I have 3 improvements / suggestions:

• 2 turns of transparent glue tape (TESA-Film) around the pump cylinder on the base improves airtightness (as a seal)
• The rockets are mechanically sensitive (breakable) at the fin area upon landing. I reinforced the fin area and eliminated the slots.
• As a different launching technique I present a blowpipe, as the lungs are always stronger as a plunger! It just needs a support below the mouthpiece for printing...