We attended the Albuquerque Maker Faire, and the coolest activity we did was to make and launch paper rockets. Turns out the launcher is pretty straightforward - it’s a PVC reservoir and is controlled with a sprinkler solenoid. The more detailed instructions are in the book.

It uses a schrader valve, so it can be easily pumped up with a bike pump. While I don’t know really how high the rockets go, they do go surprisingly high and launch with a satisfying “thunk” sound.