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{{For|the American sounding rocket|Viking (rocket)}}
{{Infobox rocket engine
|name            = Viking
|image           = Viking 5C rocketengine.jpg
|image_size      =
|caption         = Viking 5C rocket engine
|country_of_origin= France
|date            =
|first_date      = 1979
|last_date       = 2003
|designer        = Société Européenne de Propulsion (SEP)
|manufacturer    =
|purpose         =
|associated      =
|predecessor     = None
|successor       = [[Vikas (rocket engine)|Vikas]]<br>[[Vulcain (rocket engine)|Vulcain]]
|status          = Retired

|type            = Liquid
|oxidiser        = [[Dinitrogen tetroxide]]
|fuel            = [[UDMH]] or [[UH 25]]
|mixture_ratio   = 1.7–1.86
|cycle           = [[Gas-generator cycle]]
|pumps           = 3 coaxial pumps

|description     =
|combustion_chamber= Film-cooled, ablative throat insert
|nozzle_ratio    = 10 (Viking 5C)<br>30.8 (Viking 4B)<ref>George Paul Sutton, "History of Liquid Propellant Rocket Engines", p. 798</ref>

|thrust          =
|thrust_at_altitude=
|thrust(Vac)     = {{cvt|690-805|kN|lb-f}}
|thrust(SL)      = {{cvt|611-678|kN|lb-f}}
|throttle_range  =
|thrust_to_weight= 80–99
|chamber_pressure= {{cvt|5.5|MPa|psi}}
|specific_impulse=
|specific_impulse_vacuum= {{convert|281–301|isp|km/s|abbr=on|order=flip}}
|specific_impulse_sea_level= {{convert|248–284|isp|km/s|abbr=on|order=flip}}
|total_impulse   =
|burn_time       =
|restarts        = Unlimited
|gimbal          = Fixed, swiveled, and gimbaled versions were made
|capacity        =

|dimensions      =
|length          = {{cvt|2.87-3.51|m|ft}}
|diameter        = {{cvt|0.95-1.7|m|ft}}
|dry_weight      =

|used_in         = [[Ariane 1]] – [[Ariane 4]]

|references      =<ref>[http://www.dlr.de/en/DesktopDefault.aspx/tabid-5103/8592_read-21578/gallery-1/gallery_read-Image.1.12421/ News Archive 2009 Viking engine]</ref>
|notes           =
}}

The '''Viking''' rocket engines were members of a series of [[Bipropellant rocket|bipropellant]] engines for the first and second stages of the Ariane 1 through Ariane 4 commercial launch vehicles, using storable, [[hypergolic]] propellants: [[dinitrogen tetroxide]] and [[UH 25]], a mixture of 75% [[UDMH]] and 25% [[hydrazine]]<ref>Souchier, A..''Drakkar Ariane 1st stage - The concept and its originality''&nbsp;, AA(Societe Europeenne de Propulsion, Vernon, Eure, France)
International Astronautical Federation, International Astronautical Congress, 27th, Anaheim, Calif., Oct. 10–16, 1976, 4 p.</ref> (originally [[UDMH]]).

The earliest versions, developed in 1965, had a sea-level thrust of about 190&nbsp;kN. By 1971, the thrust had improved to 540&nbsp;kN, with resulting engine named Viking 1 and adopted for the Ariane program. The engine first flown on the [[Ariane 1]] rocket in 1979 was Viking 5, with thrust further improved to 623.7&nbsp;kN<ref>{{cite conference |doi=10.2514/6.1999-2902 |title=The Development of the Viking Engine |last1=Souchier |first1=Alain |last2=Rothmund |first2=Christophe |last3=Leven |first3=Peter |last4=Hagberg |first4=Jerker |date=20-24 June 1999 |publisher=American Institute of Aeronautics and Astronautics |pages=5-7 |conference=35th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit |id=}}</ref>.

The version used on the [[Ariane 4]] first stage, which used a cluster of four, had 667&nbsp;kN thrust each. The second stage of Ariane used a single Viking. Over 1000 were built, and achieved a high level of reliability from early in the programme.

The 144 Ariane 1 to 4 launchers used a total of 958 Viking engines. Only two engines led to a failure. The first failure (on second Ariane 1 flight 23 May 1980) was due to a chamber combustion instability.<ref>Guy Collins. "Europe in Space", p. 51</ref> The vehicle had lost an attitude control and broke up. Several injector changes were implemented in the aftermath of the failure, and the fuel was changed from [[UDMH]] to [[UH 25]].

The second failure was of human origin: a rag had been left in a water coolant pipe during installation, resulting in a loss of thrust and vehicle breakup due to off-centre thrust during launch on 22 February 1990.<ref>[http://www.thespacereview.com/article/1768/2 Launch failures: the “Oops!” factor]</ref> 

Initially, all the engines were tested before being integrated on a launcher. Beginning in 1998, engineers, confident of the reliability of the engine, authorized the use of untested engines on launchers. One engine per year was tested, randomly taken from the assembly workshops.<ref>[http://www.esa.int/esapub/bulletin/bullet94/GON.pdf Qualification Over Ariane’s Lifetime]</ref> This confidence is very rare in the world of space engines.

An unusual feature of the Viking engines is their water tank and water pump, used to cool the exhaust gasses of the gas generator. The hot exhaust of the gas generator is cooled by water injection to 620{{nbsp}}°C before being used to drive the three coaxial pumps (for water, fuel and oxidizer) and to pressurize the fuel tanks. The water was also used as a hydraulic fluid to actuate the valves.<ref>George Paul Sutton, "History of Liquid Propellant Rocket Engines", p. 799</ref>

==Technical data==
{| class="wikitable"
|-
!
! Viking 2
! Viking 4
! Viking 4B
! Viking 5
! Viking 5B
! Viking 5C
! Viking 6
|-
| Height
| 2.873 m
| 3.509 m
| 3.509 m
| 2.873 m
| 2.873 m
| 2.873 m
| 2.873 m
|-
| Diameter
| 0.99 m
| 1.70 m
| 1.70 m
| 0.99 m
| 0.99 m
| 0.99 m
| 0.99 m
|-
| Mass
| 776 kg
| 886 kg
| 886 kg
| 826&nbsp;kg
| 826&nbsp;kg
| 826&nbsp;kg
| 826&nbsp;kg
|-
| Propellant
| [[Dinitrogen tetroxide]] and [[UDMH]] in ratio 1.86:1
| [[Dinitrogen tetroxide]] and [[UDMH]] in ratio 1.87:1
| [[Dinitrogen tetroxide]] and [[UH 25|UH{{nbsp}}25]] in ratio 1.70:1
| [[Dinitrogen tetroxide]] and [[UDMH]] in ratio 1.892:1
| [[Dinitrogen tetroxide]] and [[UH 25|UH{{nbsp}}25]] in ratio 1.70:1
| [[Dinitrogen tetroxide]] and [[UH 25|UH{{nbsp}}25]] in ratio 1.70:1
| [[Dinitrogen tetroxide]] and [[UH 25|UH{{nbsp}}25]] in ratio 1.71:1
|-
| Propellant consumption
| 256.2&nbsp;kg/s
| 246.2&nbsp;kg/s
| 275.3&nbsp;kg/s
| 256.2&nbsp;kg/s
| 271.4&nbsp;kg/s
| 279.05&nbsp;kg/s
| 278.7&nbsp;kg/s
|-
| Performance of the turbine
| 2500&nbsp;kW, 10,000{{nbsp}}rpm
| 2500&nbsp;kW, 10,000{{nbsp}}rpm
| 2500&nbsp;kW, 10,000{{nbsp}}rpm
| 2500&nbsp;kW, 10,000{{nbsp}}rpm
| 2500&nbsp;kW, 10,000{{nbsp}}rpm
| 2500&nbsp;kW, 10,000{{nbsp}}rpm
| 2500&nbsp;kW, 10,000{{nbsp}}rpm
|-
| Vacuum thrust
| 678&nbsp;kN
| 713&nbsp;kN
| 784.8&nbsp;kN
| 695.4&nbsp;kN
| 720&nbsp;kN
| 760.5&nbsp;kN
| 749&nbsp;kN
|-
| Sea level thrust
| 588.5&nbsp;kN
| -
| -
| 623.7&nbsp;kN
| 645&nbsp;kN
| 678.75&nbsp;kN
| 670&nbsp;kN
|-
| Use
| -
| Ariane 1 second stage
| Ariane 2 - 4 second stage
| Ariane 1 first stage
| Ariane 2 - 3 first stage
| Ariane 4 first stage
| PAL (Ariane 4 liquid booster)
|}

==See also==
* {{illm|Karl-Heinz Bringer|de}} - designer of Viking and [[V-2 rocket|A4]] engine

==References==
{{Reflist}}

==External links==
{{commonscat|Viking (rocket engine)}}
* [https://web.archive.org/web/20080627121809/http://www.vernon-visite.org/rgb3/ariane.htm] Vernon, French manufacturer's history site.

{{Rocket engines}}
{{Ariane}}
{{Snecma aeroengines}}

{{DEFAULTSORT:Viking (Rocket Engine)}}
[[:Category:Rocket engines using hypergolic propellant]]
[[:Category:Rocket engines using the gas-generator cycle]]