Throatless rocket engine

John Carmack is working a potentially disruptive technology: A throatless rocket engine. Its made from plain aluminum pipes with few machined fittings. Carmack says: “The great thing about these engines is that it only takes me two nights to machine the parts, so we can test two engines a week if necessary.” It scales too: “If this line of tube engine development works out, we can make a 5,000 lbf engine with very little more effort than the test engine. [via] Link.