You can plan a bonus 2 hrs by going at 3pm, buy a ...

You can plan a bonus 2 hrs by going at 3pm, buy a twilight ticket, pay full price then return the next day for a full day.
This is where you come to see what the Orbiter looks like, piggy backed on a 747. The Orbiter is a replica and you can look inside. It is an interesting story on how this idea came to fruition. You can choose to go on the 30min and/or 90min tram tour of the old mission control room, the ISS mock up centre and the mighty Saturn V. The current mission control is on the floor above the historical one that you visit. The mock up facility is where people can train and test things on the ISS.
I found the main visitor centre was quite interesting to understand space exploration from the old Mercury program and Skylab to the ISS and new Orion program. The additional $6 for the audio guide provided insights that you may not get from the info panels. Bring your own food if you value nutrition.