The launcher was made from common plumbing parts, a 12v air pump and used very thin pvc pipe with wooden fins as rockets. The small pump could put about 65 psi in the tube for launch, which propelled them about 80-100 feet in the air. I attached a large gate valve and a pull chord for quick release. In the future I may add an electric valve similar to those made for sprinkler systems. I used quick connects on the pumps so that I could bring my larger air compressor from home in and put 90-120 psi in it. Our max launch was about 95 psi and it was incredible, I was a little worried any more might shatter the thin pvc pipe we used for the rockets. For windy days, I also made a 2 inch diameter attachment to launch plastic golf balls or pingpong balls...most went so high we lost sight and never recovered!
This launcher worked great. It rolled out into an open area and set up in seconds. The base was hinged with locks, so the launcher simply folded back down into the box. The 12v battery from my son's powerwheel made it completely portable. Make sure you are WELL AWAY from any parked cars because these things come back down fast! We had one close call before we relocated to a better place at school. I let the kids come up with their own designs for rockets on paper and then we built them, painted the rockets and they got to test their creations.
If there is interest in this, I will try to put together an Instructable for it. Suggestions are welcome!