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.

EARLY IDEAS ABOUT LUNAR CRATERS

In 1662 Robert Hooke was made curator of the recently formed Royal Society of London. He was charged with devising demonstration experiments. As an extremely skilled technical artist, in 1665 he published Micrographica, which was profusely illustrated with his own observations using a telescope and a microscope. Although he included a detailed drawing of the lunar crater Hipparchus, which is at the centre of the Moon’s disk, he had no desire to map the Moon. However, he undertook a series of experiments to investigate how craters may have formed. First he dropped heavy balls into tightly packed wet clay, and examined the imprints that they made. He also heated alabaster until it bubbled, and then let it set so that the last bubbles to break the surface produced craters. However, just as Hooke could not imagine where the projectiles could have come from to scar the Moon so intensively, nor could he conceive how the surface could have been sufficiently hot to blister on such a scale.

Following the discovery of the first two asteroids in 1801 and 1802, Marshal von Bieberstein in Germany suggested that lunar craters were created by the impact of such bodies. This was reiterated independently in 1815 by Karl Ehrenbert von Moll. In 1829 Franz von Gruithuisen agreed. However, the idea was rejected by those who supported the anti-catastrophist paradigm of uniformitarianism in terrestrial geology which was developed in the 1830s and 1840s.[4] In 1873 Richard A. Proctor published The Moon. Although this book was largely devoted to the motions of the Moon, he revived the idea that the craters marked impacts. But when the second edition of the book was issued in 1878 this section had been deleted. What puzzled the nineteenth century proponents of the impact hypothesis was that the lunar

craters are almost all circular, whereas the majority of bodies must have struck at an oblique angle and, it was presumed, produced elliptical craters.

In 1874 James Nasmyth and James Carpenter in England published The Moon, in which they attempted to explain how the surface features may have formed. As had Hooke two centuries earlier, they made model craters in experiments. They came to the conclusion that the lunar craters were produced by ‘fountains’ of material. In the early part of an eruption, when the velocity of the material ejected from the vent was great, the material would spray out in an umbrella-shaped plume and fall back some distance away to build up a concentric ring that became the wall of the crater. In many cases, as the eruption declined the fallout formed a succession of terraces interior to the wall. They presumed that in some cases the final phase of the eruption either built up the central peak, or in the case of craters with dark floors and no peak, switched to fluid lava that was confined to the cavity and buried the vent. In view of the weak gravity and absence of an atmosphere, it seemed plausible that this process could have produced very large structures.

Other explanations were offered for the origin of lunar craters. In 1854 the Danish astronomer Peter Andreas Hansen argued that the Moon bulged towards Earth, that its centre of gravity was displaced 50 km towards the far-side, and that this had drawn all the air and water on the surface around to the far-side, to where the inhabitants had relocated. In 1917 D. P. Beard suggested that the Moon was once immersed in a deep ocean, that the craters were limestone structures similar to coral reefs, and they were left exposed when the water flowed to the far-side.

On 24 September 1961 NASA announced that the Manned Spacecraft Center to be built near Houston, Texas, would supersede the Space Task Group. It would not only design, develop, evaluate and test manned spacecraft, but also train astronauts and manage mission operations. Robert R. Gilruth, head of the Space Task Group, was made Director of this new centre.

On 1 November, NASA restructured its headquarters. As part of this review, the offices of Space Flight Programs and Launch Vehicle Programs were wrapped up, and new program offices were created for Manned Space Flight, Space Sciences, and Applications. This raised Manned Space Flight to office status, as opposed to a subdivision of Space Flight Programs. The effect was to put the administration of all the agency’s activities (some of which were aeronautical) on a par with the Office of Manned Space Flight, although that office had fully three-quarters of the budget. In effect, James Webb had gathered the power of decision-making into headquarters, since the directors of all the ‘offices’ and ‘centres’ would report to Robert Seamans, the Associate Administrator who, as the agency’s ‘general manager’, would have budgetary control.

The obvious candidates to be Director of the Office of Manned Space Flight were Abe Silverstein and Wernher von Braun, but because their relationship was stormy Webb had sought an outsider, and on 21 September hired Dyer Brainerd Holmes. As general manager of the Major Defense Systems Division of the Radio Corporation

Specifically, the cameras were designated Fa (25-mm), Fb (76-mm), P1/P2 (76-mm) and P3/P4 (25-mm).

of America, Holmes had built the Ballistic Missile Early Warning System on time and on budget, which was no mean feat.7 Silverstein returned to the Lewis Research Center, this time as its Director.

Homer Newell was promoted from Silverstein’s deputy to become Director of the Office of Space Sciences. Edgar Cortright became Newell’s deputy, and Oran Nicks superseded Cortright as Director of the Lunar and Planetary Programs Division. As one of his first acts, Nicks established individual offices in the Lunar and Planetary Programs Division for Ranger and Surveyor, and also for the Mariner interplanetary program. For Ranger, William Cunningham was Program Chief, Walter Jakobow – ski was Program Engineer and Charles Sonett served in an interim capacity as Program Scientist. James Burke at JPL was delighted with this structure, because it integrated engineering and science in a single program office and greatly simplified his relationship with NASA headquarters.

Holmes promptly assigned Joseph F. Shea, a systems engineer who had run the development of the inertial guidance system for the Titan intercontinental-range ballistic missile, to resolve the protracted debate about how Apollo would fly to the Moon – the ‘mission mode’ issue.

On 28 November, NASA announced that North American Aviation of Downey, California, had been awarded the contract to develop the Apollo spacecraft. On 21 December, Holmes set up the Manned Space Flight Management Council. Drawing on senior managers at headquarters and the field centres, this would set policy for manned space planning. At its first meeting, the Council decided on a launch vehicle which would become known as the Saturn V. A single launch would be capable of dispatching an Apollo circumlunar mission. It might even be possible to undertake a lunar landing with a single launch. A landing mission involving Earth orbit rendezvous could certainly be done using just two launches.

On 20 February 1962, America finally inserted a man into orbit, with John Glenn riding an Atlas missile to circle the globe three times. On 7 June NASA decided on lunar orbit rendezvous as the mode for Apollo. On 7 November, it announced that the Grumman Aircraft Engineering Corporation of Bethpage, New York, had been awarded the contract to develop the Apollo lunar module.

By the end of 1962, therefore, NASA had taken all the key decisions that defined how it would address Kennedy’s challenge.

BMEWS used large radar stations in Alaska, Greenland and England to provide the US with the famous ‘‘fifteen minute’’ warning of a Soviet ICBM strike over the north pole.

On 12 May 1964 the Office of Space Sciences and Applications announced how Lunar Orbiter would satisfy Apollo’s requirements for maps of the Moon, as agreed with William B. Taylor of the Advanced Manned Missions Program Directorate of the Office of Manned Space Flight. The Manned Spacecraft Center in Houston was interested primarily in the near-side within 5 degrees of latitude of the equator, and had specified stringent requirements for accuracy of selenodetic and topographic data in the vicinity of selected landmarks to assist in navigation in orbit and landing site selection. The US Geological Survey was to produce a variety of maps based on Lunar Orbiter photography.

Oran Nicks suggested to Sam Phillips on 23 September 1964 that the Office of Manned Space Flight should make a study of how Lunar Orbiter could best support Apollo. This would aid the Lunar Orbiter Project Office in developing guidelines for mission planning. Bellcomm was asked to make this study, and on 25 January 1965 Douglas D. Lloyd and Robert F. Fudali submitted the report Lunar Orbiter Mission Planning. This discussed the relative merits of clockwise and anticlockwise orbits of the Moon aligned near the lunar equator. It was confirmed that to achieve the specified 1-metre resolution in the H frames the pictures could be taken from an altitude no greater than 46 km. A strategy of obtaining contiguous high-resolution coverage of multiple targets was recommended. To avoid the possibility of orbital instability as a result of such a low perilune, it was recommended that the initial inclination of the orbit should not exceed 7 degrees to the lunar equator (because gravity perturbations would tend to increase the inclination) and that the spacecraft should have sufficient propellant to perform corrective manoeuvres. Bellcomm followed up on 30 March with Apollo Lunar Site Analysis and Selection, which recommended that the Office of Manned Space Flight and the Office of Space Sciences and Applications form a Site Survey Steering Committee with responsibility for choice of measurements and their relative priorities and instruments, target selection, launch schedules, control of data handling, and methods of data analysis for the Lunar Orbiter and Surveyor missions. On 10 May Bellcomm further recommended that the Office of Manned Space Flight and the Office of Space Sciences and Applications create a joint Lunar Surface Working Group to coordinate mutual planning activities concerning site survey requirements and the means by which these should be satisfied.

In May the Surveyor/Orbiter Utilisation Committee was formed. It was chaired by Edgar Cortright, and its membership comprised senior representatives of these two programs and their project offices: Oran Nicks of Lunar and Planetary

Programs, Urner Liddel of Lunar and Planetary Science, Lee Scherer of the Lunar Orbiter Program, and Benjamin Milwitsky of the Surveyor Program, all of whom were from the Office of Space Sciences and Applications; Israel Taback of the Lunar Orbiter Project Office at Langley; Victor Charles of the Surveyor Project Office at JPL; Sam Phillips, the Apollo Program Director and Everett E. Christensen of Manned Operations, both at the Office of Manned Space Flight; and William A. Lee of the Apollo Spacecraft Project Office and William E. Stoney of Data Analysis, both at the Manned Spacecraft Center. The Committee was to coordinate the Surveyor and Lunar Orbiter projects for their mutual benefit and in support of Apollo. In July, the Apollo Site Selection Board was established in the Office of Manned Space Flight. Although the Surveyor/Orbiter Utilisation Committee would gather engineering and science information and assess proposals for Lunar Orbiter imaging coverage and for Surveyor landing sites, and later recommend landing sites for Apollo, the Apollo Site Selection Board chaired by Sam Phillips would make the decisions.

The Surveyor/Orbiter Utilisation Committee’s first meeting on 20 August 1965 discussed four Lunar Orbiter mission options which had been developed by Langley and Boeing in response to Bellcomm’s report. In order of priority they were: type 1, to photograph ten evenly distributed target areas near the equator, each of which would be covered stereoscopically with both M and H frames; type 2, to photograph four areas in order to ‘screen’ for possible Surveyor landing sites near the equator; type 3, to photograph using H frames an area containing a landed Surveyor in order to study its context; type 4, to obtain topographic data which would not otherwise be obtained. It was decided to start with the type 1 mission, in order to provide as soon as possible the data that was required by the Apollo planners. If the Office of Space Sciences and Applications had not been obliged to support Apollo, the preferred first mission would have been to enter a high circular polar orbit for a global survey at a resolution better than that obtainable using a terrestrial telescope and, significantly, to view the limbs from a vertical perspective.5 In 1963, when the Office of Manned Space Flight began to specify its requirements for Apollo in terms of surface slopes, Gene Shoemaker had hired Jack McCauley to develop methods of photoclinometry. In June 1965 the Surveyor project asked McCauley to use this technique to suggest possible landing sites for their landers. He formed a small team and compiled a list of 74 sites. Owing to uncertainty in the accuracy of Surveyor’s approach trajectory, the sites were specified in terms of ‘target circles’ 25, 50 and 100 km in radius. After factoring in vertical descent and illumination constraints, they selected only circles of 25 and 50 km radius. McCauley presented the final list to the Surveyor/Orbiter Utilisation Committee on 20 August. There were 24 sites with 50-km-radius circles on the maria, and seven in the highlands. There were also 13 ‘scientific’ targets with 25-km-radius circles that would require greater landing accuracy.6

As yet, the only images of the far-side had been provided by Luna 3 in October 1959 and Zond 3 in July 1965.

In fact, all Surveyors except the last would be sent to sites on McCauley’s list.

Mission objectives 151

On 8-9 September 1965 Langley hosted a meeting which (in part) drew up lists of photographic targets judged compatible with Apollo, Surveyor and Lunar Orbiter constraints. James Sasser of the Apollo Spacecraft Project Office in Houston argued for distributed coverage which ‘sampled’ different types of terrain near the equator, although with the emphasis on apparently smooth areas. Lawrence Rowan of the US Geological Survey described an analysis based on a map produced by the Air Force Chart and Information Center on a scale of 1:1,000,000. This analysis identified the types of terrain available for ‘sampling’ by Lunar Orbiter: namely an ordinary mare, a dark mare, mare ridges, mare rays, crater rims, deformed crater floors, and several different types of terrain in the highlands. These discussions led to the ‘A’ mission plan which was formally presented to the Surveyor/Orbiter Utilisation Committee on 29 September. This called for a type 1 mission to inspect a number of areas in the ‘Apollo zone’ – defined as being within 5 degrees of the equator and 45 degrees of the central meridian – to assess their suitability for Apollo and Surveyor landings. It would start with test pictures taken in the high-perilune initial orbit of sites between 60°E and 110°E. Although not in the Apollo zone, these pictures would show a vertical perspective of the limb region in which landmarks would later be selected for Apollo orbital navigation. After the perilune had been lowered, ten sites, mostly in the zone, would each receive a single photographic pass timed to maintain a given angle of illumination as the terminator advanced westward. The targets would cover a variety of terrains, including the Flamsteed Ring in Oceanus Procellarum, which was the favoured site for the first Surveyor. In May, a team of photo-interpreters led by Lawrence Rowan had been created by the US Geological Survey to suggest sites for Apollo. Each site was subjected to a detailed analysis, drawing in data from all sources. This work continued through the Summer Study on Lunar Exploration and Science held 19-31 July 1965 in Falmouth, Massachusetts. Rowan presented a list of ten potential Apollo landing sites to the Surveyor/Orbiter Utilisation Committee on 29 September (just over a month after the Committee received McCauley’s list of candidate Surveyor sites – some sites were on both lists). The meeting approved the ‘A’ mission proposal with nine primary (P) sites, including several that were not on the smooth maria.

The Planetology Subcommittee of the Space Sciences Steering Committee met on 21-22 October to discuss the ‘A’ mission plan. The meeting was chaired by Urner Liddel, who was a member of the Surveyor/Orbiter Utilisation Committee. Harold Masursky of the US Geological Survey explained how the methods of structural and stratigraphic geological mapping would be applied to the pictures supplied by Lunar Orbiter. Liddel then wrote to Oran Nicks on 5 November to emphasise the merit of developing a Lunar Orbiter Block II for a multifaceted scientific study of the Moon to obtain the data which would be required to plan ‘advanced’ Apollo missions.[29]

The Apollo Site Selection Board held its inaugural meeting on 16 March 1966. Although the only materials available were telescopic studies and their interpretation on the basis of close-up views of three sites provided by the Ranger project, several potential areas were identified in the expectation that it would prove possible to land the first Apollo mission at one of them.

On 4 April Leonard Reiffel, representing Apollo, informed Oran Nicks of another Apollo requirement. The original plan had been to store all the data returned by the Lunar Orbiter missions on film, but magnetic tape had a greater dynamic range and was more readily processed by computer, and NASA wished the process of analysis to be as automated as possible – in particular the photoclinometry by which the US Geological Survey was to measure the slopes. Nicks duly ordered that state-of-the – art recorders be purchased to enable the data to be written directly onto tape.

By the time of the Apollo Site Selection Board’s second meeting on 1 June 1966, Surveyor 1 had landed on the Moon and the first Lunar Orbiter was soon to attempt to photograph it to provide a sense of context which would allow the ‘ground truth’ from the lander to be applied more generally.

On 26 August 1966 the command module of CSM-012 arrived at the Cape in a container prominently labelled ‘Apollo One’.

North American Aviation was to have shipped it several weeks earlier, but the failure of a glycol pump in the environmental control system had led to the exchange of this unit with its CSM-014 counterpart. Although the customer acceptance review identified other ‘‘eleventh-hour problems’’ associated with the environmental control system, NASA had taken receipt.

The Office of Manned Space Flight held the AS-204 design certification review on 7 October, and declared that the launch vehicle and the spacecraft ‘‘conformed to design requirements’’ and would be flightworthy once a number of deficiencies had been overcome. Sam Phillips issued a list of these deficiencies to Lee B. James at the Marshall Space Flight Center, Joseph Shea at the Manned Spacecraft Center, and John G. Shinkle, Apollo Program Manager at the Kennedy Space Center, requiring speedy compliance. On 11 October Phillips was informed by Carroll Bolender of a report he had received the previous day from Shinkle detailing increasing delays in the preparation of CSM-012. When the spacecraft was delivered, 164 ‘engineering orders’ had been identified as ‘open work’ – despite the fact that the accompanying data package had listed only 126 such items. By 24 September the list had grown to 377, and Shinkle ventured that about 150 of the 213 additional orders ought to have been identifiable by the manufacturer prior to the customer acceptance review. The issues included the environmental control system (which had failed again), problems with the reaction control system, a leak in the service propulsion system, and even design deficiencies with the couches that had obliged the company to send engineers to the Cape. On 12 October Phillips wrote to Mark E. Bradley, Vice President of the Garrett Group, whose AiResearch Division had supplied the environmental control system under subcontract to North American Aviation, explaining that its reliability threatened a “major delay” to the AS-204 mission. To Phillips, the problems seemed “to lie in two categories: those arising from inadequate development testing, and those related to poor workmanship”. A replacement was delivered on 2 November, and testing resumed as soon as it was in place. However, the unit malfunctioned and had to be returned to the company.

On 25 October the propellant tanks of the service module for CSM-017, assigned to AS-501, failed catastrophically in a test at North American Aviation. The normal operating pressure was 175 psi, but it had failed after 100 minutes at the maximum requirement of 240 psi. The test had been ordered following the discovery of cracks in the tanks of CSM-101, assigned to AS-207. The failure was particularly puzzling because the tanks of CSM-017 had been subjected to 320 psi for several minutes in ‘proof testing’. ASPO set up an investigation, which was to report by 4 November. As SM-012 had been through the same test regime, Shea grounded it pending this report. The problem was determined to be stress corrosion in the titanium resulting from the use of methyl alcohol as a test liquid. The point of the test was to verify the integrity of the tanks, and because the hydrazine and nitrogen tetroxide propellants were toxic another fluid had been used – and unfortunately this had caused damage! The remedy was to switch to a fluid that was compatible with titanium, and it was decided to use freon in the oxidiser tank and isopropyl alcohol in the fuel tank, with the additional stipulations that the systems must not have been previously exposed to the actual propellants and that after the tests the system must be purged by gaseous nitrogen. With the issue resolved, the tanks of SM-012 were removed for inspection and confirmed to be free of cracks.

The crew for the CSM-014 mission was announced on 29 September 1966. Wally Schirra would be in command, flying with Donn Eisele and Walt Cunningham. They would be backed up by Frank Borman, Tom Stafford and Michael Collins. Schirra was the only experienced man of the prime crew, but all the backup astronauts were veterans. In fact, Deke Slayton had given Schirra and Borman these assignments in March, on their return from an international ‘goodwill tour’ after the rendezvous of Gemini 6/7. Stafford and Collins had been assigned following Gemini 9 in June and Gemini 10 in July, respectively. Slayton had actually earmarked the rookies Eisele and Chaffee to Grissom’s crew, but in late 1965 Eisele had injured his shoulder in weightlessness training in a KC-135 aircraft and dropped out of training, prompting Slayton to swap Eisele with Ed White, whom Slayton had earmarked for Schirra’s crew. This Apollo 2 mission was to be a straightforward rerun of Apollo 1 to further evaluate the spacecraft’s systems.

In early December 1966, accepting that Apollo 1 would not fly that year, George Mueller postponed it to February 1967 and also deleted the Block f reflight in order to prevent the slippage of CSM-012 from impacting the Block II missions scheduled for later in 1967. Schirra had hoped to put his crew first in line for the dual mission, but Slayton imposed a rule that the man who would operate the CSM alone while his colleagues flew the LM must be experienced in rendezvous, since if the LM were to become crippled he would have to perform a rescue. Eisele was a rookie but Scott had performed a rendezvous on Gemini 8, so Slayton exchanged Schirra’s crew with McDivitt’s crew. Schirra was not pleased at being given the backup role, but Slayton had always intended to assign McDivitt the dual mission.

On the new schedule, AS-206 would launch LM-1 for an unmanned test as soon as possible after Apollo 1, and if this was satisfactory McDivitt’s crew would fly the dual mission (which was now AS-205/208 because deleting CSM-014 had released AS-205) as the revised Apollo 2 in August. This revision was publicly announced on 22 December, together with the assignment of Tom Stafford, John Young and Gene Cernan to backup McDivitt’s crew. Also, if two unmanned tests proved sufficient to ‘man rate’ the Saturn V, the intention was to launch AS-503 with a CSM and LM. The crew for this mission would be Frank Borman, Michael Collins and Bill Anders, backed up by Pete Conrad, Dick Gordon and Clifton Williams. These assignments had been made after Young flew Gemini 10 in July, Conrad and Gordon flew Gemini 11 in September, and Cernan backed up Gemini 12 in November.

The Gemini missions had demonstrated that for an astronaut on a spacewalk to be able to work effectively he must be provided with mobility and stability aids. On 6 December 1966 Slayton warned Joseph Shea that without handholds and tethering points, a transfer from the forward hatch of the LM to the CSM’s hatch would not be feasible. On 26 December Slayton recommended that a spacewalk be scheduled 100 hours into AS-503, after the two firings of the LM’s descent propulsion system but prior to the descent stage being jettisoned. One of the two astronauts would egress from the forward hatch and stand on the ‘front porch’ to assess the environmental control system in the LM during depressurisation, using the hatch, the performance of the life-support backpack, and the egress procedure for the emergency transfer. In addition, whilst outside, the spacewalker was to photograph the exterior of the LM to verify that it had not been damaged during its retrieval from the S-IVB. He would then re-enter the LM and the cabin repressurisation system would be tested, simulating the end of a moonwalk.

On 26 January 1967 Schirra’s crew made a ‘full up’ systems test of CSM-012 on its AS-204 launch vehicle. But the spacecraft drew its power from the pad, and the capsule was not pressurised with pure oxygen. It had not been a very productive day. ‘‘Frankly, Gus,’’ Schirra said in the debriefing with Grissom and Shea, ‘‘I don’t like it. You’re going to be in there with full oxygen tomorrow, and if you have the same feeling I do, I suggest you get out.’’ But there was a determination to catch up on the several-times-delayed schedule.

The next day, Friday, 27 January, Grissom’s crew attempted the ‘plugs out’ test in which the spacecraft would be on internal power and pressurised with pure oxygen at 16 psi (i. e. slightly above ambient) for an integrity check. If successful, this would clear the spacecraft for flight. After a simulated countdown, they were to end the day with an emergency egress drill.

In Houston, Flight Director John Hodge was monitoring progress, but the action was at the Cape. Slayton was in the Pad 34 blockhouse talking to Director of Launch Operations, Rocco Petrone. Also present was Stu Roosa, a rookie astronaut serving as the primary communications link with the crew. The Spacecraft Test Conductor, Clarence ‘Skip’ Chauvin, was in the Automated Checkout Equipment facility of the Manned Spacecraft Operations Building.

‘‘Fire!!’’ yelled Grissom at 18:31 local time, in a hold at T-10 minutes. ‘‘We’ve got a fire in the cockpit.’’

In all, there were 25 technicians on Level A8 of Pad 34’s service structure, and five more either on the access arm or in the White Room. Henry Rogers, NASA’s Inspector of Quality Control, was in the elevator, ascending the service structure. Systems technician L. D. Reece was waiting for the ‘Go’ to disconnect the spacecraft for the ‘plugs out’ test, which had been delayed by problems with communications, most notably the whistle from an ‘open’ microphone that could not be located.

‘‘Get them out of there!’’ commanded Donald Babbitt, North American Aviation’s Pad Leader, on hearing Grissom’s call. Mechanical technician James Gleaves was closest, but a spout of flame burst from the capsule before he could react, and he was beaten back by the flame and smoke.

Gary Propst, a technician of the Radio Corporation of America, was on the first level of the pad monitoring a TV camera located in the White Room pointing at the window in the spacecraft’s hatch. On hearing Grissom’s call, he looked up and saw a brilliant light in the window and gloved hands moving about within.

As soon as Slayton realised what had happened, he sent medics Fred Kelly and Alan Harter to the pad. ‘‘You know what I’ll find,’’ Kelly observed pointedly. The best that they would be able to do would be to supervise the retrieval of the bodies. On reflection, Slayton decided to accompany them. ‘‘We were the first guys from the blockhouse to reach the pad,’’ he later pointed out. Despite the intensity of the fire, Grissom, White and Chaffee had died by asphyxiation as a result of the toxic fumes created by the incomplete combustion of the synthetic materials in the cabin. They had received second and third degree burns, but these in themselves would not have been fatal. After several minutes Slayton left the White Room to call Houston, to report the situation. Shea had just arrived back in Houston and was briefing George Low when the news came through.

The Astronaut Office in Houston was very quiet. All the ‘old hands’ were absent. With Slayton away, Don Gregory, his assistant, ran the routine Friday staffmeeting. The meeting had only just convened when the red phone on Slayton’s desk rang. Gregory answered, then reported, ‘‘There has been a fire in the spacecraft.’’ Michael Collins was the senior astronaut present. He arranged for Al Bean to track down the wives. In each case, the news had to be broken by an astronaut who was also a close friend of the family. Charles Berry and Marge Slayton went to see Betty Grissom. Pete Conrad was sent to track down Pat White. Gene Cernan would have been ideal for Martha Chaffee because they lived next door, but he was in Downey with Tom Stafford and John Young, so Collins went to give her the bad news himself.

Al Shepard was in Dallas, Texas, about to deliver a speech at a dinner. He was taken aside and told of the fire. Wally Schirra, Donn Eisele and Walt Cunningham
were flying home from the Cape, and were told upon touching down at Ellington Air Force Base. Schirra immediately called Slayton at the Cape, who filled him in on the details. James Webb, Robert Seamans, Robert Gilruth, George Mueller, Kurt Debus, Sam Phillips and Wernher von Braun were at the International Club in Washington with corporate officials, including Leland Atwood of North American Aviation, to mark the transition from Gemini to Apollo. Webb immediately ordered Seamans and Phillips to the Cape to investigate. As Webb observed to newsmen shortly thereafter, “Although everyone realised that some day space pilots would die, who would have thought the first tragedy would be on the ground?”

The Board of Inquiry was chaired by Floyd L. Thompson, Director of the Langley Research Center, with Frank Borman as the Astronaut Office’s representative. The origin of the fire was near the foot of Grissom’s couch, where components of the environmental control system had repeatedly been removed and replaced in testing. Although the investigation did not identify the specific ignition source, it did find physical indications of electrical arcing in a wiring harness. ft was concluded that at some time during either manufacturing or testing an unnoticed incidental contact had scraped the insulation from a wire and thereby created the opportunity for a spark. This had ignited nearby flammable material, and in the super-pressurised pure-oxygen situation the result had been a brief but intense ‘flash’ fire. fn fact, there had been some 32 kg of nylon netting, polyurethane foam and velcro – all of it flammable in such conditions. fn retrospect, the worst flaw was the inward-opening hatch, which even under ideal conditions took several minutes to open, and would have been impossible to open with the internal pressure above ambient. Because neither the launch vehicle nor the spacecraft had been loaded with propellants, the ‘plugs out’ test had not been judged hazardous. Nevertheless, the launch escape system was directly above the spacecraft, and if the heat from the fire had ignited the solid propellant of this rocket the White Room crew would almost certainly have been killed as well.

fn an Associated Press interview in December 1966 Grissom had told Howard Benedict: ‘‘ff we die, we want people to accept it. We are in a risky business and we hope that if anything happens to us it won’t delay the program. The conquest of space is worth the risk of life.’’

fn an effort to reduce the risk of a fire during ground testing, it was decided to use an atmosphere comprising 65 per cent oxygen and 35 per cent nitrogen. After liftoff, the nitrogen would be purged and the pressure reduced to the originally planned 100 per cent oxygen at about 5 psi.

Although the investigation into the fire would take months, on 31 January NASA headquarters directed the Manned Spacecraft Center, Marshall Space Flight Center and Kennedy Space Center to proceed as planned with preparations for AS-501 with CSM-017 and LTA-10R, except that the command module was not to be pressurised with oxygen without specific authorisation.9 On 2 February CSM-014 was delivered

LTA-10R was a refurbished LM test article serving as a mass-model.

The exterior of the fire-damaged Apollo 1 command module in which Grissom, White and Chaffee died (top left); a view through the hatch; the crew positions, with the hatch above the center couch; the vicinity of the environmental control unit, where the ignition source is believed to have been; and its disassembled outer structures. Glenn, Cooper and Young escort Grissom’s coffin.

to the Cape to assist in training the technicians who were to disassemble CM-012 for the investigation. On 3 February George Mueller announced that although manned flights were grounded indefinitely, the unmanned AS-206, AS-501 and AS-502 were to proceed as soon as delivery of the hardware allowed. While the investigation into the fire was underway, Mueller suggested that when the Block II spacecraft became available the CSM-only flight should be deleted and the effort switched to combined testing with the LM, but Robert Gilruth warned that it would not be wise to test two new vehicles at once. In March it was decided to fly an 11-day CSM-only mission, in effect to perform Grissom’s mission with the upgraded model, and Slayton tipped off Schirra that his crew would fly it, backed up by Stafford’s crew. On 21 February, the day that Apollo 1 had been scheduled to launch, Floyd Thompson gave Mueller a preliminary briefing on the investigation’s findings, and several days later Robert Seamans sent a memo to James Webb listing Thompson’s early recommendations.10

On 15 March Deke Slayton proposed that a rendezvous with the S-IVB stage be a primary objective of Schirra’s flight, and said that this should occur “after the third period of orbital darkness’’. On 5 April Sam Phillips told the Manned Spacecraft Center, Marshall Space Flight Center and Kennedy Space Center that the profile for the first manned flight would be based on that developed for Grissom’s flight, dated November 1966. As the complexity of the mission was not to exceed that previously planned, and as no rendezvous had been planned, the rendezvous exercise should be assessed in terms of how it would complicate the mission rather than how it would advance the program. As the flight was to focus on evaluating the spacecraft’s systems, Chris Kraft pointed out on 18 April that if a problem were to develop that would require the cancellation of the rendezvous, then any manoeuvres which had already been made would complicate the nominal contingency de-orbit procedures. The rendezvous should not be initiated until “after a minimum of one day of orbital flight’’ and should be “limited to a simple equi-period exercise with a target carried into orbit by the spacecraft’’. On 2 June Phillips agreed with George Low that there should be a rendezvous but insisted that this should not be listed as a primary objective. The double-hatch of the Block I had been replaced on the Block II by a single ‘unified hatch’ on a hinge that swung outward. It had a manual release for either internal or external use, could be opened in 60 seconds irrespective of the differential in pressure, and was capable of being opened in order to conduct a spacewalk. But Phillips directed that there ‘‘be no additions that require major new commitments such as opening the command module hatch in space or exercising the docking subsystem’’.

NASA announced on 20 March 1967 that the unmanned LM-1 flight would be transferred from AS-206 to AS-204, which had become available. The rationale for the AS-205/208 dual mission with CSM-101 and LM-2 had been to ensure that testing of the LM would not be held up by the Saturn V development problems. The AS-501 and AS-502 development flights were to carry refurbished LM test articles, but unless

The final report of the Apollo 204 Review Board was submitted on 5 April 1967.

the pace of LM development dramatically picked up, the heavy launcher would become available ahead of the LM, thus rendering the ad hoc dual mission redundant. It was therefore decided that if the LM-1 test flight proved unsatisfactory, AS-206 would launch LM-2 unmanned to address the remaining test objectives. On 25 March George Mueller directed that missions be numbered in the order of their launch, regardless of whether they employed the Saturn IB or Saturn V and whether they were manned or unmanned – previously only the manned missions were to be counted. On the 1966 plan, Apollo 2 was to be CSM-014 (Schirra) and Apollo 3 was to be CSM-101 (McDivitt) flying the dual mission. The cancellation of the Block I reflight advanced CSM-101 to Apollo 2. After the fire, the desire not to reassign the name Apollo 1 had resulted in CSM-101 (Schirra) being seen as Apollo 2. But with paperwork in circulation for a variety of mission plans numbered up to Apollo 3, Mueller precluded the possibility of administrative confusion by directing that the first scheduled mission, AS-501, be named Apollo 4.[47]

On 7 April 1967 Joseph Shea was transferred to Washington as Deputy Associate Administrator for Manned Space Flight, and Low succeeded him as ASPO Manager at the Manned Spacecraft Center. Several days later, Everett Christensen resigned as Director of Mission Operations at headquarters.

A joint meeting of the Manned Spacecraft Center’s Flight Operations Directorate and Mission Operations Division announced on 17 April that: (1) successful firings by the descent and ascent stages of an unmanned LM, including a ‘fire in the hole’ separation of the two stages, should be prerequisites to a manned LM being allotted these functions; (2) a demonstration of EVA transfer should not be a prerequisite to manned independent flight of the LM; (3) the Saturn V should be ‘man rated’ as rapidly as possible; (4) three manned Earth orbit flights involving both the CSM and the LM should be the minimum requirement prior to attempting a lunar landing; and (5) although a lunar orbit mission should not be a formal step in the program, this should be planned as a contingency in the event of the CSM achieving lunar-mission capability ahead of the LM.

ASPO sent the Block II Redefinition Task Team, led by Frank Borman, to North American Aviation on 27 April. Having the authority to make on-the-spot decisions which previously would have required referral to the Configuration Control Board, it was to oversee the ‘redefinition’ of the Block II spacecraft, responding promptly to questions regarding detail design, quality and reliability, test and checkout, baseline specifications, configuration control, and scheduling. Meanwhile, the company had hired William D. Bergen from the Martin Company to supersede Harrison A. Storms as Apollo Project Manager. Bergen brought with him John P. Healy to manage the production of the first Block II at Downey, and Bastian Hello to run the company’s operations at the Cape.

On 8 May 1967 George Low reaffirmed that AS-205 would launch CSM-101 on an open-ended mission of up to 11 days to evaluate its systems. The next day, James Webb told a Senate committee that this mission would be flown by Wally Schirra, Donn Eisele and Walt Cunningham. When Webb canvassed suggestions for how to impress upon Congress that the Apollo program was recovering from the setback of the fire, George Mueller urged that the Saturn V be flown as soon as possible.

Grove Karl Gilbert was born in Rochester, New York, in 1843. After conducting a number of surveys as a field geologist, he was made Senior Geologist when the US Geological Survey was founded in 1879. Over 18 nights during August, September and October 1892, Gilbert used the 26-inch refractor of the US Naval Observatory in Washington DC to study the Moon. Pointing out that lunar craters have floors lying generally below rather than above the level of the adjacent terrain, he rejected the

volcanic interpretation and argued that craters must be the result of impacts. He further proposed that the arcuate chains of mountains at the periphery of the ‘circular maria’ are the walls of craters produced by vast impacts. As evidence, Gilbert cited what he called ‘sculpture’ as the fall of ejecta thrown out during the formation of Imbrium. He announced his results in The Moon’s Face: A Study of its Origin and its Surface Features, a paper presented orally to the Philosophical Society of Washington on 10 December to mark his retirement as its president. The paper was published in the Bulletin in 1893, but as this was not a publication on the reading list of astronomers his remarkable intrusion into their bailiwick passed unnoticed.

In 1946 Harvard geologist R. A. Daly rejected the endogenic origin of craters and, argued in favour of impact, citing Gilbert’s paper. Also in 1946, geologist R. S. Dietz expanded on the subject, listing several criteria that showed how lunar craters differ from terrestrial volcanic craters.

The American geologist J. E. Spurr began to study the Moon in 1937, having been inspired by the photographs taken by Francis Pease using the 100-inch telescope on Mount Wilson. He presumed that the Moon could be described in terrestrial terms, and between 1944 and 1949 wrote up his systematic analysis in four volumes under the general title Geology Applied to Selenology, offering volcanic explanations for a wide variety of lunar features. In particular, he said that early in lunar history large calderas left cavities which were later flooded by lava to make the ‘irregular maria’, and subsequently the better preserved ‘circular maria’. Critics of the impact origin of craters pointed out that whilst there were many examples of small craters on the rims of larger ones, there were no cases of large craters overlapping smaller ones. Spurr said craters were volcanic, and were produced with progressively smaller diameters. He interpreted faults and ridges as evidence of lines of weakness in the crust. Since he mapped these up the meridian and around the limb regions, he said they were due to stresses imparted as the Moon’s rotation synchronised with its orbital period. He

claimed this ‘lunar grid system’ had significantly controlled the formation of craters. This thesis was eagerly accepted by those who believed volcanism played the main role in shaping the lunar surface. In particular, it was claimed that lines of weakness had prompted eruptions that produced ‘chains’ of large craters whose members were isolated from one other by significant distances. But critics argued that the lines of weakness were illusory, since relief highlighted by the sunrise or sunset terminator will favour north-south trends and not east-west trends. And, of course, any pair of craters can be said to be related if an observer is so inclined.

It was not until Ralph B. Baldwin made an analysis of bomb craters in the Second World War that the impact origin of lunar craters began to make real headway. As a businessman trained in physics, he developed an interest in the Moon in 1941 during a visit to a planetarium when, in viewing the pictures on display, he independently noticed Imbrium sculpture. On later reading up and finding no explanation (since he did not happen across Gilbert’s paper) Baldwin decided to conduct his own study. In an article published in the magazine Popular Astronomy in 1942 he argued that the ridges and grooves were “caused by material ejected radially from the point of explosion’’ by the impact which formed Imbrium – although, like everyone else, he presumed that the impact formed the mare itself. In a follow-up in 1943 he reasoned that the projectile had been “flattened” by the shock and had excavated the cavity in a lateral manner, which was why the nearest sculpture consisted of grooves rather than chains of craters made by plunging debris – the latter occurred further out. He published in a popular outlet because his work was rejected by professional journals – evidently the Moon was not an object for worthwhile study. In his book The Face of the Moon, published in 1949 by the University of Chicago, Baldwin reported his observations, experiments and analyses, and included a review of the literature (by now he knew of Gilbert). His own contribution as a physicist drew upon an analysis of bomb craters in which he showed that the greater the deceleration on impact, the greater the energy released. He reasoned that although the weak lunar gravity would enable an explosion to throw ejecta to a greater distance, it would not actually make the crater larger. He logarithmically plotted the relationship between the diameters and depths of explosive craters on Earth, the craters on Earth accepted to have been made by cosmic impacts, and ‘fresh-looking’ lunar craters (those which had not yet slumped and distorted the ratio that he utilised). He compiled 300 measurements of lunar craters from the literature, and measured several dozen others himself. There was a clear trend.

Significantly, Baldwin realised that although most sculpture could be attributed to Imbrium, there was some which seemed to be associated with other ‘circular maria’, from which he concluded that they resulted from individual impacts. Furthermore, the mountains peripheral to Serenitatis must have formed prior to the impact that etched the Haemus with Imbrium sculpture, yet before lava flooded the Serenitatis cavity. This established that Mare Serenitatis formed a significant interval after the impact had excavated the cavity in which it resides. Baldwin (as had Gilbert) believed all the maria to have been formed at the same time and to be associated with Imbrium, which at that time was presumed to have been the greatest impact in lunar history. However, whereas Gilbert envisaged the Imbrium impact splashing out liquid ejecta which pooled in low-lying areas to form the various maria, Baldwin saw there had been a significant interval between the formation of the Imbrium cavity and its being filled in. He proposed that the impact raised a vast dome which remained inflated for long enough to be cratered (for example by Archimedes), then collapsed (forming a system of peripheral arcuate faults) and released a pulse of extremely low viscosity lava that not only filled in the cavity but also burst through the containing walls to spread across the surface and fill in other cavities to create the maria. Irrespective of whether the maria were liquid ejecta or erupted lava, it was evident that the large circular cavities were made by individual impacts over a period of time and that there was a significant interval before the formation of the maria.

Astronomers were not impressed by Baldwin’s arguments, however, and for many years continued to associate the maria with the cavities they occupied.

After reading Baldwin’s book, Harold C. Urey developed an interest in the Moon. But Urey was not particularly interested in the surface features – as a chemist at the University of Chicago who gained the 1934 Nobel Prize for chemistry, he was more interested in the Moon’s composition. He accepted that the craters were impacts and the maria were the by-product of a giant impact, but rejected Baldwin’s inference of a significant interval between the Imbrium impact and the formation of the maria. Urey agreed with Gilbert that the maria were splashes of impact melt, and said that because they were molten they could not have preserved sculpture. He also made the remarkable suggestion that the semicircular Sinus Iridum on the northern margin of Mare Imbrium marked the ‘entry hole’ of the asteroidal body whose impact created the Imbrium cavity.

In 1943 Gerard P. Kuiper began to exploit recent technical developments to make observations of bodies in the solar system. He essentially had the field to himself, at least in professional circles, and was able to make a series of discoveries. In 1953 he turned his attention to the Moon. Although photography was the norm, he mounted a binocular eye-piece on the 82-inch reflector of the McDonald Observatory in Texas to exploit moments of exceptional ‘seeing’ to discern details of the lunar surface that

would have been blurred in photographs. In his first paper on the subject, in 1954, he argued that in the case of a body of the Moon’s size, radiogenic heating would have caused sufficient melting for dense minerals to sink to create a core and lightweight minerals to rise to form a crust. This thermal differentiation would become known as the ‘hot Moon’ hypothesis. As volcanism is a means of enabling heat to escape from the interior, Kuiper argued that the maria were formed by lava upwelling at various times from deep fractures in the floors of the cavities excavated by major impacts.

In 1891, while studying the desert between Flagstaff and Winslow in Arizona in which the Canyon Diablo meteorites had been recovered, G. K. Gilbert inspected the circular hole known as Coon Butte. It was 1.2 km in diameter, had a rim which rose 45 metres above its surroundings, and a floor lying 200 metres below the rim. If it marked the site of an impact, then, he reasoned, there might be a large iron meteorite beneath its floor. A buried iron mass should be detectable by its magnetic signature, but there was no such indication. He concluded that the hole was a marr, made some 50,000 years ago when magma caused underground ice to flash to steam and blast a hole in the overlying rock. Nevertheless, in 1903 mining engineer D. M. Barringer began to drill in search of the meteorite, to no effect. In 1916 E. J. Opik realised that a cosmic impact was such a violent event that the projectile would be vaporised, but he published in an Estonian journal and his insight passed unnoticed. In 1924 A. C.

Gifford independently came to the same conclusion and published in a New Zealand journal that had a broader readership. Opik and Gifford both realised that high­speed impacts always create circular craters because whilst momentum is a vector, energy is not, and as the projectile hits the surface it essentially explodes, liberating energy in a symmetric manner and forming a circular crater. Furthermore, they realised, the crater is always much larger than the projectile. If Coon Butte was an impact crater, then the only relic of the projectile was the field of Canyon Diablo meteorites which littered the surrounding desert.

When Eugene M. Shoemaker joined the US Geological Survey in 1948 he already had an interest in the Moon. In 1949 he made a review of the literature and turned up both Gilbert’s paper and Baldwin’s recently released book, both of which advocated the impact hypothesis. In 1955 he studied two craters about 100 metres in diameter created by underground nuclear tests at the Nevada Test Site to investigate how such explosions shocked and dispersed rock. He was impressed by their resemblance to lunar craters. In 1957, with Gilbert’s analysis in mind, he began a study of Coon Butte. He had already done the field work for his PhD thesis on salt structures, but had never gotten around to writing it up. After hearing Shoemaker give a seminar on his study of Coon Butte, his advisor at Princeton, Harry Hess, suggested that he use that as the basis of his thesis. Shoemaker put in some more field work, wrote it up, and, despite it being rather on the short side for the purpose, submitted it in 1959. The fact that the crater was recent and in a desert environment made the manner in which it was excavated readily evident. In particular, the strike had not just penetrated the surface and pushed the rock aside, as Gilbert imagined; the process, as Opik and Gifford had inferred, was explosive. Significantly, Shoemaker found that two shock waves were involved: one vaporised the projectile, and the other propagated into the ‘target rock’, compressing it so thoroughly that the rock reacted just as if an explosion had occurred beneath it. In his field work Shoemaker methodically traced how the rim and the ejecta blanket formed by the stratigraphy being flipped into an inverted sequence around a circular ‘hinge’, in the process making a hole much wider than the projectile.[5]

Early in 1960 L. R. Stieff of the US Geological Survey in Washington DC set out to obtain NASA funding for an investigation of lunar geology. NASA deliberated. In 1953 Loring Coes had produced a new very dense mineral using a hydraulic press to squeeze quartz. This ‘shocked quartz’ was named coesite. In 1956 H. H. Nininger had suggested searching for coesite at Coon Butte, but this was not done. In 1960 Stieff obtained samples of rock taken from Coon Butte which were in the archive of the Smithsonian Institution in Washington DC to enable him to say to NASA that the Survey was already at work on craters. Ed Chao identified coesite using X-ray diffraction, which proved Coon Butte to be an impact crater. A press statement was released to this effect on 20 June. When Chao wrote the scientific paper, the Survey

added Shoemaker and his assistant Beth Madsen as co-authors to imply that it had a team of specialists at work. When the paper was published in Science in July I960, Shoemaker was on his way to present a paper about Coon Butte to the Geological Congress in Copenhagen. The Rieskessel in Bavaria is a 24-km-diameter structure with the town of Nordlingen at its centre. Although widely believed to be volcanic, a study in 1904 had suggested that the circular structure might mark an impact, and its characteristics had led Baldwin to classify it as such. Shoemaker examined samples of quartz from a quarry. To his trained eye, using no more than a hand-lens, the rock showed evidence of shock. The next day he airmailed samples to Chao, who called straight back to confirm that coesite was present. In giving his paper in Copenhagen about Coon Butte, Shoemaker announced the Rieskessel finding.

With the two structures having been shown to be impacts, NASA finally released the funding to enable the Survey to undertake its lunar studies, and on 25 August the Astrogeologic Studies Group was established at the Menlo Park office, south of San Francisco, with Shoemaker in charge. A year later, in 1961, it became the Branch of Astrogeology. In March 1962 Shoemaker decided to move his team to Flagstaff. The move began in December, but some people refused to relocate and were allowed to remain at Menlo Park.