Category The First Men on the Moon

On 15 October 1962 Hamilton Standard of Windsor Locks, Connecticut, initiated development of the Portable Life-Support System (PLSS) for use by an astronaut on the lunar surface. It had to be able to accommodate the metabolic heat liberated by a man doing the equivalent of shovelling sand and, for short periods, sawing wood without overheating or fogging the visor. An attempt to use the oxygen circulation system of the space suit proved to be inadequate, and in September 1964 it was decided to develop an undergarment incorporating a network of fine tubes through which cool water could be pumped. In 1965, with the PLSS growing in size and complexity, consideration was given to cancelling it in favour of just providing the astronauts with 50-foot umbilicals that would snake out of the hatch, even though this would have restricted lunar surface activity to the immediate vicinity of the LM. Fortunately, the pace of development promptly improved. The backpack was 26 inches high, 18 inches wide and 10 inches deep, and contained: (a) a primary oxygen system to regulate the suit at 3.7 pounds per square inch; (b) a ventilator to circulate oxygen, both for breathing and to cool, dehumidify, and cleanse the suit of carbon dioxide and other contaminants; (c) a loop to circulate 4 pounds of water per minute through the liquid-coolant garment; (d) a sublimator to shed waste heat to vacuum; and (e) a communications system to provide primary and backup voice relay via the LM. Each internal system was covered by a thermal insulator of fire-resistant beta cloth, and the entire pack was covered with aluminised kapton to minimise heat transfer and fibre-glass as protection against incidental damage. It had sufficient water and oxygen for 4 hours of nominal operation, but this would begin at the time of disconnecting from the LM’s life-support system, prior to egress, and run on after ingress until switching back to the LM. However, as no one could be certain of the metabolic rate of a man on the lunar surface, and therefore of the rate at which oxygen and coolant would be consumed, it was decided to limit the first moonwalk to half of this time. If a second moonwalk were to be scheduled then the PLSS would be replenished as necessary from the LM’s resources.

When Apollo 9 lifted off on 3 March 1969 with LM-3, mission commander Jim McDivitt thought that if they achieved only 50 per cent of their demanding program they would still be able to declare the mission a success. Rusty Schweickart was to test the PLSS by emerging from the forward hatch of the LM, translating along a

Nevertheless, if it had been decided that Aldrin should egress first, it would have been possible for them to switch places prior to donning their bulky backpacks.

handrail onto the roof of the vehicle, grasping a shorter rail on the CSM and entering the command module through its side hatch, so rehearsing the external transfer that would be used in the event of a returning lunar crew being unable to employ the tunnel in the docking system. However, when Schweickart suffered ‘space sickness’ early in the flight his spacewalk was limited to the ‘porch’ of the LM. Nevertheless, the 38-minute excursion was sufficient to demonstrate the PLSS in the space environment, and no one seriously doubted that an external transfer between vehicles was feasible.

When NASA began to launch pairs of spacecraft during a single Apollo mission, it became necessary to introduce individual call signs while the vehicles were being operated independently. On seeing their CM arrive at the Cape tightly wrapped in a blue sheet, like a sweet, the Apollo 9 crew decided to name the CSM ‘Gumdrop’, and the LM was named ‘Spider’ for its arachnid appearance. In March 1969, after the Apollo 10 crew decided to name their vehicles ‘Charlie Brown’ and ‘Snoopy’ – characters in Charles L. Schulz’s comic strip Peanuts – Julian Scheer, Assistant Administrator for Public Affairs, wrote to George M. Low, Manager of the Apollo Spacecraft Program Office in Houston, to suggest that the next mission, which was to try to land on the Moon, should use more dignified names. The Apollo 11 crew, of course, were fully aware of the historical significance of their mission. As Michael Collins recalled:11

Based on accounts in Carrying the Fire: An Astronaut’s Journeys, by Michael Collins, W. H. Allen, p. 332, 1975, and ‘All we did was fly to the Moon’: Astronaut Insignias and Call Signs, by Richard L. Lattimer, The Whispering Eagle Press, Florida, p. 66, 1985.

“We had a variety of non-technical chores, such as thinking up names for our spacecraft and designing a mission emblem. We felt Apollo 11 was no ordinary flight, and we wanted no ordinary design, yet we were not professional designers. NASA offered to help us along these lines – wisely, I think. On Gemini 10, which [I flew with John Young, and] in my view has the best­looking insignia of the Gemini series, artistic Barbara Young had developed one of John’s ideas and come up with a graceful design, an aerodynamic ‘X’ devoid of names and machines. This was the approach we wanted to take on Apollo 11. We wanted to keep our three names off it, because we wanted the design to be representative of everyone who had worked toward the lunar landing – and there were thousands who could take a proprietary interest in it, yet who would never see their names woven into the fabric of a patch. Further, we wanted the design to be symbolic rather than explicit. On Apollo 7, Wally Schirra’s patch showed the Earth and an orbiting CSM trailing fire. On Apollo 9, Jim McDivitt produced a Saturn V, a CSM, and a LM. Apollo 10’s was even busier! Apollo 8’s was closer to our way of thinking, showing a figure of eight looping around Earth and Moon, on a command-module-shaped patch, but it had, like all the rest, three names printed on it. We needed something simpler, yet something which unmistakably indicated a peaceful lunar landing by the United States. Jim Lovell, Neil’s backup, introduced an American eagle into the conversation. Of course! What better symbol – eagles landed, didn’t they? At home I skimmed through my library and finally found what I wanted in a National Geographic book on birds: a bald eagle, landing gear extended, wings partially folded, coming in for a landing.[18]1 traced it on a piece of tissue paper, and sketched in an oblique view of a pockmarked lunar surface. Thus the Apollo 11 patch was born – although it had a long way to go before final approval. I added a small Earth in the background and drew the sunshine coming from the wrong direction, so that to this day our official insignia shows the Earth [incorrectly oriented] over the lunar horizon. I pencilled ‘APOLLO’ around the top of my circular design and ‘ELEVEN’ around the bottom. Neil didn’t like the ‘ELEVEN’ because it wouldn’t be understandable to foreigners, so after trying ‘XI’ and ‘11’, we settled on the latter, and put ‘APOLLO 11’ around the top. One day, outside the simulator, I was describing my efforts to Jim Lovell, and he and I both agreed that the eagle alone really didn’t convey the entire message we wanted. The Americans were about to land, but so what? Thomas L. Wilson, our computer expert and simulator instructor, overheard us and said to add an olive branch as a symbol of our peaceful expedition.

Beautiful! Where do eagles carry olive branches? In their beaks, naturally. So I sketched one in, and after a few discussions with Neil and Buzz over colour schemes, we were ready to go to press. The sky would be black, not blue, but absolute black, as in the real case. The eagle would be eagle-coloured, the Moon Moon-coloured, as described by Apollo 8, and the Earth also. So all we had left to play with, really, were the colours of the border and the lettering. We picked blue and gold, and then Stan Jacobsen in Houston assigned James R. Cooper, an illustrator at MSC, to do the artwork for us. We photographed the finished design and sent a copy through channels to Washington for approval. Washington usually rubber-stamped everything. Only this time they didn’t, and our design came back disapproved. The reason? The eagle’s landing gear – powerful talons extended stiffly below him – was unacceptable. It was too hostile, too warlike; it made the eagle appear to be swooping down on the Moon in a very menacing fashion – according to Bob Gilruth [Director of the Manned Spacecraft Center]. What to do? A gear-up approach was unthink­able. Perhaps the talons could be relaxed and softened a bit? Then someone had a brainstorm: just transfer the olive branch from beak to claw, and the menace disappeared. The eagle looked slightly uncomfortable clutching his branches tightly with both feet, but we resubmitted it anyway, and it greased on through channels and won final approval.’’

As regards the call signs, when it became apparent that Apollo 11 would be the mission, the crew began to receive suggestions for naming their spacecraft, some of which comprised pairs, others not. Names from mythology were dismissed for the simple reason that investigation invariably turned up something inappropriate. Romantic name pairings such as ‘Romeo’ and ‘Juliet’ were also rejected. ‘Castor’ and ‘Pollux’ were appealing, but were too suggestive of the Gemini program. Pat Collins argued for ‘Owl’ and ‘Pussycat’. An important factor was that the names selected should have clarity in radio transmission. For Scott Carpenter’s Mercury flight, his wife, Rene, had suggested ‘Rampart’, after the mountain range of his native Colorado, but he chose ‘Aurora’, which, lacking hard consonants, proved indistinct on the radio. It was decided that while the names must reflect American pride in the mission, they must do so with subtlety. To paraphrase Collins’s account:

‘‘The choice of an eagle as a motif for the landing led swiftly to naming the landing craft Eagle. One day, I was chatting long-distance with Julian Scheer, Assistant Administrator for Public Affairs in Washington, who suggested the name Columbia for our CSM. It sounded a bit pompous to me, but it had a lot going for it – the close similarity of Jules Verne’s mythical moon-ship cannon, the Columbiad, and the close relationship between the word ‘Columbia’ and our national origins: Columbia had almost become the name of our country. Finally, the lyrics ‘Columbia, the Gem of the Ocean’ kept popping into my mind and they argued well for the recovery of the spacecraft, which hopefully would float on the ocean. Since Neil and Buzz had no objections, and since I couldn’t come up with anything better, Columbia it was.’’

The ‘Apollo 11’ call sign would be used until such time it became necessary to discriminate, whereupon the two vehicles would employ their own names. Prior to the mission, Armstrong and Aldrin had given some thought to whether they should continue to refer to themselves by the call sign ‘Eagle’ while on the lunar surface, or introduce some other name. As Aldrin recalls:13

‘‘It would be somewhat similar to a radio call sign, but we wanted to give it added significance. Moon One? Base Camp? Moon Base? When we made our choice, we told only Charlie Duke, who would be our Capsule Communicator back in Houston, who we felt should know the exact name in case transmission was garbled. I cannot remember which of us originated the selection, but once we had thought it over it was an obvious choice. We were landing in an area known as the Sea of Tranquility, and would call our landing site Tranquility Base.’’

Approval of the call signs was not forthcoming from headquarters until the beginning of July.

Armstrong armed the descent propulsion system (DPS) and Aldrin depressed the PROCEED key on the DSKY. As the thrusters provided ullage to settle the fluids in their tanks, Puddy had intended to accurately measure the propellant quantities, but the telemetry was inadequate and he had to resort to subtracting from the initial load the amount estimated to have been used during the DOI burn, which introduced an unfortunate uncertainty into his prediction of the total firing time available to the engine.

“Ignition,” announced Armstrong when the computer decided that Eagle was at the PDI point. “10 percent.”

“Just about on time,” noted Aldrin.

It was just after 3 pm in Houston. Frustrated with the television commentary, Jan Armstrong had retired to her bedroom to listen to the powered descent on the squawk box, with Bill Anders joining her to provide technical exposition. Prior to launch, she had impressed on Slayton that if there was a problem she wanted her squawk box feed to continue. She did not want a repeat of Gemini 8, which Neil had commanded, when her audio had been cut as soon as it was realised the ship was in trouble and, even worse, on going to Mission Control to find out what was going on she had been refused entry.

Columbia was 120 nautical miles behind and above, but it would catch up and by the nominal landing time would be 200 nautical miles farther west, and near to or below the local horizon. Collins’s role was to monitor the link between Eagle and Houston, and be prepared to act should intervention prove necessary.

The mood in the Mission Operations Control Room was intense concentration, and great expectation. The main wall screen showed a plot of the nominal powered descent profile, with a travelling symbol tracing Eagle’s progress. Bales noted that at ignition the radial velocity component had been off by 20 feet per second. Being more than halfway towards the ‘abort limit’, this was concerning.[30] But he reasoned that if it was a navigational issue the magnitude of the error would remain constant because it reflected a failure of the initial conditions, whereas if it was a guidance issue the error would probably increase; time would tell.

When the computer throttled up to 100 per cent 26 seconds into the burn, there was a silent high-frequency vibration and the astronauts’ feet settled onto the floor, leaving them in no doubt that they had a good engine.

“PGNS is holding,’’ Aldrin confirmed for Armstrong, being heard by Houston because he was on VOX.

The 10-degree yaw had helped communications, but because the spacecraft’s attitude was fixed with respect to the surface as it travelled westwards, the line of sight to Earth was changing and the antenna was again being blocked. “Columbia, Houston,’’ Duke called. “We’ve lost them. Tell them to go aft omni.’’ On receiving Collins’s relay, Aldrin opted to override the automatic pointing. He selected Slew mode and specified the pitch and yaw pointing angles appropriate to this phase of the descent profile. The signal improved.

“Eagle, we’ve got you now,’’ Duke called.

“Rate of descent looks good,’’ said Aldrin, speaking to Armstrong.

“Everything’s looking good here,’’ Duke said, by way of an advisory. Noting that Aldrin had the steerable antenna in Slew, Duke passed up a recommendation for how it should be pointed after Eagle had yawed ‘windows up’.

“PGNS good? AGS good?’’ Armstrong prompted Aldrin.

‘‘AGS and PGNS agree very closely,’’ Aldrin confirmed.

The AGS was operating passively, ready for use in the event of PGNS failure. Although (as its name suggests) the AGS was for aborts, if the PGNS were to fail so close to the surface that an abort was deemed risky, the AGS would be used to continue the descent in order to land and then perform an emergency liftoff under more controlled conditions.

‘‘How are you looking, Guidance?’’ Kranz prompted.

The residual in the radial velocity had remained constant, indicating it to be the result of a simple navigational error. ‘‘The residual is still 20 foot per second,’’ Bales replied. ‘‘It looks good.’’

‘‘No change, is what you’re saying?’’ Kranz asked.

‘‘No change,’’ Bales confirmed. ‘‘That’s down track, I know it.’’ The PGNS was aiming for where it thought the target was; the fact that it had no way of knowing it was off course meant that it would land slightly downrange.

‘‘Rog,’’ acknowledged Kranz.

Armstrong confirmed to Houston, ‘‘RCS is good. No flags. DPS pressure is good. Two minutes.’’

‘‘Altitude’s a little high,’’ warned Aldrin. They were about 47,000 feet.

Having re-established tracking by the Manned Space Flight Network following a brief hiatus, Greene said, ‘‘Flight, FIDO. We’ve reinitialised our filters, and we do have an altitude difference.’’

‘‘Rog,’’ acknowledged Kranz.

Since the post-DOI ranging test, the rendezvous radar had been in Auto Track mode.

“Want to get rid of this radar?” suggested Armstrong.

“Yeah,” agreed Aldrin.

“To Slew?”

“Slew,” Aldrin confirmed.

This item on the checklist was a carry-over from the Apollo 10 mission, on which, because the plan had been to abort at the PDI point, the rendezvous radar had been set to continuously update the computer with the position of the CSM. At this point in Eagle’s descent, however, this data was not only unnecessary, it would soon prove to be a distraction to the computer.

Aldrin noticed a fluctuation in the alternating current voltage. The concern was that the landing radar would need a stable AC power supply. However, there was no fluctuation in the telemetry and the problem was concluded to be an issue with the onboard meter.

“You’re still looking good at 3 minutes,’’ Duke advised.

“Control,” Kranz called. “Let me know when he starts his yaw manoeuvre.’’

“Roger,” acknowledged Carlton.

“How’s the MSFN looking now, FIDO?’’ Kranz asked.

“We’re Go,’’ Greene replied.

“How about you, Guidance?’’

“It’s holding at about 18 feet per second,’’ Bales replied, referring to the radial velocity residual. “We’re going to make it, I think.’’

“Rog,’’ Kranz acknowledged.

On making his final downrange position check, Armstrong observed that they flew over Maskelyne-W fully 2 seconds early. At their current horizontal speed of 1 nautical mile per second, this meant that they were significantly ‘long’. Because the landmark checks at 3 minutes and 1 minute in advance of PDI had been on time, he was puzzled. At PDI, his attention had been inside, checking the performance of the engine, and he had not noticed precisely where they were at that moment. With the vehicle yawed 10 degrees to improve the line of sight of the high-gain antenna, it was difficult to estimate the crossrange error. The target ellipse was 11 nautical miles long and 3 nautical miles wide, with its major axis oriented along the direction of flight. Although they would land beyond the centre of the ellipse, he was certain they were ‘in the ball park’. ‘‘We went by the 3-minute point early,’’ he told Aldrin.

Aldrin was continuing to check their trajectory. One minute earlier they were slightly high, but the guidance system was steering towards the nominal trajectory. ‘‘The rate of descent is looking real good. Altitude is right about on.’’

Armstrong told Houston of their overshoot. ‘‘Our position checks show us to be a little ‘long’.’’

‘‘He thinks he’s a little bit ‘long’,’’ Duke informed Kranz.

‘‘We confirm that,’’ Bales pointed out.

‘‘Rog,’’ Kranz acknowledged. Knowing the western end of the ellipse was rougher terrain than the target, Kranz mused that Armstrong might have difficulty in finding a spot on which to land, and this, in turn, alerted Kranz to the likelihood that the hovering phase of the descent might prove to be protracted.

Having begun the powered descent ‘windows down’ for landmark checking, Eagle now had to rotate around the thrust axis in order that the landing radar at the rear of the underside of the vehicle would face the surface. “Now watch that signal strength, because it’s going to drop,” Armstrong warned Aldrin as he initiated the yaw. With the steerable antenna in Slew mode, Aldrin would have to manually adjust it as the vehicle turned.

“Okay all flight controllers, I’m going to go around the horn,’’ Kranz called as the 4-minute mark approached.

“We’re yawing, Flight,’’ Carlton informed Kranz, as requested.

“Boy, I tell you, this is hard to do,’’ Armstrong observed.

“Keep it going,’’ urged Aldrin.

Owing to the fact that Armstrong had neglected the checklist item to select a rapid rate of yaw, the manoeuvre began sluggishly and was erratic. Realising his error, he correctly set the Rate Switch and restarted the manoeuvre at the planned rate of 5 degrees per second. The torque from the disturbed propellants sloshing in the tanks not only made the yaw ragged, but also induced rates in the other axes, which caused much more thruster activity than he had expected. Despite Aldrin’s attempt to keep the steerable antenna pointing at Earth during the turn, communications became intermittent. Kranz told his team to make their recommendations based on their most recent data, but when telemetry was restored before he could begin his poll he allowed them another few seconds.

Finally, Kranz took his poll, “Retro?’’

“Go!’’ replied Deiterich.

“FIDO?’’

“Go!’’ replied Greene.

“Guidance?’’

“Go!’’ replied Bales.

“Control?’’

“Go!’’ replied Carlton.

“TELCOM?’’

“Go!’’ replied Puddy.

“GNC?’’

“Go!’’ replied Willoughby.

“EECOM?’’

“Go!’’ replied Aaron.

“Surgeon?’’

“Go!’’ replied Zieglschmid.

“CapCom we’re Go to continue PDI,’’ Kranz announced.

Duke relayed the advisory, “Eagle, Houston, you are Go to continue powered descent.’’

“Roger,’’ Aldrin acknowledged.

Eagle was now at 40,000 feet.

“Everybody, let’s hang tight and look for the landing radar,’’ said Kranz. The static cleared up. “Okay we’ve got data back.’’

The landing radar utilised four microwave beams to measure altitude in terms of echo-location and the rate of change of altitude by the Doppler effect. It was not expected to be very accurate above 35,000 feet. If it failed to function, a mission rule mandated an abort. However, in the event of difficulty bringing the radar on-line Kranz intended to permit the descent to continue to enable the problem to be investigated and, if it persisted, order the abort at 10,000 feet. He had selected this altitude because, in the absence of the radar, the spacecraft’s navigation was based on Manned Space Flight Network tracking, which was calculated against a mean lunar surface measured with respect to the radius of the Moon at the landing site, which might as much as 10,000 feet in error; if the spacecraft were to pass below this altitude without radar it might well hit the surface. As Eagle yawed, the radar on its base began to get ‘returns’ from the surface.

“Radar, Flight,’’ called Bales. ‘‘It looks good.’’

‘‘Rog,’’ Kranz acknowledged.

Because the yaw manoeuvre had run late, by the time it was complete Eagle was somewhat lower than intended at radar lock-on.

‘‘Lock-on,’’ Aldrin told Armstrong.

‘‘Have we got a lock-on?’’

‘‘Yes,’’ Aldrin confirmed. When the radar began to supply continuous data, a light on the control panel went out. ‘‘Altitude light’s out.’’

When the altimetry became available, the PGNS was showing them to be at an altitude of 33,500 feet. The radar said they were somewhat lower. Aldrin reported this to Houston. ‘‘Delta-H is minus 2,900 feet.’’

The computer began by considering the orbital data from the Manned Space Flight Network to be accurate, and the radar altimetry to be suspect. But if the radar was functioning properly, its data would be more accurate. If the radar data differed significantly from the computer’s navigation, the computer was to try to converge towards a compromise altitude. If the computer thought it was at 32,000 feet and the radar read 28,000 feet the computer could not simply accept this and revise its aim for the landing site, because the radar would be tracing the topography of the surface and would fluctuate. Instead, the computer would split the difference and use 30,000 feet, and iterate until it had properly ‘corrected’ its altitude, at which time it would recalculate its descent trajectory for the target. If they had found themselves in excess of 10,000 feet higher than the PGNS estimated, this would have required an abort, because if they had continued they would have run out fuel before reaching the surface.

With Eagle pitched at 77 degrees at this point in the descent, not quite on its back, its forward windows faced Earth which, because the spacecraft was east of the lunar meridian, was to the west of the zenith. Glancing out, Aldrin saw it as a half-disk of blue and white. ‘‘We have got the Earth right out our front window,’’ he observed. As the descent continued, and Eagle progressively changed its pitch angle to face its direction of motion, transitioning to a hover, the home planet would drift out of the top of the windows.

Aldrin asked the computer to calculate and show the delta-H. As a precaution against loss of communication at this juncture, he had a chart with which to judge for himself whether the radar data was valid. Armstrong sought confirmation that Houston was also monitoring this, ‘‘Houston, are you looking at our delta-H?’’

“That’s affirmative,” replied Duke.

“Looks good, Flight,’’ Bales called on the flight director’s loop.

“Is he accepting it, Guidance?’’ Kranz asked.

“Standby,” replied Bales.

As Bales studied the radar data, the yellow Master Alarm in Eagle started to flash, a tone sounded in Armstrong’s and Aldrin’s headsets and the DSKY lit the yellow ‘PROG’ light.

Armstrong keyed his PTT and, with tension evident in his voice, announced, ‘‘Program alarm.’’

Aldrin queried the computer, which flashed ‘12-02’.

‘‘It’s a 12-02,’’ Armstrong elaborated for Houston.

‘‘12-02,’’ confirmed Aldrin.

Armstrong and Aldrin turned their heads in their ‘bubble’ helmet to glance at each other; neither man had seen this alarm during simulations.

‘‘What is it?’’ Armstrong asked Aldrin.

As the computer specialist, Aldrin knew in general terms what a program alarm meant, but had no way of deciding whether this was a hardware or a programming issue. ‘‘It’s in core,’’ he mused.

Although Armstrong knew that their telemetry would enable Houston to show the status of the hardware, he was also aware that if the situation were to turn sour he might have to abort without Houston’s input.

Already psyched up by the task at hand, the alarm further boosted everyone’s adrenaline. ‘‘When I heard Neil say ‘12-02’ for the first time,’’ reflected Duke, ‘‘I tell you, my heart hit the floor.’’ The alarm caused consternation on Management Row. Gilruth, Phillips and Low sought insight from Kraft, but while he knew that some program alarms mandated an abort he was by no means an expert, and was unable to offer an explanation in this case.

Paules was the first to react, ‘‘12, 12-02 alarm.’’ After a pause, ‘‘Yeah, it’s the same thing we had.’’ He was referring to the simulation in which Koos had caught them out – although in that case it had been a 12-01. Bales switched his attention from the radar and conferred with Jack Garman, an expert in the computer, on his support team. Garman, now fully familiar with all the program alarms, said, ‘‘It’s executive overflow – if it doesn’t occur again we’ll be fine.’’

‘‘Flight, Retro,’’ called Deiterich while Bales and Garman were conferring.

‘‘Go, Retro,’’ prompted Kranz.

‘‘Throttle down, 6 plus 25,’’ announced Deiterich, drawing Kranz’s attention to the time (measured in minutes and seconds since the start of the powered descent) at which Eagle was to throttle down.

‘‘6 plus 25,’’ acknowledged Kranz, annotating his console log.

In simulations Armstrong had been primed to abort, but now he was primed to push on. Nevertheless, he was concerned by the lack of a response from Houston, ‘‘Give us a reading on the 12-02 program alarm.’’

‘‘We’re Go on that, Flight,’’ Bales finally announced, having established that, despite the alarm, the guidance system was performing its assigned tasks. But as he would reflect later, ‘‘In the Control Center any more than 3 seconds to reach a decision during powered descent is too long; and this took us about 10 to 15 seconds.”

Duke replied to Armstrong, “Roger. We gotcha. We’re Go on that alarm.”

“If it doesn’t recur, we’ll be Go,’’ Bales added.

“Rog,” acknowledged Kranz, noting the confidence in Bales’s voice. “Did you get the throttle down, CapCom?’’ Having missed it, Duke passed this information up to the spacecraft.

Eagle’s altitude was now down to 27,000 feet. Bales, returning his attention to the landing radar, announced, “He’s taking in the delta-H now.’’

“Rog,” acknowledged Kranz.

“Flight, FIDO,’’ called Greene. “We’re converging on delta-H.’’

“Rog,” acknowledged Kranz.

“Flight, Control,’’ called Carlton. “We’re on velocity.’’

“Rog,’’ acknowledged Kranz.

Having received a Go on the 12-02, indicating that the computer was healthy, Aldrin again queried delta-H, and the alarm recurred. “Same alarm,’’ he called, “It appears to come up when we have a 16/68 up.’’ Keying Verb 16 with Noun 68 told the computer to display the altitude and velocity, the range to the landing site, and the time remaining in the braking phase (in essence, the time to the pitch-over manoeuvre). Aldrin was speculating that his checking of the delta-H convergence might be prompting the executive overflow. Aldrin was correct, but the true issue was that the rendezvous radar was needlessly interrupting the computer, leaving it little time to devote to computations in addition to its navigational tasks.

“Roger. Copy,’’ acknowledged Duke.

This time Bales responded promptly, “It’s okay.’’ In the hope of relieving the load on the computer, he offered, “We’ll monitor his delta-H, Flight.’’

“Rog,’’ acknowledged Kranz.

Bales agreed with Aldrin’s line of thought. “I think that’s why he’s getting it.’’ “Okay,’’ said Kranz.

“Eagle, Houston,’’ called Duke. “We’ll monitor your delta-H.’’

“Delta-H is beautiful,’’ Bales observed.

“Delta-H is looking good to us,’’ Duke relayed.

“All flight controllers, hang tight,’’ Kranz prompted, “We should be throttling down shortly.’’

At 6 minutes 25 seconds into the powered descent, the computer throttled down the DPS engine from 100 per cent to 55 per cent.

“Throttle down on time,’’ announced Armstrong.

“Confirm throttle down,’’ Carlton noted.

“Rog, confirmed,’’ replied Kranz.

“Roger,’’ Duke responded to Armstrong. “We copy throttle down.’’

“You can feel it in here when it throttles down better than the simulator,’’ said Aldrin, tongue-in-cheek.

“Rog,’’ acknowledged Duke.

The fact that the computer throttled down the engine on time indicated that it was unaware it was coming in ‘long’, as otherwise it would have delayed the transition in

order to compensate and thereby re-establish its aim for the target.

“AGS and PGNS look real close,” noted Aldrin.

“Flight, Control,” called Carlton. “Everything looks good.”

“Rog,” acknowledged Kranz.

“Flight, FIDO,” called Greene. “We’re looking real good.”

“Rog, FIDO, good,’’ replied Kranz.

The spacecraft’s altitude was now down to 21,000 feet, and it had slowed to 1,200 feet per second.

“At 7 minutes, you’re looking great to us, Eagle,’’ Duke called.

“TELCOM,” Kranz prompted, “how’re you looking?’’

“It looks good, Flight,’’ replied Puddy.

“Rog,” acknowledged Kranz.

With the pitch angle now down to 60 degrees and the rate of change increasing, Aldrin announced, “I’m still on Slew, so you may tend to lose the high-gain as we gradually pitch over.’’ Then he had second thoughts, “Let me try Auto again now, and see what happens.’’

“Roger,’’ Duke acknowledged.

“We’re going to try the steerable again, Don,’’ Kranz warned TELCOM. “Copy, Flight,’’ replied Puddy.

“It looks like it’s holding,’’ reported Aldrin. With a clear line-of-sight and the steerable dish locked on, communications improved markedly.

“Roger,’’ acknowledged Duke. “We’ve got good data.’’

“Are we on the steerable, Don?’’ Kranz asked.

“That’s affirmative, Flight,’’ replied Puddy. “And it’s holding in there pretty good.’’

“Rog,’’ acknowledged Kranz. His concern over telemetry drop-outs abated. It seemed that he would not, after all, face the decision as to whether communications had degraded to the point of requiring an abort.

The spacecraft’s altitude was now down to 16,300 feet, and it had slowed to 760 feet per second.

“Okay, everybody hang tight,’’ Kranz said. “Seven and a half minutes.’’

“Flight, Guidance,’’ called Bales. “His landing radar’s fixed to velocity; it’s beautiful.’’

“Flight, Control. Descent 2 fuel,’’ Carlton announced. Having closely studied the redundant propellant gauging systems, he recommended monitoring the ‘low level’ sensor in gauging system number 2.

‘‘Descent 2 fuel crit,’’ said Kranz.

‘‘Descent 2 fuel, On,’’ corrected Carlton. ‘‘I didn’t want to say ‘critical’.’’

‘‘Rog,’’ acknowledged Kranz.

Duke relayed the advisory, taking care not to be ambiguous, ‘‘Eagle, Houston. Set Descent 2 fuel to Monitor.’’

‘‘Roger, 2,’’ acknowledged Armstrong.

‘‘Flight, FIDO,’’ called Greene. ‘‘It’s looking real good.’’

Pat Collins, listening to her squawk box, nervously clenched her fist.

Eagle’s altitude was now down to 13,500 feet. Having elected not to use 16/68 to

avoid further 12-02 program alarms, Aldrin asked for the time remaining in the braking phase, “Could you give us an estimated pitch-over time, please, Houston?” “Stand by,” said Duke. “You’re looking great at 8 minutes.”

“Thirty seconds to P64,’’ called Bales, responding to Aldrin’s request.

“Eagle, you’ve got 30 seconds to P64,’’ relayed Duke. The P64 program would switch to the visual approach phase of the descent.

“Have we still got landing radar, Guidance?’’ Kranz asked.

“Affirm,” replied Bales.

“Okay. Has it converged?’’ Kranz asked.

“It’s beautiful,’’ replied Bales.

“Has it converged?’’ Kranz repeated.

“Yes!” Bales replied.

“Flight, FIDO,’’ called Greene. “We look real good.’’

“Rog,” acknowledged Kranz.

“Eagle, Houston,’’ called Duke. “Coming up 8 plus 30. You’re looking great.’’ Having reached a point known as the ‘high gate’ at an altitude of 7,500 feet, Eagle’s computer initiated P64, which rapidly reduced the pitch angle from 55 degrees down to 45 degrees. Thus far, most of the thrust had been devoted to slowing the horizontal velocity. As the pitch was further reduced, more of the thrust would be directed downwards. During the pitch-over, the radar on the base of Eagle swung from its ‘Descent’ position to ‘Hover’, where it would remain, and the horizon rapidly swung up into the bottom of the windows, giving Armstrong his first view of where the computer was heading, which at this altitude was a point some 3.5 nautical miles dead ahead, just on this side of the horizon.

‘‘P64,’’ called Aldrin.

‘‘We copy,’’ Duke acknowledged.

‘‘Okay, they’ve got 64,’’ Kranz announced over the flight director’s loop. ‘‘All flight controllers, 20 seconds to Go/No-Go for landing.’’

‘‘Eagle, you’re looking great,’’ Duke confirmed. ‘‘Coming up on 9 minutes.’’

The spacecraft was down to 5,200 feet and descending at 100 feet per second, which was as planned. Armstrong tested his hand controller in pitch and yaw, and then resumed ‘hands off. ‘‘Manual attitude control is good.’’

‘‘Roger, copy,’’ acknowledged Duke.

As Eagle descended through 4,000 feet, Kranz went around the horn, ‘‘All flight controllers, Go/No-Go for landing. Retro?’’

‘‘Go!’’ called Deiterich.

‘‘FIDO?’’

‘‘Go!’’ called Greene.

‘‘Guidance?’’

‘‘Go!’’ called Bales.

‘‘Control?’’

‘‘Go!’’ called Carlton.

‘‘TELCOM?’’

‘‘Go!’’ called Puddy.

‘‘GNC?’’

“Go!” called Willoughby.

“EECOM?”

“Go!” called Aaron.

“Surgeon?”

“Go!” called Zieglschmid.

“CapCom we’re Go for landing.”

“Eagle, Houston. You’re Go for landing.’’

On hearing this, Jan Armstrong sat up on her heels at the foot of her bed. Pat Collins exclaimed, “Oh God, I can’t stand it.’’

“Roger. Understand, Go for landing,’’ acknowledged Aldrin. “3,000 feet.’’ But then, “Program alarm.’’ He keyed the DSKY for the code, “12-01.”

“Roger,” acknowledged Duke, “12-01 alarm.’’

“Same type,’’ responded Bales immediately. “We’re Go, Flight.’’

“We’re Go. Same type,’’ relayed Duke, the tension evident in his voice. “We’re Go.’’

Armstrong had wanted to look for landmarks to determine how ‘long’ they were, but this alarm distracted him, and when he next looked out they were so low that he could not see any of the landmarks he had memorised, ‘‘So,’’ he later reflected, ‘‘all those pictures Tom Stafford took on Apollo 10 to enable me to pick out where I was going and know precisely where I was, were to no avail.’’

‘‘2,000 feet,’’ called Aldrin.

Pat Collins nervously began to bite her lip.

As Aldrin had explained prior to launch, ‘‘During the landing, there is a fairly even division of labour. Neil will be looking more and more outside, his hand on the ‘stick’. He is not able to look much at the instruments. This is where we must work as a finely tuned team, to ensure that he gets the information he requires to transfer whatever he sees into something meaningful. I’ll relay this information. And at the same time I’ll be looking at the various systems to make sure they’re operating the way they should. However, here I am looking at five or six gauges, and, by telemetry, we’ve got teams of people looking at each gauge on Earth, so, really, I’m confirming what a lot of people are getting.’’

Left to itself, the computer would continue the descent until it either landed or crashed in the attempt, most likely as a result of unfavourable terrain. To find out where the computer was heading, Armstrong asked Aldrin for an angle for his Landing Point Designator, ‘‘Give me an LPD.’’

Aldrin interrogated the computer, ‘‘47 degrees.’’

The panes of Armstrong’s two-layer window were annotated with a scale. The angle was measured downward, relative to directly ‘ahead’. Positioning his head to align the scales, he sighted beyond the 47-degree mark to the position, a little more than 1 nautical mile away, where the computer was taking them. ‘‘That’s not a bad – looking area,’’ he observed to Aldrin.

Duke continued his advisories, ‘‘Eagle, looking great. You’re Go.’’

As Eagle descended through 1,400 feet, the computer issued another program alarm. ‘‘12-02,’’ called Aldrin.

‘‘Roger,’’ acknowledged Duke. ‘‘12-02.’’

“How are you doing, Control?” Kranz asked.

“We look good here, Flight,” replied Carlton.

“How about you, TELCOM?”

“Go!” replied Puddy.

“Guidance, are you happy?”

“Go!” Bales replied.

“FIDO?”

“Go!” Greene replied.

To veteran reporters such as Reginald Turnill of the BBC, who had made the effort to learn something of the systems, this determination to push on regardless of the alarms began to look as if it would end with a crash.

“What’s the LPD?” Armstrong asked.

“35 degrees,’’ replied Aldrin. “750 feet, coming down at 23 [feet per second].’’

Pat Collins now began to bite her finger.

“33 degrees,’’ Aldrin called. “700 feet, 21 down.’’

With Aldrin acting as his eyes inside, Armstrong directed his attention outside. The computer was heading for a crater the size of a football field, surrounded by a field of ejecta excavated by the impact. He later reflected, “I was surprised by the size of the boulders, some of which were the size of small automobiles.’’ The crater was 600 feet in diameter. “Pretty rocky area,’’ Armstrong observed to Aldrin.

“600 feet, down at 19,’’ Aldrin recited.

On the nominal descent, Armstrong was not to take control until Eagle was down to about 150 feet. However, in view of where it was heading, he could not let the computer continue to fly ‘blind’. He considered trying to set down short of the crater or even among its ejecta in order to be able to inspect the boulders for the scientists, but ruled this out as being too risky and instead decided to follow his piloting instincts, and ‘extend’. He selected the semi-automatic flight mode that would enable him to control attitude and horizontal velocity, while the computer – allowing for his commands – operated the throttle. At an altitude of 500 feet, at a point known as ‘low gate’ in the descent profile, he intervened. He cut the pitch angle from its current 20 degrees to about 5 degrees, thereby standing the vehicle essentially ‘upright’ to direct nearly all its thrust downwards in order to maintain the horizontal velocity of 60 feet per second and reduce the rate of descent from 19 feet per second to 9 feet per second. He then selected Attitude Hold, and let Eagle fly a shallow trajectory over the field of ejecta just north of the crater, while he looked for a clearer area further downrange.

‘‘Attitude Hold!’’ called Carlton, on noting the mode change in the telemetry.

‘‘Roger, Att-Hold,’’ acknowledged Kranz.

At this point, as Duke recalled: ‘‘We were down to the last couple of minutes. Deke Slayton is sitting next to me. We’re both glued to the screen on my console, and I’m just talking and talking and telling them all this stuff, and Deke punches me in the side and says ‘Charlie, shut up and let them land’.’’

‘‘I think I’d better be quiet, Flight,’’ Duke said.

‘‘Rog,’’ acknowledged Kranz.

Because Armstrong had overridden the computer, Aldrin deleted the LPD angle from his cycle, and instead began to report their forward velocity: “400 feet, down at 9, 58 [feet per second] forward.”

“The only call-outs now will be fuel,” Kranz directed. Carlton, monitoring the propellant gauging system, would make the calls for Duke to relay. As the tension mounted, the flight controllers unconsciously grasped the handles of their display units; these were nicknamed ‘comfort handles’.

“350 feet, down at 4,’’ called Aldrin.

‘‘P66,’’ announced Carlton, reporting that the computer had switched from the approach phase to the landing phase.

‘‘330, 6-1/2 down,’’ called Aldrin. ‘‘We’re pegged on horizontal velocity.’’ At this point, there was a burst of static on the downlink.

Although Armstrong had not explained why he had intervened, it was evident from the fact that Eagle was passing downrange on an almost horizontal trajectory at high speed that he was taking evasive action. Kranz recognised that the locus of decision-making had transferred to Eagle. The vehicle was not yet into the ‘dead man’s box’, but soon would be. The remainder of the descent would be up to Armstrong. Kranz also knew that as long as Armstrong thought he had a fair chance of making a landing he would press on. But, as Stafford had noted after the low pass by Apollo 10, the western end of the ellipse appeared to be much rougher than the aiming point.

On flying clear of the boulders around the big crater, Armstrong pitched Eagle back again in order to rapidly slow the horizontal velocity which, as a result of his evasive action, was now excessive for their altitude. On spotting a line of boulders up ahead, he neatly ‘side stepped’ off to the left – just as he had done when flying the LLTV, firstly by tilting Eagle in the direction he wished to go in order to use a component of the thrust to set up the requisite lateral velocity then, just before reaching where he wished to be, tilting in the opposite direction in order to cancel this translation, resuming the original orientation directly above his selected position. Although in such manoeuvres Eagle had the familiar sluggish response of the LLTV, he was delighted to find the LM easier to fly. To buy time, he began to use the toggle switch on the hand controller designed to adjust the rate of descent in increments of 1 foot per second; having been sceptical of this feature, Armstrong was delighted to find it very effective.

‘‘Okay, how’s the fuel?’’ asked Armstrong, as he continued to manoeuvre at an altitude of 300 feet.

‘‘8 per cent,’’ Aldrin replied.

Now well clear of the ejecta, Armstrong began to ease down.

‘‘Okay, this looks like a good area here,’’ Armstrong informed Aldrin.

Aldrin stole a glance outside and saw Eagle’s shadow on the ground ahead. He was surprised since, being at an altitude of about 260 feet with the Sun low in the east, he had expected the shadow to be too far west to be readily visible; but there it was, distinctly showing the structure of the vehicle. ‘‘I got the shadow out there,’’ he reported. Unfortunately, as a result of manoeuvring, Eagle was yawed slightly left, and the central pillar in front of the instrument panel blocked Armstrong’s view of the shadow.

“250, down at 2-1/2, 19 forward,” recited Aldrin.

“Okay, Bob. I’ll be standing by for your call-outs shortly,” Kranz prompted.

“Altitude/velocity light,’’ noted Aldrin. This warning light indicated that the radar data had degraded. The logic was that the light illuminated when the output from the radar was unusable by the computer – it was lit prior to lock-on, went out with lock-on, and thereafter would come on to alert Aldrin to the fact that the radar had lost track of the surface. Because it had been deemed impractical to try to land by ‘seat of the pants’ flying, as there would not be the visual references to give a sense of altitude and rate of descent, the mission rules stated that if the radar were to fail they would have to abort. But they continued expectantly, and after 20 seconds the radar locked on again. Then Aldrin resumed his calls, ‘‘3-1/2 down, 220 feet, 13 forward.’’

As the downlink was lost to static, Jan Armstrong slipped her arm around son Ricky’s shoulder. Joan Aldrin was standing in silence by the wall, grasping a door, her eyes moist, praying that Eagle would not crash. In Mission Control, Kranz had decided that he would not call an abort unless he was certain it was essential. As regards the mission rule that he had introduced requiring there to be telemetry for the powered descent to continue, he recalled, ‘‘Once we were close, I intended to let the crew go if everything appeared okay to them – I considered a low-altitude fire-in-the- hole abort riskier than landing without telemetry. I looked at a fire-in-the-hole abort the same way that I looked at a parachute when I was flying jets; that is, you use a parachute only when you’ve run out of options.’’ Armstrong would later say that an abort involving (1) shutting down the DPS, (2) firing the pyrotechnics to sever all the structural and electrical connections between the stages, and (3) igniting the APS ‘in the hole’ in rapid succession, in close proximity to the lunar surface, ‘‘was not something in which I had a great deal of confidence”. If the process were not to occur cleanly, it would jeopardise the ascent stage’s departure. It had been done only on the unmanned test of LM-1 in 1968. In fact, this aversion to abort-staging had led to the mission rule that if a problem were to develop after the 5-minute point in the powered descent that did not mandate an in-flight abort, then every effort would be made to land in order to lift off several minutes later. However, if the DPS were to cut off once Eagle was within 200 feet of the surface, it would be doomed as it fell in the weak lunar gravity because by the time the abort-staging sequence was concluded, the APS would not be able to impart a positive rate of climb before the ascent stage struck the surface. Eagle was almost at this critical altitude.

‘‘11 forward. Coming down nicely,’’ said Aldrin.

‘‘I’m going right over a crater,’’ Armstrong pointed out. As he was not using his PTT, Houston did not hear this remark.8

‘‘200 feet, 4-1/2 down, 5-1/2 down.’’

‘‘I’ve got to get farther over here,’’ Armstrong said, as he resumed manoeuvring.

The large rock-strewn crater towards which the computer had been heading was named ‘West’, and the 75-foot-diameter crater over which they passed at this point would later be named variously ‘Little West’ or ‘East’ Crater.

“160 feet, 6-1/2 down,” continued Aldrin.

There were ‘level sensors’ in each pair of propellant tanks, and Carlton had recommended that they use set 2. When either the fuel or oxidiser sensor in these tanks became exposed, it would illuminate the ‘Descent Quantity’ light on Eagle’s control panel and generate the ‘low level’ signal in the telemetry. The signal meant there was now only 5.6 per cent of the initial propellant load remaining, which, in hovering flight with the throttle at about 32 per cent, meant the engine would cut off in 96 seconds. With 20 seconds reserved for the preliminary action of an abort during which the DPS would be throttled up to cancel the rate of descent and impart a positive rate of climb prior to abort-staging, the low-level signal meant that in 76 seconds Armstrong would be required either to abort or forgo the option of aborting and commit himself to touching down within the next 20 seconds. Borrowing pilots’ slang, this decision point was known as the ‘bingo’ call.

‘‘Low level,’’ called Carlton over the otherwise silent flight director’s loop. He started his stopwatch.

‘‘Low level,’’ echoed Kranz. This call ‘‘really grabbed my attention’’ he would later reflect, ‘‘mainly because in training runs we’d generally landed by this time’’.

‘‘5-1/2 down, 9 forward,’’ recited Aldrin. ‘‘You’re looking good.’’ After a burst of static, he was heard to say ‘‘120 feet.’’

Armstrong again slowed the rate of descent in order to manoeuvre to a flatter spot. Slope could be judged visually while hovering because, with the Sun low to the rear, a bright patch was probably sloping up because it was well illuminated, whereas a dark patch was probably sloping down and poorly illuminated. He had to find an evenly lit location that was free of rocks. The presence of rocks could be inferred from the shadows that they cast. As he recalled, ‘‘I changed my mind several times, looking for a parking place. Something would look good, and then as we got closer it really wasn’t so good. Finally, we found an area ringed on one side by fairly good sized craters and on the other side by a boulder field; it wasn’t particularly big, a couple of hundred square feet – about the size of a big house lot.’’

‘‘100 feet, 3-1/2 down, 9 forward,’’ recited Aldrin.

At the suggestion of Bill Tindall, the illumination of the Descent Quantity light did not trigger either the caution and warning light or sound an audible tone; it was a normal event after all, not something to risk distracting the crew so near the lunar surface. It was therefore some time before Aldrin noticed the amber lamp, ‘‘Five per cent. Quantity light.’’

Carlton was focused on his stopwatch. ‘‘Coming up on 60,’’ he warned.

‘‘Rog,’’ acknowledged Kranz.

‘‘Okay,’’ continued Aldrin. ‘‘75 feet and it’s looking good.’’

‘‘60!’’ called Carlton.

‘‘60 seconds,’’ echoed Kranz.

Duke, who had been silent for some time, passed this on. Aldrin did not respond, opting instead to maintain his instrument readings for Armstrong.

Jan Armstrong sat forward, one hand over her mouth, her eyes a little brighter than usual. Joan Aldrin, tears in her eyes, was huddled against the frame of a door, one hand resting on a lamp shade, which was shaking.

Since Eagle might easily damage one of its legs (or possibly even tip over) if it were to land with a significant horizontal velocity, once Armstrong was directly over his chosen spot he focused on a point just in front as his visual reference and set about ‘nulling’ his lateral velocity components in preparation for a vertical descent. However, because he had no wish to drift backwards into an obstacle, he retained a very slow forward motion that tests had indicated the legs should be able to resist.

‘‘Light’s on,’’ reported Aldrin. The illuminated altitude/velocity light indicated that the radar data had degraded again, but this time the drop-out lasted only a few seconds. ‘‘60 feet, down 2-1/2,’’ he continued. After a pause, he added, ‘‘2 forward. That’s good.’’ And again, ‘‘40 feet, down 2-1/2.’’

Armstrong cut the throttle in order to descend. The exhaust plume was now in contact with the surface, but because the spacecraft had shed half of its mass since PDI the engine was delivering only about 1,000 pounds of thrust. Nevertheless, it stirred up the fine surface material. ‘‘Picking up some dust,’’ Aldrin reported.

Unable to billow in the absence of an atmosphere, the dust travelled radially outward on ‘flat’ trajectories. The dust moving forward created the illusion that Eagle was drifting backward. Fortunately, the semi-transparent layer of‘ground fog’ was so thin that some of the rocks poked up through it, and Armstrong was able to maintain his visual reference.

‘‘30 feet, 2-1/2 down,’’ called Aldrin. He saw the shadow of Eagle’s right leg, the probe on its foot pad indicating that it was tantalisingly close to the surface. He also noticed that although shadows on the Moon were normally sharply defined, Eagle’s shadow was softened by the dust passing just above the surface. ‘‘Faint shadow.’’ ‘‘And now for 30,’’ called Carlton, monitoring his stopwatch.

‘‘4 forward,’’ Aldrin continued. ‘‘4 forward. Drifting to the right a little.’’

‘‘30!’’ Carlton announced.

‘‘30 seconds,’’ echoed Kranz.

This was relayed by Duke with incredulity evident in his voice, ‘‘30 seconds.’’

In the Mission Operations Control Room, the flight controllers, managers and visitors began to breathe intermittently – some even ceased to breathe.

‘‘20 feet, down a half,’’ Aldrin called. ‘‘Drifting forward just a little bit. That’s good.’’ When one of the three 67-inch-long probes struck the surface it illuminated a blue lamp on the central control panel. Armstrong, his attention outside, did not see this, but Aldrin had the lamp in his peripheral vision. ‘‘Contact light!’’ Carlton had been about to call out 15 seconds as the start of a second-by-second countdown.

The final rate of descent was required not to exceed 3 feet per second, since (as factory testing had indicated) a faster sink rate could shock the legs sufficiently to damage them – possibly so much as to prevent a subsequent liftoff, during which the descent stage was to serve as the platform for the ascent stage. In practice, this meant that the vehicle was not to be allowed to fall in lunar gravity from a height exceeding 10 feet. The contact probe satisfied this requirement. Furthermore, the engine was to be shut down immediately the contact light lit, in order to preclude the possibility of back pressure from the plume in such close proximity to the surface damaging the engine, possibly causing it to explode. However, Armstrong was a second or so late, with the result that instead of falling the final 5 feet, Eagle settled onto the surface very gently at a sink rate of just 1.7 feet per second, with each of its pads pivoting to settle on the uneven surface. Although Armstrong had tried to cancel the lateral velocities and maintain a slight forward creep, it was later determined that Eagle had been drifting to the left at about 2 feet per second and the left leg was first to make contact, indicating that the vehicle had been tilted that way. As Aldrin reflected later, “I would think that it would be natural, looking out the left window and seeing dust moving left, that you’d get the impression of moving to the right and counteract by going to the left.’’ As a result of the final manoeuvring, Eagle landed yawed around at an angle of 13 degrees left. On the uneven surface, its 4.5-degree backward tilt was well within the 10-degree tolerance.

“Shutdown!” announced Armstrong.

Turning their heads in their ‘bubble’ helmets Armstrong and Aldrin grinned at each other. Armstrong later reflected: ‘‘If there was an emotional high point, it was after touchdown when Buzz and I shook hands without saying a word.’’ As Aldrin recalled the event, he was ‘‘surprised, in retrospect, that we even took time to slap each other on the shoulders’’.

Armstrong later insisted that the landing was everything he could have wished for, and the fact that it had been achieved with just seconds to spare had made it even more satisfying. In fact, he was not concerned by the narrow fuel margin, because this had always been so when flying the LLTV, which had severely limited flight time. A later analysis would show that when he began to manoeuvre, the fluids in the propellant tanks had sloshed around and because the level sensor in each tank was located on top of a 9-inch-tall rod the ‘low level’ signal had occurred 20 seconds prematurely. In fact, when Carlton’s count reached the 15-second mark, the engine could have sustained 25 seconds of hovering prior to the ‘bingo’ point; the halving of the margin from 20 seconds at the ‘low level’ signal to 10 seconds at actual touchdown presumably being because Armstrong had departed from the nominal trajectory ahead of schedule in order to manoeuvre, thereby consuming propellant at an increased rate. Telemetry showed that Armstrong’s heart rate had been 110 beats per minute at PDI, peaked at 156 during his final manoeuvres, and then rapidly dropped back to about 95.

Aldrin immediately started the post-shutdown checklist. ‘‘Engine Stop. ACA out of detent. Mode Control, both Auto. Descent Engine Command Override, Off; Engine Arm, Off; 413 is in.’’9,10

9 The Attitude Control Assembly (ACA) was the hand controller used to fly the spacecraft. It was spring-loaded to stand in its central detent. The computer not only interpreted a displacement as a request for a manoeuvre but also remembered how the stick was being used. By nudging it out of detent after shutdown, Armstrong was essentially clearing it.

10 The AGS used ‘strap down’ gyroscopes, which had a tendency to drift. Now that Eagle was on the surface, Aldrin loaded a specific value into address ‘413’ of the AGS to tell that system to store its attitude information to ensure that if (1) an emergency liftoff became necessary, and (2) by sheer ill luck the PGNS were to malfunction beforehand, obliging them to use the AGS, then this system, by virtue of having stored its attitude immediately after landing, would be able to correct for any drift in its gyros.

“Flight, we’ve had shutdown,” confirmed Carlton.

“We copy you’re down, Eagle,’’ Duke called.

“Houston, Tranquility Base here,’’ called Armstrong. “The Eagle has landed.’’

Duke had been alerted in order that he would not be caught out by a strange call sign, but he fluffed his reply. “Roger, Twank – Tranquility. We copy you on the ground.’’ A moment later he continued, “You’ve got a bunch of guys about to turn blue. We’re breathing again. Thanks a lot.’’ With that, he slumped back in his chair and grinned at Slayton, who grinned back.

In the viewing gallery people stood to applaud, cheer, and wave small flags.

The powered descent had started at 102:33:07, and Armstrong called shutdown at 102:45:41 after a duration of 12 minutes 34 seconds – about half a minute over nominal. As he updated his console log, Kranz thought, ‘My God, they’ve landed!’

At ‘contact light’ Pat Collins, head resting on her hands, broke into a smile for the first time in more than an hour. With the exception of Joan Aldrin, everyone in her house applauded at ‘engine stop’; she had her head buried against the wall and was still shaking. Although Robert Moon went over to comfort her, she escaped to the solitude of her bedroom. Michael Archer, Joan’s father, took daughter Jan, who was visibly shaken, to join her mother. After gathering her senses, Joan handed out a box of cigars. As she would reflect a few hours later, ‘‘My mind couldn’t take it all in. I blacked out. I couldn’t see anything. All I could see was a match cover on the floor. I wanted to bend down and pick it up, and I couldn’t do it. I just kept looking at that match cover.’’ With the ‘landed’ report, Jan Armstrong delightedly hugged son Ricky. A moment later, her sister Carolyn entered the room, leant against the wall and exclaimed, ‘‘Thank you, God.’’

In New York, Walter Cronkite, who was anchoring the CBS special, Man on the Moon: The Epic Journey of Apollo 11, had also been holding his breath. He removed his spectacles to wipe sweat from his forehead and, finding himself speechless, could only say, ‘‘Phew! Wow!’’ The Neilson ratings organisation later estimated that more than half of American households had had their television sets switched on during the landing. However, since all three networks were providing continuous coverage it was hard to avoid the event! Armstrong’s parents were watching on their donated colour television. A baseball game in Yankee Stadium in New York was paused to permit the landing to be announced, and the audience delivered a rendition of The Star-Spangled Banner. Canon Michael Hamilton of Washington Cathedral noted, ‘‘The older people are getting a bigger bang out of this than the younger ones, who have grown up with astronauts and space; older people remember when it was just a dream.’’ Of all the space program managers, the lunar landing must surely have meant the most to Wernher von Braun. It would not have been possible, however, without the challenge laid down by John F. Kennedy, on whose grave at Arlington National Cemetery a bouquet of flowers was deposited several hours later with the anonymous note ‘Mr President, the Eagle has landed’. In Moscow, senior military officers and a dozen cosmonauts had gathered to monitor the American television coverage, and the landing prompted a round of applause. Alexei Leonov, who had hoped to make the first lunar landing for his country, later explained this praise of the American success as ‘white envy’. On its final news bulletin of the day, Soviet television reported that the landing had succeeded, and that the Czar of the flight would soon step out onto the surface.

After watching Jan Armstrong give a press interview, Joan Aldrin went out to do likewise. A NASA Public Affairs Officer held an umbrella against the rain that had started to fall. Frustrated by banal questions such as ‘‘What are your plans for the moonwalk?’’ she burst out, ‘‘Listen! Aren’t you all excited? They did it! They did it!’’ And with that she turned and strode back into the house.

At the dawn of the ‘space age’, despite centuries of telescopic observations very little was known for certain about the Moon. For example, there were competing theories for how the craters were made, and the origin of the smooth dark plains that together cover 30 per cent of the visible surface was disputed. Because the Moon’s axial rotation is synchronised with its orbital motion around Earth, we can never view its far side. When the Soviet Union sent a spacecraft beyond the Moon in October 1959 and transmitted photographs of its far side, this was revealed to be virtually devoid of dark plains, thereby posing the mystery of why there should be such a dichotomy. One thing was certain: the Moon represented a new frontier to be explored.

Initial reconnaissance

When NASA initiated the Ranger project in December 1959, this was intended to serve as the flagship for its reconnaissance of the Moon. The first two missions in August and November 1961 were to test the spacecraft’s basic systems in the deep space environment, but the Agena rocket stages failed and stranded their payloads in low ‘parking orbit’. Nevertheless, the Jet Propulsion Laboratory (JPL) decided to proceed with the second batch of spacecraft, whose plunging dive to the Moon was to be documented by a television camera and, just prior to hitting the surface, the spacecraft was to release a shock-resistant ‘hard landing’ capsule that contained a seismometer. Unfortunately, Ranger 3’s Agena overperformed and the spacecraft missed the Moon by 20,000 nautical miles. On the next attempt the trajectory was so accurate that Ranger 4 hit the Moon, but by then an electrical fault had already crippled the spacecraft. Ranger 5, which missed the Moon by 420 nautical miles, was also disabled by a power failure. In December 1962, with its best result being an inert spacecraft striking the Moon, the project was at risk of cancellation. After a review of spacecraft assembly procedures, NASA redefined the project’s goals: the next batch of vehicles would have only the television package, and their single objective would be to gain close-up pictures of the lunar surface in order to assess whether this was capable of supporting the weight of a spacecraft. The location of the target was constrained by flight dynamics considerations. The initial television view was to match the best telescopic pictures, and the spacecraft was to execute a near-vertical dive in order to reduce ‘smearing’ in the final phase, which required a target in the western hemisphere. Unfortunately, the television on Ranger 6 was disabled by an electrical arc at launch, but this did not become evident until the system failed to start as the vehicle neared the Moon. The project’s luck changed on 31 July 1964, when Ranger 7 dived into the Sea of Clouds. Its final image showed detail only a few feet across – an improvement in resolution by a factor of a thousand over the best telescope. The terrain was fairly soft and rolling, with none of the jagged features portrayed by science fiction. A set of shallow ridges suggested that the dark plain of the ‘sea’ was a lava flow, but this was disputed. The presence of boulders indicated the surface was likely to support a spacecraft. Although an automated craft might well come to grief by setting down on a rock or in a crater, there were evidently many open spaces and an Apollo crew ought to be able to manoeuvre to a safe spot on which to set down. As Apollo’s dynamical constraints favoured eastern sites, on 20 February 1965 Ranger 8 took a shallow trajectory that crossed the central highlands en route to the Sea of Tranquility, east of the lunar meridian. Although this approach increased the surface coverage, it also created substantial smearing in the final frames. Satisfied that the dark plains would support the weight of an Apollo spacecraft, NASA released the final probe to the scientists, and on 24 March 1965 Ranger 9 was sent to dive into Alphonsus, a 60-nautical-mile-diameter crater having a central peak and a flat floor displaying interesting rilles and ‘dark halo’ craters that appeared (to some researchers) to be volcanoes. For the first time, the television was fed to the commercial networks, which broadcast it with the banner ‘LIVE FROM THE MOON’. JPL had hoped to reinstate a ‘hard landing’ instrument package and mount a series of follow-on flights, but funding was denied. Originally intended to be the primary means of studying the Moon, the project had been overtaken by the incredible pace of events following President John F. Kennedy’s challenge to send astronauts to the Moon.

Although the astronauts were at home for the holiday weekend, Saturday, 5 July, was devoted to the media. It started with a press conference in the auditorium at the Manned Spacecraft Center. As the astronauts were in their 21-day prelaunch flight crew health stabilisation program, workmen had spent two days assembling a three­sided roofed-over box with a 12-foot-square base utilising 10-foot-tall transparent panels and fitted with fans to blow air outwards; smoke tests having been made to verify this forced ventilation. After Brian Duff, the Public Affairs Officer, had explained to the members of the press – many of whom represented foreign media – the requirement for the special precautions, the astronauts made their entrance wearing rubber masks. At that point, some of the local press, who had been alerted and had purchased surgical masks, donned up to poke fun. Once in the isolation area, the astronauts removed their masks and sat behind a large desk adorned with NASA’s ‘meatball’ insignia and, now being revealed, the mission patch. A large Stars and Stripes formed the backdrop.

As mission commander, Armstrong spoke first. He reminded everybody that Apollo 11 would not have been possible without the achievements of the previous crews and of all the ground staff who assisted. Then Collins talked about how he would look after the CSM while his colleagues were on the lunar surface. Aldrin described how the descent would be conducted. There were then press questions, most of which were either directed at, or picked up by, Armstrong – although in some cases after he had said what he intended to say he invited one or other of his

Return to Earth, by Buzz Aldrin with Wayne Warga. Bantam Press, p. 213, 1974.

colleagues to continue the theme. After it was revealed that the radio call signs for the CSM and LM would be ‘Columbia’ and ‘Eagle’ respectively, Armstrong was asked whether he knew what he would say on stepping onto the lunar surface, and he replied that he had not yet decided. He did say that they intended to introduce an unofficial name for the landing site, but did not announce what this would be. When a foreign reporter asked about the plan to raise the Stars and Stripes on the lunar surface, he explained that Congress had directed that this be done. After the plaque that was to be affixed to the leg of the LM had been revealed, he pointed out, as the wording on the plaque proclaimed, that the landing was to be done for all mankind – the United States was not making a territorial claim on the Moon. Asked about the purpose of the mission, he explained that the primary objective was to demonstrate that it was possible to fly to the Moon, land, lift off and return safely to Earth – as President Kennedy had directed. When asked what would happen if the LM became stranded on the surface, he said that they would have supplies for a day or so, after which Collins would have no option but to return home alone. Asked what would be the most dangerous part of the flight, Collins replied, truthfully – though some took his remark to be flippant – that this would be the part they had overlooked in their preparations. As he would later explain, ‘‘In a test pilot’s world, boring is good because it means that you have not been surprised, that your planning has been precise, and your expectations matched; conversely, excitement means surprise, and that is generally bad.’’ Armstrong pointed out that as a result of Apollo 10 in particular, theirs would not be a mission into the unknown; only the act of landing would be new.

However, the press did not want to know about the technological challenge, they wanted to know how the astronauts felt about the mission.

Although, as George Low had surmised, the public expected its heroes to be cast from the same mould as Charles Lindbergh, attempts to coax the astronauts into a discussion of the philosophical implications of the mission were fruitless. Armstrong, Collins and Aldrin, all of whom were 38 years old, were less voluble in temperament than previous crews. Armstrong was one of the most taciturn of the astronauts, and shunned publicity. Aldrin was only marginally less reserved. Only Collins opened up to the reporters, but he was not to attempt the landing. As he would later point out, the task of a test pilot was to remember every aspect of a machine’s behaviour, and hence he was trained to suppress his emotions lest these should interfere with a cold dispassionate analysis. If NASA wished its astronauts to emote (as the vernacular had it) it should form a crew comprising a philosopher, a priest and a poet; not three test pilots. On the other hand, such a crew would be unlikely to return to give a press conference because, having emoted all the way out and back, they would probably neglect to insert the circuit breaker to enable the parachutes to deploy. Nevertheless, Armstrong was not without humour. Asked what he would most like to take with him to the Moon, he replied, ‘‘More fuel.’’

The main conference was followed by another for the wire services, one for the magazines and filmed interviews with each television network – it was a long day. As for biological isolation, the crew were directed to leave, without masks, by the corridor through which the world’s press had departed! They then went home to spend the rest of the weekend with their families. Furthermore, at the Cape they were in routine contact with secretarial staff, caretakers, suit technicians and simulator engineers. Collins would later compare flight surgeons to nervous old ladies who were convinced that their houses were haunted.

Because four of Eagle’s six batteries were in its descent stage, the ascent stage had power just for the several hours required to rendezvous. As this could begin only when Columbia was conveniently positioned, there was a brief window once per revolution. Although Columbia had just passed below the horizon, a rendezvous would be feasible if Eagle were to lift off within the next 12 minutes. Thus, even as those around them were celebrating the act of landing, the flight controllers on duty were studying their telemetry for any evidence of a problem that would oblige an immediate liftoff. In planning, it had been decided to provide two decision points, referred to as T1 and T2: the first, barely 2 minutes after landing, was to be made on the basis of ‘first impressions’; the second was to be made just before the window closed, after a more thorough study. During training, Bill Tindall had expressed concern. By tradition, decisions were expressed as Go/No-Go, but in this case he saw scope for confusion: ‘‘Once we get to the Moon, does ‘Go’ mean stay on the surface, and does ‘No-Go’ mean abort from the surface? f think the decision should be changed to ‘Stay/No-Stay’ or something like that.’’ His advice had been accepted.

‘‘Let’s go on,’’ Armstrong said to Aldrin after they had completed the post­shutdown checklist, meaning that they should prepare for an immediate liftoff. Then he called Houston, ‘‘Okay, we’re going to be busy for a minute.’’

‘‘All flight controllers, about 45 seconds to T1 Stay/No-Stay,’’ Kranz observed. Although the flight controllers had maintained discipline on their intercom loops, some of the others present were celebrating. ‘‘Keep the chatter down in this room,’’ he ordered. ‘‘Okay, T1 Stay/No-Stay? Retro?’’

‘‘Stay!’’ replied Deiterich.

‘‘FfDO?’’

‘‘Stay!’’ replied Greene.

‘‘Guidance?’’

‘‘Stay!’’ replied Bales.

‘‘Control?’’

‘‘Stay!’’ replied Carlton.

‘‘TELCOM?’’

‘‘Stay!’’ replied Puddy.

‘‘GNC?’’

‘‘Stay!’’ replied Willoughby

“EECOM?”

“Stay!” replied Aaron.

“Surgeon?”

“Stay!” replied Zieglschmid.

“CapCom, we’re Stay for Tl,” Kranz directed.

“Eagle, you are Stay for Tl,’’ Duke relayed.

“Roger. Understand, Stay for Tl,’’ Armstrong acknowledged.

“Houston,” Collins called. “How do you read Columbia on high-gain?’’ Now that he was no longer optically tracking Eagle, he had manoeuvred to enable his high-gain antenna to point at Earth.

“We read you five-by, Columbia. He’s landed at Tranquility Base. Eagle is at Tranquility.”

“Yes. I heard the whole thing,’’ Collins noted. His wife was delighted that he had not been left out.

“Eagle, Houston. You are Stay for T2.’’

“Stay for T2,’’ replied Armstrong. “We thank you.’’ This decision committed Eagle to remaining on the Moon for 2 hours until Columbia came around again. Armstrong and Aldrin began to prepare for a normal liftoff, updating the guidance system to tell it that the vehicle was on the surface, in a specific orientation. This involved aligning the platform by a procedure that inferred local vertical from the gravity vector and azimuth from a star sighting. While Aldrin prepared to do this, Armstrong offered an explanation of the final phase of the descent. “Houston, that may have seemed like a very long final phase. The Auto targeting was taking us right into a football-field-sized crater with a large number of big boulders and rocks for about one or two crater diameters around it, and it required us going in P66 and flying manually over the rock field to find a reasonably good area.’’

“It was beautiful from here, Tranquility,’’ Duke replied.

Aldrin gave his initial impression of the surface, “We will get to the details of what is around here later, but it looks like a collection of just about every variety of shape, angularity, granularity, about every variety of rock you could find. The colour varies pretty much depending on how you’re looking relative to the zero phase point.[31] There doesn’t appear to be too much of a general colour at all. However, it looks as though some of the rocks and boulders, of which there are quite a few in the near area, are going to have some interesting colours to them.’’

“Be advised there’s lots of smiling faces in this room and all over the world,’’ Duke congratulated.

“Well, there are two of them up here,’’ Armstrong pointed out.

Although Columbia was below Eagle’s horizon, Houston had set up a two-way relay. But a transmission from Eagle had to go both ways to reach Collins and this imposed an extra time delay, with the result that anything that he chose to say in response to a transmission from Eagle was made almost 3 seconds late and what he said required 1.3 seconds to reach Earth, during which interval the CapCom might respond to Eagle. On hearing Armstrong’s remark, Collins immediately chipped in, “And don’t forget one in the command module’’, meaning that he was smiling too. But before this reached Earth Duke congratulated Eagle, “That was a beautiful job, you guys’’, with the result that Collins’s remark created the impression that he was reminding Earth that he had done a beautiful job too!

“Columbia, say something,’’ Duke prompted. “They ought to be able to hear you.’’ “Tranquility Base, it sure sounded great from up here,’’ Collins called. “You guys did a fantastic job.’’

“Thank you,’’ acknowledged Armstrong. “Just keep that orbiting base ready for us up there now.’’

“Will do,’’ Collins promised.

Several minutes later, Armstrong called Houston, “The guys who said that we wouldn’t be able to tell precisely where we are – they’re the winners today. We were a little busy worrying about program alarms and things like that in the part of the descent where we would normally be picking out our landing spot. Aside from a good look at several of the craters we came over in the final descent, I have not been able to pick out anything on the horizon as a reference as yet.’’

“No sweat,’’ replied Duke. “We’ll figure out.’’

Bill Anders and Ken Danneberg, a friend of the Armstrong family, launched a $1 ‘pool’ on where Eagle had set down.

The medics had expressed concern that when the astronauts ventured outside they might have to spend some time at the foot of the ladder adapting to the local gravity prior to moving off but, as had been pointed out in response, by then they would have had several hours to acclimatise by standing in the cabin. Armstrong made this point. ‘‘You might be interested to know that I don’t think we notice any difficulty at all in adapting to one-sixth g. It seems immediately natural to us to move in this environment.’’ He then reported what he could see through his window. ‘‘The area is a relatively level plain with a fairly large number of craters of the 5- to 50-foot variety, some ridges 20 to 30 feet high, I’d guess, and literally thousands of 1- and 2- foot craters. We see some angular blocks out several hundred feet in front of us that are probably 2 feet in size. There is a hill in view, just about on the ground track ahead of us. It’s difficult to estimate, but it might be a half a mile, or a mile.’’

‘‘It sounds like it looks a lot better than it did yesterday at that very low Sun angle,’’ interjected Collins. ‘‘It looked rough as a cob then.’’

‘‘It really was rough, Mike,’’ Armstrong pointed out. ‘‘At the targeted landing area it was extremely rough with a crater and a large number of rocks that were probably larger than 5 or 10 feet in size.’’

‘‘When in doubt, land ‘long’,’’ Collins observed.

‘‘We did,’’ Armstrong agreed. Picking up his observations, he continued, ‘‘I’d say the local surface is very comparable to that we observed from orbit at this Sun angle; about 10 degrees. It’s pretty much without colour. It’s a very white, chalky grey, as you look into the zero phase; and it’s considerably darker grey, more like ashen grey

The target ellipse was 11 nautical miles long and 3 nautical miles wide, with its major axis along the intended direction of approach. Eagle came in south of track and landed at the point marked by the cross hairs. Inset: After passing over rocks north of West Crater, Eagle landed just beyond a smaller crater. (Based on S69-3716 and S69-3723)

as you look out 90 degrees to the Sun. Some of the rocks in close here that have been fractured or disturbed by the rocket engine plume are coated with this light grey on the outside; but where they’ve been broken they display a very dark grey interior – it looks like they could be country basalt.’’

While it was not necessary for mission success to determine in real-time where Eagle had landed, Collins was eager to find it by a P22 landmark tracking exercise in order to assist in the rendezvous. The sole reference was the large blocky crater that Armstrong had reported passing over. However, he had neglected to mention having later passed over a smaller crater. Nevertheless, the engineers were able to utilise tracking from the Manned Space Flight Network and telemetry from the onboard guidance systems to estimate the landing point by recreating the descent trajectory. As team member Lew Wade reflected, “All indications were that they were ‘long’, but the guidance systems didn’t agree: PGNS put them a bit north of the planned site; AGS put them in the middle. The first Manned Space Flight Network report had them to the south.’’ The various estimates were marked on a large-scale map of the ellipse, and all were within a 5-mile radius, with most clustered downrange of the big crater. Meanwhile, Gene Shoemaker’s team of geologists, working in a science support room, evaluated the crew’s descriptions of their surroundings (in particular that they were on ‘‘a relatively level plain with a fairly large number of craters’’) and reasoned that, as intended, Eagle had flown down the major axis of the ellipse; for some reason had come in ‘long’; and Armstrong had ‘extended’ in order to avoid a blocky crater. Of two candidates for this crater, one was rejected, which left one. To cut a long story short, the issue would not be resolved until the 16-millimetre Maurer film of the powered descent was studied after the mission, whereupon it was realised that Shoemaker’s team had identified the site to within 200 metres.

‘‘We cannot see any stars out the window,’’ Armstrong noted, ‘‘but out of my overhead window I’m looking at the Earth; it’s big and bright and beautiful.’’ At this point, Aldrin was preparing to take the star sighting for platform alignment. ‘‘Buzz is going to give a try at seeing some stars through the optics.’’

‘‘Columbia, Houston,’’ Duke called. ‘‘It’s coming up on 2 minutes to LOS, and you’re looking great going ‘over the hill’.’’

While Collins passed around the far side of the Moon, Armstrong and Aldrin proceeded with their activities more or less independently of Houston. As soon as Collins reappeared around the eastern limb on revolution 15, Duke gave him one estimate of the landing site, which was ‘‘about 4 miles downrange’’. He provided selenographical coordinates, which Collins entered into his computer.

‘‘Tranquility Base. Houston,’’ Duke called. ‘‘You are Stay for T3.’’

‘‘Roger.’’ Armstrong acknowledged. This terminated the preparations for a lift off, and enabled Eagle to be powered down.

On concluding his momentous shift, Kranz shook Tindall’s hand, found Koos to thank him for throwing the 12-01 program alarm into the final simulation, and then he accompanied Douglas Ward, his Public Affairs Officer, across the road to the News Center.

With Ranger, JPL had seized the initiative in the development of space probes for missions in deep space. In May 1960 it took on a much more adventurous project to develop two related spacecraft: one to enter lunar orbit to conduct mapping and the other to land. Unfortunately, the development of the powerful Centaur stage to dispatch these new probes proved protracted. In coming to terms with Kennedy’s time scale for Apollo, NASA cancelled JPL’s mapper, and instructed the Langley Research Center to build a lightweight orbiter capable of being dispatched by the Atlas-Agena. This new spacecraft was not to be a global mapper, it was simply to chart predetermined areas as potential Apollo landing sites. This unimaginatively named Lunar Orbiter project was initiated in August 1963. Although Ranger had yet to prove itself, it was apparent that developing an orbiter would not just be a matter of fitting a motor to insert Ranger into lunar orbit. While JPL’s television camera package was ideal for documenting a 20-minute plunging dive that would result in the destruction of the craft, it was capable of providing the required high surface resolution only in its final few seconds, by which time its field of view was extremely constrained. To survey wide areas with such resolution from an altitude of 35 nautical miles, Lunar Orbiter would expose film that would be developed, scanned and transmitted back to Earth. Furthermore, since the orbiter had to be lightweight, the camera could not be heavily shielded from radiation in space, and very fine-grained ‘slow’ film was employed, which in turn necessitated long exposures and a mechanism to enable the camera to compensate for the spacecraft’s motion. A twin-lens system was used, with the images from a wide lens providing the context for those from a narrower lens. In December 1963, at the same time as it cancelled the follow-on Rangers, NASA awarded the contract for Lunar Orbiter to Boeing; in effect, the budget was transferred. As with Ranger, Lunar Orbiter would fly as a 3-axis stabilised platform, but a spacecraft’s configuration is intimately related to its payload and although it was possible to use many off-the-shelf systems, the orbiter was necessarily very different from its predecessor. The budget allowed for five operational spacecraft, plus a spare for engineering trials. It was expected that three successful flights would be sufficient to survey all the candidate sites for the first Apollo landing, which was as far ahead as the agency was thinking at the time. To achieve this, Langley wrote three flight plans, designated ‘A’, ‘B’ and ‘C’.

Lunar Orbiter was to fly an almost equatorial elliptical orbit with a 35-nautical – mile perilune on the near side timed to enable the spacecraft to expose its pictures at a low Sun angle to highlight the surface relief, and let the perilune point drift to more western longitudes to follow the sunrise terminator. After 10 days the perilune point would have travelled the length of the equatorial zone in which the targets were located, documenting each under ideal illumination. Furthermore, because the zone extended 80 nautical miles to each side of the equator, it was necessary to tilt the trajectory. In fact, it was decided to adopt an inclination of 11 degrees for the first two missions, with the perilune of the first south of the equator and the perilune of the second north of the equator, and then incline the orbit of the third mission as required to fill in gaps and make follow-up studies.

Lunar Orbiter 1 was launched on 10 August 1966, and entered lunar orbit on 14 August. A motion compensator fault smeared the pictures from the narrow lens. Although the flight controllers considered raising the perilune in order to reduce the smearing and map the entire Apollo zone with a resolution of about 80 feet, it was decided to remain at low level and document the designated targets using the wide lens. On 29 August the spacecraft photographed the ninth target on its list, processed its film and transmitted the results, thereby completing its primary mission. It transmitted telemetry for a further two months to enable the degradation of its systems to be monitored, and was then de-orbited to clear the radio frequencies for its successor, which began its program on 18 November. In addition to inspecting the remaining 11 candidate targets, Lunar Orbiter 2 was able to snap a number of secondary sites which, while of no immediate interest to the Apollo planners, were of ‘scientific’ interest and possible candidates for later missions. Lunar Orbiter 2 completed its photography on 26 November. In addition to its own targets, it had taken high-resolution images of the most interesting sites photographed at medium resolution by its predecessor. Site ‘A3’ (now labelled 2P-6) was confirmed to be promising and (of the new targets) 2P-2 was deemed to be suitable. In addition to photographing the most promising targets from different angles in order to permit stereoscopic analysis of the topography, Lunar Orbiter 3 charted the routes that an Apollo spacecraft might fly to approach these sites. The US Geological Survey (USGS) produced terrain maps for the Apollo planners.

With the primary objective of the project achieved by the first three spacecraft, NASA released the remaining spacecraft to the scientists, who opted to fly them in near-polar orbits at higher altitudes in order to conduct more general mapping, particularly of the far side of the Moon which permanently faces away from Earth. Even after they had finished imaging, this series of spacecraft provided insight into the lunar interior. Although Lunar Orbiter 1 was de-orbited prior to the arrival of its successor, it was noted that its orbit was being perturbed, indicating that the Moon’s gravitational field was uneven. To study this phenomenon, the subsequent spacecraft were not de-orbited until their attitude-control propellant was almost exhausted, and by virtue of flying vehicles in both equatorial and polar orbits it was possible to chart the field in sufficient detail to infer that the dark plains in the circular basins were the loci of the most intense gravity. The discovery of these ‘mascons’ (i. e. the excess of mass concentrated in these basins) was fortunate, as otherwise their perturbations of the Apollo mission would have come as a surprise.

On flying back to the Cape on Monday, 7 July, the astronauts returned to the semi­isolation of their quarters in the Manned Spacecraft Operations Building, going out only to use the simulators in a nearby building. On 10 July, having been medically checked, Tom Paine had a private dinner with the astronauts at which he implored of them, “If you get into trouble up there, do not hesitate to abort. Come on home. Don’t get killed. If you do have to abort, I promise this crew will be slipped ahead in the mission sequence. You’ll get another chance. Just don’t get killed.’’ Collins reflected that Paine’s motivation was to eliminate “the obvious risk of letting our desire to be first on the Moon cloud our judgement in analysing the hazards’’. In fact, Paine had said the same to the crews of Apollo 8 and Apollo 10. Earlier that day, after tests had indicated an oxygen leak in the first stage of the launch vehicle, Walter Delle, a Boeing quality inspector, entered the tank and tracked the ‘hiss’ to the helium pressurant manifold. As this was such a delicate item, it was debatable which would be the least risky option: to accept the leak, or attempt to eliminate it. It was decided to try to stem the leak by applying torque to a nut using a wrench. If the manifold were to be damaged in the process, replacing it would take four days, which would require the launch to be postponed. But Delle was successful, and the final review cleared the mission to aim for launch on 16 July.

The week before launch, Charles Berry mentioned to a reporter that President Nixon had asked to have dinner with the crew on the night before launch, as Vice President Spiro T. Agnew had done with the Apollo 10 crew. Berry had stated that Nixon’s presence at such a late stage would prejudice the crew health stabilisation program, since if the Apollo 11 crew were to return with an infection it would be essential to know whether this had been contracted prior to their leaving Earth in order to enable it to be dismissed as a potential lunar infection. In fact, considering that the launch of Apollo 9 had had to be postponed several days to allow its crew to recover from a mild upper-respiratory infection, it was remarkable that Agnew had been permitted to visit the Apollo 10 crew, since they would be in deep space by the time any symptoms that would have given rise to a postponement became manifest. However, NASA headquarters took the view that Berry’s opinion was merely his recommendation; it was not for him to decide whether anybody could visit the crew. Frank Borman, assigned as space adviser to Nixon for Apollo 11, said the dinner should go ahead, since it would be a tremendous boost to crew morale. However, because the matter was now in the public domain, Nixon deferred. If an astronaut were to fall sick in space, Nixon would be open to the damning criticism of callously disregarding the professional advice of the chief flight surgeon. Although the press habitually referred to Berry as the astronauts’ personal physician, he was Director of

Medical Research and Operations at the Manned Spacecraft Center. The final comprehensive medical examination of the astronauts was on Friday, 11 July by the physicians assigned to this mission: Al Harter, Jack Teegan and Bill Carpentier. The aim was to evaluate their biological state of heath by comparing the organisms in their systems with the ‘baseline’ established on 26 June. In the early days, nurse Dee O’Hara had taken blood and urine samples of departing astronauts, but as these tasks were now done by technicians she was responsible for the paperwork – which amounted to 18 pages per man. As a result of this examination, the crew was declared fit to fly. All that remained, medically speaking, was the basic check-up on the morning of launch.

Over the weekend, the pace slackened. They continued to use the simulators, but for proficiency rather than for training, and undertook a final review of the flight plan. Ted Guillory had supervised the writing of the 240-page flight plan for Apollo

11. It weighed 2 pounds, and addressed every aspect of the mission for a nominal duration of 195 hours 40 minutes. Two copies would be needed, one for the CSM and the other for the LM. In addition, there would be some 20 pounds of reference material on board. The general consensus was that the astronauts had reached their ‘peak’ right on time. As Aldrin observed: ‘‘We could spend another year trying to isolate [the open issues] one by one, and we’d never really get them all. We could spend too much time doing that, so much that we could forget what the mission is all about.’’ On 16 May the first draft of the mission rules was issued. Updated weekly, by the time of launch it had expanded into a 350-page book that defined the actions to be taken in the event of a multitude of situations arising in flight. As such, it formalised the collective knowledge of all concerned.

Soon after Apollo 8 set off for the Moon Frank Borman had suffered a bout of ‘space sickness’, which came as a considerable surprise in view of the fact that he had he spent 14 days on board Gemini 7 in December 1965 with no ill effects. Rusty Schweickart suffered similarly on Apollo 9. It seemed that in the confined Gemini spacecraft astronauts had not been able to become disoriented, but by being able to move around in the much larger Apollo cabin they could develop motion sickness. In an effort to prime the vestibular mechanism of his inner ear for weightlessness, Collins drove down the coast to Patrick Air Force Base and flew aerobatically in a T – 38 for an hour each day over the final weekend. Aldrin flew zero-gravity arcs in the KC-135 several days later, in the hope of doing the same.

The hot news on Sunday, 13 July, was the announcement by the Soviet Union that it had launched the unmanned spacecraft, Luna 15. The speculation was that this would land on the Moon, scoop a sample, and return this to Earth. There was some concern in NASA that the spacecraft’s transmissions might interfere with Apollo 11. Since his Apollo 8 flight, Frank Borman had spent much of his time in Washington as Nixon’s space adviser and undertaking goodwill tours. Three days earlier, he had returned from a 10-day trip to the Soviet Union, and was in fact, the first astronaut to visit that country. On a Washington stopover that afternoon he received a message from Chris Kraft in Houston requesting that he use his recent contacts to gain information on the Luna 15 mission. Borman called the office of Mstislav V. Keldysh, the 68-year-old leader of the Soviet Academy of Sciences.

However, as it was 2 am in Moscow, Borman left a message and then returned to Houston. At 6 am the following morning he received a phone call from Keldysh’s office reporting that the information was en route, and several hours later identical telegrams arrived at his home and at the White House specifying the orbit intended for Luna 15 and confirming that there would be no radio interference. In view of the rivalry between the space-faring nations, this was welcome cooperation. Even if Luna 15 returned only a few ounces of lunar material, the Soviets would be able to claim that they had ‘beaten’ America as long it returned ahead of Apollo 11. The stakes were therefore high. Wernher von Braun told a reporter that although the Soviets had lost the ‘race’ to send a man, their attempt ‘‘to soft land a spacecraft on the Moon and scoop up a sample of lunar soil and fly it back to Earth’’ represented a tremendous technical challenge, in which he wished them ‘‘full success’’ even though it would ‘‘take a little bit off our program’’. Then he made the telling point that such a mission could be no impromptu effort, because ‘‘to have the hardware ready, it would have had to have been planned… years earlier’’.

In July, the afternoon temperature at the Cape regularly rose to 100°F, and the combination of heat and ocean humidity made conditions almost unbearable. The Sun blazed down day after day. The concrete was so bright that sunglasses were mandatory. But on Sunday, 13 July, it started to rain and the forecast was for several days of poor weather. Thus, even if everything else was ready, the weather might oblige the launch to be postponed, possibly to August.

On Monday, 14 July, Robert Gilruth, George Low, Deke Slayton, Chris Kraft and Max Faget flew to the Cape for the final flight readiness review, which, as expected, confirmed the launch date. At 5 pm the terminal countdown was picked up with the clock at T-28 hours, with two built-in ‘holds’ (the first to start at T-9 hours and last for 11 hours, and the second to start at T-3 hours 30 minutes and last for 1 hour 32 minutes) with a view to launching as the window opened for the primary landing site, which was 9.32 am local time on Wednesday, 16 July.

POST-LANDING ACTIVITIES

The flight plan called for the moonwalk to start about midnight Houston time. The idea had been to accommodate the possibility of the landing being delayed by one revolution, and still give Armstrong and Aldrin a period in which to wind down before starting the EVA preparations. However, as Armstrong reflected, “We had thought, even before launch, that: if everything went perfectly and we were able to touch down precisely on time; if we didn’t have any systems problems to concern us; and if we found that we could adapt to the one-sixth gravity lunar environment readily; then it would make more sense to go ahead and complete the EVA while we were still wide awake – but, in all candour, we didn’t think this was a very high probability.’’ Nevertheless, some 2 hours after landing, Aldrin called Houston, “Our recommendation at this point is to plan the EVA, with your concurrence, to start about 8 o’clock Houston time; that’s about 3 hours from now.’’

“Stand by,’’ responded Duke.

“Well,” said Aldrin, “we’ll give you some time to think about that.’’

But half a minute later Duke was back, “We’ve thought about it; we’ll support it. You’re Go at that time.’’ A moment later, he sought clarification, “Was your 8 o’clock Houston time a reference to opening the hatch, or starting the preparation for the EVA at that time?’’

“That would be hatch opening,’’ Armstrong replied.

“That’s what we thought.’’

But Armstrong then decided to play safe, “It might be a little later than that; in other words, we’ll start the preparations in about an hour or so.’’

Meanwhile, during his first pass overhead Collins had tried to see Eagle on the surface. As Columbia approached the general area of the landing site, he told his computer to slew the sextant onto the coordinates that Duke had given him. With the sextant maintaining the line of sight, he looked for either the momentary solar glint reflecting off the foil covering the vehicle, or the distinctive narrow shadow that it would project; but he saw neither. At his altitude of 69 nautical miles the 1.8- degree-wide circular field of view of the sextant covered an area of only a few square miles, and orbiting at almost 3,700 nautical miles per hour he was above 45 degrees

elevation for less than 2 minutes 30 seconds, which was barely enough to study the designated location – it was certainly insufficient time to slew the sextant around to conduct a search.

“How did Tranquility look to you down there?” Duke enquired afterwards.

“Well,” replied Collins, “the area looks smooth, but I was unable to see them.” As an afterthought, he added, “It looks like a nice area, though.”

Windler’s Maroon Team took over in order to deal with the EVA preparations, with Owen Garriott as CapCom.

“Columbia,” called Garriott, “Tranquility Base are prepared to begin the EVA early; they expect to begin depress operations in about 3 hours, at approximately 108 hours.’’

“Tell them to eat some lunch before they go,’’ recommended Collins.

About 20 minutes later, Armstrong and Aldrin reached the point in their flight plan at which they could doff their helmets and gloves. Their next item was to be lunch which, since there was no provision for hot water in Eagle, would be a cold snack. First, however, Aldrin had an item of his own. A month previously, he had asked Dean Woodruff, the minister at the Webster Presbyterian Church, “to come up with some symbol that meant a little bit more than what most people might be thinking of [immediately after the landing]’’, and they had decided that Aldrin should celebrate the Sacrament of Holy Communion. When Aldrin told Deke Slayton of this, Slayton reminded Aldrin that Apollo 8’s reading from Genesis had resulted in a law suit, and asked that he refrain from making overtly religious remarks.[32]

“This is the LM pilot,’’ Aldrin called. “I would like to take this opportunity to ask every person listening in, whoever and wherever they may be, to pause for a moment and contemplate the events of the past few hours and to give thanks in his or her own way.’’ Listening to her squawk box, his wife recognised the significance of his invitation for people to celebrate. He then switched off his microphone and drew from his personal preference kit a small silver chalice, a vial no larger than his little finger with a symbolic amount of wine, and a wafer representing bread loaf. Using the fold-down shelf in front of the DSKY as his altar he poured the wine, in the process observing that the fluid swirled around in the chalice for an inordinate time in the weak lunar gravity. He then read a card on which he had written the verse from the Book of John (15:5) traditionally used for this event: I am the vine, you are the branches; he who remains in me, and I in him, will bear much fruit; for apart from me you can do nothing. Communion was appropriate because it was a Sunday. Armstrong, who had been alerted in advance, watched in respectful silence. Unfortunately, NASA’s hope that the ceremony would remain private was foiled by the Reverend Woodruff himself, who told a reporter that he had supplied Aldrin with a Communion kit.

When the time approached at which it had been estimated that the astronauts might initiate their EVA preparations, with there having been no communications since Aldrin’s call, Garriott prompted, “We’d like some estimate of how far along you are with your eating, and when you may be ready to start your preparations.”

“I think we’ll be ready to start in about half an hour or so,’’ Armstrong said. With that, the circuit reverted to silence.

In fact, preparing for the excursion proved to be rather more time consuming than expected. In training, the cabin had been ‘clean’, with just the apparatus for the exercise present, but in reality the cabin held everything they would require for the mission, and 90 minutes had elapsed before they were ready to begin the EVA preparations, and then activities that were assigned 2 hours actually took 3 hours. It was therefore fortunate that they had opted to forgo the early rest period.

Meanwhile, Charlesworth’s Green Team took over, with Bruce McCandless as CapCom. He directed his attention to Columbia. Collins had inspected the second estimated position of the landing site, again in vain. While he would continue with these efforts, it dawned on him that although it was evident that Eagle was in the western half of the ellipse, the scatter in the estimated positions meant that Mission Control did not really know where it was.

As the mechanical properties of the lunar surface would influence the design of the LM the Apollo planners said, in October 1962, that the development of JPL’s ‘soft landing’ spacecraft should receive a higher priority than the orbital spacecraft. However, the development of the Centaur stage was so protracted that the surface investigations could not start until 1966. The planners for these Surveyor missions were faced with the same dilemma as their Apollo counterparts: where should they send their first mission? Although safety issues obliged them to select one of the dark plains, this was consistent with characterising the surface in the equatorial zone in which the Apollo targets were located. When Surveyor 1 was launched on 30 May 1966, the ‘old hands’ at JPL might well have wondered whether they were in for a rerun of the teething troubles that had plagued Ranger, but on 2 June the spacecraft landed safely near Flamsteed, in a crater that appeared to have been breached by the Ocean of Storms. As with Ranger, the single instrument was a television camera. Its first picture showed the spacecraft’s foot pad resting on the surface, which was barely indented. It then proceeded to take a multitude of individual frames from which a panoramic mosaic was later produced. There was a profusion of small craters and rocks, but the area was generally flat. Although the site seemed to be consistent with a flow of low viscosity lava, this was disputed. The camera continued to send panoramas to document the appearance of the surface under different illumination, and then the solar-powered spacecraft went into hibernation for the long lunar ‘night’ – and, to everyone’s surprise, not only did it awaken with the return of the Sun, it did so each ‘morning’ for the rest of the year. Having succeeded at the first attempt, the engineers were disappointed when Surveyor 2 tumbled during a course correction on its way to the Moon, and was lost. On 20 April 1967 Surveyor 3 set down in a 660-foot-diameter crater in the

Ocean of Storms, bouncing several times prior to coming to a halt. The inner wall was pocked by smaller craters, one of which had excavated large blocks of rock. This vehicle had an arm with which to determine the mechanical properties of the loose surficial material, dig trenches to reveal the subsurface, and roll rocks to determine the extent to which their state of erosion was selective. In contrast to its hardy predecessor, Surveyor 3 survived only one lunar night. Next, contact was lost with Surveyor 4 several minutes before it was scheduled to land. Having sampled two dark plains in the western hemisphere and failed twice to reach a site on the meridian, JPL dispatched Surveyor 5 to sample the Sea of Tranquility. It landed on 11 September 1967, just 14 nautical miles from the 2-P6 site on the short­list for the first Apollo landing. Instead of an arm, it had an instrument to investigate the chemical composition of the surficial material. After taking one reading, the spacecraft ‘pulsed’ its thrusters in order to ‘hop’ several feet, to sample a second patch. The results indicated calcium, silicon, oxygen, aluminium and magnesium, which implied basalt, but the high ratios of iron and titanium meant that the lunar basalt was subtly different from its terrestrial counterpart. Surveyor 6 was sent to the Meridian Bay to fill in for its lost forerunners, and landed without incident on 10 November 1967. The results of its chemical analysis indicated an iron-rich basalt. Since the dark plains across the Apollo landing zone had proved to be remarkably similar, NASA released the final spacecraft to the scientists, who decided to send it to Tycho, a bright ‘ray’ crater in the southern highlands, where it landed on 10 January 1968. By cutting margins, JPL enabled it to employ both the robotic arm and the chemical analyser – which proved fortunate because the analyser became stuck, and if it were not for the arm nudging it free the scientific study would have been undermined. In addition, rather than make the spacecraft hop so as to sample different patches of surface, the arm was used to place the instrument on a patch of excavated soil in order to check that this was the same as the material on the surface, and later to place it on top of a rock. Some researchers interpreted the elemental abundance data to mean that the lunar highlands were an alumina-rich basalt, but Eugene M. Shoemaker, head of the Astrogeology Branch of the USGS, argued that the dominant rock in the Tycho ejecta was anorthositic gabbro, which had interesting implications.2