Atlas-Agena

The Atlas-Agena was a space launch vehicle operated by the US Air Force from 1960-1978. It was derived from the SM-65 Atlas ICBM. The Atlas booster used two Rocketdyne XLR-89 engines as booster engines, and one Rocketdyne XLR-105 engine as the sustainer engine. The Agena upper stage was attached to the top of the Atlas booster. The Agena upper stage used a single XLR-81. The Atlas booster used a stage-and-a-half staging method where the two booster engines would share the same fuel tanks as the sustainer engine, but would then shut down and separate from the vehicle mid-flight.

Note: The booster engines will automaticly shut down and separate from the vehicle at 20,000m.