SpaceX fires up first upgraded Starship engine

A Raptor 1 engine performs a static fire in 2019. (SpaceX)

CEO Elon Musk has implicitly revealed that SpaceX recently conducted the first test of Starship’s new Raptor 2 engine.

Aside from kicking off integrated static fire testing of a refined, operationalized version of Raptor, the first prototype may have briefly become the most powerful engine of its kind ever tested before destroying itself. While not quite as successful as the first static fire campaign of a full-scale Raptor 1 engine, which survived several tests, the first Raptor 2 prototype’s early demise is still a routine part of engine development and is the start of a process that should ultimately produce a Super Heavy booster with 50% more thrust than the next most powerful rocket ever flown.

Prior to last weekend, it’s likely that competitor Blue Origin’s BE-4 – still in development and hoped to one day power ULA’s Vulcan and the company’s own reusable New Glenn – was the most powerful methane/oxygen rocket engine ever tested. BE-4 is designed to produce up to 244 tons (~539,000 lbf) of thrust. On its very first static fire, it appears that SpaceX’s first finished Raptor 2 prototype has narrowly stolen BE-4’s crown, briefly generating main combustion chamber pressures of 321 bar (~4650 psi) and as much as 245 tons (~540,000 lbf) of thrust.

To BE-4’s credit, the engine (at least as far as Blue Origin’s sparse public communications go) didn’t destroy itself after its first full-thrust static fire. Raptor 2 wasn’t so lucky and apparently exploded before completing its first test. There’s also some ambiguity as Blue Origin’s own website pegs BE-4 thrust at “2400 kN (550,000 lbf)” when 2400 kilonewtons is actually equivalent to 539,000 lbf. Regardless, designed to produce up to 230 tons (~510,000 lbf) of thrust in flight, Musk has said that Raptor 2 or V2.0 “is a major improvement in simplification” over Raptor 1, which nominally produces up to 185 tons (~410,000 lbf) of thrust at chamber pressures closer to 270 bar (~3900 psi).

It’s not all that surprising, then, that the first Raptor 2 prototype ever completed exploded when SpaceX pushed it to almost 107% of its maximum rated thrust and main chamber pressure during its first test.

Though impressive, SpaceX has technically pushed Raptor 1 prototypes further – and without failure. Musk later indicated that there was some damage present but a fairly young Raptor 1 engine still made it all the way up to 330 bar (~4800 psi) and spent about 10 seconds at chamber pressures above 320 bar without failure during an August 2020 stress test. Still, had the Raptor 2 prototype also made it to 330 bar, it would have produced around 252 tons (555,000 lbf) of thrust – 12% more than its Raptor 1 predecessor.

Super Heavy boosters will ultimately have 33 more or less identical sea-level-optimized Raptors – 13 Raptor Center (RC) engines with thrust vectoring and 20 Raptor Boost (RB) engines without. (NASASpaceflight – bocachicagal)
Starship’s design features three Raptor Centers and three Raptor Vacuums. Musk has suggested a variant with 3 RCs and 6 RVs as a possible upgrade path. (Elon Musk)

According to Musk, the main differences between Raptor 1 and Raptor 2 are “much cleaner” plumbing and wire harnesses and a wider combustion chamber throat, which allows the engine to produce more thrust in roughly the same package at the cost of a slight efficiency loss. Over the last two years, the CEO has mentioned the possibility of a power-optimized Raptor variant with up to 300 tons of thrust but in recent months, Musk says SpaceX has decided to keep the Raptor family as streamlined as possible and opted for just two variants – one with a sea-level nozzle (Raptor Center and Boost) and one with a larger vacuum-optimized nozzle (RVac).

SpaceX fires up first upgraded Starship engine
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