View source for RL10

{{short description|Liquid fuel cryogenic rocket engine, typically used on rocket upper stages}}
{{Use mdy dates|date=April 2017}}
{{update|reason=Info in the improvements section is dated|date=June 2020}}
{{Infobox rocket engine
| name                       = RL10
| image                      = RL-10 rocket engine (30432256313).jpg
| image_size                 = 250
| caption                    = An RL10A-4 engine in London's [[Science Museum, London|Science Museum]]
| country_of_origin          = [[United States]]
| first_date                 = {{Start date|1962}} (RL10A-1)
| manufacturer               = [[Aerojet Rocketdyne]]
| purpose                    = [[Upper stage]] engine
| associated                 = [[Atlas (rocket family)|Atlas]]{{, }}[[Delta III]]{{, }}[[Delta IV]]{{, }}[[Saturn I]]{{, }}[[Space Launch System|SLS]]{{, }}[[Titan IIIE]]{{, }}[[Titan IV]]{{, }}[[Vulcan Centaur]]<br>'''Canceled''': [[McDonnell Douglas DC-X|DC-X]]{{, }}[[OmegA]]{{, }}[[Shuttle-Centaur]]
| status                     = In production
| type                       = liquid
| oxidiser                   = [[LOX]]
| fuel                       = {{chem2|LH2|link=LH2}}
| mixture_ratio              = 5.88:1
| cycle                      = [[Expander cycle]]
| nozzle_ratio               = 84:1 or 280:1
| thrust(Vac)                = {{convert|110.1|kN|abbr=on}}
| specific_impulse_vacuum    = {{cvt|465.5|isp}}
| length                     = {{convert|4.15|m|abbr=on}} w/ nozzle extended
| diameter                   = {{cvt|2.15|m}}
| dry_weight                 = {{cvt|301|kg}}
| used_in                    = [[Centaur (rocket stage)|Centaur]], [[Delta Cryogenic Second Stage|DCSS]], [[S-IV]]
| references                 =<ref name="EA10B2" />
| notes                      = Performance values and dimensions are for RL10B-2.
}}

The '''RL10''' is a [[liquid-fuel rocket|liquid-fuel]] [[cryogenic rocket engine]] built in the [[United States]] by [[Aerojet Rocketdyne]] that burns [[Cryogenic fuel|cryogenic]] [[liquid hydrogen]] and [[liquid oxygen]] propellants. Modern versions produce up to {{convert|110|kN|sigfig=5|abbr=on}} of [[thrust]] per engine in vacuum. RL10 versions were produced for the [[Centaur (rocket stage)|Centaur]] [[upper stage]] of the [[Atlas V]] and the [[Delta Cryogenic Second Stage|DCSS]] of the [[Delta IV]]. More versions are in development or in use for the [[Exploration Upper Stage]] of the [[Space Launch System]] and the Centaur V of the [[Vulcan (rocket)|Vulcan]] rocket.<ref name="Aerojet Rocketdyne 2" />

The [[expander cycle]] that the engine uses drives the [[turbopump]] with waste heat absorbed by the engine combustion chamber, throat, and nozzle. This, combined with the hydrogen fuel, leads to very high [[specific impulse]]s (''I''<sub>sp</sub>) in the range of {{convert|373|to(-)|470|isp|abbr=on}} in a vacuum. Mass ranges from {{convert|131|to(-)|317|kg|abbr=on}} depending on the version of the engine.<ref>{{Cite web |title=RL-10C |url=http://www.astronautix.com/r/rl-10c.html |url-status=dead |archive-url=https://web.archive.org/web/20161228011427/http://astronautix.com/r/rl-10c.html |archive-date=December 28, 2016 |access-date=2020-04-06 |website=www.astronautix.com}}</ref><ref>{{Cite web |title=RL-10A-1 |url=http://www.astronautix.com/r/rl-10a-1.html |url-status=dead |archive-url=https://web.archive.org/web/20161228075543/http://astronautix.com/r/rl-10a-1.html |archive-date=December 28, 2016 |access-date=2020-04-06 |website=www.astronautix.com}}</ref>

==History==
The RL10 was the first liquid hydrogen rocket engine to be built in the United States, with development of the engine by [[Marshall Space Flight Center]] and [[Pratt & Whitney]] beginning in the 1950s. The RL10 was originally developed as a throttleable engine for the USAF [[Lunex Project|Lunex]] lunar lander.<ref>{{Cite encyclopedia |title=Encyclopedia Astronautica—Lunex Project page |encyclopedia=Encyclopedia Astronautica |url=http://www.astronautix.com/articles/lunex.htm |last=Wade |first=Mark |archive-url=https://web.archive.org/web/20060831191541/http://www.astronautix.com/articles/lunex.htm |archive-date=August 31, 2006 |url-status=dead |df=mdy-all}}</ref>

The RL10 was first tested on the ground in 1959, at [[Pratt & Whitney]]'s Florida Research and Development Center in [[West Palm Beach, Florida]].<ref>Connors, p 319</ref><ref name="gunter.centaur">{{Cite web |title=Centaur |url=http://space.skyrocket.de/doc_stage/centaur.htm |publisher=Gunter's Space Pages}}</ref> The first successful flight took place on November 27, 1963.<ref name="Sutton 2005">{{Cite book |last=Sutton |first=George |title=History of liquid propellant rocket engines |date=2005 |publisher=American Institute of Aeronautics and Astronautics |isbn=1-56347-649-5}}</ref><ref>{{Cite web |date=November 24, 2003 |title=Renowned Rocket Engine Celebrates 40 Years of Flight |url=http://www.pratt-whitney.com/vgn-ext-templating/v/index.jsp?vgnextoid=cabbe002c2f3c010VgnVCM1000000881000aRCRD&vgnextchannel=7dfc34890cb06110VgnVCM1000004601000aRCRD&vgnextfmt=default |url-status=dead |archive-url=https://web.archive.org/web/20110614033822/http://www.pratt-whitney.com/vgn-ext-templating/v/index.jsp?vgnextoid=cabbe002c2f3c010VgnVCM1000000881000aRCRD&vgnextchannel=7dfc34890cb06110VgnVCM1000004601000aRCRD&vgnextfmt=default |archive-date=June 14, 2011 |publisher=Pratt & Whitney |df=mdy-all}}</ref> For that launch, two RL10A-3 engines powered the [[Centaur (rocket stage)|Centaur]] upper stage of an [[Atlas-Centaur|Atlas]] launch vehicle. The launch was used to conduct a heavily instrumented performance and structural integrity test of the vehicle.<ref>{{Cite web |title=Atlas Centaur 2 |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1963-047A |website=[[National Space Science Data Center]] |publisher=NASA}}</ref>

Multiple versions of this engine have been flown. The [[S-IV]] of the [[Saturn I]] used a cluster of six RL10A-3S, a version which was modified for installation on the Saturn<ref name="Norbert">{{Cite web |last=Brügge, Norbert |title=Evolution of Pratt & Whitney's cryogenic rocket engine RL-10 |url=https://www.b14643.de/Spacerockets/Specials/P&W_RL10_engine/index.htm |access-date=16 September 2022}}</ref> and the [[Titan (rocket family)|Titan]] program included [[Centaur (rocket stage)#Centaur D-1T (Titan III)|Centaur D-1T]] upper stages powered by two RL10A-3-3 Engines.<ref name="Norbert" /><ref>{{Cite web |date=1 September 1973 |title=Titan 3E/Centaur D-1T Systems Summary REPORT NO. CASD·LVP73-007 |url=https://ntrs.nasa.gov/api/citations/19750004937/downloads/19750004937.pdf |access-date=16 September 2022 |publisher=Convair & Martin Marietta Aerospace |pages=2–4}}</ref>

Four modified RL10A-5 engines were used in the [[McDonnell Douglas DC-X]].<ref name="astro-dcx">{{Cite encyclopedia |title=DCX |encyclopedia=Encyclopedia Astronautica |url=http://www.astronautix.com/lvs/dcx.htm |access-date=January 4, 2013 |last=Wade |first=Mark |archive-url=https://web.archive.org/web/20121228125150/http://www.astronautix.com/lvs/dcx.htm |archive-date=December 28, 2012 |url-status=dead}}</ref>

A flaw in the [[brazing]] of an RL10B-2 combustion chamber was identified as the cause of failure for the 4 May 1999 [[Delta III]] launch carrying the Orion-3 [[communications satellite]].<ref>{{Cite web |date=August 16, 2000 |title=Delta 269 (Delta III) Investigation Report |url=http://www.boeing.com/defense-space/space/delta/delta3/d3_report.pdf |archive-url=https://web.archive.org/web/20010616012841/http://www.boeing.com/defense-space/space/delta/delta3/d3_report.pdf |archive-date=June 16, 2001 |publisher=[[Boeing]] |id=MDC 99H0047A}}</ref>

The [[DIRECT]] version 3.0 proposal to replace [[Ares I]] and [[Ares V]] with a family of rockets sharing a common core stage recommended the RL10 for the second stage of the J-246 and J-247 launch vehicles.<ref name="direct_v3_specs">{{Cite web |title=Jupiter Launch Vehicle – Technical Performance Summaries |url=http://www.launchcomplexmodels.com/Direct/media.htm |url-status=bot: unknown |archive-url=https://web.archive.org/web/20090129072105/http://launchcomplexmodels.com/Direct/media.htm |archive-date=January 29, 2009 |access-date=July 18, 2009}}</ref>  Up to seven RL10 engines would have been used in the proposed Jupiter Upper Stage, serving an equivalent role to the [[Space Launch System]] [[Exploration Upper Stage]].

===Common Extensible Cryogenic Engine===
[[File:Common Extensible Cryogenic Engine.jpg|thumb|The CECE at partial throttle]]

In the early 2000s, NASA contracted with [[Pratt & Whitney Rocketdyne]] to develop
the Common Extensible Cryogenic Engine (CECE) demonstrator. CECE was intended to lead to RL10 engines capable of deep throttling.<ref>{{Cite web |title=Common Extensible Cryogenic Engine (CECE) |url=http://www.pw.utc.com/products/pwr/propulsion_solutions/cece.asp |url-status=dead |archive-url=https://web.archive.org/web/20120304081145/http://www.pw.utc.com/products/pwr/propulsion_solutions/cece.asp |archive-date=March 4, 2012 |publisher=United Technologies Corporation |df=mdy-all}}</ref> In 2007, its operability (with some "chugging") was demonstrated at 11:1 throttle ratios.<ref>{{Cite web |date=July 16, 2007 |title=Throttling Back to the Moon |url=https://science.nasa.gov/headlines/y2007/16jul_cece.htm |url-status=dead |archive-url=https://web.archive.org/web/20100402064331/http://science.nasa.gov/headlines/y2007/16jul_cece.htm |archive-date=April 2, 2010 |publisher=NASA |df=mdy-all}}</ref> In 2009, NASA reported successfully throttling from 104 percent thrust to eight percent thrust, a record for an expander cycle engine of this type. Chugging was eliminated by injector and propellant feed system modifications that control the pressure, temperature and flow of propellants.<ref>{{Cite web |date=January 14, 2009 |title=NASA Tests Engine Technology for Landing Astronauts on the Moon |url=http://www.nasa.gov/home/hqnews/2009/jan/HQ_09-005_Cryo_engine_test.html |publisher=NASA}}</ref> In 2010, the throttling range was expanded further to a 17.6:1 ratio, throttling from 104% to 5.9% power.<ref>{{Cite web |last=Giuliano |first=Victor |date=July 25, 2010 |title=CECE: Expanding the Envelope of Deep Throttling Technology in Liquid Oxygen/Liquid Hydrogen Rocket Engines for NASA Exploration Missions |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100032918.pdf |website=NASA Technical Reports Server}}</ref>

===Early 2010s possible successor===
In 2012 NASA joined with the US Air Force (USAF) to study next-generation upper stage propulsion, formalizing the agencies' joint interests in a new upper stage engine to replace the Aerojet Rocketdyne RL10.
{{blockquote|"We know the list price on an RL10.  If you look at cost over time, a very large portion of the unit cost of the EELVs is attributable to the propulsion systems, and the RL10 is a very old engine, and there's a lot of craftwork associated with its manufacture. ... That's what this study will figure out, is it worthwhile to build an RL10 replacement?" |author=Dale Thomas, Associated Director Technical, Marshall Space Flight Center<ref name=FG2012/>}}

From the study, NASA hoped to find a less expensive RL10-class engine for the upper stage of the [[Space Launch System]] (SLS).<ref name=FG2012/><ref name=NASA-2012-04/>

USAF hoped to replace the Rocketdyne RL10 engines used on the upper stages of the Lockheed Martin Atlas V and the Boeing Delta IV [[Evolved Expendable Launch Vehicle]]s (EELV) that were the primary methods of putting US government satellites into space.<ref name="FG2012">{{Cite web |last=Roseberg |first=Zach |date=April 12, 2012 |title=NASA, US Air Force to study joint rocket engine |url=http://www.flightglobal.com/news/articles/nasa-us-air-force-to-study-joint-rocket-engine-370660/ |access-date=June 1, 2012 |publisher=Flight Global}}</ref> A related requirements study was conducted at the same time under the Affordable Upper Stage Engine Program (AUSEP).<ref name="NASA-2012-04">{{Cite web |last=Newton |first=Kimberly |date=April 12, 2012 |title=NASA Partners With U.S. Air Force to Study Common Rocket Propulsion Challenges |url=https://www.nasa.gov/centers/marshall/news/news/releases/2012/12-040.html |url-status=dead |archive-url=https://web.archive.org/web/20170624235440/https://www.nasa.gov/centers/marshall/news/news/releases/2012/12-040.html |archive-date=June 24, 2017 |access-date=January 10, 2018 |publisher=NASA}}</ref>

===Improvements===
The RL10 has evolved over the years. The RL10B-2 that was used on the [[Delta Cryogenic Second Stage|DCSS]] had improved performance, an [[nozzle extension|extendable]] [[carbon-carbon]] nozzle, electro-mechanical [[gimbaled thrust|gimbal]]ing for reduced weight and increased reliability, and a [[specific impulse]] of {{convert|465.5|isp}}.<ref>{{Cite web |title=RL-10B-2 |url=http://www.astronautix.com/r/rl-10b-2.html |access-date=16 September 2022 |website=astronautix.com}}</ref><ref name=pwr_rl10b-2.pdf/>

As of 2016, [[Aerojet Rocketdyne]] was working toward incorporating [[additive manufacturing]] into the RL10 construction process. The company conducted full-scale, hot-fire tests on an engine that had a printed main injector in March 2016.<ref>{{Cite press release |title=Aerojet Rocketdyne Successfully Tests Complex 3-D Printed Injector in World's Most Reliable Upper Stage Rocket Engine |date=March 7, 2016 |publisher=Aerojet Rocketdyne |url=http://www.rocket.com/article/aerojet-rocketdyne-successfully-tests-complex-3-d-printed-injector-worlds-most-reliable |access-date=April 20, 2017}}</ref> Another project by Aerojet Rocketdyne was an engine with a printed [[thrust chamber]] assembly in April 2017.<ref>{{Cite press release |title=Aerojet Rocketdyne Achieves 3-D Printing Milestone with Successful Testing of Full-Scale RL10 Copper Thrust Chamber Assembly |date=April 3, 2017 |publisher=Aerojet Rocketdyne |url=http://www.rocket.com/article/aerojet-rocketdyne-achieves-3-d-printing-milestone-successful-testing-full-scale-rl10-copper |access-date=April 11, 2017}}</ref>

==Applications==

=== Current ===
*[[Centaur (rocket stage)|Centaur III]]: The single engine centaur (SEC) version uses the RL10C-1,<ref name="Aerojet Rocketdyne 2" /> while the dual engine centaur (DEC) version retains the smaller RL10A-4-2.<ref name="EA10A1" />  An Atlas V mission (SBIRS-5) marked the first use of the RL10C-1-1 version.  The mission was successful but observed unexpected vibration, and further use of the RL10C-1-1 model is on hold until the problem is better understood.<ref>{{Cite web |date=June 23, 2021 |title=ULA delays further use of enhanced upper-stage engine pending studies |url=https://spacenews.com/ula-delays-further-use-of-enhanced-upper-stage-engine-pending-studies/}}</ref> The engine was used again successfully on SBIRS-6.
*[[Centaur V]] stage: On May 11, 2018, [[United Launch Alliance]] (ULA) announced that the RL10 upper stage engine had been selected for its [[Vulcan (rocket)|Vulcan Centaur]] rocket following a competitive procurement process.<ref>{{Cite web |date=May 11, 2018 |title=United Launch Alliance Selects Aerojet Rocketdyne's RL10 Engine |url=https://www.ulalaunch.com/about/news/2018/05/11/united-launch-alliance-selects-aerojet-rocketdyne-s-rl10-engine-for-next-generation-vulcan-centaur-upper-stage |access-date=May 13, 2018 |publisher=ULA}}</ref> Early versions of the Centaur V will use the RL10C-1-1,<ref name="Aerojet Rocketdyne 2" /> but later versions will transition to the RL10C-X.<ref>{{Cite web |title=Vulcan Cutaway Poster |url=https://www.ulalaunch.com/docs/default-source/rockets/vulcancentaur.pdf?sfvrsn=10d7f58f_2 |access-date=October 15, 2021 |website=United Launch Alliance}}</ref> Vulcan flew its successful maiden flight on January 8, 2024.<ref>{{Cite news |last=Belam |first=Martin |date=2024-01-08 |title=Nasa Peregrine 1 launch: Vulcan Centaur rocket carrying Nasa moon lander lifts off in Florida – live updates |url=https://www.theguardian.com/science/live/2024/jan/08/nasa-peregrine-1-launch-rocket-moon-latest-news-updates-live |access-date=2024-01-08 |work=the Guardian |language=en-GB |issn=0261-3077}}</ref>
*[[Interim Cryogenic Propulsion Stage]]: The Interim Cryogenic Propulsion Stage or ICPS is used for the SLS and is similar to the DCSS, except that the engine is an RL10B-2 and it is adapted to fit on top of the 8.4 meter diameter core stage with four [[RS-25]] Space Shuttle Main Engines.

=== In development ===
*[[Exploration Upper Stage]]: The Exploration Upper Stage will use four RL10C-3 engines.<ref>{{Cite news |last=Sloss |first=Philip |date=March 4, 2021 |title=NASA, Boeing looking to begin SLS Exploration Upper Stage manufacturing in 2021 |url=https://www.nasaspaceflight.com/2021/03/nasa-boeing-begin-sls-eus-2021/ |access-date=October 15, 2021 |work=NASASpaceflight}}</ref>

=== Cancelled ===
* OmegA Upper Stage: In April 2018, [[Northrop Grumman Innovation Systems]] announced that two RL10C-5-1 engines would be used on [[Omega (rocket)|OmegA]] in the upper stage.<ref>{{Cite web |date=April 16, 2018 |title=RL-10 Selected for OmegA Rocket |url=http://www.rocket.com/article/rl10-selected-omega%E2%84%A2-rocket |access-date=May 14, 2018 |publisher=Aerojet Rocketdyne}}</ref>  [[Blue Origin]]'s [[BE-3U]] and [[Airbus]] Safran's [[Vinci (rocket engine)|Vinci]] were also considered before Aerojet Rocketdyne's engine was selected.  OmegA development was halted after it failed to win a National Security Space Launch contract.<ref name="SpaceNews 2020">{{Cite web |date=2020-09-09 |title=Northrop Grumman to terminate OmegA rocket program |url=https://dev.spacenews.com/northrop-grumman-to-terminate-omega-rocket-program/ |access-date=2020-11-23 |website=SpaceNews |language=en-US}}</ref>
* [[Advanced Cryogenic Evolved Stage]]: {{as of|2009}}, an enhanced version of the RL10 was proposed to power the Advanced Cryogenic Evolved Stage (ACES), a long-duration, low-boiloff extension of existing [[United Launch Alliance|ULA]] [[Centaur (rocket stage)|Centaur]] and [[Delta Cryogenic Second Stage]] (DCSS) technology for the [[Vulcan (rocket)|Vulcan]] launch vehicle.<ref name="aiaa20096566">{{Cite journal |last1=Kutter |first1=Bernard F. |last2=Zegler |first2=Frank |last3=Barr |first3=Jon |last4=Bulk |first4=Tim |last5=Pitchford |first5=Brian |date=2009 |title=Robust Lunar Exploration Using an Efficient Lunar Lander Derived from Existing Upper Stages |url=https://info.aiaa.org/tac/SMG/STTC/White%20Papers/DualThrustAxisLander(DTAL)2009.pdf |url-status=dead |journal=AIAA |archive-url=https://web.archive.org/web/20110724230154/https://info.aiaa.org/tac/SMG/STTC/White%20Papers/DualThrustAxisLander%28DTAL%292009.pdf |archive-date=July 24, 2011 |access-date=March 9, 2011 |ref=AIAA 2009–6566}}</ref>  Long-duration ACES technology is intended to support [[geosynchronous]], [[cislunar]], and [[interplanetary mission|interplanetary]] missions. Another possible application is as in-space [[propellant depot]]s in [[low Earth orbit|LEO]] or at {{L2}} that could be used as way-stations for other rockets to stop and refuel on the way to beyond-LEO or interplanetary missions. Cleanup of [[space debris]] was also proposed.<ref name="aiaa20100902">{{Cite web |last1=Zegler |first1=Frank |last2=Bernard Kutter |date=September 2, 2010 |title=Evolving to a Depot-Based Space Transportation Architecture |url=http://www.ulalaunch.com/site/docs/publications/DepotBasedTransportationArchitecture2010.pdf |url-status=dead |archive-url=https://web.archive.org/web/20111020010301/http://www.ulalaunch.com/site/docs/publications/DepotBasedTransportationArchitecture2010.pdf |archive-date=October 20, 2011 |access-date=January 25, 2011 |website=AIAA SPACE 2010 Conference & Exposition |publisher=AIAA |quote=''ACES design conceptualization has been underway at ULA for many years. It leverages design features of both the Centaur and Delta Cryogenic Second Stage (DCSS) upper stages and intends to supplement and perhaps replace these stages in the future. ...'' |df=mdy-all}}</ref>

==Table of versions==
{{sticky header}}
{| class="wikitable sortable sticky-header"
|-
! Version
! Status
! First flight
! Dry mass
! Thrust
! [[Specific impulse|''I''<sub>sp</sub>]] ([[exhaust velocity|''v''{{sub|e}}]]), {{abbr|vac.|vacuum}}
! Length
! Nozzle diameter
! [[Thrust-to-weight ratio|T:W]]
! {{abbr|O:F|Oxidiser to fuel ratio}}
! [[Expansion ratio]]
! Chamber pressure
! Burn time
! Associated stage
! Notes
|-
| {{nowrap|RL10A-1}}
| Retired
| 1962
| {{cvt|131|kg}}
| {{cvt|15000|lb-f|kN|order=flip}}
| {{cvt|425|isp}}
| {{cvt|1.73|m}}
| {{cvt|1.53|m}}
| 52:1
| 5:1
| 40:1
| {{cvt|20.7|bar}}
| 430&nbsp;s
| [[Centaur (rocket stage)|Centaur A]]
| Prototype<br /><ref name="Norbert" /><ref name="EA10A1">{{Cite encyclopedia |title=RL-10A-1 |encyclopedia=Encyclopedia Astronautica |url=http://www.astronautix.com/engines/rl10a1.htm |access-date=February 27, 2012 |last=Wade |first=Mark |date=November 17, 2011 |archive-url=https://web.archive.org/web/20111115155200/http://www.astronautix.com/engines/rl10a1.htm |archive-date=November 15, 2011 |url-status=dead |df=mdy-all}}</ref><ref name="S2S" /><ref name="GSPAC">{{Cite web |title=Atlas Centaur |url=http://space.skyrocket.de/doc_lau/atlas_centaur.htm |access-date=February 29, 2012 |publisher=Gunter's Space Page}}</ref>
|-
| {{nowrap|RL10A-3C}}
| Retired
| 1963
| {{cvt|131|kg}}
| {{cvt|65.6|kN}}
| {{cvt|444|isp}}
| {{cvt|2.49|m}}
| {{cvt|1.53|m}}
| 51:1
| 5:1
| 57:1
| {{cvt|32.75|bar}}
| 470&nbsp;s
| [[Centaur (rocket stage)|Centaur]] B/C/D/E
|<ref name="EA10A3">{{Cite encyclopedia |title=RL-10A-3 |encyclopedia=Encyclopedia Astronautica |url=http://www.astronautix.com/engines/rl10a3.htm |access-date=February 27, 2012 |last=Wade |first=Mark |date=November 17, 2011 |archive-url=https://web.archive.org/web/20111206225154/http://www.astronautix.com/engines/rl10a3.htm |archive-date=December 6, 2011 |url-status=dead |df=mdy-all}}</ref>
|-
| {{nowrap|RL10A-3S}}
| Retired
| 1964
| {{cvt|296|lb|kg|order=flip}}
| {{cvt|15,000|lb-f|kN|order=flip}}
| {{cvt|427|isp}}
| {{cvt|1.73|m}}
|
| 51:1
| 5:1
| 40:1
| {{cvt|20.7|bar}}
|
| [[S-IV]]
|<ref name="Norbert" /><ref name="Sutton 2005" />
|-
| {{nowrap|RL10A-4}}
| Retired
| 1992
| {{cvt|168|kg}}
| {{cvt|92.5|kN}}
| {{cvt|449|isp}}
| {{cvt|2.29|m}}
| {{cvt|1.17|m}}
| 56:1
| 5.5:1
| 84:1
| {{cvt|39.8|bar}}
| 392&nbsp;s
| [[Centaur (rocket stage)|Centaur IIA]]
|<ref name="Norbert" /><ref name="EA10A4">{{Cite encyclopedia |title=RL-10A-4 |encyclopedia=Encyclopedia Astronautica |url=http://www.astronautix.com/engines/rl10a4.htm |access-date=February 27, 2012 |last=Wade |first=Mark |date=November 17, 2011 |archive-url=https://web.archive.org/web/20111115172045/http://www.astronautix.com/engines/rl10a4.htm |archive-date=November 15, 2011 |url-status=dead |df=mdy-all}}</ref>
|-
| {{nowrap|RL10A-5}}
| Retired
| 1993
| {{cvt|143|kg}}
| {{cvt|64.7|kN}}
| {{cvt|373|isp}}
| {{cvt|1.07|m}}
| {{cvt|1.02|m}}
| 46:1
| 6:1
| 4:1
| {{cvt|39.8|bar}}
| 127&nbsp;s
| [[McDonnell Douglas DC-X|DC-X]]
|<ref name="Norbert" /><ref name="EA10A5">{{Cite encyclopedia |title=RL-10A-5 |encyclopedia=Encyclopedia Astronautica |url=http://www.astronautix.com/engines/rl10a5.htm |access-date=February 27, 2012 |last=Wade |first=Mark |date=November 17, 2011 |archive-url=https://web.archive.org/web/20111115141830/http://www.astronautix.com/engines/rl10a5.htm |archive-date=November 15, 2011 |url-status=dead |df=mdy-all}}</ref>
|-
| {{nowrap|RL10B-2}}
| Retired
| 1998
| {{cvt|664|lb|order=flip}}
| {{Convert|24750|lb-f|kN|abbr=on|order=flip}}
| {{Convert|465.5|isp|abbr=on}}
|Stowed: {{cvt|7|ft|2.5|in|m|1|order=flip}}<hr>Deployed: {{cvt|13|ft|7.5|in|m|2|order=flip}}
| {{cvt|7|ft|0.5|in|m|2|order=flip}}
| 40:1
| 5.88:1
| 280:1
| {{cvt|44.12|bar}}
| 5m: 1,125&nbsp;s<hr>4m: 700&nbsp;s
| [[Delta Cryogenic Second Stage|DCSS]]<br />[[Interim Cyrogenic Propulsion Stage|ICPS]]
| Succeeded by RL10C-2.<ref name="EA10B2">{{Cite encyclopedia |title=RL-10B-2 |encyclopedia=Encyclopedia Astronautica |url=http://www.astronautix.com/engines/rl10b2.htm |access-date=February 27, 2012 |last=Wade |first=Mark |date=November 17, 2011 |archive-url=https://web.archive.org/web/20120204144940/http://www.astronautix.com/engines/rl10b2.htm |archive-date=February 4, 2012 |url-status=dead |df=mdy-all}}</ref><ref>{{Cite web |title=Delta IV Launch Services User's Guide, June 2013 |url=https://www.ulalaunch.com/docs/default-source/rockets/delta-iv-user's-guide.pdf |access-date=15 March 2018 |website=ULA Launch}}</ref>
|-
| {{nowrap|RL10A-4-1}}
| Retired
| 2000
| {{cvt|167|kg}}
| {{cvt|99.1|kN}}
| {{cvt|451|isp}}
| {{cvt|1.78|m}}
| {{cvt|1.53|m}}
| 61:1
|
| 84:1
| {{cvt|42|bar}}
| 740&nbsp;s
| [[Centaur (rocket stage)|Centaur IIIA]]
|<ref name="Norbert" /><ref name="EA10A41">{{Cite encyclopedia |title=RL-10A-4-1 |encyclopedia=Encyclopedia Astronautica |url=http://www.astronautix.com/engines/rl10a41.htm |access-date=February 27, 2012 |last=Wade |first=Mark |date=November 17, 2011 |archive-url=https://web.archive.org/web/20111117134046/http://www.astronautix.com/engines/rl10a41.htm |archive-date=November 17, 2011 |url-status=dead |df=mdy-all}}</ref>
|-
| {{nowrap|RL10A-4-2}}
| Active
| 2002
| {{cvt|370|lb|order=flip}}
| {{Convert|22300|lb-f|kN|abbr=on|order=flip}}
| {{Convert|451|isp|abbr=on}}
| {{cvt|7|ft|6|in|m|2|order=flip}}
| {{cvt|3|ft|10|in|m|2|order=flip}}
| 61:1
|
| 84:1
| {{cvt|42|bar}}
| 740&nbsp;s
| [[Centaur (rocket stage)|Centaur IIIB]]<br />Centaur SEC<br />Centaur DEC
| Used for Starliner launches.<ref name="Norbert" /><ref name="EA10A42">{{Cite encyclopedia |title=RL-10A-4-2 |encyclopedia=Encyclopedia Astronautica |url=http://www.astronautix.com/engines/rl10a42.htm |access-date=February 27, 2012 |last=Wade |first=Mark |date=November 17, 2011 |archive-url=https://web.archive.org/web/20120130143126/http://www.astronautix.com/engines/rl10a42.htm |archive-date=January 30, 2012 |url-status=dead |df=mdy-all}}</ref><ref name="Aerojet Rocketdyne" />
|-
| {{nowrap|RL10B-X}}
| Cancelled
| {{n/a}}
| {{cvt|317|kg}}
| {{cvt|93.4|kN}}
| {{cvt|470|isp}}
|
| {{cvt|1.53|m}}
| 30:1
|
| 250:1
|
| 408&nbsp;s
| [[Centaur (rocket stage)|Centaur B-X]]
|<ref name="EA10BX">{{Cite encyclopedia |title=RL-10B-X |encyclopedia=Encyclopedia Astronautica |url=http://www.astronautix.com/engines/rl10bx.htm |access-date=February 27, 2012 |last=Wade |first=Mark |date=November 17, 2011 |archive-url=https://web.archive.org/web/20111115150728/http://www.astronautix.com/engines/rl10bx.htm |archive-date=November 15, 2011 |url-status=dead |df=mdy-all}}</ref>
|-
| CECE
| Demonstrator project
| {{n/a}}
| {{cvt|160|kg}}
| {{cvt|15000|lb-f|kN|order=flip}}, throttle to 5–10%
| >{{cvt|445|isp}}
| {{cvt|1.53|m}}
|
| 43:1
|
|
|
|
|N/A
|<ref name="PWRCECE">{{Cite web |title=Commons Extensible Cryogenic Engine |url=http://www.pw.utc.com/products/pwr/propulsion_solutions/cece.asp |url-status=dead |archive-url=https://web.archive.org/web/20120304081145/http://www.pw.utc.com/products/pwr/propulsion_solutions/cece.asp |archive-date=March 4, 2012 |access-date=February 28, 2012 |publisher=Pratt & Whitney Rocketdyne |df=mdy-all}}</ref><ref>{{Cite web |title=Common Extensible Cryogenic Engine – Aerojet Rocketdyne |url=http://www.rocket.com/common-extensible-cryogenic-engine |url-status=dead |archive-url=https://web.archive.org/web/20141112144157/http://www.rocket.com/common-extensible-cryogenic-engine |archive-date=November 12, 2014 |access-date=April 8, 2018 |website=www.rocket.com}}</ref>
|-
| {{nowrap|RL10C-1}}
| Retired
| 2014
| {{cvt|420|lb|order=flip}}
| {{Convert|22820|lb-f|kN|abbr=on|order=flip}}
| {{Convert|449.7|isp|abbr=on}}
| {{cvt|7|ft|2|in|m|2|order=flip}}
| {{cvt|4|ft|9|in|m|2|order=flip}}
| 57:1
| 5.5:1
| 130:1
|
| 
| [[Centaur (rocket stage)|Centaur SEC]]<br />Centaur DEC
| Succeeded by RL-10C-1-1.<ref name="CPS">{{Cite web |date=August 5, 2011 |title=Cryogenic Propulsion Stage |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110015783.pdf |access-date=October 11, 2014 |publisher=NASA}}</ref><ref>{{Cite web |title=Atlas-V with RL10C powered Centaur |url=http://forum.nasaspaceflight.com/index.php?topic=34891.0 |access-date=April 8, 2018 |website=forum.nasaspaceflight.com}}</ref><ref>{{Cite web |title=Evolution of Pratt & Whitney's cryogenic rocket engine RL-10 |url=http://b14643.de/Spacerockets/Diverse/P&W_RL10_engine/index.htm |url-status=dead |archive-url=https://web.archive.org/web/20160303141931/http://b14643.de/Spacerockets/Diverse/P%26W_RL10_engine/index.htm |archive-date=March 3, 2016 |access-date=February 20, 2016 |df=mdy-all}}</ref><ref name="Aerojet Rocketdyne">{{Cite web |title=RL10 Engine |url=http://www.rocket.com/rl10-engine |url-status=dead |archive-url=https://web.archive.org/web/20170430183058/http://www.rocket.com/rl10-engine |archive-date=April 30, 2017 |access-date=March 13, 2016 |publisher=Aerojet Rocketdyne}}</ref>
|-
| {{nowrap|RL10C-1-1}}
| Active
| 2021
| {{cvt|415|lb|order=flip}}
| {{Convert|23825|lb-f|kN|abbr=on|order=flip}}
| {{Convert|453.8|isp|abbr=on}}
| {{cvt|8|ft|0.7|in|m|2|order=flip}}
| {{cvt|5|ft|2|in|m|2|order=flip}}
| 57:1
| 5.5:1
| 155:1
|
|Atlas: 842&nbsp;s<hr>Vulcan: 1,077&nbsp;s
| Centaur SEC<br />Centaur V
| Current standard engine for Atlas V and Vulcan Centaur.<ref name="Norbert" /><ref name="Aerojet Rocketdyne 2">{{Cite web |title=Aerojet Rocketdyne RL10 Propulsion System |url=http://rocket.com/sites/default/files/documents/Capabilities/PDFs/RL10_data_sheet.pdf |url-status=dead |archive-url=https://web.archive.org/web/20220130111530/https://rocket.com/sites/default/files/documents/Capabilities/PDFs/RL10_data_sheet.pdf |archive-date=30 January 2022 |website=Aerojet Rocketdyne}}</ref>
|-
| {{nowrap|RL10C-2-1}}
| Retired
| 2022
| {{cvt|664|lb|order=flip}}
| {{Convert|24750|lb-f|kN|abbr=on|order=flip}}
| {{Convert|465.5|isp|abbr=on}}
|Stowed: {{cvt|7|ft|2.5|in|m|1|order=flip}}<hr>Deployed: {{cvt|13|ft|7.5|in|m|2|order=flip}}
| {{cvt|7|ft|0.5|in|m|2|order=flip}}
| 37:1
| 5.88:1
| 280:1
|
|
| [[Delta Cryogenic Second Stage|DCSS]]
|<ref>{{Cite web |title=RL10 Engine {{!}} Aerojet Rocketdyne |url=https://www.rocket.com/space/liquid-engines/rl10-engine |access-date=2020-06-19 |website=www.rocket.com}}</ref><ref>{{Cite web |last=Graham |first=William |date=2022-09-24 |title=Last West Coast Delta IV Heavy launches with NROL-91 |url=https://www.nasaspaceflight.com/2022/09/delta-iv-nrol-91/ |access-date=2023-08-29 |website=NASASpaceFlight.com |language=en-US}}</ref>
|-
| {{nowrap|RL10C-2}}
| Delivered, not yet flown
| 2026 (expected)
| 
| {{cvt|24750|lb-f|kN|order=flip}}
| {{cvt|465.5|isp|}}
| Stowed: {{cvt|7|ft|2.5|in|m|1|order=flip}}<hr>Deployed: {{cvt|13|ft|7.5|in|m|2|order=flip}}
| 2.15 m (7&nbsp;ft 1 in)
| 37:1
| 5.88:1
| 280:1
|
|
| [[Interim Cyrogenic Propulsion Stage|ICPS]]
| Conversion of C-3<ref name="sls-update">{{Cite web |date=15 April 2020 |title=NASA'S SPACE LAUNCH SYSTEM BEGINS MOVING TO THE LAUNCH SITE |url=https://ntrs.nasa.gov/api/citations/20205000944/downloads/Askins%20JANNAF%202020%20PAPER%2004152020.docx.pdf |url-status=live |archive-url=https://web.archive.org/web/20211013024817/https://ntrs.nasa.gov/api/citations/20205000944/downloads/Askins%20JANNAF%202020%20PAPER%2004152020.docx.pdf |archive-date=13 October 2021 |access-date=24 May 2023 |publisher=NASA}}</ref>
|-
| {{nowrap|RL10C-3}}
| Delivered, not yet flown
| 2028 (expected)
| {{cvt|508|lb|order=flip}}
| {{Convert|24340|lb-f|kN|abbr=on|order=flip}}
| {{Convert|460.1|isp|abbr=on}}
| {{cvt|10|ft|4.3|in|m|2|order=flip}}
| {{cvt|6|ft|1|in|m|2|order=flip}}
| 48:1
| 5.7:1
| 215:1
|
|
| [[Exploration Upper Stage|EUS]]
|<ref name="Norbert" /><ref name="Aerojet Rocketdyne 2" /><ref name="sls-update" />
|-
| {{nowrap|RL10C-5-1}}
| Cancelled
| {{n/a}}
| {{cvt|188|kg}}
| 106&nbsp;kN (23,825&nbsp;{{lbf}})
| {{cvt|453.8|isp}}
| 2.46 m (8&nbsp;ft 0.7&nbsp;in)
| 1.57 m (4&nbsp;ft 9&nbsp;in)
| 57:1
| 5.5:1
|
|
|
| [[Omega (rocket)|OmegA]]
|<ref name="Aerojet Rocketdyne 2" /><ref name="SpaceNews 2020" />
|-
| {{nowrap|RL10C-X}}
| {{nowrap|In development}}
| 2025 (expected)
| {{cvt|231|kg}}
| 107.29&nbsp;kN (24,120&nbsp;{{lbf}})
| {{cvt|460.9|isp}}
| 3.31 m (130.4&nbsp;in)
| 1.87 m (73.7&nbsp;in)
| 47.29:1
| 5.5:1
|
|
|
| [[Centaur (rocket stage)#Centaur V|Centaur V]]
| Additive manufacturing<ref>{{Cite web |title=Aerojet Rocketdyne Secures Its Largest RL10 Engine Contract From ULA |url=https://ir.aerojetrocketdyne.com/news-releases/news-release-details/aerojet-rocketdyne-secures-its-largest-rl10-engine-contract |access-date=2022-04-16 |website=www.aerojetrocketdyne.com}}</ref><ref>{{Cite web |title=RL10 Engine &#124; Aerojet Rocketdyne |url=https://www.rocket.com/space/liquid-engines/rl10-engine |access-date=2022-05-07 |publisher=Rocket.com}}</ref>
|}

==Partial specifications==
===All versions===
* Contractor: Pratt & Whitney
* Propellants: liquid oxygen, liquid hydrogen<ref name="pwr_rl10b-2.pdf" />
* Design: [[expander cycle]]<ref name="Sutton1998">{{Cite journal |last1=Sutton |first1=A. M. |last2=Peery |first2=S. D. |last3=Minick |first3=A. B. |date=January 1998 |title=50K expander cycle engine demonstration |url=https://apps.dtic.mil/sti/pdfs/ADA397948.pdf |url-status=live |journal=AIP Conference Proceedings |volume=420 |pages=1062–1065 |bibcode=1998AIPC..420.1062S |doi=10.1063/1.54719 |archive-url=https://web.archive.org/web/20130408132823/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA397948 |archive-date=April 8, 2013}}</ref>
* Ignition: electric spark.<ref>{{cite web |last1=McCutcheon |first1=Kimble D. |title=U.S. Manned Rocket Propulsion Evolution, Part 8.21: The Pratt & Whitney RL10 Engine |url=https://enginehistory.org/Rockets/RPE08.21/RPE08.21.shtml |website=Aircraft Engine Historical Society |access-date=28 August 2024}}</ref>

=== RL10A ===
[[File:RL-10 rocket engine.jpg|thumb|300px|RL10A information and overview]]
* Thrust (altitude): 15,000{{nbsp}}[[pound-force|lb-f]] (66.7&nbsp;kN)<ref name="S2S">{{Cite book |last=Bilstein |first=Roger E. |url=https://history.nasa.gov/SP-4206/ch5.htm |title=Stages to Saturn; A Technological History of the Apollo/Saturn Launch Vehicles |date=1996 |publisher=NASA History Office |location=Washington, D.C. |chapter=Unconventional Cryogenics: RL-10 and J-2 |access-date=December 2, 2011}}</ref>
* [[Specific impulse]]: {{convert|433|isp}}
* Engine weight, [[dry weight|dry]]: 298&nbsp;lb (135&nbsp;kg)<!-- https://web.archive.org/web/20020826015127/http://www.astronautix.com/engines/rl10.htm says 288 lb/131 kg -->
* Height: 68{{nbsp}}in (1.73{{nbsp}}m)
* Diameter: 39{{nbsp}}in (0.99{{nbsp}}m)
* Nozzle expansion ratio: 40 to 1
* Propellant flow: 35&nbsp;lb/s (16&nbsp;kg/s)
* Vehicle application: [[Saturn I]], [[S-IV]] 2nd stage, 6 engines
* Vehicle application: [[Centaur (rocket stage)|Centaur]] upper stage, 2 engines

===RL10B-2===
[[File:Second stage of a Delta IV Medium rocket.jpg|thumb|Second stage of a Delta IV Medium rocket featuring an RL10B-2 engine]]
* Thrust (altitude): 24,750&nbsp;lbf (110.1&nbsp;kN)<ref name="pwr_rl10b-2.pdf">{{Cite web |date=2009 |title=RL10B-2 |url=http://www.pw.utc.com/products/pwr/assets/pwr_rl10b-2.pdf |url-status=dead |archive-url=https://web.archive.org/web/20120326211303/http://www.pw.utc.com/products/pwr/assets/pwr_rl10b-2.pdf |archive-date=March 26, 2012 |access-date=January 29, 2012 |publisher=[[Pratt & Whitney Rocketdyne]] |df=mdy-all}}</ref>
* [[Specific impulse]]: {{convert|465.5|isp|}}<ref name="pwr_rl10b-2.pdf" />
* Engine weight, dry: 664&nbsp;lb (301.2&nbsp;kg)<ref name="pwr_rl10b-2.pdf" />
* Height: 163.5{{nbsp}}in (4.14{{nbsp}}m)<ref name="pwr_rl10b-2.pdf" />
* Diameter: 84.5{{nbsp}}in (2.21{{nbsp}}m)<ref name="pwr_rl10b-2.pdf" />
* Expansion ratio: 280 to 1
* Mixture ratio: 5.88 to 1 oxygen:hydrogen mass ratio<ref name="pwr_rl10b-2.pdf" />
* Propellant flow: fuel, 7.72&nbsp;lb/s (3.5&nbsp;kg/s); oxidizer 45.42&nbsp;lb/s (20.6&nbsp;kg/s)<ref name="pwr_rl10b-2.pdf" />
* Vehicle application: [[Delta III]], Delta IV second stage (1 engine)

== Gallery ==
<gallery mode="packed">
File:Rl-10engine.jpg|RL10A-1
File:RL-10 with cutaway.JPG|RL10A-3S
File:500px photo (140471371).jpeg|RL10A-4
File:RL-10onstand.jpg|RL10A-4-2
File:RL-10B-2 engine during nozzle extension testing.jpg|RL10B-2
</gallery>

==Engines on display==
* An RL10A-1 is on display at the [[New England Air Museum]], [[Windsor Locks, Connecticut]]<ref>{{Cite web |title=Pratt & Whitney RL10A-1 Rocket Engine |url=http://neam.org/index.php?option=com_content&view=article&id=1112 |url-status=dead |archive-url=https://web.archive.org/web/20140427060823/http://neam.org/index.php?option=com_content&view=article&id=1112 |archive-date=27 April 2014 |website=New England Air Museum}}</ref>
* An RL10 is on display at the [[Museum of Science and Industry (Chicago)|Museum of Science and Industry]], [[Chicago]], [[Illinois]]<ref name="histspace">{{Cite web |title=Photos of Rocket Engines |url=http://historicspacecraft.com/rocket_engines.html |access-date=April 26, 2014 |website=Historic Spacecraft}}</ref>
* An RL10A-1 is on display at the [[Cernan Earth and Space Center]], [[River Grove]], [[Illinois]]
* An RL10 is on display at the [[U.S. Space & Rocket Center]], [[Huntsville, Alabama]]<ref name="histspace" />
* An RL10 is on display at [[Southern University]], [[Baton Rouge, Louisiana]]<ref>{{Cite press release |title=Pratt & Whitney Rocketdyne Donates Model of Legendary Rl10 Rocket Engine to Southern University |date=November 3, 2006 |publisher=Pratt & Whitney Rocketdyne |url=http://www.prnewswire.com/news-releases/pratt--whitney-rocketdyne-donates-model-of-legendary-rl10-rocket-engine-to-southern-university-55982567.html |last1=Colaguori |first1=Nancy |last2=Kidder |first2=Bryan |url-status=dead |archive-url=https://web.archive.org/web/20140427115735/http://www.prnewswire.com/news-releases/pratt--whitney-rocketdyne-donates-model-of-legendary-rl10-rocket-engine-to-southern-university-55982567.html |archive-date=27 April 2014 |agency=PR Newswire}}</ref>
* Two RL10 engines are on display at [[US Space Walk of Fame]], [[Titusville, Florida]]<ref>{{Cite web |title=American Space Museum & Space Walk of Fame |url=https://www.facebook.com/SpaceWalkOfFame/photos/pcb.10152534325180820/10152534320660820/?type=1&theater |url-access=limited |archive-url=https://ghostarchive.org/iarchive/facebook/175507880819/10152534320660820 |archive-date=2022-02-26 |access-date=April 8, 2018 |website=www.facebook.com}}{{cbignore}}</ref>
* An RL10 is on display at the [[Cox Science Center and Aquarium]], [[West Palm Beach, Florida]].
* An RL10 is on display in the Aerospace Engineering Department, Davis Hall at [[Auburn University]].{{citation needed|date=April 2017}}
* An RL10A-4 is on display at the [[Science Museum, London|Science Museum]] in [[London]], UK.<ref>{{Cite web |title=RL-10 engine {{!}} Science Museum Group Collection |url=https://collection.sciencemuseumgroup.org.uk/objects/co40018/rl-10-engine-engine-power-producing-equipment |access-date=2024-04-12 |website=collection.sciencemuseumgroup.org.uk |language=en}}</ref>
* An RL10 is on display at the [[Museum of Life and Science]] in [[Durham, North Carolina|Durham]], NC
* An RL10 is on display at the [[San Diego Air & Space Museum]] in [[San Diego]], CA.<ref>{{Cite web |title=San Diego Air & Space Museum - Historical Balboa Park, San Diego |url=https://sandiegoairandspace.org/collection/item/aerojet-rocketdyne-rl10-engine |access-date=2024-04-12 |website=sandiegoairandspace.org}}</ref>
* An RL10B-2 is on display outside the [[Discovery Cube Orange County]] in [[Santa Ana, CA]].

==See also==
*[[Spacecraft propulsion]]
*[[RL60]]
*[[MARC-60]]
*[[RD-0146]]
*[[XCOR Aerospace#ULA liquid hydrogen large engine development project|XCOR/ULA aluminum alloy nozzle engine]], under development in 2011

==References==
{{Reflist|30em}}

==Bibliography==
* {{Cite book |last=Connors |first=Jack |title=The Engines of Pratt & Whitney: A Technical History |date=2010 |publisher=[[American Institute of Aeronautics and Astronautics]] |isbn=978-1-60086-711-8 |location=Reston. Virginia}}

==External links==
{{Commons category|RL10 (rocket engine)|RL10}}
*[https://web.archive.org/web/20120204144940/http://www.astronautix.com/engines/rl10b2.htm RL10B-2 at Astronautix]
*[http://www.spaceflightnow.com/news/n0708/16rl10valve/ Spaceflight Now article]
*[http://www.spaceflightnow.com/news/n0901/26altair/ Spaceflight Now article]

{{Pratt & Whitney aeroengines}}
{{Rocket engines}}
{{Atlas rockets}}
{{Thor and Delta rockets}}

[[Category:North American Aviation]]
[[Category:Rocket engines of the United States]]
[[Category:Rocket engines using hydrogen propellant]]
[[Category:Rocket engines using the expander cycle]]
[[Category:Rocketdyne engines]]
[[Category:Space Launch System]]