SpaceX Merlin#Merlin 1D Vacuum

File:SpaceX Merlin engine.gif

The initial version, the Merlin 1A, used an inexpensive, expendable, ablatively cooled carbon-fiber-reinforced polymer 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,{{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 }}{{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}} and the second time on March 21, 2007, when it performed successfully.{{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 }} Both times the Merlin 1A was mounted on a Falcon 1 first stage.{{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 }}{{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 }}

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 {{cvt|150|lb|kg|order=flip}}.{{citation needed|date=April 2017}}

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.{{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 }} It was intended for Falcon 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}}.{{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}} 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 {{cvt|150|lb|kg|order=flip}}.

Another notable change over the 1A was the move to TEA–TEB (pyrophoric) ignition over torch ignition.

Initial use of the Merlin 1B was to be on the Falcon 9 launch vehicle, on whose first stage there would have been a cluster of nine of these engines. Due to experience from the Falcon 1's first flight, SpaceX moved its Merlin development to the Merlin 1C, which is regeneratively cooled. Therefore, the Merlin 1B was never used on a launch vehicle.

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{{Infobox rocket engine

| name = Merlin 1C

| country_of_origin = United States

| manufacturer = SpaceX

| purpose = {{plainlist|

• Booster stage engines
• Upper stage engine

}}

| associated = Falcon 1, Falcon 9

| status = Retired

| type = liquid

| oxidiser = LOX

| fuel = RP-1

| cycle = Gas-generator

| thrust(Vac) = {{nowrap| {{cvt|480|kN}} }}

| thrust(SL) = {{cvt|420|kN}}{{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 }}

| throttle_range =

| thrust_to_weight = 96

| chamber_pressure = {{cvt|6.77|MPa|psi}}

| specific_impulse_vacuum = {{cvt|304.8|isp}}{{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}}

| specific_impulse_sea_level = {{cvt|275|isp}}

| length = {{cvt|2.92|m}}{{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 }}

| diameter =

| dry_weight = {{cvt|1380|lb|kg|order=flip}}

}}

File:SpaceX factory Merlin engine.jpg

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%.

The Merlin 1C uses a regeneratively cooled nozzle and combustion chamber. The turbopump used is a Merlin 1B model with only slight alterations. It was fired with a full mission duty firing of 170 seconds in November 2007, first flew on a mission in August 2008, powered the "first private spaceflight liquid-fueled rocket to successfully reach orbit", Falcon 1 Flight 4, in September 2008,{{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 }} and powered the Falcon 9 on its maiden flight in June 2010.{{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 }}

As configured for use on Falcon 1 vehicles, the Merlin 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 1C engine successfully running a total of 27 minutes (counting together the duration of the various tests), which equals ten complete Falcon 1 flights.{{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 }} The Merlin 1C chamber and nozzle are cooled regeneratively by {{cvt|100|lb|order=flip}} per second of kerosene flow and are able to absorb {{cvt|10|MW}} of heat energy.{{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 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%.}}

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."{{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 }} The Merlin 1C was used in the successful fourth flight of Falcon 1 on September 28, 2008.{{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 }}

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 [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,{{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 }} 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.{{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 }}

SpaceX was planning to develop a {{cvt|560|kN|lbf}} version of Merlin 1C to be used in Falcon 9 Block II and Falcon 1E boosters.{{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}} This engine and these booster models were dropped in favor of the more advanced Merlin 1D engine and longer Falcon 9 v1.1 booster.File:Merlin 1C Vacuum engine at Hawthorne factory (2008).jpg

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 {{convert|9|ft|m|order=flip|adj=mid|sp=us|-long}} niobium alloy expansion nozzle is 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}}.{{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 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 }} 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.{{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 }} 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.{{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 }}

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 {{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.{{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 }}

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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.{{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 }} In 2011, performance goals for the engine were a vacuum thrust of {{cvt|155000|lbf|kN|order=flip}}, a vacuum specific impulse (I_sp) of {{cvt|310|isp|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 {{cvt|1410|psi|MPa|order=flip}}. 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%.{{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 }}

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.{{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 }}

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.{{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 }}. 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 {{cvt|914|kN|lbf}} and sea-level thrust to {{cvt|845|kN|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 {{cvt|845|kN|lbf}} goal had been achieved.{{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.}} 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.{{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}}

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.{{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 }}{{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 }}{{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}}

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.{{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}}

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.{{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 }}

A vacuum version of the Merlin 1D engine was developed for the Falcon 9 v1.1 and the Falcon Heavy second stage.{{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}} As of 2020, the thrust of the Merlin 1D Vacuum is {{cvt|220500|lbf|kN|abbr=}}{{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 }} with a specific impulse of 348 seconds,{{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}} the highest specific impulse ever for a U.S. hydrocarbon rocket engine.{{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}} The increase is due to the greater expansion ratio afforded by operating in vacuum, now 165:1 using an updated nozzle extension.{{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 }}

The engine can throttle down to 39% of its maximum thrust, or {{cvt|360|kN|lbf}}.

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.{{cite web |url=https://nextspaceflight.com/launches/details/6808 |title=Transporter 7 |access-date=March 17, 2023}}{{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}}

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.{{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 }}

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.{{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 9, we've got three computers in one unit on each engine in the Falcon 9, so that's 30 computers right there.}}

The Merlin LOX/RP-1 turbopump used on Merlin engines 1A–1C was designed and developed by Barber-Nichols.{{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 }} It spins at 36,000 revolutions per minute, delivering {{convert|10000|hp}}.{{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 rpm, it's 10,000 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 }}

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.Sutton, “History of Liquid Propellant Rocket Engines”, AIAA [2006].

{{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).

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.{{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}} 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.{{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}}{{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 }}

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.{{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 |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 }}{{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.

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 F-1 engines used on the Saturn V.{{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}}

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".{{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}} 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."{{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}}

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.{{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}} 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".{{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}} 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". Raptor will use liquid methane as a fuel, and was stated as having a sea-level thrust of {{convert|1500000|lbf|kN|order=flip}}.{{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}} 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.{{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 :)}}

{{div col}}

• 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

{{div col end}}

{{reflist}}

• {{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}}

{{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