I found this cheap pool toy at Target and thought it reminded me of a rocket :) I initially thought it would be short and stubby but, after I cut its head off, decided that the integral piston could be used for ejection. Since this option will require a longer stroke, I'll be adding a tail as well as wings (fins). You can see the basic components (except for fins and recovery) laid out below. The white tube fits the piston tube like a glove so it will form a reverse shoulder. The brown tube will be the lower body, the centering ring will mate the tube to the upper body. The round plug will adapt the piston to the tube. The biggest trick will be to get the pieces together so the piston doesn't bind.