Abstract: An apparatus is disclosed for stage separation and thrust termination in a multi-stage missile having an upper stage detachably connected to a lower stage rocket motor. The apparatus includes a piston located at the forward end of the lower stage rocket motor in fluid communication with the motor's combustion chamber. The piston is configured with a plurality of venting passages, and capable of deployment from a stowed position, in which the venting passages are sealed, to an extended position, in which the venting passages are unsealed. The venting passages are preferably configured to vent the combustion chamber at an angle to the upper stage, providing the lower stage rocket motor with a component of thrust away from the upper stage after detachment without damaging the upper stage. In a preferred embodiment, means for detaching the upper stage includes attachment bolts connecting the stages and explosive detachment charges configured to shear the bolts.