Build a multistage rocket from two balloons!
Space travel requires an enormous amount of energy. Much of that energy is used to lift fuel that will be used later in a flight. To avoid the engineering problems related to extremely large single-stage rockets, engineers developed multistage rockets. Engineers involved in the design and flight of rockets encounter problems similar to those encountered by students flying balloon rockets. The added fuel provided by additional staging tanks allows a rocket to travel farther. However, added tanks bring added weight and complications to the rocket, requiring yet more fuel. Your simple balloon rocket demonstrated that releasing one balloon is easy. A two-stager is much more complicated...isn't it? Want to try for three stages?