Liftoff Final seconds

At the very tip of the Saturn V stack, the rounded point of the launch escape tower (LET) included eight small holes which led to a device called the Q-ball. Shortly before launch, the cover was removed that had protected these holes from debris and insects. Their function was not dissimilar to the pitot tube seen on conventional aircraft for measuring airspeed, because the Q-ball measured how the air pressure across the eight holes changed as the vehicle rammed through the atmosphere during the ascent.

The point of having eight holes on the Saturn was not to measure airspeed, but to measure whether the air was hitting them equally and thereby determine whether the rocket was flying straight and true through the atmosphere. The angle-of-attack they sensed was displayed on a dial for the crew's benefit. If the flight had to be aborted, and the spacecraft pulled clear by the escape tower, the Q-ball would then help to determine which way round the command module and tower were flying.

With 2 minutes to go, a crewman pulled a knob in the cabin which stopped coolant flowing to radiators on the side of the spacecraft. Normally, in space, these panels received hot liquid from the cooling system and shed that heat by radiation. However, as the rocket ascended, the frictional heat generated by passing through the atmosphere warmed the radiators and temporarily made them useless, indeed counterproductive, and so for the few minutes of ascent they were bypassed.

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