My wife and I rode Mission Space over the Labor Day weekend this year. I loved it and got right back on for a second trip then returned to the park two days later to ride a third and fourth time. My wife became severely nauseated after her first ride and remained so for 30 minutes. It almost caused us to abort our entire day at Epcot, so beware. If you can tolerate Tea Cups, you might be OK.
Here is the thing: the ride simulates G forces by centrifuge. However, your view is that of BLASTING OFF into space. You see movement in a straight line which helps offset the spin that is generating G forces. Do keep your eyes open at all times. It helps. The first ride for me was the most intense because I had no idea what I was about to experience, but on subsequent rides, I began to look forward to the G force sensation. When I ride Tea Cups, I am one of the fools that like to spin their cup just as fast as it can spin. Nevertheless, I did feel a bit off-balance after riding MS the first time. It gave my stomach an un-easy feeling but not nausea.
The ride is not only that of G force from a few seconds of spin to simulate gravity both at take off as well as when passing the moon. There is a flight simulator aspect as well. The ride warns crew members of both while waiting to board. The offset to the flight simulation is that you are made to feel that you are in control of the flight. If you concentrate on the mission and operate your buttons and joystick, it will make the flight and mission more tolerable than, for example, just being a passenger on Star Tours or Body Wars.
There are three lines at the entrance: the standby, the fast pass and the singles. You will board faster if you get into the singles. The capsule is such that one does mind sitting next to strangers. You feel as if you are alone in your seat anyhow. No visual contact with your neighbor is easy nor is it recommended. Get into the singles line if the standby is longer than 15 minutes. All three lines meet at the same place. Cast Members direct fast pass holders into the standing dot zone first. Any dots on the floor not filled by fast pass holders can go to the singles or to the standby folks, but there must be enough dots on the floor for the standby groups of 2 or more which is why it is always possible for one dot to be left over for a single or two to fill. Dots divide the waiting guests into their respective crews. After the Intro movie, the crews walk to their boarding doors and get more instructions. Then the doors open and crews of four enter their capsules. Once seated and secured, the control panel swings into place close to your face and within easy hand reach. The seats tip backward and you feel you are looking up into the sky. The TV monitor shows the doors open to reveal that YEP I am looking up at the sky. Then you BLAST OFF. Grit your teeth, yell but don't close your eyes. You wouldn't want to miss ANYTHING.
Happy Landings!