Bristol Siddeley Gamma

Gamma 201

Country of origin	Britain
Manufacturer	Bristol Siddeley
Application	1st stage booster
Predecessor	Armstrong Siddeley Stentor
Successor	Gamma 301
Liquid-fuel engine
Propellant	Hydrogen peroxide / kerosene
Mixture ratio	8:1 (approx.)
Configuration
Chamber	4, gimballed in opposed pairs

Gamma 301

Black Knight tail showing engines
Application	1st stage booster
Predecessor	Gamma 201
Successor	Gamma 8
Liquid-fuel engine
Propellant	Hydrogen peroxide / kerosene
Mixture ratio	8:1 (approx.)
Configuration
Chamber	4, gimballed in opposed pairs
Performance
Specific impulse	250 seconds (2.5 km/s)
Burn time	120 seconds

Gamma 2

Gamma 2 rocket engine, used for the second stage
Application	2nd stage
Predecessor	Gamma 301
Successor	Larch (rocket engine)
Liquid-fuel engine
Propellant	Hydrogen peroxide / kerosene
Configuration
Chamber	2, extended
Performance
Thrust (at altitude)	0.68 tonnes
Burn time	110–120 seconds

Gamma 8

Gamma 8 rocket engine on Black Arrow 1st stage
Application	1st stage booster
Predecessor	Gamma 301
Liquid-fuel engine
Propellant	Hydrogen peroxide / kerosene
Configuration
Chamber	8, gimballed in pairs
Performance
Burn time	125 seconds

The Armstrong Siddeley, later Bristol Siddeley Gamma was a family of rocket engines used in British rocketry, including the Black Knight and Black Arrow launch vehicles. They burned kerosene fuel and hydrogen peroxide. Their construction was based on a common combustion chamber design, used either singly or in clusters of up to eight.

They were developed by Armstrong-Siddeley in Coventry, which later became Bristol Siddeley in 1959, and finally Rolls-Royce in 1966.

Engine static testing was carried out at High Down Rocket Test Site, near The Needles on the Isle of Wight (). (Spadeadam in Cumbria wasn't used for testing until Blue Streak, after Gamma).

Advantages of kerosene / peroxide engines

Use of kerosene / hydrogen peroxide engines has been a particularly British trait in rocket development, there being few comparable engines (such as the LR-40) from the USA.

The combustion of kerosene with hydrogen peroxide is given by the formula

CH₂ + 3H₂O₂ → CO₂ + 4H₂O

where CH₂ is the approximate formula of kerosene (see RP-1 for a discussion of kerosene rocket fuels). This compares with the combustion of kerosene and liquid oxygen (LOX)

CH₂ + 1.5O₂ → CO₂ + H₂O

showing that the exhaust from kerosene / peroxide is predominantly water. This results in a very clean exhaust (second only to cryogenic LO₂/LH₂) and a distinctive clear flame. The low molecular mass of water also helps to increase rocket thrust performance.

The oxidiser used with Gamma was 85% high-test peroxide (HTP), H₂O₂. Gamma used a silver-plated on nickel-gauze catalyst to first decompose the peroxide. For higher concentrations of H₂O₂ another catalyst would have been required, such as platinum. No ignition source was required since the very hot decomposed H₂O₂ is hypergolic (will spontaneously combust) with kerosene. Due to the high ratio (8:1) of the mass of H₂O₂ used compared to the kerosene, and also its superior heat characteristics, the H₂O₂ may also be used to regeneratively cool the engine nozzle before combustion. Any pre-combustion chamber used to power the pump turbines needs only to decompose H₂O₂ to provide the energy. This gives the efficiency advantages of closed cycle operation, without its usual major engineering problems.

All of these characteristics lead to kerosene / hydrogen peroxide engines being simpler and more reliable to construct than other liquid propellant chemistries. Gamma had a remarkably reliable service record for a rocket engine. Of the 22 Black Knight and 4 Black Arrow launchers, involving 128 Gamma engines, there were no engine failures.

Stentor

The Gamma began as the smaller cruise chamber of the two-chamber Stentor rocket engine produced by Armstrong-Siddeley for the Blue Steel stand-off missile.

Gamma 201

Bristol-Siddeley developed this stand-alone four-chamber engine from 1955 to 1957 for the Black Knight test vehicles. Gamma 201 was used for the first twelve Black Knight launches (14 in total), Gamma 301 for most of the later flights.

The initial Black Knight vehicles were single-stage rockets designed to test prototype re-entry heads for the proposed Blue Streak strategic ballistic missile. Testing of the Black Knight began at Woomera, Australia in 1958, but the Blue Streak project was cancelled in 1960. The rockets continued to be tested until 1965, as part of a planned two-stage space launcher, using the Gamma 201 for the first stage until August 1962, when it was replaced by the more powerful Gamma 301.

Gamma 301

This was basically the same as the Gamma 201, but had automatic mixture-ratio control for improved thrust. There were 9 initial test firings of the Gamma 301 engine at High Down from 16 April to 31 May 57, all of which were largely successful. Black Knight launches BK16 and BK18 used the Gamma 301. These two were the beginning of the Project Dazzle high-speed re-entry vehicle trials, where a solid fuel Cuckoo was mounted pointing downwards in the second stage, so as to increase re-entry speeds. Eight Gamma 301 launches were made in total.

Gamma 2 / Double Gamma

A two chamber version of Gamma, used for the second stage of the Black Arrow satellite launch vehicle. As the only Gamma not required to operate at sea level, the nozzles were extended to allow better expansion.

Gamma 8

This was an 8 chamber development of Gamma, used for the first stage of the Black Arrow satellite launch vehicle. Gamma thrust chambers were mounted in pairs radially, each pair on a one-axis tangential gimbal. Collective movement gave roll control, differential movement pitch.

Gallery

Bristol Siddeley Gamma rocket engines
Gamma 201 engine behind a Black Knight re-entry vehicle  Gamma 2 rocket engine, used on the Black Arrow 2nd stage  The recovered remains of Stage 1 of the Black Arrow R3 rocket, successfully launched from the Woomera Rocket Range in October 1971.