I found it by chance, really.
Same here. I stumbled upon Orbiter on a thread of
Facepunch Studios (Although the thread doesn't seem to exist any more). It was actually a thread in the gaming section made just for Orbiter 2006 and everyone was posting their thoughts on it, and pictures. I normally don't browse the off topic forums, but this day I did. So I downloaded Orbiter and gave it a quick go just for laughs
. My first picture I posted was re-entering the atmosphere in the Shuttle - backwards, with the bay doors open. That was before I even knew how to establish orbit
Turns out it is now one of my favorite games, and I went from not knowing how to establish orbit to docking with the ISS, landing on the Moon and Mars.
In case you're wondering, the Facepunch website is basically the main community forum for Garry's Mod - A building / sandbox mod for HL2. I played it for quite some time with a sweet "Spacebuild" mod. I really got into it, but the creator and admins of the forums are complete arseholes and continued updating the mod nonstop and breaking more things than they fixed every time. So eventually I told Garry off and got myself banned. I don't really think I'll go to playing the mod again.
At least something good - Orbiter - came out of it