I didn't know a lot about Mission Space, but my DD (age 9) was dying to go on this ride because of all the hype she has seen about it on the Disney Channel. She keeps repeating what she heard, that "real astronauts said it's almost exactly what it feels like when you blast off into outer space". Then, when we are in line, and we start getting closer -- she starts panicking and hyperventilating. (I've never had her do this before!) I try and get her to calm down. It will be fine. It's just a ride. Blah.. blah... blah. When we get to the point when we are at our 4 spots, ready to enter next -- she says "Mom! I have to go to the bathroom". I tell her "there is no bathroom on the ride. Hold it. You can go right afterwards." I know, I know, I am a terrible mom--- but I didn't spend all this time meandering through the line to be next up -- then leave. We board, and I keep trying to comfort her... "You're going to be fine... it's okay... don't close your eyes.... Wow! Look at that... Wow! I feel like we are really in outer space" I was talking, talking trying to get her to relax. All the button pushing was a good distraction, and she was able to push her buttons at just the right time. At the very end of the ride, she tells me "I think I'm going to throw up", so I hold her barf bag in front of her, but nothing happens. She is greatly relieved when the ride ends. She feels a little quesy afterwards, so we sit & rest next to Test Track. She tells me that she really hated that ride -- it was the worst! After about 15 minutes or so, she has recuperated (motion-wise) and we are on our way again. (She is not a kid who gets car sick a lot, although it can and has happened a few times.)
Next day, I hear a completely different version of this story. She is SO GLAD that she went! Mission Space was the coolest ride she has ever been on in her whole life! This ride was THE HIGHLIGHT of her trip to Walt Disney World! After all this hullabaloo, I ask if she wants to ride it again "No, once was enough."
So, all said, my advise to you is this. You must go on it once. If you are worried that it will spoil your day, get a fast pass for the end of the day, around 7 or 8 pm, before Illuminations. We went first thing in the morning (on an empty stomach), just to be on the safe side. We ate lunch about 2 hours later with no problems.
I didn't have any problems on this ride, but I am not prone to car or motion sickness. However, I was worried about my back, as I have am already seeing a Chiropractor 3 times a week for a pinched nerve/back injury at work. Mission Space was no problem as your head, neck, & back rest against nice thick padded seats. (I find that the roller coasters are much harder on my back). I rode Rock'nRoller coaster 2 years ago, and wrenched my back something awful & spent the entire week on pain-killers! I will never ride that one again! But, like I said, I had no problems with Mission Space.
Just my two cents worth, as we were at Mission Space just this week.
--- Rene McDaniel