The AJ10 is a

hypergolic A hypergolic propellant is a rocket propellant combination used in a rocket engine, whose components spontaneously ignite when they come into contact with each other. The two propellant components usually consist of a fuel and an oxidizer. The ...

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 ...

manufactured by

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 ...

(previously

Aerojet Aerojet was an American rocket and missile propulsion manufacturer based primarily in Rancho Cordova, California, with divisions in Redmond, Washington, Orange and Gainesville in Virginia, and Camden, Arkansas. Aerojet was owned by GenCorp, ...

). It has been used to propel the upper stages of several

launch vehicle A launch vehicle is typically a rocket-powered vehicle designed to carry a payload (a crewed spacecraft or satellites) from Earth's surface or lower atmosphere to outer space. The most common form is the ballistic missile-shaped multistage ...

s, including the

Delta II Delta II was an expendable launch system, originally designed and built by McDonnell Douglas, and sometimes known as the Thorad Delta 1. Delta II was part of the Delta rocket family, derived directly from the Delta 3000, and entered service in ...

and

Titan III Titan was a family of United States expendable rockets used between 1959 and 2005. The Titan I and Titan II were part of the US Air Force's intercontinental ballistic missile (ICBM) fleet until 1987. The space launch vehicle versions contribu ...

. Variants were and are used as the service propulsion engine for the

Apollo command and service module The Apollo command and service module (CSM) was one of two principal components of the United States Apollo (spacecraft), Apollo spacecraft, used for the Apollo program, which landed astronauts on the Moon between 1969 and 1972. The CSM functi ...

, in the

Space Shuttle The Space Shuttle is a retired, partially reusable launch system, reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. ...

Orbital Maneuvering System, and on the

European Service Module The European Service Module (ESM) is the service module component of the Orion (spacecraft), Orion spacecraft, serving as its primary power and propulsion component until it is discarded at the end of each mission. In January 2013, NASA announced ...

– part of

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

Orion spacecraft Orion (Orion Multi-Purpose Crew Vehicle or Orion MPCV) is a partially reusable crewed spacecraft used in NASA's Artemis program. The spacecraft consists of a Crew Module (CM) space capsule designed by Lockheed Martin that is paired with a Eu ...

Variants

It was first used in the Delta-A/Able second stage of the Vanguard rocket, in the AJ10-37 configuration. It was initially fueled by

nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

and

UDMH Unsymmetrical dimethylhydrazine (abbreviated as UDMH; also known as 1,1-dimethylhydrazine, heptyl or Geptil) is a chemical compound with the formula H2NN(CH3)2 that is primarily used as a rocket propellant. At room temperature, UDMH is a colorle ...

. An AJ10 engine was first fired in flight during the third Vanguard launch, on 17 March 1958, which successfully placed the

Vanguard 1 Vanguard 1 (Harvard designation: 1958-Beta 2, COSPAR ID: 1958-002B ) is an American satellite that was the fourth artificial Earth-orbiting satellite to be successfully launched, following Sputnik 1 Sputnik 1 (, , ''Satellite 1''), ...

satellite into orbit. The AJ10-101 engine was used on an uprated version of the Able stage, used on Atlas-Able and

Thor-Able The Thor-Able was an American expendable launch system used for a series of re-entry vehicle tests and spacecraft launches between 1958 and 1960. It was a two-stage rocket, consisting of a Thor IRBM as a first stage and a Vanguard-derived Abl ...

rockets. The first AJ10-101 flight, with a Thor-Able, occurred on 23 April 1958; however, the Thor failed before the upper Able stage fired. The second flight, which saw the first in flight firing of an AJ10-101 engine, occurred on 10 July 1958. The AJ10-138 engine was originally developed for Vanguard and Able, and was flown from 1964 to 1980. Two of these engines were used in the

GTO

Transtage Transtage, given the United States Air Force designation SSB-10A, was an American upper stage used on Titan III rockets, developed by Martin Marietta and Aerojet. History Transtage was developed in anticipation of a requirement to launch milita ...

, with thrust uprated from to , and with a higher specific impulse of . The AJ10-137 engine (20,500 lbf (91 kN) of thrust) was used in the

Apollo service module The Apollo command and service module (CSM) was one of two principal components of the United States Apollo spacecraft, used for the Apollo program, which landed astronauts on the Moon between 1969 and 1972. The CSM functioned as a mother ship ...

's service propulsion system from first flight in 1966. Trans-Earth injection, from lunar orbit, was the most critical usage of this engine during the

Apollo program The Apollo program, also known as Project Apollo, was the United States human spaceflight program led by NASA, which Moon landing, landed the first humans on the Moon in 1969. Apollo followed Project Mercury that put the first Americans in sp ...

. This version used

Aerozine 50 __NOTOC__ Aerozine 50 is a 50:50 mix by weight of hydrazine and unsymmetrical dimethylhydrazine (UDMH), developed in the late 1950s by Aerojet General Corporation as a storable, high-energy, hypergolic fuel for the Titan II ICBM rocket engines ...

(a 1:1 mix of UDMH and hydrazine) as fuel and

nitrogen tetroxide Dinitrogen tetroxide, commonly referred to as nitrogen tetroxide (NTO), and occasionally (usually among ex-USSR/Russian rocket engineers) as amyl, is the chemical compound N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium ...

(N₂O₄) as

oxidizer An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ''electron donor''). In ot ...

, rather than the previous nitric acid/UDMH. The AJ10-118F engine produced of thrust and was derived from the AJ10-138 engine used on the Transtage. It was used by the Delta-F upper stage of the Delta 1000 ''Straight Eight'' series rocket, starting in 1972. This version also used Aerozine 50 as fuel and nitrogen tetroxide (N₂O₄) as oxidizer. The AJ10-190 engine was used on the

Orbital Maneuvering System (OMS) for orbital insertion, on-orbit maneuvers, and de-orbiting, first flown in 1981. They produced of thrust with a

specific impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine, such as a rocket engine, rocket using propellant or a jet engine using fuel, generates thrust. In general, this is a ratio of the ''Impulse (physics), ...

(''I''_sp) of 316 seconds. Following the retirement of the Shuttle, these engines were repurposed for use on the Orion spacecraft's

service module A service module (also known as an equipment module or instrument compartment) is a component of a crewed space capsule containing a variety of support systems used for spacecraft operations. Usually located in the uninhabited area of the spacec ...

. This variant uses

Monomethylhydrazine Monomethylhydrazine (MMH) is a highly toxic, volatile hydrazine derivative with the chemical formula . It is used as a rocket propellant in bipropellant rocket engines because it is hypergolic with various oxidizers such as nitrogen tetroxide () ...

as fuel, with nitrogen tetroxide (N₂O₄) as oxidizer. The AJ10-118K engine was used on the

rocket's upper stage, Delta-K. It used Aerozine 50 as fuel and nitrogen tetroxide (N₂O₄) as oxidizer. The AJ10-118K engine variant was used from 1989 and retired at the conclusion of the

ICESat-2 ICESat-2 (Ice, Cloud, and land Elevation Satellite 2), part of NASA's Earth Observing System, is a satellite mission for measuring ice sheet elevation and sea ice thickness, as well as land topography, vegetation characteristics, and clouds. ICES ...

launch on 15 September 2018. Many AJ-10 engine variations were developed over the years, summarized on the following table:

References

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