SpaceX Raptor explained

SpaceX Raptor
Manufacturer:SpaceX
Associated:SpaceX Starship
Status:In production
Type:liquid
Oxidizer:LOX
Fuel:CH
Mixture Ratio:3.6 (78% O, 22% CH)[1] [2]
Cycle:Full-flow staged combustion
Pumps:2 turbopumps
Combustion Chamber:1
Thrust:Raptor 1: [3]
Raptor 2: Raptor 3:
Highest achieved: Raptor 2 Block 3, ~45s test
Throttle Range:40–100%[4]
Thrust To Weight:Raptor 1: 88.94Raptor 2: 141.1Raptor 3: 183.6
Thrust(Vac):-->
Specific Impulse Vacuum:380isp[5]
Specific Impulse Sea Level:327isp
Burn Time:Varies
Length:3.1m (10.2feet)[6]
Diameter:1.3m (04.3feet)
Dry Weight:Raptor 1: 2080kg (4,590lb) Raptor 2: 1630kg (3,590lb)Raptor 3: 1525kg (3,362lb)

Raptor is a family of rocket engines developed and manufactured by SpaceX. It is the third rocket engine in history designed with a full-flow staged combustion (FFSC) fuel cycle, and the first such engine to power a vehicle in flight.[7] The engine is powered by cryogenic liquid methane and liquid oxygen, a mixture known as methalox.

SpaceX's super-heavy-lift Starship uses Raptor engines in its Super Heavy booster and in the Starship second stage.[8] Starship missions include lifting payloads to Earth orbit and is also planned for missions to the Moon and Mars.[9] The engines are being designed for reuse with little maintenance.[10]

Design

Raptor is designed for extreme reliability, aiming to support airline-level of safety required by the point-to-point Earth transportation market.[11] Gwynne Shotwell claimed that Raptor would be able to deliver "long life... and more benign turbine environments".[12]

Full-flow staged combustion

Raptor is powered by subcooled liquid methane and subcooled liquid oxygen in a full-flow staged combustion (FFSC) cycle. FFSC is a twin-shaft staged combustion cycle that uses both oxidizer-rich and fuel-rich preburners. The cycle allows for the full flow of both propellants through the turbines without dumping any unburnt propellant overboard.

FFSC is a departure from the more common "open-cycle" gas generator system and LOX/kerosene propellants used by its predecessor Merlin.[13] Before 2014, no FFSC had ever been used in an actual flight and only two FFSC designs had progressed sufficiently to reach test stands: the Soviet RD-270 project in the 1960s and the Aerojet Rocketdyne Integrated Powerhead Demonstrator in the mid-2000s.[14] RS-25 engines (first used on the Space Shuttle) used a simpler form of staged combustion cycle.[15] Several Russian rocket engines, including the RD-180 and the RD-191 did as well.[16]

FFSC has the advantage that the energy produced by the preburners, and used to power the propellant pumps, is spread among the entire fuel flow, meaning that the preburner exhaust driving the propellant turbopumps is as cool as possible, even cooler than other closed engine cycles which only preburn one propellant. This contributes to a long engine life. In contrast, an open-cycle engine in which the preburner exhaust bypasses the main combustion chamber tries to minimize the amount of propellant fed through the preburner, which is achieved by operating the turbine at its maximum survivable temperature.

An oxygen-rich turbine powers an oxygen turbopump, and a fuel-rich turbine powers a methane turbopump. Both oxidizer and fuel streams are converted completely to the gas phase before they enter the combustion chamber. This speeds up mixing and combustion, reducing the size and mass of the required combustion chamber. Torch igniters are used in the preburners. Raptor 2's main combustion chamber uses an undisclosed ignition method that is allegedly less complex, lighter, cheaper, and more reliable than Merlin's. Engine ignition in Raptor Vacuum is handled by dual-redundant spark-plug lit torch igniters,[17] which eliminate the need for Merlin's dedicated, consumable igniter fluid. Raptor 2 uses coaxial swirl injectors to admit propellants to the combustion chamber, rather than Merlin's pintle injectors.[18] [19]

Propellants

Raptor is designed for deep cryogenic propellants—fluids cooled to near their freezing points, rather than their boiling points, as is typical for cryogenic rocket engines.[20] Subcooled propellants are denser, increasing propellant mass[21] as well as engine performance. Specific impulse is increased, and the risk of cavitation at inputs to the turbopumps is reduced due to the higher propellant fuel mass flow rate per unit of power generated. Cavitation (bubbles) reduces fuel flow/pressure and can starve the engine, while eroding turbine blades. The oxidizer to fuel ratio of the engine is approximately 3.8 to 1.[22]

Liquid methane and oxygen propellants have been adopted by many companies, such as Blue Origin with its BE-4 engine, as well as Chinese startup Space Epoch's Longyun-70.[23]

Manufacturing and materials

Many components of early Raptor prototypes were manufactured using 3D printing, including turbopumps and injectors, increasing the speed of development and testing.[24] The 2016 subscale development engine had 40% (by mass) of its parts manufactured by 3D printing. In 2019, engine manifolds were cast from SpaceX's in-house developed SX300 Inconel superalloy, later changed to SX500.[25]

History

Conception

SpaceX's Merlin and Kestrel rocket engines use a RP-1 and liquid oxygen ("kerolox") combination. Raptor has about triple the thrust of SpaceX's Merlin 1D engine, which powers the Falcon 9 and Falcon Heavy launch vehicles.

Raptor was conceived to burn hydrogen and oxygen propellants as of 2009.[26] SpaceX had a few staff working on the Raptor upper-stage engine at a low priority in 2011.[27] [28]

In October 2012, SpaceX announced concept work on an engine that would be "several times as powerful as the Merlin 1 series of engines, and won't use Merlin's RP-1 fuel".[29]

Development

In November 2012, Musk announced that SpaceX was working on methane-fueled rocket engines, that Raptor would be methane-based,[30] and that methane would fuel Mars colonization.[31] Because of the presence of underground water and carbon dioxide in Mars atmosphere, methane, a simple hydrocarbon, could be synthesized on Mars using the Sabatier reaction.[32] NASA found in-situ resource production on Mars to be viable for oxygen, water, and methane production.[33]

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 the Mars Colonial Transporter to the Interplanetary Transport System,[34] the Big Falcon Rocket, and ultimately, Starship.[35]

The concept evolved from a family of Raptor -designated rocket engines (2012)[36] to focus on the full-size Raptor engine (2014).[37]

In January 2016, the US Air Force awarded a development contract to SpaceX to develop a prototype Raptor for use on the upper stage of Falcon 9 and Falcon Heavy.[38] [39]

The first version was intended to operate at a chamber pressure of 250bar.[40] As of July 2022, chamber pressure had reached 300 bars in a test.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)[41] [42] and said SpaceX would aim to ultimately achieve over 330 tonnes of thrust on the sea-level booster engines.[43]

Raptor 1 and 2 engines require a heat shroud to protect pipes and wiring from engine heat, while Raptor 3 is planned to no longer need a heat shield.[43]

Testing

Initial development testing[44] of Raptor components was done at NASA's Stennis Space Center,[45] beginning in April 2014. Testing focused on startup and shutdown procedures, as well as hardware characterization and verification.

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

By early 2016, SpaceX had constructed an engine test stand at their McGregor test site in central Texas for Raptor testing. The first Raptor was manufactured at the SpaceX Hawthorne facility in California. By August 2016 it was shipped to McGregor for development testing.[46] The engine had 1MN thrust.[47] It was the first-ever FFSC methalox engine to reach a test stand.

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. It featured 200bar of chamber pressure, with a thrust of 1MN and used the SpaceX-designed SX500 alloy, created to contain hot oxygen gas in the engine at up to 12000psi.[48] It was tested on a ground test stand in McGregor, firing briefly. To eliminate flow separation problems while testing in Earth's atmosphere, the test nozzle expansion ratio was limited to 150.

By September 2017, the subscale engine had completed 1200 seconds of firings across 42 tests.[49]

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,[50] and a 33 engine test on 25 August 2023.[51] During testing, more than 50 chambers melted, and more than 20 engines exploded.[52]

SpaceX completed its first integrated flight test of 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.[53]

On the second integrated flight test all 33 booster engines remained lit until boostback burn startup, and all six Starship engines remained lit until the FTS was activated.

On the third 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.[54] 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. 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.

Starship

See main article: SpaceX Starship.

Original configuration

In November 2016, Raptor was projected to power the proposed Interplanetary Transport System (ITS), in the early 2020s. Musk discussed two engines: a sea-level variant (expansion ratio 40:1) with thrust of 3050kN at sea level for the first stage/booster, and a vacuum variant (expansion ratio 200:1) with thrust of 3285kN in space. 42 sea-level engines were envisioned in the high-level design of the first stage.

Three gimbaled sea-level Raptor engines would be used for landing the 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.[55] Raptor Vacuums were envisioned to contribute a specific impulse of 382isp, using a much larger nozzle.[56]

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 -diameter launch vehicle termed Big Falcon Rocket (BFR) and later renamed Starship.[57] The redesign was aimed at Earth-orbit and cislunar missions so that the new system might pay for itself, in part, through economic spaceflight activities in the near-Earth space zone.[58] 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.[59]

By mid-2018, SpaceX was publicly stating that the sea-level Raptor was expected to have 1700kN thrust at sea level with a specific impulse of 330isp, with a nozzle exit diameter of 1.3m (04.3feet). Raptor Vacuum would have specific impulse of 356isp in vacuum and was expected to exert 1900kN force with a specific impulse of 375isp, using a nozzle exit diameter of 2.4m (07.9feet).

In the BFR update 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." SpaceX aimed at a lifetime of 1000 flights.[60]

Proposed Falcon 9 upper stage

In January 2016, the United States Air Force (USAF) awarded a development contract to SpaceX to develop a Raptor prototype for use on the upper stage of the Falcon 9 and Falcon Heavy. The contract required double-matching funding by SpaceX of at least .[61] Engine testing was planned for NASA's Stennis Space Center in Mississippi under US Air Force supervision. The USAF contract called for a single prototype engine and ground tests.

In October 2017 USAF awarded a modification contract for a Raptor prototype for the Evolved Expendable Launch Vehicle program.[62] It was to use liquid methane and liquid oxygen, propellants, a full-flow staged combustion cycle, and to be reusable.

Production

In July 2021, SpaceX announced a second Raptor production facility, in central Texas near the existing 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.[63] [64] In 2019 the (marginal) cost of the engine was stated to be approaching . SpaceX planned to mass-produce up to 500 Raptor engines per year, each costing less than .[65]

Versions

Raptor Vacuum

Raptor Vacuum[66] (RVac) is a variant of Raptor with an extended, regeneratively-cooled nozzle for higher specific impulse in space. The vacuum-optimized Raptor targets a specific impulse of ~380isp.[5] A full-duration test of version 1 of Raptor Vacuum was completed in September 2020 at McGregor. The first in-flight ignition of a Raptor Vacuum was on S25 during the second integrated flight test.[67]

Raptor 2

Raptor 2 is a complete redesign of the Raptor 1 engine.[68] The turbomachinery, chamber, nozzle, and electronics were all redesigned. Many flanges were converted to welds, while other parts were deleted.[69] Simplifications continued after production began. On 10 February 2022, Musk showed Raptor 2 capabilities and design improvements.

By 18 December 2021, Raptor 2 had started production.[70] By November 2022, SpaceX produced more than one Raptor a day and had created a stockpile for future launches. Raptor 2s are produced at SpaceX's McGregor engine development facility.

Raptor 2s were achieving of thrust consistently by February 2022. Musk indicated that production costs were approximately half that of Raptor 1.[69]

Raptor 3

Raptor 3 is a further streamlined design of the Raptor engine aimed to ultimately achieve of thrust in the booster/sea-level configuration,[42] with one stated goal being eliminating the requirement of protective engine shrouds.[43] Raptor 3 is a much simplified design that internalizes much of the plumbing and sensors, to increase reliability and improve re-entry performance.[41] In 2024, Musk announced that Raptor 3 was entering the production phase at the McGregor facility.[71] By 2 August 2024, Raptor 3 had begun production.[72]

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, with Musk further stating "we'll have to cut them open".

Derivative engine designs

In October 2021, SpaceX initiated an effort to develop a conceptual design for a new rocket engine with the goal of keeping cost below per ton of thrust. The project was called the 1337 engine, to be pronounced "LEET" (after a coding meme).[73]

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."

, 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 has printed parts, for example."[74]

Comparison to other engines

See main article: Comparison of orbital rocket engines.

EngineRocketsdata-sort-type="number" scope="col" Thrustdata-sort-type="number" scope="col" Specific impulse,
vacuum		Thrust-to-
weight ratio		PropellantCycle
Raptor sea-levelStarship[75] 350isp200 (goal)LCH4 / LOX(subcooled)Full-flow staged combustion
Raptor vacuum380isp120 (at maximum)
Merlin 1D sea-levelFalcon booster stage914kN311isp[76] 176[77] RP-1 / LOX (subcooled)Gas generator
Merlin 1D vacuumFalcon upper stage934kN[78] 348isp180
Blue Origin BE-4New Glenn, Vulcan550000order=flipNaNorder=flip[79] 339isp[80] LCH4 / LOXOxidizer-rich staged combustion
Energomash RD-170/171MEnergia, Zenit, 7904kN[81] 337.2isp79.57RP-1 / LOX
Energomash RD-180Atlas III, Atlas V4152kN[82] 338isp78.44
Energomash RD-191/181Angara, Antares2090kN[83] 337.5isp89
Kuznetsov NK-33N1, 1638kN[84] 331isp136.66
Energomash RD-275MProton-M1832kN315.8isp174.5 / UDMH
Rocketdyne RS-25Space Shuttle, SLS2280kN453isp[85] 73[86] / LOXFuel-rich staged combustion
Aerojet Rocketdyne RS-68ADelta IV3560kN414isp51[87] / LOXGas generator
Rocketdyne F-1Saturn V7740kN304isp[88] 83RP-1 / LOXGas generator

See also

External links

Notes and References

  1. Web site: Sierra Engineering & Software, Inc.. 18 June 2019. Exhaust Plume Calculations for SpaceX Raptor Booster Engine. 17 September 2021. 1. 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.. 20 October 2021. https://web.archive.org/web/20211020054702/https://www.faa.gov/space/stakeholder_engagement/spacex_starship/media/Appendix_G_Exhaust_Plume_Calculations.pdf. live.
  2. Web site: 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. live. 17 September 2021. faa.gov. FAA Office of Commercial Space Transportation. 12. 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.. 17 September 2021. https://web.archive.org/web/20210917182019/https://www.faa.gov/space/stakeholder_engagement/spacex_starship/media/Draft_PEA_for_SpaceX_Starship_Super_Heavy_at_Boca_Chica.pdf.
  3. Web site: Bergin . Chris . 2022-01-23 . Raptor 2 testing at full throttle on the SpaceX McGregor test stands . 2022-03-22 . NASASpaceFlight.com . en-US.
  4. elonmusk . Elon . Musk . Elon Musk . 1295553672454311941 . 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. .
  5. elonmusk . Elon . Musk . Elon Musk . 1171118891671490560 . Sea level Raptor's vacuum Isp is ~350 sec, but ~380 sec with larger vacuum-optimized nozzle . 25 September 2019 . https://web.archive.org/web/20190925065050/https://twitter.com/elonmusk/status/1171118891671490560 . live.
  6. Web site: Starship | SpaceX . 2 October 2019 . 30 September 2019 . https://web.archive.org/web/20190930163150/https://www.spacex.com/starship . dead .
  7. Everyday Astronaut . Youtube . Dodd . Tim . Everyday astronaut . en-US . 2019-05-25 . Is SpaceX's Raptor engine the king of rocket engines? . 2023-05-22 . 22 May 2023 . https://web.archive.org/web/20230522144323/https://everydayastronaut.com/raptor-engine/ . live .
  8. Web site: March 2020. Starship Users Guide, Revision 1.0, March 2020. dead. https://web.archive.org/web/20200402122214/https://www.spacex.com/sites/spacex/files/starship_users_guide_v1.pdf. 2 April 2020. 18 May 2020. SpaceX/files. SpaceX. SpaceX's Starship system represents a fully reusable transportation system designed to service Earth orbit needs as well as missions to the Moon and Mars. This two-stage vehicle — composed of the Super Heavy rocket (booster) and Starship (spacecraft).
  9. News: Leone. Dan. 25 October 2013. SpaceX Could Begin Testing Methane-fueled Engine at Stennis Next Year. Space News. dead. 26 October 2013. https://archive.today/20131025232611/http://www.spacenews.com/article/launch-report/37859spacex-could-begin-testing-methane-fueled-engine-at-stennis-next-year. 25 October 2013.
  10. News: Neff . William . Steckelberg . Aaron . Davenport . Christian . 9 January 2023 . The rockets NASA and SpaceX plan to send to the moon . live . https://web.archive.org/web/20230417053038/https://www.washingtonpost.com/technology/interactive/2023/nasa-sls-spacex-starship-rockets/ . 17 April 2023 . 28 August 2023 . The Washington Post.
  11. News: Foust . Jeff . 15 October 2017 . Musk offers more technical details on BFR system . live . https://archive.today/20210307190214/https://spacenews.com/musk-offers-more-technical-details-on-bfr-system/ . 7 March 2021 . 15 October 2017 . . [initial flight testing will be with] a full-scale ship doing short hops of a few hundred kilometers altitude and lateral distance ... fairly easy on the vehicle, as no heat shield is needed, we can have a large amount of reserve propellant and don’t need the high area ratio, deep space Raptor engines. ... 'The engine thrust dropped roughly in proportion to the vehicle mass reduction from the first IAC talk,' Musk wrote when asked about that reduction in thrust. The reduction in thrust also allows for the use of multiple engines, giving the vehicle an engine-out capability for landings. ... Musk was optimistic about scaling up the Raptor engine from its current developmental model to the full-scale one. 'Thrust scaling is the easy part. Very simple to scale the dev Raptor to 170 tons,' he wrote. 'The flight engine design is much lighter and tighter, and is extremely focused on reliability.' He added the goal is to achieve 'passenger airline levels of safety' with the engine, required if the vehicle is to serve point-to-point transportation markets..
  12. Web site: Shotwell . Gwynne . 17 March 2015 . Statement of Gwynne Shotwell, President & Chief Operating Officer, Space Exploration Technologies Corp. (SpaceX) . live . https://web.archive.org/web/20160128041905/http://docs.house.gov/meetings/AS/AS29/20150317/103135/HHRG-114-AS29-Wstate-ShotwellG-20150317.pdf . 28 January 2016 . 11 January 2016 . Congressional testimony . US House of Representatives, Committee on Armed Service Subcommittee on Strategic Forces . 14–15 . SpaceX has already begun self-funded development and testing on our next-generation Raptor engine. ... Raptor development ... will not require external development funds related to this engine..
  13. News: Todd . David . 22 November 2012 . SpaceX's Mars rocket to be methane-fuelled . live . https://web.archive.org/web/20131030143636/http://www.flightglobal.com/news/articles/spacexs-mars-rocket-to-be-methane-fuelled-379326/ . 30 October 2013 . 5 December 2012 . Flightglobal . Musk said Lox and methane would be SpaceX’s propellants of choice on a mission to Mars, which has long been his stated goal. SpaceX’s initial work will be to build a Lox/methane rocket for a future upper stage, codenamed Raptor. The design of this engine would be a departure from the "open cycle" gas generator system that the current Merlin 1 engine series uses. Instead, the new rocket engine would use a much more efficient "staged combustion" cycle that many Russian rocket engines use..
  14. News: Nardi . Tom . 13 February 2019 . The "impossible" tech behind SpaceX's new engine . live . https://web.archive.org/web/20210204044128/https://hackaday.com/2019/02/13/the-impossible-tech-behind-spacexs-new-engine/ . 4 February 2021 . 15 February 2019 . Hackaday.
  15. Web site: Space Shuttle Main Engines . live . https://web.archive.org/web/20151210183632/http://www.nasa.gov/returntoflight/system/system_SSME.html . 10 December 2015 . 6 March 2013 . NASA.
  16. News: Belluscio . Alejandro G. . 3 October 2016 . ITS Propulsion – The evolution of the SpaceX Raptor engine . live . https://web.archive.org/web/20210126012458/https://www.nasaspaceflight.com/2016/10/its-propulsion-evolution-raptor-engine/ . 26 January 2021 . 3 October 2016 . NASASpaceFlight.com.
  17. News: Ralph . Eric . 27 August 2019 . SpaceX scrubs Starhopper's final Raptor-powered flight as Elon Musk talks 'finicky' igniters . live . https://web.archive.org/web/20191202122632/https://www.teslarati.com/spacex-scrubs-final-starhopper-flight-test-elon-musk/ . 2 December 2019 . 27 August 2019 . Teslarati . Raptor uses those spark plugs to ignite its ignition sources [forming] full-up blow torches ... —likely miniature rocket engines using the same methane and oxygen fuel as Raptor—then ignite the engine’s methane and oxygen preburners before finally igniting those mixed, high-pressure gases in the combustion chamber..
  18. Park . Gujeong . Oh . Sukil . Yoon . Youngbin . Choi . Jeong-Yeol . May 2019 . Characteristics of Gas-Centered Swirl-Coaxial Injector with Liquid Flow Excitation . Journal of Propulsion and Power . en . 35 . 3 . 624–631 . 10.2514/1.B36647 . 0748-4658 . 9 June 2019 . 4 February 2021 . https://web.archive.org/web/20210204072538/https://arc.aiaa.org/doi/10.2514/1.B36647 . live .
  19. Elon Musk Explains SpaceX's Raptor Engine! . Everyday Astronaut . Dodd . Tim . Everyday astronaut . Youtube . Jul 9, 2022 . en . 17 February 2023 . 17 February 2023 . https://web.archive.org/web/20230217151318/https://www.youtube.com/watch?v=E7MQb9Y4FAE&t=573s . live .
  20. Elon Musk comments on Falcon 9 explosion – Huge Blow for SpaceX . 7 July 2015 . video . 39:25–40:45 . 30 December 2015 . https://web.archive.org/web/20150906075127/https://www.youtube.com/watch?v=hJD0MMP4nkM . 6 September 2015 . dead . Elon Musk, Mike Suffradini.
  21. Web site: Fernholz . Tim . 2016-02-29 . The "super chill" reason SpaceX keeps aborting launches . live . https://web.archive.org/web/20230522194002/https://qz.com/627430/the-super-chill-reason-spacex-keeps-aborting-launches . 22 May 2023 . 2023-05-22 . . en.
  22. Web site: Urban . Tim . 2015-08-16 . How (and Why) SpaceX Will Colonize Mars — Page 4 of 5 . 2024-02-16 . Wait But Why . en-US. https://web.archive.org/web/20150817120851/http://waitbutwhy.com/2015/08/how-and-why-spacex-will-colonize-mars.html/4 . 17 August 2015. Musk: "The critical elements of the solution are rocket reusability and low cost propellant (CH and O at an O/F ratio of ~3.8). And, of course, making the return propellant on Mars, which has a handy CO atmosphere and lots of HO frozen in the soil.".
  23. Web site: Jones . Andrew . 19 January 2023 . Chinese startups conduct hot fire tests for mini version of SpaceX's Starship . live . https://web.archive.org/web/20240223204348/https://spacenews.com/chinese-startups-conduct-hot-fire-tests-for-mini-version-of-spacexs-starship/ . 23 February 2024 . 31 August 2023 . SpaceNews.
  24. Web site: Zafar . Ramish . 2021-03-23 . SpaceX's 3D Manufacturing Systems Supplier For Raptor Engine To Go Public Through SPAC Deal . https://web.archive.org/web/20221105065404/https://wccftech.com/spacexs-3d-manufacturing-systems-supplier-for-raptor-engine-to-go-public-through-spac-deal/ . 2022-11-05 . 2023-11-22 . Wccftech . en-US.
  25. Web site: SpaceX Casting Raptor Engine Parts from Supersteel Alloys Feb 2019 . live . https://web.archive.org/web/20201026120552/https://www.nextbigfuture.com/2019/02/spacex-casting-raptor-engine-parts-from-supersteel-alloys.html . 26 October 2020 . 22 October 2020.
  26. Web site: 7 July 2009 . Long term SpaceX vehicle plans . dead . https://web.archive.org/web/20100214144451/http://hobbyspace.com/nucleus/index.php?itemid=13632 . 14 February 2010 . 13 July 2009 . HobbySpace.com.
  27. News: Notes: Space Access'11: Thurs. – Afternoon session – Part 2: SpaceX . 8 April 2011 . RLV and Space Transport News . 7 April 2011 . dead . https://web.archive.org/web/20120320030007/http://www.hobbyspace.com/nucleus/index.php?itemid=28515 . 20 March 2012.
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  29. News: Rosenberg . Zach . SpaceX aims big with massive new rocket . 17 October 2012 . Flightglobal . 15 October 2012 . 18 October 2012 . https://web.archive.org/web/20121018120213/http://www.flightglobal.com/news/articles/spacex-aims-big-with-massive-new-rocket-377687/ . live .
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  31. News: Belluscio . Alejandro G. . 7 March 2014 . SpaceX advances drive for Mars rocket via Raptor power . live . https://web.archive.org/web/20150911235533/http://www.nasaspaceflight.com/2014/03/spacex-advances-drive-mars-rocket-raptor-power/ . 11 September 2015 . 7 March 2014 . NASAspaceflight.com.
  32. GPUs to Mars: Full-Scale Simulation of SpaceX's Mars Rocket Engine . 5 May 2015 . YouTube . 4 June 2015 . 19 January 2016 . https://web.archive.org/web/20160119113849/https://www.youtube.com/watch?v=vYA0f6R5KAI . live .
  33. Web site: mmooney . 8 November 2015 . In-Situ Resource Utilization – Mars Atmosphere/Gas Chemical Processing . dead . https://web.archive.org/web/20160618142308/http://sbir.nasa.gov/content/situ-resource-utilization-mars-atmospheregas-chemical-processing . 18 June 2016 . 2 June 2015 . NASA SBIR/STTR . NASA.
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  37. Broadcast 2212: Special Edition, interview with Gwynne Shotwell. 21 March 2014. Gwynne Shotwell. The Space Show. 21:25–22:10. 22 March 2014. https://web.archive.org/web/20140322013556/http://archived.thespaceshow.com/shows/2212-BWB-2014-03-21.mp3. 22 March 2014. mp3. 2212. our focus is the full Raptor size. audio file. dead.
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  42. News: Musk outlines plans to increase Starship launch rate and performance . Foust. Jeff . 6 April 2024 . 2024-04-16 . .
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  47. 1295498964205068289 . elonmusk . SN40 is about to be tested & has several upgrades over 330 bar engine. For reference, 330 bar on Raptor produces ~225 tons (half a million pounds) of force. . Elon . Musk . Elon Musk . 18 August 2020.
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  51. 1695158759717474379 . SpaceX . Super Heavy Booster 9 static fire successfully lit all 33 Raptor engines, with all but two running for the full duration. Congratulations to the SpaceX team on this exciting milestone! . SpaceX . 25 August 2023.
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