Raptor (rocket engine family)
Raptor is a staged combustion, methane-fueled rocket engine under development by SpaceX. The engines are powered by cryogenic liquid methane and liquid oxygen (LOX), rather than the RP-1 kerosene and LOX used in all previous SpaceX Falcon rockets which use or used Merlin 1A, 1C, & 1D engines. The earliest concepts for Raptor considered liquid hydrogen (LH
2) as fuel rather than methane. The Raptor engine will have about two times the thrust of the Merlin 1D engine that powers the current Falcon 9 launch vehicle.
First test firing of a Raptor development engine on 25 September 2016 in McGregor, Texas.
|Country of origin||United States|
|Propellant||Liquid oxygen / Liquid methane|
|Cycle||Full-flow staged combustion|
|Pumps||2 × multi-stage|
|Thrust||1,993 kN (448,000 lbf) |
|Chamber pressure||300 bar (30 MPa; 4,400 psi) |
anticipated value 
|Specific impulse||330 s, |
380 s (vacuum) 
|Diameter||1.3 m (4 ft 3 in)|
|BFR, BFR spaceship, BFR tanker, BFR satellite delivery spacecraft|
The broad Raptor concept as announced in 2013 was "a highly reusable methane staged-combustion engine that will power the next generation of SpaceX launch vehicles designed for the exploration and colonization of Mars". According to SpaceX founder Elon Musk, this design was explicitly intended to achieve full reusability of all rocket stages and, as a result, "a two order of magnitude reduction in the cost of spaceflight".
A variety of Raptor engines were planned to be used on both stages of the several vehicle designs announced in September 2016: ITS launch vehicle, as well as both of the long-duration spacecraft used to support all aspects of the Interplanetary Transport System on-orbit. Those vehicle designs were the ITS tanker—a transport carrier of propellant cargo to Earth orbit—and also the Interplanetary Spaceship—a very long-duration carrier of both passengers and space cargo to interplanetary destinations, and which was also to serve in the 2016 mission architecture as both a descent and ascent vehicle at Mars—were to be powered by six vacuum-optimized Raptor rocket engines with three additional sea-level-nozzle Raptor engines to be used for maneuvering. The ITS booster stage was to be powered by 42 Raptors. Unlike nearly all other launch vehicles or spacecraft, on all Earth-away launches, the long-duration spacecraft (tanker or spaceship) designs would also provide second-stage acceleration to orbital velocity; all propulsion was to be provided by Raptor engines. In a 2017 change to the launch vehicle design, Musk presented a smaller-sized (but still super heavy-lift) launch vehicle with the name BFR that would use a smaller number of Raptor engines.
The engine development from 2009 to 2015 was funded exclusively through private investment by SpaceX, and not as a result of any funding from the US government. In January 2016, SpaceX did agree with the US Air Force to take US$33.6 million in defense department funding in order to develop a particular Raptor model: a prototype of a new upper-stage variant of the Raptor engine designed for potential use as an upper stage on Falcon 9 and Falcon Heavy, with SpaceX agreeing to fund at least US$67.3 million on the same upper-stage development project, on a minimum 2:1 private-to-government funding basis. In August 2016, a development Raptor engine was shipped to their McGregor testing facility in Texas, where it has been undergoing development testing. The first test firing on a ground test stand was in September 2016.
As of September 2017[update], Raptor engines had been tested for a combined total of 1200 seconds of test firing time over 42 main engine tests. The longest test was 100 seconds, which is limited by the size of the propellant tanks at the SpaceX ground test facility. The test engine operates at 20 MPa (200 bar; 2,900 psi) pressure. The flight engine is aimed for 25 MPa (250 bar; 3,600 psi), and SpaceX expects to achieve 30 MPa (300 bar; 4,400 psi) in later iterations.
An advanced rocket engine design project named Raptor—then a hydrolox engine—was first publicly discussed by SpaceX's Max Vozoff at the American Institute of Aeronautics and Astronautics Commercial Crew/Cargo symposium in 2009. As of April 2011[update], SpaceX had a small number of staff working on the Raptor upper-stage engine, then still a LH
2/LOX concept, at a low level of priority. Further mention of the development program occurred in 2011. In March 2012, news accounts asserted that the Raptor upper-stage engine development program was underway, but that details were not being publicly released.
In October 2012, SpaceX publicly announced concept work on a rocket engine that would be "several times as powerful as the Merlin 1 series of engines, and won't use Merlin's RP-1 fuel", but declined to specify which fuel would be used. They indicated that details on a new SpaceX rocket would be forthcoming in "one to three years" and that the large engine was intended for the next-generation launch vehicle using multiple of these large engines, that would be expected to launch payload masses of the order of 150 to 200 tonnes (150,000 to 200,000 kg; 330,000 to 440,000 lb) to low Earth orbit, exceeding the payload mass capability of the NASA Space Launch System.
Methane engine announcement and component developmentEdit
In November 2012, Musk announced a new direction for the propulsion division of SpaceX: developing methane-fueled rocket engines. He further indicated that the engine concept, codenamed Raptor, would now become a methane-based design, and that methane would be the fuel of choice for SpaceX's plans for Mars colonization.
Because of the presence of water underground and carbon dioxide in the atmosphere of Mars, methane, a simple hydrocarbon, can easily be synthesized on Mars using the Sabatier reaction. In-situ resource production on Mars has been examined by NASA and found to be viable for oxygen, water, and methane production. According to a study published by researchers from the Colorado School of Mines, in-situ resource utilization such as methane from Mars makes space missions more feasible technically and economically and enables reusability.
When first mentioned by SpaceX in 2009, the term "Raptor" was applied exclusively to an upper-stage engine concept—and 2012 pronouncements indicated that it was then still a concept for an upper stage engine—but in early 2014 SpaceX confirmed that Raptor would be used both on a new second stage, as well as for the large (then, nominally a 10-meter-diameter) core of the then-named Mars Colonial Transporter (subsequently, in 2016, on both stages of the even larger ITS launch vehicle concept and then, in 2017 and 2018, on the currently-in-development 9-meter diameter BFR).
The earliest public hints that a staged-combustion methane engine was under consideration at SpaceX were given in May 2011 when SpaceX asked if the Air Force was interested in a methane-fueled engine as an option to compete with the mainline kerosene-fueled engine that had been requested in the USAF Reusable Booster System High Thrust Main Engine solicitation.
Public information released in November 2012 indicated that SpaceX might have a family of Raptor-designated rocket engines in mind; this was confirmed by SpaceX in October 2013. However, in March 2014 SpaceX COO Gwynne Shotwell clarified that the focus of the new engine development program is exclusively on the full-size Raptor engine; smaller subscale methalox engines were not planned on the development path to the very large Raptor engine.
In October 2013, SpaceX announced that they would be performing methane engine tests of Raptor engine components at the John C. Stennis Space Center in Hancock County, Mississippi, and that SpaceX would add equipment to the existing test stand infrastructure in order to support liquid methane and hot gaseous methane engine component testing. In April 2014, SpaceX completed the requisite upgrades and maintenance to the Stennis test stand to prepare for testing of Raptor components, and the engine component testing program began in earnest, focusing on the development of robust startup and shutdown procedures, something that is typically quite difficult to do for full-flow staged combustion cycle engines. Component testing at Stennis also allowed hardware characterization and verification of proprietary analytical software models that SpaceX developed to push the technology on this engine cycle that had little prior development work in the West.
October 2013 was the first time SpaceX disclosed a nominal design thrust of the Raptor engine—2,900 kN (661,000 lbf)—although early in 2014 they announced a Raptor engine with greater thrust, and in 2015, one with lower thrust that might better optimize thrust-to-weight.
In February 2014, Tom Mueller, the head of rocket engine development at SpaceX, revealed in a speech that Raptor was being designed for use on a vehicle where nine engines would "put over 100 tons of cargo up to Mars" and that the rocket would be more powerful than previously released publicly, producing greater than 4,400 kN (1,000,000 lbf). A June 2014 talk by Mueller provided more specific engine performance target specifications indicating 6,900 kN (1,600,000 lbf) of sea-level thrust, 8,200 kN (1,800,000 lbf) of vacuum thrust, and a specific impulse (Isp) of 380 s for a vacuum version. Earlier information had estimated the design Isp under vacuum conditions as only 363 s. Jeff Thornburg, who led development of the Raptor engine at SpaceX 2011–2015, noted that methane rocket engines have higher performance than kerosene/RP-1 and lower than hydrogen, with significantly fewer problems for long-term, multi-start engine designs than kerosene—methane is cleaner burning—and significantly lower cost than hydrogen, coupled with the ability to "live off the land" and produce methane directly from extraterrestrial sources.
SpaceX successfully began development testing of injectors in 2014 and completed a full-power test of a full-scale oxygen preburner in 2015. 76 hot fire tests of the preburner, totaling some 400 seconds of test time, were executed from April–August 2015. SpaceX completed its planned testing at NASA Stennis in 2014 and 2015.
In January 2015, Elon Musk stated that the thrust they were currently targeting was around 230 tonnes-force (2,300 kN; 510,000 lbf), much lower than older statements mentioned. This brought into question much of the speculation surrounding a 9-engine booster, as he stated "there will be a lot of [engines]". By August 2015, an Elon Musk statement surfaced that indicated the oxidizer to fuel ratio of the Mars-bound engine would be approximately 3.8 to 1.
In January 2016, the US Air Force awarded a US$33.6 million development contract to SpaceX to develop a prototype version of its methane-fueled reusable Raptor engine for use on the upper stage of the Falcon 9 and Falcon Heavy launch vehicles, which required double-matching funding by SpaceX of at least US$67.3 million. Work under the contract is expected to be completed in 2018, with engine performance testing to be done at NASA's John C. Stennis Space Center in Mississippi and Los Angeles Air Force Base, California.
Engine development and testEdit
By August 2016, the first integrated Raptor rocket engine, manufactured at the SpaceX Hawthorne facility in California, shipped to the McGregor rocket engine test facility in Texas for development testing. The engine had 1 MN (220,000 lbf) thrust, which makes it approximately one-third the size of the full-scale Raptor engine planned for flight tests in 2019/2020 timeframe. It is the first full-flow staged-combustion methalox engine ever to reach a test stand.
On 26 September 2016, Elon Musk tweeted two images of the first test firing of an integrated Raptor in SpaceX's McGregor test complex. On the same day Musk revealed that their target performance for Raptor was a vacuum specific impulse of 382 seconds, with a thrust of 3 MN (670,000 lbf) with a chamber pressure of 300 bar (30 MPa; 4,400 psi) and an expansion ratio of 150 for an altitude optimized version. When asked if the nozzle diameter for such version was 14 ft (4.3 m), he stated that it was pretty close to that dimension. He also disclosed that it used multi-stage turbopumps. On the 27th he clarified that 150 expansion ratio was for the development version, that the production vacuum version would have an expansion ratio of 200. Substantial additional technical details of the ITS propulsion were summarized in a technical article on the Raptor engine published the next week.
By September 2017, the 200 Bar sub-scale test engine, with a thrust of 1 meganewton (220,000 lbf) and "a new alloy to help its oxygen-rich turbopump resist oxidization, ... had completed 1200 seconds of firings across 42 tests."
While plans for Raptor flight testing have consistently been on the new-generation fiber-composite-material construction flight vehicles since 2016, the specific vehicle was not clarified until October 2017, when it was indicated that initial suborbital test flights would occur with a BFR spaceship. In November 2016, the first flight tests of the Raptor engine were projected to be on the very large 12-meter (39 ft)-diameter ITS launch vehicle, no earlier than the early 2020s. By July 2017, the plan had been modified to do flight testing on a much smaller launch vehicle and spacecraft, and the new system architecture had "evolved quite a bit" since the very large ITS launch vehicle design concept from 2016. A key driver of the 2017 architecture was to make the new system useful for substantial Earth-orbit and Cislunar launches so that the new system might pay for itself, in part, through economic spaceflight activities in the near-Earth space zone.
Elon Musk announced in September 2017 that the initial flight platform for any Raptor engine would be some part of the BFR launch vehicle. BFR is a 9 m (30 ft)-diameter launch vehicle. In October 2017, Musk clarified that "[initial flight testing will be with] a full-scale 9-meter-diameter ship doing short hops of a few hundred kilometers altitude and lateral distance ... [projected to be] 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."
Notably, Musk also announced that the new Raptor-powered BFR launch vehicle was planned to entirely replace both Falcon 9 and Falcon Heavy launch vehicles as well as the Dragon spacecraft in the existing operational SpaceX fleet in the early 2020s, initially aiming at the Earth-orbit market, but SpaceX is explicitly designing in substantial capability to the spacecraft vehicles to support long-duration spaceflight in the cislunar and Mars mission environment as well. SpaceX intends this approach to bring significant cost savings which will help the company justify the development expense of designing and building the new launch vehicle design. In addition to orbital spaceflight missions, BFR is being considered for the point-to-point Earth transportation market, with ~30–60 minute flights to nearly anywhere on the planet.
IAC 2016 proposed designsEdit
At the IAC meetings September 2016, Musk mentioned several Raptor engine designs that could be used on the ITS launch vehicle by late in the decade. In addition, a much smaller subscale engine had been built for test and validation of the new full-flow staged-combustion cycle engine. At that time, this first "subscale" Raptor development engine had been tested on a ground test stand for only one brief firing.
- "Raptor subscale development engine"
- In order to eliminate flow separation problems while being tested in Earth's atmosphere, the test nozzle expansion ratio was limited to only 150. The engine began testing in September 2016 on a ground test stand. Sources differ on the performance of this engine. In reporting during the two weeks following the Musk reveal on 27 September, NASASpaceFlight.com indicated that the development engine is only one-third the size of any of the three larger engine designs planned for the 2016-design flight vehicles, approximately 1,000 kN (220,000 lbf) thrust.
- Raptor 2016 with expansion ratio 40
- With an expansion ratio 40 nozzle, 42 of these engines were planned to power the 2016 high-level design of the ITS booster stage. 3,050 kN (690,000 lbf) of thrust at sea-level, and 3,285 kN (738,000 lbf) in vacuum. In addition, three gimbaled short-nozzle engines were to be used for maneuvering the 2016-design ITS launch vehicle second-stages; and these engines were to be used for retropropulsive landings on Mars (with mean atmospheric pressure on the Martian surface 600 Pa (0.0060 bar; 0.087 psi),), as well as, potentially, other Solar System objects.
- Raptor 2016 with expansion ratio 200
- Like the SpaceX Merlin engine, a vacuum version of the Raptor rocket engine design was shown which would target a specific impulse of 382s, using a larger nozzle giving an expansion ratio of 200. Six of these non-gimbaled engines were planned to provide primary propulsion for the 2016 designs of the Interplanetary Spaceship and the Earth-orbit ITS tanker. As designed, both of those vehicles were to play a short-term role as second stages on launches to Earth orbit, as well as provide high-Isp efficiency on transfer from geocentric to heliocentric orbit for transport to beyond-Earth-orbit celestial bodies. 3,500 kN (790,000 lbf) thrust at vacuum, the only conditions under which the six ER200 engines were expected to be fired.
At the IAC meetings of September 2017, Elon Musk announced that a smaller Raptor engine—with slightly over half as much thrust as the 2016 proposed designs—would be used on the BFR rocket than had been used on the ITS launch vehicle design unveiled a year earlier. Additionally, fewer engines would be used on each stage. BFR would have 31 Raptors on the first stage and 6 on the second stage, whereas the ITS launch vehicle design had 42 larger Raptor engines on the first stage and 9 of that same large size on the second stage. The engine design remains full-flow staged combustion cycle design using subcooled liquid-methane/liquid-oxygen propellant, just like the larger 2016 engine design. "Version 1" of the flight engine is designed to operate at 250 bars (25,000 kPa; 3,600 psi) of chamber pressure; but SpaceX expects to increase this to 300 bar (30,000 kPa; 3,000 N/cm2) in later iterations. The flight engine is designed for extreme reliability, aiming to support the airline-level of safety required by the point-to-point Earth transportation market.
- The sea-level model Raptor engine design, with a nozzle exit diameter of 1.3 m (4.3 ft), is expected to have 1,700 kilonewtons (380,000 lbf) thrust at sea-level with an Isp of 330 s increasing to an Isp of 356 s in the vacuum of space.
- The vacuum model Raptor, with a nozzle exit diameter of 2.4 m (7.9 ft), is expected to exert 1,900 kN (430,000 lbf) force with an Isp of 375 s.
In the BFR update given in September 2018, Musk showed video of a 71 second burn of a Raptor engine, and stated that "this is the Raptor engine that will power BFR, both the ship and the booster; it's the same engine. ... approximately a 200 tonnes-force (2,000 kN; 440,000 lbf) engine aiming for roughly 300 bars (30,000 kPa; 4,400 psi) chamber pressure. ... If you had it at a high expansion ration, has the potential to have a specific impulse of 380." The update also included a redesigned BFR upper stage with seven raptor engines instead of the six on the previous design.
The Raptor engine is powered by subcooled liquid methane and subcooled liquid oxygen using a more efficient staged combustion cycle, a departure from the simpler 'open cycle' gas generator system and lox/kerosene propellants that current Merlin engines use. The Space Shuttle Main Engines (SSME, with hydrolox propellant) also used a staged combustion process, as do several Russian rocket engines including the RD-180 and the very-high chamber pressure [25.74 MPa (3,733 psi)] RD-191. Stated design size for the Raptor engine varied widely during 2012–2017 as detailed design continued, from a high target of 8,200 kN (1,800,000 lbf) of vacuum thrust to a more recent, much lower target of 1,900 kN (430,000 lbf). In its 2017 iteration, the operational engine is expected to have a vacuum Isp of 375 seconds and a sea-level Isp of 300 seconds.
The Raptor engine is designed for the use of deep cryogenic methalox propellants—fluids cooled to near their freezing points, rather than nearer their boiling points which is more typical for cryogenic rocket engines. The use of subcooled propellants increases propellent density to allow more propellant mass in tanks; the engine performance is also improved with sub cooled propellents. Specific impulse is increased, and the risk of cavitation at inputs to the turbopumps is reduced due to the higher mass flow rate per unit power generated. Engine ignition for all Raptor engines, both on the pad and in the air, will be by spark ignition, which will eliminate the pyrophoric mixture of triethylaluminum-triethylborane (TEA-TEB) used for engine ignition on the Falcon 9 and Falcon Heavy.
Raptor has been explicitly designed to be able to deliver "long life ... and more benign turbine environments". Specifically, Raptor utilizes a full-flow staged combustion cycle, where 100 percent of the oxidizer—with a low-fuel ratio—will power the oxygen turbine pump, and 100 percent of the fuel—with a low-oxygen ratio—will power the methane turbine pump. Both streams—oxidizer and fuel—will be completely in the gas phase before they enter the combustion chamber. Prior to 2014, only two full-flow staged combustion rocket engines have ever progressed sufficiently to be tested on test stands: the Soviet RD-270 project in the 1960s and the Aerojet Rocketdyne Integrated Powerhead Demonstrator in the mid-2000s.
Additional characteristics of the full-flow design, projected to further increase performance or reliability include:
- eliminating the fuel-oxidizer turbine interseal, which is a potential point of failure in more traditional engine designs
- lower pressures are required through the pumping system, increasing life span and further reducing risk of catastrophic failure
- ability to increase the combustion chamber pressure, thereby either increasing overall performance, or "by using cooler gases, providing the same performance as a standard staged combustion engine but with much less stress on materials, thus significantly reducing material fatigue or [engine] weight".
The turbopump and many of the critical parts of the injectors for the initial engine development testing were, as of 2015, manufactured by using 3D printing, which increases the speed of development and iterative testing. Forty percent (by mass) of the 2016 1 MN (220,000 lbf) test stand engine was manufactured by 3D printing.
Comparison to other enginesEdit
|SpaceX Raptor vacuum
|1,900 (430,000)||375||Subcooled CH4/LOX||Full-flow staged combustion|
|SpaceX Raptor sea-level
|Blue Origin BE-4
|2,400 (550,000)||CH4/LOX||Staged combustion (oxidizer rich)|
|SpaceX Merlin 1D Vacuum||934 (210,000)||348||199||Subcooled RP-1/LOX||Gas generator|
|SpaceX Merlin 1D sea-level||914 (205,000)||311 |
||1,638 (368,000)||331||136.66||RP-1/LOX||Staged combustion (oxidizer rich)|
|Energomash RD-180||4,152 (933,000)||338||78.44||RP-1/LOX||Staged combustion (oxidizer rich)|
|Energomash RD-191||2,090 (470,000)||337.5||89|
|Energomash RD-275M||1,832 (412,000)||315.8||174.5||N2O4/UDMH||Staged combustion (oxidizer rich)|
(Space Shuttle Main Engine)
|2,280 (510,000)||453||73||LH2/LOX||Staged combustion (fuel rich)|
|Rocketdyne F-1 (Saturn V)||7,740 (1,740,000)||304||83||RP-1/LOX||Gas generator|
Initial development testing of Raptor methane engine components was done at the Stennis Space Center in Hancock County, Mississippi, where SpaceX added equipment to the existing infrastructure in order to support liquid methane engine testing. Initial testing was limited to components of the Raptor engine, since the 440 kN (100,000 lbf) test stands at the E-2 complex at Stennis were not large enough to test the full Raptor engine. The development Raptor engine discussed in the October 2013 time frame relative to Stennis testing was designed to generate more than 2,900 kN (661,000 lbf) vacuum thrust. A revised, higher-thrust, specification was discussed by the company in February 2014, but it was unclear whether that higher thrust was something that would be achieved with the initial development engines. Raptor engine component testing began in May 2014 at the E-2 test complex which SpaceX modified to support methane engine tests. The first items tested were single Raptor injector elements, various designs of high-volume gas injectors. The modifications to the test stands made by SpaceX are now a part of the Stennis test infrastructure and are available to other users of the test facility after the SpaceX facility lease was completed. SpaceX successfully completed a "round of main injector testing in late 2014" and a "full-power test of the oxygen preburner component" for Raptor by June 2015. Tests continued at least into September 2015.
By August 2016, SpaceX confirmed that a Raptor engine had been shipped to the testing site in McGregor for development tests, and the 1,000 kN (220,000 lbf) development Raptor did an initial 9-second firing test on 26 September 2016, the day before Musk's talk at the International Aeronautical Congress. The 2016 development engine had "an expansion ratio of just 150, the maximum possible within Earth’s atmosphere" to prevent flow separation problems.
By September 2017, the development Raptor engine—with 200 bars (20 MPa) chamber pressure—had undergone 1200 seconds of test fire testing in ground-test stands across 42 main engine tests, with the longest test being 100 seconds (which is limited by the capacity of the ground-test propellant tanks). As of September 2017[update], the first version of the flight engine is intended to operate at a chamber pressure of 250 bar, with the intent to raise it to 300 bar at a later time.
As of September 2016, the Raptor engine was slated to be used in, broadly, three spaceflight vehicles, which although capable of independent flight, also make up the two launch stages of an ITS launch vehicle stack. The first stage is always an Interplanetary booster while the second stage may be either an Interplanetary Spaceship (for beyond-Earth-orbit missions) or an ITS tanker (for on-orbit propellant transfer operations nearer to Earth).
The SpaceX 2016-design of the Interplanetary booster was announced with 42 sea-level optimized Raptors in the first stage of the ITS launch vehicle with a total of 128 MN (29,000,000 lbf) of thrust. The SpaceX Interplanetary Spaceship—which made up the second stage of the ICT launch vehicle on Earth launches was also an interplanetary spacecraft carrying cargo and passengers to beyond-Earth-orbit destinations after on-orbit refueling—was slated in the 2016 design to use six vacuum-optimized Raptors for primary propulsion plus three Raptors with sea-level nozzles for maneuvering.
The SpaceX 2017-design is a much smaller launch vehicle, 9 meters in diameter rather than 12 meters for the ITS launch vehicle, and is currently known by a codename BFR. The BFR booster will have 31 sea-level optimized Raptors with a total of 48 MN (11,000,000 lbf) of thrust for the initial version. The BFR spaceship and tanker will use four vacuum-optimized Raptors for primary propulsion plus three sea-level Raptors for maneuvering.
Following comments by Elon Musk in July 2017, the Raptor engine development program is ongoing.
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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.
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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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this project is strictly private industry development for commercial use
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The new Raptor upper stage engine is likely to be only the first engine in a series of lox/methane engines.
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our focus is the full Raptor size
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SpaceX is developing the Raptor as a reusable engine for a heavy-lift Mars vehicle, the first stage of which will feature 705 metric tons of thrust, making it 'slightly larger than the Apollo F-1 engine,' Tom Mueller, SpaceX vice president of propulsion development, said during a space propulsion conference last month in Cologne, Germany. The vacuum version is targeting 840 metric tons of thrust with 380 sec. of specific impulse. The company is testing subscale components using the E-2 test stand at NASA's Stennis Space Center in Mississippi, says Stennis spokeswoman Rebecca Strecker. ... Mueller said many people ask why the company switch to methane for its Mars rocket. With reusability in mind, SpaceX's cost studies revealed that 'by far the most cost-effective propellant to use is methane,' he said, which would be easier than hydrogen to manufacture on Mars.
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After completing successful test series in 2014 and 2015 on components for the new Raptor rocket engine being developed by SpaceX, there also is hope for additional test agreements with the company.
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[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.
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the updated version of the Mars architecture: Because it has evolved quite a bit since that last talk. ... The key thing that I figured out is how do you pay for it? If we downsize the Mars vehicle, make it capable of doing Earth-orbit activity as well as Mars activity, maybe we can pay for it by using it for Earth-orbit activity. That is one of the key elements in the new architecture. It is similar to what was shown at IAC, but a little bit smaller. Still big, but this one has a shot at being real on the economic front.
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