As is routine, SpaceX CEO Elon Musk has taken to Twitter to offer a few details about the status of Starship, its Raptor engines, and a few upgrades planned for both.
In mid-December, Musk revealed even more ambitious plans to upgrade Starship by stretching its propellant tanks and adding another three Raptor engines, potentially boosting the ship’s maximum thrust by 50% and substantially improving payload performance. These latest details are focused on an upgraded version of the Raptor engine and on additional changes to Starship’s structural design and assembly process.
According to Musk, as SpaceX continues to ramp up ground testing of the upgraded engine variant, “Raptor 2 now operates routinely at 300 bar main chamber pressure.” For context, on February 10th, 2019, just days after SpaceX began testing the first full-scale Raptor prototype ever completed, the engine briefly reached a main combustion chamber pressure just shy of 269 bar (3900 psi). That narrowly beat records set by Russia’s RD-270 and RD-180 engines, the latter of which is used on ULA’s Atlas V.
It took 18 months before Musk revealed clear proof that at least one Raptor prototype sustained such high chamber pressures over a minute or more of steady-state operations. The same engine peaked at an impressive 330 bar (~4800 psi), briefly producing 225 tons (~500,000 lb) of thrust and soundly beating out Russia’s never flown RD-701 engine, which crested 290-300 bar in testing. Another ~18 months after that milestone, Raptor isn’t quite operational in the sense of supporting orbital-class launches but the engine isn’t far from its first and has since supported dozens of Starship static fires and seven flight tests – five of which occurred in a period of just six months.
Already, despite the fact that Raptor 1 or 1.5 engines have yet to even attempt an orbital-class launch, SpaceX has almost entirely moved on to a new and improved variant known as Raptor 2. According to Musk, all Raptor ground testing at the company’s McGregor, Texas development campus is now focused on the new hardware, which reportedly features much cleaner plumbing and wiring. The biggest change to Raptor 2, though, is an almost 25% increase in maximum nominal thrust over Raptor 1/1.5 – from around 185 to 230 tons (408,000-507,000 lbf). That’s partially enabled by widening the ‘throat’ of Raptor’s nozzle, which sacrifices a small amount of efficiency for more power density. However, Raptor 2 also contains design improvements throughout to enable sustained, reliable operation at chamber pressures up to 300 bar – 10% higher than Raptor 1.5.
On October 24th, Musk subtly live-tweeted one of the first Raptor 2 static fires, revealing that the engine reached a chamber pressure of 321 bar (~4650 psi) and briefly produced around 245 tons (~540,000 lbf) of thrust before destroying itself. Now, a little over two months later, Musk says that Raptor 2 prototypes are routinely operating at 300 bar without major issues, meaning that they can ignite and safely shut down after burning for several minutes at those pressures. In theory, given that 300 bar is Raptor 2’s targeted chamber pressure at max thrust, that means that the engine is now “routinely” operating at the level SpaceX wants and needs to take Starship to the next level.
It’s likely that one or several months of work remain before SpaceX can begin qualifying the first Raptor 2 engines (or, more importantly, hypothetical Raptor 2 Vacuum or Boost variants) for the first Starship or Super Heavy prototypes designed for the new engine. Nonetheless, the rapid progress SpaceX has made in the first few months of Raptor 2 testing is extremely encouraging.