Editing SpaceX Merlin (section)

===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>

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