|Country of origin||United States|
|Application||Reaction control system|
|Propellant||NTO / MMH|
|Thrust, vacuum||110 pounds-force (490 N)|
|Chamber pressure||100.5 pounds per square inch (6.93 bar)|
|Specific impulse, vacuum||312 s|
|Length||12.00 inches (30.5 cm)|
|Diameter||6.00 inches (15.2 cm)|
|Dry weight||8.00 pounds (3.63 kg)|
H-II Transfer Vehicle
ESA Automated Transfer Vehicle
The R-4D is a small hypergolic rocket engine, originally designed by Marquardt Corporation for use as a reaction control system thruster on vehicles of the Apollo crewed Moon landing program. Today, Aerojet Rocketdyne manufactures and markets modern versions of the R-4D.
Developed as an attitude control thruster for the Apollo Command/Service Module and Lunar Module in the 1960s, each unit for the modules employed four quadruple clusters (pods). It was first flown on AS-201 in February 1966. Approximately 800 were produced during the Apollo program.
Post-Apollo, modernized versions of the R-4D have been used in a variety of spacecraft, including the U.S. Navy's Leasat, Insat 1, Intelsat 6, Italsat, and BulgariaSat-1. It has also been used on Japan's H-II Transfer Vehicle and the European Automated Transfer Vehicle, both of which deliver cargo to the International Space Station. It is also used on the Orion spacecraft
The R-4D is a fuel-film cooled engine. Some of the fuel is injected longitudinally down the combustion chamber, where it forms a cooling film.
The thruster's design has changed several times since its introduction. The original R-4D's combustion chamber was formed from an alloy of molybdenum, coated in a layer of disilicide. Later versions[clarification needed][when?] switched to a niobium alloy, for its greater ductility. Beginning with the R-4D-14,[when?] the design was changed again to use an iridium-lined rhenium combustion chamber, which provided greater resistance to high-temperature oxidization and promoted mixing of partially reacted gasses.
The R-4D requires no igniter as it uses hypergolic fuel.
It is rated for up to one hour of continuous thrust, 40,000 seconds total, and 20,000 individual firings.