Category Paving the Way for Apollo 11

AS-205 lifted off from Pad 34 at 15:02:45 GMT on 11 October 1968 to fly the ‘C’ mission. Flown by Wally Schirra, Donn Eisele and Walt Cunningham, Apollo 7 was

to be open-ended up to 11 days and its purpose was to assess the performance of the Block II spacecraft.

The ascent phase was nominal and the S-IVB achieved a 123 x 152-nautical mile orbit. Prior to separating from the spent stage, the crew temporarily took command of the Instrument Unit and manually manoeuvred the combined vehicle in pitch, roll, and yaw, then they returned control to the launch vehicle. By the time the spacecraft separated at 002:55:02.40, venting of S-IVB propellants had raised the orbit to 123 x 170 nautical miles. The spacecraft moved clear, flipped and moved back in as if to retrieve the LM (which was absent). Since one of the four panels of the SLA had not fully deployed, it was decided that in future the panels would be jettisoned. One of the primary objectives was to demonstrate Apollo’s rendezvous capability using the spent stage as the target. At Schirra’s insistence, one man was awake at all times to monitor the spacecraft’s systems, even though the ongoing work made sleeping difficult. The rendezvous rehearsal was successfully achieved on the second day.

Although this was the first US spacecraft to have sufficient habitable volume for a man to leave his couch and move around, the crew suffered no disorientation in the weightless state, despite efforts to induce motion sickness. However, all three men developed head colds early on, making them grumpy, and in-flight TV, which was a secondary objective, provided a focus for their frustration. When the monochrome camera was finally switched on, however, it delivered excellent results and the crew played up to their audience. But it was a long and tedious flight of monitoring the systems to evaluate their performance, always prepared to intervene in the event of a problem. In fact, it was an exercise in would later be derided as “boring holes in the sky’’.

At 11:11:48 GMT on 22 October the command module splashed in the Atlantic 1.9 nautical miles from the target point. It initially assumed an apex-down attitude, but was soon turned apex-up by the inflatable bags on its nose. The astronauts were retrieved by helicopter and arrived on USS Essex an hour later.

The Apollo 7 mission was successful in every respect, with the service propulsion system firing perfectly eight times. Indeed, afterwards Schirra described the flight as a “101 per cent success’’. In combination with previous missions and ground tests, it certified the CSM for use in Earth orbit and for tests in the cislunar and lunar orbital environments.

On 7 November 1968 George Mueller declared that AS-503 was fit for a mission to the Moon. On 11 November Sam Phillips recommended to the Manned Space Flight Management Council that Apollo 8 enter lunar orbit. Later that day, Mueller told Thomas Paine that he had discussed the mission with the Science and Technology Advisory Committee and with the President’s Science Advisory Committee, both of which had endorsed the proposal, and he recommended that it should be undertaken. After speaking to Frank Borman by telephone, who confirmed his willingness to fly the mission, Paine gave the formal go ahead and told Phillips to make the necessary arrangements. The next day, NASA announced that Apollo 8 would be launched on 21 December and attempt a lunar orbital mission. Earlier in the year, Michael Collins had withdrawn from the crew to undergo a surgical procedure, and had been replaced by his backup, James Lovell.

Tom Stafford, John Young and Gene Cernan were announced on 13 November as the prime crew of Apollo 10, backed up by Gordon Cooper, Donn Eisele and Edgar Mitchell. This established the precedent for a crew backing up one mission, skipping two, and becoming the prime crew of the mission after that. It had yet to be decided, however, whether Apollo 10 would fly the ‘F’ or the ‘G’ mission.[51]

On 9 October 1968 AS-503, complete with CSM-103 and LTA-B, was rolled out to Pad 39A. The countdown demonstration test was completed on 11 December, and the actual countdown began at 00:00 GMT on 16 December. The launch window ran from 20 to 27 December, and it had been decided to try for 21 December to enable the astronauts to inspect the ALS-1 landing site in eastern Mare Tranquillitatis soon after local sunrise.

Frank Borman, James Lovell and Bill Anders entered the spacecraft with a little under 3 hours on the clock. There were no unplanned holds, and Apollo 8 lifted off at 12:51:00 GMT on 21 December for the ‘C-prime’ mission.

The ascent was nominal and the deviations from the trajectory when the S-IVB cut off at T+ 684.98 seconds were + 1.44 ft/sec in velocity and -0.01 nautical mile in altitude, which was almost perfect. At 002:27:22, after the S-IVB and spacecraft had been thoroughly checked, Collins, serving as the CapCom in Mission Control, made the momentous call, ‘‘Apollo 8, you are ‘Go’ for TLI.’’

The 317.7-second translunar injection was started at 002:50:37.8 and produced a velocity of 35,505.4 ft/sec. The spacecraft separated 30 minutes later and the four SLA panels were jettisoned. After turning around, the spacecraft’s ability at station­keeping with the spent stage was assessed. A 1.1-ft/sec manoeuvre was performed at 003:40:01 using the reaction control system of the service module to move clear of the stage, and a 7.7-ft/sec manoeuvre at 004:45:01 increased the separation rate.

At 004:55:56.0 the S-IVB opened its hydrogen vent valve and at 005:07:55.8 it passed oxygen through the engine. At 005:25:55.8 the auxiliary propulsion system was ignited and burned to depletion. The accumulated velocity increment placed the stage on course to fly by the trailing limb of the Moon at an altitude of 681 nautical miles and pass into solar orbit. The spacecraft’s service propulsion system executed a 2.4-second, 20.4-ft/sec midcourse manoeuvre at 010:59:59.2. A 24.8-ft/sec change had been planned, but the engine delivered less thrust than expected and a correction was made at 060:59:55.9 to refine the trajectory. These burns served to calibrate the service propulsion system in advance of calculating the orbit insertion manoeuvre.

In contrast to Apollo 7, this time all three crewmen experienced nausea as a result of rapid body movement, with the symptoms lasting up to 24 hours. The first of six TV transmissions started at 031:10:36 and ran for 23 minutes 37 seconds. The wide – angle lens gave an excellent view of the inside of the spacecraft, where Lovell was preparing a meal, but the telephoto lens passed too much light and pictures of Earth were poor. After a procedure was devised to tape a filter of the still camera onto the TV camera, it produced improved pictures of Earth during a transmission starting at 055:02:45. At 055:38:40 the astronauts were alerted that they had become the first people to enter a region where the gravitational attraction of another body exceeded that of Earth. The spacecraft had been slowing as it climbed up from Earth, but now it began to accelerate as it was drawn in by the Moon. However, they were not yet committed. If a reason developed not to brake into lunar orbit, then Apollo 8 would simply continue on its ‘free return’ trajectory around the back of the Moon and be ‘slingshot’ back to Earth. Although everything was going well, the translunar coast was frustrating in the sense that at no time were the crew able to see their objective owing to the spacecraft’s trajectory in relation to the positions of the Moon and the Sun.

The lunar orbit insertion manoeuvre began at 069:08:20.4 at an altitude of 75.6 nautical miles above the far-side of the Moon, and the 246.9-second burn produced an orbit ranging between 60.0 and 168.5 nautical miles with its high point above the near-side. After the post-burn checklist had been attended to, and while still passing over the far-side, the astronauts had their first opportunity to inspect the surface of the Moon up close. At 071:40:52 they gave a 12-minute TV transmission showing the passing terrain. In contrast to geologists, the astronauts described the surface in terms of ‘‘a battlefield’’, ‘‘a sandbox torn up by children’’, ‘‘a volleyball game played on a dirty beach’’, ‘‘plaster of Paris’’, or (vaguely scientifically) as ‘‘pumice’’. Bright ray craters appeared just as if they had been made by a ‘‘pickaxe striking concrete’’. The colour was varied, sometimes appearing to be black and white, yet other times displaying a distinctly brownish tan. In terms of mood, the surface was ‘‘desolate’’, ‘‘bleak’’ and ‘‘forbidding’’. A 9.6-second burn at 073:35:06.6 circularised the orbit at 60 nautical miles.

As this was the first opportunity for humans to directly observe the Moon at close range, James Sasser of the Apollo Spacecraft Project Office in Houston had served as the ‘project scientist’ for the mission. He formed an advisory team and this drew up a program of photography and visual observations for the crew to perform using a Maurer 16-mm movie camera and a Hasselblad with a 250-mm lens. In particular, the Manned Spacecraft Center wanted views of the eastern limb to assist in selecting landmarks for a lander’s navigational checks prior to the powered descent. Some of this documentation was to be overlapping vertical and oblique pictures which would enable stereoscopic analysis to determine the geographical position and elevation of each feature, but the movie camera was also to be fitted to the spacecraft’s sextant to depict the landmarks in context. In addition, some ‘scientific’ targets were marked on the flight charts as ‘targets of opportunity’ which were to be inspected if time and circumstances allowed. These were to provide either detailed coverage of specific features or broad coverage of areas which had not been adequately imaged by the Lunar Orbiters. And, of course, the ALS-1 landing site was to be inspected. Most of the scientific observing and photography was assigned to Anders, the LMP without a lunar module. Jack Schmitt, a professional geologist who was hired as an astronaut in 1965, served as the main interface between Sasser’s team and the Apollo 8 crew in training, but some briefings were provided by US Geological Survey staff. At the suggestion of Wilmot N. Hess, Director of the Science and Applications Directorate at the Manned Spacecraft Center, SasseTr’s team had set up a ‘science support’ room in Mission Control to listen to the astronauts’ commentaries and watch the TV of the lunar landscape passing below the spacecraft.

The astronauts could recognise surface features in shadows lit by Earthshine, and could see detail on sunward-facing slopes which had been ‘washed out’ in the Lunar Orbiter pictures. In fact, they could perceive detail to within 5 degrees of the ‘zero phase’ point, which is the line of sight with the Sun directly behind the observer. In planning the lunar landing the lower limit for Sun angle had been set at 6 degrees, but the astronauts could see surface detail at angles as low as 2 degrees. They were able to confirm that the upper limit of 16 degrees provided excellent definition, and their observations suggested that it might be possible to raise the limit to 20 degrees – but no higher than this. This enabled the lighting constraints for the lunar landing to be relaxed.

Of the two candidate landing sites in Mare Tranquillitatis, ALS-1 in the east was brighter; so much so, in fact, that it was debatable whether it was truly mare material or a flatfish portion of the adjacent terra. Observing it visually from an altitude of 60 nautical miles, Lovell said it reminded him of an aerial view of Pinacate in Mexico, a volcanic field which he had been shown in training.

Owing to crew fatigue, Frank Borman took the decision at 084:30 to cancel all secondary activities during the final two revolutions, to allow the crew to rest. The only tasks during this period were an alignment of the inertial guidance system and the preparations for transearth injection. But at 085:43:03 they provided the planned 27-minute TV transmission showing the Moon and Earth, and to mark the fact that it was Christmas Eve they recited the first ten verses of the Book of Genesis from the Bible prior to signing off with, ‘‘Good night, good luck, a Merry Christmas, and God bless all of you – all of you on the good Earth.’’

Radio tracking indicated that by the time Apollo 8 was ready to head for home the mascons had perturbed its initially circular orbit into one of 58.6 x 63.6 nautical miles. At 089:19:16.6, after ten revolutions of the Moon, the 203.7-second transearth injection was made on the far-side of the Moon at an altitude of 60.2 nautical miles, which was just about perfect. After returning to the Earth’s gravitational influence, the spacecraft progressively accelerated. Only one small midcourse correction was required. It was made at 104:00:00, and the 15.0-second burn by the service module reaction control system imparted a change of 4.8 ft/sec.

On shedding the service module, the command module adopted its entry attitude and at 146:46:12.8 hit the entry interface travelling at 36,221.1 ft/sec. It pursued an automatically guided profile. The ionisation bathed the interior of the cabin in a cold

An oblique view by Apollo 8 looking northwest across the eastern part of Mare Tranquillitatis. The crater in the foreground is Taruntius-F, and one of the Cauchy clefts crosses the upper part of the picture. The ALS-1 site is out of frame to the south.

blue light as bright as daylight. At 180,000 feet, as expected, the lift vector deflected the vehicle to 210,000 feet, then it resumed its downward course. It splashed into the Pacific 1.4 nautical miles from the target at 15:51:42 on 27 December. It adopted an apex-down position, but promptly righted itself. The astronauts were soon recovered and flown by helicopter to USS Yorktown.

This audacious mission, described as the “greatest voyage since Columbus”, took NASA a giant step towards achieving Kennedy’s challenge.

On 6 January 1969 Deke Slayton called Neil Armstrong, Michael Collins and Buzz Aldrin to his office at the Manned Spacecraft Center and told them that they would fly Apollo 11 and should assume their mission would involve a lunar landing.

On 10 January 1969 John Stevenson, Director of Mission Operations at the Office of Manned Space Flight, circulated a revised version of the tentative schedule for the year that was issued early in 1968. This called for launching the delayed ‘D’ mission on 28 February. As the ‘E’ mission had been rendered irrelevant by Apollo 8, this meant that if the ‘F’ mission flew in May and was satisfactory, it should be possible to attempt the lunar landing in July. The rationale for the ‘F’ mission was to obtain experience of operating in deep space, but after Apollo 8 the issue became whether another test in lunar orbit was required. The decision was postponed until LM-3 had been put through its paces.

Apollo 9 was to be the ‘D’ mission – a lunar module manned flight demonstration in Earth orbit. The payload for the AS-504 launch vehicle was CSM-104 and LM-3. As they were to operate independently, the spacecraft were given radio call-signs. The blue wrapping of the command module for its shipment to the Cape had given it the appearance of a sweet, so it was named ‘Gumdrop’. The arachnid-like configuration of the lunar module prompted the name ‘Spider’.

The launch was scheduled for 28 February 1969 and the countdown was begun at 03:00:00 GMT on 27 February with 28 hours on the clock, but 30 minutes into the planned 3-hour hold at T-16 hours the clock was recycled to T-42 hours in order to enable the crew of James McDivitt, David Scott and Rusty Schweickart to recover from a mild respiratory infection. The count picked up at 07:30:00 on 1 March and the vehicle lifted off from Pad 39A on time at 16:00:00 GMT on 3 March.

The ascent was nominal and at S-IVB cutoff at T+664.66 seconds the deviations were +2.86 ft/sec in velocity and -0.17 nautical mile in altitude, with the result that the initial orbit was almost perfect at 100 nautical miles. At 002:41:16.0 the S-IVB released the CSM, which moved clear, turned end over end to aim its apex at the top of the LM and moved back in. At 003:01:59.3 it docked at the first attempt, marking the first use of this apparatus. Once the tunnel between the two spacecraft had been pressurised, the crew opened the apex hatch of the command module to confirm that all the latches on the docking ring had engaged, and after lines had been connected to supply power to the dormant LM the hatch was reinstalled. On a command issued by the CSM at 004:08:09 the S-IVB released the docked combination.

After the spacecraft was clear, the S-IVB reignited its engine at 004:45:55.5 to raise an apogee of 1,672 nautical miles. Then, after a period of coasting to allow the engine to cool down, it initiated a final burn at 006:07:19.3 to achieve a velocity of 31,620 ft/sec which would send it into solar orbit.

Meanwhile, at 005:59:01.1 a 5.2-second burn by the service propulsion system raised the spacecraft’s orbit to 111 x 128 nautical miles. Three further manoeuvres on the second day in space measured the oscillatory response of the docked vehicles to obtain data designed to improve the autopilot’s response in this configuration, and also burned off the CSM’s propellant to increase the fidelity of manoeuvres which it would later perform in Earth orbit to rehearse what a mission would do in lunar orbit.

On the third day in space, Schweickart entered the LM to check out its systems. McDivitt joined him 50 minutes later. At about 045:52, shortly after the landing gear was deployed, McDivitt advised Mission Control that Schweickart had twice been sick – this illness would have an impact on the EVA planned for later in the mission. At 046:28 the astronauts made a 5-minute TV transmission from inside the LM. The descent engine was ignited at 049:41:34.5 for a 371.5-second burn in which the autopilot controlled the attitude of the docked vehicles and the astronauts manually throttled the engine to full thrust. The LM was deactivated at 051:00. Several hours later, a service propulsion system burn achieved an almost circular orbit of 125.9 x 131.0 nautical miles in preparation for the rendezvous sequence.

The EVA plan had called for Schweickart to exit the LM’s forward hatch, transfer to the command module hatch, and then return. But owing to his bouts of nausea the spacewalk was cut back from 2 hours 15 minutes to just 39 minutes, to be made on a single daylight pass. The LM was depressurised at 072:45, and the hatch opened at 072:46. Schweickart initiated his egress at 72:59:02, feet first and face up, and was completely out by 073:07. He was wearing the Extravehicular Mobility Unit suit and Portable Life Support System backpack which astronauts were to wear on the lunar surface. A 25-foot nylon safety tether precluded him drifting away. For stability, he inserted his feet into a pair of ‘golden slippers’ on the ‘porch’ of the descent stage. Meanwhile, at 073:02:00 Scott opened the side hatch of the command module and poked his head and shoulders out to monitor Schweickart. Although the transfer to the command module hatch had been cancelled, Schweickart was able to make an abbreviated study of translation and body-attitude-control using handrails affixed to the upper part of the LM. Before ingressing, Schweickart shot 16-mm movie footage of Scott’s activities, and 70-mm Hasselblad pictures of the exterior of both vehicles. Although the EVA was brief and did not involve a period of orbital darkness, it was sufficient to certify the suit and backpack for use on the lunar surface. The LM was repressurised at 073:53, and the CSM several minutes later. After a TV transmission from the LM that started at 074:58:03 and lasted 15 minutes, it was deactivated and McDivitt and Schweickart rejoined Scott.

On the fifth flight day McDivitt and Schweickart were back in the LM by 088:55 in order to prepare that ship for a period of free flight and an active rendezvous. At 092:22 the CSM oriented the pair into the attitude required for undocking. This was attempted at 092:38, but the latches did not fully release until 092:39:36. This was to be the first time that astronauts flew a spacecraft that was incapable of returning to Earth if an emergency were to arise – they relied on Scott to rescue them. Once free, the LM pirouetted while Scott made a visual inspection. At 093:02:54 the CSM used the thrusters of its reaction control system to make a separation manoeuvre. Over the next 6.3 hours, the LM undertook a series of manoeuvres which set up and executed a rendezvous. In the process, the descent propulsion system was fired under different control regimes and with the throttle being varied, after which the descent stage was jettisoned and the rendezvous was performed by the ascent stage. Terminal phase braking began at 098:30:03, and was followed by a period of station-keeping, then formation flying to facilitate mutual photography prior to docking at 099:02:26. McDivitt and Schweickart then transferred back to the CSM. The ascent stage was jettisoned at 101:22:45.0, and half an hour later ignited its main engine and fired it to depletion to enter a 126.6 x 3,760.9-nautical mile orbit.

The remainder of the mission was less hectic, being devoted mainly to conducting multispectral photography to prepare for the Skylab space station. At 169:30:00.4 the service propulsion system was fired in a 24.9-second burn which established the conditions for a nominal de-orbit. Unfavorable weather in the planned recovery area prompted a postponement of the de-orbit by one revolution, and it was performed at 240:31:14.8. The service module was jettisoned a few minutes later. The command module flew the entry profile under the control of its primary guidance system, and splashed into the Atlantic at 17:00:54 on 13 March about 2.7 nautical miles from the target. It settled in the ideal apex-up flotation attitude, and within an hour the crew were onboard USS Guadalcanal.

With Apollo 9 having successfully tested the LM in Earth orbit, the next issue was whether to fly the ‘F’ mission or to push on and attempt the lunar landing. In fact, it would be impossible for LM-4 to attempt the ‘G’ mission, as the software to conduct the powered descent was still under development. Furthermore, owing to propellant restrictions in the ascent stage of this somewhat overweight LM it would be unable to lift off and rendezvous. Tom Stafford, the Apollo 10 commander, argued against his crew waiting for LM-5 to become available. ‘‘There are too many ‘unknowns’ up there,’’ he noted. ‘‘We can’t get rid of the risk element for the men who will land on the Moon but we can minimise it; our job is to find out everything we can in order that only a small amount of ‘unknown’ is left.’’

On 24 March 1969 NASA stated that Apollo 10 would fly the ‘F’ mission. The original idea had called for the LM merely to undock, enter a slightly different orbit, rendezvous and redock, but in December 1968 the Mission Planning and Analysis Division at the Manned Spacecraft Center had urged putting the descent propulsion system through a high-fidelity rehearsal in which the LM would lower its perilune sufficiently to test the ability of the landing radar to detect and lock onto the surface. Howard Tindall also proposed that the LM should initiate the powered descent and then execute an early abort by ‘fire in the hole’ staging, but his colleagues convinced him that this would be too adventurous. One aspect of the decision to go ahead with the ‘F’ mission was to evaluate the tracking and communications of two vehicles in lunar orbit. In essence, it had been decided to exploit the fortuitous relaxation in schedule pressure and improve on Apollo 8 by performing a rehearsal to the point at which a later LM would initiate its powered descent.

The finally agreed plan called for the LM to separate from the CSM in the circular lunar parking orbit, enter an elliptical orbit having a perilune of about 50,000 feet located just east of the prime landing site, execute a low pass and then jettison the descent stage to make the rendezvous.

In April 1969 the site selectors met to decide the prime target for the first Apollo landing. The photographs of ALS-1 taken by Apollo 8 indicated the presence of a smooth blanket of light-toned material that softened or masked the landscape, and a study of the craters showed that the regolith was quite thick, which in turn implied a considerable age. The fact that the site was atypical of the maria made it unattractive for dating the maria, so it was rejected. This left ALS-2 in the southwestern part of Mare Tranquillitatis as the prime target. In early May, Jack Schmitt put it to Tom Stafford that the launch of Apollo 10 be slipped 24 hours from the proposed date so that the low-perilune pass over ALS-2 could be made in illumination matching that of a mission attempting to land there. This would enable high-resolution pictures to be taken of the site and the landmarks on the approach route. Stafford was receptive. Schmitt approached George Low, who asked Chris Kraft, who sought the advice of the flight control specialists – there were issues in favour and against. When the case was put to Sam Phillips he rescheduled the launch.

AS-505 had been installed on Pad 39B on 11 March, and Apollo 10 lifted off on schedule at 16:49:00 GMT on 18 May 1969 with Tom Stafford, John Young and Gene Cernan.

When the S-IVB cutoff at T + 703.76 seconds, the deviations were -0.23 ft/sec in velocity and -0.08 nautical miles in altitude. After translunar injection, CSM-106 ‘Charlie Brown’ separated, turned around and docked with LM-4 ‘Snoopy’, then the pair were released by the stage. The S-IVB then used propulsive venting to adopt a path that would fly past the Moon and enter solar orbit. At 026:32:56.8 the service propulsion system made a 49.2-ft/sec burn to match a July lunar landing trajectory. At 075:55:54.0 the spacecraft entered an initial lunar orbit of 60.2 x 170.0 nautical miles. Two revolutions later, this was refined to 59.2 x 61.0 nautical miles. During a 30-minute colour TV transmission the astronauts showed off the lunar surface. They reported the colour of the surface to be less grey than was described by Apollo 8. In particular, Mare Serenitatis appeared ‘‘tan’’, whereas Mare Tranquillitatis appeared ‘‘dark brown’’.

After undocking at 098:29:20, the vehicles took up station 30 feet apart while Young inspected the LM, and then the CSM moved off. A 27.4-second burn by the descent propulsion system at 099:46:01.6 placed the LM into a descent orbit with its perilune 15 degrees east of ALS-2. The landing radar was tested while passing over that site at an altitude of 47,400 feet an hour later. The pictures taken were of greater resolution than those transmitted by the Lunar Orbiters. Unfortunately, the 16-mm

This oblique view looking northwest across the crater Maskelyne was taken by the Apollo 10 Lunar Module ‘Snoopy’ as it flew low over Mare Tranquillitatis towards the ALS-2 target.

movie camera failed. A descent propulsion system burn at 100:58:25.9 put the LM into an orbit of 12.1 x 190.1 nautical miles to arrange a ‘lead angle’ equivalent to that which would occur at cutoff of an ascent from the lunar surface. At 102:44:49, during preparations to start the rendezvous with the CSM, the LM started to wallow off slowly in yaw and then stopped, and several seconds later it initiated a rapid roll accompanied by small pitch and yaw rates. Subsequent analysis revealed that this anomalous motion was due to human error. The control mode of the abort guidance system had inadvertently been returned to AUTO instead of the Attitude HOLD mode for staging. In AUTO, the abort guidance system steered the LM to enable the rendezvous radar to acquire the CSM, which at this point was not in accordance with the plan. The required attitude was re-established by the commander taking manual control. The descent stage was jettisoned at 102:45:16.9, and 10 minutes later an ascent propulsion system burn achieved an orbit of 11.0×46.5 nautical miles. This matched the insertion orbit for a mission returning from the surface. The LM had the active role in the rendezvous, and docked at 106:22:02. Two hours later the ascent stage was jettisoned, and during the next revolution the ascent propulsion system was fired to depletion in order to place the vehicle into solar orbit.

At 137:39:13.7, after 31 lunar revolutions, the CSM made the transearth injection. The aim was so accurate that it required only a 2.2-ft/sec refinement 3 hours prior to shedding the service module to centre the trajectory in the ‘corridor’ for atmospheric entry. The capsule splashed into the Pacific 1.3 nautical miles off target at 16:52:23 on 26 May and adopted the apex-up flotation attitude. The astronauts were aboard USS Princeton within the hour.

While Apollo 10 was in transit to the Moon, AS-506 was rolled out to Pad 39A in preparation for the Apollo 11 mission. After the pictures taken during the low pass over ALS-2 were examined, it was confirmed as the prime site for Apollo 11. ALS-3 in Sinus Medii was 2 day’s terminator travel westward and would be the backup. If the launch had to be delayed beyond the date for ALS-3, then the target would be ALS-5 in Oceanus Procellarum. In the post-flight debriefing, Tom Stafford pointed out that although the ALS-2 aim point was acceptable, the western end of the ellipse was much rougher. He advised Neil Armstrong that if he were to find himself at the far end of the ellipse and did not have the hover time to manoeuvre among the small craters and boulders to select a spot on which to land, then he would have to ‘‘shove off” – by which Stafford meant abort.

A week before Apollo 11 was due to launch, people began to congregate at the Cape communities of Titusville, Cocoa Beach, Satellite Beach and Melbourne. They came from all around the world in order to be able to tell their grandchildren they were present when men set off to try to land on the Moon. By 15 July hotels and motels allowed late-comers to install camp beds in lounges and lobbies, but most people spent the night on the beaches and by the roadside, generating the worst congestion

in Florida’s history. With the notable exception of alarm clocks, which rapidly sold out, shops were able to supply the hoards. As it was to be a dawn launch, the parties ran through the night.

When AS-506 lifted off at 09:32:00 local time on 16 July on a mission to accept President Kennedy’s challenge of landing a man on the Moon before the decade was out, it was estimated that there were about a million people present and 1,000 times as many watching on ‘live’ television.

No-one could be certain that the objective would be achieved, but the way had certainly been well paved.

[1] He did not infer from the absence of detail in the shadows that the Moon was airless, nor did he suggest the presence of open water.

[2] In fact, one of the few names introduced by van Langren to have survived is Langrenus, by which he honoured his own family.

[3] Selene was the Greek moon-goddess.

[4] Like Herschel and Schroter, von Gruithuisen believed the Moon to be inhabited, and after using a small telescope he reported in 1824 his discovery of a city in the equatorial zone near the meridian; but this was later shown to be merely a group of shallow ridges that were visible only when the Sun was low on the local horizon.

[5] For over half a century, geologists had argued about how the Coon Butte crater formed – and this was for a structure that was accessible to in-situ examination. Could there be any hope of resolving the issue of the lunar craters, which could only be peered at from afar!?

[6] On transfer to NASA, the Langley Aeronautical Laboratory became the Langley Research Center, the Ames Aeronautical Laboratory became the Ames Research Center, the Lewis Flight Propulsion Laboratory became the Lewis Research Center and the High-Speed Flight Station became the Flight Research Center.

[7] On 3 December 1958 Eisenhower ordered that JPL be transferred to NASA. This took effect on 1 January 1959, although only under contract, since the facility was owned by Caltech, which NASA paid. In September 1959 the Pentagon voluntarily yielded the Army Ballistic Missile Agency since the military had decided it did not require the Saturn launch vehicle; it would develop the Titan III instead. On 21 October 1959 NASA announced that it was to gain von Braun’s rocket team. On 1 July 1960 the Army Ballistic Missile Agency became the Marshall Space Flight Center.

[8] Physicists James van Allen, Homer Newell, Charles Sonett and Lloyd Berkner were notable early members of the ‘sky science’ community.

[9] Colloquia were held quarterly at different venues on the West Coast through to May 1963.

[10] As would later be realised, Mare Moscoviense fills the floor of a 300-km-diameter crater and Tsiolkovsky covers a portion of the floor of a crater which has a prominent central peak.

[11] The name Ranger set a trend for lunar projects with the names Surveyor and Prospector; in contrast to Mariner for planetary missions – that is ‘land’ names as against ‘sea’ names.

[12] Later, launch operations would be made a separate field centre.

[13] In early 1962 the entire NASA launch organisation was restructured.

[14] The Soviet spacecraft fell silent on 27 February 1961, at a distance of 2З million km from Earth. A launch on 4 February had stranded a similar spacecraft in parking orbit, but its role was disguised by naming it Sputnik 7.

[15] Surface science was only one of the objectives; there were the investigations to be made during the terminal approach, and achieving these would mark an acceptable compromise on the first mission.

[16] They were Lieutenant Commander Alan Bartlett Shepard Jr, Lieutenant Malcolm Scott Carpenter and Lieutenant Commander Walter Marty Schirra Jr from the Navy; Lieutenant Colonel John Herschel Glenn Jr from the Marines; and Captain Virgil Ivan ‘Gus’ Grissom, Captain Donald Kent ‘Deke’ Slayton and Captain Leroy Gordon Cooper Jr from the Air Force.

[17] This reasoning would resurface when John F. Kennedy asked for a worthy challenge.

[18] In a reorganisation on 8 December 1959, the Office of Space Flight Development had become the Office of Space Flight Programs.

[19] In fact, NASA could have launched Shepard several weeks ahead of Gagarin’s flight. If this had been done, Kennedy may well not have issued the challenge of landing a man on the Moon before the decade was out. The fact that Shepard’s flight had been only suborbital whereas Gagarin’s was orbital, would probably not have mattered, since the world’s first ‘spaceman’ would have been an American. The fact that America ‘lost’ both the first satellite and the first man into space could be said to be directly responsible for the race to the Moon. It serves to illustrate that history is not an irresistible tide, it can be extremely sensitive to the outcome of singular events.

[20] Earth imparts a gravitational acceleration of 32.2 ft/sec2.

[21] Newell also wished to maximise the amount of science on manned flights in Earth orbit.

[22] Despite Gold’s assertion that the dust would react only slowly upon being loaded, reporters would remain fascinated by the possibility that a lander would rapidly become submerged by it!

[23] The crater made by Ranger 8 was photographed by Lunar Orbiter 2, and found to be about 13.5 metres in diameter with a mound at its centre.

[24] The converter was installed at JPL, not at Goldstone.

[25] The crater made by Ranger 9 was photographed by Apollo 16 in 1972. At 14 metres in diameter, it was similar to that of its predecessor.

[26] The delay in the Centaur stage was in part due to problems with the configuration of its propellant tanks, but also because the Marshall Space Flight Center was busy with the Saturn launch vehicles. In early 1962, therefore, the Centaur had been transferred to the Lewis Research Center.

[27] In the case of Lunar Orbiter, the wide-angle images would be referred to as medium (M) frames and the narrow-angle images as high-resolution (H) frames.

[28] In fact, Bimat was similar to the Polaroid process.

[29] In particularly, the Planetology Subcommittee called for the Lunar Orbiter Block II to undertake selenodesy, gamma-ray, X-ray, magnetometry, microwave and non-imaging radar studies from orbit.

[30] This was because on a direct ascent the translunar injection point was necessarily near the latitude of the launch site, and for a launch from Florida this was north of the equatorial plane on a southerly heading, which meant that by the time the spacecraft reached lunar distance it would be south of the equatorial plane.

[31] The Manned Space Flight Network was operated under the direction of the Goddard Space Flight Center in support of the Manned Spacecraft Center.

[32] In fact, stereoscopic analysis of the Lunar Orbiter pictures proved difficult due to the manner in which they were scanned in narrow strips for transmission, as this gave the impression of the surface as being corrugated.

[33] Whereas in summer the Moon reaches its ‘full’ phase south of the equator, in winter it does so north of the equator, and since for the early Surveyors the landing sites were well to the west of the lunar meridian with arrival soon after local sunrise in winter months the translunar injection had to be made from south of the Earth’s equator. The restartable Centaur facilitated this by using its first burn to achieve a parking orbit and, once south of the equator, using its second burn to head for the Moon.

[34] During a solar eclipse, when the Moon occults the Sun to terrestrial observers, the irregular profile of the lunar limb often allows light from small sections of the solar disk to be viewed during totality, giving rise to a phenomenon known as Baily’s Beads after the British astronomer Francis Baily who first noted them during an annular eclipse on 15 May 1836.

[35] The term ‘psia’ means pounds of force per square inch on an ‘absolute’ scale measured relative to zero. If a pressure gauge is calibrated to read zero in space, then at sea level on Earth it would read 14.7 psi, which is sea-level atmospheric pressure. A value specified in psia is therefore relative to vacuum, rather than a differential relative to the pressure at sea level on Earth. For large numbers, the difference is insignificant.

[36] The pictures taken by Lunar Orbiter 1 showing Earth against the lunar limb were in black – and-white.

[37] Both Apollo 15 and Apollo 17 were sent to sites imaged by Lunar Orbiter 5; although in the case of Apollo 17 the observations by Apollo 15 also contributed to the selection.

[38] In the late 1950s J. J. Gilvarry argued that the maria were once water oceans, and hosted life. He said the now-dry plains were sedimentary rock, and dark owing to the presence of organic material. He claimed the elemental abundance data from the alpha-scattering instrument matched mudstone even better than it did basalt.

[39] Although NASA was unaware of it, a gamma-ray spectrometer operated in lunar orbit by Luna 10 in 1966 had provided a rudimentary analysis of the composition of the lunar surface across a wide range of latitudes, and the results showed there to be no significant exposures of acidic rock in the highlands.

[40] The term ‘facies’ was introduced to geology in 1838 by the Swiss stratigrapher Amanz Gressly to specify a body of rock having given characteristics.

[41] They were: Lieutenant Charles ‘Pete’ Conrad Jr, Lieutenant Commander James Arthur Lovell Jr, and Lieutenant Commander John Watts Young from the Navy; Major Frank Frederick Borman II, Captain James Alton McDivitt, Captain Thomas Patten Stafford, and Captain Edward Higgins White II from the Air Force; Neil Alden Armstrong, a former naval aviator, now a civilian test pilot for NASA; and Elliot McKay See Jr, a civilian test pilot for the General Electric Company.

[42] Slayton had been grounded in 1962 owing to a heart irregularity while training for a Mercury mission.

[43] They were: Major Edwin Eugene ‘Buzz’ Aldrin Jr, Captain William Alison Anders, Captain Charles Arthur Bassett II, Captain Michael Collins, Captain Donn Fulton Eisele, Captain Theodore Cordy Freeman, and Captain David Randolph Scott from the Air Force; Lieutenant Alan LaVern Bean, Lieutenant Eugene Andrew Cernan, Lieutenant Roger Bruce Chaffee, and Lieutenant Commander Richard Francis Gordon Jr from the Navy; Captain Clifton Curtis Williams from the Marines; Ronnie Walter Cunningham, a research scientists at the RAND Corporation; and Russell Louis ‘Rusty’ Schweickart, a research scientist at the Massachusetts Institute of Technology.

[44] This name change officially took effect on 20 December 1963.

[45] On 26 October 1962 a nomenclature was introduced by which the pad abort tests were to run in sequence from PA-1; the Little Joe II flights were to start at A-001; missions using the Saturn I were to start at A-101; missions using the Saturn IB were to start at A-201; and missions using the Saturn V were to start at A-501, with the ‘A’ standing for ‘Apollo’. The ‘SA’ prefix was employed by the Marshall Space Flight Center (giving precedence to the launch vehicle) and the ‘AS’ prefix was used by the Manned Spacecraft Center (giving precedence to the spacecraft). In addition, the term ‘space vehicle’ was introduced to describe the integrated ‘launch vehicle’ and ‘spacecraft’, with the latter comprising the CSM, the LM (if present) and the SLA structure.

[46] NASA’s Flight Research Center at Edwards Air Force Base was renamed in Dryden’s honour.

[47] On 30 March 1967 George Low suggested that the AS-201 and AS-202 test flights be assigned the designations Apollo 2 and Apollo 3 retrospectively in order to fill in the gap, but this was rejected by Mueller on 24 April. AS-203 was not included because it did not carry a spacecraft.

[48] The last two categories represented the lunar part of the Apollo Applications Program which was being promoted by George Mueller, and when this fell by the wayside the reconnaissance surveys were deleted and the main program was expanded to include ‘enhanced capability’ landings.

[49] Times in this hhh:mm:ss format are with reference to the time of launch.

[50] It is worth noting that the guidance system in the IU performed this magnificent recovery entirely on its own.

[51] CSM-101 had flown on Apollo 7, CSM-102 had been retained by North American Aviation for ground testing, CSM-103 had been assigned to the Apollo 8 ‘C-prime’ mission, CSM-104 was to fly the Apollo 9 ‘D’ mission, CSM-105 was for ground testing, and CSM-106, which was delivered to the Cape on 25 November 1968, was assigned to Apollo 10.

For millennia human beings have peered at the Moon in the sky and wondered what it might be. Within months of its establishment on 1 October 1958, the National Aeronautics and Space Administration set out to develop a program of robotic lunar exploration. In 1961 President John F. Kennedy raised the stakes by challenging his nation to land a man on the Moon within that decade. The resulting Apollo program dominated the agency’s activities throughout the 1960s and into the early 1970s.

It is impractical to cover all the strands of this effort in a single volume in equal detail. Nor can any given strand be properly appreciated in isolation. My approach is therefore to write a series of books, each of which applies a magnifying glass to a certain number of strands and glosses over others. This book focuses on what was known about the Moon at the dawn of the space age and details the robotic projects that paved the way for the first Apollo lunar landing, in particular the Surveyors that soft-landed to investigate the physical and chemical nature of the lunar surface and the Lunar Orbiters sent to reconnoitre possible landing sites.

As such, this book complements: Apollo – The Definitive Sourcebook, which was compiled with Richard W. Orloff and supplements an account of how the Apollo program was organised with the minutiae of each flight; How NASA Learned to Fly in Space – An Exciting Account of the Gemini Missions, which explains the key contribution that the Gemini crews made to the success of Apollo; and The First Men on the Moon – The Story of Apollo 11, which covers that mission from start to finish. In Exploring the Moon – The Apollo Expeditions, which I recently reissued in enlarged format, I detailed what the astronauts of each mission did whilst on the lunar surface. It also complements the excellent To a Rocky Moon – A Geologist’s History of Lunar Exploration by Donald E. Wilhelms, and the International Atlas of Lunar Exploration by Philip J. Stooke.

I used the mission reports as my primary source of information – there are many thousands of pages available on the NASA Technical Report Server. Millions of dollars were spent developing and flying the vehicles used to take close-up pictures of the Moon and, like the mission reports, until recently they remained in archives. I have assembled some of the contiguous photographic sequences taken by the Lunar Orbiters to illustrate the process by which the site for the first Apollo landing was selected. To my knowledge, they have never previously been made available to the public in this form. I have also freely intermixed units of measure, largely following the choice of the appropriate mission reports. Unless stated otherwise, all times are GMT in 24-hour format. Launch, parking orbit, midcourse and terminal phase times are usually specified to the nearest second, but for a Surveyor spacecraft’s powered descent the event times are specified to several decimal places.

In the 1960s NASA was a young and aggressive agency which embodied the ‘can do’ spirit of America at that time in tackling audacious engineering challenges with a tremendous sense of urgency – motivated by the desire to be the first to explore a new world. This is an account of a strand of that story that is often reduced to a few paragraphs in popular histories.

David M. Harland Kelvinbridge, Glasgow January 2009

As Silverstein at NASA headquarters had arranged things, JPL reported to him for the Ranger spacecraft, deep-space tracking and control, in-flight operations and data processing. The procurement of the launch vehicle would be managed by the Office of Launch Vehicle Programs. This was directed by Donald R. Ostrander, who, as a Major General in the Air Force assigned to NASA, was well qualified to liaise with the military and its contractors. Ostrander delegated the task of procuring Agena and Centaur stages to Wernher von Braun in Huntsville. By dividing the spacecraft (JPL and the Office of Space Flight Programs) from the launchers (Huntsville and the Office of Launch Vehicle Programs), this arrangement provided considerable scope for confusion and conflict.

On 29 December 1959 Associate Administrator Richard Horner created the Space Exploration Program Council with himself in the chair. It was to seek to improve the management of space flight projects, and to reconcile the inevitable differences that would arise between headquarters and the centres managing individual projects. Its members were Abe Silverstein, Donald Ostrander, and Wernher von Braun (launch vehicles), Harry Goett of the Goddard Space Flight Center (satellites in Earth orbit) and W. H. Pickering (deep-space missions). At its inaugural meeting on 10 February I960 it discussed an internal review sent to Ostrander on 15 January that warned of potential difficulties in the procurement of the Agena B, and how this might affect Ranger. It was decided that Silverstein’s technical assistant, William A. Fleming, should chair a steering committee. This Agena B Coordination Board was formed on 19 February, and drew its membership from von Braun’s team in Huntsville (which was in the process of transferring to NASA, and in July would become the Marshall Space Flight Center), the Goddard Space Flight Center and JPL. The Council also decided that a NASA project engineer should be assigned to the plant in Sunnyvale, California, where the Missile and Space Division of Lockheed manufactured the Agena. In Huntsville, Hans Heuter was made head the Light and Medium Vehicle Office, which was to manage procurement of the Agena B and Centaur stages, and Friedrich Duerr became its Agena Systems Manager. However, whilst von Braun’s team would plan and supervise procurement, the fact that the Air Force did not want an independent line of authority leading to its supplier meant the Ballistic Missile Division would implement procurement from the contractor. The Air Force Space Systems Division in Inglewood, California, of which the Ballistic Missile Division was a part, was commanded by Major General Osmond J. Ritland. In April 1960 Major John E. Albert was assigned to assist NASA in procuring the Agena B, which meant he had responsibility for all Air Force technical matters relating to Ranger. He would work with Duerr in Huntsville for the launch vehicle and Burke at JPL for the interface between the Agena and the Ranger spacecraft. Duerr sent Robert Pace to Sunnyvale as the resident project engineer. Lockheed appointed Harold T. Luskin to work with Albert and Pace. The final contract, which was agreed only on 6 February 1961, was for nine Agena B vehicles. In terms of a production line that was making Agenas for several Air Force programs, this was a small order – and it was treated as such by the company until NASA complained. As Huntsville was

responsible for NASA’s launch operations, in addition to procuring the Atlas-Agena В it had to obtain ground support equipment and the systems required to track the vehicle in its ascent to orbit.[12]

In March I960, as the Army Ballistic Missile Agency was being incorporated into NASA, Donald Ostrander’s Office of Launch Vehicle Programs created the Launch Operations Directorate to manage NASA launches in Florida. In essence it was an expansion of the Army’s Missile Firing Laboratory, and being based at Huntsville it answered to von Braun. Kurt H. Debus, Director of Launch Operations, was keenly aware that he was responsible for activities he could not actually control, because in reality NASA was merely a tenant at the Cape and as such was limited to monitoring the preparation and launch of the vehicles by the 6555th Aerospace Test Wing. His counterpart on the Air Force side was Major General Leighton I. Davis. That same month, the Office of Space Flight Programs set up its own office at the Cape to coordinate the on-site activities of the flight project teams.

On 1 September I960 Richard Horner resigned from NASA. He was succeeded as Associate Administrator by Robert C. Seamans. Noting criticism that the Agena В Coordination Board had proved ineffective at resolving disputes, Seamans ordered a review. On 19 October, Albert Siepert of the Office of Business Administration submitted A NASA Structure for Project Management. On 19 January 1961, the day before he left office with the other Eisenhower political appointees, Keith Glennan endorsed the recommendations. In this new scheme, Silverstein’s office would set budgets for flight projects, establish objectives and review progress. The Marshall Space Flight Center, reporting to Ostrander’s office, would provide launch vehicles and launch operations in support of a project manager at a field centre. In the event of disputes, Seamans would personally decide the issue. The Agena В Coordination Board was dissolved. This revision gave JPL direct authority and responsibility for Ranger. NASA named Burke as its Ranger Project Manager, thereby giving him greater authority than he had when he was simply JPL’s Ranger Spacecraft Project Manager.

When James E. Webb became NASA Administrator in February 1961, he argued that although the Air Force might procure the rockets for NASA, the agency should be wholly responsible for preparing and launching them. On 17 July the Air Force conceded that in due course NASA could install its own launch groups to supersede the 6555th Aerospace Test Wing.[13]

The three successful Rangers satisfied the objective set for the Block III series in terms of supporting Apollo. The maria proved to be cratered on all scales, but with a smoothly undulating surface of generally shallow slopes. And the presence of large blocks of rock lying on the surface suggested sufficient bearing strength to support a lander. In addition, radio tracking had enabled the estimate of the mass of the Moon to be much improved. It also established the axis that is aligned towards Earth to be about 1 km longer, with the centre of mass being offset several kilometres from the geometric centre in a direction away from Earth.

When some 200 scientists gathered at the Goddard Space Flight Center in April 1965 to discuss the combined results of the Ranger project, Harold Urey and Gerard Kuiper still disagreed about whether the Moon was thermally differentiated. Thomas Gold insightfully noted that the pictures represented a mirror in which each person saw evidence to support his own hypothesis.

One lesson of Ranger was that lunar geological units were so severely blurred by impact ‘tilling’ at the fine scale that in undertaking photogeological mapping it was better to use a medium scale of 1:1,000,000, as was used by the Air Force Chart and Information Center in St Louis for its Lunar Astronautical Chart series.

Ranger had provided a close look at several sites, but what was required next was for an orbiter to provide a broader view at better-than-telescopic resolution and for a soft-lander to provide ‘ground truth’.

With four mare sites in the Apollo zone visited, distributed more or less uniformly in longitude from 23°E to 43°W, it was possible to draw some generalisations.

Surveyor 1 inspected a level plain in an ancient 100-km-diameter crater known as the Flamsteed Ring that had been ‘inundated’ in some way by Oceanus Procellarum; Surveyor 3 landed in a subdued medium-sized crater situated on the open plain of Oceanus Procellarum; Surveyor 5 provided a detailed inspection of a very small irregularly shaped crater in Mare Tranquillitatis; and Surveyor 6 inspected the plain of Sinus Medii within sight of a mare ridge. All four sites were very similar in terms of topography, and in terms of the structure of the surface layer and its mechanical, thermal and electrical properties; and the surfaces at the latter two sites were similar in terms of elemental composition and the content of magnetic material. ft seemed unlikely that terrestrial sites situated thousands of kilometres apart and selected in a manner similar to that by which the lunar targets were chosen would prove to be so similar.

At all sites, the undisturbed fine-grained surface material was lighter toned than the subsurface. This difference was as much as one-third for Surveyors 1, 3 and 6, but less for Surveyor 5. The fact that the albedo of the subsurface was the same at all sites meant the exceptional case of Surveyor 5 was due to the surface material being less bright. Observations of the erosion of the fine-grained surficial material by the vernier efflux during the ‘hop’ performed by Surveyor 6 and of the tracks left by the

fragments that were rolled across the surface, indicated that the bright surficial layer was limited to the uppermost few millimetres. The existence of such a well-defined ‘contact’ in a nominally undisturbed surface at four widely spaced sites on the maria implied the action of a process (or combination of processes) which had the effect of increasing the albedo of the material at the surface, for otherwise such a fine layer would be destroyed by the gardening of meteoritic bombardment. Furthermore, the fact that the material at all depths below the surface was uniformly dark, as opposed to there being a gradation in albedo, indicated that whenever an impact mixed the lightened surficial material into the subsurface, it became dark. Perhaps the process which altered exposed material had not had long to act on the material in the small fresh-looking crater in which Surveyor 5 landed. At all sites, the bright rounded rock fragments visible on the surface had textures featuring knobs and pits, whereas these were absent on the highly angular faceted blocks. This hinted that the process which produced the rounding – undoubtedly the relentless meteoroid bombardment – also gave rise to the ‘worn’ texture.

At all sites the fine-grained material was cohesive, and whilst the surficial layer was mildly compressible, its bearing strength increased rapidly with depth. But there was no observable variation in grain size with depth – evidently it was simply a case of the porosity decreasing with depth. It was estimated that the bulk density of the upper centimetre of undisturbed material was in the range 0.7 to 1.2 g/cm3, and that by a depth of several centimetres this had increased to 1.6 g/cm3.

The size-frequency distribution of small craters at all sites matched that expected for a steady-state population resulting from the protracted bombardment of primary meteoroids and the fall of ejecta from such impacts. Furthermore, this distribution was independent of individual differences in the mare surfaces and of the population of craters larger than several hundred metres in size.

The thickness of the fragmental debris layer on the mare plains was clearly related to the abundance of craters with diameters ranging between 1 and 10 km. In the part of Mare Tranquillitatis where Surveyor 5 landed the size-frequency distribution of such craters was twice that of the Oceanus Procellarum inundation of the Flamsteed Ring where Surveyor 1 landed, and the minimum size of the blocky rimmed craters at those sites indicated that the fragmental debris layer was several times thicker in Mare Tranquillitatis than in Oceanus Procellarum. Of all the maria, Sinus Medii had one of the highest size-frequency distributions of craters with diameters larger than several hundred metres, and the fragmental debris layer on the plain near Surveyor 6 was thicker to match. The fact that the cratering indicated the surface of Sinus Medii to be older than the other maria was evidence that the older the surface the thicker its fragmental debris layer. The size distribution of the material on the surface was also related to the thickness of the fragmental debris layer. When the mare lava flow was fresh and its rocky surface was exposed, small impacts were able to excavate it. As a layer of fragmental debris accumulated, it took larger and larger impacts to reach the substrate. Over time, the loose fragments were both reduced in size and increased in number. The trend was therefore towards a thickening layer of ever finer fragments. That is, the regolith ‘matured’.

The implication for Apollo was that an older surface would be a safer landing site.

When viewed from afar, an older surface might look rough by virtue of having large craters with blocky rims, but since only large craters would be able to excavate the substrate this meant that the plethora of small craters (which must be present) would not possess blocky rims. The task for the site selectors was therefore to measure the smallest craters with blocky rims on a mare surface to measure the thickness of the fragmental debris layer, and then seek a flat patch of open ground situated between such craters where it was likely to be relatively free of blocks.

CLASSICAL PHILOSOPHERS

Greek astronomy began with Thales, who was born shortly before 600 BC and lived in Miletus, a city of Ionia, which was a state on the western coast of what is now Turkey. As a philosopher he is regarded as one of the Seven Sages of Greece, and is considered to be the ‘father of science’. He set the seasons of the year and divided the year into 365 days. He also predicted a solar eclipse that occurred in 585 BC. It had been believed that the Moon was self-luminous, but he suggested that it shone by reflecting sunlight. Anaximander, a student of Thales, went to Italy in 518 BC. He opined that Earth floated in space – the prevailing view was that it was in some way supported on pillars through with the Sun passed during the night.

Pythagoras was born about 575 BC on Samos, an island off the coast of Ionia that was a crossroads between Asia, Africa and Europe. In his youth he reputedly visited Thales. Pythagoras considered the Moon to mark a fundamental boundary, in that it and everything ‘above’ was ‘perfect’, while Earth was subject to change and thus to decay. When critics argued that the markings on the face of the Moon indicated that it, too, was imperfect, it was suggested that the Moon was a mirror and the markings it displayed were really on Earth.

Around 450 BC Anaxagoras of Athens decided that Thales was correct in saying the Moon shone by reflecting sunlight. He realised that the Moon was spherical, and used this to explain its monthly cycle of ‘phases’. A generation later, Democritus, who travelled widely in ancient Greece, reasoned that the Moon was a world in its own right with a rugged surface, and he speculated that it might be an abode of life.

In the early fourth century BC, Plato, a student of Socrates, founded the Academy in Athens as the first institution of higher learning. Eudoxus briefly studied under Plato. After learning astronomy, he devised an explanation for the manner in which the constellations on view change with the seasons. He imagined the stars to be on a sphere that was centred on Earth, and the Sun to be on a slightly smaller concentric sphere made of transparent crystal which allowed the stars to be seen through it. The solar sphere turned around Earth on a daily basis, as did that with

the stars, but there was a slight differential in their rates that took a year to complete. Aristotle, another student of Plato, seized on this idea of ‘crystal spheres’ by proposing that there was one for each object that had an independent motion in the sky, and that their rotation was due to the action of angels. Although Eudoxus had envisaged crystal spheres only as a means of exposition, Aristotle believed them to be real and his views would come to dominate natural philosophy.

The points of light in the sky which move against the background of stars were called ‘planets’, meaning ‘wanderers’. In the third century BC Aristarchus of Samos suggested that the Sun might be located at the centre of the ‘planetary system’, with Earth being a sphere, rotating daily on its axis, and travelling around the Sun on an annual basis; but the idea attracted little support and was soon forgotten. Aristarchus also reasoned that because the Moon occults the Sun at a solar eclipse, the Sun must be further away – in fact, much further away. He also inferred that the stars must be considerably further away than the Sun, because they show no parallax when viewed from opposite sides of Earth’s path around the Sun. However, his reasoning on these matters was ignored. He interpreted a lunar eclipse as the Moon’s passage through the shadow cast by Earth, and made a fair estimate of the distance between the Moon and Earth in relation to the diameter of Earth. His contemporary, Eratosthenes of Cyrene, made the first realistic estimate of the Earth’s true diameter, thereby providing a scale to Aristarchus’s calculations.

At the end of the third century BC, Apollonius of Perga on the southern coast of modern Turkey was a Greek geometer with an interest in conic sections, and it was he who introduced the names to the ellipse, parabola and hyperbola. Although it was inconceivable that celestial objects should be less than perfect, detailed observations had shown their motions to be anomalous. Apollonius devised a geometrical scheme in which a celestial body would trace a small circle whose central point travelled in a circle around Earth; the small circle was termed the ‘epicycle’, and its centre was the ‘deferent’. This allowed the Moon to appear at times to lead and at other times to trail its perfect position. Furthermore, this accounted for why the size of the Moon appeared to vary in a cyclical manner. And of course, because the scheme involved only circles it restored purity.

Hipparchus, a Greek living in Alexandria, Egypt, in the second century BC, was the greatest of the classical Greek astronomers. His legacy was a star catalogue, but he also used a solar eclipse to estimate the relative distances of the Sun and Moon to a greater accuracy than had Aristarchus. He reasoned that although the Moon must orbit the Earth’s centre, the location of observers on the Earth’s surface provided the basis for parallax. On scrutinising records of eclipses that had been observed from both Alexandria and Nicaea, which lie on the same meridian but are some distance apart, he used the extents to which the Moon had masked the Sun’s disk to calculate the distance to the Moon relative to the Earth’s diameter. In fact, he calculated the distance of the Moon to within a few thousand kilometres and its diameter to within several hundred kilometres – although obviously he didn’t use kilometres as a unit of measure. Hipparchus also used measurements of the Moon’s orbit to assess Apollonius’s suggestion of deferents and epicycles, found it satisfactory, and provided measurements of the sizes of the epicycles.

In 80 AD the Greek historian Plutarch, who became a citizen of Rome, wrote the philosophical treatise Faces in Orbe Lunare in which he discussed the motion of the Moon across the sky, and how it maintained one face towards Earth as it turned on its axis. He thought that it was a world similar to Earth, and suggested it might be inhabited. A generation later, this latter point led the Greek storyteller Lucien of Samosata to write Vera Historia describing how a whirlwind lifted a ship from the sea and deposited it onto the Moon, where there was a battle in progress between the local inhabitants and invaders from the Sun. The story was a satire on the wars raged by the Greeks.

Claudius Ptolemaeus was born around 85 AD, probably in Alexandria, which was at that time under Hellenistic control. The Royal Library of Alexandria was founded at the start of the third century BC. Over the centuries it had built up an unrivalled catalogue, because whenever a ship docked in the harbour the authorities ordered copies made of any books that were on board. Ptolemy (as he is known in English) used his own observations of the stars and the resources of the library to refine the work of Hipparchus, and wrote up his findings in a book of his own. The library was sacked several times and eventually destroyed, but when this occurred is disputed. Although Ptolemy’s book was lost, an Arabic translation survived as the Almagest. He accepted Earth to be centrally located, celestial objects to be travelling in circles, Aristotle’s belief in the reality of concentric celestial spheres, and also Hipparchus’s endorsement of the deferents and epicycles as the reason for the anomalous motions. The Church of Rome accepted Aristotle’s philosophy, and so, despite its contrived nature, the ‘Ptolemaic system’ – as it became known, even although Ptolemy had not invented it – survived for over 1,000 years.