| LR99 | |
|---|---|
| |
| An XLR-99 rocket engine. | |
| Type | Liquid-propellant rocket engine |
| National origin | United States |
| Manufacturer | Reaction Motors |
| Major applications | North American X-15 |
The Reaction Motors LR99 engine was the first large, throttleable, restartable liquid-propellant rocket engine. Development began in the 1950s by the Reaction Motors Division of Thiokol Chemical Company to power the North American X-15 hypersonic research aircraft. It could deliver up to 57,000 lbf (250 kN) of thrust with a specific impulse of 279 s (2.74 km/s) or 239 s (2.34 km/s) at sea level. Thrust was variable from 50 to 100 percent, and the restart capability allowed it to be shut down and restarted during flight when necessary.