Welcome aboard, Jenny. Let's experience the adventure of space travel today on the Disney Parks Moms Panel!
My husband and I rode Mission: Space a few times before the "lighter" version was introduced, and it is certainly not for the faint of heart (or stomach). We were able to withstand the G-forces of the original, but I will unashamedly say that we have pretty much said good-bye to the Orange version and have joined Team Green!
When you approach Mission: Space, you'll see two separate queues very clearly marked for Orange or Green. There will also be Cast Members standing at the entrance who will ask you which side you want to ride and then direct you to the appropriate line. You'll also be handed a "launch ticket" clearly marked Green or Orange for the version of the attraction you've chosen. With all the precautions in place, I think you'd have to be really not paying attention to end up in the wrong line.
Even on the Green side, Mission: Space is a bouncy simulator ride, so if you're very sensitive to motion sickness you could still find it uncomfortable. Your space capsule is also pretty tight and you're basically strapped into a little bouncing box, so if claustrophobia could rear its head, just be aware of that, too.
Don't let the warnings scare you away, Jenny. I think it's just helpful to know ahead of time what to expect. Mission: Space is a lot of fun, and I'm sure your kids will love piloting their space capsule to parts unknown. I hope this helps you have a great time, and that your family has a magical Walt Disney World vacation. Please come visit us again if you have any more questions!
Kathy K.