| R-4D | |
| Type: | liquid |
| Thrust(Vac): | 110lbf |
| Specific Impulse Vacuum: | 312 s |
| Chamber Pressure: | 100.5psi |
| Thrust To Weight: | 13.74 |
| Cycle: | Pressure-fed |
| Length: | 12inches |
| Diameter: | 6inches |
| Dry Weight: | 8lb |
| Used In: | Orion (spacecraft) H-II Transfer Vehicle (1, 2, 4) Space Shuttle Apollo (spacecraft) Cassini (spacecraft) 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. Aerojet Rocketdyne manufactures and markets modern versions of the R-4D.[1]
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]
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 switched to a niobium alloy, for its greater ductility. Beginning with the R-4D-14, 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.[7]