Into lunar orbit

FLIGHT DAY 4

As Apollo ll’s trajectory was predicted to produce a closest approach to the Moon of 62 (±2) nautical miles, as against the nominal 60, Glynn Lunney, leading the overnight Black Team, decided to cancel midcourse correction 4 and, as the crew would not now require to devote time to a P52 platform realignment and the other chores for the manoeuvre, he also decided to extend the sleep period either by two hours or until the astronauts awoke of their own accord.

When the scheduled wake-up time passed without word from Houston, Aldrin, who was standing watch, put in a call, “Houston, Apollo ll.” Getting no response, he repeated the call twice more.

It was approaching 6 am in Houston on Saturday, 19 July. “Good morning,” replied Ron Evans, making his first communication of the mission as ‘graveyard’ shift CapCom.

‘‘Are you planning midcourse correction 4?’’ Aldrin asked.

‘‘That’s negative,’’ said Evans. ‘‘We were going to let you sleep in until about 71 hours, if you’d like to turn over.’’

‘‘Okay. That’ll be fine.’’

Several minutes later, however, Armstrong and Collins also stirred, and it was decided to make an early start while remaining off the air until Houston made the formal call. Armstrong and Collins had slept 7.5 hours; Aldrin for only 6.5 hours. During this hiatus, Cliff Charlesworth’s Green Team began their shift, with Bruce McCandless as CapCom.

The astronauts’ wives had an early start, too. Jan Armstrong went out onto the lawn to give the photographers the first of their daily pictures. Pat Collins went to have her hair done, only to find that three female journalists also just happened to have appointments. On returning home, she took delivery of flowers from Annie Glenn, wife of John Glenn, with a card that stated: ‘May God watch over you and your family.’ Meanwhile, Joan Aldrin welcomed Michael and Rosalind Archer, her father and step-mother, who had just arrived from Pensacola, Florida. Rusty Schweickart and his wife Clare dropped off an enormous casserole of cold roast turkey with which to help feed the growing crowd.

“Good morning again,” said Aldrin when McCandless put in the formal wake-up call at 71 hours.

After relaying the flight plan updates, McCandless, with lunar orbit insertion imminent, returned to the low-pressure indication in the combustion chamber of the main engine during midcourse correction 2. “I’ve got a few words for you on the SPS engine performance.’’

“We’re ready to listen,’’ Armstrong replied.

“The onboard combustion chamber pressure reading is due to a known gauge calibration factor between what is in the chamber and what you’re reading on the gauge. We expect a single-bank operation to be 90 psi on the gauge for an actual chamber pressure of 95 psi; in dual-bank operation, a chamber pressure of 94 psi on the gauge is an actual of 99 psi.’’ The redundant propellant-feed valves of the engine were actuated by nitrogen and could be used individually (single bank) or together (dual bank). The lunar orbit insertion burn was to be done in dual-bank mode. A mission rule required the crew to cut short the manoeuvre if the chamber pressure fell below a given value, and McCandless clarified this. “Similarly, 80 psi on the gauge correlates to 83 psi actual, and we recommend that you stick to an LOI- termination-cue of 80 psi on the gauge – that is, no change to mission rules.’’

“Roger,” replied Armstrong. “We got all that.’’

Although Apollo 11 was now only 10,000 nautical miles from the Moon, the crew had not been able to see it since flight day 2 because the geometry of their trajectory meant that when they looked in that direction they were blinded by the Sun. With the spacecraft still in PTC, sunlight flooded in through a succession of windows, but while they were having breakfast the spacecraft passed into the Moon’s shadow and the cabin was suddenly plunged into darkness. Earth orbits the Sun at an average distance of 93 million statute miles. The visible surface of the Sun, known as the photosphere, is 860,000 miles in diameter, but this is surrounded by a very hot but tenuous atmosphere. This glowing corona is normally seen by Earthlings only when the Moon’s shadow falls on Earth during a total solar eclipse – having flown into that shadow, Apollo 11 had arranged its own eclipse. On looking out, the astronauts saw the corona projecting out behind the now large, but dark, lunar disk.

Deciding to take a picture, Collins asked McCandless to suggest an exposure for the corona. He got a typically comprehensive response. “We recommend that you use high-speed black-and-white film, interior lights off, the Hasselblad with the 80- millimetre lens and, as you’ll be hand-holding the camera, an f-stop of 2.8, with a sequence of time exposures at one-eighth of a second, one-half of a second, and, if you think you can steady the camera against something, exposures of 2, 4 and 8 seconds.’’

“It’s quite an eerie sight,’’ said Aldrin. “There’s a marked 3-dimensional aspect of having the corona coming from behind the Moon the way that it is.’’ From their perspective, with the Moon occulting the Sun, most of the lunar disk was revealed by ‘Earthshine’. The phases of the Moon and Earth are opposed, in the sense that when the Moon is a crescent, Earth is gibbous – which was the case at this point in the mission. Also, owing to their actual sizes, the angular diameter of Earth’s disk is fully four times that of the Moon as viewed from Earth. Furthermore, Earth has a

A diagram of the ‘Earthshine’ illumination as Apollo 11 approached the Moon to perform the LOI-1 manoeuvre.

greater albedo, meaning that it reflects a higher percentage of the sunlight that falls on it. Thus, Earthshine illuminates the lunar nightscape more brightly than a ‘full’ Moon does a terrestrial night. ‘‘I guess what’s giving it that 3-dimensional effect is the Earthshine,” Aldrin mused. ‘‘I can see the crater Tycho fairly clearly – at least, if I’m right-side-up, I believe it’s Tycho. And, of course, the sky is lit all the way around the Moon.’’ From Apollo 11’s vantage point, it was possible to see a dark crescent of the hemisphere that faces away from Earth, with the limb silhouetted against the glowing corona.

‘‘The Earthshine coming through the window is so bright you can read a book by it,’’ Collins noted.

‘‘How far out can you see the corona extending?’’ McCandless asked.

‘‘I would suggest that along the ecliptic we can see the bright part of the corona out to about two lunar diameters; and perpendicular to that line, only one-eighth to one-quarter of the lunar radius,’’ Armstrong ventured. As their eyes adapted to the darkness, they saw the stars. ‘‘It’s been a real change for us. Now we’re able to see stars again and recognise constellations for the first time on the trip. The sky’s full of stars. It’s just like the night-side of Earth. All the way here, we have only been able to see stars occasionally, and perhaps through the monocular, but we haven’t been able to recognise any star patterns.’’

‘‘I guess it’s turned into night up there really, hasn’t it?’’ said McCandless.

‘‘It really has,’’ Armstrong agreed.

“If you have a minute or so free, we can read you up the morning news here,” McCandless offered a few minutes later.

“Let’s hear it,” Armstrong replied.

“Hot from the wires of the Manned Spacecraft Center’s Public Affairs Office, especially prepared for the crew of Apollo 11: First off, it looks like it’s going to be impossible to get away from the fact that you guys are dominating all the news back here. Even Pravda in Russia is headlining the mission, and refers to Neil as ‘The Czar of the Ship’; I think maybe they got the wrong mission.’’

Fred Haise read the next item, ‘‘West Germany has declared Monday to be ‘Apollo Day’. School children in Bavaria have been given the day off. Post Office clerks have been encouraged to bring radios to work, and Frankfurt is installing television sets in public places.’’

McCandless again, ‘‘The BBC in London is considering a special radio alarm system, to call people to their television sets in case there is a change in the EVA time on the Moon.’’

Haise, ‘‘And in Italy, Pope Paul VI has arranged for a special colour television circuit at his summer residence in order to watch you – that’s even though Italian television is still black-and-white.”

McCandless, ‘‘Here in Houston, your wives and children got together for lunch yesterday at Buzz’s house and, according to Pat, it turned out to be a gabfest. The children swam and did some high jumping over Buzz’s bamboo pole.’’

Haise, ‘‘In Moscow, space engineer Anatoli Koritsky, quoted by TASS, stated that Luna 15 could accomplish everything that has been done by the earlier Luna spacecraft. This was taken by the press to mean it could investigate gravitational fields, photograph the Moon, and then go down onto the surface to scoop up a bit for analysis.’’

McCandless, ‘‘Mike, even your kids at camp got into the news. Michael Junior was quoted as replying ‘Yeah’ when somebody asked him if his daddy was going to be in history. ‘What’s history?’ he asked, after a short pause.’’

After a sports round-up, Haise concluded with a novelty item, ‘‘You might be interested in knowing, since you are already on the way, that a Houston astrologer, Ruby Graham, says that the signs are right for your trip to the Moon. She says that Neil’s clever, Mike has good judgement and Buzz can work out intricate problems. She also says Neil tends to see the world through rose-coloured glasses, but he is always ready to help the afflicted or distressed. Neil, you are also supposed to have intuition that enables you to interpret life with feeling. Buzz is supposed to be very sociable, cannot bear to be alone and has excellent critical ability. Since she didn’t know at what hour you were born Mike, she has decided that you either have the same attributes as Neil or you’re inventive with an unconventional attitude that might seem eccentric to the unimaginative.’’

‘‘Who said all that?’’ Collins asked.

Haise laughed, ‘‘Ruby Graham, an astrologer here in Houston.’’

‘‘Tell Michael Junior that history or no history, he’d better behave himself,’’ Collins requested.

‘‘We’ll pass that along,’’ McCandless promised.

A few minutes later, Collins announced that he was going to halt PTC because the translunar coast was drawing to a close. By design, their trajectory would take the spacecraft in front of the Moon’s leading limb. However, because the Moon is 2,160 statute miles in diameter, and pursues its orbit around Earth at 2,287 miles per hour, this rendezvous required precise navigation through cislunar space.1 Although it was possible to enter lunar orbit by executing a single manoeuvre, if the engine were to fire for too long the spacecraft might dip so low thereafter as to crash. As the lunar orbit insertion (LOI) burn was required to occur on the far side of the Moon, out of communication, in planning Apollo 8 it had been decided to guard against this outcome by splitting the manoeuvre. The initial burn (LOI-1) would produce an orbit with a high apolune on the near side of the Moon, and the Manned Space Flight Network would track the spacecraft during the first two revolutions to make a precise calculation of the delta-V for the burn (LOI-2) that would circularise the orbit at the desired altitude, and this strategy had been retained by the later missions. Three hours before LOI-1 McCandless read up the details: time of ignition would be 075:49:49, the duration of the burn was to be 6 minutes 2 seconds, and the objective of the retrograde delta-V of 2917.3 feet per second was to achieve a lunar orbit with a perilune of 62 nautical miles and an apolune of 170 nautical miles. The loss of signal (LOS) as the spacecraft passed behind the Moon’s leading limb in the run-up to this manoeuvre was predicted at 075:41:23. If the burn was as intended, then the acquisition of signal (AOS) upon appearing around the trailing limb would be at 076:15:29. If for some reason the engine did not fire, acquisition would be 10 minutes earlier, and the gravitational ‘slingshot’ resulting from the encounter would have deflected the spacecraft’s trajectory back to Earth. If the engine were to cut off prematurely, then Apollo 11’s fate would depend upon whether the delta-V attained was sufficient to enable the Moon to capture it. If it attained an orbit with a very high apolune, this might possibly be lowered to continue the lunar phase of the mission. If, however, the burn did not last long enough to enable the Moon to capture the spacecraft, then it would emerge from the trailing limb heading into deep space and, in the event of the SPS being deemed unusable, their fate would rest upon whether it was possible to use the descent propulsion system of the LM to attempt a return to Earth; there was no guarantee.

At 075:30, after Charlesworth had polled his team, McCandless passed on the decision, ‘‘You’re Go for LOI.’’

‘‘Roger,’’ acknowledged Aldrin. ‘‘Go for LOI.’’

‘‘All your systems are looking good going around the corner, and we’ll see you on the other side.’’

In the event, only one of the four midcourse correction options had been necessary.