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SpaceX Raptor

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SpaceX Raptor
A Raptor 1 rocket engine ready for transport outside SpaceX's factory inHawthorne, California
Country of originUnited States
ManufacturerSpaceX
AssociatedLVSpaceX Starship
StatusIn production
Liquid-fuel engine
PropellantLOX/CH4
Mixture ratio3.6 (78% O2,22% CH4)[1][2]
CycleFull-flowstaged combustion
Pumps2 turbopumps
Configuration
Chamber1
Nozzle ratio
  • 34.34 (sea-level),[3]
  • 80 (vacuum)[4]
Performance
ThrustRaptor 1:185tf(1.81MN;408,000lbf)[5]
Raptor 2:
  • 230 tf(2.26 MN; 507,000 lbf)[6]
    (sea-level)
  • 258 tf(2.53 MN; 569,000 lbf)[7](vacuum)

Raptor 3:280 tf(2.75 MN; 617,000 lbf)

Highest achieved:269 tf(2.64 MN; 593,000 lbf)Raptor 3, ~45s test
Throttle range40–100%[10]
Thrust-to-weight ratio143.8, sea-level
Chamberpressure
  • 350 bar (5,100 psi)
Specific impulse,vacuum380 s (3.7 km/s)[8]
Specific impulse,sea-level327 s (3.21 km/s)[9]
Mass flow
  • ~650 kg/s (1,400 lb/s):[11]
    • ~510 kg/s (1,100 lb/s), O2[12]
    • ~140 kg/s (310 lb/s), CH4[12]
Burn timeVaries
Dimensions
Length3.1 m (10 ft)[13]
Diameter1.3 m (4 ft 3 in)[14]
Dry mass1,600 kg (3,500 lb)[6]

Raptoris a family ofrocket enginesdeveloped and manufactured bySpaceX.A notable trait of this engine family is the use of afull-flow staged combustion cycle(FFSC). They are powered bycryogenicliquid methaneandliquid oxygen,a mixture known asmethalox.

SpaceX'ssuper-heavy-liftStarshipuses Raptor engines in itsSuper Heavy boosterand in theStarship second stage.[15]Starship missions include lifting payloads to Earth orbit and is also planned for missions to theMoonandMars.[16]The engines are being designed for reuse with little maintenance.[17]

Raptor is the third full-flow staged combustion engine in history and the first such rocket engine to power a vehicle in flight.[18]

Design

[edit]

Full-flow staged combustion

[edit]
See also:Liquid-propellant_rocket § Engine_cycles
Simplified full-flow staged combustion rocket diagram

Raptor is powered bysubcooledliquid methaneand subcooledliquid oxygenin afull-flow staged combustion(FFSC) cycle.

FFSC is a departure from thesimpler[according to whom?]"open-cycle" gas generatorsystem and LOX/kerosene propellants used byMerlin.[19]RS-25engines (first used on theSpace Shuttle) used a simpler form of staged combustion cycle.[20]Several Russian rocket engines, including theRD-180[19]and theRD-191did as well.[21]

Liquid methane andoxygenpropellants have been adopted by many companies, such asBlue Originwith itsBE-4engine, as well as Chinese startup Space Epoch'sLongyun-70.[22]TheZhuque-2rocket ofLandSpace,which in July 2023 was the first methane-fueled launch vehicle to reach orbit.[23]

Raptor 2 rocket engine cycle diagram with estimates from open-source information and analysis
Raptor 2 rocket engine cycle diagram with estimates from open-source information and analysis

An oxygen-rich turbine powers an oxygen turbopump, and a fuel-rich turbine powers a methane turbopump. Both oxidizer and fuel streams mix completely in thegas phasebefore they enter thecombustion chamber.[18]Raptor 2 uses an undisclosed ignition method that is allegedly less complex, lighter, cheaper, and more reliable than Merlin's. Torch igniters are used in oxygen and power heads. Engine ignition in Raptor Vacuum is handled by dual-redundant spark-plug lit torch igniters,[24]which eliminated the need for Merlin's dedicated, consumable igniter fluid.[21]Raptor 2 uses coaxial swirl injectors to admit propellants to the combustion chamber, rather than Merlin'spintle injectors.[25][26]

Before 2014, only two FFSC designs had progressed sufficiently to reach test stands: the SovietRD-270project in the 1960s and theAerojet RocketdyneIntegrated Powerhead Demonstratorin the mid-2000s.[27][21][28]

Raptor is designed for extreme reliability, aiming to support airline-level of safety required by the point-to-point Earth transportation market.[29]Gwynne Shotwellclaimed that Raptor would be able to deliver "long life... and more benign turbine environments".[30][21]

Propellants

[edit]

Raptor is designed fordeepcryogenicpropellants—fluids cooled to near theirfreezing points,rather than theirboiling points,as is typical for cryogenic rocket engines.[31]Subcooled propellants are denser, increasing propellant mass[32]as well as engine performance. Specific impulse is increased, and the risk ofcavitationat inputs to the turbopumps is reduced due to the higher propellant fuel mass flow rate per unit of power generated.[21]Cavitation (bubbles) reduces fuel flow/pressure and can starve the engine, while eroding turbine blades.[33]Theoxidizertofuelratio of the engine is approximately 3.8 to 1.[34]

Performance

[edit]

Raptor's target performance was a vacuum specific impulse of 382 s (3,750 m/s), with a thrust of 3 MN (670,000 lbf), a chamber pressure of 300 bar (30 MPa; 4,400 psi), and anexpansion ratioof 150 for the vacuum-optimized variant. This was achieved with Raptor 2.

Manufacturing and materials

[edit]

Many components of early Raptor prototypes were manufactured using3D printing,including turbopumps and injectors, increasing the speed of development and testing.[31][35]The 2016 subscale development engine had 40% (by mass) of its parts manufactured by 3D printing.[21]In 2019, engine manifolds were cast from SpaceX's in-house developed SX300Inconelsuperalloy, later changed to SX500.[36]

History

[edit]
SpaceX'sMerlin engine(left) compared to a sea-level Raptor 1 engine (right)

Conception

[edit]

SpaceX'sMerlinandKestrelrocket engines use aRP-1and liquid oxygen ( "kerolox" ) combination. Raptor has about triple the thrust of SpaceX'sMerlin 1Dengine, which powers theFalcon 9andFalcon Heavylaunch vehicles.

Raptor was conceived to burnhydrogenandoxygenpropellants as of 2009.[37]SpaceX had a few staff working on the Raptor upper-stage engine at a low priority in 2011.[38][39]

In October 2012, SpaceX announced concept work on an engine that would be "several times as powerful as theMerlin1 series of engines, and won't use Merlin'sRP-1fuel ".[40]

Development

[edit]

In November 2012, Musk announced that SpaceX was working onmethane-fueled rocket engines, that Raptor would be methane-based,[41]and that methane would fuel Mars colonization.[28]Because of the presence ofunderground waterandcarbon dioxideinMars atmosphere,methane, a simplehydrocarbon,could be synthesized on Mars using theSabatier reaction.[42]NASAfoundin-situ resource productionon Mars to be viable for oxygen, water, and methane production.[43]

In early 2014 SpaceX confirmed that Raptor would be used for both first and second stages of its next rocket. This held as the design evolved from theMars Colonial Transporter[28]to theInterplanetary Transport System,[44]theBig Falcon Rocket,and ultimately, Starship.[45]

The concept evolved from a family of Raptor -designated rocket engines (2012)[46]to focus on the full-size Raptor engine (2014).[47]

In January 2016, the US Air Force awarded aUS$33.6 milliondevelopment contract to SpaceX to develop a prototype Raptor for use on theupper stageofFalcon 9andFalcon Heavy.[48][49]

The first version was intended to operate at a chamber pressure of 250 bars (25 MPa; 3,600 psi).[50]As of July 2022, chamber pressure had reached 300 bars in a test.[33] In April 2024, Musk shared the performance achieved by SpaceX with the Raptor 1 engine (sea level 185 tf, Rvac 200 tf) and Raptor 2 engine (sea level 230 tf, Rvac 258 tf) along with the target specifications for the upcoming Raptor 3 (sea level 280 tf, Rvac 306 tf)[51][52]and said SpaceX would aim to ultimately achieve over 330 tonnes of thrust on the sea-level booster engines.[53]

Raptor 1 and 2 engines require a heat shroud to protect pipes and wiring from engine heat,[33]while Raptor 3 is planned to no longer need a heat shield.[53]: 18:30 

Testing

[edit]
Testing of the Raptor 's oxygenpreburneratStennis Space Centerin 2015
First test firing of a Raptor development engine on 25 September 2016 inMcGregor, Texas

Initialdevelopmenttesting[54]of Raptor components was done at NASA'sStennis Space Center,[16][55]beginning in April 2014. Testing focused on startup and shutdown procedures, as well as hardware characterization andverification.[21]

SpaceX began testing injectors in 2014 and tested an oxygenpreburnerin 2015. 76 hot-fire tests of the preburner, totaling some 400 seconds of test time, were executed from April-August.[54]

By early 2016, SpaceX had constructed an engine test stand at theirMcGregor test sitein central Texas for Raptor testing.[21][16]The first Raptor was manufactured at theSpaceX Hawthornefacility in California. By August 2016 it was shipped to McGregor for development testing.[56]The engine had 1 MN (220,000 lbf) thrust.[57]It was the first-ever FFSC methalox engine to reach a test stand.[21]

A subscale development engine was used for design validation. It was one-third the size of the engine designs that were envisioned for flight vehicles.[21]It featured 200 bars (20 MPa; 2,900 psi) of chamber pressure, with a thrust of 1 meganewton (220,000 lbf) and used the SpaceX-designed SX500 alloy, created to contain hot oxygen gas in the engine at up to 12,000 pounds per square inch (830 bar; 83 MPa).[58]It was tested on aground test standinMcGregor,firing briefly.[21]To eliminateflow separationproblems while testing in Earth's atmosphere, the test nozzle expansion ratio was limited to 150.[21]

By September 2017, the subscale engine had completed 1200 seconds of firings across 42 tests.[59]

SpaceX completed many static fire tests on a vehicle using Raptor 2s, including a 31 engine test (intended to be 33) on 9 February 2023,[60]and a 33 engine test on 25 August 2023.[61]During testing, more than 50 chambers melted, and more than 20 engines exploded.[33]

SpaceX completed itsfirst integrated flight testof Starship on 20 April 2023. The rocket had 33 Raptor 2 engines, but three of those were shut down before the rocket lifted off from the launch mount. The flight test was terminated after climbing to an altitude of ~39 km over the Gulf of Mexico. Multiple engines were out before the flight termination system (FTS) destroyed the booster and ship.[62]

On thesecond integrated flight testall 33 booster engines remained lit until boostback burn startup, and all six Starship engines remained lit until the FTS was activated.[63][64]

On thethird integrated flight test,all 33 booster engines once again remained lit until main engine cutoff (MECO), and then following hot-staging, 13 successfully relit to perform a boostback for full duration.[65]On the booster's landing burn, only 3 engines of the planned 13 lit, with 2 shutting down rapidly, the other remained lit until a rapid unscheduled disassembly (RUD) occurred ~462 metres above sea level.[65]The ship successfully kept all 6 engines lit until second stage / secondary engine cutoff (SECO) without issues, however a planned in-space raptor re-light was cancelled due to rolling during coast.[65]

Starship

[edit]
Main article:SpaceX Starship

Original configuration

[edit]
Big Falcon Rocketwith itsSuper Heavy boosterfiring (artist's concept)

In November 2016, Raptor was projected to power the proposedInterplanetary Transport System(ITS), in the early 2020s.[21]Musk discussed two engines: a sea-level variant (expansion ratio 40:1) with thrust of 3,050 kN (690,000 lbf) at sea level for the first stage/booster, and a vacuum variant (expansion ratio 200:1) with thrust of 3,285 kN (738,000 lbf) in space. 42 sea-level engines were envisioned in the high-level design of the first stage.[21]

Threegimbaledsea-level Raptor engines would be used forlandingthe second stage. Six additional, non-gimbaled, vacuum-optimized Raptors (Raptor Vacuum) would provide primary thrust for the second stage, for a total of nine engines.[66][21]Raptor Vacuums were envisioned to contribute aspecific impulseof 382 s (3,750 m/s), using a muchlarger nozzle.[67]

In September 2017 Musk said that a smaller Raptor engine—with slightly over half as much thrust as the previous designs—would be used on the next-generation rocket, a 9 m (30 ft)-diameter launch vehicle termed Big Falcon Rocket (BFR) and later renamedStarship.[68]The redesign was aimed at Earth-orbit andcislunarmissions so that the new system mightpay for itself,in part, through economic spaceflight activities in the near-Earth space zone.[69]With the much smaller launch vehicle, fewer Raptor engines would be needed. BFR was then slated to have 31 Raptors on the first stage and 6 on the second stage.[70][21]

By mid-2018, SpaceX was publicly stating that the sea-level Raptor was expected to have 1,700 kN (380,000 lbf) thrust at sea level with a specific impulse of 330 s (3,200 m/s), with a nozzle exit diameter of 1.3 m (4.3 ft). Raptor Vacuum would have specific impulse of 356 s (3,490 m/s) in vacuum[59]and was expected to exert 1,900 kN (430,000 lbf) force with a specific impulse of 375 s (3,680 m/s), using a nozzle exit diameter of 2.4 m (7.9 ft).[59]

In theBFRupdate given in September 2018, Musk showed a video of a 71-second fire test of a Raptor engine, and stated that "this is Raptor that will power BFR, both the ship and the booster; it's the same engine. [...] approximately a 200 (metric) tons engine aiming for roughly 300 bar chamber pressure. [...] If you had it at a high expansion ratio, has the potential to have a specific impulse of 380."[9]SpaceX aimed at a lifetime of 1000 flights.[71]

Starship SN20has its tiles inspected

Proposed Falcon 9 upper stage

[edit]

In January 2016, theUnited States Air Force(USAF) awarded aUS$33.6 milliondevelopment contract to SpaceX to develop a Raptor prototype for use on theupper stageof theFalcon 9andFalcon Heavy.The contract required double-matching funding by SpaceX of at leastUS$67.3 million.[48][72]Engine testing was planned for NASA'sStennis Space CenterinMississippiunder US Air Force supervision.[48][49]The USAF contract called for a single prototype engine and ground tests.[48]

In October 2017 USAF awarded aUS$40.8 millionmodification contract for a Raptor prototype for theEvolved Expendable Launch Vehicleprogram.[73]It was to useliquid methaneandliquid oxygen,propellants, afull-flow staged combustion cycle,and to be reusable.[49]

Production

[edit]

In July 2021, SpaceX announced a second Raptor production facility, in south Texas near theexisting rocket engine test facility.The facility would concentrate on serial production of Raptor 2, while the California facility would produce Raptor Vacuum and new/experimental Raptor designs. The new facility was expected to eventually produce 800 to 1000 rocket engines each year.[74][75]In 2019 the (marginal) cost of the engine was stated to be approachingUS$1 million.SpaceX planned to mass-produce up to 500 Raptor engines per year, each costing less thanUS$250,000.[76]

Versions

[edit]

Raptor Vacuum

[edit]

Raptor Vacuum[77](RVac) is a variant of Raptor with an extended,regeneratively-coolednozzle for higher specific impulse in space. The vacuum-optimized Raptor targets a specific impulse of ~380 s (3,700 m/s).[8]A full-duration test of version 1 of Raptor Vacuum was completed in September 2020 at McGregor.[77]The first in-flight ignition of a Raptor Vacuum was on S25 during thesecond integrated flight test.[64]

Raptor 2

[edit]
A NASA employee standing between two Raptor 2 Vacuum engines (background) and a Raptor 2 sea-level (foreground). The streamlined design is due to the reduced parts visible above the engine nozzles.

Raptor 2 is a complete redesign of the Raptor 1 engine.[78]The turbomachinery, chamber, nozzle, and electronics were all redesigned. Manyflangeswere converted towelds,while other parts were deleted.[79]Simplifications continued after production began. On 10 February 2022, Musk showed Raptor 2 capabilities and design improvements.[79][80]

By 18 December 2021, Raptor 2 had started production.[81]By November 2022, SpaceX produced more than one Raptor a day and had created a stockpile for future launches.[82]Raptor 2s are produced at SpaceX's McGregorengine development facility.

Raptor 2s were achieving 230tf(510,000lbf) of thrust consistently by February 2022. Musk indicated that production costs were approximately half that of Raptor 1.[79]

Raptor 3

[edit]

Raptor 3 is a further streamlined design of the Raptor engine aimed to ultimately achieve 330tf(3.2MN) of thrust in the booster/sea-level configuration,[52]with one stated goal being eliminating the requirement of protective engine shrouds.[53] In May 2023, Musk reported a successful static fire of a Raptor 3 prototype to 350 bar (5,100 psi) for 45 seconds, producing 269 tonnes of thrust.[83]Raptor 3 is a much simplified design that internalizes much of the plumbing and sensors, to increase reliability and improvere-entryperformance.[51]In 2024, Musk announced that Raptor 3 was entering the production phase at the McGregor facility.[84][full citation needed]

Raptor 3 engines will not require a heat shield and will have integral cooling and integral secondary flow circuits that run through the various sections of the engine, and it will eliminate many of the bolted joints. This design will be more difficult to service because some parts will be beneath welded joints.[85]: 42:19–45:50 

Derivative engine designs

[edit]

In October 2021, SpaceX initiated an effort to develop a conceptual design for a new rocket engine with the goal of keeping cost belowUS$1,000per ton of thrust. The project was called the 1337 engine, to be pronounced "LEET" (after acoding meme).[82]

Although the initial design effort was halted in late 2021, the project helped define an ideal engine, and likely generated ideas that were incorporated into Raptor 3. Musk stated then that "We can't make life multiplanetary with Raptor, as it is way too expensive, but Raptor is needed to tide us over until 1337 is ready."[82]

As of 2024,the LEET concept was clarified as a total tearup of the Raptor 3 design, although Musk stated that SpaceX will "probably do that at some point.... [Raptor 3] looks like a LEET engine, but its way more expensive because it still hasprintedparts, for example. "[85]

Comparison to other engines

[edit]
Main article:Comparison of orbital rocket engines
Engine Rockets Thrust Specific impulse,
vacuum 		Thrust-to-
weight ratio 		Propellant Cycle
Raptor sea-level Starship 2,400 kN (540,000lbf)[57] 350 s (3,400 m/s)[86] 200 (goal) LCH4/LOX

(subcooled)

Full-flow staged combustion
Raptor vacuum 380 s (3,700 m/s)[86] 120 (at maximum)
Merlin 1Dsea-level Falconbooster stage 914 kN (205,000 lbf) 311 s (3,050 m/s)[87] 176[88] RP-1 / LOX

(subcooled)

Gas generator
Merlin 1D vacuum Falcon upper stage 934 kN (210,000 lbf)[89] 348 s (3,410 m/s)[89] 180[88]
Blue OriginBE-4 New Glenn,Vulcan 2,400 kN (550,000 lbf)[90] 339 s (3,320 m/s)[91] LCH4/LOX Oxidizer-richstaged combustion
EnergomashRD-170/171M Energia,Zenit,Soyuz-5 7,904 kN (1,777,000 lbf)[92] 337.2 s (3,307 m/s)[92] 79.57[92] RP-1/ LOX
EnergomashRD-180 Atlas III,Atlas V 4,152 kN (933,000 lbf)[93] 338 s (3,310 m/s)[93] 78.44[93]
EnergomashRD-191/181 Angara,Antares 2,090 kN (470,000 lbf)[94] 337.5 s (3,310 m/s)[94] 89[94]
KuznetsovNK-33 N1,Soyuz-2-1v 1,638 kN (368,000 lbf)[95] 331 s (3,250 m/s)[95] 136.66[95]
EnergomashRD-275M Proton-M 1,832 kN (412,000 lbf) 315.8 s (3,097 m/s) 174.5 N2O4/UDMH
RocketdyneRS-25 Space Shuttle,SLS 2,280 kN (510,000 lbf) 453 s (4,440 m/s)[96] 73[97] LH2/ LOX Fuel-rich staged combustion
Aerojet RocketdyneRS-68A Delta IV 3,560 kN (800,000 lbf) 414 s (4,060 m/s) 51[98] LH2/ LOX Gas generator
RocketdyneF-1 Saturn V 7,740 kN (1,740,000 lbf) 304 s (2,980 m/s)[99] 83 RP-1 / LOX Gas generator

See also

[edit]

References

[edit]
  1. ^Sierra Engineering & Software, Inc. (18 June 2019)."Exhaust Plume Calculations for SpaceX Raptor Booster Engine"(PDF).p. 1.Archived(PDF)from the original on 20 October 2021.Retrieved17 September2021.The nominal operating condition for the Raptor engine is an injector face stagnation pressure (Pc) of 3669.5 psia and a somewhat fuel-rich engine O/F mixture ratio (MR) of 3.60. The current analysis was performed for the 100% nominal engine operating pressure (Pc=3669.5 psia) and an engine MR of 3.60.
  2. ^Space Exploration Technologies Corp.(17 September 2021)."Draft Programmatic Environmental Assessment for the SpaceX Starship/Super Heavy Launch Vehicle Program at the SpaceX Boca Chica Launch Site in Cameron County, Texas"(PDF).faa.gov.FAA Office of Commercial Space Transportation.p. 12.Archived(PDF)from the original on 17 September 2021.Retrieved17 September2021.Super Heavy is expected to be equipped with up to 37 Raptor engines, and Starship will employ up to six Raptor engines. The Raptor engine is powered by liquid oxygen (LOX) and liquid methane (LCH4) in a 3.6:1 mass ratio, respectively.
  3. ^Sierra Engineering & Software, Inc. (18 June 2019)."Exhaust Plume Calculations for SpaceX Raptor Booster Engine"(PDF).p. 1.Archived(PDF)from the original on 20 October 2021.Retrieved17 September2021.The subject engine uses a closed power cycle with a 34.34:1 regeneratively-cooled thrust chamber nozzle.
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  9. ^abMusk, Elon (17 September 2018)."First Lunar BFR Mission".YouTube.Event occurs at 45:30.Archivedfrom the original on 11 February 2020.Retrieved19 September2018.And this is the Raptor engine that will power BFR both the ship and the booster, it's the same engine. And this is approximately a 200-ton thrust engine that's aiming for roughly a 300-bar or 300-atmosphere chamber pressure. And if you have it at a high expansion ratio it has the potential to have a specific impulse of 380.
  10. ^@elonmusk (17 August 2020)."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"(Tweet) – viaTwitter.
  11. ^At 2.23MN thrust and 350s specific impulse
  12. ^ab78% O2,22% CH4mixture ratio
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