Followers of the Church of Elon will no doubt already be aware of SpaceX’s latest technical triumph: the test firing of the first full-scale Raptor engine. Of course, it was hardly a secret. As he often does, Elon has been “leaking” behind the scenes information, pictures, and even video of the event on his Twitter account. Combined with the relative transparency of SpaceX to begin with, this gives us an exceptionally clear look at how literal rocket science is performed at the Hawthorne, California based company.

This openness has been a key part of SpaceX’s popularity on the Internet (that, and the big rockets), but its been especially illuminating in regards to the Raptor. The technology behind this next generation engine, known as “full-flow staged combustion” has for decades been considered all but impossible by the traditional aerospace players. Despite extensive research into the technology by the Soviet Union and the United States, no engine utilizing this complex combustion system has even been flown. Yet, just six years after Elon announced SpaceX was designing the Raptor, they’ve completed their first flight-ready engine.

The full-flow staged combustion engine is often considered the “Holy Grail” of rocketry, as it promises to extract the most possible energy from its liquid propellants. In a field where every ounce is important, being able to squeeze even a few percent more thrust out of the vehicle is worth fighting for. Especially if, like SpaceX, you’re planning on putting these new full-flow engines into the world’s largest operational booster rocket and spacecraft.

But what makes full-flow staged combustion more efficient, and why has it been so difficult to build an engine that utilizes it? To understand that, we’ll need to first take a closer look at more traditional rocket engines, and the design paradigms which have defined them since the very beginning.

The Open Cycle Engine: Wasteful by Design

Many of the best known rockets to have ever flown have used engines based on what is known as the gas-generator cycle, including the Saturn V, the Soyuz, the Delta IV, and even the Falcon 9. In fact, outside of the Space Shuttle, you could probably argue that nearly every milestone in the history of spaceflight was made with a gas-generator cycle engine. It’s a technology that dates back to the V-2 rocket, and is one of the key breakthroughs that made liquid-fueled rockets possible. But despite its incredible success, the technology is not without its faults.

Put simply, the gas-generator produces the gasses that spin a turbine, which in turn drives the propellant pumps. In some engines, the gas-generator operates on a different principle than the engine itself and has its own separate fuel supply. For example, the turbine of the V-2 rocket was spun with steam created by the chemical reaction between hydrogen peroxide and warm sodium permanganate.

The downside of this method is that the secondary fuel system for the gas generator adds additional weight and complexity, the last thing you want …read more

Source:: Hackaday