Wernher von Braun – “Space Frontier”, 1969

“For manned rockets, too, fins offer a definite advantage. Since the flight path – usually into orbit – is predetermined, and thus ideally suited to programed (sic) changes in gain setting, it might appear that there should be no need for fins. The problem of manned rockets, however, lies in the area of emergency provisions. – more specifically, in what we call “abort procedures”.

“Suppose a large launch vehicle such as Saturn V has a serious autopilot failure at the most critical part of the ascent through the atmosphere – the “high-stagnation-pressure” period when the speeding rocket bucks the most severe aerodynamic forces. A failure in a swivel actuator may throw one of the five booster engines into a hard-over deflection, while an additional electrical failure may prevent the other engines from counteracting the unwanted turning moment.

“In such a case, if high inherent aerodynamic instability assisted in rapidly increasing the angle of attack, structural overload might break up the rocket before the astronauts could put a safe distance between themselves and the ensuing fireball in the sky.

“It is in this area of crew safety that fins come in handy. In Saturn V the booster fins are not used to provide perfect aerodynamic stability under all conditions – that would take fins of excessive size. But the fins reduce the aerodynamic instability enough to make sure the astronauts can safely abort, no matter what technical trouble may afflict the space vehicle.”

Arf