Raptor (rocket engine)
|Country of origin||United States|
|Application||multistage and deep-space propulsion|
|Propellant||LOX / liquid methane|
|Cycle||Full-flow staged combustion|
|Thrust (vac.)||8,200 kN (840 tonnes-force)|
|Thrust (SL)||6,900 kN (705 tonnes-force)|
|Isp (vac.)||380 s|
|Isp (SL)||321 s|
|Mars Colonial Transporter, MCT launch vehicle|
Raptor is the first member of a family of methane-fueled rocket engines under development by SpaceX. It is specifically intended to power high performance lower and upper stages for SpaceX super-heavy launch vehicles. The engine will be powered by methane and liquid oxygen (LOX), rather than the RP-1 kerosene and LOX used in all previous Falcon 9 upper stages, which use a Merlin vacuum engine. Earlier concepts for Raptor would have used liquid hydrogen (LH2) fuel rather than methane.
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."
Raptor was first publicly discussed by SpaceX's Max Vozoff at the AIAA 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 LH2/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 the specific fuel to be used. 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.
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. He further indicated that the engine concept that had been codenamed Raptor would now become a methane-based design, and that methane would be the fuel of choice for SpaceX' plans for Mars colonization.
When first mentioned by SpaceX in 2009, the term "Raptor" was applied exclusively to an upper-stage engine concept—and 2012 pronouncements indicate that it still was 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 10-meter-diameter core of the Mars Colonial Transporter. Each booster core will utilize nine Raptor engines, similar to the use of nine Merlin 1s on each Falcon 9 booster core.
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.
Public information released in November 2012 indicated that SpaceX may have a family of Raptor-designated rocket engines in mind; this was confirmed by SpaceX in October 2013. 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.
In October 2013, SpaceX announced that they would be performing methane engine tests of the Raptor engine at the 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 engine testing. 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. 
October 2013 was the first time SpaceX disclosed the design thrust of the Raptor engine—2,940 kN (661,000 lbf)—although early in 2014 they announced a Raptor engine with greater thrust.
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 (705 tonnes-force) of sea-level thrust, 8,200 kN (840 tonnes-force) of vacuum thrust, and a specific impulse of 380 s.
The Raptor engine will be powered by liquid methane and liquid oxygen using a more efficient staged combustion cycle, a departure from the 'open cycle' gas generator system and lox/kerosene propellants that current Merlin engines use. The Space Shuttle Main Engines (SSME) also used a staged combustion process, as do several Russian rocket engines.
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 demonstration project in the mid-2000s.
Raptor is being designed to produce 8,200 kN (1,800,000 lbf) of vacuum thrust—6,900 kN (1,600,000 lbf) thrust at lift-off—with a vacuum Isp of 380 seconds and a sea-level Isp of 321 seconds. Final thrust and Isp specifications for the as-built engines are expected to be refined as SpaceX moves the engine through the multi-year development cycle.
Additional characteristics of the full-flow design that are 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."
Comparison to other engine designs
|Engine name||Vacuum thrust
|Vacuum specific impulse
|SpaceX Raptor (targeted)||8,200 (1,800,000)||380||Methane/LOX full-flow staged combustion|
|Blue Origin BE-4||2,400 (550,000)||Methane/LOX oxygen-rich staged combustion|
|SpaceX Merlin 1D||801 (180,000)||309||150||RP-1/LOX gas generator|
|SpaceX Merlin 1C||610 (140,000)||304||96||RP-1/LOX gas generator|
|RD-180||4,150 (930,000)||338||78||RP-1/LOX staged combustion|
|Space Shuttle Main Engine||2,280 (510,000)||453||73||LH/LOX staged combustion|
|Rocketdyne F-1 (Saturn V)||7,740 (1,740,000)||304||83||RP-1/LOX gas generator|
Initial testing of Raptor methane engine components will be done at the Stennis Space Center in Hancock County, Mississippi, where SpaceX has added equipment to the existing infrastructure in order to support liquid methane engine testing. Initial testing at Stennis will be limited to components of the Raptor engine, since the 440 kN (100,000 lbf) test stands at the E-2 complex at Stennis are 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. 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.
Raptor engine component testing is expected to begin tests prior to the end of May 2014, at the E-2 test complex which SpaceX modified to support methane engine tests. The first item to be tested will be a single Raptor injector element. In August 2014, SpaceX clarified that the initial components being tested at Stennis are the high-volume gas injectors.
The modifications 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.
SpaceX will need to construct a new engine test stand or reconstruct an existing one to handle the larger thrust of the full Raptor engine. The B-2 test stand at Stennis Space Center is already being upgraded to accommodate testing of NASA's 7,440 kN SLS core stage.
- Advanced Common Evolved Stage
- Falcon Heavy
- Falcon series of LOX/RP-1 launch vehicles from SpaceX
- SpaceX rocket engine family
- Butler, Amy; Svitak, Amy. "AR1 vs. Raptor: New rocket program will likely pit kerosene against methane" (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."
- Todd, David (2012-11-20). "Musk goes for methane-burning reusable rockets as step to colonise Mars". FlightGlobal Hyperbola. Retrieved 2012-11-22. ""We are going to do methane." Musk announced as he described his future plans for reusable launch vehicles including those designed to take astronauts to Mars within 15 years, "The energy cost of methane is the lowest and it has a slight Isp (Specific Impulse) advantage over Kerosene," said Musk adding, "And it does not have the pain in the ass factor that hydrogen has"."
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