SpaceX made rocketry history yesterday, conducting a full-power test of the most advanced rocket motor design ever conceived. The new rocket engine family, called “Raptor,” is unique in several ways.
Unlike the majority of rocket engines flown, which use a combination of hydrogen and oxygen as the fuel/oxidizer mix, known as “hydrolox,” the Raptor uses a combination of methane and oxygen, known as “methalox.” This is because eventually the rocket will have to refuel on Mars, where it’s easier to produce large quantities of methane rather than hydrogen.
But the Raptor is groundbreaking in another regard: It is the only full-flow staged combustion (FFSC) cycle engine in existence. Most modern rocket designs separate a small amount of fuel and oxidizer into what is called a “pre-burner” chamber. The energy extracted from this chamber is used to drive the high-pressure/high-temperature turbo pumps that inject fuel from the storage tanks into the main combustion chamber of the engine.
For most rockets, any exhaust byproduct from this pre-burning is vented uselessly after being expended. This type of open-cycle design is less complex to build and requires less maintenance to maintain. But it also means that the rocket is less efficient, as the exhaust gases could instead be redirected back into the main combustion chamber to give more power to the rocket.
This is the Raptor’s true accomplishment. The FFSC design uses a combination of fuel-rich and oxidizer-rich pre-burner chambers to drive two turbo pumps, which feed fuel and oxidizer into the main chamber. Any exhaust gases from the pre-burn are similarly redirected into the main chamber, creating a rocket motor that is more efficient than any other in history.
There have been only two other attempts at creating a rocket motor like this, the first being the Soviet RD-270 engine in the 1960s and the second being the Integrated Powerhead Demonstrator engine designed by NASA in the mid-2000s. Neither engine made it past the demo stage.
When the SpaceX Starship launches, it will be powered by the most advanced, complex, and efficient rocket motor design ever engineered.