 To save weight, the two motors are integrated with a burst disc between them; it is designed to tolerate the pressure of the launch motor from one side, but to easily rupture from the other when the flight motor ignites.The motors use a common nozzle, with the flight motor's exhaust flowing through the expended launch motor.Because the launch motor casing remains in place, an unusual annular (ring-shaped) igniter is used to start it; a normal igniter would be blown out the back of the missile when the flight motor ignited and could injure the operator.