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Viking
	Viking 5C rocket engine
Country of origin	France
First flight	1979
Last flight	2003
Designer	Société Européenne de Propulsion (SEP)
Predecessor	None
Successor	Vikas; Vulcain
Status	Retired
Liquid-fuel engine
Propellant	Dinitrogen tetroxide / UDMH or UH 25
Configuration
Chamber	Film-cooled, ablative throat insert
Nozzle ratio	10 (Viking 5C); 30.8 (Viking 4B)
Performance
Thrust, vacuum	690–805 kN (155,000–181,000 lbf)
Thrust, sea-level	611–678 kN (137,000–152,000 lbf)
Thrust-to-weight ratio	80–99
Chamber pressure	5.5 MPa (800 psi)
Specific impulse, vacuum	2.76–2.95 km/s (281–301 s)
Specific impulse, sea-level	2.43–2.79 km/s (248–284 s)
Restarts	Unlimited
Gimbal range	Fixed, swiveled, and gimbaled versions were made
Dimensions
Length	2.87–3.51 m (9.4–11.5 ft)
Diameter	0.95–1.7 m (3.1–5.6 ft)
Used in
	Ariane 1 – Ariane 4
References
References

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The Viking rocket engines were members of a series of 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^[3] (originally UDMH).

The earliest versions, developed in 1965, had a sea-level thrust of about 190 kN. By 1971, the thrust had improved to 540 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 kN^[4].

The version used on the Ariane 4 first stage, which used a cluster of four, had 667 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.^[5] 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.^[6]

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.^[7] 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 °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.^[8]

Technical data

	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 kg	826 kg	826 kg	826 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 in ratio 1.70:1	Dinitrogen tetroxide and UDMH in ratio 1.892:1	Dinitrogen tetroxide and UH 25 in ratio 1.70:1	Dinitrogen tetroxide and UH 25 in ratio 1.70:1	Dinitrogen tetroxide and UH 25 in ratio 1.71:1
Propellant consumption	256.2 kg/s	246.2 kg/s	275.3 kg/s	256.2 kg/s	271.4 kg/s	279.05 kg/s	278.7 kg/s
Performance of the turbine	2500 kW, 10,000 rpm	2500 kW, 10,000 rpm	2500 kW, 10,000 rpm	2500 kW, 10,000 rpm	2500 kW, 10,000 rpm	2500 kW, 10,000 rpm	2500 kW, 10,000 rpm
Vacuum thrust	678 kN	713 kN	784.8 kN	695.4 kN	720 kN	760.5 kN	749 kN
Sea level thrust	588.5 kN	-	-	623.7 kN	645 kN	678.75 kN	670 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)

References

^ George Paul Sutton, "History of Liquid Propellant Rocket Engines", p. 798
^ News Archive 2009 Viking engine
^ Souchier, A..Drakkar Ariane 1st stage - The concept and its originality , AA(Societe Europeenne de Propulsion, Vernon, Eure, France) International Astronautical Federation, International Astronautical Congress, 27th, Anaheim, Calif., Oct. 10–16, 1976, 4 p.
^ Souchier, Alain; Rothmund, Christophe; Leven, Peter; Hagberg, Jerker (20–24 June 1999). The Development of the Viking Engine. 35th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit. American Institute of Aeronautics and Astronautics. pp. 5–7. doi:10.2514/6.1999-2902.{{cite conference}}: CS1 maint: date format (link)
^ Guy Collins. "Europe in Space", p. 51
^ Launch failures: the “Oops!” factor
^ Qualification Over Ariane’s Lifetime
^ George Paul Sutton, "History of Liquid Propellant Rocket Engines", p. 799