Reaction Motors XLR99

The Reaction Motors XLR99 was the first large, controlled, wiederstartbare liquid-propellant rocket motor.

It was developed by the Reaction Motors Division for the X -15. The X-15 was a rocket-powered high-speed research aircraft. The data collected were used, together with the results of the lifting -body flights to the U.S. space program, such as the Space Shuttle.

The engine could deliver up to 254 kN of thrust at sea level with a specific impulse () of 239 seconds. In vacuum, the thrust was 310 kN at a of 279 seconds. The pusher could be controlled from 50 to 100 % continuously. The engine was turned off and back in flight. The fuels liquid oxygen and ammonia were pumped by a turbo pump with up to 4,500 kg per minute.

The allowable life to the overhaul was one hour. The burning time of the X -15 engine was at full thrust 83 seconds (150 seconds with auxiliary tanks ) so that 20-40 flights to overhaul were therefore possible.

Like modern liquid-fuel rocket engines were regeneratively cooled by numerous thin lines in the combustion chamber wall and the nozzle combustion chamber and nozzle. Was used as the fuel prior to injection into the combustion chamber as a coolant. The engine weighed 413 kg.