Apollo RCS quad.jpg
RCS quad containing four R-4D thrusters, as used on the Apollo Service Module
Country of originUnited States
ManufacturerKaiser Marquardt
Aerojet Rocketdyne
ApplicationReaction control system
Liquid-fuel engine
PropellantNTO / MMH
Thrust, vacuum110 pounds-force (490 N)
Thrust-to-weight ratio13.74
Chamber pressure100.5 pounds per square inch (6.93 bar)
Specific impulse, vacuum312 s
Length12.00 inches (30.5 cm)
Diameter6.00 inches (15.2 cm)
Dry weight8.00 pounds (3.63 kg)
Used in
Orion (spacecraft)
H-II Transfer Vehicle
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. Today, 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 deliver 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[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


  1. ^ "Bipropellant Rocket Engines". Aerojet Rocketdyne. Retrieved 7 May 2014.
  2. ^ a b David Meerman Scott (November 2013). "Marquardt R-4D Apollo spacecraft attitude control engine". Apollo Artifacts. Retrieved 5 February 2016.
  3. ^ "BulgariaSat-1". spaceflight101. Retrieved 23 June 2017.
  4. ^ Stechman, Carl; Harper, Steve (July 2010). "Performance Improvements in Small Earth Storable Rocket Engines". 46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference. AIAA. "Derivates of this engine are still used today on satellites and spacecraft including the European autonomous transfer vehicle (ATV) and the Japanese H-2 transfer vehicle (HTV) propulsion systems and the future Orion service module.
  5. ^ "Artemis 1".
  6. ^ a b c Stechman, Carl; Harper, Steve (2010). "Performance Improvements in Small Earth Storable Rocket Engines- An Era of Approaching the Theoretical". 46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit. The American Institute of Aeronautics and Astronautics. doi:10.2514/6.2010-6884. ISBN 978-1-60086-958-7. S2CID 111626089.
  7. ^ "R-4D". Astronautix. Archived from the original on August 26, 2002. Retrieved 5 February 2016.