## Leaving Earth

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 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.

Astronaut Michael Collins understood the significance of the TLI burn and wrote about it in his autobiography, Carrying the Fire. He was at the Capcom console in the mission operations control room (MOCR) in Houston, usually called simply mission control, and acted as the intermediary between the crew of Apollo 8 and the huge team of people occupying the building with him. He realised that TLI was what made this first manned flight to the Moon different from all the flights that had preceded it. On his own flight, Apollo 11, he yearned for a deeper appreciation of what TLI really meant.

"The umbilical snipping ceremony carries about as much drama as asking for a second lump of sugar. 'Apollo 11, this is Houston. You are Go for TLI.' I answer, 'Apollo 11. Thank you.' There should be more to it.''

Only 30 minutes after the completion of the TLI burn, the stack was already approaching an altitude equivalent to Earth's radius. The home planet no longer filled half the sky as it had when their spacecraft hugged the world in its parking orbit. Now the crew could see the planet as a globe and view entire continents in a single glance.

''You could see all of the United States. If the pictures come out, there will really be some pictures.'' This was praise indeed from the laconic John Young during the debriefing for Apollo 16. His CMP Ken Mattingly concurred. ''The Earth was right there in the window. And centred right in the middle of the Earth was the United States, without a cloud over it.''

''All the way from the Great Lakes to Brownsville,'' added Charlie Duke.

''Just as if you had drawn it and set it up so you could take a picture of it,'' continued Mattingly.

Young then changed the subject. ''Why don't you talk about TD&E, Ken?"

Young was referring to transposition, docking and extraction, a typically NASA-ese piece of nomenclature concerning the CSM's separation from the S-IVB, a short coast away, turning, coming back, docking with the LM and pulling it away from the nearly spent stage. By Apollo 16, Mattingly was familiar with this series of tasks. ''That's got to be the simplest manoeuvre performed in space flight,'' he said afterwards. ''That was exactly like the simulator.''

During the Gemini programme, NASA learned how to safely dock two spacecraft

Earth, as seen from Apollo 16 after it left for the Moon. The Baja California peninsula is visible in the centre.

together, in the knowledge that it would be an important part of future operations in space. For Apollo missions, once the third stage of the Saturn launch vehicle had set them on course for the Moon, the crew put the techniques learned to good use and docking became a means to an end rather than an end in itself.

The lunar module sat below the command and service modules, hidden away in a conical shroud known as the SLA (pronounced 'slaw') which took the vehicle's diameter from the 6.6-metre-wide S-FVB to that of the 3.9-metre service module. The initials SLA variously stood for spacecraft or service module to lunar module adapter, and it was the CMP's task to retrieve the LM from its embrace in the final intensive task that had to be completed before the crew could settle down to the translunar coast. It did not always go according to plan.

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