Category Paving the Way for Apollo 11

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.

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.

Luna 2 was launched at 06:40 GMT on 12 September 1959, and 33.5 hours later it smashed into the Moon in the triangle defined by the craters Archimedes, Aristillus and Autolycus. On striking the ground at 3 km/sec, the probe would have vaporised. It carried similar instruments to its predecessor. In extending the particles and fields survey down to the surface, it found no appreciable magnetic field and no evidence of a radiation belt. The Earth’s field is generated by electric currents in molten iron in the core. The absence of a dipole field suggested that either the Moon had never developed a molten core, or it had and either the rate of the Moon’s rotation was too slow to generate electric currents or the core had since solidified.9

When Luna 3 was launched at 00:44 GMT on 4 October 1959, it was to undertake the eagerly anticipated photographic mission. It was inserted into a highly eccentric orbit of Earth which would provide a view of the far-side of the Moon. The 279-kg probe was 1.3 metres long. The main body was a 1.2-metre-diameter cylinder, and it had solar transducer cells in fixed positions on its exterior. The earlier probes in this series were battery powered, but a battery would not provide the duration required to undertake this particular mission. In addition to particles and fields instruments, the probe had a camera. Its trajectory crossed the radius of the Moon’s orbit 6,200 km to the south of the Moon. The point of closest approach was at 14:16 on 6 October, and lunar gravity deflected the trajectory northward. While coasting, the probe was spin stabilised. On approaching the Earth-Moon plane, beyond the Moon, gas jets halted the spin, a Sun sensor locked on, and the vehicle rolled until another sensor enabled the optics to view the Moon.

The camera had a 200-mm f/5.6 lens and a 500-mm f/9.6 narrow-angle lens, with the optical axes coaligned. Starting at 03:30 on 7 October, at a range of 65,200 km, pairs of pictures were captured simultaneously on 35-mm film which had a ‘slow’ rating in order to resist being ‘fogged’ by the radiation in the space environment. After 40 minutes of photography, the vehicle resumed its spin for stability. The film was wet-developed, fixed and dried. After the probe had achieved the 480,000-km apogee on 10 October, it headed back for the 47,500-km perigee on 18 October. The film was scanned using a constant-brightness light beam which was detected by a photoelectric multiplier whose output took the form of an analogue signal. The scanner had two transmission rates: a slow rate for when far away from Earth and a higher rate for perigee. Contact with the probe was lost on 22 October. On Earth, the signal was recorded on magnetic tape for further processing. The raw images were marred by bands of ‘noise’, which had to be ‘removed’, and the contrast was drawn

A picture taken by Luna 3 on 7 October 1959 showing Mare Crisium (on the left) and a large portion of the hitherto unobserved hemisphere of the Moon.

out to emphasise detail. In the wide lens the lunar disk spanned 10 mm, and in the narrow lens it was 25 mm.

The phase of the Moon was ‘new’ on 2 October and ‘first quarter’ on 9 October. Therefore, when the pictures were taken on 7 October a portion of the near-side was illuminated. The prominent presence of Mare Crisium gave a sense of perspective. The remainder of the illuminated zone was 70 per cent of the hitherto unobserved region. As the Sun was directly behind the camera, the lack of shadow detail made it impossible to discern the topography. However, the results did show there to be few dark features – revealing the hemispheres which faced towards and away from Earth to be different. The maria cover 30 per cent of the near-side, but only 2 per cent of the far-side; in total about 16 per cent. The likelihood of there being fewer maria had been inferred from the paucity of maria on the limb, with those present being patchy rather than major plains, but their virtual absence was a surprise. The fact that the Moon’s rotation is ‘tidally locked’ with Earth was evidently an important factor in creating the dichotomy between the two hemispheres.

The results were published in 1960 as Atlas Obratnoy Storony Luny by N. P. Barabashov, A. A. Mikhaylov and Yu. N. Lipskiy. They unilaterally assigned names to the far-side features, with the two most prominent dark patches becoming Mare Moscoviense and Tsiolkovsky.[10] The atlas listed some 500 features of various types on a scale which represented the Moon as a disk 35 cm in diameter.

The Luna 3 mission was a remarkable success for the first attempt at a difficult task.

Now that Ranger Block III had proved itself, the Office of Manned Space Flight asserted its right to specify the requirements for future targets. On 16 October 1964 Sam Phillips, the Apollo Program Director, told Oran Nicks that Ranger 8 should investigate a mare plain in the Apollo zone at a position which was not crossed by rays. At a meeting at JPL on 19 November, the scientists argued for comparing the ‘reddish’ Mare Nubium with a ‘bluish’ one in the eastern hemisphere. Nicks made the formal recommendation to Homer Newell on 9 February 1965, who concurred. The target for the first day of the launch window was to be Mare Tranquillitatis, but if the launch were delayed then it would move westward along the Apollo zone to keep pace with the migrating terminator. The launch window for Ranger 8 opened on 17 February. The Moon was ‘full’ on 16 February and would be ‘last quarter’ on 23 February.

Launch was at 17:05 GMT on 17 February. The translunar injection produced a flyby at a range of 1,828 km. The trajectory was refined by a 59-second midcourse manoeuvre at 10:27 on 18 February. When Ranger 8 made its approach to the Moon, it was decided to start the cameras several minutes early so that the initial pictures would be comparable to the best attainable by a terrestrial telescope. A total of 7,137 pictures were received – almost twice as many as from Ranger 7 owing to the extended sequence. Whereas Ranger 7 had made a near-vertical descent west of the meridian, the target for Ranger 8 was 24 degrees east of the meridian and to reach it the spacecraft had to make a slanting approach. Whilst this significantly increased the areal coverage, in particular depicting the central highlands at an unprecedented resolution, it meant there was no overlap between the frames later on and the lateral velocity smeared the final frames. The impact occurred at 09:57:38 on 20 February. Don Wilhelms was watching through the 36-inch refractor at the Lick Observatory near San Jose in California and listening to a radio countdown from JPL, but saw no flash. Alika Herring of the Lunar and Planetary Laboratory was using the 84-inch reflector at the Kitt Peak National Observatory in Arizona, but did not see anything either. As a result of the lack of overlap, the impact point was not actually within the final frame – not that it really mattered, it was calculated from the trajectory as being 24 km from the aim point.[23] In this case, owing to the smearing of the final images, the best resolution was 1.5 metres.

At a press conference 30 minutes later given by W. H. Pickering, Edgar Cortright, William Cunningham and Harris Schurmeier, the latter delightedly summed up the mission as “another textbook flight”.

The experimenters presented some of the pictures later in the day. There were more rocks than at the Mare Nubium site, once again indicating a substantial bearing strength. In fact, this area was one of the ‘hot spots’ in near-infrared measurements made during the lunar eclipse of 19 December 1964, and the exposed rock supported the interpretation of such thermal anomalies as being due to rocks slowly radiating their heat when the Moon entered into the Earth’s shadow.

Despite the intention to investigate a mare site free of rays, it was discovered that Ranger 8 came down over a faint ray from Theophilus. One striking observation was that the surface of Mare Tranquillitatis appeared remarkably similar to that of Mare Nubium. In fact, Gerard Kuiper, showing one of the final frames, remarked, ‘‘If you didn’t know that this was taken by Ranger 8, you’d think it was one of the Ranger 7 pictures.’’ It was ventured that ‘‘probably all lunar maria are pretty much this way’’.

Harold Urey introduced the term ‘dimple crater’ for irregular rimless pits which, it was speculated, might be where loose surficial material had drained into a cavity in much the same way as sand drains in an hourglass. Noting that tubes and cavities occur in terrestrial lava fields, and believing the lunar maria to be lava flows, Kuiper speculated that such pits might pose a ‘‘treacherous’’ threat to an Apollo lander. To Gene Shoemaker, however, they appeared merely to be degraded secondary impact craters.

On the larger scale, the scientists were pleased that as Ranger 8 made its slanting approach it provided views of Ritter and Sabine in unprecedented detail. These two 30-km-diameter craters in the southwestern Mare Tranquillitatis lacked radial ejecta and secondary craters, and their depth-to-diameter ratios made them anomalously shallow in terms of the curve plotted for impacts by Ralph Baldwin. The fact that they were aligned along the Hypatia rilles, were located on the fringe of a mare and had ‘raised floors’ had led some people to interpret them as volcanic calderas. Even people who favoured the impact origin of craters allowed that Ritter and Sabine

might be ‘hybrid craters’ that were excavated by impacts and later modified by volcanism stimulated by their formation – indeed, they were the exemplars of this hypothesis.

A RISKY DESCENT

Surveyor 5 was the first of the project to be assigned to an eastern portion of the Apollo zone. The target was a 60-km-diameter circle in the southwestern region of Mare Tranquillitatis, centred 80 km east of Sabine. The highlands to the west were characterised by prominent southeast-tending ridges and valleys that formed part of the Imbrium sculpture. The target was about 70 km north of the southern boundary of the mare, and 38 km northwest of Moltke. It was also 60 km southwest of where Ranger 8 struck. There were no mare ridges in the immediate vicinity, but the area was crossed by faint rays from Theophilus 350 km to the south. In fact, owing to the magnitude of the gravity turn required to cancel the approach angle relative to local vertical, this site was about as far east as a Surveyor was capable of venturing.

Launch from Pad 36B was at 07:57:01 GMT on 8 September 1967. The Centaur fired for 320 seconds and achieved parking orbit at 08:06:48. It emerged from the Earth’s shadow about 10 seconds later. After coasting for 6.7 minutes, it reignited for the 113-second translunar injection. The spacecraft was released at 08:16:27 and established its cruise mode without incident.

The fact that the initial trajectory would reach the Moon just 46 km from the aim point made this the best performance to date for an American launch vehicle sending a payload towards the Moon. At 01:32:57 on 9 September the spacecraft began to manoeuvre to the attitude for the minor midcourse burn, and at 01:42:28 the squib was fired to open the helium regulator’s valve to increase the six propellant tanks of the vernier propulsion system from their initial pressure of 264 psi to their operating pressure of 720 psi. Immediately beforehand, the helium tank pressure was stable at 5,160 psi. The decrease in helium pressure due to pressurising the propellant tanks was 182 psi, as expected. The burn was initiated at 01:45:02. It lasted 14.25 seconds, and the 45.5-ft/sec change refined the trajectory as desired. As the spacecraft was in the process of re-establishing its cruise attitude, the engineers checking the telemetry were alarmed to observe that instead of holding at 720 psi, the propellant pressure

was rising. It was conjectured that a particle of contaminant had lodged in the seat of the helium regulator and was preventing the valve from closing properly.

There was nominally a 1-hour time constraint between vernier firings, but in view of the need for haste this was waived. Additional firings were made in unsuccessful attempts to clear the valve. As there were bladders in the propellant tanks, there was no mixing of helium and propellant, and whenever the pressure reached 825 psia a relief valve opened to vent the excess pressurant to space. As a result, the helium tank was losing pressure at a rate of about 10 psi per minute. This promised disaster when the vehicle attempted its descent to the Moon, as the verniers would fizzle out from propellant starvation far above the lunar surface.

The first impromptu vernier firing was made with the vehicle’s main axis pointing at the Sun, because the vehicle had already re-established that attitude. The burn was made at 02:12:03, some 27 minutes after the midcourse manoeuvre. It lasted for 10.1 seconds and the change in velocity of 32.1 ft/sec had the effect of driving the aim point 1,600 km along the equator to longitude 77.5°E. This was only a temporary digression, however, because the vehicle was then yawed through 180 degrees and a second burn was initiated at 02:39:51. This lasted 23.0 seconds and the change in velocity of 73.9 ft/sec drove the aim point 2,685 km westward, to longitude 12°W. For these burns the pre-ignition temperatures exceeded the engines’ operating limit, but they fired satisfactorily. Unfortunately, the helium regulator continued to leak.

After a period of deliberation, it was decided to make a third impromptu burn. In addition to a ‘critical component’ of 27.2 ft/sec to re-establish the aim point, there was a non-critical component of 36.1 ft/sec designed both to increase the flight time and to burn off propellant in order to reduce mass and thereby the velocity at retro burnout. To further improve the chances of clearing the regulator valve, the required 13-second duration would be built up by firing the engines for 12 seconds and then twice pausing for 1 second and ‘blipping’ them for half a second. This sequence was started at 04:18:48 and imparted a change in velocity of 45.3 ft/sec, but did not clear the valve.

At 05:50 one team of engineers was assigned to work out a manoeuvre that would enable Surveyor 5 to avoid the Moon and remain in an Earth orbit possessing a high apogee, in case it was decided to abandon the Moon as the target. Meanwhile, other engineers calculated that if sufficient propellant could be burned off to lighten the vehicle and thus reduce the velocity at retro burnout, and if retro ignition were to be postponed to a much lower altitude, then it might be possible to achieve a landing despite the helium problem. At 07:43 it was decided to attempt to accomplish the lunar mission.

The fourth impromptu vernier firing was to burn off propellant in order to further reduce the retro burnout velocity and increase the volume available in the propellant tanks for the helium leaking from the regulator. The latter would both minimise the rate of venting and maximise the impulse available for operating the engines in the vernier descent. The burn was initiated at 08:24:03, lasted 33.0 seconds, changed the velocity by 106.0 ft/sec, and drove the aim point into the central highlands. For the next 13 hours the spacecraft was tracked to precisely define its trajectory. Given the uncertainty about whether a soft-landing would be achieved, it was decided to test the alpha-scattering instrument to check its calibration and assess whether there was a significant cosmic background. Power was applied to the instrument at 10:36. The calibration rates transmitted by an omni-directional antenna were monitored for two 10-minute periods by the Deep Space Network station at Canberra in Australia, then the instrument was switched off at 11:25. The fact that the background was very low was good news; if this should prove to be the only scientific data from the mission, it would assist with the next one. The fifth and final impromptu burn had a critical component of 12.7 ft/sec to draw the trajectory 267 km back towards the target, and a non-critical component of 11.8 ft/sec to further reduce the retro burnout velocity and increase the gas volume in the propellant tanks. ft was made at 23:30:58, lasted 5.45 seconds and imparted a change in velocity of 17.3 ft/sec that returned the aim point to within 30 km of the target. By 23:46:37 the spacecraft had re-established its cruise attitude. The midcourse manoeuvre itself had used 11.3 pounds of propellant, and the impromptu firings had consumed another 67 pounds.

A new descent profile had been devised to minimise the total impulse requirement for the verniers, to enable them to accomplish the landing by operating solely on the residual helium pressurant. On a normal descent the altitude of retro burnout was selected to allow ample time for the verniers to initiate the gravity turn in advance of reaching the ‘descent contour’, but now this margin had to be minimised to reduce the duration of the vernier-only phase of the descent.

The altitude marking radar would still issue its mark at a slant range of 100 km, but the programmed delay would be increased to 12.325 seconds in order to reduce the altitude at which to initiate braking. fn the case of Surveyor 1, whose target was at 43°W, the approach angle had been at 6.1 degrees to the local vertical; for Surveyor 3, at 23°W, the angle was 23.6 degrees; for Surveyor 4, on the meridian, it was 31.5 degrees; for Surveyor 5, aiming for 23°E, the angle would be 46.5 degrees – even on the original plan, this was to have been the most demanding descent to date. fnstead of aligning the thrust axis precisely with the velocity vector, it had been decided to offset it by 0.78 degree in order to enable a component of the powerful retro-rocket’s thrust to contribute to reducing the approach angle, and thereby reduce the gravity turn the verniers would have to perform. And to ensure the most accurate alignment of the retro axis the pre-retro roll was timed for when the divergence in the Canopus sensor would be zero, and the yaw for when the Sun would be precisely aligned in that sensor – as calculated by monitoring the oscillations in the alignment. Whilst the pre-retro sequence in which the vehicle departed from its cruise attitude would usually include a roll to optimise post-landing operations, for this descent the only factor considered was the RADVS, and because the first roll would satisfy this requirement the second roll was deleted. fn essence, therefore, the powered descent would be initiated later than usual in order that instead of retro burnout occurring at an altitude of 35,000 feet this would take place at 4,260 feet, and instead of the total velocity being 400-500 ft/ sec it would be just 100 ft/sec. fn addition, the release of the spent retro-rocket casing was revised to advance the onset of RADVS-controlled flight by 4 seconds – since this time every second would count! These changes were designed to make the most efficient use of the remaining helium pressurant, but the descent would be much more risky than the usual profile.

VELOCITY, FEET PER SECOND

The helium pressurant problem suffered by Surveyor 5 required the burnout of its retro – rocket to occur at an unprecedented low altitude. Note that the 99% dispersion ellipse for retro burnout extends below ground level!

The pre-retro roll of +73.8 degrees was started at 00:12:15 on 11 September, and the yaw of +119.6 degrees at 00:16:20. The altitude marking radar was enabled at 00:43:01 and issued its 100-km slant-range mark at 00:44:39.118, at which time the vehicle was travelling at 8,441 ft/sec. During the specified delay of 12.325 seconds it would travel 104,000 feet, and, in view of the angle of the trajectory, the altitude would reduce by some 74,000 feet prior to retro ignition – this delay being to fly the revised powered descent profile.

The verniers ignited at 00:44:51.443, and the retro-rocket at 00:44:52.533. The helium pressure at vernier ignition was 836 psia, which was sufficient to provide the desired total vernier thrust of 152 pounds for this phase of the descent. The RADVS was switched on at 00:44:53.456, and the radar altimeter locked on at a slant range of 16,000 feet. The acceleration switch noted the peak thrust of 9,740 pounds fall to 3,500 pounds at 00:45:31.355, indicating a burn duration of 39 seconds. The spent casing was jettisoned at 00:45:40.395. The flight control system throttled the three verniers to full thrust at 00:45:40.955 to ensure that the casing fell clear. At burnout, the angle between the thrust vector and velocity vector was 45 degrees.

At 00:45:42.395 control was passed to the RADVS. The altitude was 4,139 feet (a slant range of 6,300 feet owing to the approach angle) and the velocity was 79 ft/sec (the vertical component of which was 46 ft/sec). Attitude control was switched from inertial to radar, and the vehicle immediately resumed the gravity turn by holding a constant deceleration of 0.9 lunar gravity whilst maintaining the thrust in line with the instantaneous velocity vector. At 00:46:19.697 the radar indicated the 1,000-foot mark. On a normal descent, the vehicle would intercept the ‘descent contour’ at a slant range of 18,000 to 25,000 feet, travelling at 400 to 500 ft/sec with 100 seconds remaining to landing. On this revised profile it was to have reached the contour at a slant range of 1,500 feet, but it did so at 806 feet with just 22 seconds remaining for the closed-loop throttling phase. The 10-ft/sec mark was issued at 00:46:37.097, at a height of 50 feet. Some 5.6 seconds later, at 00:46:42.697, the verniers were cut off with a sink rate of 5.2 m/s, and Surveyor 5 fell freely for 1.7 seconds.

After leg no. 1 hit the surface at a vertical rate of 13.5 ft/sec, the vehicle pitched over at an angular rate which was faster than the gyroscopes were able to measure, and 190 milliseconds after first contact the other legs slammed down at 13.8 ft/sec and it came to rest tilted at 19.5 degrees. It was the harshest landing of the project to date, but still within the design specification. Fortunately, the lateral velocity component was negligible and the widely splayed legs prevented the lander from toppling over.

The time spent under RADVS control was a mere 62 seconds. The descent had burned 60 pounds of propellant – a little less than was consumed by the impromptu firings after the midcourse manoeuvre. Although about 45 pounds remained, the issue had not been a shortage of propellant; it was a shortage of helium pressurant to force the propellants into the engines, and by the end of the descent the helium, fuel and oxidiser pressures were identical at 560 psia – in effect, the vernier propulsion system had been in ‘blow down’ mode. Some engineers had estimated the likelihood of achieving a soft-landing at no better than 40 per cent, so this success came as a great relief! The engineering recommendation was to improve quality control in the

The descent of the Surveyor 5 spacecraft depicted in two sections, one for slant ranges above 1,000 feet and the other below 1,000 feet. The delayed retro-rocket braking meant the vehicle did not join the contour until the third segment of the linear approximation to the ideal parabolic trajectory.

The history of Surveyor 5’s helium pressurant from launch to lunar touchdown, showing the leak that developed when the valve of the regulator was activated and the stabilisation of the depleted level by the impromptu midcourse manoeuvres.

manufacture of the helium regulator to eliminate contaminants that could prevent the proper reseating of the valve.

In-flight tracking indicated that it landed some 30 km northwest of the target, at a point that was just off the edge of frame H-78 taken by Lunar Orbiter 5 the previous month – the only high-resolution picture of this particular area – and the best that could be done was to mark a medium-resolution frame with an ellipse based on the post-landing tracking data and give the selenographic coordinates of its centre. The site was either in, or close to, a faint ray from Theophilus.

Surveyor 5 arrived some 35 hours after local sunrise, with the Sun at an elevation of 17 degrees. The first 200-line picture was taken at 02:01, and the entire initial sequence of 18 frames had been transmitted by 02:39. Although it was evident that the lander was on a steep slope, its orientation was uncertain, and this complicated the task of aligning the high-gain antenna. This began to scan the sky at 02:58, with Goldstone monitoring the strength of the received signal and directing the search. Meanwhile, the solar panel locked onto the Sun at 04:10. The antenna finally locked on at 05:21, and the first 600-line picture was transmitted at 05:30.

TV AUXILIARY UNIT.

SIGNAL PROCESSOR,

I TRANSMITTER

THERMAL COMPARTMENTS

The camera provided for Surveyor 5 had a modified hood for the mirror assembly.

It was soon realised that foot pad no. 1 was resting on the southwestern margin of a small irregularly shaped crater 12 metres long by 9 metres wide and a fraction over 1 metre deep, and the other legs were inside the cavity. The crater was rimless, with the slope increasing towards the centre, where there was a distinctly concave floor spanning about 2.4 metres. In fact, the crater was of a type which had been classified in the Ranger imagery as a ‘dimple’, and the lack of a rim had led some people to argue that such pits marked where the loose surface material had drained into a subterranean space – with the implication that such features were not of impact origin.1 The major axis of the crater was northwest-southeast, and the vehicle was on the southwestern interior wall, tilting northeast. It seemed to be the largest member of a chain of small elongated craters, all oriented with their major axes in line with the chain, and there were other chains in the area sharing this directionality.

Pad no. 1 had struck just outside the crater, and the others on its interior slope. As the vehicle rebounded, it slid downslope, causing pads no. 2 and 3 to scrape furrows about 1 metre long before they came to rest near the base of the wall. So, although this lander did not possess a soil mechanics surface sampler with which to scrape a trench, its legs served this role. As the vehicle slid down into the crater, pad no. 1 was dragged closer to the edge and the fragmental material that it displaced came to rest directly beneath the camera. Furthermore, as pads no. 2 and 3 ploughed their furrows they hinged and drove their outer edges into the surface, causing material to spill onto their upper surfaces where it was conveniently situated for examination by the camera. The furrows varied in depth between a few centimetres and 12 cm, most likely because the slide coincided with the rebounding of the legs following the initial impact. Furthermore, in addition to piling up material downslope, pads no. 2 and 3 splattered ejecta for a distance of about 1 metre across the concave floor – in fact, this was the greatest displacement of lunar material of any landing to date. The cohesion of the aggregates was evident from the fact that one clod remained intact on settling on the floor of the crater. The frequency-size distribution of the lumpy fragmental material pushed downslope was much coarser than that on the undisturbed surface.

The walls of the crater in which Surveyor 5 landed provided a view into the upper half-metre of the fragmental debris layer. There were bright angular fragments that seemed to be rocks, rounded aggregates of fine-grained material with bright angular chips bound into a dark matrix, and dark lumpy aggregates of aggregates. Beneath a depth of 10 cm it appeared to be a uniform mass of fine-grained material containing small rocks and shock-compressed aggregates several centimetres in size. Although the albedo of the disturbed material was comparable to that at the previous sites, the undisturbed surface was less bright, making the difference less pronounced. The flat mirrors which had been installed on leg no. 1 of Surveyor 3 had been superseded by convex mirrors to improve the view beneath the lander. Material around the bottom

The ‘dimple’ craters are now known to be secondaries made by the fall of ejecta issued by larger impacts.

A detailed map of the small crater in which Surveyor 5 landed and the immediately surrounding plain, produced by R. M. Batson, R. Jordan and K. B. Larson of the US Geological Survey.

edge of crushable block no. 3 implied that it struck the surface at the time of landing, but any imprint had been masked by the material thrown forward by pad no. 1 when this was dragged towards the crater as the other legs slid down the interior slope.

As the mirror of the camera was only 1.2 metres above the plane of the foot pads and was between legs no. 2 and 3, it too was ‘inside’ the crater, with the result that more than 80 per cent of the field of view was within a range of 6 metres. The view of the peripheral terrain was highly foreshortened. In fact, although the mirror was
about 80 cm above the northern rim, the fact that the rim was higher to the southeast meant that the mirror was only 30 cm above the southern rim. For a lander on open ground the horizon would have been 2 km away. In this case, the camera was able to see to a distance of about 1 km to the north and west, but less far to the south and east. In one sector to the south the horizon was barely 100 metres away because it was the raised rim of a 20-metre-diameter crater. There was a strewn field of blocks associated with this crater that extended almost to the crater in which the lander was situated. When the closest blocks of this field were examined at high resolution they proved to be angular to sub-rounded and less than 50 cm in their longest dimension. Some had a mottled appearance reminiscent of a rock at the Surveyor 1 site. There was another strewn field associated with a 15-metre crater situated 200 metres to the north. On the basis of these strewn fields and other raised-rim craters in the middle distance, it was possible to estimate the fragmental debris layer in this part of Mare Tranquillitatis to be no greater than 5 metres thick.

On Surveyor 5, the soil mechanics surface sampler was replaced by an instrument to study the composition of the lunar surface material. This was developed by a team headed by Anthony L. Turkevich, a nuclear chemist at the University of Chicago. It comprised an electronics package in a thermally controlled compartment which was mounted high on the vehicle’s frame, and a box-shaped sensor head that was stowed midway between legs no. 2 and 3, immediately to the left of where the electronics package for the surface sampler would have been if this were present. Including the ancillary hardware, the mass of the experiment was 13 kg. The head was held by its deployment mechanism until needed, then lowered on a nylon cable to the surface with a ribbon cable linking it to its electronics. The head was about 13 cm tall with a 17 x 16-cm cross section. To prevent the box from sinking into soft material, it had a D-shaped 15-cm-radius plate on its base. Six curium-242 alpha-particle sources inside the head were collimated to irradiate the surface through a 10.8-cm hole at the centre of the base plate. This isotope was chosen for its short (163-day) half-life, to obtain a high emission rate and a narrow energy distribution in the irradiation. A pair of sensors were positioned to detect alpha particles which were scattered back from the surface. There were also four sensors for any protons issued by nuclear reactions resulting from the irradiation of the surface. The instrument would be calibrated by alpha particles emitted by a ‘standard sample’ of einsteinium-254. The instrument was completed in September 1966 and, after acceptance tests, was delivered to Hughes on 18 January 1967 for use on this mission. Although the alpha­scattering technique could measure the abundances of elements with masses ranging from carbon up to iron, its ability to identify atomic weights at the heavier end of this range relied on achieving a high signal-to-noise ratio in the energy spectrum. The data was to be transmitted to Earth as a sequence of 10-bit words in real-time (although not on a continuous basis since the instrument and the camera could not use the high-gain antenna simultaneously) and stored on magnetic tape for later analysis. The elemental abundances would yield no direct information of how the elements were combined as chemical compounds, nor of how these compounds were combined as minerals – such insight would have to be inferred from assumptions about the nature of the sample.

Alpha-scattering instrument and auxiliary hardware. The sensor head is the part of the instrument which was lowered to the lunar surface. In its stowed position, the head was held on the deployment mechanism in contact with the standard sample. The digital electronics and auxiliary electronics were housed in thermal compartment ‘C’.

.J

LUNAR SURFACE

The operation of the alpha-scattering instrument’s deployment mechanism.

The operating procedure was designed to obtain, in turn: data on the performance of the sensor with the head in its stowed position; the background radiation in the lunar environment with the head partially deployed; and the composition of the lunar surface with the head fully deployed. The first stage would be done with the head in its stowed configuration, in which it could view the standard sample. About 2 hours after landing, the instrument was checked out. Power was applied at 02:50 and the system interrogated, then it was switched off at 04:40. Following the handover from Goldstone to Canberra, the camera surveyed the area where the head would deploy, both directly and by using an auxiliary mirror affixed to leg no. 1, and revealed that the head would drop onto material which had been dislodged from the wall of the crater by the vehicle’s arrival. Although mainly aggregates of fine-grained material, the sample area was fairly smooth with the largest aggregate about 3 cm in size. The instrument’s beam of alpha particles was capable of penetrating only a few microns, but the aggregates were probably typical of the subsurface, and hence representative of the mare. Ideally, the calibration would be given 6 hours, as would measuring the background. But a complication now arose.

At about 08:00 it was decided that during the second Goldstone session a static firing of the verniers should be performed, before the engines overheated as the Sun continued to rise in the sky. As this left only about 12 hours in which to deploy the alpha-scattering instrument, this had to be abbreviated. Three 20-minute readings of the standard sample proved the detector to be working satisfactorily. It was therefore

decided to remove the standard sample. To save time, the scheduled pictures were cancelled. Instead, Canberra monitored the data in real-time using an oscilloscope, and when the command was sent at 12:14 the rate fell by a factor of ten, confirming that the standard sample had swung clear to expose the aperture in the base plate of the head about 60 cm above the ground. After measuring the background of cosmic rays, solar protons and possible surface radioactivity for 170 minutes, it was decided to proceed with the deployment to obtain some sample data before the vernier firing. The head was to be lowered to the surface by a nylon cord wrapped around a geared cylinder. A pyrotechnic charge released the locking pin, and the cord unreeled under the weight of the head, lowering it in several controlled steps. As previously, the TV coverage was cancelled and real-time monitoring of the data by Madrid confirmed that the head touched down at 15:36. On the surface, the count rate sharply increased – almost to the level of the standard sample. A surface sample would require a total integration time of at least 24 hours – the longer the better, to improve the signal-to-noise ratio. About 5 hours of data had been obtained when Goldstone took over. By then it had been decided to postpone the vernier test by 24 hours, and so Goldstone spent its session photographing the surface in the immediately vicinity

of the lander as a point of reference for the study of erosional effects. The pictures showed that in settling on the slope, the base plate of the head had partially embedded itself on the downslope side. The instrument renewed integrating at 06:18 on 12 September, via Canberra. Twelve hours of data was accumulated over the next 17 hours, and then the instrument was switched off. A total of 18.3 hours of data had been obtained for the surface sample.

After the verniers were fired at 05:38 on 13 September, Goldstone took a second set of pictures. These showed that the engine blast had further embedded the base plate of the head and tilted it sufficiently to raise the near side of the plate 2 cm off the ground. About 3 hours later, the instrument was restarted and established to be still functional. Because the aperture of the plate had been displaced by more than one diameter’s distance, the new data was treated as a second sample. About 9 hours of data had been obtained by the end of that day. The maximum permitted operating temperature of the head was 55°C, and that for the electronics box was 50°C. Only 1 hour of data was obtained on 14 September and the instrument was not used at all on 15 September. But on 16 September the shadow of the high-gain antenna fell on the head and sampling was able to resume. Noon was at 01:47 on 17 September. By the time the final data was taken on 23 September the temperature of the head had fallen to -56°C, which was 16°C below its operating minimum. The next day, the Sun set. In all, 66 hours of data had been obtained for the second sample.

The three most abundant elements found by Surveyor 5 proved to be the same as those which are most prevalent in the Earth’s crust – namely (in decreasing order): oxygen, silicon and aluminium. By the process of gardening, the uppermost layer of material could be expected to be primarily fragments of what lay beneath (although there would be some material tossed in from elsewhere) and hence could reasonably be presumed to be characteristic of the bedrock at that locality. Although the retro – rocket burn was made at a much lower altitude than usual, there was little chance of solid particles of aluminium oxide in the exhaust contaminating the analysis that was later performed by the lander, especially as the sample was not undisturbed surface material.

As a chemist, Harold Urey believed the Moon to be ‘pristine’ material condensed from the solar nebula, and hence of an ultrabasic composition. The alpha-scattering data showed that the analysed material was too poor in magnesium to be ultrabasic, and too rich in iron and calcium to be an acidic rock such as granite. A good match was a basalt created by chemical fractionation of ultrabasic silicates. The similarity in the general character of the three mare sites visited by Surveyors implied that this analysis was probably representative. Superposition relationships of geological units indicated that the ‘circular maria’ were not created at the same time as the basins in which they reside. This ruled out the maria forming by fractionation of a splash of impact melt – they simply had to be volcanic flows. This was clear evidence that the Moon was thermally differentiated and argued in favour of the ‘hot Moon’ theory expounded by Gerard Kuiper.[38]

On Surveyor 5, foot pad no. 2 had two bars mounted on its vertical side in view of the TV camera, one of which was magnetic to assess the presence of material with a high magnetic susceptibility, and the other was non-magnetic to act as the ‘control’ by indicating the extent to which the lunar material would adhere to a metal bar. The magnet was strong enough to attract the ferrimagnetic mineral magnetite – which is common in igneous rocks on Earth, with different types of rock possessing differing percentages of this mineral – and the ferromagnetic metals iron, nickel and cobalt. To expose the magnet to contact, the pad needed to penetrate the surface to a depth of at least 6 cm. Serendipitously, this pad was one of those that scraped a furrow as the vehicle slid into the crater, and the magnet was in direct contact with material for most, if not all, of this time. However, in the orientation in which the lander came to rest, the magnet was in the shadow of the foot pad and could not be inspected until later in the lunar day, when it was revealed to be stained with a small quantity of magnetic material of a grain size finer than the camera’s resolution – which at that range was between 0.5 and 1 mm. After making comparative laboratory tests, it was concluded that the observations were consistent with pulverised basalt in the 40-50- micron size range, with a 10-12 per cent fraction of magnetite and no more than 1 per cent of admixed metallic iron. Because it had been believed there would be an accumulation of meteoritic iron on the surface in the form of dust, this was much less metallic iron than most people had expected.

To follow up the observation that Surveyor 3’s verniers seemed to have disturbed the surface during its ‘hot’ touchdowns, it was decided that Surveyor 5 should fire its verniers for a duration of 0.55 second at a total thrust less than its weight in lunar gravity, in order not to cause it to move. One motivation was that, like Surveyor, an Apollo lander was to cut off its engine a few feet above the surface, and a grounded Surveyor firing its verniers at low thrust would impart a comparable loading on the lunar surface to an Apollo lander in the final part of its descent – so this test would provide information that would enable the Apollo planners to estimate the effects of their lander’s arrival. The specific objective was to determine the type and degree of erosion caused by the interaction of rocket efflux with the surface material, thereby estimating its cohesivity and permeability. Three processes of erosion were possible. Viscous erosion was entrainment of particles as the gas flowed across the surface. Gas diffusion erosion was due to gas penetrating the pores in the surface material while the engine was firing, with an upward force during and after the firing causing the movement of material. Explosive cratering would occur if the pressure of the gas impinging on the surface exceeded the material’s bearing capacity, compressing and excavating it. In the lunar environment, where full expansion of the plume produced by the verniers at low thrust would be possible, explosive cratering was not expected to play a significant role. At its second bounce, Surveyor 3 appeared to have caused some viscous erosion, but because it had lifted off again there was no sudden engine shutdown and hence no opportunity to study diffused gas eruption. The aim of the Surveyor 5 experiment was therefore to investigate the effects of engine shutdown. Prior to the test, the surface in the immediate vicinity of the lander was documented in detail.

At 09:30 on 12 September the flight control system was powered up to verify its status. The temperatures of the components of the vernier propulsion system, and in particular the pre-ignition temperatures of the solenoid-operated propellant valves of the engines, were the dominant factors in deciding when to perform the test. The fact that the vehicle was inside a crater having steep interior slopes affected the heat – rejection capability of the thermally controlled compartments, because the slopes re­radiated heat onto the vehicle in a manner that would not have occurred if the lander had been standing on a level surface. Shortly after landing, vernier no. 2 significantly exceeded its pre-ignition temperature limit. It cooled down, but did so only slowly. Meanwhile, with leg no. 1 ‘exposed’ on the rim of the crater, vernier no. 1 progressively rose in temperature. Early on 13 September it was decided to make the test without further delay. At 05:38:05, some 53 hours after arrival, the verniers were ignited at minimum thrust. Despite their high temperatures, the solenoid-operated propellant valves functioned correctly. The engines fired for about 0.57 ( + 0.15) seconds, with vernier no. 1 delivering 22 pounds of thrust, no. 2 delivering 17 pounds and no. 3 delivering 26 pounds. Despite the slope, the vehicle did not slide any further down into the crater. When the shock absorbers had been commanded to lock following landing, the legs on the downslope side had not done so, and their flexure during the vernier firing increased the tilt by 0.2 degree.

Because no pictures could be taken whilst firing the engines, the analysis utilised before-and-after views of the surface. A key source of data was the surface beneath vernier no. 3, both by direct viewing and by the auxiliary mirror on leg no. 1. This suffered two types of erosion. As the engine cut off, the sudden removal of pressure on the surface evidently allowed the gas which had diffused into the surface to erupt and displace material to erode an arcuate depression some 20 cm in diameter and up to 1.3 cm deep directly under the engine, whose nozzle was 13 cm in diameter with its aperture 37 cm off the ground. There was also viscous erosion which removed a 1-cm-thick layer of material out to a radius of 60 cm and had lesser effects out to about 2 metres. Most, if not all, of the small objects in the immediate vicinity were displaced. The largest fragment known to have been displaced was 4.4 cm in size. The permeability suggested that most of the particles in the surface material were in the 2-60-micron size range – which was consistent with an analysis of the imprint left by one of Surveyor 3’s foot pads. The efflux blew away the dust which had adhered to the control strip and brackets of the magnet experiment on pad no. 2, but did not significantly alter the coating on the magnet itself. It also deposited material on the radiator on top of one of the equipment compartments. A clod must have been ejected by the diffused gas erupting from the surface at engine cutoff and followed an almost vertical trajectory, breaking apart on striking the mirrored surface. When the blast hit the vertical sides of the 2.2-kg head of the alpha-scattering instrument, this was driven about 10 cm downslope and rotated 15 degrees. The ability of the fine­grained material to adhere to a smooth vertical metal surface was indicated by a stain on the previously highly reflective head.

Sunset was at 10:56 on 24 September. Between 11:02 and 14:28 Surveyor 5 took 37 images to observe the solar corona with the solar disk just below the horizon. The longest exposures of 10 minutes showed coronal streamers out to 6 solar radii from the centre of the disk, and provided the first measurements of the brightness of the corona to a distance of 30 radii. After reporting the temperature for about 115 hours, the lander was ordered into hibernation at 06:37 on 29 September. Since Surveyor 1

had reported for 48 hours and Surveyor 3 for a mere 2 hours, this monitoring greatly increased the post-sunset data.

Surveyor 5’s camera had suffered none of the problems that impaired Surveyor 3. There was no evidence of dust or vernier efflux on the mirror, and the azimuth and elevation actions worked perfectly. It returned 18,006 pictures of excellent quality in all illuminations, and the 180 mosaics that it produced made the crater in which this vehicle landed the best documented feature on the Moon! To improve the accuracy of its pointing system for celestial observations, a new procedure was used in which the rotational matrix of the camera relative to the frame of the lander was calibrated by taking a set of pictures of fixed reference points. The alpha-scattering instrument also functioned perfectly, and provided just over 83 hours of data for a total of two samples of surface material.

After being allowed to ‘warm up’ for 147 hours after sunrise, Surveyor 5 replied promptly to a command sent at 08:07 on 15 October. As the temperature declined about 12 hours before sunset of the first lunar day, the unlocked shock absorbers had compressed, deflecting leg no. 2 by 4.4 degrees and leg no. 3 by 6.9 degrees, further increasing the tilt of the vehicle. The fact that the shock absorbers re­extended at the start of the second lunar day indicated that their relaxation at sunset was not due to a pressure leak but to a decrease in fluid volume owing to the declining temperature. The camera’s electronics had suffered from the cold during the night, but it was able to provide another 1,048 pictures. The alpha-scattering instrument was reactivated for 22 hours, but the low signal-to-noise ratio indicated that it had deteriorated and this data was rejected. On 18 October the Moon passed through the Earth’s shadow. Surveyor 5 reported thermal data but, in spite of its tilt, was unable to view Earth. After sunset on 24 October, the lander monitored the temperatures for 215 hours until it was ordered into hibernation again at 12:15 on 1 November 1967.

To date, Surveyor 1 had provided a view of an open mare plain, Surveyor 3 had inspected the interior of a medium-sized mare crater, and Surveyor 5 had landed in a very small crater on a mare plain. The main conclusion was that Mare Tranquillitatis was generally similar to the sites in Oceanus Procellarum. In fact, perhaps the most significant observation was that the three sites were so similar that it was difficult to tell them apart!

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