Reaction Motors XLR99 Rocket. The XLR99 powered the record-breaking X-15 on its fastest flights at nearly seven times the speed of sound. It was the first large, throttleable, restartable liquid propellant rocket engine to be used in a piloted vehicle. The engine was used only in the X-15 program, which rocketed humans to the edge of space. The X-15A-2 in this gallery has an XLR99 engine.
TECHNICAL NOTES:
Thrust: 50,000 lbs. at sea level; 57,000 lbs at 45,000 ft; 57,850 lbs. at 100,000 feet
Propellants: Liquid anhydrous ammonia fuel and liquid oxygen oxidizer
Weight: 915 lbs. including turbopump