Kerbal Space Program is an awesome spaceflight simulator. Achieving escape velocity or orbit is fairly easy, but even just hitting the moon is pretty hard! I haven't managed a soft landing yet, not to mention returning safely to Earth, I mean Kerbal.

+Craig Brown might enjoy this too.
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Mike Lawther's profile photoCraig Brown's profile photo
 
I never cease to be amazed that Apollo made it to the moon in nine years, in the 1960s!
 
Mike, I don't know you but we have a mutual friend (acquaintance for you?) in Tobias Thierer. He sent me this link to the Kerbal Space Program because I've written an essay called "The Man in the Moon" at http://craigssenseofwonder.wordpress.com/man-in-the-moon/ I don't know, but maybe you'd be interested. Check it out! G'day! Craig Brown