Test firing of the Merlin 1D at SpaceX’s McGregor test stand
|Country of origin||United States|
|Associated L/V||Falcon 9, Falcon Heavy|
|Propellant||LOX / RP-1|
|Thrust (vac.)||981 kN (221,000 lbf)|
|Thrust (SL)||854 kN (192,000 lbf)|
|Thrust-to-weight ratio||179.8 [needs update]|
|Chamber pressure||9.7 MPa (1,410 psi)|
|Isp (vac.)||311 s (3.05 km/s)|
|Isp (SL)||282 s (2.77 km/s)|
|Diameter||1.25 m (4.1 ft)|
|Dry weight||470 kg (1,030 lb)|
The SpaceX Merlin is a family of rocket engines developed by SpaceX for use on its Falcon 1, Falcon 9 and Falcon Heavy launch vehicles. Merlin engines use RP-1 and liquid oxygen as rocket propellants in a gas-generator power cycle. The Merlin engine was originally designed for sea recovery and reuse.
Propellants are fed via a single shaft, dual impeller turbopump. The turbopump also provides high-pressure fluid for the hydraulic actuators, which then recycles into the low-pressure inlet. This eliminates the need for a separate hydraulic drive system and means that thrust vectoring control failure by running out of hydraulic fluid is not possible.
The initial version, the Merlin 1A, used an inexpensive, expendable, ablatively cooled carbon-fiber-reinforced polymer composite nozzle, and produced 340 kN (76,000 lbf) of thrust. The Merlin 1A flew only twice: First on March 24, 2006, when it caught fire and failed due to a fuel leak shortly after launch, and the second time on March 21, 2007, when it performed successfully. Both times the Merlin 1A was mounted on a Falcon 1 first stage.
The SpaceX turbopump was an entirely new, clean sheet design contracted to Barber-Nichols, Inc. in 2002 who performed all design, engineering analysis, and construction; the company had previously worked on turbopumps for the RS-88 (Bantam) and NASA Fastrac engine programs. The Merlin 1A turbopump used a unique friction-welded main shaft, with Inconel 718 ends and an integral aluminum RP-1 impeller in the middle. The turbopump housing was constructed using investment castings, with Inconel at the turbine end, aluminum in the center, and 300-series stainless steel at the LOX end. The turbine was a partial-admission (i.e., working fluid is only admitted through part of the rotation of the turbine; an arc not the whole circumference) impulse design and turned at up to 20,000 rpm, with a total weight of 68 kg (150 lb).
The Merlin 1B rocket engine was an upgraded version of the Merlin 1A engine. The turbopump upgrades were handled by Barber-Nichols, Inc. for SpaceX. It was intended for Falcon 1 launch vehicles, capable of producing 380 kN (85,000 lbf) of thrust at sea level, and 420 kN (95,000 lbf) in vacuum, and performing with a specific impulse of 261 s (2.56 km/s) at sea level and 303 s (2.97 km/s) in vacuum. The Merlin 1B was enhanced over the 1A with a turbine upgrade, increasing power output from 1,500 kW (2,000 hp) to 1,900 kW (2,500 hp). The turbine upgrade was accomplished by adding additional nozzles, turning the previously partial-admission design to full admission. Slightly enlarged impellers for both RP-1 and LOX were part of the upgrade. This model turned at a faster 22,000 rpm and developed higher discharge pressures. Turbopump weight was unchanged at 68 kg (150 lb) Another notable change over the 1A was the move to TEA–TEB (pyrophoric) ignition over torch ignition.
Initial use of the Merlin 1B was to be on the Falcon 9 launch vehicle, on whose first stage there would have been a cluster of nine of these engines. Due to experience from the Falcon 1's first flight, SpaceX moved its Merlin development to the Merlin 1C, which is regeneratively cooled. Therefore, the Merlin 1B was never used on a launch vehicle.
Merlin 1C under construction at SpaceX
|Country of origin||United States|
|Application||Main stage engine, Upper stage engine|
|Associated L/V||Falcon 9|
|Propellant||LOX / RP-1 (rocket grade kerosene)|
|Thrust (vac.)||480 kN (110,000 lbf)|
|Thrust (SL)||420 kN (94,000 lbf)|
|Chamber pressure||6.77 MPa (982 psi)|
|Isp (vac.)||304.8 s (3.0 km/s)|
|Isp (SL)||275 s (2.6 km/s)|
|Length||2,920 mm (115 in)|
|Dry weight||630 kilograms (1,380 lb)|
Three versions of the Merlin 1C engine were produced. The Merlin engine for Falcon 1 had a movable turbopump exhaust assembly which was used to provide roll control by vectoring the exhaust. The Merlin 1C engine for the Falcon 9 first stage is nearly identical to the variant used for the Falcon 1, although the turbopump exhaust assembly is not movable. Finally, a Merlin 1C vacuum variant is used on the Falcon 9 second stage. This engine differs from the Falcon 9 first stage variant in that it uses a larger exhaust nozzle optimized for vacuum operation and can be throttled between 60 and 100 percent.
The Merlin 1C uses a regeneratively cooled nozzle and combustion chamber. The turbopump used is a Merlin 1B model with only slight alterations. It was fired with a full mission duty firing of 170 seconds in November 2007, first flew on a mission in August 2008, powered the "first privately-developed liquid-fueled rocket to successfully reach orbit", Falcon 1 Flight 4, in September 2008, and powered the Falcon 9 on its maiden flight in June 2010.
As configured for use on Falcon 1 vehicles, the Merlin 1C had a sea level thrust of 350 kN (78,000 lbf), a vacuum thrust of 400 kN (90,000 lbf) and a vacuum specific impulse of 304 s (2.98 km/s). In this configuration, the engine consumed 140 kg (300 lb) of propellant per second. Tests have been conducted with a single Merlin 1C engine successfully running a total of 27 minutes (counting together the duration of the various tests), which equals ten complete Falcon 1 flights. The Merlin 1C chamber and nozzle are cooled regeneratively by 45 kilograms (100 lb) per second of kerosene flow and are able to absorb 10 megawatts (13,000 hp) of thermal heat energy.
A Merlin 1C was first used as part of the unsuccessful third attempt to launch a Falcon 1. In discussing the failure, Elon Musk noted, "The flight of our first stage, with the new Merlin 1C engine that will be used in Falcon 9, was picture perfect." The Merlin 1C was used in the successful fourth flight of Falcon 1 on September 28, 2008.
On October 7, 2012, a Merlin 1C (Engine No. 1) of the CRS-1 mission experienced an anomaly at T+00:01:20 which appears on CRS-1 launch video as a flash. The failure occurred just as the vehicle achieved max-Q (maximum aerodynamic pressure). SpaceX's internal review found that the engine was shut down after a sudden pressure loss and that only the aerodynamic shell was destroyed, generating the debris seen in the video; the engine did not explode, as SpaceX ground control continued to receive data from it throughout the flight. The primary mission was unaffected by the anomaly due to the nominal operation of the remaining eight engines and an onboard readjustment of the flight trajectory, but the secondary mission payload failed to reach its target orbit due to safety protocols in place to prevent collisions with the ISS. These protocols prevented a second firing of the upper stage for the secondary payload.
SpaceX was planning to develop a 560 kN (130,000 lbf) version of Merlin 1C to be used in Falcon 9 Block II and Falcon 1E boosters. This engine and these booster models were dropped in favor of the more advanced Merlin 1D engine and longer Falcon 9 v1.1 booster.
Merlin Vacuum (1C)
On March 10, 2009, a SpaceX press release announced successful testing of the Merlin Vacuum engine. A variant of the 1C engine, Merlin Vacuum features a larger exhaust section and a significantly larger expansion nozzle to maximize the engine's efficiency in the vacuum of space. Its combustion chamber is regeneratively cooled, while the 2.7 metres (9 ft)-long niobium alloy expansion nozzle is radiatively cooled. The engine delivers a vacuum thrust of 411 kN (92,500 lbf) and a vacuum specific impulse of 342 s (3.35 km/s). The first production Merlin Vacuum engine underwent a full duration orbital insertion firing (329 seconds) of the integrated Falcon 9 second stage on January 2, 2010. It was flown on the second stage for the inaugural Falcon 9 flight on June 4, 2010. At full power and as of 10 March 2009, the Merlin Vacuum engine operates with the greatest efficiency of an American-made hydrocarbon-fueled rocket engine.
An unplanned test of a modified Merlin Vacuum engine was made in December 2010. Shortly before the scheduled second flight of the Falcon 9, two cracks were discovered in the 2.7 metres (9 ft)-long niobium-alloy-sheet nozzle of the Merlin Vacuum engine. The engineering solution was to cut off the lower 1.2 metres (4 ft) of the nozzle and launch two days later, as the extra performance that would have been gained from the longer nozzle was not necessary to meet the objectives of the mission. The modified engine successfully placed the second-stage into an orbit of 11,000 kilometres (6,800 mi) altitude.
The Merlin 1D engine was developed by SpaceX between 2011 and 2012, with first flight in 2013. The design goals for the new engine included increased reliability, improved performance, and improved manufacturability. In 2011, performance goals for the engine were a vacuum thrust of 690 kN (155,000 lbf), a vacuum specific impulse (Isp) of 310 s (3.0 km/s), an expansion ratio of 16 (as opposed to the previous 14.5 of the Merlin 1C) and chamber pressure in the "sweet spot" of 9.7 MPa (1,410 psi). Merlin 1D was originally designed to throttle between 100% and 70% max thrust, however further refinements since 2013 now allow the engine to throttle to 40%.
The basic Merlin fuel/oxidizer mixture ratio is controlled by the sizing of the propellant supply tubes to each engine, with only a small amount of the total flow trimmed out by a "servo-motor-controlled butterfly valve" to provide fine control of the mixture ratio.
On November 24, 2013, Elon Musk stated that the engine was actually operating at 85% of its potential, and they anticipated to be able to increase the sea level thrust to about 730 kN (165,000 lbf) and a thrust-to-weight ratio of 180. This version of the Merlin 1D was used on Falcon 9 Full Thrust and first flew on Flight 20.
In May 2016, SpaceX announced plans to further upgrade the Merlin 1D by increasing vacuum thrust to 914 kN (205,000 lbf) and sea-level thrust to 845 kN (190,000 lbf); according to SpaceX, the additional thrust will increase the Falcon 9 LEO payload capability to about 22 metric tons on a fully expendable mission. SpaceX also noted that unlike the previous Full Thrust iteration of the Falcon 9 vehicle, the increase in performance is solely due to upgraded engines and no other significant changes to the vehicle are publicly planned.
In May 2018, ahead of the first flight of Falcon 9 Block 5, SpaceX announced that the 190,000 lbf (850 kN) goal had been achieved. The Merlin 1D is now close to the sea level thrust of the retired Rocketdyne H-1 / RS-27 engines used on Saturn I, Saturn IB, and Delta II.
Merlin 1D Vacuum
A vacuum version of the Merlin 1D engine was developed for the Falcon 9 v1.1 and the Falcon Heavy second stage. As of 2019, the thrust of the Merlin 1D Vacuum is 934 kN (210,000 lbf) with a specific impulse of 348 seconds, the highest specific impulse ever for a U.S. hydrocarbon rocket engine. The increase is due to the greater expansion ratio afforded by operating in a vacuum, now 165:1 using an updated nozzle extension.
The engine can throttle down to 39% of its maximum thrust, or 360 kN (81,000 lbf).
SpaceX uses a triple-redundant design in the Merlin engine computers. The system uses three computers in each processing unit, each constantly checking on the others, to instantiate a fault-tolerant design. One processing unit is part of each of the ten Merlin engines (nine on the first stage, one on the second stage) used on the Falcon 9 launch vehicle.
The LOX/RP-1 turbopump on each Merlin engine is powered by a fuel-rich open-cycle gas generator similar to that used in the Apollo-era Rocketdyne F-1 engine. During tests of that engine (ca. 1966), Rocketdyne showed that open-cycle RP-1 gas generators of this type yield 20 - 200 pounds of class-1 carcinogens, such as benzene and butadiene, per ton of RP-1 fuel. Note that by the current date, the thermal-cracking/condensation-polymerization chemistry of fuel-rich aliphatic hydrocarbon combustion has been well-understood for decades. Due to their carcinogenicity, these combustion products are now legally regulated within the US, providing community and worker health protections which did not exist during the Apollo era. During free-flight of the Falcon launch vehicle in the lower troposphere, the extremely hot main-engine exhaust and substantial partial pressure of atmospheric oxygen are observed to ignite and burn off the gas generator exhaust. However, during the test-stand and launch-stand (pre-lift-off) water deluges, as well as in-flight at altitudes above the lower troposphere, this post-combustion is extinguished, and these chemicals are released to the environment. SpaceX Environmental Assessments have provided no data on this important chemistry.
As of August 2011[update], SpaceX was producing Merlin engines at the rate of eight per month, planning eventually to raise production to about 33 engines per month (or 400 per year). By September 2013, SpaceX total manufacturing space had increased to nearly 93,000 square meters (1,000,000 sq ft) and the factory had been configured to achieve a maximum production rate of up to 40 rocket cores per year, enough to use the 400 annual engines envisioned by the earlier engine plan. By October 2014, SpaceX announced it had manufactured the 100th Merlin 1D engine and that engines were now being produced at a rate of 4 per week, soon to be increased to 5.
By June 2015, SpaceX was producing Merlin engines at the rate of four Merlin 1D engines per week, with a total production capacity in the factory of a maximum of five per week.
In February 2016, SpaceX indicated that the company will need to build hundreds of engines a year in order to support a Falcon 9/Falcon Heavy build rate of 30 rocket cores per year by the end of 2016.
- SpaceX Draco – SpaceX RCS thruster.
- SpaceX Kestrel – SpaceX small upper stage engine for Falcon 1.
- SpaceX Raptor – SpaceX methane/LOX engine for the Starship
- Comparison of orbital rocket engines
- Rocket engine
- Pintle injector
- TR-106 – Low Cost Pintle Engine (LCPE) using LOX/LH2 developed by TRW in 2000.
- TR-107 – RP-1 engine developed under SLI for future reusable launch vehicles.
- RS-27A – RP-1 engine used in the US Delta II launcher; Saturn 1B H-1 heritage.
- Rocketdyne F-1 – LOX/RP-1 main engine of the Saturn V moon rocket.
- "Falcon User's Guide January 2019" (PDF). Retrieved May 23, 2019.
- Mueller, Thomas (June 8, 2015). "Is SpaceX's Merlin 1D's thrust-to-weight ratio of 150+ believable?". Retrieved July 9, 2015.
The Merlin 1D weighs 1030 pounds, including the hydraulic steering (TVC) actuators. It makes 162,500 pounds of thrust in vacuum. that is nearly 158 thrust/weight. The new full thrust variant weighs the same and makes about 185,500 lbs force in vacuum.
- "SpaceX Unveils Plans To Be World's Top Rocket Maker". AviationWeek. August 11, 2011. Archived from the original on June 21, 2015. Retrieved June 28, 2014.
- "Merlin section of Falcon 9 page". SpaceX. Archived from the original on July 15, 2013. Retrieved October 16, 2012.CS1 maint: unfit url (link)
- Berger, Brian (July 19, 2006). "Falcon 1 Failure Traced to a Busted Nut". Space.com.
- "Findings of the Falcon return to flight board". SpaceX.com. July 25, 2006. Archived from the original on March 3, 2013.
- "Demo Flight 2 Flight Review Update" (PDF). SpaceX. June 15, 2007. Archived from the original (PDF) on March 6, 2012.
- Whitesides, Loretta Hidalgo (November 12, 2007). "SpaceX Completes Development of Rocket Engine for Falcon 1 and 9". Wired Science. Retrieved February 28, 2008.
- Gaskill, Braddock (August 5, 2006). "SpaceX has magical goals for Falcon 9". Nasa Spaceflight. Retrieved February 28, 2008.
- "Merlin LOX/RP-1 Turbopump". Barber Nichols. Retrieved May 28, 2018.
- Elon Musk. "Feb 2005 through May 2005 Update". SpaceX. Archived from the original on April 15, 2008.
- "SpaceX Completes Development of Merlin Regeneratively Cooled Rocket Engine". Business Wire. November 13, 2007.
- Dinardi, Aaron; Capozzoli, Peter; Shotwell, Gwynne (2008). Low-cost Launch Opportunities Provided by the Falcon Family of Launch Vehicles (PDF). Fourth Asian Space Conference. Taipei. Archived from the original (PDF) on March 15, 2012.
- "The SpaceX Falcon 1 Launch Vehicle Flight 3 Results, Future Developments, and Falcon 9 Evolution" (PDF). Retrieved December 29, 2012.
Clark, Stephen (September 28, 2008). "Sweet Success at Last for Falcon 1 Rocket". Spaceflight Now. Retrieved April 6, 2011.
the first privately-developed liquid-fueled rocket to successfully reach orbit.
- Boyle, Alan (June 4, 2010). "Shuttle successor succeeds in first test flight". NBC News. Retrieved June 5, 2010.
- "SpaceX Completes Qualification Testing of Merlin Regeneratively Cooled Engine" (Press release). SpaceX. February 25, 2008. Retrieved May 31, 2016.
"Updates: December 2007". Updates Archive. SpaceX. December 2007. Archived from the original on April 5, 2013. Retrieved December 27, 2012.
(2007:) Merlin has a thrust at sea level of 95,000 lbs, a vacuum thrust of over 108,000 pounds, vacuum specific impulse of 304 seconds and sea level thrust to weight ratio of 92. In generating this thrust, Merlin consumes 350 lbs/second of propellant and the chamber and nozzle, cooled by 100 lbs/sec of kerosene, are capable of absorbing 10 MW of heat energy. A planned turbo pump upgrade in 2009 will improve the thrust by over 20% and the thrust to weight ratio by approximately 25%.
- Bergin, Chris; Davis, Matt. "SpaceX Falcon I fails during first stage flight". NASAspaceflight.
- Clark, Stephen (September 28, 2008). "Sweet success at last for Falcon 1 rocket". Spaceflight Now. Retrieved September 28, 2008.
- Nelson, Katherine (October 8, 2012). "SpaceX CRS-1 Mission Update". SpaceX. Retrieved May 31, 2016.
- Clark, Stephen (October 11, 2012). "Orbcomm craft falls to Earth, company claims total loss". Spaceflight Now. Retrieved October 11, 2012.
- "Falcon 1 Users Guide (Rev 7)" (PDF). SpaceX. August 26, 2008. p. 8. Archived from the original (PDF) on October 2, 2012.
Klotz, Irene (December 13, 2010). "SpaceX Sees ISS Meet-up in 2011". Aviation Week. Retrieved February 8, 2011.
The second stage went up to 11,000 km.—and that’s with the shortie skirt
- "SpaceX Falcon 9 upper stage engine successfully completes full mission duration firing" (Press release). SpaceX. March 10, 2009. Retrieved March 12, 2009.
- Full Duration Orbit Insertion Firing. SpaceX. January 2, 2010.
- "SpaceX Falcon 9 Upper Stage Engine Successfully Completes Full Mission Duration Firing". SpaceX. March 10, 2009. Retrieved May 31, 2016.
- "SpaceX to begin testing on Reusable Falcon 9 technology this year". NASASpaceFlight.com. January 11, 2012. Retrieved January 11, 2020.
- Mage, Buff (May 6, 2016). "@lukealization Max is just 3X Merlin thrust and min is ~40% of 1 Merlin. Two outer engines shut off before the center does". @elonmusk. Retrieved January 11, 2020.
"Servo Motors Survive Space X Launch Conditions". MICROMO/Faulhabler. 2015. Retrieved August 14, 2015.
the fuel-trim valve adjusts the mixture in real time. The fuel-trim device consists of a servo-motor-controlled butterfly valve. To achieve the proper speed and torque, the design incorporates a planetary gearbox for a roughly 151:1 reduction ratio, gearing internal to the unit. The shaft of the motor interfaces with the valve directly to make fine adjustments. 'The basic mixture ratio is given by the sizing of the tubes, and a small amount of the flow of each one gets trimmed out,' explains Frefel. 'We only adjust a fraction of the whole fuel flow.'
- Elon, Musk (November 24, 2013). "SES-8 Prelaunch Teleconference". Archived from the original on November 28, 2013. Retrieved November 28, 2013.
- Berger, Eric [@SciGuySpace] (May 10, 2018). "Musk: Merlin rocket engine thrust increased by 8 percent, to 190,000 lbf" (Tweet) – via Twitter.
- "Falcon 9". SpaceX. 2017. Archived from the original on February 8, 2018.
- "SpaceX Falcon 9 Data Sheet". Space Launch Report. Retrieved September 21, 2019.
- "Falcon 9 Launch Vehicle Payload User's Guide" (PDF). Revision 2. SpaceX. October 21, 2015. Retrieved November 29, 2015.
Svitak, Amy (November 18, 2012). "Dragon's "Radiation-Tolerant" Design". Aviation Week. Archived from the original on December 3, 2013. Retrieved November 6, 2013.
"We've got computers in the Falcon 9, we've got three computers in one unit on each engine in the Falcon 9, so that's 30 computers right there."
- "Merlin LOX/RP-1 Turbopump". website "Products" page: Rocket Engine Turbopumps. Barber-Nichols. Retrieved November 22, 2012.
- Musk, Elon (October 13, 2018). "Full Q&A: Tesla and SpaceX CEO Elon Musk on Recode Decode" (offset 01:02:08) (Interview). Interviewed by Kara Swisher. Retrieved November 2, 2018.
the turbopump on the Merlin engine runs at 36,000 rpm, it's 10,000 hp, and weighs … [cut off]
- Sutton, “History of Liquid Propellant Rocket Engines,” AIAA 
- Thompson, J. D., “A Study of Radiative Properties and Composition of the Turbine Exhaust Products in the F-1 Engine,” Rocketdyne Report R-6743 Canoga Park, CA 
- Aksoy, "Hematotoxicity and Carcinogenicity of Benzene," doi: 10.1289/ehp.8982193 
- "Carcinogenic Effects of Benzene...," EPA/600/P-97/001F, NCEA 
- Melnick, et al., "Carcinogenicity of 1,3-butadiene," Env. Health Persp. 
- IARC "1,3-butadiene," IARC Monograph 100F [1992, 1998, 2008, 2018]
- Martı́nez-Escandell, et al., Pyrolysis of Petroleum Residues: I. Yields and Product Analyses," V37; 10, CARBON 
- Badger, "Pyrolysis of Hydrocarbons," Prog. Phys. Organic Chem., Wiley Interscience 
- Bockhorn, "Soot Formation In Combustion: Mechanisms and Models," Springer Chem. Phys. 
- Krestinin, “Detailed Modeling of Soot Formation in Hydrocarbon Pyrolysis,” Combustion and Flame, v. 121, pp.513–524(2000)
- Dworkin, et al., “Application of an Enhanced PAH Growth Model to Soot Formation in a Laminar Coflow Ethylene/Air Diffusion Flame,” Combustion and Flame, Volume 158, Issue 9, September 2011
- Siegla and Smith, “Particulate Carbon Formation During Combustion,” Springer Science 1981
- Richter, et al., “Detailed Modeling of PAH and Soot Formation…,” Proc. Of Comb. Inst. 30 
- EPA/CERCLA/EPCRA List of Lists, https://www.epa.gov/sites/production/files/2015-03/documents/list_of_lists.pdf 
- "Benzene" (PDF). www.epa.gov. Retrieved May 28, 2020.
- "Butadiene" (PDF). www.epa.gov. Retrieved May 28, 2020.
- Calhoon, "Computational Assessment of Afterburning Cessation...," J. Propulsion and Power, 
- Viswanathan, et al., "Investigation of Soot Combustion in Underexpanded Jet Plume Flows," J. Thermophys. and Heat Trans.
- Environmental Assessment, SpaceX Falcon Program, Environmental Assessment, 27 September 2007 note: Table 2.3 Results of Deluge Water Contamination Test : benzene is 26% of legal limits from a single engine for a 5 second firing.
- Aerostar Environmental Serv., “Environmental Assessment for the Operation and Launch of Falcon 1 and Falcon 9 Space Vehicles at Cape Canaveral Air Force Station, Florida,” Nov. 2007; APPENDIX D
- SpaceX Environmental Assessment, "Falcon Heavy Launch Operations..." Nelson Engineering Co., Oct. 14, 2013
- "Final Supplemental Environmental Assesssment..." 45th Space Wing, Patrick AFB, Aug. 2013
- "Final Environmental Impact Statement SpaceX Texas Launch Site," FAA Office of Commercial Space Transport, Vol I, May 2014
- "Final Environmental Impact Statement SpaceX Texas Launch Site - Appendices," FAA Office of Commercial Space Transport, Vol II, May 2014
- "Production at SpaceX". SpaceX. September 24, 2013. Archived from the original on April 3, 2016. Retrieved September 30, 2013.
- "SpaceX Completes 100th Merlin 1D Engine". SpaceX. October 22, 2014. Archived from the original on April 4, 2016. Retrieved October 16, 2014.
"SpaceX Prepared Testimony by Jeffrey Thornburg". SpaceRef.com. June 26, 2015.
the Merlin engine has now successfully flown to space more than 180 times (with 130 on the Merlin 1D), reliably delivering multiple payloads for U.S, Government and commercial customers to complex orbits. Due to the engine's highly manufacturable design, SpaceX is now producing 4 Merlin 1D engines per week, with current production capacity to produce 5 engines per week, far more than any other private rocket engine producer in the world.
- Foust, Jeff (February 4, 2016). "SpaceX seeks to accelerate Falcon 9 production and launch rates this year". SpaceNews. Retrieved February 6, 2016.
- Belfiore, Michael (January 18, 2005). "Race for Next Space Prize Ignites". Wired.
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