[Jeff Bezos] might be getting all the credit for developing a rocket that can take off and land vertically, but [Joe Barnard] is doing it the hard way. He’s doing it with Estes motors you can pick up ...

There is a reason building a rocket engine is harder than most things you want to build. If you are building, say, a car, your goal is to not have it explode. If you are building a bomb, you want that ...