both real and imaginary. It works just like a normal flight simulator when you are in the atmosphere but you can also try orbital maneuvers, de-orbits, and even interplanetary flight. There are also several spacecraft to choose from both real (like the space shuttle) and fictional (I love the delta glider - it's an awesome rocket plane/spacecraft). The graphics are pretty good and there is a TON of add-ons from additional spaceports/airports, additional spacecraft, military aircraft, and upgraded textures. Here are some screen grabs: The shuttle Atlantis lifts off! The cockpit of the Delta Glider (it's a fully 3D cockpit, you can also switch to a standard 2D cockpit) The Delta Glider, ready for takeoff: The Delta Glider Takes off! Here is the Delta Glider in orbit: The moon from the Kennedy Space center - you can fly to it (and land there) if you really want to: Earth from space (specular reflections on the water and atmospheric haze - the sky even turns red at sunset and sunrise!): Mars from space, it has a working atmosphere too!