Category Paving the Way for Apollo 11

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.