There's a real Saturn 5 rocket here -- the rocket that took men to the moon. This is the only original launchable rocket that remains. There are also rocket displays from the Mercury and Gemini manned space programs.
You must drive past the Space Center guard shack like you were entering the Space Center, but you pause at the shack to tell the guard where you're going. Don't let this intimidate you, Rocket Park is open to the public. I was told the area opens at 9AM and closes at 6PM. The guard who told me this seemed confident about the closing time, but I got the feeling he was guessing about when it opens, so if you're adventurous you can try earlier, then report the results in your log. I've driven by and seen the gates open at 8AM.
Most people miss the Longhorn Cattle Project located immediately behind the large building. Take a few more minutes while you're there and visit the genuine Texas Longhorns out the back door.
To claim this find email me the date on the bottom right of the plaque in the parking lot. The date after the word "engineers."