Reaction Motors XLR99
The Reaction Motors XLR99 was the first large, controllable, restartable liquid fuel rocket motor .
It was developed by the Reaction Motors Division for the X-15 . The X-15 was a high-speed rocket propelled research aircraft. The collected data, together with the results of the lifting body flights, served the US 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 a vacuum, the thrust was 310 kN with a time of 279 seconds. The thrust could be regulated continuously from 50 to 100%. The engine could be switched off and on again in flight. The fuels liquid oxygen and ammonia were conveyed by a turbo pump at up to 4,500 kg per minute.
The permissible operating time until the overhaul was one hour. The burn time of the X-15 engine at full thrust was 83 seconds (150 seconds with additional tanks), so 20 to 40 flights were possible before the overhaul.
Like modern liquid rocket motors, the combustion chamber and nozzle were regeneratively cooled via numerous thin lines in the combustion chamber wall or the nozzle. The fuel served as a coolant before it was injected into the combustion chamber. The engine weighed 413 kg.