The pack has a set of launch platforms designed to hold, fill, and propel 2-liter plastic bottles skyward using water and air pressure. The objective is to build a rocket that fits the launch pad mechanism and holds together well enough to be used more than once. 

Scouts can bring as many rockets as they want to test – we’ll have multiple launchers to make sure everyone has plenty of attempts!  THIS IS ALSO A GREAT RECRUITING EVENT TO BRING FRIENDS WHO ARE INTERESTED IN JOINING THE PACK!!!

Fabricate and decorate however you like as long as you keep a 1-1/2" clearance from the bottle opening. That’s where the latch holds the bottle before launch (see picture). Build the basic structure using the example links below. Add fins, a nosecone, parachute, plenty of decorations - whatever you like. Fins are highly recommended for a more predictable flight and a nosecone to absorb the impact of landing improves your chances of flying more than once.

NOTE: Only 2 liter bottles will fit properly on the launch pads. Smaller bottles such as flavored water or 20 ounce bottles don't work on this system.

Example links: 

https://www.instructables.com/id/How-To-Make-A-Bottle-Rocket/

https://sites.google.com/a/bcsemail.org/wdstem/phase-ii/water-bottle-rockets

http://www.science-sparks.com/making-a-bottle-rocket/

Here is a great all-in-one document with a lot of detail and fin templates: Water Rockets with Fin Templates PDF