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Raptor is a family of developed and manufactured by SpaceX. It is the third rocket engine in history designed with a full-flow staged combustion fuel cycle, and the first such engine to power a vehicle in flight. The engine is powered by cryogenic liquid methane and liquid oxygen, a combination known as methalox.
SpaceX's super-heavy-lift SpaceX Starship uses Raptor engines in its Super Heavy booster and in the Starship second stage. Starship missions include lifting payloads to Earth orbit and is also planned for missions to the Starship HLS and Mars. The engines are being designed for reuse with little maintenance.
Full-flow staged combustion is a departure from the more traditional "open-cycle" gas generator system and LOX/kerosene propellants used by its predecessor Merlin. Before Raptor, no full-flow staged combustion engine had ever been used inflight and only two designs had progressed sufficiently to reach test stands: the Soviet RD-270 project in the 1960s, a full scale test engine and the Aerojet Rocketdyne Integrated Powerhead Demonstrator in the mid-2000s, which only demonstrated the powerhead. RS-25 engines (first used on the Space Shuttle) used a simpler form of staged combustion cycle. Several Russian rocket engines, including the RD-180 and the RD-191 did as well.
Full-flow staged combustion 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.
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. Because of the high temperatures of the preburner exhaust, the main combustion chamber of Raptor 2 has no main igniter, 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 .
Liquid methane and Liquid 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.
Raptor was conceived to burn Liquid hydrogen and Liquid oxygen propellants as of 2009. SpaceX had a few staff working on the Raptor upper-stage engine at a low priority in 2011.
In October 2012, SpaceX announced concept work on an engine that would be "several times as powerful as the SpaceX Merlin 1 series of engines, and won't use Merlin's RP-1 fuel".
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, the Big Falcon Rocket, and ultimately, Starship.
The concept evolved from a family of Raptor-designated rocket engines (2012) to focus on the full-size Raptor engine (2014).
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.
The first version was intended to operate at a chamber pressure of . 68th annual meeting of the International Astronautical Congress in Adelaide, Australia 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) and said SpaceX would aim to ultimately achieve over 330 tonnes of thrust on the sea-level booster engines.
Raptor 1 and 2 engines require a heat shroud to protect pipes and wiring from the heat of high-velocity atmospheric re-entry, while Raptor 3 is designed so that it does not require an external heat shield.
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 SpaceX McGregor 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. The engine had thrust. It was the first-ever full-flow staged combustion 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 of chamber pressure, with a thrust of and used the SpaceX-designed SX500 alloy, created to contain hot oxygen gas in the engine at up to . It was tested on a ground test stand in SpaceX 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.
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, and a 33 engine test on 25 August 2023. During testing, more than 50 chambers melted, and more than 20 engines exploded.
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.
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, and then following hot-staging, 13 successfully relit to perform a boostback for full duration. 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. The ship successfully kept all 6 engines lit until second stage / secondary engine cutoff without issues, however a planned in-space Raptor re-light was cancelled due to rolling during coast.
The seventh flight test featured the first reflown Raptor engine, which was successfully flown during Super Heavy booster 14's ascent burn and was recovered after its successful catch.
Booster 14 will be reflown for the first time on Starship's ninth test flight, with 29 out of 33 Raptors from its previous mission accompanying it.
Three gimbaling sea-level Raptor engines would be used for landing the second stage. Six additional, non-gimbaling vacuum-optimized Raptor Vacuum engines would provide primary thrust for the second stage, for a total of nine engines. Raptor Vacuums were envisioned to contribute a specific impulse of , using a nozzle extension.
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 SpaceX Starship. The redesign was aimed at Earth-orbit and Cislunar space missions so that the new system might pay for itself, in part, through economic spaceflight activities in the near-Earth space zone. 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.
By mid-2018, SpaceX was publicly stating that the sea-level Raptor was expected to have thrust at sea level with a specific impulse of , with a nozzle exit diameter of . Raptor Vacuum would have specific impulse of in vacuum and was expected to exert force with a specific impulse of , using a nozzle exit diameter of .
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. has its tiles inspected]]
In October 2017 USAF awarded a modification contract for a Raptor prototype for the Evolved Expendable Launch Vehicle program. It was to use liquid methane and liquid oxygen propellants, a full-flow staged combustion cycle, and be reusable.
| +SpaceX rocket engines
!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 |
By 18 December 2021, Raptor 2 had started production. 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 SpaceX McGregor.
Raptor 2s were achieving of thrust consistently by February 2022. Musk indicated that production costs were approximately half that of Raptor 1.
Another goal is to eliminate protective engine shrouds. Raptor 3 moves much of the plumbing and sensors into the housing wall, 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. 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.
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.
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."
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 looks like a LEET engine, but its way more expensive because it still has printed parts, for example."
Raptor 3
Raptor 3 is aimed to ultimately achieve of thrust in the booster/sea-level configuration. As of August 2024, it had reached 280 tf. It weighs 1525 kg. Chamber pressure reached .
LEET
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 Leet). (2023). 9781982181284, Simon & Schuster. ISBN 9781982181284
Comparison to other engines
Raptor 3 sea-level Super Heavy, Starship 200 LNG / Liquid oxygen
(subcooled) Full-flow staged combustion Raptor 3 vacuum Starship 120 (at maximum) Merlin 1D sea-level Falcon booster stage 176 RP-1 / LOX
(subcooled) Gas generator Merlin 1D vacuum Falcon upper stage 180 Blue Origin BE-4 New Glenn, Vulcan LNG / Liquid oxygen Oxidizer-rich staged combustion NPO Energomash RD-170/171M Energia, Zenit, 79.57 RP-1 / LOX Energomash RD-180 Atlas III, Atlas V 78.44 Energomash RD-191/181 Angara, Antares 89 Kuznetsov NK-33 N1, 136.66 Energomash RD-275M Proton-M 174.5 / UDMH Rocketdyne RS-25 Space Shuttle, SLS 73 / LOX Fuel-rich staged combustion Aerojet Rocketdyne RS-68A Delta IV 51 / LOX Gas generator Rocketdyne F-1 Saturn V 83 RP-1 / LOX Gas generator
See also
External links
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