I saw Space Mountain brand spankin' new when I nine or ten and I was hooked for life. I've always been fascinated with how things work; what efforts and engineering went into creating the Magical illusions. One of my earliest Disney fixations was the desire to "map" the intertwining track paths of the original Space Mountain.
The Holy Grail of that particular religion would have to be getting inside the Mountain when the lights are on... which, it turns out, is not easy to arrange; you just have to be in the right place at the right time. It's rather like the lottery that way.
The Good News is that this lifelong desire came true for me a couple years ago... we had just crested the lift hill when all the sound eerily fell away, and I noticed emergency lighting begin to flicker on.
I got to ride pretty much all of Space Mountain with the lights on.
And I understood the truth of the CM legend "WDW's scariest ride is Space Mountain with the lights on."
The ride engineering concept of the safety envelope has already been mentioned... it's the equation that factors in guest size and physics to determine how far from the ride vehicle the structure needs to be to be adequately sure of safety. Because of track cambers and centrifugal and centripetal forces, it usually turns out that supports can be safely placed much closer to one side of a curve than the other.
At six-feet-four-inces tall, with my butt firmly planted in my seat, I was easily able to reach out my hand and "clip" different series of beams and risers with my fingertips... like clicking a stick down a picket fence. Yes, I did have to brace myself against the side of the car and make the effort to reach the "opposite" direction from that which the forces acting on the train were pushing me, but I never raised from my seat.
So how does this affect the conversation at hand? I suppose it doesn't, really. It is certainly true that relatively normal sized people can come into contact with the Space Mountain structure while they remain seated, but certainly not with their heads.
Perhaps I just wanted to neener neener everybody about the single most memorable Disney ride experience of my life.
-WFH
PS: In case you're wondering, the "Bad News" implied up above was that the SM problem was minor enough that we didn't have time to get over to the WEDway in time to video the track layout with the lights up.