As the spacecraft coasted past the Moon and was pulled around its far side, communications were instantly and completely cut off. NASA referred to this event as loss of .signal (LOS) and it occurred with alarming predictability by virtue of the deep understanding the trajectory experts had of an Apollo's flight path. The first time it occurred was during the Apollo 8 mission, and Frank Borman found the accuracy of Houston's predictions awe-inspiring. At the precise time that he had been told communications would disappear, they did. "Geeze!" he said to his crewmates, there being no one else to hear. "That was great, wasn't it?" Then he mused: "I wonder if they've turned it off." Bill Anders laughingly replied: "Chris [Kraft, the boss in Houston] probably said, `No matter what happens, turn it off." Bill's humorous suggestion was that, in order not to worry the crew if the predictions had not been as accurate as they had hoped, Kraft would have ordered the people at the transmitting station to turn off the radio signal at just the right moment. Borman wondered, however. When next they spoke to Capcom Jerry Carr, he reported: "Houston, for your information, we lost radio contact at the exact second you predicted." Carr confirmed that that was what had happened. Borman probed further. "Are you sure you didn't turn off the transmitters at that time?" "Honest Injun, we didn't," came Carr's joking reply.
Despite being nearer to the Moon than any human in history, and with the exception of some sightings that Lovell had made through the spacecraft's optics, this crew had yet to view their quarry. This was partly because the three largest of their five windows had fogged up owing to a design problem with the sealant around them. Additionally, they had spent most of their time during the coast broadside to the Sun, twirling slowly in the barbecue mode, in which attitude their two good windows, which looked along the direction the craft was pointed, showing only deep space. As with many of the moon shots, Apollo 8 arrived over the western side of the lunar disk at the same time as the Sun was rising over the eastern side. The nearer they got to the Moon, the closer it came into line with the Sun until, in the final few hours before arrival, the spacecraft entered the Moon's shadow and plunged the crew into darkness. Apollo 10 arrived at the Moon under similar lighting conditions and its commander Tom Stafford still gained no view of the approaching planet. "Just tried looking out as far as I can, out the top hatch window, and still can't see the Moon; but we'll take your word that it's there." "Roger, 10. That's guaranteed; it's there," said Charlie Duke in mission control.
Apollo had become a part of the Cold War, a grab for prestige by the United States at a time when they and the Soviet Union stared at each other, each with nuclear weapons in hand, waiting for the other to blink. There were serious concerns that the Soviets might try to interfere with the Apollo flights, perhaps by jamming radio transmissions, therefore it was decided that the guidance and navigation system should be completely autonomous.
When production of computers for the Apollo programme was at its peak, it consumed fully half of the world's output of integrated circuits to construct only the 75 units that were built between 1963 and 1969.
From Apollo 13 onwards, all S-IVB stages were steered onto trajectories that led to a violent end, each forming a new crater on the Moon's surface.
In the years that have elapsed since the Apollo programme, people have forgotten the scale of what the S-IVB was designed to achieve. There is little appreciation of the difference between low Earth orbit and the reaches of space to which this engine took the Apollo crews. In any case, many fail to understand the relative scale of the Earth-Moon system. I once gave a talk to schoolchildren about the Moon and used the popular method of scaling the solar system down to what our minds can handle. As props, along with a model of the Saturn V launch vehicle and some good photographs, I took my own model of the Earth-Moon system. Earth was represented by a 20-centimetre globe that I had been given some years earlier. The Moon was represented by a lucky find I made during a visit to the holy grail of aerospace memorabilia: the National Air and Space Museum in Washington, DC, in the USA. While browsing the museum's gift shop, I had come across a 5-centimetre-diameter diameter foam ball, grey and pockmarked with craters, that perfectly matched the scale of my globe of the Earth, as the Moon's diameter is very nearly one-quarter that of Earth. During the talk, I threw my foam Moon out among the schoolchildren and asked the boy who caught it to come forward and hold the Moon beside my Earth at what he thought would be its correct distance. Repeated attempts by various children suggested distances between 0.5 and 1 metre. Of course, I had previously calculated the correct distance and cut a piece of string to length, which I had rolled up around a pencil. I asked the final child to place the foam Moon at the end of the string and walk back until I had fed out its full length. Back she went up the aisle between the rows of seated children. Their teacher sat at the far end of the aisle and I noticed how her eyes widened as the schoolgirl took my Moon up to where she was seated. On the scale of my little model, the mean distance between Earth and the Moon was represented by a piece of string 6 metres long. I then explained how every flight into space by humans since the end of the Apollo programme had risen above Earth between 300 and 600 kilometres, no more than the thickness of that girl's little finger. It was by the power of the S-IVB that Apollo transcended any space exploration before or since, and took men into the realms of deep space.
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 German rocket pioneers in the VfR, who maintained its use after their move to the United States.
The entire space vehicle with its launcher and transporter was substantially heavier than the Eiffel Tower.
It was Apollo 8's next manoeuvre that really scared the managers. Although the SPS engine had been designed for utmost reliability, everyone was aware that its failure would doom the crew to stay forever in the Moon's grasp. Worse, as the firing of the engine would take place around the Moon's far side, no one on Earth would be able to monitor its progress, and instead would have to wait until the spacecraft re-emerged, hopefully on a path for home. Shortly after midnight in Houston, Texas, on Christmas Day, Apollo 8 reappeared around the Moon's eastern limb exactly on time, with Jim Lovell playfully informing mission control, "Please be informed, there is a Santa Claus."
Although Apollo 17 ended the lunar phase of the Apollo programme, America's investment in its hardware and infrastructure continued to pay back for three more years. A spare S-IVB IVB stage became an orbital workshop called Skylab. This massive 77-tonne space station was launched by a Saturn V on 14 May 1973 and serviced by three crews riding modified Apollo CSMs launched by Saturn 113s. The crews stayed on board for 1, 2 and 3 months respectively. The final Apollo flight was also to Earth orbit as part of the Apollo-Soyuz Soyuz Test Project in 1975, again using a Saturn IB, when an American Apollo and a Soviet Soyuz spacecraft met and docked in space as a political act of detente, thereby ending the `space-race' amicably. The two remaining Saturn Vs were turned into lawn ornaments.