Eco-friendly alternatives to fossil fuels are venturing beyond Earth—and into space.

Al Williams and I were talking about water rockets on the podcast the other day, and I realized that this was a perfect example of an open-ended simple project. It sounds really easy: you put some ...

Look for air bubbles in the water when you pump. If no, make sure the valve can open to let air through from the pump. It may be damaged or screwed shut. If the rocket does fly but not very well ...