Once Elon Musk decided to build a reusable spacecraft to carry his dreams of Martian colonization, the engineers at SpaceX knew they would need a special engine for the world’s most powerful rocket.
Starship, as the vehicle came to be called, demanded what’s known as a “full-flow, staged combustion” engine. Wringing every last ounce of power from rocket fuel demands a machine that can precisely control an explosion again and again — failing in that mission means picking pieces of it out of the ocean. The design is so complex that it had never been used: The Soviets built one and tested it on the ground in the 1960s, but never sent it into space.