I think Mark's train of thought was that the air bag be mounted in an air tight (and hopefully explosion proof) enclosure, the only exit from which is a tube that holds the tennis ball. The air bag being mounted in the enclosure.
As the bag expands in the enclosure it will force air up the tube and hopefully blow the ball into orbit.
You're close, but the bag will be removed from the air bag unit leaving just the charge to go off inside the chamber.
Umm, explosion proof, hadn't thought about it that way.
Was just going to use some 2mm plate for the enclosure, maybe something a little thicker is in order.