Category The First Men on the Moon

After breakfast Aldrin went into the lower equipment bay, removed his constant – wear garment, reinstalled his urine-collection and fecal-containment utilities and put on his liquid-cooled garment, the fishnet fabric of which had a network of narrow flexible plastic tubes sewn into it through which cold water would be pumped to manage the heat generated by the exertion of the moonwalk. It had to be donned now, since they were to remain suited while in the LM. Aldrin then went into the LM, vacating the lower equipment bay to Armstrong, who suited up with Collins assisting with the zippers and checking fixtures – a process that took 30 minutes. When Armstrong went into the LM, Aldrin returned to suit up. Collins also suited up as a precaution against inadvertent decompression during undocking, or the need for an early abort in which Eagle’s crew would conduct an external transfer using the side hatch.4

At AOS on revolution 11, Aldrin was well into powering up Eagle’s systems. When Duke requested a status report, it became evident that Aldrin was running about 30 minutes ahead of the flight plan. When the steerable high-gain antenna mounted on a boom on the right-hand side of the roof was pointed to Earth, the LM flight controllers received their first significant telemetry of the mission.

The two crews worked independently in their preparations, but certain events required coordination. One item was setting Eagle’s clock, which was to be done by synchronising it with its counterpart in Columbia.

‘‘I have 097:03:30 set in,’’ called Armstrong.

Collins counted down, ‘‘15 seconds to go. 10, 5, 4, 3, 2, 1. MARK.’’

‘‘Got it,’’ confirmed Armstrong.

Another task, some time later, was to coarsely align the platform of Eagle’s

Only once Eagle was safely on the surface would Collins remove his suit, and he would don it again shortly prior to liftoff.

inertial navigation system. In essence, two humans acted as an interface between two machines.

“I’m ready to start on a docked IMU coarse-align,’’ Armstrong said. “When you’re ready, go to Attitude Hold with Minimum Deadband.’’ Once Collins had confirmed that he was holding the docked vehicles stea­dy, Armstrong said, “I need your Noun 20.’’

“I’ve got Verb 06, Noun 20. Give me a Mark on it,’’ Collins replied. “MARK!” called Armstrong. “Register 1, plus 11202, plus 20741, plus 00211,’’ said Collins, reading the display on his DSKY. The numbers represented the CSM’s attitude with respect to the current REFSMMAT.

Armstrong gave a read-back for confirmation, “11202, 20741, 00211.’’ “That’s correct,’’ Collins agreed. After performing an arithmetical transformation to allow for the fact that the designers of the vehicles had specified their Cartesian axes differently, Armstrong keyed the attitude into his DSKY.

The alignment showed up in the telemetry, and Duke reported, “That coarse align looks good to us.’’

“Okay, Mike,’’ said Armstrong. “Your Attitude Hold is no longer required.’’

If necessary, Eagle would later make star sightings for its equivalent of a P52 to refine the alignment.

Once he had installed the probe and drogue assemblies in the tunnel and fully extended the probe, Collins called to Eagle, “The capture latches are engaged in the drogue. Would you like to check them from your side?’’

“Stand by,’’ Armstrong replied. He looked up through the open hatch to verify that the tip of the probe projected through the hole in the centre of the drogue and the three small latches, each no larger than a finger nail, were engaged. “Mike, the capture latches look good.’’ Armstrong then closed the upper hatch to make Eagle air-tight.

At this point, Apollo 11 passed around the far side of the Moon. They were to continue with the preparations during revolution 12, and undock prior to AOS on revolution 13.

Collins slowly retracted the probe until the latches established a firm grip of the drogue. The next task was to release the main latches in the docking units. To guard against the possibility of depressurisation, he donned his helmet and gloves.

Five minutes later, Aldrin called, “Mike, let us know how you’re coming up there, now and then.’’

“I’m doing just fine,’’ Collins replied. He was physically priming the latches, imparting the stored energy they would need to re-engage on the redocking. “I’ve cocked eight latches, and everything is going nominally.’’ And then a minute later, “All 12 docking latches are cocked.’’

“Okay,” acknowledged Aldrin.

“I’m ready to button up the hatch,’’ Collins announced.

Although the vehicles were now held together only by the capture latches, these were able to maintain the hermetic seal in the tunnel because the interface had been compressed by the hard docking. “Mike, have you got to the Tunnel Vent step yet?’’ Aldrin asked.

“I’m just coming to that,’’ replied Collins. “What can I do for you?’’

“Well, we’re waiting on you,’’ Aldrin noted. Although ahead of schedule, the LM crew had to wait for Collins to vent the tunnel before they could proceed.

Two minutes later, Collins reported, “I’m ready to go to LM Tunnel Vent.’’ He opened the valve to space. The process was expected to take about 8 minutes.

“How’re you doing, Mike?’’ Armstrong asked several minutes after that time had elapsed.

“Stand by, and I’ll give you the delta-P reading,’’ replied Collins. He reset the valve to enable a nearby gauge to measure the difference in pressure between the tunnel and the command module, which was at about 5 psi. “It’s 3.0 psi.’’ There was still a significant amount of air remaining in the tunnel.

In Eagle, Armstrong and Aldrin donned their helmets and gloves to check the hermetic integrity of their suits.

Meanwhile, Collins started to manoeuvre into the attitude required for the next P22 landmark tracking, which would be Site 130-prime, a crater inside Crater 130 in the Foaming Sea. Because this had been selected as a reference by John Young on Apollo 10 for the reason that it was both readily identified and small enough to be accurately marked using the sextant, it was also referred to as John Young’s crater. The sightings were to be used to update Houston’s knowledge of the orbit, and where the spacecraft was in that orbit, in order to calculate the precise time at which to initiate Eagle’s powered descent.

When the manoeuvre was finished, Armstrong called Collins, “We’re going to put our gear down.’’

“Master Arm,’’ said Aldrin on intercom, reading the checklist. “Landing Gear Deploy, Fire.’’

“Here we go, Mike,’’ Armstrong warned before detonating the pyrotechnics to release the spring-loaded legs.

“Bam, it’s out. There ain’t no doubt about that,’’ Aldrin mused. “Master Arm, Off.’’

“The gear went down okay, Mike,’’ Armstrong called. There were redundant circuits, but the primary had successfully fired the pyrotechnics to deploy the legs. The 67-inch-long probes, whose tips had been latched against the inner parts of the legs, hinged on the undersides of the lateral and rear foot pads to project ‘straight down’. For Apollo 5 in February 1968, a Saturn IB had launched LM-1 absent its legs for an unmanned test. LM-3 had demonstrated the deployment of the legs on Apollo 9 in March 1969. At that time the design had included a probe on each of the pads but, at Armstrong’s request, it had been decided to delete the probe from the forward leg lest it be bent on touchdown in such a manner as to cause him to slip (or worse, puncture his suit) as he jumped backwards down off the ladder.

As Apollo 11 appeared around the trailing limb on revolution 12, Duke made them aware that communications had been restored. “Apollo 11, Houston. We’re standing by.’’ There was a lot of static on the downlinks. With no response, in all likelihood owing to the fact that he had not directed his call to a specific vehicle, Duke persisted. “Columbia, Houston. Do you read?’’

“Loud and clear,’’ Collins acknowledged.

“Eagle, Houston. Do you read?’’ No response.

“Eagle, do you read Columbia?’’ asked Collins.

“Yes,’’ acknowledged Aldrin. “I’m working on the high-gain right now.’’ He slewed the steerable dish as per the flight plan, but could not establish contact with Earth. “Are you in the right attitude, Mike?’’

“That’s affirm.’’

“Columbia, Houston,’’ called Duke.

“Houston, Columbia. You’re loud and clear.’’

“Eagle, Houston. Will you verify you are on the forward omni?’’ No response. “Columbia, Houston. We have no voice with Eagle. Would you please verify that Eagle is on the forward omni.’’

“Buzz,’’ Collins called. “Are you on the forward omni?’’ When there was no response, he repeated the call.

“Roger. I am,’’ confirmed Aldrin.

“Houston, Columbia. Eagle is on the forward omni.’’

Duke tried again, “Eagle, Houston.’’

“Roger, I’ve got you now,’’ acknowledged Aldrin. “I fed in those angles for the S – Band, and couldn’t get a lock-on. It appears as though the antenna would have to be looking through the LM in order to reach the Earth.’’

Because the docked vehicles were oriented to facilitate P22 landmark tracking shortly after flying around the limb, it was difficult for the boom-mounted S-Band antenna cluster on Columbia to point at Earth, and the body of the LM blocked the line of sight of its steerable dish. In this attitude the vehicles would have to rely on their respective omnidirectional antennas.

“Eagle, Houston. Could you give us an idea where you are in the activation?’’

“We’re just sitting around waiting for something to do,’’ Aldrin replied. “We need a state vector and a REFSMMAT before we can proceed to the AGS calibration, and we need you to watch our digital autopilot data load, the gimbal drive check and the throttle test.’’

Although Armstrong and Aldrin were well ahead in their LM activation, they were again obliged to wait until Houston was able to upload information and monitor their telemetry, which could not be done until they could use their high-gain antenna, which in turn meant waiting until Collins had performed his landmark

tracking. While getting ahead created a margin against encountering a problem that might slip them behind schedule, the need to do certain tasks at given times meant that being ahead early on did not in itself enable the process to be completed ahead of the flight plan.

“It’ll be about another 10 minutes or so before we get the P22 and manoeuvre to an attitude for the high-gain,’’ Duke pointed out.

Armstrong and Aldrin proceeded with those items that could be done using the low data-rate provided by an omnidirectional antenna.

“We’re ready to pressurise the RCS,’’ Aldrin announced.

“You can go ahead with RCS pressurisation,’’ Duke agreed, “but we’d like to hold off on the RCS hot-fire checks until we get the high bit-rate.’’

“Eagle, Columbia. My P22 is complete,’’ Collins reported. He manoeuvred to let the high-gain antennas on both of the vehicles see Earth, and communications markedly improved. With high data-rates on both its uplink and downlink, Eagle was able to complete data uploading and checkout.

“Houston, Eagle,’’ Aldrin called. “Both RCS helium pressures are 2,900 psi.’’ “Let me know when you come to your RCS hot-fire checks,’’ said Collins, “so I can disable my roll thrusters.’’

Fifteen seconds later, Aldrin announced that they were ready. “Columbia,’’ he called, “We’d like Attitude Hold with Wide Deadband.’’

“You got it,’’ Collins replied. A wide deadband on the Attitude Hold would allow the testing of Eagle’s thrusters to disturb the attitude of the docked vehicles without prompting Columbia’s control system to waste propellant in attempting to intervene. “My roll is disabled. Give me a call as soon as your hot-fire is complete, please.’’ “Houston, Eagle,’’ Aldrin called several minutes later. “The RCS hot-fire test is complete. How did you observe it?’’

“It looked super to us,’’ Duke confirmed.

“I’ve got my roll jets back on now,’’ Collins announced.

At this point, Kranz polled his flight controllers, and Duke relayed the result, “Apollo 11 Houston. You’re Go for undocking.’’

“Understand,’’ replied Aldrin.

Apollo 11 had proved the ability of the LM to land on the Moon, but the fact that it came down off target was frustrating. The ability to land within about 1,000 feet of a specific point was a prerequisite to being able to undertake a planned geological traverse. After the flight dynamics team had devised a simple method to correct for the perturbations of the mascons, they were so confident that they reduced the size of the target ellipse. In addition, it was decided to cut the number of backup sites from two to one. There were five prime sites on the short-list for the first landing. The easterly ALS-1 and ALS-2 sites in the Sea of Tranquility had been backed up by ALS-3 in the Meridian Bay, with ALS-4 and ALS-5 in the Ocean of Storms in reserve against a major launch delay. It would have been natural to send Apollo 12 to one of these sites, but the conservative constraints had resulted in the choice of ‘open’ sites, and the geologists were eager to sample the ejecta of a sizeable crater. In fact, even before Apollo 11, the site selectors had re-examined sites rejected due to the inconvenient proximity of a crater, and listed them for a later mission. In the end, however, in order to convincingly demonstrate the ability to address a ‘pin-point’ target it was decided to land alongside an unmanned probe. The relaxation of the operational constraints allowed the reinstatement of the Surveyor 1 site (ALS-6) in the Ocean of Storms. However, because this was so far west that it did not permit a backup, it was decided instead to visit Surveyor 3 in the eastern Ocean of Storms. Originally designated 3P-9, this site became ALS-7. Pete Conrad and Al Bean landed their LM, ‘Intrepid’, within 600 feet of Surveyor 3 on 19 November 1969. On their first excursion they deployed the deferred ALSEP, and during a 3-hour traverse the next day they ranged 1,200 feet from home, collected samples, and cut parts off the Surveyor as trophies. Meanwhile, in orbit, Dick Gordon photographed the site being considered for the next mission.

A pre-mission investigation of the morphology of the craters at the Apollo 12 site predicted that the regolith would not exceed 6 feet in thickness, and that the large impacts would have excavated bedrock. Whereas breccias and basalts were represented equally by number in the Apollo 11 samples, just two of the 34 rocks returned by Apollo 12 were breccias. The crystalline rocks were coarser and more texturally diverse. In view of the fact that they contained less titanium, it appeared, on reflection, that the basalt of the Sea of Tranquility was unusually enriched in this element. This chemical variation confirmed that the dark plains were not from a single source. Indeed, the fact that four kinds of basalt were identified at the Apollo 12 site meant that there had been several distinct flows in this local area.[52] However, the crystallisation dates clustered within a fairly narrow window, which suggested that the extrusions were the result of partial melting of pockets of rock at shallow depth. The initial results were confusing, but it was immediately recognised that something profound had been discovered concerning early lunar history. The first measurement yielded an age of 2.7 (±0.2) billion years, which meant a billion years had elapsed between the extrusions in the Sea of Tranquility and the Ocean of Storms. The next result pushed this up to 3.4 billion years, but as the analyses continued the dates converged on 3.2 billion years. This 500-million-year span in ages for the lavas at the two landing sites indicated that the driving process had been persistent. Geochemist Paul W. Gast made a surprising discovery in the basalts, in the form of an abundance of potassium, phosphorus and some of the ‘rare earth’ elements. By linking their chemical symbols, Gast coined the label ‘KREEP’. On trying to isolate this material, he realised that it was not present as a mineral. The term is an adjective, and it is more correct to describe the Ocean of Storms basalts as being KREEPy. By way of an ‘instant science’ explanation for the media, Gast suggested this chemical additive might have been picked up from the ancient crust that some scientists believed formed the ‘basement’ of the dark plains, and he even speculated that it might be associated with the putative light-toned basalt believed (by some) to be prevalent in the highlands, but when the material proved to be rich in radioactive elements, in particular thorium and uranium, it was realised that this could not be typical of the crust because the heat of radioactive decay would have prevented the crust from solidifying. This KREEPy additive became a mystery for a subsequent mission to resolve.

After being discarded, the ascent stage of the LM was deliberately de-orbited, and the ALSEP seismometer recorded the crust ‘ringing’ for nearly an hour with a signature quite unlike a terrestrial signal. At the Lunar Science Conference, Gary V. Latham, the principal investigator for the seismic instruments, noted it had been difficult to tell the difference between a moonquake and an impact until this strike had provided a point of reference, whereupon it was found that surprisingly few of the 150 seismic events on record were internal quakes. It seemed that the crust was brecciated to a depth of about 18 nautical miles, indicating that, after the crust had solidified, further impacts had churned this up to a considerable depth, forming a

‘megaregolith’. In order to probe to greater depths, it was decided that on future missions the spent S-IVB should be made to impact the Moon.

LUNAR SURFACE EXPERIMENTS

During a meeting in the summer of 1964 at Woods Hole, Massachusetts, the Space Science Board of the National Academy of Sciences listed basic questions relating to the Moon that ought to be studied either by spacecraft placed into lunar orbit or by instruments emplaced on the lunar surface.

On 19 November 1964, after tests conducted on an aircraft providing one-sixth gravity established that astronauts would be able to offload scientific instruments from the descent stage of the LM onto the lunar surface, the Manned Spacecraft Center began to study how instruments might be powered. It was decided that the best source would be a radioisotope thermal generator (RTG) in which heat was converted by thermocouples into electricity. The Grumman Aircraft Engineering Corporation of Bethpage, New York, which was developing the LM, was asked to give some thought to how an RTG might be packaged and carried. Grumman was also asked to develop a prototype for a container in which to return to Earth samples of lunar material. This would require to be carried on the exterior of the vehicle, accessed while on the surface, loaded, hermetically sealed, transferred into the ascent stage, and later passed through the tunnel into the command module and stowed for the flight home.

In January 1965 NASA undertook a time-and-motion investigation in order to assess how best to use the limited time that would be available to the first Apollo crew to land on the Moon. In May, a preliminary list of surface experiments was drawn up, and George E. Mueller, Director of the Office of Manned Space Flight, initiated a two-phase procurement process: the definition phase was to be done in parallel by a number of companies, one of which would be selected to develop the hardware for flight. In June the Manned Spacecraft Center set up the Experiments Program Office within its Engineering Development Directorate to manage all experiments for manned spacecraft, and Robert O. Piland, formerly deputy manager of the Apollo Spacecraft Program Office, was selected to head it. On 7 June Mueller approved the procurement of the Lunar Surface Experiments Package (LSEP) and assigned responsibility for its development to the Experiments Program Office. It was to be an RTG-powered suite of instruments that had to be able to be deployed

by two men in 1 hour, and was to transmit data to Earth for 1 year. Overall, it was envisaged as a passive seismometer to monitor moonquakes; an active seismometer that would detonate calibrated explosive charges in order to seismically probe the shallow subsurface; a gravimeter to measure tidal effects that might shed light on the deep interior; an instrument to measure the heat flowing from the interior; radiation and meteoroid detectors; and an instrument to analyse the composition of any lunar atmosphere. The instruments would be electrically connected to a central station that would transmit to Earth. Mueller specified that the package should be available for the first landing mission. On 3 August NASA announced that Bendix Systems, TRW Systems and Space-General Corporation had each been given a 6-month contract worth $500,000 to propose designs. On 14 October NASA contracted the General Electric Company to supply the RTG under the supervision of the Atomic Energy Commission. An instrument to investigate any lunar magnetic field was added to the suite on 15 December. By early 1966 the instrument suite had been renamed the Apollo Lunar Surface Experiments Package (ALSEP). On 16 March NASA Administrator James E. Webb decided that, in view of the company’s experience in developing experiments for automated lunar spacecraft, Bendix of Ann Arbor, Michigan, would receive the contract to design, manufacture, test and supply four ALSEPs (three flight units and one in reserve), the first of which was to be delivered no later than 1 July 1967.

Homer E. Newell, Associate Administrator for Space Science and Applications, wrote to Mueller on 6 July 1966, “the highest scientific priority for the Apollo mission is the return to Earth of lunar surface material’’, with the position of each sample being carefully documented prior to sampling. Newell recommended that on the first moonwalk the astronauts start by collecting an assortment of readily accessible samples (a ‘grab bag’ in the vernacular of field geology), deploy the ALSEP, and end with a ‘traverse’ to collect a number of ‘documented samples’, utilising a range of tools, including core tubes.

By the autumn of 1966 the magnetometer was having serious developmental problems, and the central data-processor was in a critical state. At the end of the year, NASA headquarters suggested that an instrument on the second ALSEP be brought forward as a replacement for the magnetometer, but as the scientists said that the magnetometer would be required to properly interpret the data from the other instruments, it was decided to develop a simpler magnetometer as a stand-by. It was also necessary to consider the ‘fuel cask’ of plutonium-238 for the RTG. The cask gave structural support and thermal insulation to the fuel capsule: in the case of the SNAP-27 unit for the ALSEP this comprised 8.4 pounds of plutonium. On the Moon, an astronaut would require to remove the 500°C fuel capsule from the cask on the exterior of the LM and insert it into the thermocouple assembly. When simulations revealed flaws in this procedure, the design had to be modified, and after several launch failures unrelated to the Apollo program the cask had also to be ‘hardened’ to ensure that it would not spill its contents. The Manned Spacecraft Center established the Science and Applications Directorate in December, which took over the activities of the Experiments Program Office and, as Newell had long urged, put science on a par with engineering and operations. Wilmot N. Hess, formerly of the Goddard Space Flight Center, was appointed as Director of the Science and Applications Directorate, with Piland as his deputy.

On 4 January 1967 Christopher C. Kraft, Director of Flight Operations at the Manned Spacecraft Center, said that if a lunar landing was to involve two surface excursions, the first outing should facilitate lunar environment familiarisation, an inspection of the vehicle, photographic documentation and contingency sampling. The ALSEP should be deployed on the second outing, and be followed by a more systematic geological survey. Conversely, if only one excursion was planned, that mission should not be provided with an ALSEP since its deployment would use a disproportionate amount of the time. This rationale applied particularly to the first landing, when the mass saved by deleting the instruments would undoubtedly be able to be put to good use. It was also decided that the astronauts should be provided with a rough time line but be allowed to make real-time decisions; the surface operations must not be micro-managed by Mission Control, at least not on the first mission, when there would be so many unknowns and the people on the spot would be best positioned to make decisions. On 16 March NASA announced that 110 scientists, including 27 working in laboratories outside the USA, had been selected to receive lunar samples. In June, Apollo Program Director Samuel C. Phillips formed an ad hoc team to review the status of the magnetometer. It was concluded that while the technical problems were certain to be resolved, the instrument was unlikely to be ready for the first landing, which at that time was thought might occur in the latter part of 1968. Unfortunately, neither would the simpler magnetometer be ready for that date, so work on this was terminated. Leonard Reiffel, on Phillips’s science staff, recommended on 20 June that in view of the uncertainties concerning an astronaut’s ability to work in one-sixth gravity, “an uncrowded time line’’ would be “more contributory to the advance of science than attempting to do so much that we do none of it well’’.

By mid-September 1967, on the basis of the LM spending 22.5 hours on the lunar surface, the planners recommended that two excursions should be defined, but the second, to follow a sleep period, should not be listed as a primary objective. The decision on whether to conduct the second excursion – on which the ALSEP would be deployed – should be made on the basis of the astronauts’ performance during the first outing. However, one year later, on 6 September 1968, with the LM significantly overweight and the development of the RTG behind schedule, Robert R. Gilruth, Director of the Manned Spacecraft Center, recommended that the first landing should make a single excursion of 2.5 hours; the ALSEP should not be carried (as it could not function without the RTG); the high-gain antenna for the television should not be carried (instead, the 210-foot-diameter antenna at Goldstone in California could receive a transmission from a smaller antenna on the LM); and the geological activities be restricted to the ‘minimum lunar sample’. As Gilruth put it, “I’m sure all will agree that if we successfully land on the Moon, transmit television directly from the surface, and return with lunar samples and detailed photographic coverage, our achievement will have been tremendous by both scientific and technological standards.’’ However, Hess argued for a compromise in which, in view of the development problems of the ALSEP, a smaller package should be assigned to this

mission using instruments that would be easier to deploy, with the duration of the outing being open ended. On 9 October the Manned Space Flight Management Council, chaired by Mueller, agreed to the development of three lightweight experiments for the first landing mission – a solar-powered passive seismometer, an unpowered laser reflector, and a solar wind composition experiment that would be deployed and later retrieved for return to Earth. It was decided to carry the erectable antenna for the television transmission in case the time of the moonwalk did not coincide with a line-of-sight to Goldstone. The mass saved by not carrying the ALSEP would allow more fuel to be carried, and thereby increase the time available for the hovering phase of the descent. In effect, the first landing was to be an ‘operational pathfinder’ for its successors. On 5 November Bendix was told to make the three-instrument Early Apollo Surface Experiments Package (EASEP), which was to be shipped by mid-May 1969. On 6 December Phillips said that if the special tools under development for the geological investigation were ready, and if the astronauts had sufficient time to train in their use, they would be carried. One such item was a camera designed by Thomas Gold, an astronomer at Cornell University. In the early 1960s he had argued, on the basis of radar reflections, that the lunar surface was a thick blanket of extremely fine dust into which a spacecraft would sink without trace, and he maintained this position even after automated landers settled on firm ground. His camera was designed to take stereoscopic close-up pictures of the lunar dust.

FIRST MAN OUT

At the press conference in Houston on 10 January 1969 that introduced the crew of Apollo 11, a reporter enquired about which of them would be first to set foot on the Moon. Armstrong turned to Deke Slayton, Director of Flight Crew Operations, for guidance. Slayton said the matter had not yet been decided, but would be resolved by the training exercises. This ambiguity provoked much speculation in the media. The Gemini precedent was that a commander remained in the spacecraft while his copilot undertook extravehicular activity. In March, after the success of Apollo 9 increased the likelihood of Apollo 11 being assigned the first lunar landing, Kraft and George M. Low, Manager of the Apollo Spacecraft Program Office in Houston, had an informal discussion and both felt that since the first man to set foot on the Moon should be a Lindbergh-like figure, Armstrong would be preferable to Aldrin. On hearing a rumour that Armstrong had been chosen to egress first because (despite his being a former naval aviator) he was ‘‘a civilian’’, Aldrin discussed the issue with Armstrong, who said simply that since it was not their decision to make they must wait and see. Several days later, Aldrin went to Low and urged that a decision be made in order to facilitate training. This was a reasonable request, because one of Aldrin’s assignments in planning the mission was to refine procedural issues. Low and Kraft then met with Gilruth and Slayton, and they formally decided that the first man to exit the LM would be Armstrong, if only for the fact that the hatch was hinged to open towards the man on the right, meaning that the man on the left, the

Portable life-support system 17

commander, must exit first. When Slayton called the astronauts into his office, he cited the hinge on the hatch as the reason for Armstrong being first out and last in.1 On Monday, 14 April, Low announced to the press that if all went well, Armstrong would be the first man to set foot on the lunar surface.

Apollo spacecraft CSM-107 was built by North American Rockwell at its plant at Downey, California. The conical command module was 11 feet 5 inches high, 12 feet 10 inches in diameter, and provided a habitable volume of 210 cubic feet. The cylindrical service module was 12 feet 10 inches in diameter and 24 feet 7 inches tall. Radial beams divided it into a central tunnel, which contained tanks of helium pressurant, and six outer compartments, four of which held propellant tanks, one contained the fuel cell system and the sixth was unused.9 The systems tests on the individual modules were completed on 12 October 1968, and the integrated tests on 6 December. The modules were flown to the Cape on 23 January 1969 by a ‘Super Guppy’ aircraft of Aerospace Lines. They were mated on 29 January, passed their combined systems testing on 17 February and altitude chamber tests on 24 March. At the Grumman Aircraft Engineering plant at Bethpage on Long Island, LM-5 completed its integrated test on 21 October 1968, and its factory acceptance test on 13 December. The ascent stage arrived at the Cape on 8 January 1969 and the descent stage on 12 January. After acceptance checks, the stages were mated on 14 February, passed their integrated systems tests on 17 February, and altitude chamber tests on 25 March. Overall, the vehicle stood 22 feet 11 inches tall. The descent stage was 10 feet 7 inches high and had a diagonal span of 31 feet across its foot pads. Two layers of parallel beams in a cruciform shape gave it a central cubic compartment (housing the descent engine), four cubic side compartments (each housing a propellant tank) and four triangular side compartments (carrying apparatus the astronauts would require during their moonwalk). The ascent stage comprised a pressurised crew compartment and midsection with a total volume of 235 cubic feet, and an unpressurised aft equipment bay.

The 138-foot-long, 33-foot-diameter S-IC first stage of the sixth launch vehicle in the Saturn V series was fabricated by Boeing at the Michoud Assembly Facility in Louisiana, and moved in a horizontal configuration by barge up the Intracoastal Waterway to the Mississippi Test Facility, arriving on 6 August 1968. It was then shipped around the southern tip of Florida, to the Kennedy Space Center. On arrival on 20 February 1969 the 24-wheeled trailer bearing the stage was offloaded by a

The fuel cell system had three fuel cells, two tanks of cryogenic oxygen and two tanks of cryogenic hydrogen, and provided 28 volts.

prime mover and driven into the ‘low bay’ annex of the Vehicle Assembly Building. The S-II second stage had the same diameter as the S-IC, but was only 81 feet 6 inches in length. After assembly at the North American Rockwell plant at Seal Beach in California, it was shipped via the Panama Canal to the Mississippi Test Facility, where it was tested on 3 October 1968. On arriving at the Cape on 6 February 1969, the S-II, complete with its 18-foot-tall aft interstage ‘skirt’, was driven on its 12­wheeled trailer to the low bay. After tests at the Douglas Aircraft Corporation facility in Sacramento, California, the S-IVB third stage was flown to the Cape by ‘Super Guppy’ on 19 January 1969. In all, some 12,000 companies across America participated in the production of the launch vehicle.

The principal structure of the Vehicle Assembly Building was 718 feet long, 517 feet wide and 525 feet tall. Its internal volume of almost 130 million cubic feet required a 10,000-ton air-conditioning system to prevent a ‘weather system’ with its own rainfall developing. The cavernous interior provided four ‘high bays’ for simultaneous assembly of Saturn V vehicles. Each pair of bays shared a bridge crane located 462 feet above the floor. The operator was in walkie-talkie contact with his colleagues at the work sites, and used a computer to move loads of up to 250 tons with a tolerance of 1/228th of an inch. Mobile Launch Platform 1 was a two-level steel structure 160 feet long, 135 feet wide and 25 feet high. At one end was the Launch Umbilical Tower, which rose 398 feet above the deck, and offset towards the other end of the platform was a 45-foot-square hole to allow launch vehicle exhaust to pass through. On 21 February the S-IC was hoisted, turned to vertical, and clamped to the supporting arms, one on each side of the hole. The S-II was added on 4 March. The next day the 260-inch-diameter S-IVB, now with its flared aft skirt fitted, was added, and the Instrument Unit containing the guidance system for the launch vehicle (which had arrived on 27 February) was placed on top. The 28-foot – long truncated-cone to house the LM and support the 154-inch-diameter CSM was fabricated at the North American Rockwell plant in Tulsa, Oklahoma, and delivered on 10 January. The integrated CSM, LM, adapter and launch escape system tower was referred to as the ‘spacecraft’ because it was the payload of the three-stage launch vehicle. Its addition on 14 April completed the ‘stack’. From the aperture of the F-1 engines of the first stage to the tip of the escape tower, the ‘space vehicle’, as the integrated launch vehicle and spacecraft was known, stood 363 feet tall. Nine hydraulically operated arms on the umbilical tower provided access to key sections of the vehicle.[17] The combined systems test of LM-5 was finished on 18 April. The integrated systems test of CSM-107 was completed on 22 April, and the spacecraft was electrically mated with the launch vehicle on 5 May. The overall test of the space vehicle was accomplished on 14 May.

The 6-million-pound transporter for the mobile launch system was 131 feet long,

VHF ANTENNA(2)

TRANSFcR TUNNEL AND OVERHEAD HATCH

EVA ANTENNA

AFT EQUIPMENT BAY

REPLACEABLE ELECTRONIC ASSEMBLY

FUEL TANK (REACTION CONTROL)

REACTION CONTROL

INGRESS/EGRESS HATCH

CREW COMPARTMENT

LAND NG

PAD (4)

LUNAR SURFACE SENSING PROBE

A cutaway diagram of the two LM stages.

Launch Escape System (LES)

ty, ‘ у Command module (CM)

Service module (SM)

Spacecraft/LM adapter (SLA)

Lunar Module (LM)

Instrument Unit (IU)

S-IVB

From the point of view of the Saturn V launch vehicle, the ‘spacecraft’ comprises the Launch Escape System, the CSM, and the LM contained within the adapter.

– –

CSM-107 is mated with the adapter of the Apollo 11 launch vehicle on 11 April 1969.

The space vehicle for Apollo 11 is ‘stacked’ in the Vehicle Assembly Building (clockwise from top left): a crane hoists the S-IC on 21 February; the S-II is added on 4 March; the S-IVB is added on 5 March; and the spacecraft is added on 14 April 1969.

On 20 May 1969 the Apollo 11 space vehicle starts up the incline to Pad 39A.

On 22 May 1969 the Mobile Service Structure is driven up to Pad 39A.

114 feet wide, and travelled on four independent double-tracked crawlers, each ‘shoe’ of which weighed about 1 ton. The access road was comparable in width to an 8-lane highway. It comprised three layers, averaging a total depth of 7 feet. The base was a 2-foot-6-inch-thick layer of hydraulic fill. Next was a 3-foot-thick layer of crushed rock. This was sealed by asphalt. On top was an 8-inch layer of river rock to reduce friction during steering. The vehicle was operated jointly by drivers in cabs located on opposite diagonals, who communicated by intercom. On 20 May the Apollo 11 space vehicle was driven to Pad A, the southernmost of the two launch sites of Launch Complex 39. Because the concrete pad was built above ground level to accommodate a 43-foot-tall flame deflector in the flame trench, the transporter had to climb a 5 per cent gradient while tilting the platform such that the tip of the launch escape system tower did not diverge more than 1 foot from the vertical alignment. Once in position, hydraulic jacks lowered the platform to emplace it on six 22-foot-high steel pedestals on the pad. In all, the ‘roll out’ lasted 6 hours. In its final orientation, the umbilical tower stood towards the north, with the axis of the central trench aligned north and south. After the transporter had withdrawn, the flame deflector was rolled in beneath the hole in the platform. On 22 May, the transporter collected the Mobile Service Structure from its parking place alongside the access road, and delivered it to the pad. The flight readiness test was completed on 6 June. The countdown demonstration test started on 27 June; the ‘wet’ phase was completed on 2 July, and the ‘dry’ phase on 3 July. As Kurt H. Debus, Director of the Kennedy Space Center, once said in jest, ‘‘When the weight of the paperwork equals the weight of the stack, it is time to launch!’’

After the P22 landmark tracking, Collins had initiated a manoeuvre to orient the docked vehicles to enable Eagle to calibrate its abort guidance system (AGS). As he waited for this to finish, he noted that there was an advantage to being behind the Moon, as they then were, “It’s nice and quiet over here, isn’t it?’’

“You bet,’’ agreed Aldrin.

On finishing the manoeuvre, Collins nulled out the rates and then went ‘free’ while Eagle performed the calibration. After five minutes Collins asked, ‘‘How’s the Czar over there? He’s so quiet.’’

‘‘I’m punching buttons,’’ replied Armstrong, referring to the DSKY activity.

A few minutes later, Collins, having been thinking ahead, urged, ‘‘You cats take it easy on the lunar surface. If I hear you huffing and puffing, I’m going to start bitching at you.’’

“Okay, Mike,’’ Aldrin promised.

During the calibration, the only tasks that could be performed were those that would not induce vibrations. One permissible operation was to open the helium valves to pressurise the DPS propellant tanks. Once the calibration was finished, Collins called, “I’m going to manoeuvre to the undocking attitude.’’ He aligned the docked vehicles ‘vertically’, with the CSM beneath. “How about 100 hours and 12 minutes as an undocking time? Does that suit your fancy?’’

“That’ll be fine,’’ agreed Armstrong.

‘‘Are you guys all set?’’ Collins asked, as the clock ticked down.

‘‘We’re all set when you are, Mike,’’ Armstrong confirmed.

‘‘15 seconds,’’ called Collins. He released the capture latches. If these were to fail to release, the design allowed for a suited crewman to manually release them, either by Collins pulling a handle or by a LM crewman pushing a button on the tip of the probe; in either case, the cabin would require to be depressurised and the appropriate hatch opened to gain access to the mechanism. The latches, however, did release. As the residual air in the tunnel escaped, it made the vehicles slowly drift apart.

Since it was desired that the LM remain in the orbit resulting from the LOI-2 manoeuvre, the parameters of which had been precisely defined by Manned Space Flight Network tracking, the same state vector had been loaded into both vehicles and as soon as Eagle was free Armstrong cancelled the 0.4-foot-per-second rate of separation that the PGNS indicated had resulted from the undocking.[23]

‘‘I’ve killed my rates, Mike,’’ Armstrong announced, ‘‘so you drift on out to the distance you like and then stop.’’

When Collins was about 65 feet away, he halted to station-keep.

Meanwhile, in the Aldrin home, son Andrew wondered aloud why NASA had not installed a communications satellite to relay while the spacecraft was behind the Moon.[24] In the Collins home, Joe and Mary Engle were looking after the children. Pat Collins, flight plan on her lap, was eager for AOS to find out if the undocking had occurred. Jan Armstrong was also at home with her flight plan, thinking the same thoughts.

‘‘Eagle. Houston. We’re standing by,’’ called Duke as the vehicles appeared on revolution 13.

‘‘The Eagle has wings,’’ replied Armstrong.

Collins had installed his 16-millimetre Maurer in window 4 to document this part of the mission. On the flight plan, the television camera was to have been set up

alongside it to provide ‘live’ television, but about 57 hours into the translunar coast Houston had cancelled this telecast owing to the lack of an available channel on a geostationary satellite to relay the transmission from the Madrid receiving station to Houston for conversion. In any case, as Collins had said shortly prior to LOS, he was too busy to set up the television system. The loss of ‘live’ views of Eagle in flight was a disappointment to the national television networks, which had hoped to use it to introduce their uninterrupted coverage of the next phase of the mission.

Several minutes into the near-side pass, Armstrong yawed Eagle around and pitched it up in order to place it ‘side on’ to Columbia, and then slowly yawed it through 360 degrees to enable Collins to visually confirm that the legs had fully deployed and the probes were in position. An unusual sound late in the translunar coast had prompted Armstrong to speculate that the hinged panel on the right side of the vehicle had prematurely deployed, but Collins confirmed that this was in its stowed configuration. ‘‘You’ve got a fine-looking flying machine,’’ he assured.

‘‘See you later,’’ promised Armstrong, as the separation manoeuvre loomed.

‘‘You guys take care,’’ said Collins. With his spacecraft oriented apex-up, he fired his forward-facing RCS for 8 seconds to impart a downward radial thrust in order to withdraw at 2.5 feet per second, during which time the rendezvous radar mounted on Eagle’s ‘forehead’ tracked Columbia as a test of the radar’s ability to lock onto the transponder on the other vehicle, and Columbia tested its VHF ranging apparatus; these tests being designed to verify the rendezvous systems prior to Eagle entering the descent orbit. The separation burn occurred about 10 degrees east of the landing site, and placed Columbia into an equi-period orbit with its perilune 90 degrees later, and some 5 nautical miles lower.

Meanwhile, at home

Astronauts cycled back and forth between the Armstrong and Aldrin homes, as indeed did their wives, although rarely together because their efforts were divided between the families – it was a routine that Jan and Joan understood, as they had done the same thing themselves, and there was no need to play host because it was a self-organising process.

The flight dynamics team felt sufficiently confident to further reduce the size of the target ellipse and reject the requirement that the landing site be free of terrain relief, to permit the next mission to tackle a more confined site in rougher terrain. In 1962 Gene Shoemaker and R. J. Hackman had issued a stratigraphic map of part of the Imbrium Basin’s rim. In extending this map, R. E. Eggleton classified the peripheral hummocky terrain as ejecta from the Imbrium impact, and called it the Fra Mauro Formation. Although one geological unit, this terrain was distributed in isolated patches around the periphery of the basin. In terms of total area, it was the largest distinct stratigraphic unit on the near side. Contemporary understanding of lunar history was based on how the ejecta from the Imbrium impact had splattered across thousands of miles. Dating this impact was the single most important item on the lunar science agenda, as it would ‘lock in’ many other structures. It was not just a matter of learning about the Moon. The lunar basins indicated that the early Solar System was an extremely violent place. If the Moon had suffered such an intense bombardment so, too, must Earth. Studying the Moon would provide insight into the early history of our own planet. The terrestrial record of this age is missing, in part because of erosion but mainly because the crust is recycled by plate tectonics. The Moon, however, is so endogenically inert that its face has remained essentially unchanged for billions of years. The task was to find a crater in the hummocky Fra Mauro Formation which had a rocky rim, offered a safe line of approach from the east, and was within a mile of a landing site. A 1,200-foot-diameter pit situated 22 nautical miles north of the large crater Fra Mauro, south of the Imbrium Basin, was chosen. As a result of its shape, the ‘drill hole’ crater to be sampled was named Cone. The best landing site was on the undulatory plain 1,000 yards further west, but the target was set twice as far out in order to avoid the fringe of Cone’s ejecta. So great were the results to be gained from this site that after Apollo 13 had to abort and make an emergency return to Earth, Apollo 14 was reassigned this site and the target moved to the optimal landing place.

On 5 February 1971 Al Shepard and Ed Mitchell landed their LM, ‘Antares’. Following the pattern, they deployed their ALSEP on the first day and made the traverse on the second. Since the rocks were consolidations of shattered precursors (i. e. breccias) the analysis was rather more complicated than for previous missions. The primary objective was to date when the fragments had been bound together, in order to date the impact that applied the shock. This was achieved by exploiting the fact that the isotopic ‘clocks’ used to measure formation date are ‘reset’ when a rock is melted. This was not an issue for basalts from the dark plains, but the study of a breccia involved dating its individual clasts. The samples tended to cluster in two age ranges, one spanning the interval 3.96 to 3.87 billion years and the other spanning the interval 3.85 to 3.82 billion years. It was therefore inferred that the breccias

formed around 3.84 billion years ago as ejecta splashed from the Imbrium impact. The older dates provided the formation ages of the rocks shattered by that impact. It had been hoped that samples taken from right on Cone’s rim would characterise the basement on which the Fra Mauro Formation resided, which was expected (by some) to be volcanic. At first, several intriguing samples did look as if they might represent such volcanism, but they proved to be the first instances of another type of breccia. In fact, there proved to be many forms of breccia. The terms ‘fragmental breccia’ was coined for clasts of shattered rock bound up in a matrix of pulverised rock. As further samples were studied, it was found that fragments of individual minerals could become bound into breccias, showing that not all clasts were lithic. Also, since breccias themselves could be caught in impacts, there were ‘breccias of breccias’ in which the clasts of one breccia were fragments of earlier breccias, and the term ‘one-rock’ and ‘two-rock’ were coined to reflect this history. The samples initially thought to be volcanic were a type of breccia in which clasts were bound in impact-melt.4 Despite the violence of the shock-melting, the breccias contained very fragile crystals that could only have been formed by diffusion as mineral-rich vapour escaped from the ejecta. This crystallisation process was very similar to sulphur encrustation of volcanic vents on Earth, but in this case the gas was released by the ejecta itself rather than from the ground on which the ejecta sat, indicating that the rubble was hot when it was deposited and then fused as it congealed. Intriguingly, the impact-melt breccias proved to be KREEPy. Analysis revealed that they were originally a gabbro (i. e. a basalt that solidified deep underground rather than on the surface) that derived from the magma ocean. In the process of crystallisation, an element is accepted or rejected according to whether it fits the crystalline structure; elements that do not fit are known as ‘incompatibles’. As trace elements tend not to participate in mineralisation, they remain in the melt as the ‘compatible’ elements are extracted, with the result that their concentration progressively increases. The radioactives at depth helped to maintain this reservoir molten, and were locked in when it finally solidified. The impact that made the Imbrium Basin had penetrated sufficiently deep to excavate and scatter some of this material across the surface; mystery solved.

THE END OF THE BEGINNING

Apollo 14 drew to a conclusion the initial phase of the exploration of the Moon in which astronauts traversed on foot. Even before Apollo 11, NASA had ordered the design of a battery powered Lunar Roving Vehicle to enable the so-called ‘J’-class missions to range far and wide across their sites, carry a variety of tools, and return a large amount of material. . . but the stories of these missions are for another book.

Impact melt resembles basalt to the extent that it is a solidified rock melt, but endogenic basalt is homogeneous.

On 14 April 1969 Neil Armstrong, Buzz Aldrin and Mike Collins donned their training suits to have their Apollo 11 portrait taken in front of a 5-foot-diameter picture of the Moon.

As Apollo 11 lifts off, the lower arms of the tower swing away.

Apollo 11 clears the tower.

A view from Apollo 11 while in ‘parking orbit’ around Earth.

Following undocking, Collins inspected Eagle’s landing gear.

Frames from the 16-millimetre camera showing Neil Armstrong collecting the contingency sample alongside Eagle, setting up the television camera, and, with Buzz Aldrin, erecting the Stars and Stripes.

The commemorative plaque on Eagle’s forward leg.

Buzz Aldrin stands alongside the SWC. The rim of the crater that Eagle passed over immediately prior to landing forms the horizon, marred by the glare of the Sun.

Part of a panoramic sequence taken by Buzz Aldrin looking north across Eagle’s shadow, showing the television tripod, the Stars and Stripes and Neil Armstrong working at the MESA.

An impromptu (but iconic) picture of Buzz Aldrin.

A view of Eagle and the SWC taken by Buzz Aldrin while taking a panoramic sequence from a position north of the vehicle.

Having left the ALSCC where he took the previous picture, Neil Armstrong moved further out to take a panoramic sequence, catching Buzz Aldrin placing the PSE on the ground. The LRRR is still in the SEQ bay. Notice the ‘washed out’ landscape down-Sun, due to backscattered sunlight and the fact that shadows are masked by the objects that cast them.

Лі.

Neil Armstrong photographed Buzz Aldrin in the process of deploying the PSE.

Buzz Aldrin working on the first ‘core’ sample.

The view from Aldrin’s window after the moonwalk.

As Eagle completed its rendezvous with Columbia, Mike Collins took this picture with Earth in the background.

With the three BIG-clad astronauts safely in a raft, Clancey Hatleberg tends to Columbia’s hatch.

[1] Madalyn Murray O’Hair, a militant atheist, described by Life magazine in 1964 as “the most hated woman in America’’, sued the federal government over Apollo 8’s reading from Genesis, arguing that this violated the separation of state and church. This was rejected by the Supreme Court.

[2] In 1967 North American Aviation merged with the Rockwell Standard Corporation, as North American Rockwell; in 1973 this became Rockwell International.

[3] The Stars and Stripes shoulder patch was introduced by Jim McDivitt and Ed White after being prohibited from naming their Gemini 4 spacecraft ‘American Eagle’. In addition to retaining the flag, for their Gemini 5 flight Gordon Cooper and Pete Conrad introduced a mission patch. Both became standard adornments.

[4] Asa treat, in his personal preference kit Armstrong had an opal that Wendt had supplied, which, upon its return to Earth, Wendt intended to give to his wife Herma.

[5] Wendt kept the trout in his deep freeze until having it remounted in a more conventional way.

[6] Britain’s ambassador to Washington, John Freeman, having attended the launch of Apollo 10, declined his invitation to Apollo 11 on the basis that – as an embassy spokesman put it – ‘‘when you’ve seen one Apollo launch, you’ve seen them all’’.

[7] The Saturn V was so much more powerful than its predecessors that the sound of the first launch on 9 November 1967 took everyone by surprise. ft not only rattled the tin roof of the VfP bleacher but also threatened to collapse the booth from which Walter Cronkite was providing his television commentary.

[8] NASA preferred to use nautical rather than statute miles for space missions. One nautical mile is 2,000 yards, or 6,000 feet; whereas a statute mile is only 1,760 yards or 5,280 feet.

[9] Three of these names were coined by Gus Grissom to celebrate his Apollo 1 crew (‘Navi’ was his middle name, ‘Ivan’, spelt in reverse; ‘Dnoces’ was the reverse spelling of ‘second’, as in Edward H. White II; and ‘Regor’ was the reverse spelling of ‘Roger’, as in Roger B. Chaffee) and, as far as the International Astronomical Union was concerned, they were unofficial.

[10] Of the ‘Original Seven’ astronauts, Wally Schirra, Gus Grissom and Gordon Cooper were on the active list; Deke Slayton and Al Shepard had been grounded for medical reasons; Scott Carpenter had returned to the Navy; and John Glenn, who had been grounded on the basis that as a national icon he was too valuable to risk on a second mission, had left to pursue a political career.

[11] Being detachable, the magazine of a Hasselblad is traditionally referred to simply as a ‘back’.

[12] The engine did not ‘burn’ its propellant; instead a silver catalyst in the chamber converted the H2O2 to superheated steam and oxygen, and the gas passed through the nozzle to produce thrust.

[13] The Lunar Landing Research Facility at the Langley Research Center became operational on 30 June 1965. It was a 260-foot-tall 400-foot-long frame structure with a system of travelling pulleys to suspend a vehicle in such a manner as to balance five-sixths of its weight. It provided a ‘flying volume’ 180 feet in height and 360 feet in length, with a lateral range of 42 feet. Its main role was to test instruments and software to be used by the LM during the final 150 feet of a lunar descent, but astronauts used it to familiarise themselves with flying in one-sixth gravity prior to advancing to the LLTV.

[14] Based on an account in First on the Moon: A Voyage with Neil Armstrong, Michael Collins and Edwin E. Aldrin Jr, by Gene Farmer and Dora Jane Hamblin. Michael Joseph, pp. 216­218, 1970.

[15] In his debriefing after Apollo 11, Armstrong confirmed the fidelity of the LLTV, and thereafter each mission commander trained with it.

[16] The hypergolic propellants were nitrogen tetroxide oxidiser and a fuel comprising a 50:50 mix of hydrazine with monomethyl hydrazine. The RCS of the CSM required 300 pounds, the SPS of the CSM required 41,000 pounds, and the LM’s propulsion systems required a total of 23,245 pounds.

[17] The swing arm numbers and their interface points are: 1, S-IC intertank; 2, S-IC forward; 3, S-II aft; 4, S-II intermediate; 5, S-II forward; 6, S-IVB aft; 7, S-IVB/IU forward; 8, SM; 9,

crew access.

[18] The eagle that attracted Collins’s interest appeared on p. 236 of the book, Water, Prey, and Game Birds of North America, published by the National Geographic Society in 1965. In fact, the plate in the book was a mirror image of the original painting by Walter Alios Weber, which was published in the July 1950 issue of National Geographic Magazine. The eagle on the mission patch matches the orientation in the original.

[19] Telemetry showed the RCS propellant supply to be about 20 pounds below nominal following the transposition manoeuvre.

[20] In some ways, the most unfortunate person involved in the mission was the man who opened the hatch immediately following splashdown!

[21] Prior to the dawning of the space age, astronomers had defined lunar longitudes in terms of their view of the Moon in the terrestrial sky, with the leading limb being east. However, in 1961 the International Astronomical Union had redefined the system to place east in the direction of sunrise as seen from the lunar surface, which reversed the old scheme.

[22] At the post-flight party, the flight controllers voted Bill Tindall an honorary flight director, with the team colour grey.

[23] As was realised later, however, although the impulse from the tunnel venting was cancelled, this manoeuvre, and others made while ‘displaying’ Eagle to Collins, imparted slight residuals which, when propagated forward in time through the DOI manoeuvre, nudged Eagle’s trajectory slightly ‘off at the PDI point.

[24] Some at NASA would later suggest doing precisely this for later missions.

[25] The ground level of Mission Control held the Real-Time Computer Complex, and each of the two upper levels held a Mission Operations Control Room. Apollo 11 was managed from the top level.

[26] What no one realised was that the program driving the antenna was flawed, with the result that at certain times what was expected to be a clear line of sight to Earth was blocked by the structure of the vehicle.

[27] For the LM, yaw was a rotation around the thrust axis.

[28] There was a spare Maurer body, and Aldrin had tested both cameras during his inspection earlier in the mission; the spare was not needed (and was jettisoned with the trash after the moonwalk).

[29] This was long before the advent of computer-generated imagery, so the animations now appear quaint!

[30] Post-mission analysis established that several interrelated factors contributed to the position-velocity error at PDI – including uncoupled attitude manoeuvres such as station­keeping, hot-fire thruster testing, and venting of the sublimator cooling system – but most of these perturbations were more or less self-cancelling. The principal error was the propagation forward of the impulse imparted at undocking due to the incomplete venting of the tunnel; this was not a mistake by Collins, it was an oversight in planning. Due to the ‘vertical’ attitude of the stack at undocking, the perturbation was to the radial component of Eagle’s velocity.

[31] The down-Sun line was called the ‘zero phase’. With the Sun low in the east, the shadows of rocks and craters were hidden when looking west, and coherent backscatter from cleavage planes in the fractured crystalline rocks produced a very strong solar reflection that tended to ‘wash out’ the scene.

[32] At the time of Apollo 11, the law suit brought by Madalyn Murray O’Hair regarding the reading from Genesis by the Apollo 8 crew was still pending.

[33] Due to Armstrong’s manner of speech, he appears to have appended the ‘a’ to ‘for’, which came out as ‘for-a’, thereby giving the impression that he misspoke and uttered something meaningless!

[34] The time in Houston was 9.56 pm on Sunday, 20 July 1969.

[35] Vesicles were a characteristic of igneous rock in which the melt contained bubbles of gas that left spherical holes in the solidified rock. Since this occurs more readily in lava that has been extruded onto the surface or is at shallow depth, it supported the inference that the landing site was a basalt lava flow. Armstrong would expand on this observation later in the excursion.

[36] Phenocrysts were crystals embedded in the finely grained matrix of an igneous rock.

[37] These accounts are derived from interviews compiled by Glen E. Swanson in Before this Decade is Out… Personal Reflections on the Apollo Program, SP-4223, NASA, 1999.

[38] As indeed would happen at this point in the mission of Apollo 12.

[39] Engineers in Houston designed a ‘stand’ which, when deployed, would display the flags of the member states of the United Nations in the style of a tree.

[40] This picture of Aldrin became the iconic Apollo 11 ‘Man on the Moon’ image. It is on the front cover of this book.

[41] Although McCandless was told that a laser reflection had been detected while Eagle was still on the surface, and he relayed this news to Collins, this was not so.

[42] The seismometer included a detector to measure dust accumulation and radiation damage to the solar cells, and an isotope heater to keep the electronics warm during the long lunar night. Despite operating temperatures that exceeded the planned maximum by 30°C, the instrument functioned normally through the maximum heating around lunar noon. With the power output from the solar arrays in decline about 5 hours before local sunset (on 3 August 1969) transmission was halted by command from Earth. ft was turned on again on the next lunar day, but (on 27 August) near noon of this second lunar day the instrument ceased to accept commands and the experiment was terminated.

[43] The platform began to be unusable after 4 hours, and the computer failed just over 3 hours later. Both items had operated for considerably longer than had been predicted. The other systems were still functioning. The last contact with Eagle was at 137:55, when the battery output dipped below that required for the AGS to maintain the vehicle’s attitude within the antenna’s requirements for communication with Earth. Although Eagle was released in an almost circular orbit, perturbations by the mascons would soon have caused it to strike the surface, but it is not known when or where this occurred.

[44] On subsequent missions, crews would tease Duke about this misidentification.

[45] In fact, Armstrong was in error because Columbiad was the name of the giant cannon that fired Verne’s spaceship to the Moon; the ship did not have a name, always being referred to simply as ‘‘the projectile”.

[46] Note that there was a presumption that the astronauts would not get sea sick while wearing their suits, as the mask would have to have been removed in order to vomit, which would have violated the isolation.

[47] There are several Hasselblad pictures of Armstrong on the lunar surface, but he is in shadow and it was some time before his presence on these frames was noted.

[48] The aim point was at 0°42’50"N, 23°42’28"E.

[49] Actually, as Apollo 11 was heading home, NASA decided to withdraw one Saturn V from the lunar program in order to launch the Skylab space station, but this had not yet been announced.

[50] This is what Pete Conrad and Al Bean did after walking on the Moon on Apollo 12. Their CMP, Dick Gordon, remained in the lunar program in the hope of commanding Apollo 18, but this flight was cancelled.

[51] The name ‘armalcolite’ was derived from the first letters of the astronauts’ surnames. Some years later this mineral was found on Earth, too.

[52] These could be characterised in terms of their terrestrial equivalents as olivine basalt, pyroxene basalt, ilmenite basalt and feldspathic basalt.

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.