A system used to rescue astronauts during a launch emergency. It consists of a small rocket or rockets on a tower above the command module. If the launch fails, the rockets fire to lift the spacecraft clear. The Mercury and Apollo spacecraft had one escape rocket on a 3-m high steel frame. An abort handle to the left of the commander's seat would activate the rocket's 25 200-kg thrust. During a successful launch, the tower was jettisoned at the altitude of 97 km, which was too high for its use. A space shuttle has no launch escape system: the weight of any rocket that could pull the shuttle out and away from a malfunctioning solid rocket booster or external fuel tank would be prohibitive.