Country of origin  United States
Date 1957—Present
Manufacturer Aerojet
Application Upper stage/Spacecraft propulsion
Status In use
Liquid-fuel engine
Propellant N2O4 / Aerozine 50
Cycle Pressure-fed cycle
Chamber 1
Thrust (vac.) 43.7kN
Chamber pressure 7 - 9 Atm[1]
Isp (vac.) 319s [2]
Diameter 0.84 m
Dry weight 90 - 100 kg
Used in

The AJ-10 or AJ10 is a hypergolic rocket engine manufactured by Aerojet. It has been used to propel the upper stages of several carrier rockets, including the Delta II and Titan III. It is intended for use as the main engine of NASA's Orion capsule.

It was first used in the Able second stage of the Vanguard rocket, in the AJ10-118 configuration. It was initially fueled by nitric acid and UDMH.[3] An AJ10 engine was first fired in flight during the third Vanguard launch, on 17 March 1958, which successfully placed the Vanguard 1 satellite into orbit.

The AJ10-101 engine was used on an uprated version of the Able, used on Atlas-Able and Thor-Able rockets. The first flight, of a Thor-Able, occurred on 23 April 1958, however the Thor failed before the upper stage fired. The second flight, which saw the first firing of an AJ10-101 engine, occurred on 10 July 1958.[4]

The AJ10-118F engine produces 4.08 tonnes of thrust and was derived from the Titan 3 Aerojet Transtage engine.  Used in Delta 1000 ("Straight Eight") series.
This version used Aerozine 50 (a 50-50 mix of UDMH and hydrazine) as fuel and nitrogen tetroxide (N2O4) as oxidizer, rather than the previous nitric acid/UDMH.[5]

The AJ10-118K engine is currently in use on the Delta II rocket's upper stage. It uses Aerozine 50 as fuel and nitrogen tetroxide (N2O4) as oxidizer.

The AJ10-137 engine was used in the Apollo Service Module's Service Propulsion System. Trans-earth injection, from lunar orbit, was the most critical usage of this engine during the Apollo program. This version also used Aerozine 50 as fuel and nitrogen tetroxide (N2O4) as oxidizer.

The AJ10-138 engine originally developed for Vanguard and Able, flown from 1964 to 1980.
Two of these engines were used in the Titan III Transtage, with thrust uprated from 3540 kgf to 3628 kgf, with higher specific impulse. Isp=311s.

The AJ10-190 engine used on the Space Shuttle Orbital Maneuvering System (OMS) for on-orbit maneuvers and necessary for de-orbiting for re-entry and eventual landing.

See also