Category Paving the Way for Apollo 11

Explorer 1 restored national honour, but the Department of Defense was deeply concerned that the Soviet launch vehicle was so much more powerful than its own. On 7 February 1958 President Eisenhower created the Advanced Research Projects Agency headed by Roy W. Johnson, who would report directly to the Secretary of Defense. Its was to develop national goals and coordinate, but not itself conduct, the necessary research.

On 21 October 1957, three weeks after the launch of Sputnik, W. H. Pickering, since 1954 Director of the Jet Propulsion Laboratory (JPL) in Pasadena, California, had proposed that a spin-stabilised probe be launched towards the Moon, possibly as soon as June 1958.2 The purpose of this Project Red Socks would be to produce “a significant technological advance over the Soviet Union” that would enable America to “regain its stature in the eyes of the world”. The Pentagon sent the proposal to Roy Johnson, who was eager “to surpass the Soviet Union in any way possible”. The fact that the Soviets had not yet announced a lunar flight prompted him to accept the challenge of America being the first to do so. Neil H. McElroy, who had superseded Charles Wilson as Secretary of Defense just a few days before the Soviets launched Sputnik, announced on 27 March 1958 the US decision to “determine our capability of exploring space in the vicinity of the Moon, to obtain useful data concerning the Moon, and provide a close look at the Moon”. It would be undertaken as part of America’s contribution to the International Geophysical Year.

The project was named Pioneer. To pre-empt calls for it to be assigned to one or other of the services, the Air Force and Army were to work in parallel on their own contributions. The Air Force would modify its Thor missile to use the upper stages made for Vanguard. Meanwhile, the Army, just as it had used the Jupiter-C variant of the Redstone in a configuration named Juno I to launch Explorer 1, would fit its Jupiter missile with upper stages by clustering solid rockets to create the Juno II. As conceived, there would be five flight opportunities: three for the Air Force and two for the Army.

The Air Force assigned the technical direction of its part of the project, including the provision of the payload, to the Space Technology Laboratories of Redondo Beach, California. This company served as the contract manager for the Air Force’s ballistic missile program. The plan was for the launch vehicle to undertake a ‘direct ascent’ from Earth and release the probe on a trajectory that would enable it to enter orbit around the Moon. The design of the probe was finished in June 1958, just three months after the project was given the go-ahead. It comprised a pair of squat cones with their bases on a short cylindrical section. The body was 74 cm in diameter and 46 cm tall. It was to be spun at 200 rpm for stability. The mass of 38 kg included the solid-fuelled retro-rocket to brake into lunar orbit and 18 kg of scientific payload. The Advanced Research Projects Agency stipulated that the probe have an imaging system, but the scientists considered the primary payload to be their instruments to follow up the discovery by Explorer 1 of charged-particle radiation near Earth, and in this case the ‘particles and fields’ instruments were a magnetometer to measure magnetic fields in cislunar space and a micrometeoroid impact counter.

At 12:18 GMT on 17 August 1958 the Thor-Able lifted off from Pad 17A at Cape Canaveral, but the seizure of a turbopump bearing 77 seconds later brought the

flight to a premature end. Intended to be named Pioneer 1, this inauspicious start entered the history books as Pioneer 0.

Meanwhile, Lyndon Johnson began to argue for a new government agency to run a major space program – it featured in a speech he gave in January 1958 in which he ‘signalled’ his intention to seek the party’s nomination to run for the presidency in I960.

As Eisenhower’s Special Assistant for Science and Technology, James R. Killian chaired the President’s Science Advisory Committee. This reported ‘‘space’’ to be ‘‘inevitable’’, citing as reasons: (1) defence implications, (2) national prestige, and (3) opportunities for scientific research. The Committee warned that if the Pentagon was allowed to run a ‘national’ program, grandiose proposals would jeopardise the scientific work. It would be better to organise the scientific program independently of the military. The Committee recommended assigning it to a body modelled on the National Advisory Council for Aeronautics, which had been established in 1915 to coordinate aeronautical research. On 2 April 1958 Eisenhower signed an executive order calling for the National Advisory Council for Aeronautics to be subsumed into the National Aeronautics and Space Administration (NASA) in order to manage the national civilian space program. He also created the National Aeronautics and Space Board to advise on policy. The National Aeronautics and Space Act was passed by Congress on 16 July, and signed into law on 29 July. The new agency inherited all of its predecessor’s facilities: the Langley Aeronautical Laboratory at Langley Field, which had been established in Hampton, Virginia, in 1917, together with its Pilotless Aircraft Research Station at Wallops Island; the Ames Aeronautical Laboratory at Moffett Field, established in 1939 in Mountain View, California; the Lewis Flight Propulsion Laboratory, which was established in 1941 in Cleveland, Ohio; and the High-Speed Flight Station, established in 1949 at Muroc Field in the high desert of California and renamed Edwards Air Force Base in 1950.[6] Although NASA’s remit

was much broader than that of its predecessor, it did not immediately gain control of the rocketry expertise at either JPL or the Army Ballistic Missile Agency.[7]

On 8 August Thomas Keith Glennan, for the last decade President of the Case Institute of Technology in Cleveland, Ohio, was nominated as NASA Adminis­trator. Hugh Latimer Dryden, Director of the National Advisory Council for Aeronautics since 1947, was to provide continuity by serving as his deputy. Congress confirmed the appointments within days. When NASA became operational on 1 October 1958, it inherited the Pioneer project from the Advanced Research Projects Agency.

The Air Force’s second probe rose from Pad 17A at 08:32 GMT on 11 October. The Thor performed flawlessly, but a guidance error caused the second stage to shut down prematurely. The third stage took over, but was incapable of making up the 250-m/s shortfall in velocity. Pioneer 1 was successfully released, but upon attaining an altitude of 115,350 km, about one-third of the way to the Moon, it fell back and burned up in the atmosphere on 13 October. The trajectory precluded the electronic TV imager from viewing the Moon. The scientists welcomed the data provided by the magnetometer and micrometeoroid detector. This flight also had an ion chamber supplied by James van Allen, but it developed a leak and the data was difficult to interpret.

The scientists augmented the third probe with a proportional counter supplied by the University of Chicago. The Thor-Able lifted off at 07:30 GMT on 8 November 1958. The first two stages worked, but the engine of the third stage failed to ignite. The trajectory of Pioneer 2 peaked at an altitude of only 1,550 km and it fell back into the atmosphere 6.8 hours after launch, having returned no significant data.

The Army’s probe was developed by JPL, which had supplied Explorer 1. It was a cone mated at its base to a cylindrical section, stood 51 cm tall and had a maximum diameter of 24 cm. Whereas the Air Force had used an optical-electronic sensor that scanned as the probe rotated, JPL designed a camera whose film would be wet – developed, scanned optically and transmitted to Earth for reproduction by facsimile methods. The image was to be taken from a lunar altitude of 24,000 km, with the shutter being triggered when a photocell noted the presence of the Moon in its field of view. The first flight was to test this sensor. Its successor would carry the entire camera and loop around the back of the Moon to take a picture of the mysterious far-side at a resolution of 32 km. However, when studies by Explorers 3 and 4 revealed that the charged-particle radiation in the Earth’s vicinity would ‘fog’ the film of the Moon-bound probe, the Army cancelled the film camera in August 1958

in favour of the development of a lightweight slow-scan TV camera and a magnetic tape recorder to store the image for transmission.

A Juno II launched Pioneer 3 from Pad 5 at 05:45 GMT on 6 December 1958. The probe was intended to make a direct ascent, fly close to the Moon and pass into solar orbit. But the Jupiter first stage shut down prematurely, and the upper stages were unable to make up the 286-m/s shortfall in velocity. The 6-kg probe peaked at an altitude of 102,300 km, fell back and burned up 38 hours 6 minutes after launch. Nevertheless, it produced useful data. In place of the camera, it had a pair of Geiger – Mueller tubes supplied by James van Allen to measure radiation in cislunar space, and these revealed the existence of a second zone of radiation some distance above the one already identified: the intensity peaked at 5,000 km and again at 16,000 km, then diminished to the probe’s peak altitude. At van Allen’s suggestion, the imaging system was deleted from the second probe to enable his instrument to fly again. In addition, lead shielding was installed on one of the Geiger-Mueller tubes to screen out the low-energy charged particles. With the imaging cancelled, the trajectory was revised from a loop around the back of the Moon to a flyby into solar orbit – as had been intended for the first probe. After lifting off at 05:45 GMT on 3 March 1959, Pioneer 4 successfully flew by the Moon at 22:25 on 4 March. Unfortunately, the range of 60,500 km was twice that planned, with the result that the photocell test

failed – but as there was no follow-up probe available to carry the camera this was of little consequence. The Geiger-Mueller results provided further support for the hypothesis that the Earth’s magnetic field traps charged particles that originate from the Sun.5

The idea of streams of particles flowing outward from the Sun was first suggested by British astronomer Richard C. Carrington. In 1859 he made the first observation of what would later be named a solar flare. The occurrence of a geomagnetic storm the following day prompted him to suspect a connection. In the 1950s the German scientist Ludwig Biermann cited the fact that the tail of a comet always points away from the Sun irrespective of the comet’s direction of travel, as evidence that the Sun emits particles. In 1958 Eugene Parker in America postulated a supersonic flow of high-energy charged particles, primarily protons and electrons, streaming from the corona in the form of a ‘solar wind’. The presence of charged particles circulating in the Earth’s magnetic field strongly supported this hypothesis.

Assembly of the first Block III began on 1 July 1963. The Radio Corporation of America delivered the high-resolution TV subsystem on 15 August. At 366 kg, the spacecraft was about 25 kg heavier than its immediate predecessor. On 6 December W. H. Pickering suggested to Homer Newell that NASA appoint a small group for an independent assessment of Ranger 6, which had just completed its pre­acceptance testing. Newell sent some members of the Kelley Board, with William Cunningham (Program Chief) and Walter Jakobowski (Program Engineer) representing the Office of Space Sciences and Applications. After being accepted, the spacecraft left JPL by truck on 19 December and arrived at the Cape on 23 December.

As the Block III did not have a surface capsule, it could tolerate a lateral velocity component in its terminal dive, but at the expense of smearing in the final images – those of greatest interest to Apollo. The launch window for Ranger 6 was 30 January to 6 February 1964. The Moon was ‘full’ on 28 January and would be ‘last quarter’ on 5 February. The target longitude would vary with the date of launch, migrating westward with the evening terminator. The constraints on latitude were less strict, but the Apollo planners were primarily interested in the equatorial maria. The target for a launch at the start of the window was in the equatorial zone 15 degrees east of the lunar meridian, in Mare Tranquillitatis.

The countdown started in the morning darkness of 30 January, and ran smoothly to liftoff at 15:49 GMT. The Atlas delivered a flawless performance. The Agena made translunar injection as planned. The only anomaly was about 2 minutes after launch, when the spacecraft’s telemetry showed that the TV subsystem had switched on for a period of 67 seconds. When Johannesburg picked up Ranger 6, it was on its way to the Moon and gave every appearance of being healthy. After locking onto the Sun and Earth, it deployed its high-gain antenna. A small midcourse manoeuvre was

made on 31 January. “I’m cautiously optimistic,” Pickering told reporters at a press conference shortly after the manoeuvre.

As Ranger 6 neared the Moon on 2 February, it was accelerated by that body’s gravity. Radio tracking indicated that it would hit within a few kilometres of the aim point. Homer Newell and Edgar Cortright were observers in the VIP gallery of the Space Flight Operations Center. Walter Downhower, Chief of the Systems Design Section, gave a running commentary for the journalists in the auditorium. Since the spacecraft’s cruise attitude was compatible with imaging, Harris Schurmeier decided not to attempt the terminal manoeuvre lest this fail and ruin the mission. With 18 minutes to the predicted impact, the wide-angle cameras began their 5-minute warm­up, followed a few minutes later by the narrow-angle cameras. They were to switch over to full power at T-13 minutes and T-10 minutes respectively, and start to take pictures.

“Thirteen minutes to impact,’’ noted Downhower. “There is no indication of full power.’’ In due course, he followed up with, “Ten minutes to impact. We’re still awaiting transmission from the spacecraft of full-power video.’’

At this point Schurmeier told Goldstone to issue an emergency command to the spacecraft to switch on its TV system. This was done. Ranger 6 accepted the uplink and executed the command, but to no effect. When an audio representation of the downlink telemetry suddenly ceased at 09:24:32 GMT, Downhower observed, “We have our first report of impact. Still no indication of full-power video.’’ On striking the surface at a speed of 9,500 km/hour, the spacecraft vaporised. A movie camera had been mounted on a telescope in an effort to record any sign of the impact, but no flash or cloud of dust was evident.

A few hours later, Pickering set up an investigation headed by Donald Kindt, the JPL project engineer for the TV subsystem, and the next day Pickering appointed a group of section chiefs, chaired by Downhower, to monitor the investigation and to study its conclusions and recommendations. It was found that the failure occurred when the TV subsystem had briefly switched on during the ascent to orbit. Electrical arcing had destroyed the high-voltage power supply of the cameras and transmitters. The likely cause was shorting across the exposed pins of the umbilical connector of the Agena fairing which gave electrical access to the TV subsystem prior to launch. In the absence of a positive identification of the cause of the arcing, the investigation recommended (in part) that the subsystem be ‘locked out’ during the ascent to orbit, and enabled only after the spacecraft had separated from the Agena. On 11 February 1964 Pickering told Newell that Ranger 7 would have to be postponed, pending a definitive resolution of the issue.

Meanwhile, on 3 February Robert Seamans had established a NASA Board of Inquiry chaired by one of his deputies, Earl D. Hilburn. Concerned that JPL had not been able to positively identify the reason for the TV subsystem’s failure to transmit pictures, the Board reviewed the situation and on 14 February Hilburn alerted Hugh Dryden to the fact that his investigation had uncovered a number of deficiencies in the design and testing of the TV subsystem, pointing out in particular that the ‘split’ architecture was not entirely redundant. Hilburn judged JPL’s proposal to ‘lock out’ the TV subsystem during the ascent to be inadequate, and instead recommended that the system be completely redesigned – which would mean delaying the next mission by a year or more. Dryden was appalled at the prospect of such a long delay. Homer Newell feared that it would be decided simply to abandon the Ranger project. After considering the matter further, on 17 March Hilburn submitted his final report. This concluded that there must have been ‘‘two or more failures’’ in the TV subsystem; that the system was not as redundant as the designers had believed; and that testing had been inadequate – in particular, the report pointed out that the system had not been verified at full power during the pre-launch checks. In fact, JPL had decided early on in the project not to apply full power to ‘experiments’ in pre-launch checks lest a short circuit ignite the midcourse engine with a fuelled launch vehicle below. The recommendation was to redesign the TV subsystem. James Webb received the report, but took no immediate action.

On 23 March Harris Schurmeier, having seen Hilburn’s report, directed Maurice Piroumian of the Launch Vehicle Systems Section to further investigate the arcing issue. At liftoff, the plug of the ground equipment had withdrawn from the multi-pin connector and a flap had swung shut and latched to protect the connector. As this was the first flight of the TV subsystem and the connector was a new feature of the vehicle, it was possible that some aspect of its design was flawed. Tests were made over the next several months to try to determine how arcing might have taken place across these pins.

Alexander Bratenahl of the Space Sciences Division drew attention to the fact that the anomaly had coincided with the Atlas jettisoning its booster section. A study of long-range tracking camera footage showed that when this occurred the vehicle was briefly obscured by a large white cloud. On being informed by General Dynamics-

Astronautics that 180 kg of propellant drained out of the feed pipes when the lines were severed, Bratenahl speculated that suddenly dumping so much liquid into the rarefied air had produced a physical shockwave that was able to momentarily buckle the hinged flap inwards and mechanically short the pins; but an analysis showed that this was not feasible. At the end of June, Schurmeier terminated the investigation and classified the anomaly as a one-off.

Meanwhile, despite Hilburn’s report, it was decided to accept the Kindt team’s recommendation to ‘lock out’ the TV subsystem during the ascent; and on 11 May Schurmeier scheduled Ranger 7 for the window that would open on 27 July – as late as possible before priority would have to be assigned to the two Mariner missions to Mars scheduled for later in the year.

Bratenahl, however, continued to ponder the manner in which the Atlas staged. Intrigued when a more detailed analysis of the film showed flashes within the white cloud, he realised that the fluid dump had comprised both kerosene and oxygen, and that what he had naively presumed to be a simple physical shockwave was actually a detonation flash as the plume of the still-firing sustainer engine ignited the dumped propellants. The rapidly expanding spherical flashwave had washed over the vehicle, allowing plasma to penetrate the umbilical compartment to induce short circuiting. The timing was compelling: the Atlas shed its booster section at T + 140.008 seconds and the TV subsystem switched on at 140.498, coinciding with the progress of the flashwave up the length of the vehicle. On 30 July Bratenahl wrote a memo pointing out that arcing could be precluded if the cover flap were revised to form a hermetic seal. But by then Ranger 7 was in-flight to the Moon and the memo remained buried in an ‘in tray’ until after that mission.

In effect, NASA was learning by experience the many ways in which a spacecraft could be disabled. Although the chances of success increased as the failure modes were eliminated, the issue was whether Ranger would run out of spacecraft before it could deliver useful data!

GLOBAL MAPPING

In March 1967 the Surveyor/Orbiter Utilisation Committee agreed that since the first three Lunar Orbiter missions had achieved that project’s commitment in support of Apollo, the next should “perform a broad systematic photographic survey of lunar surface features in order to increase scientific knowledge of their nature, origin and processes, and to serve as a basis for selecting sites for more detailed scientific study by subsequent orbital and landing missions’’. This plan had been conceived at the Summer Study on Lunar Exploration and Science held in Falmouth, Massachusetts, between 19 and 31 July 1965, in the hope that the opportunity to undertake it would arise. The primary objective was to obtain contiguous coverage of at least 80 per cent of the near-side of the Moon at a resolution better than 100 metres. In fact, if the project’s priority had not been to reconnoitre specific areas in support of Apollo, the scientists would have started by mapping on a global basis.

To map in this way, the spacecraft would require to fly in a near-polar orbit with a perilune altitude fifty times greater than its predecessors, and as it would spend most of its time in sunlight the heat-rejection capacity of its protective base was enhanced by the installation of several hundred small quartz mirrors.

Lunar Orbiter 4 lifted off at 22:25:01 GMT on 4 May 1967. A midcourse burn of 60.8 m/s was required to deflect the trajectory away from the equatorial zone for a polar trajectory. This 53-second manoeuvre was made at 16:45 on 5 May. A further refinement was cancelled.

At 15:09 on 8 May the engine was reignited for 502 seconds to slow by 660 m/s and enter an orbit of 2,706 x 6,114 km with a period of 12 hours. The orbital plane was inclined at 85.5 degrees to the lunar equator, and oriented to enable the ground track to follow the migrating terminator to highlight topographic relief. The phase of the Moon was ‘new’ on 9 May; ‘first quarter’ would occur on 17 May and ‘full’ on 23 May. The photographic mission began at 15:46 on 11 May, while passing south to north on the eastern limb, and viewed Mare Australe and Mare Smythii. Given the

processor. It would also risk moisture in the hermetically sealed compartment condensing on the lenses. It soon became evident that the longer the exposed film spent in the loopers before being processed, the greater was the light pollution. Tests by Boeing indicated that it should be safe to repeatedly partially close and fully open the door. When this was done, the light leakage was reduced to an acceptable level. To overcome the loss of image contrast arising from dew on the lenses, the vehicle was briefly oriented at the start of each orbit to let the heat of the Sun clear the condensation. By the time that the difficulties were completely overcome, the plane of the orbit had migrated about 60 degrees in longitude. However, it proved possible to rephotograph much of this area again from apolune later in the mission.

On 20 May the drive mechanism of the film scanner began to misbehave. Clifford Nelson, the Project Manager at Langley, debated the irrevocable step of cutting the Bimat strip immediately versus continuing in the hope that all would be well. Jack McCauley argued for extending the contiguous coverage beyond the western limb to document the Orientale basin. Nelson agreed. When the scanner problem worsened on 25 May, it was decided to cut the Bimat. Although the photography had reached 100°W, the readout was at only 70°W and the challenge was to coax the remaining

processed exposures through the scanner in a manner which fooled the faulty logic unit. This task was successfully completed on 1 June.

The resolution of the mapping varied with altitude, but at perilune it was as fine as 60 metres, which was considerably better than was attainable from Earth. The results revealed hitherto unknown geological detail of the near-side polar and limb regions, and also increased to about 80 per cent the project’s coverage of the far-side. Frame M-187, taken from an altitude of 2,723 km, showed the Orientale basin in startling detail. Secondary exposures included westward-looking oblique pictures of Apollo sites. The micrometeoroid experiment had reported two hits. Manoeuvres on 5 and 8 June lowered the orbit to 77 x 3,943 km to approximate that intended for Lunar Orbiter 5 and to obtain selenodesy to assist in the planning of that mission. (Meanwhile, tracking of Lunar Orbiters 2 and 3 was showing that a low perilune would decay unless maintained by engine firings.) Contact with Lunar Orbiter 4 was lost on 17 July, and calculations indicated that its diminishing perilune would have caused it to crash at the end of October 1967. There was no ‘screening’ after this mission, as the images were for scientific research rather than Apollo landing site certification.

Although the Advanced Research Projects Agency had hoped to beat the Soviets to the vicinity of the Moon, by the time Pioneer 4 became the first American probe to do so this particular race had been won by the Soviets. Luna 1 lifted off at 16:41 GMT on 2 January 1959 on a direct ascent trajectory, and on 4 January flew by the Moon at a range of 5,500 km and passed into solar orbit. In fact, the objective was to hit the Moon, but the Soviets gave the impression that the plan had been to make a flyby. The 1.2-metre-diameter 361-kg spherical probe was not stabilised in flight. Its particles and fields instruments included a magnetometer on a 1-metre-long boom. The transmissions continued for 62 hours, by which time it was 600,000 km from Earth. It detected plasma in interplanetary space, further supporting the existence of the solar wind, but no evidence that the Moon possessed a magnetic field.

NASA EMBRACES LUNAR SCIENCE

The term ‘sky science’ was coined by JPL historian Cargill Hall to encompass the study of the Earth’s upper atmosphere and ionosphere, particles and fields in space and micrometeoroid particles. It included solar and cosmic rays, plasma dynamics and the interaction of the solar and terrestrial magnetic fields. By the late 1950s, sky scientists had a range of instruments with which to pursue their interests. These had been developed and refined initially by balloon-borne packages and, more recently, by sounding rockets. Its members were a cohesive group with impeccable academic pedigrees. By way of the National Academy of Sciences they had played key roles in

The charged particles trapped in the Earth’s magnetic field became known as the van Allen radiation belts.

selecting the experiments for the sounding rockets fired by the United States for the International Geophysical Year, and had dominated planning for the Vanguard and Explorer satellites and Pioneer space probes.[8] As a group, they were not interested in physical bodies such as the Moon other than as sources of magnetic fields, and they were certainly not interested in the geological history of the lunar surface.

In early 1958 ‘planetary scientists’ began a series of informal Lunar and Planetary Exploration Colloquia. The first meeting on 13 May 1958 was jointly sponsored by the RAND Corporation, the California Research Corporation and North American Aviation, and it was hosted by the latter in Downey, California. The three principal objectives were (1) to bring together people of common interest for the exchange of scientific and engineering information; (2) to define the scientific and engineering aspects of lunar and planetary exploration and to provide a means for their long­term appraisal; and (3) to make available, nationally, the collective opinions of a qualified group on this subject.[9]

In June 1958 the National Academy of Sciences, a private organisation chartered in 1863 to promote the advancement of science and, when requested, to advise the government on scientific matters, established the Space Science Board, chaired by Lloyd Berkner, to advise the not-yet-active NASA on space research priorities. By the end of 1958, both the President’s Science Advisory Committee and the Space Science Board had cited ‘lunar exploration’ as a worthwhile scientific objective for the new agency.

The only interest in the Moon as a body in its own right expressed by the Pioneer project started by the Advanced Research Projects Agency was to photograph its far-side. But this was not achieved by the Air Force probes, and the discoveries made by the first Army probe led to the deletion of the imaging system of the second probe in order to obtain further particles and fields observations. To be fair, this data was an important contribution to a rapidly developing field of the International Geophysical Year.

The first lunar project authorised by NASA was the Atlas-Able, which was an Air Force launch of a probe supplied by the Space Technology Laboratories. The initial idea had been to use the Atlas, which was much more powerful than the Thor, for a program that would make two launches to send probes towards Venus and then two to insert probes into lunar orbit, but Luna 1’s flyby of the Moon prompted NASA to order the planetary payloads to be replaced by lunar orbiters. The 170-kg probes were to have a spin-stabilised 1-metre-diameter spherical structure with four ‘paddle wheel’ solar arrays around the equator. They would use liquid-propellant engines to make a midcourse correction on the way to the Moon and later to enter orbit around that body. In addition to a suite of particles and fields instruments, they would carry the TV system made for the Thor-launched probes. The first probe was destroyed on 24 September 1959, when the Atlas exploded during a static test. The second lifted off at 07:26 GMT on 26 November from Pad 14 on a direct ascent trajectory, but the aerodynamic shroud protecting the probe failed 45 seconds into the flight. The third lifted off at 15:13 GMT on 25 September I960 from Pad 12, but the first of the two Able stages malfunctioned and fell into the atmosphere 17 minutes after launch. The final probe was launched at 08:40 GMT on 14 December 1960 from Pad 12 but the vehicle exploded 68 seconds later. Although in each case the plan was to enter lunar orbit, most of the 55-kg scientific payload was for particles and fields investigations; indeed, the TV system was deleted from the second pair of probes to accommodate additional radiation detectors. In fact, the Moon was to serve merely as an ‘anchor’ in space away from Earth. In no way could this series of probes be said to constitute ‘lunar exploration’. However, even as the Atlas-Able probes were being developed the situation was changing.

As Assistant Director of the Lewis Laboratory of the National Advisory Council for Aeronautics, in the summer of 1958 Abraham Silverstein played a leading role in the establishment of NASA. When the new agency set up the Office of Space Plight Development at its headquarters, Silverstein became its Director. He promptly hired Homer E. Newell as his assistant for Space Sciences. Newell had joined the Naval Research Laboratory in 1944, and the next year started to conduct research into the upper atmosphere using sounding rockets – in particular investigating the interaction between the magnetic fields of the Sun and Earth. He served as the Science Program Coordinator for the Vanguard project of the International Geophysical Year.

At NASA, Newell created a division staffed by members of the upper atmosphere research group of the Naval Research Laboratory, to organise the agency’s activities in that field. In November, he appointed Robert Jastrow to chair another division to address astronomy, cosmology and planetary sciences. As a sky scientist, Jastrow set out to learn about these topics by visiting the leading proponents.

On reaching the age of 65 in 1958, Harold Urey had retired from the University of Chicago and taken a research position at the University of California at San Diego. He was a member of the Space Science Board of the National Academy of Sciences, and in a paper entitled The Chemistry of the Moon given on 29 October 1958 at the third Lunar and Planetary Exploration Colloquia he had explained the significance of sending a probe to photograph the far-side of the Moon.

When Jastrow visited Urey in early January 1959, Urey emphasised the ‘‘unique importance’’ of the Moon for achieving an understanding of the origin of the planets. As Jastrow recalled of this meeting in his 1967 book Red Giants and White Dwarfs: ‘‘I was fascinated by [his] story, which had never been told to me before in 14 years of study and research in physics.’’ The following week, at Jastrow’s invitation, Urey gave a 2-day presentation at NASA headquarters in which he urged that probes be sent to the Moon. After deliberating, Newell concluded that NASA should initiate a program to study the Moon as an object in its own right. He formed an ad hoc Working Group on Lunar Exploration, with Jastrow in the chair and Urey as a member, to evaluate and recommend experiments which should be placed into orbit around the Moon or landed on its surface. This gave the lunar (and later planetary) scientists a presence at NASA headquarters to match that of the sky scientists.

At that time, JPL was drawing up a proposal for a program of a dozen deep-space missions, of which five would study the Moon. On 5 February 1959 Jastrow sent a contingent to JPL to pass the word that NASA was keen to undertake lunar exploration. The options were for probes to report results as they plunged to their destruction by smashing into the Moon, to enter lunar orbit, and to land instruments on the surface. JPL was authorised to initiate preliminary work. It formed a study group chaired by Albert R. Hibbs.

In fact, in 1959 JPL engineers and scientists were more interested in the challenge of sending probes to Venus and Mars than they were in studying the Moon. There were ‘windows’ for efficiently sending probes to Mars at 25-month intervals and to Venus at 18-month intervals. As the next windows were October I960 for Mars and January 1961 for Venus, the feeling was that the immediate effort should be devoted to these opportunities, rather than the Moon, which could be reached at almost any time. In 1958 JPL had proposed to NASA the development of a new upper stage for the Atlas. This Vega stage would be powered by the engine of the Viking ‘sounding rocket’, modified for ignition in the upper atmosphere. The Atlas-Vega was to be used to launch satellites. A third stage would dispatch deep-space probes. The Soviet lunar flyby in January 1959 spurred the US Congress to authorise the development of the Vega stage. On 30 April JPL sent NASA a 5-year plan of deep-space missions using the Atlas-Vega. The aim was to devote the early effort to flybys of Venus and Mars, and postpone lunar science until 1961. A rough lander would be followed up by an orbiter equipped to investigate the space environment near the Moon and to obtain high-resolution pictures to enable a site for a soft lander to be chosen. Jastrow recommended to Newell the development of a seismometer, communication system and power supply for the package that would be delivered to the lunar surface by the rough landing method. It was later decided to operate a magnetometer, gamma-ray spectrometer and X-ray fluorescence spectrometer during the approach phase. On 25 May 1959, Silverstein and Newell decided to follow the rough lander launched by the Atlas-Vega with two soft landers launched by the Atlas-Centaur, the latter using a powerful stage that was expected to enter service in 1962. In June 1959 Silverstein told JPL to cancel the Mars mission and reassign its launcher to a lunar orbiter.

On 23 July Keith Glennan, Hugh Dryden and Associate Administrator Richard E. Horner met George B. Kistiakowsky, who had succeeded James Killian as Eisenhower’s Special Assistant for Science of Technology, to discuss the objectives of the space program. Glennan warned that slippage in the development of the Vega stage made planetary flights in 1960-1961 impractical. Windows for the Moon were not only more frequent, the flight time was days rather than months. Glennan recommended that the agency focus on lunar missions in order to address the short­term objectives recently specified by the National Security Council’s policy paper, Preliminary US Policy on Outer Space? This was agreed. Several days later, Silverstein cancelled the Venus mission and directed JPL to prepare a new schedule which focused on the Moon. Meanwhile, Newell had established the Lunar and

Document NSC5814/1.

More Soviet successes 53

Planetary Programs Office and transformed Jastrow’s ad hoc Working Group on Lunar Exploration into a standing committee as the Lunar Science Group.

SUCCESS AT LAST

Ranger 7 was mated with its launch vehicle on 6 July 1964. The countdown began early in the morning of 27 July, but was scrubbed owing to a problem with the Atlas. It lifted off at 16:50 GMT on 28 July, the Atlas performed flawlessly, and the Agena achieved a circular parking orbit at 185 km then performed the translunar injection.

As to the target, Maxime Faget of the Manned Spacecraft Center had suggested investigating the crater made by its predecessor in order to use that calibrated impact to calculate the strength of the surface material, but the Moon was ‘full’ on 24 July and ‘last quarter’ on 1 August, with the result that the Sun would have set for Mare Tranquillitatis. After an analysis found that the best region would be in the vicinity of Guericke in Mare Nubium, in early July Homer Newell approved aiming for a point where the mare was crossed by bright rays from both Copernicus and Tycho. The translunar injection of 39,461 km/hour was within 6.5 km/hour of that planned. It would have caused the spacecraft to skim the leading limb of the Moon and crash on the far-side. The 50-second midcourse manoeuvre at 10:27 on 29 July established the desired trajectory. Afterwards, the terminal approach was analysed in terms of the angle of illumination of the lunar surface, the direction of the velocity vector of the spacecraft and the optical axis of the camera system, and it was decided that no terminal manoeuvre would be required for the photographic operation on 31 July.

The 3-storey Space Flight Operations Facility had been completed several months earlier. It had a main room for engineers and controllers, and nearby science support rooms for scientists to receive and analyse the incoming data. All these rooms were windowless for 24-hour use. Homer Newell, Edgar Cortright and Oran Nicks joined W. H. Pickering in the VIP gallery. Harris Schurmeier and Patrick Rygh supervised the flight control team. Gerard Kuiper’s experimenters congregated in their room. With 20 minutes remaining, George Nichols informed the auditorium that the wide – angle cameras had started to warm up. The duration of this process had been halved, and 90 seconds later he reported they were on full power, prompting a round of applause. These cameras began to take pictures at 13:08:36. The narrow-angle

cameras followed suit at 13:12:09. It was early morning at JPL, but there was a large crowd of technical staff on hand, and they applauded and cheered when Goldstone announced that both video streams were coming in. Impact was at 13:25:49, within 12 km of the aim point.1 This was the first American lunar spacecraft of any type to fully achieve its mission. Schurmeier produced several cases of champagne for the flight controllers, then led the VIPs to join the experimenters.

When Pickering, Newell and Schurmeier entered the auditorium an hour later for a press conference, they received a standing ovation. A total of 4,316 pictures were received. The first was taken at an altitude of 2,100 km and the last at about 500 metres. Goldstone converted the signal to TV format, and simultaneously stored this on magnetic tape and displayed it on a high-speed monitor. A camera whose action was synchronised with the incoming frame rate recorded each TV frame on 35-mm film – this film was then transferred to a vault. As this was going on, a technician ‘sampled’ another screen using a Polaroid camera to provide an initial evaluation of the quality of the results. The tape was replayed to make another film that was flown to the Hollywood-Burbank Airport for processing by Consolidated Film Industries. In the late afternoon local time, prints and slides were driven to JPL. While the experimenters examined the masters, the VIPs viewed copies. The press conference

The crater that Ranger 7 made was identified in Apollo 16 photography in 1972.

by the experimenters that evening was broadcast ‘live’ by the national TV networks. After Pickering introduced the team, Kuiper, the principal investigator, began the presentation: ‘‘This is a great day for science, and this is a great day for the United States. We have made progress in resolution of lunar detail not by a factor of 10, as hoped would be possible with this flight, nor by a factor of 100, which would have been already very remarkable, but by a factor of 1,000.’’ In fact, he was being a little optimistic, as the resolution of the final frame was about half a metre.

The experimenters were obliged to provide ‘instant science’, to explain what the pictures showed.

Harold Urey pointed out that he was ‘‘pleasantly surprised’’ at the amount of information that could be inferred from the pictures. The surface was cratered, right down to the limiting resolution of the final frame. The bright rays appeared to have been formed by ‘secondary’ impacts as ejecta fell back on low-energy ballistic trajectories from an energetic ‘primary’ impact. Science fiction authors had reasoned that since the Moon had no atmosphere there could be no erosion, and this had led artists to depict an extremely rugged landscape. The fact that the surface was gently undulating was clear evidence that the incessant rain of meteoritic material was a potent form of erosion. Urey introduced the term ‘gardening’ to describe the process by which impacts ‘turn over’ the material.

Kuiper said the pictures supported his belief that the mare plains were lava flows, the surface of which, having been exposed to the vacuum of space, must be ‘frothy’. This was based on laboratory experiments in which fluids of various viscosities had been exposed to vacuum. He ventured that when an astronaut walked on the surface, the experience would be similar to walking on crunchy snow. He accepted that there would be a layer of impact-generated fragmental debris, at least in some places, but thought it would be very thin, perhaps no more than a few centimetres.

Given the presence of large and obviously heavy blocks of rock, Gene Shoemaker was confident that the surface would bear the weight of a lander.

Nevertheless, Thomas Gold of Cornell University, who was not on the experiment team and not at the conference, had a theory that the maria were deep accumulations of fine dust. On seeing the Ranger 7 pictures Gold told reporters that whilst the dust would flow and tend to smooth out small-scale deformations, the rate at which it did so might be as little as a millimetre per year. As evidence of such flow, he pointed out that the rims of the older-looking craters were softer than the rims of the newer – looking ones.[22]

Although the Ranger 7 results were consistent with the ‘hot Moon’ hypothesis, in which the maria were volcanic lava flows, Urey did not give up on his ‘cold Moon’ hypothesis in which they were splashes of impact melt.

Several days later, Robert Gilruth, the Director of the Manned Spacecraft Center,

and Joseph Shea, the Apollo Spacecraft Program Manager in Houston, visited JPL to be briefed by the experimenters. Shea later told reporters that in the pictures much of the mare plain appeared “relatively benign’’. Overall, Gilruth said, an Apollo landing should be “easier than we thought’’.

On 28 August NASA hosted the Interim Scientific Results Conference, chaired by Oran Nicks. The visual highlight was a 5-minute movie of successive frames of the picture sequence showing Ranger 7’s dive. Immediately afterwards, the experiment team went to the International Astronomical Union meeting in Hamburg, Germany, and showed the movie again. The Union designated the Ranger 7 target area Mare Cognitum – the Known Sea. Shortly afterwards, as the pictures were being used to make an atlas of this region, Gerard Kuiper marvelled, “To have looked at the Moon for so many years, and then to see this. . . it’s a tremendous experience.’’ Ranger 7 gave a flood of data to a community which had been starving for years. The population statistics for primary projectiles is such that there is a small number of really large ones and increasing numbers of ever smaller ones. An airless surface exposed to such a population will gain many small craters, and progressively fewer larger ones. Given actual numbers for the populations, the cratering density (derived from counting) provides an age estimate – at least in terms of a presumption of how the population of projectiles changed over time. The simplest hypothesis is that this has remained constant, so that although the sheer number of potential projectiles has declined, their proportions have remained the same. It was evident that large caters would stand apart, but there would be a size of crater at which a given surface would be saturated – i. e. such craters would be so numerous that they would be rim to rim, and each new crater would mask an old one. This saturation would produce a sharp transition in the ‘crater curve’. Dating by this method can be done only using craters which exceed the saturation size. It was not possible to determine this telescopically, but Ranger 7’s pictures enabled the saturation size for this patch of Mare Nubium to be estimated at 300 metres. At less than this size, the surface was in a ‘steady state’. The areal coverage of Ranger 7 did not include many craters larger than 300 metres, but William Hartmann at the Lunar and Planetary Laboratory of the University of Arizona attempted the measurement and derived an age of 3.6 billion years. During the 1950s C. C. Patterson at Caltech had radiologically dated a number of meteorites, and reached the conclusion that the solar system formed 4.55 ( + 0.07) billion years ago. If the Moon formed at that time, Hartmann’s crater counting indicated that the surface of Mare Nubium was about a billion years younger.

While the scientists digested the Ranger 7 results, there was a hiatus in the project to accommodate the launches of Mariner 3 and Mariner 4 in November 1964, which also used the Atlas-Agena and hence the same pad facilities at the Cape.

On 7 March 1967, several days after Lunar Orbiter 3’s readout was curtailed, the project established a working group to develop the strategy for the final mission of the series. It was decided that if Lunar Orbiter 4 was successful in its mapping, then Lunar Orbiter 5 should undertake a scientific mission involving multiple targets. The photographic objectives were: (1) to obtain additional near-vertical, stereoscopic and westward-looking oblique frames of the eastern candidate sites for the early Apollo landings; (2) to accomplish broad survey coverage of those portions of the far-side which had been in darkness during previous missions; (3) to obtain pictures of sites of interest to the Surveyor project; (4) to reconnoitre potential targets for advanced Apollo landings – i. e. sites outside the equatorial zone; and (5) to take a close look at as many scientifically interesting sites as possible. The main criterion for a site being considered to be interesting was its perceived ‘freshness’. The pictures from Ranger and the Lunar Orbiters to date had revealed most lunar terrain to appear subdued, so it had been decided to seek terrains which had not been exposed for long enough to have been significantly weathered by the incessant rain of material from space.

The preliminary plan was put to Boeing on 21 March, and a meeting on 26 May designed an orbit that would enable the spacecraft to address the widely distributed targets without violating any of its operating constraints. It would have to fly in a near-polar orbit to gain the latitude coverage, on a track with the Sun at an elevation of between 8 and 24 degrees to highlight the topography, and the perilune at about 100 km to provide the requisite 2-metre resolution.

Lawrence Rowan had led the US Geological Survey’s participation in the Apollo site selection process, but he stood down after Lunar Orbiter 3. Donald E. Wilhelms took over this role for Lunar Orbiter 5, with its focus on advanced Apollo missions.

On 15 March Bellcomm had hired Farouk El-Baz, an Egyptian geologist with a PhD from the University of Missouri, and he undertook much of the organisational work. Whereas the sites short-listed for the early Apollo landings were on open plains with as few craters and rocks as possible, it was evident that advanced landings would be best made at sites where craters had excavated boulders. And, of course, there were mountains, rilles and features which appeared to be of volcanic origin. However, to be viable a target required a clear line of approach from the east, and this favoured interesting sites adjacent to smooth plains over which an Apollo lander could make its approach. Of course, if the landing site was several kilometres from the ‘feature’ that attracted the interest of the selectors, some form of surface transportation would require to be provided in order to enable the astronauts to reach their true objective.

On 14 June the Surveyor/Orbiter Utilisation Committee approved the overall plan. The initial target list was compiled largely from telescopic studies, but almost half of the items were revised following a review of the Lunar Orbiter 4 results. The agreed objectives were (1) to inspect 36 sites of scientific interest on the near-side, (2) to obtain additional views of five potential Apollo sites and a number of Surveyor sites, and (3) to map most of the far-side that had not previously been covered.

Lunar Orbiter 5 lifted off at 22:23:01 GMT on 1 August 1967. Its Canopus sensor had difficulty finding its target star, but locked on in time for the 26-second, 30-m/s midcourse manoeuvre at 06:00 on 3 August. A 508-second, 644-m/s insertion burn initiated at 16:48 on 5 August attained a 195 x 6,028-km orbit inclined at 85 degrees with a period of 8 hours 27 minutes. The phase of the Moon was ‘new’ on 6 August, and would be ‘full’ on 20 August. Most of the far-side pictures were to be taken in this initial orbit. The first picture was taken at 23:22 on 6 August, near apolune. An 11.4-second burn at 08:44 on 7 August lowered the perilune to 100 km. At 09:05 an impromptu picture was taken of Earth. A 153-second burn at 05:08 on 9 August lowered the apolune to 1,500 km and reduced the period to 3 hours 11 minutes. The Bimat was cut at 03:30 on 19 August, and the readout was concluded on 27 August.

The Apollo sites had been assigned 44 frame-pairs, which was about 20 per cent of the total. The sites of scientific interest on the near-side had included the rilles in Mare Serenitatis near the crater Littrow and near Sulpicius Gallus; some lava flow features in Mare Imbrium; the craters Copernicus, Dionysus, Alphonsus, Dawes and Fra Mauro; secondary craters associated with Copernicus; the Aristarchus plateau; and small domes near Gruithuisen, Tobias Mayer and Marius. All of these sites were regarded as possible targets for advanced Apollo missions.[37]

On 21 January 1968, during the extended mission, the 61-inch telescope of the University of Arizona successfully photographed the orbiter against the stars when it was at apolune. Ten days later, the spacecraft was deliberately crashed in Oceanus Procellarum.

Astronomers had inferred that either the Moon’s shape or its density distribution (or perhaps both) were irregular. The radio tracking of the Lunar Orbiters did not settle the question of the Moon’s shape, but did yield a major discovery. The early missions in near-equatorial orbits had revealed the Moon’s gravitational field on the near-side to be irregular – after allowing for the variation of velocity with altitude in an elliptical orbit, the vehicles kept speeding up and slowing down. The tracking of Lunar Orbiter 5 in its low polar orbit enabled a gravimetric map to be compiled with sufficient resolution for the ‘anomalies’ to be correlated with surface features. It was found that a vehicle was accelerated as it approached one of the ‘circular maria’ and decelerated afterwards.

Such sites included Imbrium, Crisium, Smythii, Serenitatis, Humorum, Nectaris, Humboldtianum, Orientale and Grimaldi. As the maria were low-lying rather than elevated landforms, it was apparent that they must be of a greater density than their surroundings. One early suggestion was that the ‘attractor’ was the buried body of the impactor which excavated the basin that was later filled in by mare material, but this hypothesis was rejected when it was realised that there were negative anomalies associated with basins that had not been filled in by maria. John O’Keefe argued that the attractor was the infill itself. That is, the anomalies were the due to magma from deep in the interior having erupted onto the surface – gravitational attraction falls off with the inverse square of range, and dense material on the surface would produce a significant local attraction. Negative anomalies included craters such as Copernicus, which had essentially excavated ‘holes’ in the maria. Since the positive anomalies represented concentrations of mass, they were dubbed ‘mascons’. The discovery was reported in a paper in Nature in August 1968 by Paul M. Muller and William L. Sjogren.

If the lunar crust had been able to adjust isostatically to the eruption of dense lava onto the surface there would be no anomalies today; the fact that this had not occurred was evidence that the crust was sufficiently rigid at the time the lava was erupted to support its weight. In 1968 Ralph Baldwin provided an explanation. A basin formed and was ‘dry’ for a while, during which its floor began to adjust isostatically to the removal of the crustal material. But before it could achieve equilibrium, fractures in the floor allowed lava to well up and fill in the low-lying areas. This process of infill occurred in many pulses over an extended time. Being dense, the mare pool tended to sink, thereby forming compression wrinkles in its centre and opening rilles at its periphery. When it was unable to achieve isostatic equilibrium the result was a local mascon. A further realisation (obvious in retrospect) was that the sudden removal of crustal material in the excavation of a basin would relieve the pressure on the mantle below and induce deep melting, which would in turn cause a plume to rise, lift and fracture the floor of the basin, and drive enormous volumes of low-viscosity magma to the surface. A question for further research was why most of the basins on the far-side were ‘dry’ – was the crust thicker on that side of the Moon?

WRAPPING UP

The five Lunar Orbiter missions were launched within a 12-month interval. They suffered various technical problems, but the primary objective of providing pictures in support of Apollo was achieved. Only 78 per cent of the frames were classified as ‘useful’, but a large batch of useless ones were the H frames from the first mission. Although solar flares occurred during missions, photography continued. The worst radiation dose was on 2 September 1966, but the flood of energetic protons did not fog Lunar Orbiter 2’s film. This confirmed the wisdom of using a very ‘slow’ film. The radiation detector data confirmed that the Apollo vehicles and spacesuits would protect astronauts from an average exposure to solar plasma, and indeed from short­term greater-than-average exposure. In all, the five Lunar Orbiters reported a total of 22 micrometeoroid strikes over their entire time in space. The hazard in lunar orbit proved to be about half of that in low Earth orbit. An additional benefit to Apollo from the extended missions of the Lunar Orbiters, was the experience gained by the Manned Space Flight Network in tracking vehicles in lunar orbit. If the existence of mascons had not been discovered prior to the first Apollo mission venturing out to the Moon, the astronauts would have found their orbit varying in an unpredictable (and alarming) manner. This was the value of making a thorough reconnaissance!

Boeing had sufficient parts to assemble a sixth spacecraft, and even before Lunar Orbiter 5 was launched the Office of Space Sciences and Applications considered an additional mission. On 5 July 1967 Lee Scherer explained that this could perform a survey of the far-side at a resolution similar to that provided by Lunar Orbiter 4 of the near-side. One suggestion was that it should carry the gamma-ray spectrometer built for Ranger, in order to make a preliminary map the composition of the surface. On 14 July Homer Newell wrote to Robert Seamans putting the case for launching a sixth mission in November. Seamans refused, in part because it would not directly contribute to Apollo – which was not capable of landing on the far-side.

The scientists had hoped to develop Lunar Orbiter Block II to conduct a series of missions utilising a variety of sensors. In late 1964 the Office of Space Sciences and Applications compiled an experiment list: a gamma-ray spectrometer to survey the abundances of radioactive isotopes on the lunar surface; and infrared experiment to map the surface temperatures; a photometry/colorimetry experiment to determine the variation in the photometric function and colour of the surface material; a radiometer to measure surface thermal gradients; an X-ray fluorescence spectro­meter to survey the relative abundances of nickel and iron on the surface; a solar plasma experiment to measure the spatial and temporal variation in flux and energy distribution of low-energy protons and electrons; a magnetometer to determine whether the Moon had a magnetic field; an instrument to test for a low-density ionospheric plasma; and using the transmitter for a bi-static radar experiment to study the roughness and dielectric properties of the surface. But without the leverage of the Office of Manned Space Flight this proposal failed to attract funding.

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