RS-68#Variants

One of the main goals of the RS-68 program was to produce a simple engine that would be cost-effective when used for a single launch. To achieve this, the RS-68 has 80% fewer parts than the multi-launch RS-25 Space Shuttle Main Engine (SSME).[http://www.pwrengineering.com/dataresources/PropulsionForThe21stCentury-RS-68.doc "AIAA 2002-4324, Propulsion for the 21st Century—RS-68"] {{webarchive | url=https://web.archive.org/web/20090319075127/http://www.pwrengineering.com/dataresources/PropulsionForThe21stCentury-RS-68.doc | date=19 March 2009}}. AIAA, 8–10 July 2002. The adverse consequences of this simplicity were a significantly lower thrust-to-weight ratio and a 10% lower specific impulse compared to the SSME. The benefit of this simplicity is the RS-68's reduced construction cost.

The RS-68 was developed at Rocketdyne Propulsion and Power, located in Canoga Park, Los Angeles, California, where the SSME was manufactured. It was designed to power the Delta IV Evolved Expendable Launch Vehicle (EELV). The initial development engines were assembled at the nearby Santa Susana Field Laboratory where the Saturn V's Rocketdyne F-1 engines were developed and tested for the Apollo missions to the Moon. The initial testing of the RS-68 occurred at the Air Force Research Laboratory (AFRL), Edwards Air Force Base, California, and later at NASA's Stennis Space Center.{{Cite web |date=23 April 2001 |title=Boeing Tests RS-68 Rocket Engine (Apr. 24) |url=https://www.defense-aerospace.com/boeing-tests-rs-68-rocket-engine-apr-24/ |access-date=26 June 2023 |website=Defense Aerospace}}{{Cite press release |title=Boeing Delta IV CBC/RS-68 Engine Successfully Completes Test Program |date=9 May 2001 |publisher=Boeing |url=https://boeing.mediaroom.com/2001-05-09-Boeing-Delta-IV-CBC-RS-68-Engine-Successfully-Completes-Test-Program |access-date=26 June 2023}} The RS-68 was certified in December 2001 for use on Delta IV rockets.{{Cite press release |title=Rocketdyne RS-68 Engine Certified for Boeing Delta IV |date=19 December 2001 |publisher=Boeing |url=http://www.boeing.com/news/releases/2001/q4/nr_011219s.html |url-status=dead |archive-url=https://web.archive.org/web/20121010153432/http://www.boeing.com/news/releases/2001/q4/nr_011219s.html |archive-date=10 October 2012}}

An RS-68 was part of each Delta IV Common Booster Core. The largest of the launch vehicles, the Delta IV Heavy, used three CBCs mounted together.{{Cite web |title=Atlas V and Delta IV Technical Summary |url=https://www.ulalaunch.com/docs/default-source/rockets/atlas-v-and-delta-iv-technical-summary.pdf}}

The engine produced {{convert|758000|lbf|kN|sigfig=3|lk=on}} in a vacuum and {{convert|663000|lbf|kN|sigfig=3}} at sea level. The engine's mass was {{convert|14560|lb|kg}}. With this thrust, the engine had a thrust-to-weight ratio of 51.2 and a specific impulse of {{convert|410|isp}} in a vacuum and {{convert|365|isp}} at sea level.{{Cite web |title=United Launch Alliance Delta IV Heavy |url=https://www.ulalaunch.com/rockets/delta-iv}} The RS-68 was gimbaled hydraulically and was capable of throttling between 58% and 102% thrust.[http://www.engineeringatboeing.com/dataresources/PropulsionForThe21stCentury-RS-68.doc Boeing white paper on RS-68 development] {{webarchive | url=https://web.archive.org/web/20070415124430/http://www.engineeringatboeing.com/dataresources/PropulsionForThe21stCentury-RS-68.doc | date=15 April 2007}}

The RS-68A is an updated version of the RS-68, with increased specific impulse and thrust (to over {{convert|700000|lbf|kN|sigfig=2}} at sea level).{{Cite press release |title=United Launch Alliance First RS-68A Hot-Fire Engine Test a Success |date=25 September 2008 |publisher=United Launch Alliance |url=https://www.ulalaunch.com/about/news/2008/09/25/ula-first-rs-68a-hot-fire-engine-test-a-success |quote=Currently, the RS-68 engine can deliver more than 660,000 pounds of sea level thrust and the upgraded RS-68A will increase this to more than 700,000 pounds. The RS-68A also improves on the specific impulse, or fuel efficiency, of the RS-68. |access-date=10 April 2023}} The first launch on 29 June 2012, from the Cape Canaveral Air Force Station used three RS-68A engines mounted in a Delta IV Heavy rocket.{{Cite press release |title=United Launch Alliance Upgraded Delta IV Heavy rocket successfully Launches Second Payload in Nine Days for the National Reconnaissance Office |date=29 June 2012 |publisher=United Launch Alliance |url=http://www.ulalaunch.com/united-launch-alliance-upgraded-delta-iv.aspx?title=United+Launch+Alliance+Upgraded+Delta+IV+Heavy+Rocket++Successfully+Launches+Second+Payload+in+Nine+Days+for+the++National+Reconnaissance+Office&archived=True&Category=all&Page=22 |url-status=live |archive-url=https://web.archive.org/web/20160820020437/http://www.ulalaunch.com/united-launch-alliance-upgraded-delta-iv.aspx?title=United+Launch+Alliance+Upgraded+Delta+IV+Heavy+Rocket++Successfully+Launches+Second+Payload+in+Nine+Days+for+the++National+Reconnaissance+Office&archived=true&category=all&page=22 |archive-date=20 August 2016}}

The RS-68 was retired as of the last Delta IV Heavy flight in April 2024.

In 2006, NASA announced an intention to use five RS-68 engines instead of SSMEs on the planned Ares V. NASA chose the RS-68 because of its lower cost, about $20 million per engine including the cost of NASA's upgrades. The upgrades included a different ablative nozzle to accommodate a longer burn, a shorter start sequence, hardware changes to limit free hydrogen at ignition, and a reduction in the amount of helium used during countdown and flight. Thrust and specific impulse increases would occur under a separate upgrade program for the Delta IV rocket.{{Cite press release |title=NASA's Exploration Systems Progress Report |date=18 May 2006 |publisher=National Aeronautics and Space Administration |url=http://www.nasa.gov/home/hqnews/2006/may/HQ_06226_RS-68_ENGINE.html |access-date=30 May 2006 |url-status=live |archive-url=https://web.archive.org/web/20120405050707/http://www.nasa.gov/home/hqnews/2006/may/HQ_06226_RS-68_ENGINE.html |archive-date=5 April 2012}} Later, the Ares V was changed to use six RS-68 engines, designated the RS-68B.{{Cite web |title=Overview: Ares V Cargo Launch Vehicle |url=http://www.nasa.gov/mission_pages/constellation/ares/aresV/index.html |archive-url=https://web.archive.org/web/20080926214451/http://www.nasa.gov/mission_pages/constellation/ares/aresV/index.html |archive-date=26 September 2008 |access-date=30 September 2008 |publisher=National Aeronautics and Space Administration}} Ares V was dropped as part of the cancellation of the Constellation program in 2010.{{Cite news |last=Amos |first=Jonathan |date=11 October 2010 |title=Obama signs Nasa up to new future |url=https://www.bbc.com/news/science-environment-11518049 |access-date=7 June 2019 |agency=BBC news}} NASA's current successor heavy-lift vehicle, the Space Launch System, uses four RS-25 engines instead.{{Cite web |title=Space Launch System Factsheet |url=https://www.nasa.gov/sites/default/files/atoms/files/0080_sls_fact_sheet_10092018.pdf |access-date=7 June 2019 |publisher=National Aeronautics and Space Administration |archive-date=13 May 2019 |archive-url=https://web.archive.org/web/20190513024103/https://www.nasa.gov/sites/default/files/atoms/files/0080_sls_fact_sheet_10092018.pdf |url-status=dead }}

In 2008, it was reported that the RS-68 needed over 200 changes to receive a human-rating certification.{{Cite web |date=27 September 2008 |title=United Launch Alliance First RS-68A Hot-Fire Engine Test a Success |url=http://forum.nasaspaceflight.com/index.php?topic=14446.msg318877#msg318877 |url-status=live |archive-url=https://web.archive.org/web/20180328171435/http://forum.nasaspaceflight.com/index.php?topic=14446.msg318877#msg318877 |archive-date=28 March 2018 |website=NASAspaceflight.com}} NASA has stated that those changes include health monitoring, removal of the fuel-rich environment at liftoff, and improving the robustness of its subsystems.{{Cite web |title=Frequently Asked Questions, question 3 |url=http://www.nasa.gov/exploration/about/faq.html#3 |url-status=live |archive-url=https://web.archive.org/web/20100112151132/http://www.nasa.gov/exploration/about/faq.html#3 |archive-date=12 January 2010 |publisher=National Aeronautics and Space Administration ESMD}}{{Cite web |last=Bearden |first=David A. |last2=Skratt |first2=John P. |last3=Hart |first3=Matthew J. |date=1 June 2009 |title=Human Rated Delta IV Heavy Study Constellation Impacts |url=http://www.nasa.gov/pdf/377875main_081109%20Human%20Rated%20Delta%20IV.pdf |url-status=live |archive-url=https://web.archive.org/web/20170228145012/https://www.nasa.gov/pdf/377875main_081109%20Human%20Rated%20Delta%20IV.pdf |archive-date=28 February 2017 |publisher=National Aeronautics and Space Administration |page=8}}

• RS-68 is the original version. It produces {{convert|663000|lbf|kN|lk=on|sigfig=3}} thrust at sea level.{{Cite web |date=October 2005 |title=RS-68 Propulsion System |url=http://www.pw.utc.com/StaticFiles/Pratt%20&%20Whitney%20New/Media%20Center/Assets/1%20Static%20Files/Docs/pwr_RS-68.pdf |url-status=dead |archive-url=https://web.archive.org/web/20180714135306/http://www.pw.utc.com/StaticFiles/Pratt%20%26%20Whitney%20New/Media%20Center/Assets/1%20Static%20Files/Docs/pwr_RS-68.pdf |archive-date=14 July 2018 |access-date=7 April 2019 |publisher=Pratt & Whitney Rocketdyne}}
• RS-68A is an improved version. It produces {{convert|705000|lbf|kN|abbr=on|sigfig=3}} thrust at sea level and {{convert|800000|lbf|kN|abbr=on|sigfig=3}} thrust in a vacuum.{{Cite web |title=P&W Successfully Completes Hot-Fire Test on 2nd RS-68A Certi |url=http://www.asdnews.com/news/32037/P&W_Successfully_Completes_Hot-Fire_Test_on_2nd_RS-68A_Certification_Engine.htm |url-status=live |archive-url=https://web.archive.org/web/20110725014233/http://www.asdnews.com/news/32037/P%26W_Successfully_Completes_Hot-Fire_Test_on_2nd_RS-68A_Certification_Engine.htm |archive-date=25 July 2011 |access-date=25 April 2018 |website=asdnews.com}} Its specific impulse in a vacuum is {{convert|411.9|isp}}.{{Cite web |date=June 2013 |title=Delta IV User's Guide |url=http://www.ulalaunch.com/uploads/docs/Launch_Vehicles/Delta_IV_Users_Guide_June_2013.pdf |url-status=live |archive-url=https://web.archive.org/web/20140710005717/http://www.ulalaunch.com/uploads/docs/Launch_Vehicles/Delta_IV_Users_Guide_June_2013.pdf |archive-date=10 July 2014 |access-date=13 July 2014 |publisher=United Launch Alliance}} Certification was completed in April 2011.{{Cite web |title=RS-68A {{!}} L3Harris® Fast. Forward. |url=https://www.l3harris.com/all-capabilities/rs-68a |access-date=6 February 2024 |website=www.l3harris.com |language=en}}
• RS-68B was a proposed upgrade to be used in the Ares V launch vehicle for NASA's Constellation program. The Ares V was to use six RS-68B engines on a {{convert|10|m}} diameter core stage, along with two 5.5-segment solid rocket boosters. It was later determined that the ablative nozzle of the RS-68 was poorly suited to this multi-engine environment, causing reduced engine efficiency and extreme heating at the base of the vehicle.{{Cite web |date=June 2013 |title=The engines that refused to retire – RS-25s prepare for SLS testing |url=http://www.nasaspaceflight.com/2013/06/engines-refused-retire-rs-25s-prepare-sls-testing/ |url-status=live |archive-url=https://web.archive.org/web/20170830160316/https://www.nasaspaceflight.com/2013/06/engines-refused-retire-rs-25s-prepare-sls-testing/ |archive-date=30 August 2017 |website=nasaspaceflight.com}}

• Comparison of orbital rocket engines
• M-1 (rocket engine)
• National Launch System
• Rocketdyne J-2
• RS-83
• Space Launch Initiative
• TR-106

{{reflist}}

{{Commons category|RS-68 (rocket engine)}}

• [https://www.rocket.com/space/liquid-engines/rs-68a Aerojet Rocketdyne's RS-68 page]
• [https://web.archive.org/web/20020626221732/http://www.astronautix.com/engines/rs68.htm RS-68 page on Astronautix.com]
• {{Cite conference |last=Wood |first=B.K. |year=2002 |title=Propulsion for the 21st Century—RS-68 |url=http://www.pwrengineering.com/dataresources/PropulsionForThe21stCentury-RS-68.doc |format=doc |conference=38th Joint Liquid Propulsion Conference |location=Indianapolis, Indiana |publisher=AIAA |archive-url=https://web.archive.org/web/20090319075127/http://www.pwrengineering.com/dataresources/PropulsionForThe21stCentury-RS-68.doc |archive-date=19 March 2009 |url-status=dead}}

{{Rocket engines}}

{{Project Constellation}}

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Category:Rocketdyne engines

Category:Rocket engines using the gas-generator cycle

Category:Rocket engines of the United States