The Rocketdyne AR2, also known by the military designation LR42, was a family of liquid-fuelled rocket engines designed and produced in the United States (US) during the 1950s and 1960s.

The Rocketdyne division of North American Aviation developed a relatively small liquid-fuelled rocket engine for thrust augmentation of manned aircraft during the late 1950s. The AR2 is a single-chamber rocket engine burning kerosene (JP-4 or JP-5) jet fuel, oxidised with 90% High Test Peroxide (H₂O₂ / HTP), allowing the engine to use the same fuel as an aircraft fuel system.^[1] The variable-thrust AR2 is a direct development of the fixed thrust AR1, which was given the military designation LR36.

The AR2-3 had variable-thrust and single lever throttle control, regulating flow of oxidiser to the turbo-pump gas-generator and thus flow of propellants to the combustion chamber.^[1]

Initial flight trials were carried out attached to the belly of North American F-86F-30-NA Sabre (52-4608 / FU-608) re-designated F-86F(R), boosting performance to a top speed of M1.22 at 60,000 ft (18,288 m).^[2]

The AR2-3 was evaluated in 1999 as part of the Future-X Demonstrator Engine project, for possible use in the Boeing X-37 Reusable Upper Stage Vehicle at a thrust of 6,600 lbf (29.34 kN), with a specific impulse of 245 seconds.^[3][4]

AR-1

(YLR36-NA-2) Initial fixed-thrust variant.^[5]

AR2-1

(YLR42-NA-2) prototype, test and development variable-thrust engines.^[6][5]

AR2-2

test and development engines.^[6]

AR2-3

Production engines for research and development projects like the NF-104A.^[7]

• North American F-86F(R)
• Lockheed NF-104A

Data from Astronautix : AR2-3 ^[3] and Aircraft engines of the World 1964/65.^[1]