CEO Elon Musk has revealed that SpaceX crushed a global rocketry record during a recent Raptor engine test, pushing the crucial Starship component past years-old performance targets.
On August 17th, the SpaceX CEO unexpectedly released a photo of a Raptor test and a corresponding graph showing the engine’s chamber pressure, confirming that the company had successfully pushed the engine to record-breaking levels. Musk says that an unspecified Raptor – possibly serial number 39 (SN39) – briefly reached a main combustion chamber pressure of 330 bar (~4800 psi) during a controlled burn – and remained intact after shutdown.
Outside of subscale laboratory tests, the highest main combustion chamber known to full-scale, orbital-class rocketry was achieved by the Soviet Union in the 1980s with the RD-701 engine. Although the exceptionally unique engine was canceled before it could be used, it reportedly reached pressures of 290-300 bar in one mode of operation. Now, however, SpaceX and its Raptor engine appear to be the new world record holders – and by a huge margin.
Raptor’s new crown comes roughly 18 months after Elon Musk revealed that the engine had beaten the Soviet RD-270 full-flow staged combustion (FFSC) with a higher sustained chamber pressure (~257 bar vs 255 bar). A few days later, the same Raptor went even further, cresting the Russian RD-180 engine’s 257 bar operating pressure with a peak of 268 bar. Still, SpaceX needed 6-12 more months to refine Raptor into an engine capable of operating even close to those pressures for more than ~10 seconds. In July and August 2019, Raptor engine SN6 flew twice on Starhopper, culminating in a ~60-second, 150-meter hop that ended with the engine nearly destroying itself seconds before landing.
Almost exactly one year later, Raptor SN27 launched on Starship SN5 on the same 150m trajectory and appeared to perform flawlessly. Exhibiting barely a stutter or flare, SN27 never came close to the flamethrower-like death throes Raptor SN6 suffered in August 2019. In short, SpaceX continued to do what SpaceX does best, continuously refining rough prototypes into increasingly polished end products.
Originally revealed in 2016 as a methane/oxygen full-flow staged combustion engine with an operating combustion chamber pressure of 300 bar (4350 psi), Raptor’s August 17th achievement means that SpaceX has already exceeded one of its performance goals. Of course, combustion chamber pressure is significant but still far less important than engine longevity, burn duration limits, and reusability in the context of Starship. SpaceX likely wouldn’t be pushing the envelope of chamber pressure if it wasn’t confident about Raptor’s many other important attributes, but it’s still unknown if Raptor has ever burned for longer than ~90 seconds.
Regardless, if Raptor can actually sustain chamber pressures of 330 bar without damaging itself, the milestone could mean that SpaceX has already boosted Raptor’s maximum thrust from ~200 metric tons to ~225 metric tons (440,000-500,000 lbf. For Starship and Super Heavy, that 10% increase in thrust could easily translate to a 5-10% increase in payload to orbit per launch.
To reach orbit, though, Raptor still has a ways to go. For Super Heavy to be able to complete a normal launch, SpaceX will need to dramatically expand Raptor production (~31 engines per booster) and ensure that Raptor can reliably operate for 3-5+ minutes and reignite multiple times in flight. For Starship, SpaceX needs – at the minimum – to mature Raptor until it can burn continuously for 5-10 minutes to reach orbit. The company will likely also need to finish developing a custom vacuum-optimized version of Raptor for efficient orbital Starship flights.
Given just how quiet SpaceX is about most Raptor milestones, there’s a chance the company has already made substantial progress along those lines. For example, Starship SN8 – already well on its way to completion – will likely be the first prototype to fly with three Raptor engines and will need the ability to stop and start those engines in-flight to perform full-fidelity 20 km (~12.5 mi) launch and landing tests. Even just sustaining 330 bar for 10-100+ seconds without destroying the engine is likely several Raptor iterations away. Still, given SpaceX’s track record, all of those milestones are likely just a matter of time and perseverance.
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