We went there in 2014. Did a viator tour from Orlando. They have a real space shuttle on show, complete with re-entry burn marks and the original control consoles used in the Lunar Landings. You can see it all in a day.
If you plan to get to Washington, the Smithsonian has 2 parts. One down town and one at the airport for the huge exhibits. The one down town has the Wright Flyer and mercury capsules for example, the one at the airport has large aircraft. We didn't realise this and missed out on the airport one.
https://airandspace.si.edu/udvar-hazy-center