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SpaceX Raptor

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This article is about the spacecraft engine for the Mars launch vehicle. For the upper stage engine for Falcon 9 and Falcon Heavy, see Raptor prototype upper-stage engine.

Raptor
First test firing of a Raptor engine on September 25, 2016 in McGregor, Texas.
Country of originUnited States
ManufacturerSpaceX
Applicationmultistage and deep-space propulsion
StatusIn development
Liquid-fuel engine
PropellantLOX / liquid methane
Mixture ratio3.8
CycleFull-flow staged combustion
Pumps2 × multi-stage
Configuration
Chamber1
Nozzle ratio40[1]
Performance
Thrust, vacuum3,285 kN (738,000 lbf)[1]
Thrust, sea-level3,050 kN (690,000 lbf)[1]
Chamber pressure30 MPa (4,400 psi)[1]
Specific impulse, vacuum361 s[1]
Specific impulse, sea-level334 s[1]
Used in
Interplanetary Transport System, ITS Launch Vehicle
Raptor Vacuum
First test firing of the Raptor engine on September 25, 2016 in McGregor, Texas.
Country of originUnited States
ManufacturerSpaceX
Applicationmultistage and deep-space propulsion
StatusDevelopment
Liquid-fuel engine
PropellantLOX / liquid methane
Mixture ratio3.8
CycleFull-flow staged combustion
Pumps2 × multi-stage
Configuration
Chamber1
Nozzle ratio200
Performance
Thrust3,500 kN (790,000 lbf)[1]
Chamber pressure30 MPa (4,400 psi)[1]
Specific impulse382 s[1]
Dimensions
Diameter~4 m (13 ft)
Used in
Interplanetary Transport System, ITS Launch Vehicle

Raptor is the first member of a family of cryogenic[2] methane-fueled rocket engines under development by SpaceX. It is specifically intended to power high-performance lower and upper stages for the Interplanetary Transport System. The engine will be powered by liquid methane[3] and liquid oxygen (LOX),[4] rather than the RP-1 kerosene and LOX used in all previous Falcon 9 rockets, which use Merlin 1C & D engines. Earlier concepts for Raptor would have used liquid hydrogen (LH2) fuel rather than methane.[5]

The Raptor engine will have several times the thrust of the Merlin 1D vacuum engine that powers the second stage of the current Falcon 9, the Falcon 9 Full Thrust. The broader Raptor concept "is 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".[6] According to Elon Musk, this design will be able to achieve full reusability (all rocket stages) and, as a result, "a two order of magnitude reduction in the cost of spaceflight".[2]

The engine development from 2009 to 2015 was funded exclusively by private investment by SpaceX, and not as a result of any funding from the US government.[7][8] 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 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.[9]

In August 2016, a development Raptor engine was shipped to their McGregor testing facility in Texas,[10] where it is undergoing development testing.[11]

History

Raptor was first publicly discussed by SpaceX's Max Vozoff at the American Institute of Aeronautics and Astronautics Commercial Crew/Cargo symposium in 2009.[12] As of April 2011, SpaceX had a small number of staff working on the Raptor upper-stage engine, then still a LH2/LOX concept, at a low level of priority.[13] Further mention of the development program occurred in 2011.[14] In March 2012, news accounts asserted that the Raptor upper-stage engine development program was underway, but that details were not being publicly released.[15]

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 the specific fuel to be used.[16] They indicated that details would be forthcoming in "one to three years" and that the large engine was intended for a new SpaceX rocket, using multiple of these large engines, that would notionally launch payload masses of the order of 150 to 200 tonnes (150,000 to 200,000 kg) to low Earth orbit, exceeding the payload mass capability of the NASA Space Launch System.[16]

This was cleared up the next month when, in November 2012, CEO Elon Musk announced a new direction for the propulsion division of SpaceX: developing methane-fueled rocket engines.[4] He further indicated that the engine concept that had been codenamed Raptor would now become a methane-based design,[4] and that methane would be the fuel of choice for SpaceX's plans for Mars colonization.[17]

Potential sources and sinks of methane (CH4) on Mars.

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.[18] In-situ resource production on Mars has been examined by NASA and found to be viable for oxygen, water, and methane production.[19] 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.[20]

When first mentioned by SpaceX in 2009, the term "Raptor" was applied exclusively to an upper-stage engine concept[12]—and 2012 pronouncements indicate that it still was a concept for an upper stage engine[21]—but in early 2014 SpaceX confirmed that Raptor would be used both on a new second stage, as well as for the large (nominally, 10-meter-diameter) core of the Interplanetary Transport System. Each booster core will utilize nine Raptor engines, similar to the use of nine Merlin 1s on each Falcon 9 booster core.[17]

Early 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.[17]

Public information released in November 2012 indicated that SpaceX may have a family of Raptor-designated rocket engines in mind;[22] this was confirmed by SpaceX in October 2013.[6] However, SpaceX COO Gwynne Shotwell clarified in March 2014 that the focus of the new engine development program is exclusively on the full-size Raptor engine; smaller subscale methalox engines are not planned on the development path to the very large Raptor engine.[23]

In October 2013, SpaceX announced that they would be performing methane engine tests of the Raptor engine at the John C. Stennis Space Center in Hancock County, Mississippi,[24][25] and that SpaceX would add equipment to the existing test stand infrastructure in order to support liquid methane engine testing.[26] In April 2014, SpaceX completed the requisite upgrades and maintenance to the Stennis test stand to prepare for testing of Raptor components, and expects to begin tests at the facility prior to the end of May 2014.[27]

October 2013 was the first time SpaceX disclosed a nominal design thrust of the Raptor engine—2,940 kN (661,000 lbf)[6]—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).[17][28] 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.[29] Earlier information had estimated the design Isp under vacuum conditions as only 363 s.[17] 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.[30][31][32]

In January 2015, Elon Musk made a statement that the thrust they were currently targeting was around 2,300 kN (510,000 lbf), much lower than older comments mentioned. This brought into question much of the speculation surrounding a 9-engine booster, as he stated "there will be a lot of [engines]"[33] 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.[34]

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.[8] SpaceX completed its planned testing at NASA Stennis in 2014 and 2015, although as of February 2016, the Stennis center was hopeful of establishing additional test agreements.[35]

In January 2016, the US Air Force awarded a US$33.6 million development contract to SpaceX 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, and engine performance testing will be done at NASA's John C. Stennis Space Center in Mississippi.[9][36]

By August 2016, the first integrated Raptor rocket engine, manufactured at the SpaceX Hawthorne facility in California, had shipped to the McGregor rocket engine test facility in Texas for development testing.[10]

On September 26th, 2016, Elon Musk tweeted two images of the first test firing of an integrated Raptor in SpaceX's McGreggor test complex.[37][38] 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 30 MPa (4,400 psi) and an expansion ratio of 150 for the altitude optimized version.[39][40][41] 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.[42][43] On the 27th he clarified that 150 expansion ratio was for the development version, that the production vacuum version would have have an expansion ratio of 200.[44]

Design

File:Raptor Engine Render.jpg
Raptor engine CAD render as of September 2016.

The Raptor engine will be powered by liquid methane and liquid oxygen using a more efficient staged combustion cycle,[21] a departure from the 'open cycle' gas generator system and lox/kerosene propellants that current Merlin engines use.[21] The Space Shuttle Main Engines (SSME) also used a staged combustion process,[45] as do several Russian rocket engines (such as the RD-180).[21]

Raptor is being explicitly designed to be able to deliver "long life ... and more benign turbine environments".[7]

More specifically, Raptor will utilize 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.[17]

Full-flow staged combustion rocket cycle

The Raptor engine is designed to work using 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.[46]

The turbopump and many of the critical parts of the injectors will be manufactured by using 3D printing, which also increases the speed of development and iterative testing.[46]

Stated design size for the Raptor engine has varied widely as design continues, from a high target of 8,200 kN (1,800,000 lbf) of vacuum thrust[47] to a more recent, much lower target of 3,500 kN (790,000 lbf). The engine targets a vacuum Isp of 382 seconds[48] and a sea-level Isp of 334 seconds.[48] and an expansion ratio of 40.[48]

Additional characteristics of the full-flow design that are projected to further increase performance or reliability include:[17]

  • 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".[17]

Vacuum version

Like the SpaceX Merlin engine, a vacuum version of the Raptor rocket engine is planned which would target a specific impulse of 382s,[48] using a larger nozzle to allow more expansion by exhaust gases. The expansion ratio will be 200.[48]

Comparison to other engine designs

Main article: Comparison of orbital rocket engines
Engine name Vacuum thrust
[kilonewtons (lbf)] 		Vacuum specific impulse
[seconds] 		Thrust-to-
weight ratio 		Propellant Cycle
SpaceX Raptor Vacuum Nozzle 3,500 (790,000)*[1] 382[1] Methane/LOX full-flow staged combustion
SpaceX Raptor Sea-Level Nozzle 3,050 (690,000)*[1] 361[1]
Blue Origin BE-4 2,400 (550,000)[49] Methane/LOX staged combustion (oxidizer rich)
SpaceX Merlin 1D Vacuum 934 (210,000)[50] 348[50] 180[51] RP-1/LOX gas generator
SpaceX Merlin 1D Sea-Level 914 (205,000) 311 [52]
NK-33 1,638 (368,000)[53] 331[53] 136.66[53] RP-1/LOX staged combustion (oxidizer rich)
RD-180 4,152 (933,000)[54] 338[54] 78.44[54] RP-1/LOX staged combustion (oxidizer rich)
RD-191 2,090 (470,000)[55] 337.5[55] 89[55]
RD-270 6,710 (1,510,000) 322 125.77 N2O4/UDMH full-flow staged combustion
RD-276 1,832 (412,000) 315.8 174.5 N2O4/UDMH staged combustion (oxidizer rich)
Space Shuttle Main Engine 2,280 (510,000) 453[56] 73[57] LH/LOX staged combustion (fuel rich)
Rocketdyne F-1 (Saturn V) 7,740 (1,740,000) 304[58] 83 RP-1/LOX gas generator
TR-107 4,900 (1,100,000)[59] [59] [59] RP-1/LOX staged combustion (oxidizer rich)

Engine testing

Testing of the Raptor's oxygen preburner at Stennis in 2015

Initial development testing[8] 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.[6][26] Initial testing at Stennis has been 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 2,940 kN (661,000 lbf) vacuum thrust.[6] A revised, higher-thrust, specification was discussed by the company in February 2014; but it is unclear whether that higher thrust is something that would be achieved with the initial development engines.[17]

By April 2014, Raptor engine component testing was expected to initiate testing the next month,[27] at the E-2 test complex which SpaceX modified to support methane engine tests.[6] The first items tested were single Raptor injector elements,[60] various designs of high-volume gas injectors.[61]

The modifications to the test stands made by SpaceX are now a part of the Stennis test infrastructure and will be available to other users of the test facility after the SpaceX facility lease is completed.[6]

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 are continuing on Raptor preburner components as of September 2015.[8]

SpaceX is constructing a new engine test stand at their site of McGregor in central Texas that can handle the larger thrust of the full Raptor engine.[6] The B-2 test stand at Stennis Space Center is already being upgraded to accommodate testing of NASA's 7,440 kN (1,670,000 lbf) SLS core stage.[62]

In August 2016, SpaceX confirmed a Raptor engine has been shipped to the testing site in McGregor Texas for developmental tests.[63]

On September 25, 2016 Elon Musk tweeted that the first test of the engine had been completed.[38] On September 27, he clarified that the development engine would have an expansion ratio of 150, which was the limit to avoid problems with flow separation on Earth's atmosphere.[44]

Applications

As of September 2016, the Raptor engine is 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 Interplanetary booster will use 42 sea-level optimized Raptors in the first stage of the ITS launch vehicle. The SpaceX Interplanetary Spaceship—which makes up the second stage of the ICT launch vehicle on Earth launches is also an interplanetary spacecraft carrying cargo and passengers to beyond-Earth-orbit destinations after on-orbit refueling—will use six vacuum-optimized Raptors for primary propulsion plus three Raptors with sea-level nozzles for manuevering.[1]

See also

References

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  3. ^ http://spaceref.com/news/viewsr.html?pid=47400
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  22. ^ Todd, David (20 November 2012). "Musk goes for methane-burning reusable rockets as step to colonise Mars". FlightGlobal Hyperbola. Retrieved 22 November 2012. The new Raptor upper stage engine is likely to be only the first engine in a series of lox/methane engines.
  23. ^ Gwynne Shotwell (21 March 2014). Broadcast 2212: Special Edition, interview with Gwynne Shotwell (audio file). The Space Show. Event occurs at 21:25–22:10. 2212. Archived from the original (mp3) on 22 March 2014. Retrieved 22 March 2014. our focus is the full Raptor size
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  29. ^ Butler, Amy; Svitak, Amy. "AR1 vs. Raptor: New rocket program will likely pit kerosene against methane". No. 2014-06-09. Aviation Week & Space Technology. 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. {{cite news}}: |access-date= requires |url= (help)
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  31. ^ House testimony bio, HHRG-114-AS29, June 2015]
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  34. ^ How (and Why) SpaceX Will Colonize Mars, accessed 19 August 2015. Musk: "The critical elements of the solution are rocket reusability and low cost propellant (CH4 and O2 at an O/F ratio of ~3.8). And, of course, making the return propellant on Mars, which has a handy CO2 atmosphere and lots of H2O frozen in the soil."
  35. ^ "Stennis set for busy 2016 test schedule" (PDF). Lagniappe. NASA-John C. Stennis Space Center. February 2016. p. 3. Retrieved 2 March 2016. 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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  42. ^ Musk, Elon (26 September 2016). "based on your other specs, is that like a ~14 foot diameter nozzle? Elon Musk: pretty close". Twitter.com. Archived from the original on 26 September 2016. Retrieved 26 September 2016.
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  44. ^ a b Musk, Elon (26 September 2016). "Meant to say 200 AR for production vac engine. Dev will be up to 150. Beyond that, too much flow separation in Earth atmos". Twitter.com. Archived from the original on 26 September 2016. Retrieved 26 September 2016. {{cite web}}: |archive-date= / |archive-url= timestamp mismatch; 27 September 2016 suggested (help)
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External links

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