Wikipedia

SpaceX Raptor

(Redirected from Raptor (rocket engine family))

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.[15] The engine is powered by cryogenic liquid methane and liquid oxygen, a combination known as methalox.

SpaceX Raptor
A Raptor 1 rocket engine ready for transport outside SpaceX's factory in Hawthorne, California
Country of originUnited States
ManufacturerSpaceX
Associated LVSpaceX Starship
StatusIn production
Liquid-fuel engine
PropellantLOX / CH4
Mixture ratio3.6 (78% O2, 22% CH4)[1][2]
CycleFull-flow staged combustion
Pumps2 turbopumps
Configuration
Chamber1
Nozzle ratio
  • 34.34 (sea-level),[3]
  • 80 (vacuum)[4]
Performance
ThrustRaptor 1: 185 tf (1.81 MN; 408,000 lbf)[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)
Throttle range40–100%[10]
Thrust-to-weight ratioRaptor 1: 88.94

Raptor 2: 141.1

Raptor 3: 183.6
Chamber pressure
  • 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 massRaptor 1: 2,080 kg (4,590 lb)

Raptor 2: 1,630 kg (3,590 lb)

Raptor 3: 1,525 kg (3,362 lb)

SpaceX's super-heavy-lift Starship uses Raptor engines in its Super Heavy booster and in the Starship second stage.[16] Starship missions include lifting payloads to Earth orbit and is also planned for missions to the Moon and Mars.[17] The engines are being designed for reuse with little maintenance.[18]

Design

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Raptor is designed for extreme reliability, aiming to support the airline-level safety required by the point-to-point Earth transportation market.[19] Gwynne Shotwell claimed that Raptor would be able to deliver "long life... and more benign turbine environments".[20][21]

Full-flow staged combustion

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See also: Liquid-propellant rocket § Engine cycles
 
Simplified full-flow staged combustion rocket diagram

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.[22] Before Raptor, 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.[15][23][21][24] RS-25 engines (first used on the Space Shuttle) used a simpler form of staged combustion cycle.[25] Several Russian rocket engines, including the RD-180[22] and the RD-191 did as well.[21]

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 that 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.

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 are converted completely to the gas phase before they enter the combustion chamber.[15] 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,[26] which eliminate 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's pintle injectors.[27][28]

Propellants

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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.[29] Subcooled propellants are denser, increasing propellant mass per volume[30] 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.[21] Cavitation (bubbles) reduces fuel flow/pressure and can starve the engine, while eroding turbine blades.[31] The oxidizer to fuel ratio of the engine is approximately 3.8 to 1.[32] Methalox burns relatively cleanly, reducing carbon build-up in the engine.

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.[33]

Manufacturing and materials

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Many components of early Raptor prototypes were manufactured using 3D printing, including turbopumps and injectors, increasing the speed of development and testing.[29][34] 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 SX300 Inconel superalloy, later changed to SX500.[35]

History

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SpaceX's Merlin engine (left) compared to a sea-level Raptor 1 engine (right)

Conception

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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.[36] SpaceX had a few staff working on the Raptor upper-stage engine at a low priority in 2011.[37][38]

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".[39]

Development

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In November 2012, Musk announced that SpaceX was working on methane-fueled rocket engines, that Raptor would be methane-based,[40] and that methane would fuel Mars colonization.[24] 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.[41] NASA found in-situ resource production on Mars to be viable for oxygen, water, and methane production.[42]

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[24] to the Interplanetary Transport System,[43] the Big Falcon Rocket, and ultimately, Starship.[44]

The concept evolved from a family of Raptor-designated rocket engines (2012)[45] to focus on the full-size Raptor engine (2014).[46]

In January 2016, the US Air Force awarded a US$33.6 million development contract to SpaceX to develop a prototype Raptor for use on the upper stage of Falcon 9 and Falcon Heavy.[47][48]

The first version was intended to operate at a chamber pressure of 250 bars (25 MPa; 3,600 psi).[49] As of July 2022, chamber pressure had reached 300 bars in a test.[31] 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)[50][51] and said SpaceX would aim to ultimately achieve over 330 tonnes of thrust on the sea-level booster engines.[52]

Raptor 1 and 2 engines require a heat shroud to protect pipes and wiring from the heat of high-velocity atmospheric re-entry,[31] while Raptor 3 is designed so that it does not require an external heat shield.[53]

Testing

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Testing of the Raptor 's oxygen preburner at Stennis Space Center in 2015
 
First test firing of a Raptor development engine on 25 September 2016 in McGregor, Texas

Initial development testing[54] of Raptor components was done at NASA's Stennis Space Center,[17][55] beginning in April 2014. Testing focused on startup and shutdown procedures, as well as hardware characterization and verification.[21]

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.[54]

By early 2016, SpaceX had constructed an engine test stand at their McGregor test site in central Texas for Raptor testing.[21][17] The first Raptor was manufactured at the SpaceX Hawthorne facility 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).[35] It was tested on a ground test stand in McGregor, firing briefly.[21] To eliminate flow separation problems 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.[58]

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,[59] and a 33 engine test on 25 August 2023.[60] During testing, more than 50 chambers melted, and more than 20 engines exploded.[31]

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.[61]

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.[62][63]

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.[64] On the booster's landing burn, only 3 engines of the planned 13 lit, with 2 shutting down rapidly, the other remained lit until the booster was destroyed ~462 metres above sea level.[64] 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.[64]

Starship

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Main article: SpaceX Starship

Original configuration

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Big Falcon Rocket with its Super Heavy booster firing (artist's concept)

In November 2016, Raptor was projected to power the proposed Interplanetary 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]

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.[65][21] Raptor Vacuums were envisioned to contribute a specific impulse of 382 s (3,750 m/s), using a much larger nozzle.[66]

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 renamed Starship.[67] 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.[68] 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.[69][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[58] 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).[58]

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."[9] SpaceX aimed at a lifetime of 1000 flights.[70]

 
Starship SN20 has its tiles inspected

Proposed Falcon 9 upper stage

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In January 2016, the United States Air Force (USAF) awarded a US$33.6 million 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 US$67.3 million.[47][71] Engine testing was planned for NASA's Stennis Space Center in Mississippi under US Air Force supervision.[47][48] The USAF contract called for a single prototype engine and ground tests.[47]

In October 2017 USAF awarded a US$40.8 million modification contract for a Raptor prototype for the Evolved Expendable Launch Vehicle program.[72] It was to use liquid methane and liquid oxygen propellants, a full-flow staged combustion cycle, and be reusable.[48]

Production

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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.[73][74] In 2019 the (marginal) cost of the engine was stated to be approaching US$1 million. SpaceX planned to mass-produce up to 500 Raptor engines per year, each costing less than US$250,000.[75]

Versions

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Raptor has evolved significantly since it was revealed.

SpaceX rocket engines[76][77]
Version Mass (kg) Thrust (t) Chamber
pressure (bar) 		Specific
impulse (s) 		Engine only TWR
Raptor 1 2080 185 250 350 89
Raptor 2 1630 230 300 347 141
Raptor 3 1525 280 350 350 184

Raptor Vacuum

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Each version of the engine has a corresponding Raptor Vacuum (RVac) variant[78] with an extended, regeneratively-cooled nozzle 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.[78] The first in-flight ignition of a Raptor Vacuum was on S25 during the second integrated flight test.[63]

Raptor 2

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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.[79] The turbomachinery, chamber, nozzle, and electronics were all redesigned. Many flanges were converted to welds, while other parts were deleted.[80] Simplifications continued after production began. On 10 February 2022, Musk showed Raptor 2 capabilities and design improvements.[80][81]

By 18 December 2021, Raptor 2 had started production.[82] By November 2022, SpaceX produced more than one Raptor a day and had created a stockpile for future launches.[83] Raptor 2s are produced at SpaceX's McGregor engine development facility.

Raptor 2s were achieving 230 tf (510,000 lbf) of thrust consistently by February 2022. Musk indicated that production costs were approximately half that of Raptor 1.[80]

Raptor 3

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Raptor 3 is aimed to ultimately achieve 300 tf (2.9 MN) of thrust in the booster/sea-level configuration.[51][84] As of August 2024, it had reached 280 tf. It weighs 1525 kg. Chamber pressure reached 350 bar.[85]

Another goal is to eliminate protective engine shrouds.[52] Raptor 3 moves much of the plumbing and sensors into the housing wall,[50] where integral cooling and integral secondary flow circuits run through various sections of the engine, obviating the need for a separate heat shield. On 2 August 2024, Raptor 3 SN1 was revealed.[86] The reduction in externally visible components was so extreme that the CEO of United Launch Alliance, Tory Bruno, mistakenly accused SpaceX of revealing a "partially assembled" engine while comparing it to fully assembled engines.[87][88]

Many bolted joints in Raptor 2 have been eliminated/replaced by single parts. However, servicing is more difficult, as some parts lie beneath welded joints.[89]: 42:19–45:50 

LEET

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In October 2021, SpaceX initiated an effort to develop a conceptual design for a new rocket engine with the goal of keeping cost below US$1,000 per ton of thrust. The project was called the 1337 engine, to be pronounced "LEET" (after a coding meme).[83]

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."[83]

In June 2024, the LEET concept was clarified as a total tearup of the Raptor 3 design, with Musk stating 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."[89]

Comparison to other engines

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Main article: Comparison of orbital rocket engines
Engine Rockets Thrust Specific impulse,
vacuum 		Thrust-to-
weight ratio 		Propellant Cycle
Raptor 3 sea-level Super Heavy, Starship 2,750 kN (620,000 lbf)[77] 350 s (3,400 m/s)[77] 200 LCH
4 / LOX

(subcooled)

Full-flow staged combustion
Raptor 3 vacuum Starship 2,980 kN (670,000 lbf)[77] 380 s (3,700 m/s)[8] 120 (at maximum)
Merlin 1D sea-level Falcon booster stage 914 kN (205,000 lbf) 311 s (3,050 m/s)[90] 176[91] RP-1 / LOX

(subcooled)

Gas generator
Merlin 1D vacuum Falcon upper stage 934 kN (210,000 lbf)[92] 348 s (3,410 m/s)[92] 180[91]
Blue Origin BE-4 New Glenn, Vulcan 2,400 kN (550,000 lbf)[93] 339 s (3,320 m/s)[94] LCH
4 / LOX 		Oxidizer-rich staged combustion
Energomash RD-170/171M Energia, Zenit, Soyuz-5 7,904 kN (1,777,000 lbf)[95] 337.2 s (3,307 m/s)[95] 79.57[95] RP-1 / LOX
Energomash RD-180 Atlas III, Atlas V 4,152 kN (933,000 lbf)[96] 338 s (3,310 m/s)[96] 78.44[96]
Energomash RD-191/181 Angara, Antares 2,090 kN (470,000 lbf)[97] 337.5 s (3,310 m/s)[97] 89[97]
Kuznetsov NK-33 N1, Soyuz-2-1v 1,638 kN (368,000 lbf)[98] 331 s (3,250 m/s)[98] 136.66[98]
Energomash RD-275M Proton-M 1,832 kN (412,000 lbf) 315.8 s (3,097 m/s) 174.5 N2O4 / UDMH
Rocketdyne RS-25 Space Shuttle, SLS 2,280 kN (510,000 lbf) 453 s (4,440 m/s)[99] 73[100] LH2 / LOX Fuel-rich staged combustion
Aerojet Rocketdyne RS-68A Delta IV 3,560 kN (800,000 lbf) 414 s (4,060 m/s) 51[101] LH2 / LOX Gas generator
Rocketdyne F-1 Saturn V 7,740 kN (1,740,000 lbf) 304 s (2,980 m/s)[102] 83 RP-1 / LOX Gas generator

See also

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References

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  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. Retrieved 17 September 2021. 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. Retrieved 17 September 2021. 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. Retrieved 17 September 2021. The subject engine uses a closed power cycle with a 34.34:1 regeneratively-cooled thrust chamber nozzle.
  4. ^ Dodd, Tim (7 August 2021). ""Starbase Tour with Elon Musk [PART 2]"". Everyday Astronaut. 4 minutes in. Youtube. Archived from the original on 17 February 2024. Retrieved 23 February 2024.
  5. ^ Bergin, Chris (23 January 2022). "Raptor 2 testing at full throttle on the SpaceX McGregor test stands". NASASpaceFlight.com. Retrieved 22 March 2022.
  6. ^ Dodd, Tim (14 July 2022). "Raptor 1 VS Raptor 2: What's New // What's Different". Everyday Astronaut. Youtube. Archived from the original on 15 July 2022. Retrieved 15 July 2022.
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  8. ^ a b c Musk, Elon [@elonmusk] (9 September 2019). "Sea level Raptor's vacuum Isp is ~350 sec, but ~380 sec with larger vacuum-optimized nozzle" (Tweet). Archived from the original on 25 September 2019 – via Twitter.
  9. ^ a b Musk, Elon (17 September 2018). "First Lunar BFR Mission". YouTube. Event occurs at 45:30. Archived from the original on 11 February 2020. Retrieved 19 September 2018. 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. ^ Musk, Elon [@elonmusk] (18 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) – via Twitter.
  11. ^ At 2.23 MN thrust and 350 s specific impulse
  12. ^ a b 78% O2, 22% CH4 mixture ratio
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  16. ^ "Starship Users Guide, Revision 1.0, March 2020" (PDF). SpaceX/files. SpaceX. March 2020. Archived from the original (PDF) on 2 April 2020. Retrieved 18 May 2020. 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)
  17. ^ a b c Leone, Dan (25 October 2013). "SpaceX Could Begin Testing Methane-fueled Engine at Stennis Next Year". Space News. Archived from the original on 25 October 2013. Retrieved 26 October 2013.
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  19. ^ Foust, Jeff (15 October 2017). "Musk offers more technical details on BFR system". SpaceNews. Archived from the original on 7 March 2021. Retrieved 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.
  20. ^ Shotwell, Gwynne (17 March 2015). "Statement of Gwynne Shotwell, President & Chief Operating Officer, Space Exploration Technologies Corp. (SpaceX)" (PDF). Congressional testimony. US House of Representatives, Committee on Armed Service Subcommittee on Strategic Forces. pp. 14–15. Archived (PDF) from the original on 28 January 2016. Retrieved 11 January 2016. 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.
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  26. ^ Ralph, Eric (27 August 2019). "SpaceX scrubs Starhopper's final Raptor-powered flight as Elon Musk talks 'finicky' igniters". Teslarati. Archived from the original on 2 December 2019. Retrieved 27 August 2019. 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.
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