I don't mean this as in insult to anyone, but the reality is that unless you have an inner ear problem a lot of motion sickness is a self fulfilling prophecy. If you think you will, you will. Spinning is a more popular one that causes just that reaction. You get motion sickness on something like the Tea Cups because you are visually witnessing the world going around in circles. It confuses the brain and causes a degree of disorientation that can trigger dizziness and sickness.
The thing about Mission Space is that you do not have that visual reference and therefore your balance and brain are not confused UNLESS you do have an inner ear sensitivity. The fluids in your ear canal will shift when G-forces are applied and could cause a feeling of dizziness and therefore illness. And it's not just spinning, but even the green side can cause it because of its unexpected movement.
One of the possible ways to know if motion sickness is self induced is in the case of a person that gets car sick as a passenger but can drive for hours with no problem. It's the same motion, it should be the same reaction. Reading while riding is a different thing. Then your peripheral vision is recording movement on the sides but steady looking forward. Confused signals cause orientation problems.
I originally stayed away from MS because it was during the time when a couple of deaths had been reported and many reports of motion sickness. I stayed away because of fear. Then I finally remembered that I have never, ever had motion sickness in my life, why did I think I would get it now. I tried Orange and was fine. In fact, my exact word when the ride was over was AWESOME!