The R-4D is a small hypergolic

rocket engine A rocket engine is a reaction engine, producing thrust in accordance with Newton's third law by ejecting reaction mass rearward, usually a high-speed Jet (fluid), jet of high-temperature gas produced by the combustion of rocket propellants stor ...

, originally designed by

Marquardt Corporation Marquardt Corporation was an aeronautical engineering firm started in 1944 as Marquardt Aircraft Company and initially dedicated almost entirely to the development of the ramjet engine. Marquardt designs were developed from the mid-1940s into t ...

for use as a

reaction control system A reaction control system (RCS) is a spacecraft system that uses Thrusters (spacecraft), thrusters to provide Spacecraft attitude control, attitude control and translation (physics), translation. Alternatively, reaction wheels can be used for at ...

thruster on vehicles of the Apollo crewed Moon landing program.

Aerojet Rocketdyne Aerojet Rocketdyne is a subsidiary of American Arms industry, defense company L3Harris that manufactures rocket, Hypersonic flight, hypersonic, and electric propulsive systems for space, defense, civil and commercial applications. Aerojet traces ...

manufactures and markets modern versions of the R-4D.

History

Developed as an attitude control thruster for the Apollo Command/Service Module and

Lunar Module The Apollo Lunar Module (LM ), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed s ...

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 Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

H-II Transfer Vehicle The H-II Transfer Vehicle (HTV), also called , is an Expendable launch system, expendable Japanese Cargo spacecraft, automated cargo spacecraft designed for International Space Station (ISS) resupply missions, particularly the Kibo (ISS module ...

and the European Automated Transfer Vehicle, both of which delivered cargo to the

International Space Station The International Space Station (ISS) is a large space station that was Assembly of the International Space Station, assembled and is maintained in low Earth orbit by a collaboration of five space agencies and their contractors: NASA (United ...

. It is also used on the Orion spacecraft.

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. The thruster's design has changed several times since its introduction. The original R-4D's combustion chamber was formed from an

alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

molybdenum Molybdenum is a chemical element; it has Symbol (chemistry), symbol Mo (from Neo-Latin ''molybdaenum'') and atomic number 42. The name derived from Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals hav ...

, coated in a layer of disilicide. Later versions switched to a

niobium Niobium is a chemical element; it has chemical symbol, symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and Ductility, ductile transition metal. Pure niobium has a Mohs scale of mineral hardness, Mohs h ...

alloy, for its greater ductility. Beginning with the R-4D-14, the design was changed again to use an

iridium Iridium is a chemical element; it has the symbol Ir and atomic number 77. This very hard, brittle, silvery-white transition metal of the platinum group, is considered the second-densest naturally occurring metal (after osmium) with a density ...

-lined

rhenium Rhenium is a chemical element; it has symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one ...

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.

Additional literature

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

References

{{Orbital spacecraft rocket engines Rocket engines using hypergolic propellant Rocket engines using the pressure-fed cycle