Category Paving the Way for Apollo 11

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.

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.

The historic flight of Apollo 11 in July 1969 did not sprout from the head of Zeus, fully grown like Athena. The events from when men first gazed at the Moon up in the night sky until the launch of humanity’s first voyage to another world is a broad and complex topic and is the subject of this book.

Readers of David Harland’s previous books on the exploration of the Moon are well acquainted with his detailed research, lucid style and ability to summarise complex events. But on this present topic, David has truly surpassed himself. The story of the detailed study, preparation and flight of robotic space missions that prepared us to send people to the Moon is a long and complicated one, with many simultaneous events occurring in different parts of the world and on the Moon. His account clearly details how we advanced our understanding of the Moon, from a beacon in the night sky to a neighboring world with its own history and processes.

Before people could land on the Moon, we needed to know what awaited these explorers – one can only surmise so much by peering through a telescope from a range of over 400,000 km. The robotic precursor program that blazed a trail to the Moon involved crash landers, orbiters and soft landers. This progression now seems logical and well considered, but in fact at that time it was one that grew piecemeal in response to geopolitical, budgetary and bureaucratic pressures. Understanding this complicated and sometimes confusing story is necessary in order to appreciate fully the accomplishment of the Apollo program.

Paving the Way for Apollo 11 holds many lessons for our return to the Moon, some depressingly familiar. Different factions within NASA had differing agendas and desires which were usually worked out for the best, but not always. Science and engineering in the space program were in constant tension then, and have been ever since. The pressing need to know what the Soviets were up to on the Moon led to accelerated schedules and simultaneous exploration programs and missions. Some investigators predicted that disaster awaited us on the Moon, with spacecraft likely to be swallowed whole by giant bowls of choking dust. The information from these robotic probes disproved some of the wilder speculations on lunar surface conditions and allowed us to plan and execute the Apollo missions in a near flawless manner.

In this book David Harland recounts this fascinating story with clarity and verve, re-creating the excitement of the Apollo days when we were not merely going to the

Moon, but racing there. People of that time didn’t know how events would unfold, yet they made many excellent decisions, and from these efforts we gained a new and more complete understanding of the Moon, the Earth and their intimate relationship and history. The exploration of the Moon revolutionised science in ways we are still trying to understand. And now, the Moon beckons us to return and capitalise on that wonderful legacy.

Paul D. Spudis

Lunar and Planetary Institute

Houston, Texas

FIRMING UP THE PLAN

The spectacular Soviet achievement of photographing the far-side of the Moon in October 1959 prompted NASA to revise its planning. The Air Force was developing the Agena В as a variant of an upper stage which could restart its engine in space. The payload projection for low Earth orbit of an Atlas-Agena В exceeded that projected for the two-stage Atlas-Vega, and almost matched that of the three-stage variant. On 7 November 1959 NASA decided that all satellites scheduled to use the Atlas-Vega should be transferred to the Atlas-Agena В; the Vega stage would be used only for lunar probes. But on 11 December it was decided that the lunar probes would switch too, and the Vega was cancelled. The Atlas-Agena В was seen as the interim launch vehicle for deep-space probes, pending the introduction of the Atlas-Centaur.

On 21 December 1959 Abe Silverstein of the Office of Space Flight Development at NASA headquarters told JPL to prepare five spacecraft to reconnoitre the Moon in 1961-1962. The objectives now included obtaining high-resolution pictures of the lunar surface during the terminal approach, which would require to be transmitted in real-time since the vehicle would be destroyed on impact. This imaging was to make up for the loss of the orbiter – which Silverstein had ordered in June 1959 and now cancelled because a review had judged it to be too complex for this early point in the program. In addition, Silverstein told JPL to consider adding instruments to perform particles and fields investigations during the cruise to the Moon. This project was to be completed within 36 months, in order to pass on to the next project of the lunar exploration program. It was acknowledged to be a high-risk venture on a short-term schedule, but was intended, in addition to studying the Moon, “to seize the initiative in space exploration from the Soviets”.

In January 1960 Silverstein created the Lunar and Planetary Programs Division, with Edgar M. Cortright as its Director. In March Oran W. Nicks was made Chief of Lunar Flight Systems, and given the task of monitoring the project’s progress. After NASA formally approved the project in February 1960, Clifford I. Cummings at

JPL proposed that it be named ‘Ranger’.[11] Silverstein was not keen, but the moniker was made official and on 4 May Cummings announced it to the Los Angeles Herald – Examiner.

At the end of 1959 Keith Glennan reorganised NASA headquarters. The dominant office in terms of budget and activities remained Silverstein’s, now called the Office of Space Flight Programs.

W. H. Pickering reorganised JPL at the end of 1959 by creating the Lunar Program Office under Cummings, with James D. Burke as his deputy. Cummings duly made Burke Ranger Spacecraft Project Manager. JPL managed the new NASA projects by superimposing small ‘project offices’ on the existing functionally arrayed technical (‘line’) divisions that comprised the laboratory’s core expertise. Indeed, the Ranger Project Office initially comprised only two men and a secretary. Burke’s task was to allocate funds, plan, schedule, assign tasks to the divisions and review progress, but he had no direct supervisory authority over the work since each division did its own design and development and divisional chiefs set their own priorities and assigned engineers within their bailiwicks. Initially, Ranger was the focus of activity, but as other projects claimed attention, most notably the Mariner interplanetary missions, engineers were reassigned and Ranger suffered.

As another element of his restructuring, Pickering added a Systems Division to develop, build and test spacecraft, and a Space Sciences Division to install scientific experiments. For Ranger, the Systems Division would be responsible for systems analysis, including launch to orbit, departure to the Moon, and the requirements of midcourse and terminal manoeuvres; the design and integration of the spacecraft’s systems, including qualification and performance testing, and quality assurance; and assembly and checkout for launch. It would call upon other divisions as subcontractors. Harris M. Schurmeier was the Chief of the Systems Division, and as such he became Burke’s main point of contact with the technical side of the laboratory. In February I960 Schurmeier appointed Gordon P. Kautz as the Project Engineer for Ranger in the Systems Division, but in October Kautz was reassigned as Burke’s deputy and Allen E. Wolfe took the vacated post. The Space Sciences Division, led by Albert R. Hibbs, consolidated JPL’s experimenters into a single group. The Guidance Division was headed by Eugene Giberson. The Engineering Mechanics Division was under Charles Cole. The Telecommunications Division was under Eberhardt Rechtin. The Propulsion Division was under Geoffrey Robillard.

In May 1960 NASA directed JPL to start work on the Surveyor project. As it was doing with Ranger and Mariner, JPL sought to maximise commonality of systems between the two forms of the Surveyor – one for orbital reconnaissance of the Moon and the other to soft land and investigate the physical and chemical properties of the surface. It was expected that because a rough landing from a direct approach would be simpler than entering orbit or soft landing, Ranger would be able to be completed while Surveyor was in development.

Management issues 57

On 27 February 1965 the Ranger experimenters met at JPL with representatives of the Surveyor and Apollo projects to consider the target for the final Block III with a window that would open on 19 March. The Moon would be ‘full’ on 17 March and ‘last quarter’ on 25 March. The Surveyor people argued for Oceanus Procellarum at the western end of the Apollo zone, to identify a safe target for their first soft-lander, but this was rejected. Accepting that the maria were probably all much the same, the Apollo people suggested inspecting a blanket of ejecta, to gain an impression of the roughness of such terrain. The Ranger experimenters themselves argued for a target of particular scientific interest, and this was accepted.

The Ranger team met again on 2 March to consider specific features. To obtain unique data, they considered a variety of locations that were unlikely to be visited by either Surveyor or Apollo – three being Copernicus, Kepler, and Schroter’s Valley near Aristarchus. However, Harold Urey and Gerard Kuiper were both in favour of the crater Alphonsus. Its floor was generally flat, but contained irregular rilles and a number of small ‘dark-halo’ craters which some people thought might be of volcanic origin. Following reports by Dinsmore Alter in America in 1956 of a slight ‘‘veiling’’ of the floor of Alphonsus, Nikolai Kozyrev had monitored the crater for any further such ‘transient events’, and on 3 November 1958 obtained a spectrogram of a ‘‘glow’’ obscuring the 1,100-metre-tall central peak using the 48- inch reflector of the Crimean Observatory. The spectrogram was disputed, but Kozyrev interpreted it as a release of gas. Alphonsus was therefore selected as the primary target for Ranger 9.

The experimenters could not agree a target east of the meridian for early in the window, but a launch on 21 March was compatible with Alphonsus, and thereafter Copernicus, Kepler and Aristarchus on successive days. This list was sent to the Office of Space Sciences and Applications on 10 March. Oran Nicks endorsed it, and passed it to Homer Newell, who concurred. However, NASA had scheduled the Gemini 3 manned mission for 22 March, and the Air Force required a clear 24 hours to reconfigure the Eastern Test Range for a different type of launch vehicle. On 15 March Robert Seamans ordered Gemini 3 postponed to 23 March to give Ranger 9 a chance at its primary target. When the countdown began, the Cape was cloudy and the low-altitude winds were gusty. The clock was held to await an improvement in conditions. Although it remained cloudy, when the winds declined it was decided to proceed.

Soon after lifting off at 21:37 GMT on 21 March (just before that day’s window closed) the vehicle penetrated the cloud deck and was lost from sight. But everything went to plan. The midcourse manoeuvre was deferred to enable radio tracking by the Deep Space Network to precisely define the initial trajectory. It was calculated that

the spacecraft would impact some 640 km north of Alphonsus. The 31-second burn at 12:30 on 23 March ensured that it would fall into the 112-km-diameter crater. The aim point was midway between the central peak, the rilles and the dark-halo craters so that they would all be visible during the approach at a resolution better than was possible telescopically; but they would not appear in the final images, which would give a view of the floor of the crater.

As Ranger 9 approached the Moon on 24 March it became the first spacecraft in the project to make a terminal manoeuvre. At 13:31 the vehicle departed its cruise attitude by pitching, yawing, and pitching again whilst holding its high-gain antenna pointing at Earth. By aiming the cameras along the velocity vector, this manoeuvre would optimise the resolution of the final frames. Ray Heacock, the JPL member of the experiment team, provided the commentary in the auditorium. The electronic scan converter made for the Surveyor project had been hastily modified to process the Ranger video for ‘live’ broadcast by the TV networks. In essence, this comprised two sets of vidicon tubes (one for the wide-angle stream and the other one for the narrow-angle stream) and in each case one vidicon viewed the image displayed on its counterpart, in the process converting the 1,132 lines per frame received from the spacecraft into the 500 lines of the commercial

Ranger triumphs

The sites inspected by the successful Ranger missions.

system.[24] Imaging began at an altitude of 2,400 km, lasted 18 minutes, and ended with impact at 14:08:20 when the spacecraft hit the ground at 9,617 km/hour within 6 km of the aim point.[25] The final picture of the 5,814-frame sequence had a resolution of 25 cm. It was a spectacular way to conclude the Ranger project! The transmission impressed not only the public, but also those scientists who had not appreciated the value of imagery.

At the experimenters’ press conference later in the day, Gerard Kuiper said the ‘dark halo’ craters on the floor of Alphonsus appeared to be volcanic. Harold Urey, no fan of the ‘hot’ Moon hypothesis, allowed that they were probably ‘‘due to some sort of plutonic activity’’. The rilles were revealed not to be clefts but chains of small irregular craters, which some people argued were volcanic. The walls of Alphonsus were very smooth. The central peak was not the harsh edifice depicted by artists. There was no indication that it was a volcano, but neither was there evidence that it was not. There was no clue as to the cause of the ‘transient events’ seen by Alter or Kozyrev.

Mission accomplished 135

In June 1967 the Surveyor Scientific Evaluation Advisory Team considered sending Surveyor 6 to a ‘scientific’ target, with one option being the hummocky Fra Mauro Formation, but NASA headquarters specified Sinus Medii, which would be the ‘first backup’ for an Apollo primary target in the eastern hemisphere. Surveyor 6 would be the project’s third attempt at the meridian – Surveyor 2 had been lost attempting its midcourse manoeuvre, and contact had been lost with Surveyor 4 towards the end of its retro-rocket burn.

Sinus Medii was a relatively small mare plain about 170 km across, bounded to the north and south by highlands. The fact that the northwest-southeast structural trends of the adjacent terrain were radial to Imbrium indicated its origin as sculpture from the creation of that basin. The shapes and trends of the wrinkle ridges, crater chains and small shallow trenches on the plain reflected this structural pattern. The fact that the mare had a larger number of craters with diameters exceeding several hundred metres indicated its surface to be older than most maria. Telescopic studies showed it to have a higher average albedo than most maria. The largest crater on the plain was Bruce, at 7 km in diameter. The centre of the 60-km-diameter target circle was 55 km southwest of Bruce. It was hoped that the lander would set down within sight of a wrinkle ridge.

The launch window for Surveyor 6 was 7-12 November 1967. Although the first unmanned test of the Saturn V launch vehicle was due on 7 November, preparations for the lunar mission went ahead because if it were to become evident that the other mission would not meet its schedule, Surveyor 6 would attempt the first day of its window; otherwise it would be slipped – the Cape’s tracking system required at least 24 hours to reconfigure for different types of vehicle. In the event, the Saturn V was postponed.

Surveyor 6 lifted off from Pad 36B at 07:39:01 GMT on 7 November. Since this was a predawn launch, the Centaur achieved parking orbit in darkness. It flew into sunlight at 07:53:22, initiated the 115-second translunar injection at 08:01:35 and released the spacecraft at 08:04:30. At 02:15:59 on 8 November, once the spacecraft had adopted the attitude for the midcourse manoeuvre, the helium valve was opened to pressurise the vernier propellant tanks. In raising the propellant to 764 psi, the helium fell by 180 psi from its initial 5,182 psia. The burn at 02:20:02 lasted 10.3 seconds, and the 33.1 ft/sec change in velocity moved the aim point 90 km closer to the centre of the target circle. After declining by 208 psi during the burn, the helium regulator maintained the propellant pressures constant throughout the remainder of the cruise.

The pre-retro manoeuvre in which the spacecraft departed from its cruise attitude involved initiating a roll of +82.0 degrees at 00:25:20 on 10 November, a yaw of + 111.8 degrees at 00:29:38 and a final roll of +120.5 degrees at 00:34:56. The initial approach was at 24.3 degrees to the local vertical. The altitude marking radar was enabled at 00:56:16, and issued its 100-km slant-range mark at 00:57:57.038. The delay to the initiation of the braking manoeuvre was specified as 5.875 seconds.

The verniers ignited precisely on time, and the retro-rocket 1.1 seconds later. At that time the vehicle was travelling at 8,460 ft/sec. The RADVS was switched on at 00:58:05.798. The acceleration switch noted the peak thrust of 9,700 pounds fall to 3,500 pounds at 00:58:43.397, indicating a burn duration of 39.4 seconds. After allowing time for the solid rocket thrust to tail off, the verniers were throttled up to their maximum thrust at 00:58:53.297 for a duration of 2 seconds, during which the motor was jettisoned. At burnout, the angle between the vehicle’s thrust vector and velocity vector was 26 degrees. The RADVS-controlled phase of the flight began at 00:58:57.737, when the slant range was 40,574 feet (and because the velocity vector at burnout was offset to vertical, the altitude was 36,625 feet) and the total velocity was 515 ft/sec (and since the vehicle had maintained its thrust along the velocity vector extant at the time of retro ignition, the longitudinal rate was 463 ft/sec). The vehicle immediately aligned the thrust axis along the velocity vector extant at retro burnout and flew with the verniers at 0.9 lunar gravity, very slowly accelerating as it descended. When the altimeter locked on at 00:58:59.892, at a slant range of 35,924 feet, attitude control was switched from inertial to radar and the thrust axis was swung in line with the instantaneous velocity vector to initiate the gravity turn. On intercepting the ‘descent contour’ at 00:59:21.276, the slant range was 24,730 feet and the speed was 552 ft/sec. By the 1,000-foot mark at 01:00:40.534, the vehicle was descending very nearly vertically at 106 ft/sec. The 10-ft/sec mark was issued at 01:00:57.634 at a height of 50 feet.

On receiving the 14-foot mark at 01:01:04.133, the flight control system cut the verniers. At that time the rate of descent was 4.6 ft/sec. After falling freely for 1.3 seconds, the vehicle touched down at 01:01:05.467 with a vertical rate of 11.2 ft/sec. Foot pad no. 1 made contact first, then legs no. 2 and 3 some 25 and 40 milliseconds later, respectively. It rebounded slightly, then settled, with the lateral rate of 1.0 ft/ sec in the direction of leg no. 1 causing each pad to produce a pair of overlapping imprints. The gyroscopes indicated that it was within 1 degree of local vertical. It was a perfect landing!

The verniers had consumed 8.4 pounds of propellant in the midcourse manoeuvre, 41.1 pounds in the retro phase of the descent and 96.8 pounds in the vernier phase – a total of 146.3 pounds of the initial propellant load of 182.6 pounds. The total time spent under RADVS control was 2 minutes 6 seconds, with 1 minute 43 seconds of that flying the descent contour. In contrast, in its improvised descent Surveyor 5 had spent just 62 seconds under RADVS control. In order to have their full functionality available in the event of attempting a ‘lift off and translation’ experiment, it had been decided not to lock the legs as part of the post-landing sequence.

The first 200-line picture was sent at 01:50, and this 24-frame survey of the arc between foot pads no. 2 and 3 continued to 02:35. At an elevation of 3 degrees, the

Sun was barely above the horizon. At 02:55 the solar panel began to scan in azimuth for the Sun, and located it at 03:19. With the landing site at the centre of the Moon’s disk, Earth near the zenith and the vehicle upright, the alignment of the high-gain antenna was simple. It locked on at 03:40. The first 600-line picture was transmitted at 04:02. This camera was the first to have the new box-shaped hood, the mirror of which could seal the aperture to prevent dust or efflux from penetrating the optical system during landing.

The first 360-degree wide-angle panorama was completed by 05:00 and showed a relatively smooth, heavily cratered plain, but there was a feature on the southeastern horizon which, in the low-angle illumination, looked as if it might be a ridge. When this was examined again on Goldstone’s second pass, with the Sun about 13 degrees higher, this identification was confirmed and a series of narrow-angle pictures were taken to record it in detail. The ridge was identified in Lunar Orbiter 2 frame M-113, and when the individual features visible to the lander were located on H-121 by that

orbiter the lander proved to be 10.5 km from the aim point. In high-resolution orbital imagery, the ridge was seen to be 40 km long and to zig-zag generally east-to- west with its individual segments ranging from 300 metres to 2 km in length. It vanished about 1 km southwest of the lander. The base of the nearest section of the ridge was 200 metres from the lander, it was several hundred metres wide and its crest rose about 30 metres above the adjacent plain.

To improve visibility of the surface beneath the vernier engines, Surveyor 6 was provided with three convex mirrors instead of two. Its orientation on the surface was determined by star sightings. Like its predecessor, it had a magnet on foot pad no. 2 to study the concentration of magnetic particles in the surface material. The colour filters had been superseded by polarising filters, and pictures were taken of selected areas during successive Goldstone sessions to build up a dataset in which the Sun’s elevation changed at intervals of about 13 degrees, and thus measure the variation of the polarised component of surface reflection as a function of solar phase angle; the results proved to be insignificant, however.

The fragments displaced and ejected by the foot pads were composed primarily of aggregates of fine-grained material, and in many cases included small bright rock chips. In the immediate vicinity of the lander there were fewer fragments exceeding 2 cm in size than at the other sites, but a greater number smaller than this size. There was also a relative paucity of blocks within 50 metres of the lander – there were only six larger than 20 cm, and the largest was about 50 cm in size. Some were tabular, resembling the layered rocks seen by Surveyor 3 in its medium-sized crater. Most of the fragments within this range were subangular to subrounded, and although many were resting on the surface others were partially buried.

On the plain, craters up to about 150 metres in diameter generally possessed low subdued rims, but some were rimless. The fact that the smallest craters observed by Surveyor 6 on the plain to possess blocky rims exceeded this size indicated that the fragmental debris layer was up to 20 metres thick. For one crater the rim was not actually visible to the lander, just the associated field of blocks. This was visible in high-resolution Lunar Orbiter pictures, which also showed a bench in the wall of the crater at a depth of about 20 metres that could have marked the contact between the fragmental debris layer and the substrate.

In contrast, the lander observed a crater on the flank of the ridge about 30 metres in diameter and one on the crest of 20 metres diameter with blocky rims, indicating that the fragmental debris layer on the ridge was only 8 to 10 metres in thickness. On the crest to the south of the lander there was a crater 180 metres in diameter that was littered with blocks ranging up to 3 metres in size. In the high-resolution Lunar Orbiter pictures, it was possible to see blocks up to 6 metres in size elsewhere on the ridge. The coarse blocks within strewn fields were angular and faceted, and mostly appeared to be exposed on the surface. In terms of small craters, the size-frequency distribution on the ridge was comparable to that of the plain at the landing site. But a close inspection of the lander’s pictures and the high-resolution orbital imagery indicated there to be many more coarse blocks on the ridge than on the adjacent plain – in this respect the ridge was similar to other examples of wrinkles, suggesting that it was representative. The origin of the ridge was disputed. One idea was that it marked where lava had extruded from a fracture (a dyke) and solidified in place. If

this were the case, then the ridge could have formed at any time since the lava flow that made the plain. But there was no evidence in the cratering to suggest that the ridge was significantly younger than the plain. Another theory was that such ridges were produced when a mare plain was deformed by compressional stress. In this case, the manner in which the ridge zig-zagged suggested that its formation was controlled by regional structures. Such stresses could have been imposed at any time after the formation of the mare. The fact that the fragmental debris layer on the ridge was thinner than on the plain was explicable by the slow but progressive flow of loose material downslope. The profusion of large blocks on the crest was certainly consistent with such ‘mass wastage’. The effect was to smooth the transition between the plain and the ridge. Indeed, in frame H-121 provided by Lunar Orbiter 2 it was difficult to precisely identify the outline of the ridge.

The experiment in which Surveyor 1 pulsed a cold-gas attitude control thruster to study surface erosion had been inconclusive, so Surveyor 6 was to repeat this test by firing a thruster continuously. Since any disturbance of the surface would be subtle, the test was made on 11 November, while the Sun was still low in the east to maximise shadow detail in the impingement area. The downward-aimed thruster on leg no. 2 was fired at 03:23 for 4 seconds, and again at 03:47 for 60 seconds. The ground beneath it was surveyed by the camera prior to, between and after the firings. The nozzle was 10.4 cm above the surface and inclined at 24 degrees to the lander’s vertical axis. Both firings displaced fine grains and individual clumps, and produced

partial erosion of some of the clumps that were too large to be moved. The radius of disturbance was 15 cm for the 4-second firing, and 25 cm for the 60-second firing. The fact that no crater was formed implied that the dimple beneath the mildly pulsed jet on Surveyor 1 had been coincidental.

Surveyor 6 was equipped with an alpha-particle instrument. This was powered up at 05:38 on 10 November. After two 10-minute calibrations of the standard sample between 05:41 and 06:21, activity was suspended for 3.5 hours in order to allow TV surveys to be conducted before the Moon set for Goldstone. Calibration of the alpha-scattering instrument resumed when Canberra took over. A total of 318 minutes had been obtained by 21:00, and at 21:18 Madrid commanded the head to deploy ready to measure the background. The first session began at 21:37, and lasted 33 minutes. Then operations reverted to Goldstone, which undertook TV work. The background measurements resumed at 05:00 on 11 November, and a total of 367 minutes of data had been obtained by 12:07. These operations were allowed more time than in the case of Surveyor 5, whose preliminaries had been abbreviated. The head was finally lowered to the surface at 12:08, some 35 hours into the surface mission. The sample was undisturbed surface. There were few fragments exceeding

several millimetres in size, and the largest in the sampled area was about 1.5 cm in size. Some 7.2 hours of data had been obtained by 23:00, when the instrument was switched off in order to resume TV work. Data collection resumed at 07:48 on 12 November, and a total of 15.7 hours of data had been obtained by 19:55. Activity had to cease at 23:39, when the head exceeded its maximum operating temperature of 50°C. The instrument was off through local noon, but was able to resume sampling at 16:50 on 16 November, when the Sun’s elevation had decreased to 79 degrees and the shadow cast by the solar panel allowed the head to cool. By the time the instrument was switched off at 03:30 on 17 November a total of 30.5 hours had been obtained.

Surveyor 6 was to investigate further how the lunar surface was affected by rocket exhaust. The static vernier firing by Surveyor 5 had produced both viscous erosion and gas diffusion erosion – the latter resulting from the fact that the pressure on the surface was relieved suddenly as the engines were cut off whilst the vehicle was still on the surface. In the case of Surveyor 6, the engines were to deliver a greater thrust and for longer to emphasise viscous erosion, and because such a burn would lift the vehicle off the ground the pressure on the surface would be relieved slowly and thus minimise the disruptive effects of gas diffusion. And since the vehicle was to lift off, it had been decided to impart a horizontal displacement so that upon touchdown the camera would be able to view the original imprints made by the foot pads and the erosional effects of firing the verniers.

This ‘liftoff and translation’ was scheduled for 17 November. As a preliminary, high-resolution pictures were taken to document the state of the area immediately in front of the camera. As the Sun was high in the sky, the solar panel and high-gain antenna were temporarily repositioned to shade and cool the engines to a permissible

pre-ignition temperature. At 08:00 the flight control system was powered up for 35 minutes to verify its status. When the solar panel was stowed in order to prevent its being damaged by the stresses of the manoeuvre, this placed the vehicle on battery power. As the camera installed between legs no. 2 and 3 was on the east side of the vehicle, the flight control system was to fire vernier no. 1 at a lower thrust than the other two engines to make the vehicle lift off inclined at an angle of 7 degrees in the direction of foot pad no. 1, thereby displacing the vehicle to the west whilst causing the material eroded from the surface to be displaced preferentially in the opposite direction. Afterwards, the camera should have a good view of the erosional effects. At 09:46 the flight control system was reactivated, and at 10:32:02 the verniers were ignited and throttled to deliver a total thrust of 150 pounds. The intended period of firing was 2.0 seconds, but the cutoff failed and by the time the backup command took effect a total of 2.5 seconds had elapsed. The manoeuvre consumed 1.5 pounds of propellant. Once the telemetry had been examined to verify the systems, the solar panel and high-gain antenna were redeployed, and within 35 minutes photography had resumed.

The ‘hop’ lasted about 6 seconds, peaked at a height of 12.5 feet, and ended about 8 feet from the initial position in a direction slightly north of west. The vertical rate on making contact with the surface was 12.3 ft/sec, and the horizontal rate was 1.8 ft/sec – which was greater than that of the original landing and caused the foot pads to displace material as ejecta. The post-hop pictures showed the double imprints of pads no. 2 and 3 and the single imprints of the crushable blocks on those legs made at the time of the lander’s arrival. But because the vehicle rolled 5.5 degrees in an anticlockwise direction around its main axis during the hop the imprints of pad no. 1 ended up beneath crushable block no. 3 and thus were not visible for inspection. The imprint of the alpha-scattering head in between legs no. 2 and 3 was obliterated by the blast. At the initial landing, the verniers had been cut off at a height of 12 feet to minimise disturbing the surface, but for the hop they had been fired at even greater

A section of a panorama taken by Surveyor 6 after its ‘hop’, showing the original imprints and the erosional effects of firing the verniers. (Courtesy of Philip J. Stooke, adapted from International Atlas of Lunar Exploration, 2007)

thrust within a foot of the ground. Nevertheless, there was no evidence of explosive cratering – the surface was sufficiently cohesive to resist bearing capacity failure at the imparted gas pressure. Furthermore, although in the case of Surveyor 6 the pressure of the gas on the surface from firing the verniers was thrice that of the static test by Surveyor 5 and the higher pressure would have increased the diffusion into the surface, the rate at which the gas pressure on the surface declined as the vehicle rose was sufficiently slow to inhibit the gas diffused into the surface from escaping violently, with the result that the gas diffusion erosion was no worse than the static test. However, viscous erosion blew dark subsurface material across the undisturbed surface, and there was a striking pattern of fine rays radiating from below where the verniers had been when they ignited. Most of the displaced material was from where the surface had been previously disturbed by the foot pads and crushable blocks. The fact that 1-2-cm fragments left dark trails as they rolled on the undisturbed surface was evidence that the lighter-toned surface material was at most several millimetres thick. Some larger fragments were ejected on ballistic trajectories. One clod of fine­grained material splattered the photometric target on omni-directional antenna boom ‘B’, almost obscuring its pattern.

When Surveyor 6 arrived, the magnet on foot pad no. 2 had made no contact with the surface material. No changes were observed after firing the cold-gas thruster on that leg. But when pad no. 2 came into contact with the surface following the hop it penetrated to a depth of 10 cm, bounced and came to rest about 12 cm away, thereby not only leaving an overlapping imprint for the soil mechanics team to study but also finally giving the magnet scientists a coating of material to examine. The horizontal displacement from the hop also provided the camera with a baseline for stereoscopic

imaging. Later photogrammetric analysis enabled an extremely detailed topographic map to be produced extending out about 50 metres from the lander.

After the hop, the sensor head was observed to have come to rest upside down! It was switched on at 12:48 on 17 November and found to be too hot, so was turned off again at 12:52 and allowed to cool before undergoing a test to determine whether it could provide any worthwhile data in this orientation – it could monitor solar wind protons bathing the lunar surface, and was operated in this manner for a total of 13 hours between 18 to 20 November and 22 to 24 November, with this experiment concluding at sunset. The alpha-scattering instrument operated for a total of 108.3 hours during which it provided 59 hours of science data, but only 30.5 hours of this was of the surface material and 10 per cent of the data was rejected because it had a low signal to noise ratio – which left 27 hours of surface data for integration.

In the case of Surveyor 5, whose ad hoc descent had required the retro-rocket to operate to within 4,200 feet of the ground, it was conceivable that the aluminium abundance measured by the alpha-scattering instrument was inflated by efflux from the solid-propellant rocket motor. But Surveyor 6 jettisoned its motor at a height of 35,000 feet and measured essentially the same abundances, and this implied that the Surveyor 5 data was valid. The analyses at the two sites suggested that the elements in the lunar surface material were in the form of oxides, and formed compounds and minerals that were familiar on Earth. It was not pristine material condensed from the solar nebula. As in the case of Earth, the Moon has undergone significant chemical differentiation. Although it was concluded that the maria were of a basaltic composition, the data was insufficient to identify the particular type of basalt. The observations of the magnets on these landers were consistent with the fine-grained material being pulverised basalt with little (if any) admixed meteoritic iron.

On 19 November the oxidiser part of the vernier propulsion system developed a leak, possibly owing to the degradation of a rubber o-ring seal. This automatically opened the helium regulator to top up the pressure, which was impossible – with the result that by 25 November both the oxidiser and helium had been completely lost. This leak pre-empted a tentative plan to perform a second hop.

With sunset imminent, the lander recharged its battery to sustain itself through the lunar night. At 16:08 on 22 November the shock absorbers of the legs were locked in order to preclude the deflections suffered by Surveyor 5 when its unlocked legs relaxed upon being chilled.

Sunset was at 13:53 on 24 November. Over the next 6 hours, pictures were taken using the polarising filters to study the solar corona. Between 16:23 and 16:50, and between 19:05 and 19:28, pictures were also taken of foot pad no. 2 illuminated by Earthshine. At 19:03, at the start of the final 10-minute corona exposure, the upper limb of the Sun was about 10 solar radii below the horizon. Camera activity ended at 20:04. It sent some 14,500 pictures prior to the liftoff and translation experiment and by the time it was switched off it had provided a total of 29,952 pictures. The final data from the alpha-scattering instrument on the protons impinging on the Moon was obtained 4 hours after sunset. Temperature monitoring was concluded at 06:41 on 26 November, after 41 hours – it had been hoped to obtain 130 hours of such

A picture of the ‘horizon glow’ phenomenon taken by Surveyor 6 at 14:25 GMT on 24 November 1967, about half an hour after sunset. The sketch shows the position of the solar disk in relation to the horizon and the ‘beads’ at that time. The position of the Sun was determined in relation to the marked stars, the magnitudes of which are indicated beside the circles. The grid coordinates are relative to the digital frame. The diffuse glow is the solar corona.

data, but a problem involving the bimetallically activated switches in the thermally controlled compartments obliged the lander to hibernate early.

Surveyor 6 provided the first measurements of the polarisation of the solar corona out to 30 solar radii, which was several times further than was attainable for a solar eclipse seen from Earth. Pictures taken during the first hour after sunset revealed a surprising ‘horizon glow’. This consisted of a number of glowing segments along a 5- degree arc due west. As the Sun passed progressively further beneath the horizon, these disappeared in groups. Whilst the later exposures were longer than the initial ones in which the band of light was prominent, it had completely disappeared by the time the centre of the solar disk (which spans about half a degree) was 1.2 degrees below the horizon. In fact, this phenomenon had been photographed by Surveyor 1, but it was not recognised until after the Surveyor 6 discovery. One speculation was that the glow was the diffraction of sunlight by fine-grained material on the surface at the horizon. Another idea was forward scattering by particles possessing a mean size of less than 10 microns that were electrostatically levitated a fraction of a metre above the ground at the horizon. ft was impossible to draw a firm conclusion on the data available.

An attempt to awaken Surveyor 6 on 13 December was unsuccessful. Contact was re-established at 16:41 on 14 December, but was lost 3 hours later. Efforts to revive the lander continued until 21 December, and were then abandoned since sunset was once again imminent.

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

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

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

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

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

David M. Harland Kelvinbridge, Glasgow January 2009