View source for Engineering:Centaur (rocket stage)

{{Short description|Family of rocket stages which can be used as a space tug}}
{{Infobox rocket stage
| image   = Landsat-9_Centaur_1_(cropped).jpg
| imsize  =  270
| caption =  A single-engine Centaur III being raised for mating to an [[Engineering:Atlas V|Atlas V]] rocket
| name           = Centaur III
| manufacturer   = [[Company:United Launch Alliance|United Launch Alliance]]
| country-origin = 
| rockets     =
:Current
::[[Engineering:Atlas V|Atlas V]]: Centaur III
::Vulcan: Centaur V
:Historical
::[[Engineering:Atlas-Centaur|Atlas-Centaur]]
::[[Astronomy:Saturn I|Saturn I]]
::Titan III
::Titan IV
::[[Engineering:Atlas II|Atlas II]]
::[[Engineering:Atlas III|Atlas III]]
::[[Engineering:Shuttle-Centaur|Shuttle-Centaur]](not flown)
| derivatives = Centaur V<br/>[[Engineering:Advanced Cryogenic Evolved Stage|Advanced Cryogenic Evolved Stage]]
| comparable  =
| status   =  Active
| launches = 271 {{As of|2024|01|lc=y}}<ref name="GSPCentaur"/>
| success  =
| fail     =
| noburn   =
| partial  =
| first    = {{Start date and age|May 9, 1962}}
| last    =
<!-- General Characteristics - Centaur III -->
| height = {{convert|12.68|m|in|abbr=on}}<ref name="Altas5Users">{{cite web |title=Altas 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}}
| empty = {{convert|2247|kg|lbs|abbr=on}}, single engine<br/>{{convert|2462|kg|lbs|abbr=on}}, dual engine
{{Infobox rocket/stage
| name          = Centaur III
| engines       = 1 or 2 RL10
| thrust        = {{convert|99.2|kN|lbf|abbr=on}}, per engine
| SI            = {{convert|450.5|isp}}
| burntime      = Variable
| fuel          = LH<sub>2</sub> / [[Physics:Liquid oxygen|LOX]]
}}
| propmass = {{convert|20830|kg|lbs|abbr=on}}
}}
[[File:Centaur rocket stage.jpg|thumb|A dual engine Centaur stage]]
[[File:Centaur stage during assembly 1962.jpg|thumb|Centaur stage during assembly at General Dynamics,<ref>{{cite web | url = https://www1.grc.nasa.gov/historic-facilities/altitude-wind-tunnel/spc-centaur-testing/ | title = SPC Centaur Testing | author = NASA | date = n.d. | access-date = February 12, 2012 }}</ref> 1962]]
[[File:Centaur-propellant-system.jpg|thumb|Diagram of the Centaur stage tank]]
The '''Centaur''' is a family of rocket propelled upper stages that has been in use since 1962. It is currently produced by U.S. [[Engineering:Launch service provider|launch service provider]] [[Company:United Launch Alliance|United Launch Alliance]], with one main active version and one version under development. The {{convert|3.05|m|ft|abbr=on}} diameter Common Centaur/Centaur III flies as the upper stage of the [[Engineering:Atlas V|Atlas V]] launch vehicle, and the {{convert|5.4|m|ft|abbr=on}} diameter Centaur V has been developed as the upper stage of ULA's new Vulcan rocket.<ref name="ars20171211">{{cite web
 |url=https://arstechnica.com/science/2018/12/talking-rockets-with-tory-bruno-vulcan-the-moon-and-hat-condiments/
 |title=Getting Vulcan up to speed: Part one of our interview with Tory Bruno
 |last=Berger
 |first=Eric
 |date=December 11, 2018
 |website=Ars Technica
 |access-date=December 12, 2018
 |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
 |url=https://www.ulalaunch.com/rockets/vulcan-centaur
 |title=Vulcan Centaur
 |author=<!--Not stated-->
 |date=2018
 |publisher=United Launch Alliance
 |access-date=December 12, 2018}}</ref> Centaur was the first rocket stage to use [[Chemistry:Liquid hydrogen|liquid hydrogen]] (LH<sub>2</sub>) and [[Physics:Liquid oxygen|liquid oxygen]] (LOX) [[Chemistry:Rocket propellant|propellants]], a high-energy combination that is ideal for upper stages but has significant handling difficulties.<ref>{{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=Launch Vehicles |chapter-url=https://www.history.nasa.gov/SP-4402/ch1.htm |quote=because it proposed to make first use of the theoretically powerful but problem-making liquid hydrogen as fuel. |page=11 |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>

==Characteristics==
Common Centaur is built around [[Chemistry:Stainless steel|stainless steel]] pressure stabilized [[Engineering: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/> The thin walls minimize the mass of the tanks, maximizing the stage's overall performance.<ref>{{cite book |last1=Stiennon |first1=Patrick J. G. |last2=Hoerr |first2=David M. |date=July 15, 2005 |title=The Rocket Company |publisher=[[Organization:American Institute of Aeronautics and Astronautics|American Institute of Aeronautics and Astronautics]] |page=93 |isbn=1-56347-696-7}}</ref>

A common bulkhead separates the [[Physics:Liquid oxygen|LOX]] and [[Chemistry:Liquid hydrogen|LH<sub>2</sub>]] tanks, further reducing the tank mass. It is made of two stainless steel skins separated by a fiberglass honeycomb. The fiberglass honeycomb minimizes heat transfer between the extremely cold LH<sub>2</sub> and less cold LOX.<ref name="Dawson2004">{{cite book |last1=Dawson |first1=Virginia P. |last2=Bowles |first2=Mark D. |title=Taming Liquid Hydrogen: The Centaur Upper Stage Rocket 1958–2002 |year= 2004 |publisher=NASA |url=https://history.nasa.gov/SP-4230.pdf}}</ref>{{rp|19}}

The main propulsion system consists of one or two [[Company:Aerojet Rocketdyne|Aerojet Rocketdyne]] RL10 engines.<ref name="nasa"/> The stage is capable of up to twelve restarts, limited by propellant, orbital lifetime, and mission requirements. Combined with the insulation of the propellant tanks, this allows Centaur to perform the multi-hour coasts and multiple engine burns required on complex orbital insertions.<ref name="bruno_centaur_tweet">{{cite tweet |user=ToryBruno |number=1131638302761578496 |date=23 May 2019 |title=Yes. The Amazing Centaur in its dual RL10 configuration.}}</ref>

The [[Engineering:Reaction control system|reaction control system]] (RCS) also provides [[Engineering:Ullage#Rocketry|ullage]] and consists of twenty [[Chemistry:Hydrazine|hydrazine]] [[Engineering:Monopropellant rocket|monopropellant]] engines located around the stage in two 2-thruster pods and four 4-thruster pods. For propellant, {{cvt|340|lb|kg|order=flip}} of Hydrazine is stored in a pair of bladder tanks and fed to the RCS engines with pressurized [[Chemistry:Helium|helium]] gas, which is also used to accomplish some main engine functions.<ref name=TCUSV />

==Current versions==
As of 2019, all but two of the many Centaur variants had been retired: Common Centaur/Centaur III (active) and Centaur V (flight proven).<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 />

===Current engines===
Each Centaur stage uses two engines.  The engines have evolved over time, and three versions are in use as of 2024 (see table below).  All versions utilize liquid hydrogen and liquid oxygen.
{| class="sortable wikitable"
! scope="col" | Version
! scope="col" | Stage used on
! scope="col" | Dry mass
! scope="col" | Thrust
! scope="col" | [[Physics:Specific impulse|''I''<sub>sp</sub>]], {{abbr|vac.|vacuum}}
! scope="col" | Length
! scope="col" | Diameter
! scope="col" | Notes
|-
! scope="row" | RL10A-4-2 
| Centaur III
| {{convert|168|kg|lb|abbr=on}}
| {{convert|99.1|kN|lbf|abbr=on}}
| 451 s
|
| {{convert|1.17|m|ft|abbr=on}}
| <ref name="EA10A42">{{cite encyclopedia |url=http://www.astronautix.com/engines/rl10a42.htm |title=RL-10A-4-2 |encyclopedia=Encyclopedia Astronautica |first=Mark |last=Wade |access-date=February 27, 2012 |date=November 17, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20120130143126/http://www.astronautix.com/engines/rl10a42.htm |archive-date=January 30, 2012 |df=mdy-all}}</ref><ref name=":0" />
|-
! scope="row" | RL10C-1 
| Centaur III (SEC), ([[Engineering:Delta Cryogenic Second Stage|DCSS]])
| {{convert|190|kg|lb|abbr=on}}
| {{convert|101.8|kN|lbf|abbr=on}}
| 449.7 s
| {{convert|2.12|m|ft|abbr=on}}
| {{convert|1.45|m|ft|abbr=on}}
| <ref name="CPS">{{cite web |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110015783.pdf |title=Cryogenic Propulsion Stage |date=August 5, 2011 |publisher=NASA |access-date=October 11, 2014}}</ref><ref>{{cite web|url=http://forum.nasaspaceflight.com/index.php?topic=34891.0|title=Atlas-V with RL10C powered Centaur|website=forum.nasaspaceflight.com|access-date=April 8, 2018}}</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 |access-date=February 20, 2016 |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 |df=mdy-all }}</ref><ref name=":0">{{cite web |title=RL10 Engine |url=http://www.rocket.com/rl10-engine |publisher=Aerojet Rocketdyne |access-date=July 1, 2019 |archive-url=https://web.archive.org/web/20170430183058/http://www.rocket.com/rl10-engine |archive-date=April 30, 2017 |url-status=dead }}</ref>
|-
! scope="row" |RL10C-1-1
|Centaur V
|{{convert|188|kg|lb|abbr=on}}
|{{convert|106|kN|lbf|abbr=on}}
|453.8 s
|{{convert|2.46|m|ft|abbr=on}}
|{{convert|1.57|m|ft|abbr=on}}
|<ref name=":1">{{Cite web|url=http://rocket.com/sites/default/files/documents/Capabilities/PDFs/RL10_data_sheet.pdf|title=Aerojet Rocketdyne RL10 Propulsion System|date=March 2019|website=Aerojet Rocketdyne|access-date=July 1, 2019|archive-date=June 29, 2019|archive-url=https://web.archive.org/web/20190629113826/http://rocket.com/sites/default/files/documents/Capabilities/PDFs/RL10_data_sheet.pdf|url-status=dead}}</ref>
|}

===Centaur III/Common Centaur===
Common Centaur is the upper stage of the [[Engineering:Atlas V|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 [[Engineering:Delta Cryogenic Second Stage|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 [[Engineering:Payload fairing|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 [[Astronomy:CST-100 Starliner|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 [[Astronomy: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===
Centaur V is the upper stage of the new Vulcan launch vehicle developed by the [[Company:United Launch Alliance|United Launch Alliance]] to meet the needs of the [[Engineering:National Security Space Launch|National Security Space Launch]] (NSSL) program.<ref>{{cite web |url=http://www.denverpost.com/business/ci_27905093/america-meet-vulcan-your-next-united-launch-alliance |title=America, meet Vulcan, your next United Launch Alliance rocket |work=Denver Post |date=2015-04-13 |access-date=2015-04-17 }}</ref> Vulcan was initially intended to enter service with an upgraded variant of the Common Centaur,<ref name="sn20171010">{{cite news |url= http://spacenews.com/op-ed-building-on-a-successful-record-in-space-to-meet-the-challenges-ahead/ |publisher= Space News |title= Building on a successful record in space to meet the challenges ahead |date= October 10, 2017 |author= Bruno, Tory}}</ref> with an upgrade to the [[Engineering:Advanced Cryogenic Evolved Stage|Advanced Cryogenic Evolved Stage]] (ACES) planned after the first few years of flights.<ref name="sn20150413">
{{cite news |last1=Gruss|first1=Mike |url=http://spacenews.com/ulas-vulcan-rocket-to-be-rolled-out-in-stages/ |work=SpaceNews |title=ULA's Vulcan Rocket To be Rolled out in Stages |date=2015-04-13 |access-date=2015-04-17 }}</ref><ref name="sfn20150414">{{cite news |last1=Ray|first1=Justin |url=http://spaceflightnow.com/2015/04/14/ula-chief-explains-reusability-and-innovation-of-new-rocket/ |title=ULA chief explains reusability and innovation of new rocket |work=Spaceflight Now |date=April 14, 2015 |access-date=2015-04-17 }}</ref>

In late 2017, ULA decided to bring elements of the ACES upper stage forward and begin work on Centaur V. Centaur V will have ACES' {{convert|5.4|m|ft|abbr=on}} diameter and advanced insulation, but does not include the Integrated Vehicle Fluids (IVF) feature expected to allow the extension of upper stage on-orbit life from hours to weeks.<ref name=sn20150413/> Centaur V uses two different versions of the RL10-C engine with nozzle extensions to improve the fuel consumption for the heaviest payloads.<ref>{{Cite web|url=https://www.ulalaunch.com/docs/default-source/rockets/vulcancentaur.pdf?sfvrsn=10d7f58f_2|title=Vulcan Centaur Cutaway Poster|date=September 25, 2019|website=ULA Launch}}</ref> This increased capability over Common Centaur was intended to permit ULA to meet NSSL requirements and retire both the Atlas V and Delta IV Heavy rocket families earlier than initially planned. The new rocket publicly became the Vulcan Centaur in March 2018.<ref name="sn20180325">{{cite news |last=Erwin|first=Sandra |url=https://tools.wmflabs.org/makeref/ |title=Air Force stakes future on privately funded launch vehicles. Will the gamble pay off? |work=SpaceNews |date=March 25, 2018 |access-date=2018-06-24}}</ref><ref>{{cite tweet |last=Bruno |first=Tory |user=torybruno |number=972220666110857216 |date=March 9, 2018 |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' |access-date=December 12, 2018}}</ref> In May 2018, the Aerojet Rocketdyne RL10 was announced as Centaur V's engine following a competitive procurement process against the [[Company:Blue Origin|Blue Origin]] BE-3. Each stage will mount two engines.<ref>{{cite web |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 |publisher=ULA |access-date=May 13, 2018 |date=May 11, 2018}}</ref> In September 2020, ULA announced that ACES was no longer being developed, and that Centaur V would be used instead.<ref>{{cite web |title=ULA studying long-term upgrades to Vulcan  |date= September 11, 2020 |publisher= SpaceNews |url=https://spacenews.com/ula-studying-long-term-upgrades-to-vulcan/ |access-date=9 October 2020}}</ref> Tory Bruno, ULA's CEO, stated that the Vulcan's Centaur 5 will have 40% more endurance and two and a half times more energy than the upper stage ULA currently flies. “But that’s just the tip of the iceberg,” Bruno elaborated. “I’m going to be pushing up to 450, 500, 600 times the endurance over just the next handful of years. That will enable a whole new set of missions that you cannot even imagine doing today.”<ref>{{cite web | url=https://spacenews.com/bruno-the-next-big-thing-for-ula-is-a-long-endurance-upper-stage/ | title=Bruno: The next big thing for ULA is a long-endurance upper stage | date=April 7, 2021 }}</ref>

Vulcan finally launched on 8 January 2024 and the stage performed flawlessly 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>

==History==
The Centaur concept originated in 1956 when [[Company:Convair|Convair]] 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 {{wipe|U.S. Air Force}}. In 1959, [[Organization:NASA|NASA]] assumed ARPA's role. Centaur initially flew as the upper stage of the [[Engineering:Atlas-Centaur|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 [[Company:General Dynamics|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|An Atlas-Centaur rocket launches Surveyor 1|229x229px]]
{{main|Engineering:Atlas-Centaur}}
The Centaur was originally developed for use with the [[Engineering:Atlas (rocket family)|Atlas launch vehicle family]]. Known in early planning as the 'high-energy upper stage', the choice of the 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 [[Engineering:Atlas-Centaur|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. After extensive redesigns, the only Centaur-B flight on 26 November 1963 was successful. Centaur-C flew three times with two failures and one launch declared successful although the Centaur failed to restart. Centaur-D was the first version to enter operational service, 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>

On 30 May 1966, an [[Engineering:Atlas-Centaur|Atlas-Centaur]] boosted the first [[Astronomy: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 [[Engineering:Atlas-Agena|Atlas-Agena]] vehicle for NASA planetary probes.<ref name="Dawson2004"/>{{rp|103–166}}

By the end of 1989, Centaur-D and -G 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|Engineering:S-V}}
[[File:SA-1 launch.jpg|thumb|279x279px|A Saturn I launches with a ballasted S-V stage]]
The [[Astronomy:Saturn I|Saturn I]] was designed to fly with a S-V third stage to enable payloads to go beyond [[Astronomy:Low Earth orbit|low Earth orbit]] (LEO). The S-V stage was intended to be powered by two RL-10A-1 engines burning [[Chemistry:Liquid hydrogen|liquid hydrogen]] as fuel and [[Physics:Liquid oxygen|liquid oxygen]] as oxidizer. The S-V stage was flown four times on missions [[Engineering:Saturn I SA-1|SA-1]] through [[Engineering: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|A [[Engineering:Titan (rocket family)|Titan IIIE-Centaur]] rocket launches ''Voyager 2''|264x264px]]

The Centaur D was improved for use on the far more powerful Titan III booster in the 1970s, 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 [[Engineering: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, ''[[Astronomy:Viking 1|Viking 1]]'', ''[[Astronomy:Viking 2|Viking 2]]'', 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> ''[[Astronomy:Voyager 1|Voyager 1]]'', and ''[[Astronomy:Voyager 2|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  (Atlas G)===
Centaur was introduced on the Atlas G and was carried over to the very similar Atlas I.{{citation_needed|date=July 2019}}

===Shuttle-Centaur (Centaur G and G-Prime)===

{{main|Engineering:Shuttle-Centaur}}
[[File:SHUTTLE-CENTAUR.JPG|thumb|Illustration of Shuttle-Centaur with ''Ulysses''|202x202px]]
[[Engineering:Shuttle-Centaur|Shuttle-Centaur]] was a proposed [[Engineering:Space Shuttle|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 Prime, which was planned to launch the ''[[Engineering:Galileo (spacecraft)|Galileo]]'' and ''[[Engineering: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 U.S. DoD payloads and the ''[[Engineering: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 [[Engineering:Space Shuttle Challenger disaster|Space Shuttle ''Challenger'' accident]], and 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 [[Engineering:Inertial Upper Stage|IUS]], with ''Galileo'' needing multiple gravitational assists from Venus and Earth to reach Jupiter.

===Centaur (Titan IV)===
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'' Saturn probe was the first flight of the Titan 401B, with an additional six launches wrapping up in 2003 including one [[Engineering: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 II (Atlas II/III)===
{{main|Engineering:Atlas II}}
Centaur II was initially developed for use on the [[Engineering:Atlas II|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|Engineering:Atlas III}}
Atlas IIIB introduced the Common Centaur, a longer and initially dual engine Centaur II.<ref name=TCUSV />

===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 {{wipe|U.S. Air Force}} and [[Company:United Launch Alliance|United Launch Alliance]] (ULA) performed an experimental demonstration on the modified Centaur upper stage of DMSP-18 [[Engineering:Atlas V#Atlas V launches|launch]] to improve "understanding of [[Chemistry:Propellant depot#Propellant settling|propellant settling]] and [[Physics: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 [[Astronomy:Low Earth orbit|on-orbit]] demonstrations were conducted over 2.4 hours, concluding with a [[Astronomy: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 }}, ''[[Company:United Launch Alliance|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, ''[[Company:United Launch Alliance|United Launch Alliance]]'', FISO Colloquium, 2010-11-10, accessed 2011-01-10.</ref> and will increase the [[Engineering:Technology readiness level|TRL]] of the [[Engineering:Advanced Cryogenic Evolved Stage|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>
* May 9, 1971; Centaur guidance failed, destroying itself and the [[Astronomy:Mariner 8|Mariner 8]] spacecraft bound for [[Astronomy:Mars|Mars]] orbit.<ref name="Pyle2012">{{cite book |last=Pyle|first=Rod |title=Destination Mars |year=2012 |publisher=[[Philosophy:Prometheus Books|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:  Centaur failed due to particles from the scouring pads used to clean the propellant ducts getting stuck in the turbopump, preventing start-up.<ref>{{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: Centaur failed to restart (icing problem).<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 ([[Engineering:Milstar|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 [[Engineering:Atlas V|Atlas V]] shut down early, leaving its payload&nbsp;— a pair of National Reconnaissance Office ocean 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=[[Organization:European Space Agency|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 [[Astronomy:Space debris|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=[[Organization:International Academy of Astronautics|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>

==Centaur III specifications==
Source: Atlas V551 specifications, as of 2015.<ref>{{cite web|url=http://www.spaceflight101.com/atlas-v-551.html|title=Atlas V 551|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 27-N thrusters, 8 40-N thrusters
** '''Propellant''': Hydrazine
{{Div col end}}

== 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)}}
{{USAF space vehicles}}
{{Upper stages}}

{{DEFAULTSORT:Centaur (Rocket Stage)}}
[[Category:Rocket stages]]
[[Category:NASA space launch vehicles]]

{{Sourceattribution|Centaur (rocket stage)}}