I have been following this simulator for years now, and it is one of the best space simulators on the market. You may or may not know this but it is completely FREE of charge.
Orbiter is a free and realistic space flight simulation program for the Windows PC.
Brief Description: Fed up with space games that insult your intelligence and violate every law of physics? Orbiter is a simulator that gives you an idea what space flight really feels like - today and in the not so distant future. And best of all: you can download it for free!
Launch the Space Shuttle from Kennedy Space Center and rendezvous with the International Space Station.
Recreate historic flights with addon spacecraft packages: Mercury, Gemini, Apollo, Vostok and more.
Plan interplanetary slingshots and tour the solar system with futuristic space craft.
Design your own rockets, or download addons created by other users.
Learn about the concepts of space flight and orbital mechanics by playing and experimenting.
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Here is the website link: http://orbit.medphys.ucl.ac.uk/
Here are some screenshots
Enjoy!