The Raptor, SpaceX's engine used to power the upcoming Starship, has been reaching new levels of power during its development.
On Monday, CEO Elon Musk announced that the engine reached 330 bar of chamber pressure without exploding. That's 31 bar higher than what the engine achieved back in February 2019, when it beat the previous record-holder for an operational engine, Russia's RD-180. Teslarati noted that the engine beat the Soviet Union's RD-701 engine, which at 300 bar, previously held the public record for the highest combustion chamber pressure for an orbital-class rocket.
It's big news for the Starship, which needs all the help it can get to complete its ambitious missions. The ship is designed to send humans to Mars, the Moon, and beyond with the ability to transport up to 150 tons or 100 people into space at a time.
The Raptor engine uses liquid oxygen and methane, unlike the Merlin engine fueled by rocket propellant that powers the Falcon 9. That, combined with the Starship's fully-reusable design, means humans can travel to Mars, harvest the planet's resources, and use that to fuel the return trip.
The new record gives the Raptor engine more power to achieve these goals.
A new era of engines — A rocket engine, as NASA explains, is basically a system where fuel is ignited in a combustion chamber. That produces a high temperature, high-pressure exhaust gas that goes through a nozzle and produces thrust. The system is based on Newton's third law of motion, where every action has an equal and opposite reaction. That means the chamber pressure is linked to the resultant thrust.
In Musk's post, the chamber pressure has been measured in bars. Under these units, the ambient pressure at sea level is 1.01325 bar. Another measure sometimes used is pounds per square inch, or psi, where that same measurement would show as 14.6959 psi.
The Raptor engine's chamber pressure greatly exceeds that of the Merlin 1D, which a NASA document states has a pressure of 1,410 psi or 97 bar. The new record beats the engine's previous success back in February 2019, when it reached 269 bar. After that success, the Raptor engine had beat the Russian RD-180 engine, which offers 258 bar and has been flying on the ULA Atlas V rocket since 2000. But the 2020 result, which not only beat all of these, also exceeds Musk's goal for the Raptor, which in September 2016 he claimed was to reach 300 bar.
Musk also noted that the Raptor can reduce its strength in a similar way to the Merlin:
"Max demonstrated Raptor thrust is ~225 tons & min is ~90 tons, so they’re actually quite similar. Both Merlin & Raptor could throttle way lower with added design complexity. Raptor preburner & Merlin gas generator flameout are what limit lower bound."
What does all this mean for thrust? On Monday, Musk claimed that the engine would provide half a million pounds of force, or around 225 tons. In May 2020, Musk stated that the Super Heavy booster used to lift the Starship away from Earth was currently using 31 engines, rather than the 37 engines he previously stated. SpaceX's website lists the Super Heavy booster as ultimately offering 16 million pounds of thrust.
How does that compare to the Falcon 9, the rocket that the Starship could ultimately replace? The current rocket offers 1.7 million pounds of thrust at sea level. That means, all in all, the Starship packs an impressive punch.
The Inverse analysis – The Raptor's power levels are impressive, and its strength should become clearer during more hop tests. The ship looks set to stand around 400 feet tall when paired with the Super Heavy booster. As SpaceX aims to host more "hop tests" past the 150-meter mark, the visual of a giant ship soaring into the sky will likely do more to communicate the Raptor's impressive strength to the general public.
Update 08/21 5:20 a.m. Eastern time: An earlier version of this story incorrectly referred to Newton's third law as relating to aerodynamics. It has since been corrected.