Editing SpaceX Merlin (section)

===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>