Ed Mitchell, LMP on Apollo 14, once wrote. "Preparing for a burn is a serious business, and before each one. Slu [Roosa] would announce, ‘It s sweaty palms lime again, gentlemen."’ The TEI burn tvas the one where mission control sweated more than usual, and that of Apollo 8 on Christmas Eve of 1968 was viewed with greater apprehension than any other, simply because it was the first. Its CSM was only the second Block II Apollo spacecraft to have flown in space, and they had sent it and its living human cargo all the way around ihc Moon. While ihc engineers had complete confidence in the reliability of the SPS engine, there was always a deep fear that, somewhere in ihc system, human frailly would cause a problem. In the MOCR, a clock counted down to the moment w’hen, if the burn had gone well, the spacecraft should come around the limb. The Earth station at Honeysuckle Creek in Australia was mosi favoured and its 26-mcirc anienna listened carefully.

The time for acquisition of signal (AOS) arrived, and almost immediately, engineers ai Honeysuckle reported a Unified S-band radio signal coming from the spacecraft.

"Apollo 8, Houston," Capcom Ken Mattingly called out to the crew as the engineers in Australia worked to lock ihc great dish’s receivers and transmitters onto the spacecraft.

"Apollo 8. Houston. Apollo 8, Houston,” continued Mattingly.

"Apollo 8. Houston. Apollo 8, Houston.”

"Houston, Apollo 8. Over.” called Jim Lovell from the speeding spacecraft.

"Hello. Apollo 8. Loud and clear.” replied Mattingly, speaking on behalf of all at mission control, all of them relieved that they had pulled off the most daring part of the flight.

"Roger.” said Lovell. Then, with the holiday period in mind. "Please be informed, there is a Santa Claus.”

"Thai’s affirmative,” agreed Mattingly. "You are the best ones to know.”

Soon after CSM Charlie Brown appeared on its way home after TEI on Apollo 10, commander Tom Stafford, wiio tvas an enthusiastic proponent of television from Apollo, turned the spacecraft around to aim their colour TV camera at the receding Moon. One of his impressions when seeing the entire ball of the Moon in one view’ was: "It’s a good thing we came in backwards at night lime where we couldn’t see it, because if we came in from this angle, you’d really have to shut your eyes.”

When Columbia similarly reappeared on time after Apollo ll’s TEI burn. Duke was ready to quiz the crew.

"Hello Apollo 11. Houston. How did it go? Over.”

Collins cheerily replied, "Time to open up the LRL doors. Charlie.” The crew

The Moon’s far side from Apollo 15 as it departed for Earth. Jenner is top right with its central peak, and Yallis Schrodinger is the gash near the bottom. (NASA)

were now officially in quarantine and were destined to spend most of the next three weeks isolated in the Lunar Receiving Laboratory in Houston.

"Roger,” said Duke. "We got you coming home. It’s well stocked.” Armstrong provided the details of the bum and then praised their trusty SPS engine. "That was a beautiful bum. They don’t come any finer.”

David Scott concurred with how well the SPS worked on Apollo 15: "What a smooth bum that one was. Just can’t beat these rocket engines for travelling.” On his mission, and all the J-missions, it was customary to adjust the spacecraft’s attitude so that the mapping camera could photograph the retreating Moon, and perhaps image more of the polar regions which had been relatively poorly covered by the Lunar Orbiters. Each succeeding exposure showed the Moon receding further and further into the darkness of space.

Apollo 16’s view of the receding Moon taken by its mapping camera. At first, only the far side was visible, but gradually, the eastern mare came into view. (NASA)

As Alan Bean watched the stark lunar globe move away from Yankee Clipper on Apollo 12, he and his crewmates were struck by the unreality of their situation. "This Moon is just this white ball right out in the middle of a big black void, and there just doesn’t seem to be any rhyme or reason why we are here, or why it’s sitting out there. All the time we were in lunar orbit we were discussing this thing – how unreal it looked. And it is amazing to us to fly around it as it is. When you just think about going to the Moon, it is very, very unreal to be there. It’s really getting small in a hurry. It’s just sort of unreal to look outside. It is almost like a photograph moving away from you. It doesn’t seem possible it can be a whole sphere that you were orbiting a couple of hours ago.”

When the CSM left Earth, the service module’s tanks were loaded with 18.5 tonnes of propellant. By the time it was on its way back, the majority of this had

been consumed. What remained had been kept aside as a contingency in case the CSM had to make manoeuvres to rcseue a stricken LM in lunar orbit. For the Apollo 8 flight, with no LM to transport to lunar orbit, the tanks were still a quarter full after TEI. while for Apollo 11, which did have a heavy LM. only an eighth remained. Not all of this remaining propellant was usable. By Apollo 17, the planners had become more knowledgeable about the spacecraft and its capabilities and felt confident to plan the mission such that, after TEI, only four per cent of usable propellant remained in its tanks.