View source for Centaur (rocket stage)

{{Short description|Family of rocket stages which can be used as a space tug}}
{{Use mdy dates|date=June 2019}}
{{Infobox rocket stage
| image   = Landsat-9_Centaur_1_(cropped).jpg
| caption =  A single-engine Centaur III being raised for mating to an [[Atlas V]] rocket

| name         = Centaur
| manufacturer = [[United Launch Alliance]]
| rockets      =
:Current
::[[Atlas V]]: Centaur III
::[[Vulcan (rocket)|Vulcan]]: Centaur V
:Historical
::[[Atlas-Centaur]]
::[[Saturn I]]
::[[Titan III]]
::[[Titan IV]]
::[[Atlas II]]
::[[Atlas III]]
::[[Shuttle-Centaur]] (not flown)

| derivatives = [[Advanced Cryogenic Evolved Stage]] (cancelled, not flown)

| status   =  Active
| launches = 273 {{As of|2024|10|lc=y}}<ref name="GSPCentaur"/>
| success  = 254
| fail     = 15 <!--As of October 2024, 5 of these were partial failures-->
| noburn   = 4
| first    = {{Start date and age|1962|05|9}}
| last     =

| stagedata = 
{{Infobox rocket/stage
| name     = Centaur III
| length   = {{convert|12.68|m|in|abbr=on}}<ref name="Altas5Users">{{cite web |title=Atlas V Launch Services User's Guide |url=http://www.ulalaunch.com/uploads/docs/AtlasVUsersGuide2010.pdf |publisher=United Launch Alliance |access-date=July 9, 2015 |date=March 2010 |archive-url=https://web.archive.org/web/20120306002859/http://www.ulalaunch.com/site/docs/product_cards/guides/AtlasVUsersGuide2010.pdf |archive-date=March 6, 2012 |url-status=dead }}</ref>
| diameter = {{convert|3.05|m|in|abbr=on}}
| propmass = {{convert|20830|kg|lbs|abbr=on}}
| empty    = {{convert|2247|kg|lbs|abbr=on}}, single engine<br/>{{convert|2462|kg|lbs|abbr=on}}, dual engine
| engines  = {{nowrap|1 × [[RL10|RL10A]]}}, {{nowrap|2 × RL10A}} or {{nowrap|1 × [[RL10|RL10C]]}}
| thrust   = {{convert|99.2|kN|lbf|abbr=on}}, per engine
| SI       = {{convert|450.5|isp}}
| burntime = 904 seconds <!--521 3-Burn GSO total-->
  | fuel           = [[Liquid oxygen|LOX]] / {{chem2|LH2|link=Liquid hydrogen}}
}}
{{Infobox rocket/stage
  | name           = Centaur V
  | length         = {{Unbulleted indent list
    | {{Abbr|CV-L|Centaur V Low Earth Orbit}}: {{cvt|10.66|m|0}}
	| {{Abbr|CV-HE|Centaur V High Energy}}: {{cvt|12.6|m}}<ref name="Kanayama 2022">{{Cite news |last=Kanayama |first=Lee |date=May 9, 2022 |title=As Centaur turns 60 years old, ULA prepares to evolve Centaur V |url=https://www.nasaspaceflight.com/2022/05/centaur-turns-60/ |url-status=live |archive-url=https://web.archive.org/web/20230801020510/https://www.nasaspaceflight.com/2022/05/centaur-turns-60/ |archive-date=August 1, 2023 |access-date=May 29, 2022 |work=[[NASASpaceFlight.com]]}}</ref>
	}} 
  | diameter     = {{cvt|5.4|m|1}}
  | empty        = {{Abbr|CV-HE|Centaur V High Energy}}: {{cvt|7100|kg}}<ref name=Raketen/>
  | gross        = {{Abbr|CV-HE|Centaur V High Energy}}: {{cvt|53600|kg}}<ref name=Raketen/>
  | propmass       = <!-- propellant mass carried by a single stage in kilograms, use {{cvt|PROPMASS|kg}}, optional -->
  | engines        = {{Unbulleted indent list
   | 2 × [[RL10|RL10C]]<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 |url-status=live |archive-url=https://web.archive.org/web/20180512130637/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 |archive-date=May 12, 2018 |access-date=May 13, 2018 |publisher=ULA}}</ref>
   | 2 × [[RL10|RL10E]] ''(planned upgrade)''<ref name="Foust 2023">{{Cite news |last=Foust |first=Jeff |date=November 28, 2023 |title=New RL10 engine to be introduced on Vulcan in 2025 |url=https://spacenews.com/new-rl10-engine-to-be-introduced-on-vulcan-in-2025/ |access-date=December 23, 2024 |work=SpaceNews |language=en-US}}</ref>
   }}
  | thrust         = {{Unbulleted indent list
   | RL10C: {{cvt|{{#expr:22890*2}}|lb-f|kN|order=flip}}
   | RL10E: {{cvt|{{#expr:24120*2}}|lb-f|kN|order=flip}}<ref name="RL10 Datasheet">{{Cite web |title=RL10 Propulsion System Datasheet |url=https://www.l3harris.com/sites/default/files/2024-07/l3harris-ar-rl10-spec-sheet.pdf |access-date=December 23, 2024 |publisher=L3Harris}}</ref>
   }}
  | SI             = {{Unbulleted indent list
   | RL10C: {{cvt|453.8|isp}}
   | RL10E: {{cvt|460.9|isp}}<ref name="RL10 Datasheet" />
   }}
  | burntime       = {{Abbr|CV-HE|Centaur V High Energy}}: 1,077 seconds<!--Three-Burn Direct Inject GEO total--><ref name="Vulcan User Guide">{{Cite web |date=October 16, 2023 |editor-last=Peller |editor-first=Mark |editor2-last=Wentz |editor2-first=Gary L. |editor3-last=Burkholder |editor3-first=Tom |title=Vulcan Launch Systems User's Guide |url=https://www.ulalaunch.com/docs/default-source/default-document-library/2023_vulcan_user_guide.pdf |url-status=live |archive-url=https://web.archive.org/web/20240924213601/https://www.ulalaunch.com/docs/default-source/default-document-library/2023_vulcan_user_guide.pdf |archive-date=September 24, 2024 |access-date=October 1, 2024 |website=[[United Launch Alliance]]}}</ref>
  | fuel           = [[Liquid oxygen|LOX]] / {{chem2|LH2|link=Liquid hydrogen}}
  
  }}
}}

The '''Centaur''' is a family of rocket-propelled upper stages that has been in use since 1962. It is currently produced by [[United Launch Alliance]] (ULA) in two main versions. The {{convert|3.05|m|ft|0|abbr=on}} diameter '''Centaur III''' (also known as the Common Centaur) serves as the second stage of the retiring [[Atlas V]] rocket, and the {{convert|5.4|m|ft|1|abbr=on}} diameter '''Centaur V''' is used as the second stage of the [[Vulcan Centaur]] rocket.<ref name="ars20171211">{{cite web |last=Berger |first=Eric |date=December 11, 2018 |title=Getting Vulcan up to speed: Part one of our interview with Tory Bruno |url=https://arstechnica.com/science/2018/12/talking-rockets-with-tory-bruno-vulcan-the-moon-and-hat-condiments/ |access-date=December 12, 2018 |website=Ars Technica |quote=Centaur 3 (which flies on the Atlas V rocket) is 3.8 meters in diameter. The very first Centaur we fly on Vulcan will go straight to 5.4 meters in diameter.}}</ref><ref name="ulaVulcanCentaur">{{cite web |author=<!--Not stated--> |date=2018 |title=Vulcan Centaur |url=https://www.ulalaunch.com/rockets/vulcan-centaur |access-date=December 12, 2018 |publisher=United Launch Alliance}}</ref> Centaur was the first rocket stage to use [[Hydrolox|hydrolox propellant]]—[[liquid hydrogen]] (LH<sub>2</sub>) and [[liquid oxygen]] (LOX)—a high-energy combination well suited for upper stages but difficult to handle because both propellants must be stored at extremely low [[Cryogenics|cryogenic]] temperatures.<ref>{{cite book |author1=Helen T. Wells |url=https://www.history.nasa.gov/SP-4402/contents.htm |title=Origin of NASA Names |author2=Susan H. Whiteley |author3=Carrie E. Karegeannes |publisher=NASA Science and Technical Information Office |page=11 |chapter=Launch Vehicles |quote=because it proposed to make first use of the theoretically powerful but problem-making liquid hydrogen as fuel. |access-date=March 29, 2019 |chapter-url=https://www.history.nasa.gov/SP-4402/ch1.htm |archive-url=https://web.archive.org/web/20190714113745/https://history.nasa.gov/SP-4402/contents.htm |archive-date=July 14, 2019 |url-status=dead}}</ref>

==Characteristics==
Centaur stages are built around [[stainless steel]] pressure-stabilized [[Balloon tank|balloon propellant tanks]]<ref name="nasa">[https://www.nasa.gov/centers/glenn/about/history/centaur.html NASA.gov]</ref> with {{cvt|0.020|in|mm|order=flip|adj=on}} thick walls. It can lift payloads of up to {{convert|19000|kg|lb|abbr=on}}.<ref name="bruno_centaur_tweet">{{cite tweet |number=1131638302761578496 |user=ToryBruno |title=Yes. The Amazing Centaur in its dual RL10 configuration. |date=23 May 2019}}</ref> The thin tank walls minimize mass, maximizing overall stage performance.<ref>{{cite book |last1=Stiennon |first1=Patrick J. G. |last2=Hoerr |first2=David M. |date=July 15, 2005 |title=The Rocket Company |publisher=[[American Institute of Aeronautics and Astronautics]] |page=93 |isbn=1-56347-696-7}}</ref>

A common [[Bulkhead (partition)|bulkhead]] separates the LOX and LH<sub>2</sub> tanks, further reducing weight. The bulkhead consists of two stainless steel skins separated by a fiberglass honeycomb, which limits heat transfer between the extremely cold LH<sub>2</sub> and the comparatively warmer LOX.<ref name="Dawson2004">{{cite book |last1=Dawson |first1=Virginia P. |url=https://history.nasa.gov/SP-4230.pdf |title=Taming Liquid Hydrogen: The Centaur Upper Stage Rocket 1958–2002 |last2=Bowles |first2=Mark D. |publisher=NASA |year=2004}}</ref>{{rp|19}}

The main propulsion system consists of one or two [[RL10]] engines made by [[Aerojet Rocketdyne]].<ref name="nasa" /> The stage is capable of up to multiple restarts, constrained by propellant supply, orbital lifetime, and mission requirements. In combination with insulation on the propellant tanks, this enables Centaur to perform multi-hour coast phases and multiple engine burns for complex orbital insertions.<ref name="bruno_centaur_tweet" />

The stage is equipped with a reaction control system (RCS), which also provides [[Ullage#Rocketry|ullage]].

On the Centaur III the RCS system consists of twenty [[hydrazine]] [[monopropellant rocket|monopropellant]] thrusters, arranged in two two-thruster pods and four four-thruster pods. Approximately {{cvt|340|lb|kg|order=flip}} of hydrazine is stored in two bladder tanks and fed to the thrusters by pressurized [[helium]], which also supports some main engine functions.<ref name="TCUSV" />

On some Centaur V stages, the hydrazine system is replaced with hydrolox thrusters supplied by gaseous propellants from the main tanks.<ref name="Tory Infographic Centaur Variants">{{Cite tweet |number=1961123896847147380 |user=torybruno |title=ICYMI: Great discussion with Amanda Bacchetti, one of our Directors for Vulcan Development – we talked reuse, Centaur V development and our focus on long duration, including ACES |first=Tory |last=Bruno |author-link=Tory Bruno |date=August 28, 2025 |access-date=September 2, 2025}}</ref><ref>{{Cite tweet |number=1245046200010559488 |user=torybruno |title=Good catch. It should say H2/O2. A thruster that uses propellant from the main tank instead of a stand alone system |first=Tory |last=Bruno |author-link=Tory Bruno |date=March 31, 2020 |access-date=September 2, 2025}}</ref>

== Current versions ==
{{As of|2025}}, two Centaur variants are in use: Centaur III on Atlas V,<ref>{{cite web | url=https://aerospace.org/article/atlas-v-ussf-12-launch-delivers-two-national-security-space-payloads-geo | title=Atlas V USSF-12 Launch Delivers Two National Security Space Payloads to GEO &#124; the Aerospace Corporation }}</ref><ref>{{cite web | url=https://www.space.com/boeing-starliner-crew-flight-test-launch | title=Boeing's Starliner launches astronauts for 1st time in historic liftoff (Photos, video) | website=[[Space.com]] | date=June 5, 2024 }}</ref> and Centaur V on Vulcan Centaur.<ref>{{cite web | url=https://www.nasaspaceflight.com/2024/01/vulcan-launch-peregrine-inaugural-flight/ | title=Vulcan successfully launches Peregrine lunar lander on inaugural flight | date=January 7, 2024 }}</ref> All of the many other Centaur variants have been retired.<ref name="aiaa20100902">{{cite web|last=Zegler |first=Frank |title=Evolving to a Depot-Based Space Transportation Architecture |url=http://www.ulalaunch.com/site/docs/publications/DepotBasedTransportationArchitecture2010.pdf |work=AIAA SPACE 2010 Conference & Exposition |publisher=AIAA |access-date=2011-01-25 |author2=Bernard Kutter |date=2010-09-02 |url-status=dead |archive-url=https://web.archive.org/web/20111020010301/http://www.ulalaunch.com/site/docs/publications/DepotBasedTransportationArchitecture2010.pdf |archive-date=2011-10-20 }}</ref><ref name="sn20150413">{{cite news |last1=Gruss |first1=Mike |date=2015-04-13 |title=ULA's Vulcan Rocket To be Rolled out in Stages |url=http://spacenews.com/ulas-vulcan-rocket-to-be-rolled-out-in-stages/ |access-date=2015-04-17 |work=SpaceNews}}</ref>

=== Centaur III/Common Centaur ===
[[File:Centaur upper stage being lifted.jpg|thumb|upright|Single Engine Centaur (SEC) stage]]
Common Centaur is the upper stage of the [[Atlas V]] rocket.<ref name="TCUSV" />  Earlier Common Centaurs were propelled by the RL10-A-4-2 version of the RL-10. Since 2014, Common Centaur has flown with the [[RL10]]-C-1 engine, which is shared with the [[Delta Cryogenic Second Stage]], to reduce costs.<ref name="NROL35Updates">{{cite web|url=http://www.spaceflight101.net/atlas-v---nrol-35-launch-updates.html|title=Atlas V NROL-35 Launch Updates|publisher=Spaceflight 101|date=December 13, 2014|access-date=September 9, 2016|archive-date=March 5, 2017|archive-url=https://web.archive.org/web/20170305001847/http://www.spaceflight101.net/atlas-v---nrol-35-launch-updates.html|url-status=dead}}</ref><ref name="SFINROL35">{{cite web|url=http://www.spaceflightinsider.com/missions/defense/new-rl10c-engine-debuts-classified-nrol-35-launch/|title=new RL10C engine debuts on classified NROL-35 launch|author=Rae Botsford End|publisher=Spaceflight Insider|date=December 13, 2014|access-date=September 9, 2016}}</ref> The Dual Engine Centaur (DEC) configuration will continue to use the smaller RL10-A-4-2 to accommodate two engines in the available space.<ref name="SFINROL35" />

The Atlas V can fly in multiple configurations, but only one affects the way Centaur integrates with the booster and fairing: the {{convert|5.4|m|ft|abbr=on}} diameter Atlas V [[payload fairing]] attaches to the booster and encapsulates the upper stage and payload, routing fairing-induced aerodynamic loads into the booster. If the {{convert|4|m|ft|abbr=on}} diameter payload fairing is used, the attachment point is at the top (forward end) of Centaur, routing loads through the Centaur tank structure.<ref>{{Cite web|url=https://www.ulalaunch.com/docs/default-source/rockets/atlasv-cutaway.pdf?sfvrsn=3bf92929_4|title=Atlas V Cutaway|date=2019|website=United Launch Alliance}}</ref>

The latest Common Centaurs can accommodate secondary payloads using an Aft Bulkhead Carrier attached to the engine end of the stage.<ref>{{cite web|url=http://www.ulalaunch.com/uploads/docs/Launch_Vehicles/ABC_Users_Guide_2014.pdf|title=Aft Bulkhead Carrier Auxiliary Payload User's Guide|publisher=United Launch Alliance|access-date=September 10, 2016|archive-url=https://web.archive.org/web/20170305011653/http://www.ulalaunch.com/uploads/docs/Launch_Vehicles/ABC_Users_Guide_2014.pdf|archive-date=March 5, 2017|url-status=dead}}</ref>

==== Single Engine Centaur (SEC) ====
Most payloads launch on Single Engine Centaur (SEC) with one [[RL10]]. This is the variant for all normal flights of the Atlas V (indicated by the last digit of the naming system, for example Atlas V 421).

==== Dual Engine Centaur (DEC) ====
A dual engine variant with two RL-10 engines is available, but only for launching the [[CST-100 Starliner]] crewed spacecraft. The higher thrust of two engines allows a gentler ascent with more horizontal velocity and less vertical velocity, which reduces deceleration to survivable levels in the event of a [[Launch escape system|launch abort]] and ballistic reentry occurring at any point in the flight.<ref>{{cite web |url=https://www.rocket.com/dual-rl10-engine-centaur-debuts-atlas-v-ensure-safe-launch-astronauts-low-earth-orbit |title=DUAL RL10 ENGINE CENTAUR DEBUTS ON ATLAS V TO ENSURE SAFE LAUNCH OF ASTRONAUTS TO LOW EARTH ORBIT |publisher=Aerojet Rocket}}</ref>

=== Centaur V ===
[[File:Centaur V (CLPS PM-1 Astrobotic-ULA Rollout for Launch) (cropped).jpg|thumb|upright|Centaur V stage on [[Vulcan Centaur]] rocket carrying [[Peregrine Mission One|Peregrine lunar lander]]]]

Centaur V is the upper stage of the [[Vulcan Centaur|Vulcan]] launch vehicle developed by United Launch Alliance (ULA) beginning in 2014 to meet the requirements of the [[National Security Space Launch]] (NSSL) program.<ref>{{cite web |date=2015-04-13 |title=America, meet Vulcan, your next United Launch Alliance rocket |url=http://www.denverpost.com/business/ci_27905093/america-meet-vulcan-your-next-united-launch-alliance |access-date=2015-04-17 |work=Denver Post}}</ref> 

==== Development ====
ULA initially intended the Centaur V, an upgraded version of the Common Centaur,<ref name="sn20171010">{{cite news |author=Bruno, Tory |date=October 10, 2017 |title=Building on a successful record in space to meet the challenges ahead |url=http://spacenews.com/op-ed-building-on-a-successful-record-in-space-to-meet-the-challenges-ahead/ |publisher=Space News}}</ref> to only be used on a interim basis until a transition to the [[Advanced Cryogenic Evolved Stage]] (ACES) planned after the first few years of flights.<ref name="sn20150413" /><ref name="sfn20150414">{{cite news |last1=Ray |first1=Justin |date=April 14, 2015 |title=ULA chief explains reusability and innovation of new rocket |url=http://spaceflightnow.com/2015/04/14/ula-chief-explains-reusability-and-innovation-of-new-rocket/ |access-date=2015-04-17 |work=Spaceflight Now}}</ref> 

In late 2017, the company began development of Centaur V by accelerating elements of the ACES design, including a {{Convert|5.4|m|4=1|sp=us}} diameter and advanced insulation. The [[Integrated Vehicle Fluids]] (IVF) system, which had been intended to extend on-orbit lifetime from hours to weeks, was omitted.<ref name="sn20150413" />

Centaur V was designed to provide higher performance than the Common Centaur, fulfilling NSSL requirements and supporting the planned retirement of the Atlas V and Delta IV Heavy families. The stage was officially named Vulcan Centaur in March 2018,<ref name="sn20180325">{{cite news |last=Erwin |first=Sandra |date=March 25, 2018 |title=Air Force stakes future on privately funded launch vehicles. Will the gamble pay off? |url=https://tools.wmflabs.org/makeref/ |access-date=2018-06-24 |work=[[SpaceNews]]}}</ref><ref>{{cite tweet |number=972220666110857216 |user=torybruno |title=Internally, the current version of Centaur flying atop Atlas is technically a 'Centaur III.' Since we are only flying one Centaur at present, we've just call it 'Centaur.' Vulcan will have an upgraded Centaur. Internally, we refer to that as the 'Centaur V' |first=Tory |last=Bruno |date=March 9, 2018 |access-date=December 12, 2018}}</ref>  and in May 2018 ULA selected Aerojet Rocketdyne’s RL10 engine over [[Blue Origin]]'s [[BE-3]]. Each Centaur V uses two RL10 engines.<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>

In September 2020, ULA confirmed that ACES would no longer be developed and that Centaur V would remain Vulcan’s upper stage.<ref>{{cite web |date=September 11, 2020 |title=ULA studying long-term upgrades to Vulcan |url=https://spacenews.com/ula-studying-long-term-upgrades-to-vulcan/ |access-date=9 October 2020 |publisher=SpaceNews}}</ref> The company said that the initial versions of the Centaur V offers 40% more endurance and 250% more energy than the Common Centaur.<ref name=":3">{{cite web |last=Erwin |first=Sandra |date=April 7, 2021 |title=Bruno: The next big thing for ULA is a long-endurance upper stage |url=https://spacenews.com/bruno-the-next-big-thing-for-ula-is-a-long-endurance-upper-stage/ |website=SpaceNews}}</ref>

Vulcan launched successfully on January 8, 2024, with Centaur V performing as planned on its maiden flight.<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>

Starting in late 2025, ULA plans to upgrade the stage with the RL10E engine, featuring a fixed nozzle extension and modest improvements in thrust and specific impulse, offering minor improvements to payload capacities.<ref name="Foust 2023">{{Cite news |last=Foust |first=Jeff |date=November 28, 2023 |title=New RL10 engine to be introduced on Vulcan in 2025 |url=https://spacenews.com/new-rl10-engine-to-be-introduced-on-vulcan-in-2025/ |access-date=December 23, 2024 |work=SpaceNews |language=en-US}}</ref><ref>{{Cite web |date=September 25, 2019 |title=Vulcan Centaur Cutaway Poster |url=https://www.ulalaunch.com/docs/default-source/rockets/vulcancentaur.pdf?sfvrsn=10d7f58f_2 |website=ULA Launch}}</ref>

==== CV-L ====
During the Vulcan Cert-2 mission broadcast on October 4, 2024, ULA announced a "LEO Optimized Centaur" variant, later designated CV-L, scheduled to debut in 2025.<ref>{{Cite AV media |url=https://www.youtube.com/watch?v=fAUatH8O6Ng |title=Oct. 4 LIVE Broadcast: Vulcan Cert-2 |language=en |publisher=[[United Launch Alliance]] |time=2:18:50 |access-date=October 24, 2024 |via=YouTube}}</ref> CV-L is {{Convert|1.94|m|abbr=on|sp=us}} shorter than the baseline Centaur V, which was redesignated CV-HE (Centaur V High Energy). Unlike CV-HE, which uses a hydrolox RCS, CV-L returns to using a simpler hydrazine monopropellant RCS.<ref name="Tory Infographic Centaur Variants" />

==== ACES revival ====
On August 28, 2025, in an infographic by ULA posted by Tory Bruno, a variant of Centaur V was referred as "ACES", this time standing for "Advanced Centaur Endurance Stage". Few details were provided about this updated ACES concept, other than a mention of "Smart Propulsion", which was not further explained.<ref name="Tory Infographic Centaur Variants" /> Previously, Bruno has suggested that future upper stages could offer up to 600% more endurance than the Common Centaur.<ref name=":3" />

=== Current engines ===
Centaur engines have evolved over time, and three versions (RL10A-4-2, RL10C-1 and RL10C-1-1) are in use as of 2024 (see table below).  All versions utilize liquid hydrogen and liquid oxygen.<ref>{{cite web | url=https://www.l3harris.com/all-capabilities/rl10-engine | title=RL10 Engine &#124; L3Harris® Fast. Forward. }}</ref>
{| class="sortable wikitable"
|+Centaur engines
! scope="col" | Engine
! scope="col" | Upper Stage
! scope="col" | Dry mass
! scope="col" | Thrust
! scope="col" | [[Specific impulse]], {{abbr|vac.|vacuum}}
! scope="col" | Length
! scope="col" | Diameter
! scope="col" | Ref
|-
!{{nowrap|RL10A-4-2}}
|Centaur&nbsp;III
|{{convert|168|kg|lb|abbr=on}}
|{{convert|99.1|kN|lbf|abbr=on}}
|{{convert|451|isp|abbr=on}}
|{{convert|7|ft|6|in|m|order=flip|abbr=on}}
|{{convert|1.17|m|ftin|abbr=on}}
|<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=":0">{{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=July 1, 2019 |publisher=Aerojet Rocketdyne}}</ref>
|-
!{{nowrap|RL10C-1}}
|Centaur&nbsp;III (SEC)
|{{convert|190|kg|lb|abbr=on}}
|{{convert|101.8|kN|lbf|abbr=on}}
|{{convert|449.7|isp|abbr=on}}
|{{convert|2.12|m|ftin|abbr=on}}
|{{convert|1.45|m|ftin|abbr=on}}
|<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=":0" />
|-
!{{nowrap|RL10C-1-1}}
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|{{convert|188|kg|lb|abbr=on}}
|{{convert|106|kN|lbf|abbr=on}}
|{{convert|453.8|isp|abbr=on}}
|{{convert|2.46|m|ftin|abbr=on}}
|{{convert|1.57|m|ftin|abbr=on}}
|<ref name=":1">{{Cite web |date=March 2019 |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/20190629113826/http://rocket.com/sites/default/files/documents/Capabilities/PDFs/RL10_data_sheet.pdf |archive-date=June 29, 2019 |access-date=July 1, 2019 |website=Aerojet Rocketdyne}}</ref>
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|{{convert|510|lb|kg|order=flip|abbr=on}}
|{{convert|24120|lbf|kN|order=flip|abbr=on}}
|{{convert|460.9|isp|abbr=on}}
|{{convert|10|ft|10.4|in|m|order=flip|abbr=on}}
|{{convert|6|ft|1.7|in|m|order=flip|abbr=on}}
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|}

== History ==
[[File:Centaur stage during assembly 1962.jpg|thumb|Centaur stage during assembly at General Dynamics,<ref>{{cite web |author=[[NASA]] |date=n.d. |title=SPC Centaur Testing |url=https://www1.grc.nasa.gov/historic-facilities/altitude-wind-tunnel/spc-centaur-testing/ |access-date=February 12, 2012}}</ref> 1962]]
[[File:Centaur-propellant-system.jpg|thumb|upright|Diagram of the Centaur stage tank]]

The Centaur concept originated in 1956 when the [[Convair]] division of [[General Dynamics]] began studying a liquid hydrogen fueled upper stage. The ensuing project began in 1958 as a joint venture among Convair, the [[Advanced Research Projects Agency]] (ARPA), and the [[U.S. Air Force]]. In 1959, [[NASA]] assumed ARPA's role. Centaur initially flew as the upper stage of the [[Atlas-Centaur]] launch vehicle, encountering a number of early developmental issues due to the pioneering nature of the effort and the use of liquid hydrogen.<ref>{{cite web |url=http://www.spacelaunchreport.com/aclv3cb.html |archive-url=https://archive.today/20120910124529/http://www.spacelaunchreport.com/aclv3cb.html |url-status=usurped |archive-date=September 10, 2012 |title=Atlas Centaur LV-3C Development History}}</ref> In 1994 General Dynamics sold their Space Systems division to [[Lockheed-Martin]].<ref>https://www.gd.com/about-gd/our-history  1990–1994</ref>

=== Centaur A-D (Atlas) ===
[[File:Surveyor 1 launch.jpg|thumb|upright|An [[Atlas-Centaur]] rocket (Centaur D stage) launches [[Surveyor 1]]]]
{{See also|Atlas-Centaur}}

The Centaur was originally developed for use with the [[Atlas (rocket family)|Atlas launch vehicle family]]. Known in early planning as the 'high-energy upper stage', the choice of the [[Centaur (mythology)|mythological Centaur]] as a namesake was intended to represent the combination of the brute force of the Atlas booster and finesse of the upper stage.<ref name="nasanames1975">{{cite book |title=Origin of NASA Names |author1=Helen T. Wells |author2=Susan H. Whiteley |author3=Carrie E. Karegeannes |publisher=NASA Science and Technical Information Office |url=https://www.history.nasa.gov/SP-4402/contents.htm |chapter=I. Launch Vehicles |chapter-url=https://www.history.nasa.gov/SP-4402/ch1.htm |page=10 |access-date=March 29, 2019 |archive-date=July 14, 2019 |archive-url=https://web.archive.org/web/20190714113745/https://history.nasa.gov/SP-4402/contents.htm |url-status=dead }}</ref>

Initial [[Atlas-Centaur]] launches used developmental versions, labeled Centaur-A through -C.

The only '''Centaur-A''' launch on 8 May 1962 ended in an explosion 54 seconds after liftoff when insulation panels on the Centaur separated early, causing the LH<sub>2</sub> tank to overheat and rupture. This version was powered by two [[RL-10A|RL10A-1]] engines.<ref name=":2">{{Cite web |title=Centaur |url=https://space.skyrocket.de/doc_stage/centaur.htm |access-date=2024-09-14 |website=space.skyrocket.de}}</ref>

After extensive redesigns, the only '''Centaur-B''' flight on 26 November 1963 was successful. This version was powered by two RL10A-3 engines.<ref name=":2" />

'''Centaur-C''' flew three times between 1964 and 1965,<ref name=":2" /> with two failures and one launch declared successful although the Centaur failed to restart. This version was also powered by two RL10A-3 engines.<ref name=":2" />

'''Centaur-D''' was the first version to enter operational service in 1965 ,<ref name=":2" /> with fifty-six launches.<ref name="AWC">{{cite web|url=http://www.alternatewars.com/BBOW/Boosters/Centaur/Centaur.htm|title=Centaur Upper Stage Family|access-date=September 10, 2016|archive-date=September 27, 2016|archive-url=https://web.archive.org/web/20160927010306/http://www.alternatewars.com/BBOW/Boosters/Centaur/Centaur.htm|url-status=dead}}</ref> It was powered by two RL10A-3-1 or RL10A-3-3 engines.<ref name=":2" />

On 30 May 1966, an [[Atlas-Centaur]] boosted the first [[Surveyor program|Surveyor lander]] towards the Moon. This was followed by six more Surveyor launches over the next two years, with the Atlas-Centaur performing as expected. The Surveyor program demonstrated the feasibility of reigniting a hydrogen engine in space and provided information on the behavior of LH<sub>2</sub> in space.<ref name="Dawson2004" />{{rp|96}}

By the 1970s, Centaur was fully mature and had become the standard rocket stage for launching larger civilian payloads into high Earth orbit, also replacing the [[Atlas-Agena]] vehicle for NASA planetary probes.<ref name="Dawson2004" />{{rp|103–166}}

An updated version, called '''Centaur-D1A''' (powered by RL10A-3-3 engines), was used on the [[Atlas SLV-3|Atlas-SLV3D]] came into use during the 1970s.<ref>{{Cite web |title=Atlas-SLV3D Centaur-D1A |url=https://space.skyrocket.de/doc_lau_det/atlas-slv3d_centaur-d1a.htm |access-date=2024-09-18 |website=Gunter's Space Page |language=en}}</ref><ref>{{Cite web |title=Atlas-SLV3C Centaur-D Star-37E |url=https://space.skyrocket.de/doc_lau_det/atlas-slv3c_centaur-d_star-37e.htm |access-date=2024-09-18 |website=Gunter's Space Page |language=en}}</ref><ref name=":2" />

The '''Centaur-D1AR''' was used for the [[Atlas SLV-3|Atlas-SLV3D]] and [[Atlas G]] came into use during the 1970s and 1980s.<ref>{{Cite web |title=Atlas-SLV3D Centaur-D1AR |url=https://space.skyrocket.de/doc_lau_det/atlas-slv3d_centaur-d1ar.htm |access-date=2024-09-18 |website=Gunter's Space Page |language=en}}</ref><ref name=":2" /><ref>{{Cite web |title=Atlas-G Centaur-D1AR |url=https://space.skyrocket.de/doc_lau_det/atlas-g_centaur-d1ar.htm |access-date=2024-09-18 |website=Gunter's Space Page |language=en}}</ref>

By the end of 1989, Centaur-D had been used as the upper stage for 63 Atlas rocket launches, 55 of which were successful.<ref name="GSPCentaur">{{cite web |last=Krebs |first=Gunter |title=Centaur |work=Gunter's Space Page |url=http://space.skyrocket.de/doc_stage/centaur.htm}}</ref>

=== Saturn I S-V ===
{{Main|S-V}}
The [[Saturn I]] was designed to fly with a S-V third stage to enable payloads to go beyond [[low Earth orbit]] (LEO). The S-V stage was intended to be powered by two [[RL10|RL-10A-1]] engines burning [[liquid hydrogen]] as fuel and [[liquid oxygen]] as oxidizer. The S-V stage was flown four times on missions [[Saturn I SA-1|SA-1]] through [[Saturn I SA-4|SA-4]], all four of these missions had the S-V's tanks filled with water to be used a ballast during launch. The stage was not flown in an active configuration.

=== Centaur D-1T (Titan III) ===
[[File:Titan 3E Centaur launches Voyager 2.jpg|thumb|upright|A [[Titan (rocket family)|Titan IIIE-Centaur]] rocket (Centaur D-1T stage) launches ''[[Voyager 2]]'']]

The '''Centaur D-1T''' (powered by RL10A-3-3 engines) was an improved version for use on the far more powerful [[Titan III]] booster in the 1970s,<ref name=":2" /> with the first launch of the resulting [[Titan IIIE]] in 1974. The Titan IIIE more than tripled the payload capacity of Atlas-Centaur, and incorporated improved thermal insulation, allowing an orbital lifespan of up to five hours, an increase over the 30 minutes of the Atlas-Centaur.<ref name="Dawson2004" />{{rp|143}}

The first launch of Titan IIIE in February 1974 was unsuccessful, with the loss of the Space Plasma High Voltage Experiment (SPHINX) and a mockup of the [[Viking program|Viking]] probe. It was eventually determined that Centaur's engines had ingested an incorrectly installed clip from the oxygen tank.<ref name="Dawson2004" />{{rp|145–146}}

The next Titan-Centaurs launched [[Helios 1]], ''[[Viking 1]]'', ''[[Viking 2]]'', [[Helios 2 (NASA)|Helios 2]],<ref>{{cite web |url=http://io9.com/5786083/what-are-the-fastest-spacecrafts-ever-built |title=What are the fastest spacecraft we've ever built? |website=io9.com |date=March 26, 2011 |access-date=July 26, 2014}}</ref> ''[[Voyager 1]]'', and ''[[Voyager 2]]''. The Titan booster used to launch ''Voyager 1'' had a hardware problem that caused a premature shutdown, which the Centaur stage detected and successfully compensated for. Centaur ended its burn with less than 4 seconds of fuel remaining.<ref name="Dawson2004" />{{rp|160}}

==== Centaur D-1T specifications ====
The '''Centaur D-1T''' had the following general specifications:<ref>{{Cite web |date=2016-09-27 |title=Centaur Upper Stage Family |url=http://www.alternatewars.com/BBOW/Boosters/Centaur/Centaur.htm |access-date=2024-10-02 |archive-url=https://web.archive.org/web/20160927010306/http://www.alternatewars.com/BBOW/Boosters/Centaur/Centaur.htm |archive-date=September 27, 2016 }}</ref>

{{Div col|colwidth=25em}}
* '''Diameter''': {{cvt|126|in|m|order=flip}}
* '''Length''': {{cvt|31.5|ft|m|order=flip}}
* '''Inert mass''': {{cvt|4028|lb|kg|order=flip}}
* '''Fuel''': Liquid hydrogen
* '''Oxidizer''': Liquid oxygen
* '''Fuel and oxidizer mass''': {{cvt|29750|lb|kg|order=flip}}
* '''Guidance''':
* '''Thrust''':
* '''Burn Capability''': 3 to 4 burns
* '''Engine''': 2 x RL10A-3-3
* '''Engine start''': Restartable
* '''Attitude control''': 4 x {{cvt|6|lbf|N|order=flip}} thrusters
{{Div col end}}

=== Shuttle-Centaur ===
[[File:SHUTTLE-CENTAUR.JPG|thumb|Illustration of Shuttle-Centaur G{{nbhyph}}Prime with ''Ulysses'']]
{{Main|Shuttle-Centaur}}

[[Shuttle-Centaur]] was a proposed [[Space Shuttle]] upper stage. To enable its installation in shuttle payload bays, the diameter of the Centaur's hydrogen tank was increased to {{cvt|14|ft|m|order=flip}}, with the LOX tank diameter remaining at {{cvt|10|ft|order=flip}}. Two variants were proposed: Centaur G{{nbhyph}}Prime, which was planned to launch the ''[[Galileo (spacecraft)|Galileo]]'' and ''[[Ulysses (spacecraft)|Ulysses]]'' robotic probes, and Centaur G, a shortened version, reduced in length from approximately {{cvt|30|to|20|ft|order=flip|sigfig=1}}, planned for [[United States Department of Defense|U.S. DoD]] payloads and the ''[[Magellan (spacecraft)|Magellan]]'' Venus probe.<ref>{{cite web |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19920022007_1992022007.pdf |title=Graphite/Epoxy Composite Adapters for the Space Shuttle/Centaur Vehicle |author1=Harold J. Kasper |author2=Darryl S. Ring |publisher=Scientific and Technical Information Division of the NASA Office of Management |year=1980 |access-date=December 15, 2013 |page=1}}</ref>

After the [[Space Shuttle Challenger disaster|Space Shuttle ''Challenger'' disaster]], just months before the Shuttle-Centaur had been scheduled to fly, NASA concluded that it was too risky to fly the Centaur on the Shuttle.<ref name="pd111211" /> The probes were launched with the much less powerful solid-fueled [[Inertial Upper Stage]], with ''Galileo'' needing multiple gravitational assists from Venus and Earth to reach Jupiter.

=== Centaur T (Titan IV) ===
[[File:Centaur-T stage of a Titan IV rocket.jpg|thumb|upright|Centaur-T stage of a Titan IV rocket]]
The capability gap left by the termination of the Shuttle-Centaur program was filled by a new launch vehicle, the [[Titan IV]]. The 401A/B versions used a Centaur upper stage with a {{convert|14|ft|m|order=flip|adj=on|sp=us}} diameter hydrogen tank. In the Titan 401A version, a Centaur-T was launched nine times between 1994 and 1998. The 1997 ''[[Cassini Huygens|Cassini-Huygens]]'' Saturn probe was the first flight of the Titan 401B, with an additional six launches wrapping up in 2003 including one [[solid rocket booster|SRB]] failure.<ref>{{cite web |title=Titan 4 Launch |website=[[Space.com]] |url=http://www.space.com/missionlaunches/titan4_launch_030909.html |url-status=dead |archive-url=https://web.archive.org/web/20080708234022/http://www.space.com/missionlaunches/titan4_launch_030909.html|archive-date=July 8, 2008}}</ref>

=== Centaur I (Atlas I) ===
{{Main|Atlas I}}
The upper stage of the [[Atlas I]] was the '''Centaur I''' stage, derived from earlier models of Centaur that also flew atop Atlas boosters. Centaur I featured two RL-10-A-3A engines burning liquid hydrogen and liquid oxygen, making the stage extremely efficient. To help slow the boiloff of liquid hydrogen in the tanks, Centaur featured fiberglass insulation panels that were jettisoned 25 seconds after the first stage booster engines were jettisoned.<ref name="astronautix">{{Cite web |author=Mark Wade |title=Atlas I |url=http://www.astronautix.com/a/atlasi.html |url-status=dead |archive-url=https://web.archive.org/web/20161016025613/http://www.astronautix.com/a/atlasi.html |archive-date=October 16, 2016 |access-date=2020-08-18 |website=www.astronautix.com}}</ref> Centaur I was the last version of the stage to feature separating insulation panels.

=== Centaur II (Atlas II/III) ===
{{Main|Atlas II}}
Centaur II was initially developed for use on the [[Atlas II]] series of rockets.<ref name=AWC /> Centaur II also flew on the initial [[Atlas IIIA]] launches.<ref name="TCUSV">{{cite web|url=https://www.ulalaunch.com/docs/default-source/upper-stages/the-centaur-upper-stage-vehicle.pdf|title=The Centaur Upper Stage Vehicle|author1=Thomas J Rudman|author2=Kurt L Austad|publisher=Lockheed Martin|date=December 3, 2002}}</ref>

=== Centaur III/Common Centaur (Atlas III/V) ===
{{Main|Atlas III}}
[[Atlas IIIB]] introduced the Common Centaur, a longer and initially dual engine Centaur II.<ref name=TCUSV />

==== Centaur III specifications ====
Source: Atlas V551 specifications, as of 2015.<ref>{{cite web |title=Atlas V 551 |url=http://www.spaceflight101.com/atlas-v-551.html |access-date=April 21, 2015}}</ref>
{{Div col|colwidth=25em}}
* '''Diameter''': 3.05&nbsp;m (10&nbsp;ft)
* '''Length''': 12.68&nbsp;m (42&nbsp;ft)
* '''Inert mass''': 2,247&nbsp;kg (4,954&nbsp;lb)
* '''Fuel''': Liquid hydrogen
* '''Oxidizer''': Liquid oxygen
* '''Fuel and oxidizer mass''': 20,830&nbsp;kg (45,922&nbsp;lb)
* '''Guidance''': Inertial
* '''Thrust''': 99.2&nbsp;kN (22,300&nbsp;lbf)
* '''Burn time''': Variable; e.g., 842 seconds on Atlas V
* '''Engine''': RL10-C-1
* '''Engine length''': 2.32&nbsp;m (7.6&nbsp;ft)
* '''Engine diameter''': 1.53&nbsp;m (5&nbsp;ft)
* '''Engine dry weight''': 168&nbsp;kg (370&nbsp;lb)
* '''Engine start''': Restartable
* '''Attitude control''': 4 x {{cvt|27|N|lbf}} thrusters, 8 x {{cvt|40|N|lbf}} thrusters
** '''Propellant''': [[Hydrazine]]
{{Div col end}}

=== Atlas V cryogenic fluid management experiments ===
Most Common Centaurs launched on Atlas V have hundreds to thousands of kilograms of propellants remaining on payload separation. In 2006 these propellants were identified as a possible experimental resource for testing in-space cryogenic fluid management techniques.<ref>{{cite web |url=http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?all/CR-2006-214410.html |title=Centaur Test Bed (CTB) for Cryogenic Fluid Management |last=Sakla |first=Steven |author2=Kutter, Bernard |author3=Wall, John |year=2006 |publisher=NASA |url-status=dead |archive-url=https://web.archive.org/web/20090619214938/http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?all%2FCR-2006-214410.html |archive-date=2009-06-19 }}</ref>

In October 2009, the [[U.S. Air Force|Air Force]] and [[United Launch Alliance]] (ULA) performed an experimental demonstration on the modified Centaur upper stage of [[DMSP-18]] [[Atlas V#Atlas V launches|launch]] to improve "understanding of [[Propellant depot#Propellant settling|propellant settling]] and [[Slosh dynamics|slosh]], pressure control, [[RL10]] chilldown and RL10 two-phase shutdown operations.  DMSP-18 was a low mass payload, with approximately 28% ({{convert|5400|kg|lb|abbr=on}}) of LH<sub>2</sub>/LOX propellant remaining after separation. Several [[low Earth orbit|on-orbit]] demonstrations were conducted over 2.4 hours, concluding with a [[Orbital maneuver#Impulsive maneuvers|deorbit burn]].<ref name="ula200910">[http://www.ulalaunch.com/site/docs/publications/SuccessfulFlightDemonstrationConductedbytheAirForceandUnitedLaunchAllianceWillEnhanceSpaceTransportation_.pdf Successful Flight Demonstration Conducted by the Air Force and United Launch Alliance Will Enhance Space Transportation: DMSP-18] {{webarchive|url=https://web.archive.org/web/20110717153030/http://www.ulalaunch.com/site/docs/publications/SuccessfulFlightDemonstrationConductedbytheAirForceandUnitedLaunchAllianceWillEnhanceSpaceTransportation_.pdf |date=2011-07-17 }}, ''[[United Launch Alliance]]'', October 2009, accessed 2011-01-23.</ref> The initial demonstration was intended to prepare for more-advanced cryogenic fluid management experiments planned under the Centaur-based [[CRYOTE]] technology development program in 2012–2014,<ref name="fiso20101110">[http://spirit.as.utexas.edu/~fiso/telecon/Kutter_11-10-10/Kutter_11-10-10.pdf Propellant Depots Made Simple] {{Webarchive|url=https://web.archive.org/web/20110206042325/http://spirit.as.utexas.edu/~fiso/telecon/Kutter_11-10-10/Kutter_11-10-10.pdf |date=February 6, 2011 }}, Bernard Kutter, ''[[United Launch Alliance]]'', FISO Colloquium, 2010-11-10, accessed 2011-01-10.</ref> and will increase the [[Technology readiness level|TRL]] of the [[Advanced Cryogenic Evolved Stage]] Centaur successor.<ref name=aiaa20100902 />

== Mishaps ==
Although Centaur has a long and successful flight history, it has experienced a number of mishaps:
* April 7, 1966: Centaur did not restart after coast&nbsp;— ullage motors ran out of fuel.<ref name="ea">{{cite web|url=http://www.astronautix.com/t/titan.html|archive-url=https://web.archive.org/web/20160907152809/http://www.astronautix.com/t/titan.html|url-status=dead|archive-date=September 7, 2016|title=Titan|last=Wade|first=Mark|publisher=Encyclopedia Astronautica|access-date=December 12, 2018}}</ref>
* August 10, 1968: AC-17. Centaur did not restart after coast&nbsp;— icing of the hydrogen peroxide supply lines.<ref>Lewis Research Center (1972) [https://ntrs.nasa.gov/citations/19720017275 ''Atlas-Centaur AC-17 performance for applications technology satellite ATS-D mission''] NASA TM X-2525</ref>
* May 9, 1971: Centaur guidance failed, destroying itself and the [[Mariner 8]] spacecraft bound for [[Mars]] orbit.<ref name="Pyle2012">{{cite book |last=Pyle|first=Rod |title=Destination Mars |year=2012 |publisher=[[Prometheus Books]] |isbn=978-1-61614-589-7 |pages=73–78 |quote=''Mariner 8 launched in May but failed early in flight and ended its mission by splashing into the Atlantic Ocean.''}}</ref>
* April 18, 1991: AC-70. Centaur failed to restart (icing problem). Incomplete failure investigation initially stated that Centaur failed due to particles from the scouring pads used to clean the propellant ducts getting stuck in the turbopump, preventing start-up.<ref name="thespacereview.com">{{Cite web|url=http://www.thespacereview.com/article/1321/1|title=The Space Review: Launch failures: an Atlas Groundhog Day|website=www.thespacereview.com|access-date=2018-11-17}}</ref>
* August 22, 1992: AC-71. Centaur failed to restart (same icing problem as the prior incident).<ref name="thespacereview.com"/><ref>{{cite book |last=Rummerman |first=Judy A. |title=NASA Historical Data Book |publisher=National Aeronautics and Space Administration |date=1988 |page=123 |isbn=9780160805011 |url=https://books.google.com/books?id=c39sVNPngJoC&pg=PA123}}</ref>
* April 30, 1999: Launch of the USA-143 ([[Milstar]] DFS-3m) communications satellite failed when a Centaur database error resulted in uncontrolled roll rate and loss of attitude control, placing the satellite in a useless orbit.<ref>[https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1999-023A ''MILSTAR 3''&nbsp;— Description.]</ref>
* June 15, 2007: the engine in the Centaur upper stage of an [[Atlas V]] shut down early, leaving its payload&nbsp;— a pair of [[National Reconnaissance Office]] ocean [[Spy satellite|surveillance satellites]]&nbsp;— in a lower than intended orbit.<ref>{{cite magazine |url=http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=defense&id=news/NRO062207.xml |title=NRO Shortfall May Delay Upcoming ULA Missions |magazine=Aviation Week |access-date=March 2, 2022 |archive-date=February 5, 2012 |archive-url=https://web.archive.org/web/20120205112909/http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=defense&id=news%2FNRO062207.xml |url-status=dead }}</ref> The failure was called "A major disappointment," though later statements claim the spacecraft will still be able to complete their mission.<ref name="af">{{cite web |last=Covault |first=Craig |title=AF Holds To EELV Schedule |publisher=Aerospace Daily & Defense Report |date=July 3, 2007 |url=http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/eelv070307.xml |access-date=July 11, 2007 |archive-date=May 21, 2011 |archive-url=https://web.archive.org/web/20110521052825/http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/eelv070307.xml |url-status=dead }}</ref> The cause was traced to a stuck-open valve that depleted some of the hydrogen fuel, resulting in the second burn terminating four seconds early.<ref name="af"/>  The problem was fixed,<ref>{{cite web |url=http://www.space.com/missionlaunches/sfn-071009-atlas5-prelaunch.html |title=Atlas Rocket Team Ready for Wednesday Satellite Launch |last=Ray |first=Justin |date=October 9, 2007 |publisher=Spaceflight Now}}</ref> and the next flight was nominal.<ref>{{cite web |url=http://spaceflightnow.com/atlas/av011/status.html |title=AV-011: Mission Status Center |last=Ray |first=Justin |publisher=Spaceflight Now}}</ref>
* March 23–25, 2018: Atlas V Centaur passivated second stage launched on September 8, 2009, broke up.<ref>{{cite web |url=http://www.esa.int/Our_Activities/Space_Safety/Rocket_break-up_provides_rare_chance_to_test_debris_formation |title=Rocket break up provides rare chance to test debris formation |author=<!--Not stated--> |date=April 12, 2019 |publisher=[[European Space Agency]] |access-date=April 22, 2019}}</ref><ref>{{cite web |url=http://www.leonarddavid.com/cluttering-up-space-u-s-rocket-stage-explodes/ |title=Cluttering Up Space: U.S. Rocket Stage Explodes |last=David |first=Leonard |date=April 23, 2019 |access-date=April 22, 2019}}</ref>
* August 30, 2018: Atlas V Centaur passivated second stage launched on September 17, 2014, broke up, creating [[space debris]].<ref>{{cite web |url=http://iaaweb.org/iaa/Scientific%20Activity/debrisminutes09184.pdf |archive-url=https://web.archive.org/web/20190819102532/http://iaaweb.org/iaa/Scientific%20Activity/debrisminutes09184.pdf |url-status=dead |archive-date=August 19, 2019 |title=Major fragmentation of Atlas 5 Centaur upper stage 2014-055B (SSN #40209) |publication-place=Bremen |last=Agapov |first=Vladimir |date=September 29, 2018 |publisher=[[International Academy of Astronautics]] Space Debris Committee |access-date=April 22, 2019 }}</ref>
* April 6, 2019: Atlas V Centaur passivated second stage launched on October 17, 2018, broke up.<ref>{{cite tweet |user=18SPCS |number=1121184362559496192 |date=April 24, 2019 |title=#18SPCS confirmed breakup of ATLAS 5 CENTAUR R/B (2018-079B, #43652) on April 6, 2019. Tracking 14 associated pieces – no indication caused by collision.}}</ref><ref>{{cite web |url=https://www.n2yo.com/satellite/?s=43652 |title=ATLAS 5 CENTAUR R/B |author=<!--Not stated--> |website=N2YO.com |access-date=April 22, 2019}}</ref>
* September 6, 2024: Atlas V Centaur passivated second stage launched on March 1, 2018, broke up.<ref>{{cite web | url=https://spacenews.com/faa-to-complete-orbital-debris-upper-stage-regulations-in-2025/ | title=FAA to complete orbital debris upper stage regulations in 2025 | date=September 9, 2024 }}</ref>

== References ==
{{Reflist|colwidth=35em|refs=
<ref name="pd111211">{{cite news |first=John |last=Mangels |work=[[The Plain Dealer]] |location=[[Cleveland, OH]] |title=Long-forgotten Shuttle/Centaur boosted Cleveland's NASA center into manned space program and controversy |url=http://www.cleveland.com/science/index.ssf/2011/12/long-forgotten_shuttlecentaur.html |date=December 11, 2011 |access-date=December 11, 2011}}</ref>
}}

{{Commons and category|Centaur (rocket stage)|Centaur (rocket stage)}}
{{United Launch Alliance}}
{{USAF space vehicles}}
{{Upper stages}}
{{Authority control}}

{{DEFAULTSORT:Centaur (Rocket Stage)}}
[[Category:Rocket engines using hydrogen propellant]]
[[Category:Rocket stages]]
[[Category:NASA space launch vehicles]]
[[Category:United Launch Alliance]]