Editing SpaceX Merlin (section)

{{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.