Category Paving the Way for Apollo 11

The Apollo commitment

THE ROLE OF MAN IN SPACE

In 1958 NASA was assigned the task of exploring space for scientific purposes, but no immediate objectives were specified. The National Aeronautics and Space Act left the agency to set its own goals.

Accordingly, within days Keith Glennan established the Space Task Group at the Langley Research Center to manage Project Mercury, which was to launch a man into orbit as soon as possible. This was not exactly what President Eisenhower had had in mind, but he saw it as a one-off venture. At a packed press conference on 9 April 1959, Glennan introduced the seven military test pilots who had been chosen to be astronauts.[16]

On 25-26 May 1959 Harry J. Goett of the Ames Research Center chaired the first meeting of the Research Steering Committee on Manned Space Flight, which was to consider possible man-in-space objectives for the coming decade. These included:

• launching and operating a small orbital laboratory

• assembling a large permanent space station

• flying circumlunar and lunar orbital missions

• making a lunar landing.

George M. Low, who represented headquarters, was firmly of the view that only a manned lunar landing provided a reasonable ultimate objective – it was an ‘end’, not just an intermediate step along a path. Whilst less demanding, the alternatives were not as definitive – either a man landed on the Moon or he did not; there was no way

to redefine it as something simpler and assert this to be equivalent.[17] It was therefore decided to set the long-range goal of achieving a manned lunar landing in the 1970s. This would gave a framework in which to define a series of intermediate objectives for the 1960s.

On 5 July 1960 the House Committee on Science and Astronautics said, “NASA’s 10-year program is a good program as far as it goes, but it does not go far enough.’’ In other words, it urged NASA to accelerate its long-range plan. In the committee’s view, “A high priority program should be undertaken to place a manned expedition on the Moon in this decade. A firm plan with this goal in view should be drawn up and submitted to the Congress by NASA.’’ But it warned that this plan, “should be completely integrated with other goals, to minimise total costs. The modular concept deserves close study. Particular attention should be paid immediately to long lead­time phases of such a program.’’

Eisenhower responded by asking his science advisor, James R. Killian, whether a manned lunar landing represented a scientific venture which could be justified in the same manner as launching a satellite for the International Geophysical Year. Killian convened a meeting of scientists, and their report, written by Donald F. Hornig of Princeton University, was dismissive: “At the present time, man-in-space cannot be justified on purely scientific grounds.’’ The rationale for sending men to the Moon seemed to be “emotional compulsion and national aspirations’’. Hence Eisenhower refused funding for manned space flight beyond Project Mercury, and in particular the proposal for a three-man Apollo spacecraft. He had no problem with the agency using the new Saturn booster to launch heavy satellites, but he withdrew funding for the upper stages intended to enable this to launch a manned spacecraft. Nevertheless, on 12-13 September the Space Task Group held a briefing for potential bidders to develop the Apollo spacecraft with the Moon as the ultimate objective, and released the formal request for proposals. On 17 October, Low told Abe Silverstein, Director of the Office of Space Flight Programs, that he was going to set up a committee to study the circumlunar objective in greater detail, to ensure that the Apollo spacecraft would be capable of supporting a landing mission.[18] On 25 October NASA issued contracts to three companies to provide feasibility studies for the Apollo spacecraft.

The national election of November 1960 was won by John F. Kennedy. He was inaugurated on 20 January 1961. In giving his final budget speech prior to leaving office, Eisenhower said on 18 January 1961 that Congress would have to determine “whether there are any vital scientific reasons for extending manned space flight beyond Mercury’’. In a campaign statement, Kennedy had said: “We’re in a strategic space race with the Russians, and we are losing. If a man orbits Earth this year, his name will be Ivan. If the Soviets control space they can control the Earth, as in past centuries the nation that controlled the seas has dominated the continents. We

cannot afford to run second in this vital race. To insure peace and freedom we must be first. Space is our great New Frontier.” The contrast with Eisenhower’s view was stark. Kennedy also had an appreciation of national prestige, which in the Cold War meant a comparison with the achievements of the Soviet Union. The issue of prestige had been dismissed by Eisenhower.

During the transitional period, Kennedy assigned a number of task forces to draw up policy recommendations. The Committee on Space was chaired by Jerome B. Wiesner, who served on the President’s Science Advisory Committee during James Killian’s chairmanship and was to become Kennedy’s Special Assistant for Science and Technology. The Committee on Space in turn set up the Panel on Man-in-Space, composed largely of scientists, and its report on 18 November I960 criticised the program envisaged by NASA.4 Although it agreed the need for large launch vehicles and urged an emphasis on space science and applications, it criticised “the popular belief that man in space is the most important aim of our non-military space effort’’. Wiesner recommended that Project Mercury be ended as soon as it had achieved its objective of placing a man in orbit, and that there should be no follow-on. However, Kennedy had made Vice President Lyndon B. Johnson chairman of the National Aeronautics and Space Council, and Johnson was in favour of expanding the space program.

And when the Space Science Board of the National Academy of Sciences issued a position paper on Man’s Role in the National Space Program on 27 March 1961 it said, “scientific exploration of the Moon and planets should be clearly stated as the ultimate objective of the US space program for the foreseeable future. This objective should be promptly adopted as the official goal of the United States space program and clearly announced, discussed and supported.’’ It also advised that whilst it was “not now possible to decide whether man will be able to accompany expeditions to the Moon and planets’’, NASA should proceed with its planning “on the premise that man will be included’’. Taking the broader view, it said that such exploration would be “potentially the greatest inspirational venture of the century and one in which the entire world can share; inherent here are great and fundamental philosophical and spiritual values which find a response in man’s questing spirit’’. Clearly this national scientific body, established to advise NASA on policy, was taking a much broader view than the sky scientists involved in space research at that time.

PLANS AND SCHEDULES

In view of the reason for his predecessor’s resignation, George Mueller ordered a review of Apollo, and this confirmed the project to be in trouble. On 29 October 1963 Mueller informed the Manned Space Flight Management Council that the only way to recover time would be to reduce the number of development flights. The plan drawn up by the Marshall Space Flight Center in March 1962 envisaged a series of launches of the Saturn V in which the stages were tested in sequence – with only the first stage being ‘live’ on the first test scheduled for late 1965. The aim was to ‘man rate’ this vehicle by the summer of 1967, then use it to launch at least six manned missions in Earth and lunar orbit prior to attempting a lunar landing in late 1968 or early 1969. Mueller proposed to reduce this research and development phase by ‘all up’ testing in which each launch would use only ‘live’ stages, modules, systems and spacecraft. Wernher von Braun and Robert Gilruth objected, but Mueller had the support of James Webb.

In addition, a recent study by Bellcomm had recommended reassigning the early tests of the Apollo Block I spacecraft from the Saturn I to the Saturn IB, and so on 30 October Mueller cancelled the four manned test flights with the Saturn I that had been set for 1965. The development of the Saturn IB for manned missions would be accelerated and the ‘all up’ testing strategy employed in this case too. After coming to terms with this, Gilruth asked von Braun whether the Saturn IB could lift both the CSM and LEM, and was advised that it would be feasible only if their weights were controlled. At the White Sands Missile Range in New Mexico on 7 November the Apollo launch escape system successfully performed its first ‘pad abort’ test. On 18 November 1963 Mueller directed that if the LEM was not ready in time, the early Saturn IB flights would fly without it. But it must be phased into the test program as quickly as possible. Furthermore, Mueller directed that two successful development flights for each of the Saturn IB and Saturn V would serve to ‘man rate’ them. The schedule that he issued on 31 December 1963 listed the first Saturn IB test in early 1966 and the first manned mission later that year. The first Saturn V test was to be in the first quarter of 1967, with the first manned flight (hopefully on the third launch) later that year. Mueller then established the Apollo Program Office with himself as Director, and hired Samuel C. Phillips, who had managed the development of the Air Force’s Minuteman missile, as Deputy Director.

On 17 September 1962 NASA had announced the nine men of its second intake of astronauts.1 At the same time, Deke Slayton was appointed Coordinator of Astronaut Activities, reporting to Robert Gilruth.[41] [42] In addition to the administrative tasks of the Astronaut Office, which Slayton managed in the manner of a military unit, he was responsible for making flight crew assignments. On 18 October 1963 the fourteen men of the third astronaut group were announced.[43] By now James Elms was Deputy Director of the Manned Spacecraft Center, and on 5 November 1963 Gilruth inserted Assistant Directors under Elms in order to strengthen the local management of flight operations: Chris Kraft was redesignated as Assistant Director for Flight Operations, Deke Slayton as Assistant Director for Flight Crew Operations and Maxime Faget as Assistant Director for Engineering and Development. In addition, Merritt Preston was assigned to manage Manned Spacecraft Center operations in Florida. However, on 17 January 1964 Elms resigned, and two days later George Low was reassigned from headquarters to replace him.

President Kennedy flew to Cape Canaveral on 16 November 1963 to inspect the ‘moonport’ which NASA was beginning to construct on nearby Merritt Island. He was shown models to illustrate the enormous size of the Saturn V. On 22 November he was assassinated in Dallas, Texas, and later that day Lyndon Johnson was sworn in as his successor. In a TV address on 28 November Johnson directed that Cape Canaveral be renamed Cape Kennedy, and the next day he signed an executive order in which the Launch Operations Center was renamed the John F. Kennedy Space Center.[44]

On 15 January 1964 the Manned Spacecraft Center proposed to Apollo Spacecraft Program Manager Joseph Shea that two of the Saturn IB ‘all up’

Group 1, seated (left to right): Captain Leroy Gordon Cooper Jr, Captain Virgil Ivan ‘Gus’ Grissom, Lieutenant Malcolm Scott Carpenter, Lieutenant Commander Walter Marty Schirra Jr, Lieutenant Colonel John Herschel Glenn Jr, Lieutenant Commander Alan Bartlett Shepard Jr and Captain Donald Kent ‘Deke’ Slayton. Group 2, standing (left to right): Captain Edward Higgins White II, Captain James Alton McDivitt, Lieutenant Commander John Watts Young, Elliot McKay See Jr, Lieutenant Charles ‘Pete’ Conrad Jr, Major Frank Frederick Borman II, Neil Alden Armstrong, Captain Thomas Patten Stafford and Lieutenant Commander James Arthur Lovell Jr.

Group 3, seated (left to right): Major Edwin Eugene ‘Buzz’ Aldrin Jr, Captain William Alison Anders, Captain Charles Arthur Bassett II, Lieutenant Alan LaVern Bean, Lieutenant Eugene Andrew Cernan and Lieutenant Roger Bruce Chaffee; standing (left to right): Captain Michael Collins, Ronnie Walter Cunningham, Captain Donn Fulton Eisele, Captain Theodore Cordy Freeman, Lieutenant Commander Richard Francis Gordon Jr, Russell Louis ‘Rusty’ Schweickart, Captain David Randolph Scott and Captain Clifton Curtis Williams.

During a visit to Cape Canaveral on 16 November 1963 John F. Kennedy is briefed by George E. Mueller on the ‘mobile launcher’ concept for Apollo. To Kennedy’s right are (in turn) James E. Webb, Robert C. Seamans, Kurt H. Debus and George M. Low. To his left are Hugh L. Dryden, Wernher von Braun, General Leighton I. Davis and Florida Senator George A. Smathers.

development flights be used to test the heat shield of the Apollo command module, because this would enable the early tests of the Saturn V to be classified as ‘demonstration’ rather than ‘development’ for the spacecraft.[45] On 7 February Grumman was directed to provide two LEM test articles (LTA) and eleven flightworthy LEMs, the first three of which were to be capable of either manned or unmanned operation. On 23 March George Mueller ordered that if the first two unmanned CSM test flights were successful, the next mission would be a long- duration manned flight, after which there would be two tests of the LEM, the first

Table 15.1: Outline schedule for Apollo drawn up in November 1964

Mission

Payload

Launch Date

AS-201

CSM-009 (unmanned)

1965

AS-202

CSM-011 (unmanned)

1966

AS-203

No spacecraft (S-IVB development flight)

Jul 1966

AS-204

CSM-012 (manned)

Oct 1966

AS-205

CSM-014 (manned)

Jan 1967

AS-206

LEM-1 (unmanned)

Apr 1967

AS-207

CSM-101 (manned) and LEM-2

Jul 1967

one unmanned and the second together with a manned CSM – so long as the Saturn IB proved capable of lifting both vehicles together. In November 1964 Joseph Shea, George Mueller and Sam Phillips drew up an outline schedule for testing Apollo hardware in advance of the introduction of the Saturn V, but it remained uncertain whether the weights of the two spacecraft were sufficiently constrained for them to be lifted together by a Saturn IB for the joint mission. On 16 December Shea directed that the Block I manned missions must use low orbits from which the spacecraft could use its reaction control system thrusters to de-orbit itself in the event of the failure of the service propulsion system; and in the event of these too failing, the orbit must decay naturally and result in re-entry within an acceptable duration.6

On 31 August 1964 Lead Flight Director Chris Kraft appointed John D. Hodge, Eugene F. Kranz and Glynn S. Lunney to alternate in round-the-clock flight operations. On 24 December Everett E. Christensen was made Director of Mission Operations, a position which effectively superseded Deputy Associate Administrator for Manned Space Flight Operations – vacant since the resignation of Walter Williams in April. At the same time, two posts of Mission Director were also created, with the intention that the appointees would run alternate missions. In addition, activities at the Cape were consolidated, with Kurt H. Debus being made Director of Launch Operations and Merritt Preston, who had been managing the Manned Spacecraft Center’s activities at the Cape, becoming his Deputy.

Joseph Shea, Chris Kraft and Deke Slayton were briefed on 18 January 1965 by the Mission Planning and Analysis Division of the Manned Spacecraft Center about the Saturn IB and early Saturn V flights. On 21 January, in response to a question by Sam Phillips, Shea said the current estimate was that the Saturn IB would be able to insert 35,500 pounds into a circular orbit at 105 nautical miles. This, however, was less than the combined ‘control weights’ of the CSM and LEM by 870 pounds, and both vehicles were currently above their control weights. Shea argued that in view of the difficulty in constraining the weights, the best solution would be to find a way of increasing the launcher’s capacity by 1,000 pounds. In fact, the Saturn IB had a

This precaution was reputedly a headquarters response to the situation depicted by Martin Caidin in his recent novel Marooned.

‘control payload’ which was the specified minimum mass that it was to be capable of placing into the reference orbit, and a ‘design goal’ which exceeded this. On 23 February Phillips told Shea that the Marshall Space Flight Center would endeavour to increase the payload by 1,000 pounds. The development version of the cluster of eight H-1 engines had yielded 1.3 million pounds of thrust, but the fifth flight of the Saturn I had introduced an upgraded cluster that finally achieved its specification of 1.5 million pounds of thrust. In August 1963 Rocketdyne had proposed an upgrade for 1.6 million pounds of thrust, and on 8 November of that year NASA had ordered this be done. By 23 April 1965 the improved engine had completed its qualification testing. On 12 May Huntsville reported that it would be possible to uprate the engine by an additional 5,000 pounds of thrust, to raise the total to 1.64 million pounds. But the rocket engineers were fighting a losing battle, as by then both spacecraft had put on even more weight.

On 13 January 1965 Shea had established the Configuration Control Board, with himself in the chair. This was to rule on all proposals for engineering changes to the spacecraft. On 10 May he faced a dilemma: the ‘all up’ testing regime required that all spacecraft incorporate a full set of subsystems, but it had been proposed that the landing radars be omitted from LEM-1 and LEM-2 on the basis that a radar would serve no function on an Earth orbital mission. Omitting the radar on these early test flights would save money and assist in the effort to trim the weight of the vehicle at this critical juncture, but doing so would establish the precedent for a series of one – of-a-kind spacecraft, each tailored to achieving specific development objectives and with none demonstrating all of the systems in conjunction. Furthermore, by relieving the pressure on the effort to trim weight in the short term, such compromises might jeopardise it in the long term. On 27 May the Manned Spacecraft Center reaffirmed that LEM-1 must test the radar. But on 25 June ASPO Assistant Manager Harry L. Reynolds warned Owen E. Maynard, Chief of the Systems Engineering Division at the Manned Spacecraft Center, that it was ‘‘becoming increasingly clear that we are going to have a difficult job keeping the LEM weight below the control weight’’. On 6 July Grumman requested to be allowed to deliver the early LEMs without some subsystems installed, but Shea insisted they must all leave the factory in a fully functional condition. At that time, LEM-1 was to be delivered to the Kennedy Space Center in November 1966, with the next five vehicles following in 1967, but it was becoming increasingly evident that this schedule would be difficult to achieve. On 13 September 1965 Shea established the Weight Control Board to enable subsystem managers to meet on a weekly basis and report progress in controlling the weights of the two spacecraft, and when appropriate to create ad hoc task forces to chase up specific issues and report back.

Meanwhile, on 17 February 1965 Shea clarified for North American Aviation the Block I schedule. CSM-009 and CSM-011 were to be configured for unmanned use and fly as AS-201 and AS-202 to test the heat shield. CSM-012 and CSM-014 were to be delivered for manned missions, but be capable of being adapted at the Cape for unmanned flight. The decision for CSM-012 would be made 6 months ahead of the scheduled launch date for AS-204, and if flown unmanned this would be done either to gain additional data on the spacecraft’s characteristics or to provide more time for

the Marshall Space Flight Center to prepare AS-203 to obtain data on the behaviour of the S-IVB stage in space. North American Aviation was told that CSM-017 and CSM-020, assigned to the early tests of the Saturn V, need not be capable of manned use. The first manned Block II would be CSM-101, which was to fly in conjunction with LEM-2. On 22 March Glynn Lunney, Chief of the Flight Dynamics Branch of the Flight Control Division in Houston, was appointed Assistant Flight Director for AS-201 and AS-202. On 25 June Carroll H. Bolender was made Deputy Director of Mission Operations at the Office of Manned Space Flight, and his first task was to plan these two preliminary missions.

On 10 August 1965 ASPO named LEM-1 to AS-206, LEM-2 to AS-207, LEM-3 to AS-503, LEM-4 to AS-504, LEM-5 to AS-505 and LEM-6 to AS-506. Of the six test articles, LTA-1 was kept by Grumman at Bethpage to resolve issues during the initial fabrication, assembly and checkout procedures, LTA-2 went to the Marshall Space Flight Center for launch vibration tests, LTA-3 and LTA-5 were to be used to assess the structural effects of engine firing, LTA-8 went to the Manned Spacecraft Center for thermal-vacuum environmental testing, and LTA-10 went to the North American Aviation factory in Tulsa, Oklahoma, for fit-checks with the SLA, which was being manufactured there. To cut costs, in July Grumman had been directed to delete LTA – 4 (intended for vibration tests), the ascent stage of LTA-5 and the two flight test articles and instead to refurbish two of the test articles for flight once their ground testing role was complete. The company said it would refurbish LTA-10 and LTA-2 in case they were needed for the first two Saturn V test flights. The first three LEMs were to incorporate development flight instrumentation so as to record the dynamic environment at launch. A key requirement was that the differences between LEM-3 and LEM-4 be minimised and that all subsequent production vehicles be identical.

On 21 October 1965 Sam Phillips slipped AS-201 to January 1966 and AS-202 to June 1966 to accommodate the revised delivery dates for CSM-009 and CSM-011, but otherwise preserved the outline schedule which had been drawn up in November 1964. On 2 December 1965 Hugh Dryden died of cancer.[46] Robert Seamans replaced him as Deputy Administrator on 21 December. He retained the duties of Associate Administrator until Homer Newell gained this post in August 1967, and was in turn superseded as Associate Administrator for Space Sciences and Applications by John E. Naugle.

Meanwhile, an operational step toward the chosen Apollo ‘mission mode’ was achieved when Gemini 6 rendezvoused with Gemini 7 on 15 December 1965. The straightforward manner in which this was done raised the prospect of undertaking the manned test of the LEM without reducing the weights of the CSM and LEM to enable the Saturn IB to lift them both together. On 28 January 1966 Sam Phillips asked ASPO to assess the impact, including the effects on ground support equipment and mission control, of a dual AS-207/208 mission as early as the scheduled date for

AS-207, which was the Saturn IB that was nominally to have sent them into orbit together. The idea was for near-simultaneous launches of AS-207 with CSM-101 and AS-208 with LEM-2 to facilitate a rendezvous and docking, at which point the mission would unfold as originally planned. On 2 February John P. Mayer, Chief of the Mission Planning and Analysis Division at the Manned Spacecraft Center, informed Chris Kraft, Assistant Director for Flight Operations, that the main constraint would be programming the Real-Time Computer Complex in Houston to plan and support such a mission – in which case the decision on whether it was to be attempted must be taken very soon. Mayer also urged that if the IBM staff who worked on the Gemini 6/7 rendezvous could be spared, they should be reassigned to help to plan the new dual mission. On 4 February John Hodge, Chief of the Flight Control Division, noted that some of the operational issues associated with near­simultaneous launches would be obviated if the interval were extended. On 24 February Mayer’s assistant, Howard W. Tindall, recommended that the CSM be launched first and the LEM follow it either 24 hours later or at a recurring daily window. On 1 March Joseph Shea endorsed the concept. On 8 March Sam Phillips directed the Manned Spacecraft Center, Marshall Space Flight Center and Kennedy Space Center to endeavour to launch the dual mission a month later than intended for AS-207 on the previous schedule.

REPEAT PERFORMANCE

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

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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.

WHENCE THE MOON?

A number of theories have been suggested over the years to explain the origin of the Moon, which is unique as a planetary satellite in that it has the greatest mass as a fraction of its primary, with the result that its orbital angular momentum exceeds the rotational momentum of the planet.

Whence the Moon? 31

In 1796 the French mathematician Pierre Simon de Laplace, inspired by the rings of Saturn, proposed that the solar system formed by the gravitational collapse of an enormous cloud of gas which was in a state of rotation. The conservation of angular momentum would have required the rate of rotation to increase, causing material to be shed every so often and making a series of concentric rings in a single plane. The central mass eventually formed the Sun, which was sufficiently hot to become self­luminous. As each ring of material condensed to become a planet, the process would have shed local rings which in turn formed satellites – in Earth’s case, the Moon. In Laplace’s time, the solar system appeared to comprise the entire celestial realm apart from the stars, and therefore his nebular hypothesis was the first serious attempt at cosmogony. Although accepted for many years, mathematical analysis later showed that it would not work as Laplace had imagined.

In 1878 George H. Darwin posited that the Earth and Moon formed together. The rapidly rotating body of hot liquid became an ellipsoid, rotating about its minor axis in an unstable equilibrium with two forces acting upon it: its own natural period of vibration, and tides raised by the Sun’s gravity. Once the forces achieved resonance, the shape became progressively more like a dumbbell until one day the narrow ‘neck’ collapsed, leaving two masses, the larger becoming Earth and the smaller the Moon. This fission hypothesis was popular for some time, but was later discarded owing to mathematical deficiencies, not least because a rapidly spinning ball of fluid would tend to divide into two more or less comparable masses, whereas the Moon has only 1/81st the mass of Earth.

In The Planets: Their Origin and Development, which was based on lectures he gave at Yale University and published in 1952, Harold Urey discussed the Moon in relation to the solar system as a whole. He argued that the Moon condensed from the solar nebula independently, and was later captured by Earth. Furthermore, he said it had never undergone thermal differentiation and that, consequently, its surface had no volcanic structures. This was dubbed the ‘cold Moon’ hypothesis.

In 1954 Gerard Kuiper proposed that the Earth and Moon formed simulta­neously in a common envelope within the solar nebula, and soon became gravitationally bound. He said the preponderance of craters was due to the Moon sweeping up all the debris in the neighbourhood. As the Moon’s mass is relatively large as a ratio of its primary, this made the Earth and its Moon essentially a ‘double planet’.

Nevertheless, as the space age dawned the origin of the Moon and the state of its interior were contested.

APOLLO SITE SHORT-LIST

When the Apollo Site Selection Board met on 30 March 1967 the Apollo officials announced that whilst they would seek further Lunar Orbiter data, that from the first three missions satisfied “the minimal requirements of the Apollo program for site survey for the first Apollo landing”. By now nine mare sites in the Apollo zone were deemed to be suitable as ‘prime sites’ for the early Apollo landings: one in Mare Foecunditatis, two in Mare Tranquillitatis, one in Sinus Medii and five in Oceanus Procellarum. These were designated ‘Set B’.4 For each such site, the US Geological Survey produced geological maps at scales of 1:25,000 and 1:100,000 to supplement the 1:1,000,000 regional maps. It was noticed that the sites on the eastern maria had high densities of large but shallow craters, and the sites on the western maria were generally flatter but rougher in detail. The astronomers had long ago noted that there was a difference in spectral hue, with the eastern maria being bluish and the western maria reddish.

On 15 December 1967 the Apollo Site Selection Board convened at the Manned Spacecraft Center to refine the target list for the first Apollo landing. All of the sites of Set B were acceptable in terms of their approach routes. However, as a landing in Mare Foecunditatis would not allow sufficient time after rounding the eastern limb for radio tracking to verify the lander’s trajectory prior to powered descent, this site was discarded. Five sites were short-listed as ‘Set C’. It was decided that three of these must be selected as options for the first landing mission, forming a prime site and two backups spaced in lunar longitude to accommodate successive 2-day delays in launch. It was recognised that the need for the crew to familiarise themselves with three sites would increase their training burden, but there would be no impact on the surface activities because the first landing was not to include a mapped traverse. In east to west sequence, the five sites were II-P-2, II-P-6, II-P-8, III-P-11 and II-P-13. Whilst it was clear that the prime site would be in the eastern hemisphere, the meeting did not specify whether it should be II-P-2 or II-P-6.

On 26 September 1968 the Set C ellipses were ‘stretched’ from 5.3 x 7.9 km to 5.0 x 15.0 km to allow for uncertainties in the Moon’s gravitational field that might cause a lander to come in either ‘short’ or ‘long’ of the designated aim point. On 3 June 1969 the Set C sites were renamed Apollo Landing Site (ALS) 1 through 5 respectively.

They were I-P-1 in Mare Foecunditatis, II-P-2 and II-P-6 in Mare Tranquillitatis, II-P-8 in Sinus Medii, and II-P-11, III-P-9, III-P-11, III-P-12 and II-P-13 in Oceanus Procellarum.