Delta II second stage.jpg
Country of originUnited States
ManufacturerAerojet, Aerojet Rocketdyne
ApplicationUpper stage/spacecraft propulsion
StatusIn use
Liquid-fuel engine
/ Aerozine 50
CyclePressure-fed engine
Thrust, vacuum43.7 kN
Chamber pressure7–9 bars (700–900 kPa)[1]
Specific impulse, vacuumfrom 270 seconds (2.6 km/s) on AJ10-101[2] to 319 seconds (3.13 km/s) on AJ10-118K [3]
Diameter0.84 m
Dry weight90–100 kg
Used in

The AJ10 is a hypergolic rocket engine manufactured by Aerojet Rocketdyne (previously Aerojet). It has been used to propel the upper stages of several launch vehicles, including the Delta II and Titan III. Variants were and are used as the service propulsion engine for the Apollo command and service module, in the Space Shuttle Orbital Maneuvering System, and on NASA's Orion spacecraft.


It was first used in the Delta-A/Able second stage of the Vanguard rocket, in the AJ10-118 configuration. It was initially fueled by nitric acid and UDMH.[4] 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 stage, used on Atlas-Able and Thor-Able 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.[5]

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 Titan III GTO Transtage, with thrust uprated from 7,800 lbf (35 kN) to 8,000 lbf (36 kN), and with a higher specific impulse of 311 s (3.05 km/s).[6]

The AJ10-137 engine (20,500 lbf (91 kN) of thrust) was used in the Apollo service module'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. This version used Aerozine 50 (a 1:1 mix of UDMH and hydrazine) as fuel and nitrogen tetroxide (N2O4) as oxidizer, rather than the previous nitric acid/UDMH.[7]

The AJ10-118F engine produced 9,000 lbf (40 kN) 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 Space Shuttle Orbital Maneuvering System (OMS) for orbital insertion, on-orbit maneuvers, and de-orbiting, first flown in 1981. They produced 26.7 kilonewtons (6,000 lbf) of thrust with a specific impulse (Isp) of 316 seconds.[8] Following the retirement of the Shuttle, these engines was repurposed for use on the Orion spacecraft's service module.[9] This variant uses Monomethylhydrazine as fuel, with nitrogen tetroxide (N2O4) as oxidizer.[10]

The AJ10-118K engine was used on the Delta II rocket's upper stage, Delta-K. It used Aerozine 50 as fuel and nitrogen tetroxide (N2O4) as oxidizer.[11] The AJ10-118K engine variant was used from 1989 and retired at the conclusion of the ICESat-2 launch on 15 September 2018.


  1. ^ "AJ10-118". Encyclopedia Astronautica. Archived from the original on 2008-07-06. Retrieved 2008-06-22.
  2. ^ "AJ10-101". Retrieved 25 October 2022.
  3. ^ "Delta II Design". Gunter's Space Page. Retrieved 6 June 2012.
  4. ^ Wade, Mark. "AJ10-118". Encyclopedia Astronautica. Archived from the original on 6 July 2008. Retrieved 2008-06-22.
  5. ^ Wade, Mark. "Thor-Able". Encyclopedia Astronautica. Archived from the original on February 28, 2002. Retrieved 2008-05-24.
  6. ^ Wade, Mark. "AJ10-138". Encyclopedia Astronautica. Archived from the original on December 28, 2016. Retrieved 2019-07-24.
  7. ^ Kyle, Ed (8 April 2010). "Long Tank Thor-Delta". Space Launch Report. Retrieved 6 June 2012.
  8. ^ Encyclopedia Astronautica (2009). "OME". Encyclopedia Astronautica. Archived from the original on 13 January 2010. Retrieved 4 January 2010.
  9. ^ Bergin, Chris (20 June 2015). "Plum Brook prepped for EM-1 Orion Service Module testing". NASASpaceFlight.com. Retrieved 28 July 2015.
  10. ^ "Aerojet Rocketdyne - In-Space Propulsion Data Sheets" (PDF). Archived from the original (PDF) on 2020-01-11. Retrieved 2019-12-07.
  11. ^ "Delta II Stage 2 Engine". Aerojet Rocketdyne. Archived from the original on 14 March 2017. Retrieved 22 January 2017.