What is an "abort" in Mercury-Redstone? It is any unplanned termination of the flight mission. The possibility of such aborts has been foreseen and provided for in the program through the inclusion of an escape rocket mounted on a tower above the spacecraft and through the provision of both automatic and manual means of firing the escape rocket to pull the spacecraft away from an impending launch vehicle malfunction. In addition, an elevating boom known as a "cherry picker" has been provided to remove the pilot during an emergency arising during the final 90 minutes of the countdown.

Once the Redstone launch vehicle has received its firing signal and even before it has lifted off the pad, automatic failure-detecting systems especially built into the vehicle will sense impending trouble and will initiate an abort. When this happens, the clamp ring which attaches the spacecraft to the launch vehicle is released by explosive bolts, as the retrorocket package attached to the spacecraft heat shield is jettisoned, and the escape rocket is fired.the thrust of the escape rocket is sufficient to pull the spacecraft to an altitude of over 2000 feet and wellto one side of the launch pad. As the spacecraft reaches its peak altitude in this abort flight explosive bolts are fired to release another clamp ring which attaches the escape rocket and tower to the spacecraft. A small rocket mounted beneath the escape rocket begins thrusting to carry the tower and now empty escape rocket away from the spacecraft and clear the way for deploying parachutes from the small upper end of the spacecraft. When the tower has gone the small 6-foot drogue parachute is deployed. This parachute stops any rotation of the spacecraft, then pulls away the antenna can and deploys the 63-foot main landing parachute. When the landing parachute is deployed the heat shield is released and this, in turn, extends the landing-impact bag which forms a pneumatic cushion to absorb the shock of landing. The impact bag is needed primarily for impacts on land but it is also required for landings on water when wind and waves are high.

In addition to the automatic system described above, the escape rocket can be fired, if necessary, by the astronaut or by radio command from the Redstone blockhouse, the Mercury Control Center, or the Atlantic Missile Range safety officer from the AMR Central Control Building.

For impending booster malfunctions after lift-off the automatic system described above goes through the same sequence to assure that the spacecraft is moved well away from any potential booster explosion.

For other emergencies such as systems malfunctions within the spacecraft the astronaut and the flight monitors in the Mercury Control Center can also initiate an abort, thus separating the spacecraft from the booster and safely terminating the flight.

The attached brochure entitled "IF" describes a number of the possible emergencies that could lead to an abort in a Mercury flight mission and also describes the many steps that have been taken to minimize the number of such emergencies that could reach the stage of requiring an abort.