Space Mountain is so fast, and you can't see where you're going. It's dark, because it says "Space" in the name. Because Space Mountain is in stars, it feels like you are in space.
Xcelerator is so fast it makes smoke. It goes up this huge hill, and then it twists down. Xcelerator shoots off and goes about 200 feet. Then, it comes back down and turns, and then it's over.