Mission:Space is kind of a weird bird. I do not do spinning. The freaking Dumbo ride will make me feel queasy. The tea cups will wreck me for the day, but I can ride M:S orange without a problem because you can not see that I am spinning.
I would give green a go first and see how he does and then make the call on orange. Green is still fun...I would put it on par with a smother version of Star Tours. Orange, if you can take it, is pretty awesome.
If he is willing to give orange a try, there are a few things you must be aware of and rules you must follow.
1. This is the most important. Keep your head back, straight and keep your eyes open. With the way it is set up your brain is fooled into thinking you are moving forward. This is because you inner ear lines up with the rotation and the video helps your brain confirm it. Where it can go wrong is if you move your head out of the upright and straight position. If you do this your inner ear is no longer in line with the arc and sends a signal to your brain that you are tumbling. If he does this, the barf bags placed in the cabin will get used and you will both have a bad time.
2. If he is claustrophobic, forget about the attraction entirely. The cabin is seriously tight with the view screen maybe 12" from your face.
3 . There are several times during the ride that you will feel positive Gs. It feels roughly like someone putting about 50lbs on your chest and it will make it just slightly harder to breathe. This will generate a panic attack for some people. If he is prone to that kind of reaction skip the orange side.