R-4D

For the aircraft with this designation in US Navy service, see Douglas C-47 Skytrain.

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. Aerojet Rocketdyne manufactures and markets modern versions of the R-4D.^[1]

R-4D

RCS quad containing four R-4D thrusters, as used on the Apollo Service Module
Country of origin	United States
Manufacturer	Kaiser Marquardt Aerojet Rocketdyne
Application	Reaction control system
Liquid-fuel engine
Propellant	NTO / MMH
Cycle	Pressure-fed
Performance
Thrust, vacuum	110 pounds-force (490 N)
Thrust-to-weight ratio	13.74
Chamber pressure	100.5 pounds per square inch (6.93 bar)
Specific impulse, vacuum	312 s
Dimensions
Length	12.00 inches (30.5 cm)
Diameter	6.00 inches (15.2 cm)
Dry mass	8.00 pounds (3.63 kg)
Used in
Orion (spacecraft) H-II Transfer Vehicle (1, 2, 4) Space Shuttle Apollo (spacecraft) Cassini (spacecraft) ESA Automated Transfer Vehicle

History

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.^[2]

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.^[3] It has also been used on Japan's H-II Transfer Vehicle and the European Automated Transfer Vehicle, both of which delivered cargo to the International Space Station.^[4] It is also used on the Orion spacecraft.^[5]

Design

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.^[6]

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.^[2] 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.^[6]

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.^[6][7]

Additional literature

• Remembering the Giants: Apollo Rocket Propulsion Development - Chapter Three & Appendix E