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According to a tweet by Elon Musk, SpaceX’s new Raptor rocket engine has achieved during testing a chamber pressure that exceeds that of Russia’s RD-180 engine, which for decades has held the record.
First and foremost, it’s far too early to actually crown Raptor as the new official record-holder for combustion chamber pressure. RD-180 has been reliably flying on ULA’s Atlas V rocket with chamber pressures as high ~257.5 bar (3735 psi) since the year 2000, while Raptor has been performing subscale integrated testing for roughly two years and full-scale integrated testing for less than seven days. As such, the fact that full-scale Raptor has achieved ~269 bar (3900 psi) is an almost unbelievably impressive achievement but probably shouldn’t be used to jump to any conclusions just yet.
Thanks to the 10-20% performance boost supercool liquid methane and oxygen will bring Raptor, currently stuck using propellant just barely cold enough to remain liquid, the engine performing tests could already be made to reach its design specification of 300+ bar (4350+ psi), although Musk cautioned that he wasn’t sure Raptor would be able to survive that power in its current iteration. Nevertheless, 250 bar is apparently more than enough to operate Starship and its Super Heavy booster during most regimes of flight, although maximum thrust (and thus max chamber pressures) is probably desirable for the first minute or so after launch when gravity losses are most significant. [emphasis in original]
If the Raptor meets these goals, it will make most of Musk’s dreams for Startship and Super Heavy very possible.