Editing RL10 (section)

==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>