Hi Jesica!
Thank you for bringing your question to the Disney Parks Moms Panel!
Space Mountain is my family's favorite ride at
Magic Kingdom Park. I have two boys and they have been riding it ever since they met the 44 inch (112 cm) height requirement. It is most definitely a thrill ride with the added factor of being totally in the dark.
Whether or not your son will like it really depends on him. I see a lot of kids that age who love it, but if he is timid and easily scared then it may not be for him. When my boys were younger, my husband and I always made sure to have them sit in front of us in the ride vehicle so that we could place our hands on their shoulders. It was reassuring to them that we were there, and also reassuring to us that we could feel them safely in their seats.
One suggestion for you is to have your son watch some YouTube videos of "Space Mountain on-ride experiences". It might help him get a feel for what the ride will be like. Be sure to view them before showing him to make sure they have appropriate language. One of my sons will try anything at anytime, while my other son likes to know what is going to happen. If your son doesn't like to be surprised, one of those videos could help prepare him for the ride.
I hope this helps! Please let me know if you have any other questions about planning your trip.