Rehearsal

Three weeks prior to launch brought rehearsals for launch day. The most important of these was the Countdown Demonstration Test. Simply put, the Countdown Demonstration Test was a complete stab at preparations for the launch of the space vehicle up to, but not including, the ignition of the F-l engines of the first stage. The spacecraft was fully powered, fuelled with its highly toxic propellants, and occupied by the prime crew. All the Saturn’s propellants were loaded according to plan, including the cryogenic hydrogen and oxygen, and all the tanks were pressurised. Everyone in the nearby launch control room and at the Mission Control Center in Houston were at their consoles, each ensuring that their system was operating within limits. This attention to detail and procedure paid off by the excellent record the launch team would attain throughout the Apollo/Saturn period.

Countdown to launch

The numbers that express the scale of the Saturn V are often quoted: 110 metres tall, 10 metres wide, weighing about 3,000 tonnes at launch. But there was something about it which surpassed quantitative expression. The Saturn V was a sleek, white, slender ship that rose to the heavens like no other machine before or since. It was not only
functional; it was beautiful and seemed to be perfectly styled for the task of taking mortals to heavenly realms.

Moreover, its beauty was set against the ugliness of the steel towers that nursed it to the point of its departure.

Chock full of extreme technologies, this ship hid many ways to kill or injure the men who would ride it. Yet it, and the smaller Saturns that served with it – all swords turned to ploughshares; peaceful ships derived from military technology – had an excellent record of success, in some cases flying on in the face of failure and danger to accomplish their peaceful goals.

The launch of a Saturn V was orchestrated around the familiar countdown, a timeline leading up to the moment of launch and beyond, during which everyone and everything associated with getting the rocket off the ground coordinated their tasks.

German film maker Fritz Lang is usually credited with introducing the concept of the countdown as a device to raise suspense in his 1929 film Frau im Mond (The Girl in the Moon). It was adopted by the rocket pioneers in the German rockery club, the VfR, who maintained its use after their move to the United States.

The countdown was not continuous as it progressed towards the launch. At preplanned points it was deliberately paused to allow engineers to catch up with tasks and resynchronise their preparations. In many cases, these holds allowed small technical gremlins to be analysed and rectified. If a problem seemed to require a longer time to correct, a hold could be extended, but only up to the point where the delay would push the time of launch beyond acceptable limits.

Although the countdown has been retained in the American rocket industry, its precise implementation can vary. In the case of the Saturn V, the descending count eventually led to the point where the vehicle left the pad. With other rockets, such as the Titan II that lifted the Gemini spacecraft to orbit, the zero point was when the engines were ignited.