View source for SpaceX Merlin

{{short description|Rocket engine in SpaceX Falcon launch vehicles}}
{{About|the line of rocket engines developed by SpaceX|the line of airplane engines also named Merlin|Rolls-Royce Merlin}}
{{Infobox rocket engine
| name                       = Merlin 1D
| image                      = SpaceX Testing Merlin 1D Engine In Texas.jpg
| image_size                 = 275
| caption                    = Test firing of the Merlin 1D at SpaceX’s McGregor test stand
| country_of_origin          = [[United States]]
| manufacturer               = [[SpaceX]]
| purpose                    = {{plainlist|
* [[Booster (rocketry)|Booster stage]] engine
* [[Upper stage]] engine
}}
| associated                 = [[Falcon 1]]{{, }}[[Falcon 9]]{{, }}[[Falcon Heavy]]
| status                     = Active
| type                       = liquid
| oxidiser                   = [[LOX]]
| fuel                       = [[RP-1]]
| cycle                      = [[Gas-generator cycle|Gas-generator]]
| thrust(Vac)                = {{cvt|981|kN}}<ref name="falconguide202004">{{cite web |url=https://www.spacex.com/media/falcon_users_guide_042020.pdf |title=Falcon User's Guide |publisher=SpaceX |date=April 2020 |access-date=August 1, 2020 |archive-date=December 2, 2020 |archive-url=https://web.archive.org/web/20201202093334/https://www.spacex.com/media/falcon_users_guide_042020.pdf |url-status=live }}</ref>
| thrust(SL)                 = {{cvt|845|kN}}<ref name="falconguide202004"/>
| thrust_to_weight           = 184
| chamber_pressure           = {{cvt|1410|psi|MPa|order=flip|lk=in}}<ref name="awst20110811"/>
| specific_impulse_vacuum    = {{cvt|311|isp}}<ref name="spacexfalcon9Merlinpage">{{cite web |url=http://www.spacex.com/falcon9.php#merlin_engine |title=Merlin section of Falcon 9 page |publisher=SpaceX |access-date=October 16, 2012 |archive-url=https://web.archive.org/web/20130715094112/http://www.spacex.com/falcon9#merlin_engine |archive-date=July 15, 2013 |url-status=unfit}}</ref> {{update after|2020|07|31|reason=Figures are from 2013 and do not reflect current engine performance}}
| specific_impulse_sea_level = {{cvt|282|isp}}<ref name="spacexfalcon9Merlinpage"/> {{update after|2020|07|31|reason=Figures are from 2013 and do not reflect current engine performance}}
| diameter                   = Sea level: {{cvt|0.92|m|ft}}<br/>Vacuum: {{cvt|3.3|m|ft}}
| dry_weight                 = {{cvt|1030|lb|kg|order=flip}}<ref name="quora-M1Dquestion">{{cite web |last=Mueller |first=Thomas |title=Is SpaceX's Merlin 1D's thrust-to-weight ratio of 150+ believable? |url=https://www.quora.com/Is-SpaceXs-Merlin-1Ds-thrust-to-weight-ratio-of-150+-believable/answer/Thomas-Mueller-11 |access-date=July 9, 2015 |date=June 8, 2015 |quote=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.}}</ref>
}}'''Merlin''' is a family of [[rocket engine]]s 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 propellant]]s in a [[Gas-generator cycle|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 injector|pintle]] type that was first used in the [[Apollo Lunar Module]] landing engine ([[Descent propulsion system|LMDE]]). Propellants are fed by a single-shaft, dual-[[impeller]] [[turbopump]]. The turbopump also provides high-pressure fluid for the hydraulic [[actuator]]s, 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==
[[File:SpaceX Merlin engine.gif|thumb|left|upright=0.5|SpaceX Merlin 1A]]

===Merlin 1A===
The initial version, the '''Merlin 1A''', used an inexpensive, expendable, [[Ablation|ablatively cooled]] [[carbon-fiber-reinforced polymer]] [[Composite material|composite]] nozzle and produced {{cvt|340|kN|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,<ref name="NTmuf">{{cite news |first=Brian |last=Berger |url=http://www.space.com/missionlaunches/060719_falcon1_update.html |title=Falcon 1 Failure Traced to a Busted Nut |date=July 19, 2006 |publisher=Space.com |access-date=August 2, 2008 |archive-date=June 4, 2010 |archive-url=https://web.archive.org/web/20100604062301/http://www.space.com/missionlaunches/060719_falcon1_update.html |url-status=live }}</ref><ref name="cFfqL">{{cite news |archive-url=https://web.archive.org/web/20130303034924/http://www.spacex.com/updates_archive.php?page=0606-1206#Flight1_update |archive-date=March 3, 2013 |url-status=dead |url=http://www.spacex.com/updates_archive.php?page=0606-1206#Flight1_update |title=Findings of the Falcon return to flight board |date=July 25, 2006 |publisher=SpaceX.com}}</ref> and the second time on March 21, 2007, when it performed successfully.<ref name="MkWhi">{{cite web |title=Demo Flight 2 Flight Review Update |date=June 15, 2007 |publisher=SpaceX |archive-url=https://web.archive.org/web/20120306015017/http://www.spacex.com/F1-DemoFlight2-Flight-Review.pdf |archive-date=March 6, 2012 |url-status=dead |url=http://www.spacex.com/F1-DemoFlight2-Flight-Review.pdf }}</ref> Both times the Merlin&nbsp;1A was mounted on a [[Falcon&nbsp;1]] first stage.<ref name="merlin_wired">{{cite web |first=Loretta Hidalgo |last=Whitesides |url=http://blog.wired.com/wiredscience/2007/11/spacex-complete.html |title=SpaceX Completes Development of Rocket Engine for Falcon 1 and 9 |publisher=Wired Science |date=November 12, 2007 |access-date=February 28, 2008 |archive-date=March 23, 2008 |archive-url=https://web.archive.org/web/20080323162937/http://blog.wired.com/wiredscience/2007/11/spacex-complete.html |url-status=live }}</ref><ref name="merlin_nasaspaceflight">{{cite web |first=Braddock |last=Gaskill |url=http://www.nasaspaceflight.com/2006/08/spacex-has-magical-goals-for-falcon-9/ |title=SpaceX has magical goals for Falcon 9 |publisher=Nasa Spaceflight |date=August 5, 2006 |access-date=February 28, 2008 |archive-date=March 4, 2016 |archive-url=https://web.archive.org/web/20160304024753/http://www.nasaspaceflight.com/2006/08/spacex-has-magical-goals-for-falcon-9/ |url-status=live }}</ref>

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 (rocket engine)|Fastrac]] engine programs. The Merlin&nbsp;1A turbopump used a unique [[Friction welding|friction-welded]] main shaft, with [[Inconel]]&nbsp;718 ends and an integral aluminum RP-1 impeller in the middle. The turbopump housing was constructed using [[investment casting]]s, 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&nbsp;rpm, with a total weight of {{cvt|150|lb|kg|order=flip}}.{{citation needed|date=April 2017}}

===Merlin 1B===
The '''Merlin 1B''' rocket engine was an upgraded version of the Merlin&nbsp;1A engine. The turbopump upgrades were handled by Barber-Nichols, Inc. for SpaceX.<ref name="BNI">{{cite web |url=https://www.barber-nichols.com/products/rocket-engine-turbopumps |title=Merlin LOX/RP-1 Turbopump |publisher=Barber Nichols |access-date=May 28, 2018 |archive-date=May 29, 2018 |archive-url=https://web.archive.org/web/20180529203257/https://www.barber-nichols.com/products/rocket-engine-turbopumps |url-status=live }}</ref> It was intended for [[Falcon&nbsp;1]] launch vehicles, capable of producing {{cvt|85000|lbf|kN|order=flip}} of thrust at sea level and {{cvt|95000|lbf|kN|order=flip}} in vacuum, and performing with a specific impulse of {{cvt|261|isp|km/s}} at sea level and {{cvt|303|isp|km/s}} in vacuum.

The Merlin 1B was enhanced over the 1A with a [[turbine]] upgrade, increasing power output from {{cvt|2000|hp|kW|order=flip}} to {{cvt|2500|hp|kW|order=flip}}.<ref name="feb05update">{{cite web |archive-url=https://web.archive.org/web/20080415015952/http://www.spacex.com/updates_archive.php?page=0205-0505 |archive-date=April 15, 2008 |url-status=dead |url=http://www.spacex.com/updates_archive.php?page=0205-0505 |publisher=SpaceX |author=Elon Musk |title=Feb 2005 through May 2005 Update}}</ref> 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&nbsp;rpm and developed higher discharge pressures. Turbopump weight was unchanged at {{cvt|150|lb|kg|order=flip}}.<ref name="BNI"/>
Another notable change over the 1A was the move to [[Triethylaluminium|TEA]]–[[Triethylborane|TEB]] ([[pyrophoric]]) ignition over torch ignition.<ref name="feb05update"/>

Initial use of the Merlin 1B was to be on the [[Falcon&nbsp;9]] launch vehicle, on whose first stage there would have been a cluster of nine of these engines. Due to experience from the Falcon&nbsp;1's first flight, SpaceX moved its Merlin development to the Merlin&nbsp;1C, which is regeneratively cooled. Therefore, the Merlin&nbsp;1B was never used on a launch vehicle.<ref name="merlin_wired"/><ref name="merlin_nasaspaceflight"/>
{{clear}}

===Merlin 1C===
{{Infobox rocket engine
| name                       = Merlin 1C
| country_of_origin          = [[United States]]
| manufacturer               = [[SpaceX]]
| purpose                    = {{plainlist|
* [[Booster (rocketry)|Booster stage]] engines
* [[Upper stage]] engine
}}
| associated                 = [[Falcon 1]], [[Falcon 9]]
| status                     = Retired
| type                       = liquid
| oxidiser                   = [[LOX]]
| fuel                       = [[RP-1]]
| cycle                      = [[Gas-generator cycle|Gas-generator]]
| thrust(Vac)                = {{nowrap| {{cvt|480|kN}}<ref name="BWire_Regen"/> }}
| thrust(SL)                 = {{cvt|420|kN}}<ref name="BWire_Regen">{{cite news |url=http://home.businesswire.com/portal/site/google/index.jsp?ndmViewId=news_view&newsId=20071112005019&newsLang=en |title=SpaceX Completes Development of Merlin Regeneratively Cooled Rocket Engine |publisher=Business Wire |date=November 13, 2007 |access-date=November 12, 2007 |archive-date=January 3, 2008 |archive-url=https://web.archive.org/web/20080103164100/http://www.businesswire.com/portal/site/google/index.jsp?ndmViewId=news_view |url-status=live }}</ref>
| throttle_range             = 
| thrust_to_weight           = 96
| chamber_pressure           = {{cvt|6.77|MPa|psi}}<ref name="NSPO"/>
| specific_impulse_vacuum    = {{cvt|304.8|isp}}<ref name="NSPO">{{cite conference |url=http://www2.nspo.org.tw/ASC2008/4th%20Asian%20Space%20Conference%202008/oral/S12-11.pdf |title=Low-cost Launch Opportunities Provided by the Falcon Family of Launch Vehicles |conference=Fourth Asian Space Conference |location=Taipei |first1=Aaron |last1=Dinardi |first2=Peter |last2=Capozzoli |first3=Gwynne |last3=Shotwell |year=2008 |archive-url=https://web.archive.org/web/20120315135217/http://www2.nspo.org.tw/ASC2008/4th%20Asian%20Space%20Conference%202008/oral/S12-11.pdf |archive-date=March 15, 2012 |url-status=dead}}</ref>
| specific_impulse_sea_level = {{cvt|275|isp}}
| length                     = {{cvt|2.92|m}}<ref name="iacse.commercial-space.net">{{cite web |url=http://iacse.commercial-space.net/wp-content/uploads/2008/10/iac-08d213.pdf |title=The SpaceX Falcon 1 Launch Vehicle Flight 3 Results, Future Developments, and Falcon 9 Evolution |access-date=December 29, 2012 |archive-date=March 4, 2016 |archive-url=https://web.archive.org/web/20160304062239/http://iacse.commercial-space.net/wp-content/uploads/2008/10/iac-08d213.pdf |url-status=live }}</ref>
| diameter                   = 
| dry_weight                 = {{cvt|1380|lb|kg|order=flip}}
}}

[[File:SpaceX factory Merlin engine.jpg|thumb|left|Merlin 1C under construction at SpaceX]]
Three versions of the '''Merlin 1C''' engine were produced. The Merlin engine for Falcon&nbsp;1 had a movable turbopump exhaust assembly, which was used to provide roll control by vectoring the exhaust. The Merlin&nbsp;1C engine for the Falcon&nbsp;9 first stage is nearly identical to the variant used for the Falcon&nbsp;1, although the turbopump exhaust assembly is not movable. Finally, a Merlin&nbsp;1C [[vacuum]] variant is used on the Falcon&nbsp;9 second stage. This engine differs from the Falcon&nbsp;9 first-stage variant in that it uses a larger exhaust nozzle optimized for vacuum operation and can be throttled between 60% and 100%.<ref name="NSPO"/>

The Merlin 1C uses a [[Regenerative cooling (rocket)|regeneratively cooled]] nozzle and combustion chamber. The turbopump used is a Merlin&nbsp;1B model with only slight alterations. It was fired with a full mission duty firing of 170&nbsp;seconds in November 2007,<ref name="BWire_Regen"/> first flew on a [[List of Falcon 1 launches#Third flight|mission]] in August 2008,<ref name="sfn20080928"/> powered the "first [[private spaceflight|{{Sic|hide=y|privately|-}}developed]] liquid-fueled rocket to successfully reach orbit", [[Falcon&nbsp;1 Flight&nbsp;4]], in September 2008,<ref name="sfn20080928">{{cite web |last=Clark |first=Stephen |title=Sweet Success at Last for Falcon 1 Rocket |date=September 28, 2008 |publisher=Spaceflight Now |url=http://www.spaceflightnow.com/falcon/004/index.html |access-date=April 6, 2011 |quote=the first {{Sic|hide=y|privately|-}}developed liquid-fueled rocket to successfully reach orbit |archive-date=September 24, 2015 |archive-url=https://web.archive.org/web/20150924182644/http://www.spaceflightnow.com/falcon/004/index.html |url-status=live }}</ref> and powered the [[Falcon 9 Flight 1|Falcon&nbsp;9 on its maiden flight]] in June 2010.<ref name="msnbc20100604">{{cite news |last=Boyle |first=Alan |title=Shuttle successor succeeds in first test flight |url=http://www.nbcnews.com/id/37509776 |access-date=June 5, 2010 |newspaper=[[NBC News]] |date=June 4, 2010 |archive-date=December 21, 2019 |archive-url=https://web.archive.org/web/20191221015812/http://www.nbcnews.com/id/37509776 |url-status=dead }}</ref>

As configured for use on Falcon 1 vehicles, the Merlin&nbsp;1C had a sea-level thrust of {{cvt|78000|lbf|kN|order=flip}}, a vacuum thrust of {{cvt|90000|lbf|kN|order=flip}} and a vacuum [[specific impulse]] of {{cvt|304|isp|km/s}}. In this configuration, the engine consumed {{cvt|300|lb|kg|order=flip}} of propellant per second. Tests have been conducted with a single Merlin&nbsp;1C engine successfully running a total of 27&nbsp;minutes (counting together the duration of the various tests), which equals ten complete [[Falcon&nbsp;1]] flights.<ref name="v11rO">{{cite press release |url=http://www.spacex.com/press/2012/12/19/spacex-completes-qualification-testing-merlin-regeneratively-cooled-engine |title=SpaceX Completes Qualification Testing of Merlin Regeneratively Cooled Engine |publisher=SpaceX |date=February 25, 2008 |access-date=May 31, 2016 |archive-date=August 22, 2016 |archive-url=https://web.archive.org/web/20160822175301/http://www.spacex.com/press/2012/12/19/spacex-completes-qualification-testing-merlin-regeneratively-cooled-engine |url-status=live }}</ref> The Merlin&nbsp;1C chamber and nozzle are cooled [[Regenerative cooling (rocketry)|regeneratively]] by {{cvt|100|lb|order=flip}} per second of kerosene flow and are able to absorb {{cvt|10|MW}} of [[heat energy]].<ref name="sxua200712">{{cite web |title=Updates: December 2007 |archive-url=https://web.archive.org/web/20130405083840/http://www.spacex.com/updates_archive.php?page=121007 |archive-date=April 5, 2013 |url-status=dead |url=http://www.spacex.com/updates_archive.php?page=121007 |date=Dec 2007 |work=Updates Archive |publisher=SpaceX |access-date=December 27, 2012 |quote=(2007:) Merlin has a thrust at sea level of 95,000&nbsp;lbs, a vacuum thrust of over 108,000&nbsp;pounds, vacuum specific impulse of 304&nbsp;seconds and sea level thrust to weight ratio of 92. In generating this thrust, Merlin consumes 350&nbsp;lbs/second of propellant and the chamber and nozzle, cooled by 100&nbsp;lbs/sec of kerosene, are capable of absorbing 10&nbsp;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%.}}</ref>

A Merlin 1C was first used as part of the unsuccessful third attempt to launch a Falcon&nbsp;1. In discussing the failure, Elon Musk noted: "The flight of our first stage, with the new Merlin&nbsp;1C engine that will be used in Falcon&nbsp;9, was picture perfect."<ref name="Mwo6O">{{cite web |url=http://www.nasaspaceflight.com/2008/08/spacex-falcon-i-fails-during-first-stage-flight/ |title=SpaceX Falcon I fails during first stage flight |first=Chris |last=Bergin |author2=Davis, Matt |date=August 2, 2008 |publisher=NASAspaceflight |access-date=February 26, 2010 |archive-date=March 3, 2016 |archive-url=https://web.archive.org/web/20160303210834/http://www.nasaspaceflight.com/2008/08/spacex-falcon-i-fails-during-first-stage-flight/ |url-status=live }}</ref> The Merlin&nbsp;1C was used in the successful [[Ratsat|fourth flight]] of Falcon&nbsp;1 on September 28, 2008.<ref name="MSC">{{cite web |url=http://www.spaceflightnow.com/falcon/004/ |title=Sweet success at last for Falcon 1 rocket |last=Clark |first=Stephen |date=September 28, 2008 |publisher=Spaceflight Now |access-date=September 28, 2008 |archive-date=March 3, 2016 |archive-url=https://web.archive.org/web/20160303211418/http://www.spaceflightnow.com/falcon/004/ |url-status=live }}</ref>

On October 7, 2012, a Merlin 1C (Engine No.&nbsp;1) of the [[SpaceX CRS-1|CRS-1]] mission experienced an [[SpaceX CRS-1#Falcon 9 engine anomaly|anomaly]] at T+00:01:20, which appears on [https://www.youtube.com/watch?v=tRTYh71D9P0 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,<ref name="cQ3yS">{{cite web |last=Nelson |first=Katherine |title=SpaceX CRS-1 Mission Update |url=http://www.spacex.com/press/2012/12/19/spacex-crs-1-mission-update |publisher=SpaceX |date=October 8, 2012 |access-date=May 31, 2016 |archive-date=April 12, 2017 |archive-url=https://web.archive.org/web/20170412004145/http://www.spacex.com/press/2012/12/19/spacex-crs-1-mission-update |url-status=live }}</ref> 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.<ref name="sfn20121011">{{cite web |url=http://www.spaceflightnow.com/falcon9/004/121011orbcomm/ |title=Orbcomm craft falls to Earth, company claims total loss |publisher=Spaceflight Now |first=Stephen |last=Clark |access-date=October 11, 2012 |date=October 11, 2012 |archive-date=March 15, 2016 |archive-url=https://web.archive.org/web/20160315001856/http://spaceflightnow.com/falcon9/004/121011orbcomm/ |url-status=live }}</ref>

SpaceX was planning to develop a {{cvt|560|kN|lbf}} version of Merlin&nbsp;1C to be used in Falcon&nbsp;9 Block&nbsp;II and Falcon&nbsp;1E boosters.<ref name="ltDQy">{{cite web |archive-url=https://web.archive.org/web/20121002181416/http://www.spacex.com/Falcon1UsersGuide.pdf |archive-date=October 2, 2012 |url-status=dead |url=http://www.spacex.com/Falcon1UsersGuide.pdf |title=Falcon 1 Users Guide (Rev 7) |publisher=SpaceX |date=August 26, 2008 |page=8}}</ref> This engine and these booster models were dropped in favor of the more advanced Merlin&nbsp;1D engine and longer Falcon&nbsp;9&nbsp;v1.1 booster.[[File:Merlin 1C Vacuum engine at Hawthorne factory (2008).jpg|thumb|left|upright=0.6|Merlin 1C Vacuum engine at Hawthorne factory in 2008]]

===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 [[Regenerative cooling (rocketry)|regeneratively cooled]], while the {{convert|9|ft|m|order=flip|adj=mid|sp=us|-long}}<ref name="aw20101213"/> [[niobium alloy]]<ref name="NSPO"/> expansion nozzle is [[Radiative cooling|radiatively cooled]]. The engine delivers a vacuum thrust of {{cvt|92500|lbf|kN|order=flip}} and a vacuum [[specific impulse]] of {{cvt|342|isp|km/s}}.<ref name="f0h2i">{{cite press release |url=http://www.spacex.com/press/2012/12/19/spacex-falcon-9-upper-stage-engine-successfully-completes-full-mission-duration |title=SpaceX Falcon&nbsp;9 upper stage engine successfully completes full mission duration firing |date=March 10, 2009 |publisher=SpaceX |access-date=March 12, 2009 |archive-date=December 13, 2014 |archive-url=https://web.archive.org/web/20141213023346/http://www.spacex.com/press/2012/12/19/spacex-falcon-9-upper-stage-engine-successfully-completes-full-mission-duration |url-status=dead }}</ref> The first production Merlin Vacuum engine underwent a full-duration orbital-insertion firing (329&nbsp;seconds) of the integrated Falcon&nbsp;9 second stage on January 2, 2010.<ref name="bFIrM">{{cite video |publisher=SpaceX |url=http://spacex.com/multimedia/videos.php?id=44 |title=Full Duration Orbit Insertion Firing |date=January 2, 2010 |access-date=January 5, 2010 |archive-date=April 19, 2012 |archive-url=https://web.archive.org/web/20120419062753/http://www.spacex.com/multimedia/videos.php?id=44 |url-status=dead }}</ref> It was flown on the second stage for the inaugural Falcon&nbsp;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.<ref name="SDotA">{{cite web |url=http://www.spacex.com/press/2012/12/19/spacex-falcon-9-upper-stage-engine-successfully-completes-full-mission-duration |title=SpaceX Falcon 9 Upper Stage Engine Successfully Completes Full Mission Duration Firing |date=March 10, 2009 |publisher=SpaceX |access-date=May 31, 2016 |archive-date=December 13, 2014 |archive-url=https://web.archive.org/web/20141213023346/http://www.spacex.com/press/2012/12/19/spacex-falcon-9-upper-stage-engine-successfully-completes-full-mission-duration |url-status=dead }}</ref>

An unplanned test of a modified Merlin Vacuum engine was made in December 2010. Shortly before the scheduled [[COTS Demo Flight 1|second flight]] of the [[Falcon&nbsp;9]], two cracks were discovered in the {{convert|9|ft|m|order=flip|adj=mid|sp=us|-long}} niobium-alloy-sheet nozzle of the Merlin Vacuum engine. The engineering solution was to cut off the lower {{cvt|4|ft|order=flip}} 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 {{cvt|11000|km}} altitude.<ref name="aw20101213">{{cite news |last=Klotz |first=Irene |title=SpaceX Sees ISS Meet-up in 2011 |url=http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/awst/2010/12/13/AW_12_13_2010_p22-275434.xml |access-date=February 8, 2011 |newspaper=Aviation Week |date=December 13, 2010 |quote=The second stage went up to 11,000 km.—and that’s with the shortie skirt }}{{Dead link|date=May 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

{{clear}}

===Merlin 1D===
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.<ref name="i9MbN">{{cite web |url=https://www.nasaspaceflight.com/2012/01/spacex-testing-reusable-falcon-9-technology-this-year/ |title=SpaceX to begin testing on Reusable Falcon 9 technology this year |date=January 11, 2012 |website=NASASpaceFlight.com |language=en-US |access-date=January 11, 2020 |archive-date=January 9, 2020 |archive-url=https://web.archive.org/web/20200109110231/https://www.nasaspaceflight.com/2012/01/spacex-testing-reusable-falcon-9-technology-this-year/ |url-status=live }}</ref> In 2011, performance goals for the engine were a vacuum thrust of {{cvt|155000|lbf|kN|order=flip}}, a vacuum specific impulse (''I''<sub>sp</sub>) of {{cvt|310|isp|km/s}}, an expansion ratio of 16 (as opposed to the previous 14.5 of the Merlin&nbsp;1C) and chamber pressure in the "sweet spot" of {{cvt|1410|psi|MPa|order=flip}}. Merlin&nbsp;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%.<ref name="crin4">{{cite web |url=https://twitter.com/elonmusk/status/728753234811060224 |title=@lukealization Max is just 3X Merlin thrust and min is ~40% of 1 Merlin. Two outer engines shut off before the center does. |last=Mage |first=Buff |date=May 6, 2016 |website=@elonmusk |language=en |access-date=January 11, 2020 |archive-date=February 5, 2017 |archive-url=https://web.archive.org/web/20170205184532/https://twitter.com/elonmusk/status/728753234811060224 |url-status=live }}</ref>

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 control|servo-motor-controlled]] [[butterfly valve]]" to provide [[Vernier throttle|fine control]] of the mixture ratio.<ref name="micromo201508">{{cite web |title=Servo Motors Survive Space X Launch Conditions |url=http://www.micromo.com/applications/aerospace-defense/space-x-shuttle-launch |access-date=August 14, 2015 |publisher=MICROMO/Faulhabler |date=2015 |quote=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.' |archive-date=February 20, 2017 |archive-url=https://web.archive.org/web/20170220212836/http://www.micromo.com/applications/aerospace-defense/space-x-shuttle-launch |url-status=live }}</ref>

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 {{cvt|165000|lbf|kN|order=flip}} and a thrust-to-weight ratio of 180.<ref name="ses8teleconference">{{cite web |last=Elon |first=Musk |title=SES-8 Prelaunch Teleconference |url=http://forum.nasaspaceflight.com/index.php?topic=33335.msg1125118#msg1125118 |access-date=November 28, 2013 |archive-url=https://web.archive.org/web/20131203033340/http://forum.nasaspaceflight.com/index.php?topic=33335.msg1125118#msg1125118 |archive-date=December 3, 2013 |date=November 24, 2013 }} Also [https://soundcloud.com/matthew-clarke-30/spacex-ses-8-pre-launch at SoundCloud] {{Webarchive|url=https://web.archive.org/web/20131207132151/http://soundcloud.com/matthew-clarke-30/spacex-ses-8-pre-launch |date=December 7, 2013 }}.</ref> This version of the Merlin&nbsp;1D was used on [[Falcon&nbsp;9 Full Thrust]] and first flew on [[Falcon 9 flight 20|Flight&nbsp;20]].

In May 2016, SpaceX announced plans to further upgrade the Merlin&nbsp;1D by increasing vacuum thrust to {{cvt|914|kN|lbf}} and sea-level thrust to {{cvt|845|kN|lbf}}; according to SpaceX, the additional thrust will increase the Falcon&nbsp;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&nbsp;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&nbsp;9 Block&nbsp;5]], SpaceX announced that the {{cvt|845|kN|lbf}} goal had been achieved.<ref name="1RmZI">{{cite tweet |first=Eric |last=Berger |user=SciGuySpace |number=994649495861432321 |date=May 10, 2018 |title=Musk: Merlin rocket engine thrust increased by 8 percent, to 190,000 lbf.}}</ref> 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.<ref name="RB242">{{cite tweet |user=SpaceX | number=1760882381148623202 |date=February 23, 2024 |title=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}}</ref>

==== Anomalies ====
The March 18, 2020, launch of [[Starlink]] satellites on board a [[Falcon&nbsp;9]] experienced an early engine shutdown on ascent. The shutdown occurred 2&nbsp;minutes 22&nbsp;seconds into the flight and was accompanied with an "event" seen on camera. The rest of the Falcon&nbsp;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.<ref name="BJbif">{{Cite web |last=Clark |first=Stephen |title=Falcon 9 rocket overcomes engine failure to deploy Starlink satellites |website=Spaceflight Now |url=https://spaceflightnow.com/2020/03/18/falcon-9-rocket-overcomes-engine-failure-to-deploy-starlink-satellites/ |access-date=November 1, 2020 |language=en-US |archive-date=October 26, 2020 |archive-url=https://web.archive.org/web/20201026101330/https://spaceflightnow.com/2020/03/18/falcon-9-rocket-overcomes-engine-failure-to-deploy-starlink-satellites/ |url-status=live }}</ref><ref name="Vnfs2">{{Cite web |last=Clark |first=Stephen |title=SpaceX's Starlink network surpasses 400-satellite mark after successful launch |website=Spaceflight Now |url=https://spaceflightnow.com/2020/04/22/spacexs-starlink-network-surpasses-400-satellite-mark-after-successful-launch/ |access-date=November 1, 2020 |language=en-US |archive-date=April 30, 2020 |archive-url=https://web.archive.org/web/20200430031030/https://spaceflightnow.com/2020/04/22/spacexs-starlink-network-surpasses-400-satellite-mark-after-successful-launch/ |url-status=live }}</ref><ref name="GjzNf">{{Cite web |date=April 23, 2020 |title=Safety panel concludes May launch of commercial crew test flight is feasible |url=https://spacenews.com/safety-panel-concludes-may-launch-of-commercial-crew-test-flight-is-feasible/ |access-date=November 1, 2020 |website=SpaceNews |language=en-US}}</ref>

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.<ref>{{Cite web|last=Berger|first=Eric|date=October 28, 2020|title=How a tiny bit of lacquer grounded new Falcon 9 rockets for a month|url=https://arstechnica.com/science/2020/10/nasa-and-spacex-set-new-date-for-crew-launch-explain-merlin-engine-issue/|access-date=October 24, 2021|website=Ars Technica|language=en-us}}</ref>

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.<ref>{{cite web |last=Cao |first=Sissi |date=February 16, 2021 |title=SpaceX Fails Falcon 9 Rocket Landing in Rare Miss During Latest Starlink Mission |url=https://observer.com/2021/02/spacex-fail-landing-starlink-mission-falcon9/ |access-date=February 26, 2021 |website=Observer }}</ref>

===Merlin 1D Vacuum===
A vacuum version of the Merlin 1D engine was developed for the [[Falcon&nbsp;9&nbsp;v1.1]] and the [[Falcon Heavy]] second&nbsp;stage.<ref name="awst20110811">{{cite news |url=http://aviationweek.com/awin/spacex-unveils-plans-be-world-s-top-rocket-maker |title=SpaceX Unveils Plans To Be World's Top Rocket Maker |date=August 11, 2011 |newspaper=AviationWeek |access-date=June 28, 2014 |url-status=dead |archive-url=https://web.archive.org/web/20150621134912/http://aviationweek.com/awin/spacex-unveils-plans-be-world-s-top-rocket-maker |archive-date=June 21, 2015}}</ref> As of 2020, the thrust of the Merlin&nbsp;1D Vacuum is {{cvt|220500|lbf|kN|abbr=}}<ref name="7BFCT">{{Cite web |title=SpaceX |url=http://www.spacex.com/ |access-date=September 24, 2020 |website=SpaceX |language=en |archive-date=March 7, 2011 |archive-url=https://web.archive.org/web/20110307010135/http://www.spacex.com/ |url-status=live }}</ref> with a specific impulse of 348&nbsp;seconds,<ref name="sxf9ProductPage20130808">{{cite web |url=http://www.spacex.com/falcon9 |title=Falcon 9 |date=2017 |publisher=SpaceX |archive-url=https://web.archive.org/web/20180208031148/http://www.spacex.com/falcon9 |archive-date=February 8, 2018}}</ref> the highest specific impulse ever for a U.S. hydrocarbon rocket engine.<ref name="TDZWY">{{cite web |title=SpaceX Falcon 9 Data Sheet |url=https://www.spacelaunchreport.com/falcon9.html |website=Space Launch Report |access-date=September 21, 2019 |archive-date=December 4, 2019 |archive-url=https://web.archive.org/web/20191204173318/http://www.spacelaunchreport.com/falcon9.html |url-status=usurped}}</ref> The increase is due to the greater [[Rocket engine expansion|expansion ratio]] afforded by operating in vacuum, now 165:1 using an updated nozzle extension.<ref name="sxf9ProductPage20130808"/><ref name="f9userguide2015">{{cite web |url=http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf |title=Falcon 9 Launch Vehicle Payload User's Guide |publisher=SpaceX |version=Revision 2 |date=October 21, 2015 |access-date=November 29, 2015 |archive-date=March 14, 2017 |archive-url=https://web.archive.org/web/20170314002928/http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf |url-status=dead }}</ref>

The engine can throttle down to 39% of its maximum thrust, or {{cvt|360|kN|lbf}}.<ref name="f9userguide2015"/>
====Merlin 1D Vacuum improvements and variants====
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.<ref name=TR7>{{cite web |url=https://nextspaceflight.com/launches/details/6808 |title=Transporter 7 |access-date=March 17, 2023}}</ref><ref name=":0">{{Cite web |last=Sesnic |first=Trevor |date=July 22, 2023 |title=EchoStar 24 {{!}} Falcon Heavy |url=https://everydayastronaut.com/echostar-24-falcon-heavy/ |access-date=July 29, 2023 |website=Everyday Astronaut |language=en-US}}</ref>

==== Anomalies ====

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.<ref>{{cite web |last=Musk |first=Elon |date=June 11, 2024 |title=SpaceX X Post regarding Starlink 9-3 anomoly. |url=https://x.com/SpaceX/status/1811635860481454487 |access-date=June 11, 2024 |website=X.com }}</ref>

==Design==
===Engine control===
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&nbsp;9 launch vehicle.<ref name="aw20121118">{{cite news |last=Svitak |first=Amy |title=Dragon's "Radiation-Tolerant" Design |archive-url=https://web.archive.org/web/20131203204735/http://www.aviationweek.com/Blogs.aspx?plckBlogId=Blog%3A04ce340e-4b63-4d23-9695-d49ab661f385&plckPostId=Blog%3A04ce340e-4b63-4d23-9695-d49ab661f385Post%3Aa8b87703-93f9-4cdf-885f-9429605e14df |archive-date=December 3, 2013 |url-status=dead |url=http://www.aviationweek.com/Blogs.aspx?plckBlogId=Blog%3a04ce340e-4b63-4d23-9695-d49ab661f385&plckPostId=Blog%3a04ce340e-4b63-4d23-9695-d49ab661f385Post%3aa8b87703-93f9-4cdf-885f-9429605e14df |access-date=November 6, 2013 |newspaper=Aviation Week |date=November 18, 2012 |quote=We've got computers in the Falcon&nbsp;9, we've got three computers in one unit on each engine in the Falcon&nbsp;9, so that's 30 computers right there.}}</ref>

===Turbopump===
The Merlin LOX/RP-1 [[turbopump]] used on Merlin engines 1A–1C was designed and developed by Barber-Nichols.<ref name="bn20120610">{{cite web |title=Merlin LOX/RP-1 Turbopump |url=http://www.barber-nichols.com/products/rocket-engine-turbopumps |work=website "Products" page: Rocket Engine Turbopumps |publisher=Barber-Nichols |access-date=November 22, 2012 |archive-date=March 13, 2016 |archive-url=https://web.archive.org/web/20160313145237/http://www.barber-nichols.com/products/rocket-engine-turbopumps |url-status=live }}</ref> It spins at 36,000&nbsp;[[revolutions per minute]], delivering {{convert|10000|hp}}.<ref name="swisher-20181102">{{cite interview |first=Elon |last=Musk |author-link=Elon Musk |interviewer=[[Kara Swisher]] |url=https://www.recode.net/2018/11/2/18053428/recode-decode-full-podcast-transcript-elon-musk-tesla-spacex-boring-company-kara-swisher |title=Full Q&A: Tesla and SpaceX CEO Elon Musk on Recode Decode |format=offset 01:02:08 |date=October 13, 2018 |access-date=November 2, 2018 |quote=the turbopump on the Merlin engine runs at 36,000&nbsp;rpm, it's 10,000&nbsp;hp |archive-date=November 2, 2018 |archive-url=https://web.archive.org/web/20181102115155/https://www.recode.net/2018/11/2/18053428/recode-decode-full-podcast-transcript-elon-musk-tesla-spacex-boring-company-kara-swisher |url-status=live }}</ref>

===Gas generator===
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.<ref name="ZRUYD">Sutton, “History of Liquid Propellant Rocket Engines”, AIAA [2006].</ref>

==Production==
{{as of|2011|08}}, 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).<ref name="awst20110811"/>
By September 2013, SpaceX total manufacturing space had increased to nearly {{convert|1|e6ft2|order=flip|sp=us|abbr=off}}, 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.<ref name="sxProd20130924">{{cite web |title=Production at SpaceX |archive-url=https://web.archive.org/web/20160403055117/http://www.spacex.com/news/2013/09/24/production-spacex |archive-date=April 3, 2016 |url-status=live |url=http://www.spacex.com/news/2013/09/24/production-spacex |date=September 24, 2013 |publisher=SpaceX |access-date=September 30, 2013}}</ref> By October 2014, SpaceX announced that it had manufactured the 100th Merlin&nbsp;1D engine and that engines were now being produced at a rate of four per week, soon to be increased to five.<ref name="sxProd20141022">{{cite web |title=SpaceX Completes 100th Merlin 1D Engine |archive-url=https://web.archive.org/web/20160404045516/http://www.spacex.com/news/2014/10/16/spacex-completes-100th-merlin-1d-engine |archive-date=April 4, 2016 |url-status=live |url=http://www.spacex.com/news/2014/10/16/spacex-completes-100th-merlin-1d-engine |date=October 22, 2014 |publisher=SpaceX |access-date=October 16, 2014}}</ref><ref name="spaceref20150626">{{cite web |title=SpaceX Prepared Testimony by Jeffrey Thornburg |url=http://spaceref.com/news/viewsr.html?pid=47400 |work=SpaceRef.com |date=June 26, 2015 |quote=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. |access-date=December 27, 2015 |archive-date=March 19, 2023 |archive-url=https://web.archive.org/web/20230319120440/https://spaceref.com/status-report/spacex-prepared-testimony-by-jeffrey-thornburg/ |url-status=dead }}</ref>

In February 2016, SpaceX indicated that the company will need to build hundreds of engines a year in order to support a Falcon&nbsp;9/Falcon Heavy build rate of 30 rocket cores per year by the end of 2016.<ref name="sn20160204">{{cite news |last=Foust |first=Jeff |url=http://spacenews.com/spacex-seeks-to-accelerate-falcon-9-production-and-launch-rates-this-year/ |title=SpaceX seeks to accelerate Falcon 9 production and launch rates this year |work=[[SpaceNews (publication)|SpaceNews]] |date=February 4, 2016 |access-date=February 6, 2016 |archive-date=February 9, 2016 |archive-url=https://archive.today/20160209152801/http://spacenews.com/spacex-seeks-to-accelerate-falcon-9-production-and-launch-rates-this-year/ |url-status=live }}</ref><!-- no specific Merlin number was given in the Feb 2016 article, but nine M1D engines are used on each rocket core plus one M1Dvac used on each F9/FH second stage; implied number then (for late 2016) is something like 290/52 or 11 engines every two weeks, so roughly in line with their 5/wk mid-2015 number. -->{{update inline|date=November 2020}}

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 ==
===Merlin 2 concept===
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 {{convert|1700000|lbf|kN|abbr=on|order=flip}} of thrust at sea level and {{convert|1920000|lbf|kN|abbr=on|order=flip}} 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 [[Rocketdyne F-1|F-1 engines]] used on the [[Saturn V]].<ref>{{cite web |url=http://hobbyspace.com/nucleus/index.php?itemid=22430 |title=SpaceX Merlin 2 engine, heavy lift designs |website=Hobbyspace.com |date=July 30, 2010 |archiveurl=https://web.archive.org/web/20111013051925/http://hobbyspace.com/nucleus/index.php?itemid=22430 |archivedate=October 13, 2011 |url-status=dead}}</ref>

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".<ref name=aw20100805>{{cite news |url=http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/asd/2010/08/05/07.xml&headline=SpaceX%20Unveils%20Heavy-Lift%20Vehicle%20Plan |title=SpaceX Unveils Heavy-Lift Vehicle Plan |work=[[Aviation Week & Space Technology]] |first=Guy |last=Norris |date=August 5, 2010 |archiveurl=https://web.archive.org/web/20100821051110/http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/asd/2010/08/05/07.xml&headline=SpaceX%20Unveils%20Heavy-Lift%20Vehicle%20Plan |archivedate=August 21, 2010}}</ref> 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."<ref name=aw20100811>{{cite news |url=http://www.aviationweek.com/aw/generic/story_channel.jspchannel=space&id=news/asd/2010/08/11/07.xml&headline=Musk%20Clarifies%20SpaceX%20Position%20On%20 |title=Exploration Musk Clarifies SpaceX Position On Exploration |work=[[Aviation Week & Space Technology]] |date=August 11, 2010 |accessdate=August 16, 2010 }} {{subscription required}}</ref>

Since the original discussion, no work on any "Merlin 2" [[kerolox]]<!-- RP-1 and LOX --> 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 combustion cycle|staged cycle engine]].<ref name="Musk & Shotwell">{{cite web |url=http://www.hobbyspace.com/nucleus/index.php?itemid=31359 |title=Webcasts of Elon Musk & Gwynne Shotwell at AIAA mtg |website=Hobbyspace.com |date=August 1, 2011 |archiveurl=https://web.archive.org/web/20111102183102/http://www.hobbyspace.com/nucleus/index.php?itemid=31359 |archivedate=November 2, 2011 |url-status=dead}}</ref> 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".<ref name=fg20121017>{{cite news |url=https://www.flightglobal.com/news/articles/spacex-aims-big-with-massive-new-rocket-377687/ |title=SpaceX aims big with massive new rocket |work=[[Flightglobal]] |last=Rosenberg |first=Zach |date=October 15, 2012 |accessdate=October 17, 2012}}</ref> 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 {{convert|150|to|200|tonne|ST|lk=on}} to [[low-Earth orbit]]. The forthcoming engine currently under development by SpaceX has been named "[[Raptor (rocket engine)|Raptor]]". Raptor will use [[liquid methane]] as a fuel, and was stated as having a sea-level thrust of {{convert|1500000|lbf|kN|order=flip}}.<ref name=pbt20140219>{{cite news |url=http://www.pacbiztimes.com/2014/02/19/spacexs-propulsion-chief-elevates-crowd-in-santa-barbara/ |title=SpaceX propulsion chief elevates crowd in Santa Barbara |work=Pacific Business Times |first=Stephen |last=Nellis |date=February 19, 2014 |accessdate=February 22, 2014}}</ref> Since the initial announcement of Raptor, Musk has updated the specification to approximately {{convert|230|tonne-force|kN lbf|abbr=out}}—about one-third the original published figure—based on the results of optimizing for thrust-to-weight ratio.<ref name="reddit20150106">{{cite web |url=http://www.reddit.com/r/IAmA/comments/2rgsan/i_am_elon_musk_ceocto_of_a_rocket_company_ama/cnfpuwi |title=I am Elon Musk, CEO/CTO of a rocket company, AMA! |website=Reddit.com |first=Elon |last=Musk |date=January 6, 2015 |accessdate=January 30, 2016 |quote=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 :)}}</ref>

==See also==
{{div col}}
* [[SpaceX Draco]] – SpaceX [[Reaction Control System|RCS]] thruster for [[SpaceX Dragon]]
* [[SpaceX Kestrel]] – SpaceX small upper stage engine for Falcon 1
* [[SpaceX Raptor]] – SpaceX methane/LOX engine for the [[SpaceX Starship|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 (rocket engine)|H-1]] heritage
* [[Rocketdyne F-1]] – LOX/RP-1 main engine of the [[Saturn V]] Moon rocket
{{div col end}}

==References==
{{reflist}}

===Sources===
* {{cite web |url=https://www.wired.com/2005/01/race-for-next-space-prize-ignites/ |title=Race for Next Space Prize Ignites |publisher=Wired |first=Michael |last=Belfiore |date=January 18, 2005}}

==External links==
{{Commons category|Merlin (rocket engine)}}
* [http://www.spacex.com SpaceX official website]

{{Rocket engines}}
{{SpaceX}}

{{Use mdy dates|date=March 2025}}

{{DEFAULTSORT:Merlin (Rocket Engine)}}
[[Category:SpaceX rocket engines]]
[[Category:Rocket engines using kerosene propellant]]
[[Category:Rocket engines using the gas-generator cycle]]
[[Category:Rocket engines of the United States]]