I can't be sure when it started for me - I missed pretty much all the big defining moments in space history. I think it was a combination of watching the fledgling ISS sailing over in the early 2000's, watching Mars Odyssey launch in 2001, then coming home to the UK and learning all about it, doing some basic astronomy with my Dad, learning space facts from him, and later developing an interest in aviation, which led to space when I first played Orbiter. My interest in space has also developed slightly so that my main passion is astronomy, but I guess they are very similar things.