The Marquardt R-4D was developed as an attitude control thruster for the Apollo Service Module and Lunar Module.
Sixteen engines just like this were mounted on the exterior of each lunar module in four quadruple clusters and sixteen on each service module. Because both the lunar module and service module were jettisoned during the Apollo missions, no flown examples exist.
The Marquardt Corporation was awarded the contract to build the reaction-control rocket engines for the Apollo spacecraft in 1963. They were first flown in the unmanned Apollo-Saturn 201 test flight launched in February 1966. Designed for maneuvering in space, this was a bipropellant engine using hypergolic nitrogen tetroxide and hydrazine as propellants, generating 100+ pounds of thrust.
The combustion chamber and nozzle are radiation cooled disilicide coated molybdenum to an expansion ration of 6.8 at which point a light-weight, thin-walled L-605 super alloy (Columbium alloy formally known as Nobium) expansion bell is attached which expands to a 40:1 area ratio.
Engine: 3.63 kg (8.00 lb). Chamber Pressure: 6.93 bar. Area Ratio: 164. Thrust to Weight Ratio: 13.7366869592086. Oxidizer to Fuel Ratio: 1.65. Coefficient of Thrust vacuum: 1.88806724749259.
Unfuelled mass: 3.63 kg (8.00 lb).
Height: 0.55 m (1.82 ft).
Diameter: 0.28 m (0.92 ft).
Thrust: 490 N (110 lbf).
Specific impulse: 312 s.