Community hub
Recent from talks
Contribute something
Nothing was collected or created yet.
SpaceX Merlin
View on Wikipedia Test firing of the Merlin 1D at SpaceX’s McGregor test stand | |
| Country of origin | United States |
|---|---|
| Manufacturer | SpaceX |
| Application |
|
| Associated LV | Falcon 1 · Falcon 9 · Falcon Heavy |
| Status | Active |
| Liquid-fuel engine | |
| Propellant | LOX / RP-1 |
| Cycle | Gas-generator |
| Performance | |
| Thrust, vacuum | 981 kN (221,000 lbf)[1] |
| Thrust, sea-level | 845 kN (190,000 lbf)[1] |
| Thrust-to-weight ratio | 184 |
| Chamber pressure | 9.7 MPa (1,410 psi)[2] |
| Specific impulse, vacuum | 311 s (3.05 km/s)[3] [needs update] |
| Specific impulse, sea-level | 282 s (2.77 km/s)[3] [needs update] |
| Dimensions | |
| Diameter | Sea level: 0.92 m (3.0 ft) Vacuum: 3.3 m (11 ft) |
| Dry mass | 470 kg (1,030 lb)[4] |
Merlin is a family of rocket engines developed by SpaceX. They are currently a part of the Falcon 9 and Falcon Heavy launch vehicles, and were formerly used on the Falcon 1. 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, but since 2016 the entire Falcon 9 booster is recovered for reuse by landing vertically on a landing pad using one of its nine Merlin engines.
The injector at the heart of Merlin is of the pintle type that was first used in the Apollo Lunar Module landing engine (LMDE). Propellants are fed by 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.
Revisions
[edit]
Merlin 1A
[edit]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,[5][6] and the second time on March 21, 2007, when it performed successfully.[7] Both times the Merlin 1A was mounted on a Falcon 1 first stage.[8][9]
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).[citation needed]
Merlin 1B
[edit]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.[10] 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).[11] 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).[10] Another notable change over the 1A was the move to TEA–TEB (pyrophoric) ignition over torch ignition.[11]
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.[8][9]
Merlin 1C
[edit]| Country of origin | United States |
|---|---|
| Manufacturer | SpaceX |
| Application |
|
| Associated LV | Falcon 1, Falcon 9 |
| Status | Retired |
| Liquid-fuel engine | |
| Propellant | LOX / RP-1 |
| Cycle | Gas-generator |
| Performance | |
| Thrust, vacuum | 480 kN (110,000 lbf)[12] |
| Thrust, sea-level | 420 kN (94,000 lbf)[12] |
| Thrust-to-weight ratio | 96 |
| Chamber pressure | 6.77 MPa (982 psi)[13] |
| Specific impulse, vacuum | 304.8 s (2.989 km/s)[13] |
| Specific impulse, sea-level | 275 s (2.70 km/s) |
| Dimensions | |
| Length | 2.92 m (9 ft 7 in)[14] |
| Dry mass | 630 kg (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%.[13]
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,[12] first flew on a mission in August 2008,[15] powered the "first privately-developed liquid-fueled rocket to successfully reach orbit", Falcon 1 Flight 4, in September 2008,[15] and powered the Falcon 9 on its maiden flight in June 2010.[16]
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.[17] The Merlin 1C chamber and nozzle are cooled regeneratively by 45 kg (100 lb) per second of kerosene flow and are able to absorb 10 MW (13,000 hp) of heat energy.[18]
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."[19] The Merlin 1C was used in the successful fourth flight of Falcon 1 on September 28, 2008.[20]
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,[21] 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.[22]
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.[23] This engine and these booster models were dropped in favor of the more advanced Merlin 1D engine and longer Falcon 9 v1.1 booster.
.jpg)
Merlin Vacuum (1C)
[edit]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-meter-long (9 ft)[24] niobium alloy[13] 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).[25] 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.[26] It was flown on the second stage for the inaugural Falcon 9 flight on June 4, 2010. At full power and as of March 10, 2009, the Merlin Vacuum engine operates with the greatest efficiency of any American-made hydrocarbon-fueled rocket engine.[27]
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-meter-long (9 ft) niobium-alloy-sheet nozzle of the Merlin Vacuum engine. The engineering solution was to cut off the lower 1.2 m (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 km (6,800 mi) altitude.[24]
Merlin 1D
[edit]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.[28] 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% of maximal thrust; however, further refinements since 2013 now allow the engine to throttle to 40%.[29]
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.[30]
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.[31] 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 845 kN (190,000 lbf) goal had been achieved.[32] 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.
On February 23, 2024, one of the nine Merlin engines powering that launch flew its 22nd mission, which was at the time the flight leading engine. It is already the most flown rocket engine to date, surpassing Space Shuttle Main Engine no. 2019's record of 19 flights.[33]
Anomalies
[edit]The March 18, 2020, launch of Starlink satellites on board a Falcon 9 experienced an early engine shutdown on ascent. The shutdown occurred 2 minutes 22 seconds into the flight and was accompanied with an "event" seen on camera. The rest of the Falcon 9 engines burned longer and did deliver the payload to orbit. However, the first stage was not successfully recovered. In a subsequent investigation SpaceX found that isopropyl alcohol, used as cleaning fluid, was trapped and ignited, causing the engine to be shut down. To address the issue, in a following launch SpaceX indicated that the cleaning process was not done.[34][35][36]
On October 2, 2020, the launch of a GPS-III satellite was aborted at T-2 seconds due to a detected early startup on 2 of the 9 engines on the first stage. The engines were removed for further testing and it was found that a port in the gas generator was blocked. After removing the blockage the engines started as intended. After this, SpaceX inspected other engines across its fleet and found that two of the engines on the Falcon 9 rocket intended for the Crew-1 launch also had this problem. Those engines were replaced with new M1D engines.[37]
On February 16, 2021, on Falcon 9 flight 108 launching Starlink satellites, an engine shut down early due to hot exhaust gasses passing through a damaged heat-shielding cover. The mission was a success, but the booster could not be recovered.[38]
Merlin 1D Vacuum
[edit]A vacuum version of the Merlin 1D engine was developed for the Falcon 9 v1.1 and the Falcon Heavy second stage.[2] As of 2020, the thrust of the Merlin 1D Vacuum is 220,500 lbf (981 kN)[39] with a specific impulse of 348 seconds,[40] the highest specific impulse ever for a U.S. hydrocarbon rocket engine.[41] The increase is due to the greater expansion ratio afforded by operating in vacuum, now 165:1 using an updated nozzle extension.[40][42]
The engine can throttle down to 39% of its maximum thrust, or 360 kN (81,000 lbf).[42]
Merlin 1D Vacuum improvements and variants
[edit]Transporter-7 mission launch debuted a new Merlin Vacuum engine (MVac for short) nozzle extension design or variant aimed at increasing cadence and reducing costs. This new nozzle extension is shorter and, as a result, decreases both performance and material usage. This nozzle is only used on lower-performance missions, as with this nozzle, the MVac engine produces 10% less thrust in space. The nozzle decreases the amount of material needed by 75%; this means that SpaceX can launch over three times as many missions with the same amount of rare niobium metal as with the longer design.[43][44]
Anomalies
[edit]On July 11, 2024, Falcon 9 flight 354 launching Starlink group 9-3 from Vandenberg AFB in California experienced an anomaly with its MVac during an engine relight attempt to raise the perigee of the 22 Starlink satellites for deployment. On X, Elon Musk and SpaceX both confirmed the engine failed explosively during a second attempted relight, albeit in a manner that did not appear to damage the second stage of the vehicle as the stage went on to deploy the satellites on board.[45]
Design
[edit]Engine control
[edit]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.[46]
Turbopump
[edit]The Merlin LOX/RP-1 turbopump used on Merlin engines 1A–1C was designed and developed by Barber-Nichols.[47] It spins at 36,000 revolutions per minute, delivering 10,000 horsepower (7,500 kW).[48]
Gas generator
[edit]The LOX/RP-1 triump rocket 3 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.[49]
Production
[edit]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).[2] By September 2013, SpaceX total manufacturing space had increased to nearly 93,000 square meters (1 million square feet), 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.[50] By October 2014, SpaceX announced that it had manufactured the 100th Merlin 1D engine and that engines were now being produced at a rate of four per week, soon to be increased to five.[51][52]
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.[53][needs update]
Each Falcon 9 booster uses nine Merlin engines, and the second stage uses one Merlin vacuum engine. The second stage is expended, so each launch consumes one Merlin Vacuum engine. SpaceX designed the booster with its engines to be recovered for reuse by propulsive landing, and the first recovered booster was reused in March 2017. By 2020, only five of the 26 Falcon 9 launched that year used new boosters. By 2021, only two of the 31 Falcon 9 launches used new boosters.
Past engine concepts
[edit]Merlin 2 concept
[edit]At the American Institute of Aeronautics and Astronautics Joint Propulsion conference on July 30, 2010, SpaceX McGregor rocket development facility director Tom Markusic shared some information from the initial stages of planning for a new engine. SpaceX’s Merlin 2 LOX/RP-1-fueled engine on a gas-generator cycle, capable of a projected 7,600 kN (1,700,000 lbf) of thrust at sea level and 8,500 kN (1,920,000 lbf) in a vacuum and would provide the power for conceptual super-heavy-lift launch vehicles from SpaceX, which Markusic dubbed Falcon X and Falcon XX. Such a capability, if built, would have resulted in an engine with more thrust than the F-1 engines used on the Saturn V.[54]
Conceived to be potentially used on more capable variants of the Falcon 9 Heavy, Markusic indicated that the Merlin 2 "could be qualified in three years for $1 billion".[55] By mid-August, SpaceX CEO Elon Musk clarified that while the Merlin 2 engine architecture was a key element of any effort SpaceX would make toward their objective of "super-heavy lift" launch vehicles—and that SpaceX did indeed want to "move toward super heavy lift"—the specific potential design configurations of the particular launch vehicles shown by Markusic at the propulsion conference were merely conceptual "brainstorming ideas", just a "bunch of ideas for discussion."[56]
Since the original discussion, no work on any "Merlin 2" kerolox engine has been pursued and made public. At the 2011 Joint Propulsion Conference, Elon Musk stated that SpaceX were instead working towards a potential staged cycle engine.[57] 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".[58] They indicated that the large engine was intended for a new SpaceX rocket, using multiple of these large engines could notionally launch payload masses of the order of 150 to 200 tonnes (170 to 220 short tons) to low-Earth orbit. The forthcoming engine currently under development by SpaceX has been named "Raptor". Raptor will use liquid methane as a fuel, and was stated as having a sea-level thrust of 6,700 kilonewtons (1,500,000 lbf).[59] Since the initial announcement of Raptor, Musk has updated the specification to approximately 230 tonnes-force (2,300 kN; 510,000 lbf)—about one-third the original published figure—based on the results of optimizing for thrust-to-weight ratio.[60]
See also
[edit]- SpaceX Draco – SpaceX RCS thruster for SpaceX Dragon
- SpaceX Kestrel – SpaceX small upper stage engine for Falcon 1
- SpaceX Raptor – SpaceX methane/LOX engine for the Starship
- Falcon 1 – First rocket powered by Merlin 1A
- 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
References
[edit]- ^ a b "Falcon User's Guide" (PDF). SpaceX. April 2020. Archived (PDF) from the original on December 2, 2020. Retrieved August 1, 2020.
- ^ a b c "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.
- ^ a b "Merlin section of Falcon 9 page". SpaceX. Archived from the original on July 15, 2013. Retrieved October 16, 2012.
- ^ 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.
- ^ Berger, Brian (July 19, 2006). "Falcon 1 Failure Traced to a Busted Nut". Space.com. Archived from the original on June 4, 2010. Retrieved August 2, 2008.
- ^ "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.
- ^ a b Whitesides, Loretta Hidalgo (November 12, 2007). "SpaceX Completes Development of Rocket Engine for Falcon 1 and 9". Wired Science. Archived from the original on March 23, 2008. Retrieved February 28, 2008.
- ^ a b Gaskill, Braddock (August 5, 2006). "SpaceX has magical goals for Falcon 9". Nasa Spaceflight. Archived from the original on March 4, 2016. Retrieved February 28, 2008.
- ^ a b "Merlin LOX/RP-1 Turbopump". Barber Nichols. Archived from the original on May 29, 2018. Retrieved May 28, 2018.
- ^ a b Elon Musk. "Feb 2005 through May 2005 Update". SpaceX. Archived from the original on April 15, 2008.
- ^ a b c "SpaceX Completes Development of Merlin Regeneratively Cooled Rocket Engine". Business Wire. November 13, 2007. Archived from the original on January 3, 2008. Retrieved November 12, 2007.
- ^ a b c d 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). Archived (PDF) from the original on March 4, 2016. Retrieved December 29, 2012.
- ^ a b Clark, Stephen (September 28, 2008). "Sweet Success at Last for Falcon 1 Rocket". Spaceflight Now. Archived from the original on September 24, 2015. 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. Archived from the original on December 21, 2019. Retrieved June 5, 2010.
- ^ "SpaceX Completes Qualification Testing of Merlin Regeneratively Cooled Engine" (Press release). SpaceX. February 25, 2008. Archived from the original on August 22, 2016. 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 (August 2, 2008). "SpaceX Falcon I fails during first stage flight". NASAspaceflight. Archived from the original on March 3, 2016. Retrieved February 26, 2010.
- ^ Clark, Stephen (September 28, 2008). "Sweet success at last for Falcon 1 rocket". Spaceflight Now. Archived from the original on March 3, 2016. Retrieved September 28, 2008.
- ^ Nelson, Katherine (October 8, 2012). "SpaceX CRS-1 Mission Update". SpaceX. Archived from the original on April 12, 2017. Retrieved May 31, 2016.
- ^ Clark, Stephen (October 11, 2012). "Orbcomm craft falls to Earth, company claims total loss". Spaceflight Now. Archived from the original on March 15, 2016. 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.
- ^ a b 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
[permanent dead link] - ^ "SpaceX Falcon 9 upper stage engine successfully completes full mission duration firing" (Press release). SpaceX. March 10, 2009. Archived from the original on December 13, 2014. Retrieved March 12, 2009.
- ^ Full Duration Orbit Insertion Firing. SpaceX. January 2, 2010. Archived from the original on April 19, 2012. Retrieved January 5, 2010.
- ^ "SpaceX Falcon 9 Upper Stage Engine Successfully Completes Full Mission Duration Firing". SpaceX. March 10, 2009. Archived from the original on December 13, 2014. Retrieved May 31, 2016.
- ^ "SpaceX to begin testing on Reusable Falcon 9 technology this year". NASASpaceFlight.com. January 11, 2012. Archived from the original on January 9, 2020. 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. Archived from the original on February 5, 2017. Retrieved January 11, 2020.
- ^ "Servo Motors Survive Space X Launch Conditions". MICROMO/Faulhabler. 2015. Archived from the original on February 20, 2017. 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 December 3, 2013. Retrieved November 28, 2013. Also at SoundCloud Archived December 7, 2013, at the Wayback Machine.
- ^ Berger, Eric [@SciGuySpace] (May 10, 2018). "Musk: Merlin rocket engine thrust increased by 8 percent, to 190,000 lbf" (Tweet) – via Twitter.
- ^ @SpaceX (February 23, 2024). "Main engine cutoff and stage separation. One of the nine Merlin engines powering tonight's first stage is our flight leader, powering its 22nd mission to Earth orbit" (Tweet) – via Twitter.
- ^ Clark, Stephen. "Falcon 9 rocket overcomes engine failure to deploy Starlink satellites". Spaceflight Now. Archived from the original on October 26, 2020. Retrieved November 1, 2020.
- ^ Clark, Stephen. "SpaceX's Starlink network surpasses 400-satellite mark after successful launch". Spaceflight Now. Archived from the original on April 30, 2020. Retrieved November 1, 2020.
- ^ "Safety panel concludes May launch of commercial crew test flight is feasible". SpaceNews. April 23, 2020. Retrieved November 1, 2020.
- ^ Berger, Eric (October 28, 2020). "How a tiny bit of lacquer grounded new Falcon 9 rockets for a month". Ars Technica. Retrieved October 24, 2021.
- ^ Cao, Sissi (February 16, 2021). "SpaceX Fails Falcon 9 Rocket Landing in Rare Miss During Latest Starlink Mission". Observer. Retrieved February 26, 2021.
- ^ "SpaceX". SpaceX. Archived from the original on March 7, 2011. Retrieved September 24, 2020.
- ^ a b "Falcon 9". SpaceX. 2017. Archived from the original on February 8, 2018.
- ^ "SpaceX Falcon 9 Data Sheet". Space Launch Report. Archived from the original on December 4, 2019. Retrieved September 21, 2019.
- ^ a b "Falcon 9 Launch Vehicle Payload User's Guide" (PDF). Revision 2. SpaceX. October 21, 2015. Archived from the original (PDF) on March 14, 2017. Retrieved November 29, 2015.
- ^ "Transporter 7". Retrieved March 17, 2023.
- ^ Sesnic, Trevor (July 22, 2023). "EchoStar 24 | Falcon Heavy". Everyday Astronaut. Retrieved July 29, 2023.
- ^ Musk, Elon (June 11, 2024). "SpaceX X Post regarding Starlink 9-3 anomoly". X.com. Retrieved June 11, 2024.
- ^ 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. Archived from the original on March 13, 2016. 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. Archived from the original on November 2, 2018. Retrieved November 2, 2018.
the turbopump on the Merlin engine runs at 36,000 rpm, it's 10,000 hp
- ^ Sutton, “History of Liquid Propellant Rocket Engines”, AIAA [2006].
- ^ "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. Archived from the original on March 19, 2023. Retrieved December 27, 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. Archived from the original on February 9, 2016. Retrieved February 6, 2016.
- ^ "SpaceX Merlin 2 engine, heavy lift designs". Hobbyspace.com. July 30, 2010. Archived from the original on October 13, 2011.
- ^ Norris, Guy (August 5, 2010). "SpaceX Unveils Heavy-Lift Vehicle Plan". Aviation Week & Space Technology. Archived from the original on August 21, 2010.
- ^ "Exploration Musk Clarifies SpaceX Position On Exploration". Aviation Week & Space Technology. August 11, 2010. Retrieved August 16, 2010. (subscription required)
- ^ "Webcasts of Elon Musk & Gwynne Shotwell at AIAA mtg". Hobbyspace.com. August 1, 2011. Archived from the original on November 2, 2011.
- ^ Rosenberg, Zach (October 15, 2012). "SpaceX aims big with massive new rocket". Flightglobal. Retrieved October 17, 2012.
- ^ Nellis, Stephen (February 19, 2014). "SpaceX propulsion chief elevates crowd in Santa Barbara". Pacific Business Times. Retrieved February 22, 2014.
- ^ Musk, Elon (January 6, 2015). "I am Elon Musk, CEO/CTO of a rocket company, AMA!". Reddit.com. Retrieved January 30, 2016.
Thrust to weight is optimizing for a surprisingly low thrust level, even when accounting for the added mass of plumbing and structure for many engines. Looks like a little over 230 metric tons (~500 klbf) of thrust per engine, but we will have a lot of them :)
Sources
[edit]- Belfiore, Michael (January 18, 2005). "Race for Next Space Prize Ignites". Wired.
External links
[edit]
| Liquid fuel |
|  | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Solid fuel |
| |||||||||||||||||
| ||||||||||||||||||
| Launch vehicles |
| ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Spacecraft |
| ||||||||
| Test vehicles |
| ||||||||
| Rocket engines | |||||||||
| Lists of missions | |||||||||
| Launch facilities | |||||||||
| Landing sites |
| ||||||||
| Other facilities | |||||||||
| Support |
| ||||||||
| Contracts | |||||||||
| R&D programs | |||||||||
| Key people |
| ||||||||
| Related | |||||||||
* denotes unflown vehicles or engines, and future missions or sites. † denotes failed missions, destroyed vehicles, and abandoned sites.
| |||||||||
SpaceX Merlin
View on GrokipediaOverview
Engine Description
The Merlin is a family of rocket engines developed by SpaceX for use in its Falcon launch vehicle series, including the Falcon 9 and Falcon Heavy, utilizing rocket-grade kerosene (RP-1) and liquid oxygen (LOX) as propellants.[1] These engines power the first and second stages of these vehicles, enabling reliable orbital insertion and reusability. The name "Merlin" draws from the small falcon species known for its agility, as well as the Arthurian wizard symbolizing ingenuity and power.[8][9] In its basic configuration, the Merlin employs an open gas-generator cycle with a single combustion chamber and is designed to be gimbaled for thrust vector control, allowing precise steering during ascent.[1] On the Falcon 9 first stage, nine Merlin engines are arranged in an octagonal pattern—eight surrounding a central engine—to provide redundancy and engine-out capability.[1] The Falcon Heavy extends this by clustering 27 engines across three cores, while vacuum-optimized variants equip the second stages of both vehicles for efficient performance in space.[1] The Merlin achieved its first flight on March 24, 2006, aboard the Falcon 1 rocket.[10] As of 2025, it stands as a mature, reusable engine with high-volume production supporting SpaceX's launch cadence, having accumulated extensive flight heritage across hundreds of missions.[1]Performance Specifications
The Merlin 1D engine, used in the first stage of Falcon 9 and Falcon Heavy rockets, produces a sea-level thrust of 845 kN (190,000 lbf) per engine.[1] The Merlin 1D Vacuum variant, employed in the second stage, generates a vacuum thrust of 981 kN (220,500 lbf).[2] These engines operate at a chamber pressure of 9.7 MPa (1,410 psi), enabling efficient combustion of liquid oxygen and RP-1 propellants with an approximate mass flow rate of 300 kg/s for the Merlin 1D.[4] Specific impulse for the Merlin 1D is 282 seconds at sea level and 311 seconds in vacuum, while the Merlin 1D Vacuum achieves 348 seconds in vacuum, reflecting the optimized nozzle expansion for upper-stage performance.[4] The engines support a throttling range of 40–100% thrust, allowing precise control for launch, orbit insertion, and reusable landing maneuvers.[1] The sea-level version measures 1.8 m in length and 0.94 m in diameter, with a dry mass of 432 kg, contributing to the overall compactness and reusability of the Falcon vehicle architecture.[1] The following table compares key specifications between the Merlin 1D and Merlin 1D Vacuum engines:| Parameter | Merlin 1D (Sea-Level) | Merlin 1D Vacuum |
|---|---|---|
| Thrust | 845 kN (190,000 lbf) at sea level | 981 kN (220,500 lbf) in vacuum |
| Specific Impulse | 282 s (sea level); 311 s (vacuum) | 348 s (vacuum) |
| Chamber Pressure | 9.7 MPa (1,410 psi) | 9.7 MPa (1,410 psi) |
| Propellant Mass Flow | ~300 kg/s | ~300 kg/s |
| Throttling Range | 40–100% | 40–100% |
| Dimensions (Length × Diameter) | 1.8 m × 0.94 m | 3.0 m × 0.94 m (extended nozzle) |
| Dry Mass | 432 kg | 432 kg |
Development History
Early Prototypes (1A–1C)
The development of the Merlin engine began in 2003, with SpaceX conducting its first hot-fire test of an early prototype that month, achieving full expected thrust of 60,000 pounds-force (approximately 267 kN) and 93% combustion efficiency using liquid oxygen and RP-1 kerosene propellants.[11] This marked the start of iterative testing at SpaceX's facilities in California and later Texas, aimed at creating a cost-effective, reliable engine for the Falcon 1 launch vehicle. In August 2006, NASA awarded SpaceX up to $278 million through the Commercial Orbital Transportation Services (COTS) program via a Space Act Agreement, providing milestone-based funding to support engine and vehicle development for potential ISS resupply missions.[12] The Merlin 1A, developed from 2003 to 2006, was the first flight-ready prototype and featured a pressure-fed architecture with ablative cooling. It produced 340 kN of sea-level thrust and powered the initial Falcon 1 test flights, including three attempts from 2006 to 2008. Two of these flights failed due to issues including low thrust margins and excessive vibrations leading to structural problems, such as fuel leaks and stage separation anomalies.[13] These early challenges highlighted limitations in the engine's thrust-to-weight ratio, which was below optimal levels for reliable orbital insertion, prompting rapid design iterations.[3] The Merlin 1B was planned in 2006 as an interim upgrade, incorporating a turbopump for improved propellant delivery over the pressure-fed system of the 1A and generating approximately 380 kN of thrust. However, it was superseded by the Merlin 1C before any flight. The turbopump, spinning at up to 36,000 rpm and designed with external partner Barber-Nichols, represented a key transition toward pump-fed architectures, enabling higher chamber pressures and better overall performance.[3] The Merlin 1C, refined from 2007 to 2010, focused on enhancing reliability through regenerative cooling of the combustion chamber and nozzle. For Falcon 1, it produced 350 kN of sea-level thrust; an upgraded variant for early Falcon 9 flights delivered 420 kN. It powered the final three Falcon 1 flights (2008–2009), all successful and validating orbital insertion capabilities. Qualification testing in November 2007 included a 170-second hot-fire at the McGregor facility, confirming durability equivalent to multiple missions. The 1C also supported initial Falcon 9 development tests, accumulating over 27 minutes of runtime on single engines during qualification. By 2010, thrust-to-weight ratio challenges from earlier versions were largely resolved through material optimizations and design simplifications, laying the groundwork for subsequent evolutions.[14]Merlin 1D Evolution
The Merlin 1D engine marked a significant advancement in SpaceX's rocket propulsion technology, entering development in 2011 as a redesign of the preceding Merlin 1C to address limitations in thrust, efficiency, and integration for the Falcon 9 launch vehicle.[15] Introduced to power the first stage of Falcon 9 v1.1, the initial version delivered approximately 624 kN of sea-level thrust, a substantial increase from the Merlin 1C's 420 kN, achieved primarily through a higher chamber pressure of 9.7 MPa compared to the 1C's 6.2 MPa.[16][4] This evolution incorporated full regenerative cooling for both the combustion chamber and nozzle, along with advanced material upgrades such as improved alloys to withstand the elevated pressures and thermal loads, enabling greater performance without excessive weight penalties.[1] Key design refinements in the Merlin 1D included an integrated thrust vector control (TVC) actuator directly mounted on the engine gimbal, which simplified the overall system by reducing external hardware and improving response times for steering.[15] Additionally, streamlined plumbing reduced the number of propellant lines and valves, enhancing reliability and manufacturability while minimizing potential leak points.[1] Pre-1D flight tests occurred as early as 2010 during developmental firings, but the Merlin 1D achieved full-duration hot-fire qualification in June 2012 with a 185-second burn at target thrust levels.[17] Operational deployment began in 2013 with the CASSIOPE mission (Falcon 9 Flight 6), marking the engine's debut in space and demonstrating its throttle range from 70% to 100% for precise ascent control.[18] Subsequent iterations of the Merlin 1D further boosted performance, with thrust rising to 845 kN at sea level by the Falcon 9 Block 5 introduction in 2018, reflecting ongoing optimizations in turbopump efficiency and combustion stability.[1][19] By November 2025, the Merlin 1D had powered over 570 Falcon 9 and Falcon Heavy first-stage boosts, including numerous successes like the inaugural Commercial Resupply Services mission in 2012—though that flight used the prior 1C variant—and establishing itself as the backbone of SpaceX's orbital fleet with a mission success rate exceeding 99%. These enhancements, built on lessons from early prototypes' lower thrust and integration challenges, solidified the 1D's role in enabling reusable rocket architectures.[15] As of 2025, the Merlin 1D remains the standard engine for all Falcon 9 and Falcon Heavy first stages, with minor tuning such as adjusted mixture ratios for heavy-lift configurations to optimize payload capacity without altering core hardware.[1] This iterative maturation has supported SpaceX's rapid launch cadence, underscoring the engine's evolution from a developmental prototype to a high-volume, production-proven component central to the company's operations.Vacuum Engine Variants
The Merlin Vacuum 1C engine, introduced in 2010, represented the first adaptation of the Merlin series for vacuum operations, powering the second stage of the Falcon 9 v1.0 launch vehicle. This variant delivered approximately 420 kN of vacuum thrust and achieved a specific impulse of 342 seconds, enabling efficient upper-stage performance in space.[20][21] The Merlin 1D Vacuum, operational from 2013 to the present, builds on this foundation with significant enhancements for higher performance in vacuum environments. It features a substantially larger nozzle with an expansion ratio of 165:1, compared to 14.5:1 on sea-level Merlin engines, generating 981 kN of vacuum thrust and a specific impulse of 348 seconds. Its inaugural flight occurred on September 29, 2013, during the CASSIOPE mission (Falcon 9 Flight 6).[1][22] Key improvements in the 1D Vacuum variant include the use of a carbon composite overwrap on the nozzle for structural reinforcement and a radiatively cooled extension to manage thermal loads without active cooling, resulting in a roughly 50% mass reduction relative to the 1C version—bringing the engine weight down to approximately 490 kg. These modifications enhance efficiency and reliability for prolonged vacuum burns.[3][23] Subtle variants of the 1D Vacuum engine incorporate mission-specific thrust tuning, allowing adjustments such as elevated initial thrust profiles to accommodate heavy payloads on demanding trajectories. In the Falcon 9 second stage, a single Merlin Vacuum engine provides propulsion, with demonstrated multiple restart capability—designed for up to 10 ignitions—to support complex orbital insertions and maneuvering. By November 2025, the Merlin Vacuum had supported over 570 successful upper-stage missions, contributing to SpaceX's high-reliability record.[1][24]Design Features
Cycle and Architecture
The Merlin engine utilizes a gas-generator cycle, an open thermodynamic power cycle in which a portion of the RP-1 and liquid oxygen propellants is diverted to a separate gas generator for combustion, powering the turbopump while the resulting exhaust is dumped overboard without contributing significantly to main thrust.[2][25] The engine's architecture centers on a single Merlin core integrated with a gimbal mount that enables thrust vectoring via deflection angles of up to ±10 degrees for vehicle steering. It operates with RP-1 (rocket-grade kerosene) and liquid oxygen in a mass mixture ratio of 2.34:1, optimizing combustion stability and performance.[1] This gas-generator approach provides key advantages through its relative design simplicity, which supports rapid reusability, high reliability, and lower development and production costs relative to staged combustion cycles.[26] Cycle efficiency, as measured by specific impulse, can be conceptually understood through the theoretical equation for ideal nozzle exhaust velocity in a rocket engine: where is standard gravitational acceleration, the ratio of specific heats, the universal gas constant, the chamber temperature, the exhaust molecular weight, and and the nozzle exit and chamber pressures, respectively. This relation highlights how propellant properties and nozzle design influence performance without requiring full derivation. Unlike closed cycles such as the full-flow staged combustion used in the Raptor engine, where all propellants are routed through separate preburners to maximize energy recovery and efficiency in the main chamber, the Merlin's open cycle prioritizes straightforward implementation over peak thermodynamic performance.[27]Turbopump and Propellant Feed
The Merlin engine's turbopump system is essential for pressurizing and delivering liquid oxygen (LOX) and RP-1 propellants to the combustion chamber, enabling the high chamber pressures required for efficient performance. The assembly consists of a single-shaft turbopump with dual impellers—one for LOX and one for RP-1—driven by the hot exhaust gases from a single preburner gas generator cycle. This configuration allows for compact design and efficient power transfer, with the turbopump also supplying hydraulic fluid for engine actuators before recycling it to the low-pressure inlet.[28][29] The LOX turbopump incorporates an axial-flow inducer to suppress cavitation and a centrifugal impeller to boost pressure to approximately 1,500 psi, while the RP-1 turbopump uses a similar centrifugal impeller tailored to the fuel's higher density. These components handle high flow rates, with LOX at around 214 kg/s and RP-1 at about 91 kg/s for a total propellant mass flow of roughly 305 kg/s in the Merlin 1D, supporting the engine's sea-level thrust of 845 kN. The turbopump operates at speeds up to 36,000 RPM, delivering over 7,500 kW of power in a lightweight package that is among the most efficient in its class.[30][31][28] In the evolution to the Merlin 1D, SpaceX developed the turbopump in-house, replacing the earlier Barber-Nichols design used in prototypes 1A through 1C, with key upgrades including advanced bearings, maraging steel shafts, and 3D-printed Inconel turbine blades for improved durability and reduced manufacturing time. These enhancements enable the turbopump to withstand over 100 reuses while maintaining reliability, as evidenced by helium-purged bearings that prevent propellant mixing and cavitation-resistant inducers validated through computational fluid dynamics simulations. By 2025, the Merlin turbopump has accumulated over 1 million seconds of hot-fire testing across development and flight programs, underscoring its robustness in operational environments.[29][30][1]Combustion Chamber and Nozzle
The combustion chamber of the SpaceX Merlin engine features a regeneratively cooled design, where rocket-grade kerosene (RP-1) circulates through integrated channels in a milled copper alloy liner to absorb and dissipate the intense heat generated during operation.[1] This cooling method protects the chamber walls from the extreme combustion temperatures of approximately 3,500 K, while preheating the RP-1 to improve combustion efficiency upon injection.[23] The chamber operates at a nominal pressure of 9.7 MPa (1,410 psi), which facilitates stable and complete propellant burning within the confined volume.[4] At the forward end of the chamber, the Merlin employs a pintle injector design, originally derived from the Apollo Lunar Module Descent Engine, to atomize and mix the RP-1 fuel and liquid oxygen (LOX) propellants.[32] The pintle configuration uses a central movable rod surrounded by an annular orifice for one propellant and radial slots for the other, creating a variable-area flow that ensures uniform mixing and inherent combustion stability across a wide range of throttle settings. Propellants are delivered to the injector from the engine's turbopump assembly. This setup minimizes mixing inefficiencies and reduces the risk of acoustic instabilities, contributing to reliable ignition and sustained performance. Ignition is achieved using triethylaluminum-triethylborane (TEA-TEB) hypergolic igniters, enabling multiple restarts.[1] The nozzle assembly converts the high-pressure, high-temperature gases from the combustion chamber into directed thrust through controlled expansion. For sea-level variants, it uses a convergent-divergent bell shape with an expansion ratio of 16:1, balancing efficiency in dense atmosphere while avoiding flow separation. Vacuum-optimized versions incorporate an extended nozzle section to achieve higher expansion ratios, enhancing performance in space. To mitigate thermal loads, particularly in the divergent section, the nozzle employs film cooling, where a boundary layer of unburned RP-1 or gas-generator exhaust is injected along the inner walls to shield the structure from melting.[23] Advanced manufacturing techniques, including 3D printing of Inconel superalloy components for intricate features like cooling channels and injector elements, allow for greater design complexity in the chamber and nozzle while reducing the number of welds from over 100 in conventional assemblies to significantly fewer, improving structural integrity and production speed.[33] The thrust produced by the Merlin engine follows the fundamental rocket thrust equation: where is the total thrust, is the mass flow rate of the exhaust gases, is the effective exhaust velocity at the nozzle exit, and are the pressures at the nozzle exit and in the ambient environment, respectively, and is the nozzle exit area.[34] The exit velocity , which encapsulates the nozzle's role in accelerating the exhaust, is primarily a function of the chamber temperature, molecular weight of the exhaust products, and the nozzle's expansion ratio; it represents the conversion of combustion energy into directed momentum, with higher yielding greater propulsive efficiency. The pressure difference term accounts for momentum contributions from pressure imbalances, which is negligible in vacuum but aids thrust augmentation at sea level.Control Systems
The control systems for the SpaceX Merlin engine integrate electronics, software, and actuators to manage startup, throttling, gimballing, and shutdown sequences, ensuring precise operation during ascent and reusability phases. The engine employs a fault-tolerant avionics architecture with a three-string redundant design, incorporating flight computers, inertial measurement units, and dedicated controllers for propulsion and valve operations.[1] This redundancy allows the system to tolerate multiple failures while maintaining control, supporting the engine's integration into multi-engine clusters on Falcon vehicles.[1] Throttling is achieved through a variable-position valve on the gas generator cycle, enabling the Merlin 1D to operate across a deep range—deeply throttleable to maintain steady-state acceleration limits during flight and facilitate precision landings.[1] For the sea-level variant, this spans from full thrust of 190,000 lbf (845 kN) down to approximately 40% (76,000 lbf or 338 kN) for booster descent control, with capabilities refined since reusable landings began in 2015. The system supports multiple restarts, critical for second-stage operations and recovery maneuvers.[1] Gimballing for thrust vector control (TVC) utilizes hydraulic actuators mounted on the engine, enabling pitch and yaw adjustments with the center and outer engines providing primary steering.[35] These actuators, powered by high-pressure kerosene from the engine's turbopump, allow rapid response to vehicle dynamics without a separate hydraulic system, eliminating risks like fluid depletion.[35] Roll control is handled collectively by differential throttling across the engine cluster.[1] Health monitoring relies on automated flight computer oversight of engine parameters, with individual sensors tracking pressures, temperatures, and performance metrics during prelaunch and ascent.[1] If off-nominal conditions are detected—such as exceeding redline thresholds—the system triggers autonomous preemptive shutdowns or aborts to protect the vehicle, demonstrated through consistent mission success rates.[1] Software upgrades since 2015 have enhanced these capabilities, incorporating iterative algorithms for reusability, including optimized deep throttling profiles for precise booster landings.[1]Production and Operations
Manufacturing Process
The manufacturing of SpaceX Merlin engines primarily occurs at the company's headquarters and production facility in Hawthorne, California, where assembly, integration, and initial testing take place. Engines are then shipped to the Rocket Development and Test Facility in McGregor, Texas, for rigorous qualification firings and performance validation. This dual-site approach enables efficient scaling, with Hawthorne focusing on high-volume fabrication and McGregor handling destructive and non-destructive evaluations to ensure reliability.[36][37] Key fabrication techniques emphasize advanced additive manufacturing and precision joining to enhance scalability and reduce costs. Since 2014, SpaceX has incorporated 3D printing for complex components such as injectors and turbopump elements, including turbines. The combustion chamber and nozzle are constructed using friction stir welding, a solid-state process that joins high-strength alloys like Inconel without melting, providing superior leak resistance and structural integrity compared to conventional fusion welding. Impellers within the turbopump are produced via investment casting, using aluminum or Inconel alloys to achieve precise geometries essential for high-pressure propellant handling. These methods, combined with computer numerical control (CNC) machining for final tolerances, support rapid iteration and production rates necessary for Falcon launch cadences.[38][39][40][41] Vertical integration has driven significant cost reductions in Merlin production, dropping from approximately $1 million per engine around 2010 to about $250,000 by 2025 through in-house design, tooling, and supply of critical components. This strategy eliminates external supplier markups and enables proprietary processes like proprietary alloy formulations and automated assembly lines, achieving economies of scale while maintaining performance. For propellants, SpaceX sources rocket-grade kerosene (RP-1) and liquid oxygen (LOX) from industrial suppliers such as Air Liquide.[42][43] Quality control is integral, with every Merlin engine undergoing 100% hot-fire acceptance testing at McGregor to simulate flight conditions, accumulating seconds to minutes of burn time per unit to verify thrust, stability, and restart capability. Non-destructive testing methods, including ultrasonic inspection, radiographic evaluation, and fluorescent penetrant testing, are applied throughout fabrication to detect subsurface defects in welds, castings, and printed parts without compromising integrity. These protocols, informed by iterative failure analysis from early prototypes, ensure a high yield rate and contribute to the engine's operational reliability in reusable configurations.[44][45]Production Milestones
The production of Merlin engines began in the early 2000s to support SpaceX's Falcon 1 launch vehicle, with initial efforts focused on the Merlin 1A variant. By 2006, SpaceX had manufactured 10 Merlin engines for development testing and the first Falcon 1 flights, including the inaugural launch on March 24, 2006. These early units enabled iterative improvements leading to the Merlin 1C, which powered the successful orbital flights of Falcon 1 in 2008 and 2009.[14] As SpaceX shifted focus to the Falcon 9 program, Merlin production scaled dramatically to meet growing launch demands. In 2010, output was approximately one engine per month during the initial qualification and debut flight of Falcon 9. By 2011, the rate had increased to eight engines per month, with ambitions to reach 400 annually to sustain over 40 launches per year. The 100th Merlin engine was completed in 2012, followed by the 200th in 2015, reflecting accelerated in-house manufacturing capabilities.[46] Production continued to ramp up with the introduction of the Merlin 1D variant. By October 2014, SpaceX announced the completion of its 100th Merlin 1D engine, with rates reaching four per week and plans to increase to five. In December 2017, the 400th Merlin 1D rolled off the line, coinciding with the qualification of the first batch of engines for reusability on the Falcon 9 first stage. This milestone supported the historic reflights of recovered boosters, beginning with the SES-10 mission on March 30, 2017. Cumulative production exceeded 1,000 engines by November 2025, supporting over 570 Falcon missions amid sustained activity, though rates are expected to decline with the transition to Starship's Raptor engines.[47][48] To accommodate the high-cadence demands of missions like Starlink constellation deployments starting in 2019, Merlin production rates grew to approximately 25 engines per month by the early 2020s, enabling reliable supply for both new and refurbished boosters. This scaling, achieved through optimized manufacturing processes at SpaceX's Hawthorne facility, has been pivotal to the Falcon 9's economic viability, with reusability further reducing marginal per-flight expenses to under $30 million in many cases.[49]Reliability and Anomalies
The Merlin engine has demonstrated exceptional reliability in operational use, achieving a success rate exceeding 99% across more than 5,000 individual engine flights by November 2025, as evidenced by the cumulative Falcon 9 and Falcon Heavy missions powered by these engines.[1][50] This high reliability stems from rigorous pre-flight testing and the engine's design tolerance for anomalies, including the Falcon 9's engine-out capability, which allows the vehicle to complete missions even with a single engine shutdown.[51] Reusability has further underscored this performance, with individual Merlin engines on first-stage boosters routinely achieving more than 20 flights per core before retirement, contributing to a mean time between failures (MTBF) greater than 10 flights per engine.[52] Despite this track record, several major anomalies have occurred, though most were not directly attributable to the Merlin engine itself. In June 2015, during the CRS-7 mission, a Falcon 9 exploded approximately 139 seconds after liftoff due to the failure of a support strut in the second-stage liquid oxygen tank, which dislodged a helium composite overwrapped pressure vessel (COPV) and triggered a tank rupture; the Merlin engines operated nominally until the structural failure.[53] SpaceX responded by redesigning and reinforcing the struts to prevent recurrence, a fix implemented for subsequent flights starting in late 2015.[54] Similarly, in September 2016, a pre-launch static fire test for the AMOS-6 mission resulted in an explosion caused by a COPV failure in the second-stage oxygen tank during helium loading, again unrelated to engine performance but highlighting pressurization system vulnerabilities.[55] Post-incident analysis led to modified helium loading procedures and enhanced COPV testing protocols, enabling a return to flight in January 2017 without further such issues.[56] More recently, in July 2024, a Falcon 9 second-stage Merlin Vacuum engine experienced an in-flight anomaly during the Starlink Group 9-3 mission, where a liquid oxygen leak—likely from a cracked pressure sense line—caused an early shutdown and deployed 20 satellites into an unsustainable low orbit, resulting in their atmospheric reentry.[57][58] The U.S. Federal Aviation Administration (FAA) grounded the Falcon 9 fleet pending investigation, which confirmed the leak as the root cause; SpaceX implemented corrective actions, including improved line inspections and material reinforcements, allowing resumption of launches within weeks.[59] These incidents, while rare, represent less than 1% of total missions and have driven iterative enhancements without compromising the engine's overall flight heritage. To support reusability and reliability, Merlin engines undergo extensive ground testing at SpaceX's McGregor facility in Texas, including multiple restarts and burns exceeding 180 seconds to simulate ascent, reentry heating, and landing profiles.[51] Such tests, often totaling over 30 minutes of cumulative runtime per engine during qualification, validate the turbopump and combustion components under repeated thermal cycles, ensuring performance consistency across reused hardware.[60]Applications
Falcon 9 Integration
The first stage of the Falcon 9 launch vehicle integrates nine Merlin 1D engines in an octaweb configuration, where eight engines are arranged in an octagonal pattern surrounding a central engine.[61] This layout optimizes the thrust structure by reducing length and weight while streamlining manufacturing, with the central engine uniquely capable of deep throttling down to 40% of nominal thrust to enable precise propulsive landings.[1] The engines are mounted on a common thrust plate, allowing for gimbaling to provide three-axis control during ascent.[2] Engine startup occurs during the hold-down phase on the launch pad, where all nine Merlin 1D engines ignite nearly simultaneously using triethylaluminum-triethylborane (TEA-TEB) pyrophoric fluid to initiate combustion, followed by the flow of liquid oxygen and RP-1 propellants.[62] This sequence ensures stable thrust buildup before the hold-down clamps release, with the vehicle's grid fins remaining stowed during ignition but deploying later for reentry stability if a booster recovery is planned.[2] The clustered Merlin 1D engines deliver a total sea-level thrust of approximately 7.6 MN (1.7 million pounds-force), enabling the Falcon 9 to lift up to 22,800 kg to low Earth orbit in expendable mode.[1] This performance supports a wide range of missions, including satellite deployments and human spaceflight.[2] For reusability, the Falcon 9 first stage employs four titanium grid fins near the interstage for aerodynamic control during reentry and descent, while cold gas thrusters using nitrogen provide fine attitude adjustments, particularly during boostback and entry burns to orient the booster for landing.[2] The center Merlin engine facilitates the boostback burn by relighting to reverse trajectory toward the launch site or droneship.[1] By November 2025, this integration has enabled routine operations, with over 300 Falcon 9 launches dedicated to Starlink constellation deployments and multiple crewed missions to the International Space Station, such as Crew-11.[63][64]Falcon Heavy Configuration
The Falcon Heavy launch vehicle incorporates 27 Merlin 1D engines in its first stage configuration, distributed across three Falcon 9-derived cores: two side boosters and one center core, each equipped with nine engines. This tri-core architecture enables the vehicle to generate over 22.8 MN (5.13 million lbf) of thrust at liftoff, providing significantly greater payload capacity to geosynchronous transfer orbit and beyond compared to the single-core Falcon 9.[1][7] On each core, the nine Merlin 1D engines are arranged in an octagonal pattern, with eight engines surrounding a single center engine mounted in the octaweb thrust structure, facilitating efficient propellant flow and structural integration. All engines operate on a liquid oxygen (LOX) and rocket-grade kerosene (RP-1) propellant combination, using a gas-generator cycle for reliable performance. The engines are gimbaled for three-axis control, with the side boosters and center core collectively providing the necessary vectoring during ascent.[1] During launch, the side boosters ignite first to verify performance, followed by the center core engines, establishing a staged thrust profile to limit acceleration to approximately 3-4 g. The center core engines throttle down to around 60% shortly after liftoff to manage initial loads, while the full complement of 27 engines operates at full thrust for the first phase. After booster separation at roughly two minutes into flight, the center core's nine engines throttle back up, continuing to propel the upper stage and payload; this core can also perform an entry burn using three center engines and a landing burn with one center engine for recovery. Merlin 1D engines in this setup demonstrate throttleability from 40% to 100% of nominal thrust (845 kN or 190,000 lbf at sea level per engine), enabling precise control without cross-feed propellant transfer between cores, which relies instead on sequential depletion of side booster tanks followed by the center core.[1][7]Reusability and Flight Heritage
The Merlin engine's design incorporates features that support the reusability of the Falcon 9 first stage, enabling controlled vertical landings following orbital insertion. The first successful landing of a Falcon 9 booster, powered by nine Merlin 1D engines, occurred on December 21, 2015, during the Orbcomm OG2 Mission-2 launch from Cape Canaveral. By November 2025, SpaceX had completed over 500 successful booster landings, with more than 95% of attempted recoveries succeeding since the program's inception.[65] Post-landing inspections and refurbishments of the Merlin engines typically allow for 10 to 20 flights per engine set, with minimal major overhauls required for early reuses; engines are routinely checked for wear on turbopumps, injectors, and nozzles before reflights.[1] The Merlin engine debuted in 2006 aboard the Falcon 1 rocket, powering its first stage during a suborbital test flight on March 24 from Omelek Island in the Pacific. Since then, Merlins have supported over 550 launches in the Falcon family, including Falcon 9 and Falcon Heavy missions, achieving a success rate exceeding 99% across thousands of engine firings.[66] This flight heritage includes the engine's evolution from the initial Merlin 1A variant, which flew five times on Falcon 1, to the mature Merlin 1D+ used in current Block 5 configurations, demonstrating progressive improvements in reliability and throttle control for reentry and landing burns. Since the introduction of the Falcon 9 Block 5 booster in May 2018, Merlin engines have enabled unprecedented reuse records for orbital-class hardware, with individual boosters achieving up to 31 flights—the highest for any such vehicle.[67] Rapid turnaround times, often as short as 21 days between launches for the same booster, have been facilitated by the engines' robust design and streamlined refurbishment processes.[68] These achievements have dramatically lowered launch costs to approximately $2,700 per kilogram to low Earth orbit, primarily through booster reuse, allowing high-cadence operations such as the deployment of over 2,500 Starlink satellites in 2025 alone.[69]| Falcon Version | Merlin Variant | Approximate Total Flights (as of Nov 2025) | Notable Reuse Achievements |
|---|---|---|---|
| Falcon 1 (2006–2009) | Merlin 1A/1C | 5 | No reusability; developmental flights |
| Falcon 9 v1.0/v1.1 (2010–2015) | Merlin 1C/1D | ~20 | Early grid fin tests; no full reuses |
| Falcon 9 Full Thrust (2016–2018) | Merlin 1D | ~80 | Initial landings (3 successes); 1 reuse |
| Falcon 9 Block 5 (2018–present) | Merlin 1D+ | ~450+ | >500 landings; up to 31 reuses per booster; 100% success on reflights[1] |