Category Paving the Way for Apollo 11

As Silverstein at NASA headquarters had arranged things, JPL reported to him for the Ranger spacecraft, deep-space tracking and control, in-flight operations and data processing. The procurement of the launch vehicle would be managed by the Office of Launch Vehicle Programs. This was directed by Donald R. Ostrander, who, as a Major General in the Air Force assigned to NASA, was well qualified to liaise with the military and its contractors. Ostrander delegated the task of procuring Agena and Centaur stages to Wernher von Braun in Huntsville. By dividing the spacecraft (JPL and the Office of Space Flight Programs) from the launchers (Huntsville and the Office of Launch Vehicle Programs), this arrangement provided considerable scope for confusion and conflict.

On 29 December 1959 Associate Administrator Richard Horner created the Space Exploration Program Council with himself in the chair. It was to seek to improve the management of space flight projects, and to reconcile the inevitable differences that would arise between headquarters and the centres managing individual projects. Its members were Abe Silverstein, Donald Ostrander, and Wernher von Braun (launch vehicles), Harry Goett of the Goddard Space Flight Center (satellites in Earth orbit) and W. H. Pickering (deep-space missions). At its inaugural meeting on 10 February I960 it discussed an internal review sent to Ostrander on 15 January that warned of potential difficulties in the procurement of the Agena B, and how this might affect Ranger. It was decided that Silverstein’s technical assistant, William A. Fleming, should chair a steering committee. This Agena B Coordination Board was formed on 19 February, and drew its membership from von Braun’s team in Huntsville (which was in the process of transferring to NASA, and in July would become the Marshall Space Flight Center), the Goddard Space Flight Center and JPL. The Council also decided that a NASA project engineer should be assigned to the plant in Sunnyvale, California, where the Missile and Space Division of Lockheed manufactured the Agena. In Huntsville, Hans Heuter was made head the Light and Medium Vehicle Office, which was to manage procurement of the Agena B and Centaur stages, and Friedrich Duerr became its Agena Systems Manager. However, whilst von Braun’s team would plan and supervise procurement, the fact that the Air Force did not want an independent line of authority leading to its supplier meant the Ballistic Missile Division would implement procurement from the contractor. The Air Force Space Systems Division in Inglewood, California, of which the Ballistic Missile Division was a part, was commanded by Major General Osmond J. Ritland. In April 1960 Major John E. Albert was assigned to assist NASA in procuring the Agena B, which meant he had responsibility for all Air Force technical matters relating to Ranger. He would work with Duerr in Huntsville for the launch vehicle and Burke at JPL for the interface between the Agena and the Ranger spacecraft. Duerr sent Robert Pace to Sunnyvale as the resident project engineer. Lockheed appointed Harold T. Luskin to work with Albert and Pace. The final contract, which was agreed only on 6 February 1961, was for nine Agena B vehicles. In terms of a production line that was making Agenas for several Air Force programs, this was a small order – and it was treated as such by the company until NASA complained. As Huntsville was

responsible for NASA’s launch operations, in addition to procuring the Atlas-Agena В it had to obtain ground support equipment and the systems required to track the vehicle in its ascent to orbit.[12]

In March I960, as the Army Ballistic Missile Agency was being incorporated into NASA, Donald Ostrander’s Office of Launch Vehicle Programs created the Launch Operations Directorate to manage NASA launches in Florida. In essence it was an expansion of the Army’s Missile Firing Laboratory, and being based at Huntsville it answered to von Braun. Kurt H. Debus, Director of Launch Operations, was keenly aware that he was responsible for activities he could not actually control, because in reality NASA was merely a tenant at the Cape and as such was limited to monitoring the preparation and launch of the vehicles by the 6555th Aerospace Test Wing. His counterpart on the Air Force side was Major General Leighton I. Davis. That same month, the Office of Space Flight Programs set up its own office at the Cape to coordinate the on-site activities of the flight project teams.

On 1 September I960 Richard Horner resigned from NASA. He was succeeded as Associate Administrator by Robert C. Seamans. Noting criticism that the Agena В Coordination Board had proved ineffective at resolving disputes, Seamans ordered a review. On 19 October, Albert Siepert of the Office of Business Administration submitted A NASA Structure for Project Management. On 19 January 1961, the day before he left office with the other Eisenhower political appointees, Keith Glennan endorsed the recommendations. In this new scheme, Silverstein’s office would set budgets for flight projects, establish objectives and review progress. The Marshall Space Flight Center, reporting to Ostrander’s office, would provide launch vehicles and launch operations in support of a project manager at a field centre. In the event of disputes, Seamans would personally decide the issue. The Agena В Coordination Board was dissolved. This revision gave JPL direct authority and responsibility for Ranger. NASA named Burke as its Ranger Project Manager, thereby giving him greater authority than he had when he was simply JPL’s Ranger Spacecraft Project Manager.

When James E. Webb became NASA Administrator in February 1961, he argued that although the Air Force might procure the rockets for NASA, the agency should be wholly responsible for preparing and launching them. On 17 July the Air Force conceded that in due course NASA could install its own launch groups to supersede the 6555th Aerospace Test Wing.[13]

The three successful Rangers satisfied the objective set for the Block III series in terms of supporting Apollo. The maria proved to be cratered on all scales, but with a smoothly undulating surface of generally shallow slopes. And the presence of large blocks of rock lying on the surface suggested sufficient bearing strength to support a lander. In addition, radio tracking had enabled the estimate of the mass of the Moon to be much improved. It also established the axis that is aligned towards Earth to be about 1 km longer, with the centre of mass being offset several kilometres from the geometric centre in a direction away from Earth.

When some 200 scientists gathered at the Goddard Space Flight Center in April 1965 to discuss the combined results of the Ranger project, Harold Urey and Gerard Kuiper still disagreed about whether the Moon was thermally differentiated. Thomas Gold insightfully noted that the pictures represented a mirror in which each person saw evidence to support his own hypothesis.

One lesson of Ranger was that lunar geological units were so severely blurred by impact ‘tilling’ at the fine scale that in undertaking photogeological mapping it was better to use a medium scale of 1:1,000,000, as was used by the Air Force Chart and Information Center in St Louis for its Lunar Astronautical Chart series.

Ranger had provided a close look at several sites, but what was required next was for an orbiter to provide a broader view at better-than-telescopic resolution and for a soft-lander to provide ‘ground truth’.

With four mare sites in the Apollo zone visited, distributed more or less uniformly in longitude from 23°E to 43°W, it was possible to draw some generalisations.

Surveyor 1 inspected a level plain in an ancient 100-km-diameter crater known as the Flamsteed Ring that had been ‘inundated’ in some way by Oceanus Procellarum; Surveyor 3 landed in a subdued medium-sized crater situated on the open plain of Oceanus Procellarum; Surveyor 5 provided a detailed inspection of a very small irregularly shaped crater in Mare Tranquillitatis; and Surveyor 6 inspected the plain of Sinus Medii within sight of a mare ridge. All four sites were very similar in terms of topography, and in terms of the structure of the surface layer and its mechanical, thermal and electrical properties; and the surfaces at the latter two sites were similar in terms of elemental composition and the content of magnetic material. ft seemed unlikely that terrestrial sites situated thousands of kilometres apart and selected in a manner similar to that by which the lunar targets were chosen would prove to be so similar.

At all sites, the undisturbed fine-grained surface material was lighter toned than the subsurface. This difference was as much as one-third for Surveyors 1, 3 and 6, but less for Surveyor 5. The fact that the albedo of the subsurface was the same at all sites meant the exceptional case of Surveyor 5 was due to the surface material being less bright. Observations of the erosion of the fine-grained surficial material by the vernier efflux during the ‘hop’ performed by Surveyor 6 and of the tracks left by the

fragments that were rolled across the surface, indicated that the bright surficial layer was limited to the uppermost few millimetres. The existence of such a well-defined ‘contact’ in a nominally undisturbed surface at four widely spaced sites on the maria implied the action of a process (or combination of processes) which had the effect of increasing the albedo of the material at the surface, for otherwise such a fine layer would be destroyed by the gardening of meteoritic bombardment. Furthermore, the fact that the material at all depths below the surface was uniformly dark, as opposed to there being a gradation in albedo, indicated that whenever an impact mixed the lightened surficial material into the subsurface, it became dark. Perhaps the process which altered exposed material had not had long to act on the material in the small fresh-looking crater in which Surveyor 5 landed. At all sites, the bright rounded rock fragments visible on the surface had textures featuring knobs and pits, whereas these were absent on the highly angular faceted blocks. This hinted that the process which produced the rounding – undoubtedly the relentless meteoroid bombardment – also gave rise to the ‘worn’ texture.

At all sites the fine-grained material was cohesive, and whilst the surficial layer was mildly compressible, its bearing strength increased rapidly with depth. But there was no observable variation in grain size with depth – evidently it was simply a case of the porosity decreasing with depth. It was estimated that the bulk density of the upper centimetre of undisturbed material was in the range 0.7 to 1.2 g/cm3, and that by a depth of several centimetres this had increased to 1.6 g/cm3.

The size-frequency distribution of small craters at all sites matched that expected for a steady-state population resulting from the protracted bombardment of primary meteoroids and the fall of ejecta from such impacts. Furthermore, this distribution was independent of individual differences in the mare surfaces and of the population of craters larger than several hundred metres in size.

The thickness of the fragmental debris layer on the mare plains was clearly related to the abundance of craters with diameters ranging between 1 and 10 km. In the part of Mare Tranquillitatis where Surveyor 5 landed the size-frequency distribution of such craters was twice that of the Oceanus Procellarum inundation of the Flamsteed Ring where Surveyor 1 landed, and the minimum size of the blocky rimmed craters at those sites indicated that the fragmental debris layer was several times thicker in Mare Tranquillitatis than in Oceanus Procellarum. Of all the maria, Sinus Medii had one of the highest size-frequency distributions of craters with diameters larger than several hundred metres, and the fragmental debris layer on the plain near Surveyor 6 was thicker to match. The fact that the cratering indicated the surface of Sinus Medii to be older than the other maria was evidence that the older the surface the thicker its fragmental debris layer. The size distribution of the material on the surface was also related to the thickness of the fragmental debris layer. When the mare lava flow was fresh and its rocky surface was exposed, small impacts were able to excavate it. As a layer of fragmental debris accumulated, it took larger and larger impacts to reach the substrate. Over time, the loose fragments were both reduced in size and increased in number. The trend was therefore towards a thickening layer of ever finer fragments. That is, the regolith ‘matured’.

The implication for Apollo was that an older surface would be a safer landing site.

When viewed from afar, an older surface might look rough by virtue of having large craters with blocky rims, but since only large craters would be able to excavate the substrate this meant that the plethora of small craters (which must be present) would not possess blocky rims. The task for the site selectors was therefore to measure the smallest craters with blocky rims on a mare surface to measure the thickness of the fragmental debris layer, and then seek a flat patch of open ground situated between such craters where it was likely to be relatively free of blocks.

CLASSICAL PHILOSOPHERS

Greek astronomy began with Thales, who was born shortly before 600 BC and lived in Miletus, a city of Ionia, which was a state on the western coast of what is now Turkey. As a philosopher he is regarded as one of the Seven Sages of Greece, and is considered to be the ‘father of science’. He set the seasons of the year and divided the year into 365 days. He also predicted a solar eclipse that occurred in 585 BC. It had been believed that the Moon was self-luminous, but he suggested that it shone by reflecting sunlight. Anaximander, a student of Thales, went to Italy in 518 BC. He opined that Earth floated in space – the prevailing view was that it was in some way supported on pillars through with the Sun passed during the night.

Pythagoras was born about 575 BC on Samos, an island off the coast of Ionia that was a crossroads between Asia, Africa and Europe. In his youth he reputedly visited Thales. Pythagoras considered the Moon to mark a fundamental boundary, in that it and everything ‘above’ was ‘perfect’, while Earth was subject to change and thus to decay. When critics argued that the markings on the face of the Moon indicated that it, too, was imperfect, it was suggested that the Moon was a mirror and the markings it displayed were really on Earth.

Around 450 BC Anaxagoras of Athens decided that Thales was correct in saying the Moon shone by reflecting sunlight. He realised that the Moon was spherical, and used this to explain its monthly cycle of ‘phases’. A generation later, Democritus, who travelled widely in ancient Greece, reasoned that the Moon was a world in its own right with a rugged surface, and he speculated that it might be an abode of life.

In the early fourth century BC, Plato, a student of Socrates, founded the Academy in Athens as the first institution of higher learning. Eudoxus briefly studied under Plato. After learning astronomy, he devised an explanation for the manner in which the constellations on view change with the seasons. He imagined the stars to be on a sphere that was centred on Earth, and the Sun to be on a slightly smaller concentric sphere made of transparent crystal which allowed the stars to be seen through it. The solar sphere turned around Earth on a daily basis, as did that with

the stars, but there was a slight differential in their rates that took a year to complete. Aristotle, another student of Plato, seized on this idea of ‘crystal spheres’ by proposing that there was one for each object that had an independent motion in the sky, and that their rotation was due to the action of angels. Although Eudoxus had envisaged crystal spheres only as a means of exposition, Aristotle believed them to be real and his views would come to dominate natural philosophy.

The points of light in the sky which move against the background of stars were called ‘planets’, meaning ‘wanderers’. In the third century BC Aristarchus of Samos suggested that the Sun might be located at the centre of the ‘planetary system’, with Earth being a sphere, rotating daily on its axis, and travelling around the Sun on an annual basis; but the idea attracted little support and was soon forgotten. Aristarchus also reasoned that because the Moon occults the Sun at a solar eclipse, the Sun must be further away – in fact, much further away. He also inferred that the stars must be considerably further away than the Sun, because they show no parallax when viewed from opposite sides of Earth’s path around the Sun. However, his reasoning on these matters was ignored. He interpreted a lunar eclipse as the Moon’s passage through the shadow cast by Earth, and made a fair estimate of the distance between the Moon and Earth in relation to the diameter of Earth. His contemporary, Eratosthenes of Cyrene, made the first realistic estimate of the Earth’s true diameter, thereby providing a scale to Aristarchus’s calculations.

At the end of the third century BC, Apollonius of Perga on the southern coast of modern Turkey was a Greek geometer with an interest in conic sections, and it was he who introduced the names to the ellipse, parabola and hyperbola. Although it was inconceivable that celestial objects should be less than perfect, detailed observations had shown their motions to be anomalous. Apollonius devised a geometrical scheme in which a celestial body would trace a small circle whose central point travelled in a circle around Earth; the small circle was termed the ‘epicycle’, and its centre was the ‘deferent’. This allowed the Moon to appear at times to lead and at other times to trail its perfect position. Furthermore, this accounted for why the size of the Moon appeared to vary in a cyclical manner. And of course, because the scheme involved only circles it restored purity.

Hipparchus, a Greek living in Alexandria, Egypt, in the second century BC, was the greatest of the classical Greek astronomers. His legacy was a star catalogue, but he also used a solar eclipse to estimate the relative distances of the Sun and Moon to a greater accuracy than had Aristarchus. He reasoned that although the Moon must orbit the Earth’s centre, the location of observers on the Earth’s surface provided the basis for parallax. On scrutinising records of eclipses that had been observed from both Alexandria and Nicaea, which lie on the same meridian but are some distance apart, he used the extents to which the Moon had masked the Sun’s disk to calculate the distance to the Moon relative to the Earth’s diameter. In fact, he calculated the distance of the Moon to within a few thousand kilometres and its diameter to within several hundred kilometres – although obviously he didn’t use kilometres as a unit of measure. Hipparchus also used measurements of the Moon’s orbit to assess Apollonius’s suggestion of deferents and epicycles, found it satisfactory, and provided measurements of the sizes of the epicycles.

In 80 AD the Greek historian Plutarch, who became a citizen of Rome, wrote the philosophical treatise Faces in Orbe Lunare in which he discussed the motion of the Moon across the sky, and how it maintained one face towards Earth as it turned on its axis. He thought that it was a world similar to Earth, and suggested it might be inhabited. A generation later, this latter point led the Greek storyteller Lucien of Samosata to write Vera Historia describing how a whirlwind lifted a ship from the sea and deposited it onto the Moon, where there was a battle in progress between the local inhabitants and invaders from the Sun. The story was a satire on the wars raged by the Greeks.

Claudius Ptolemaeus was born around 85 AD, probably in Alexandria, which was at that time under Hellenistic control. The Royal Library of Alexandria was founded at the start of the third century BC. Over the centuries it had built up an unrivalled catalogue, because whenever a ship docked in the harbour the authorities ordered copies made of any books that were on board. Ptolemy (as he is known in English) used his own observations of the stars and the resources of the library to refine the work of Hipparchus, and wrote up his findings in a book of his own. The library was sacked several times and eventually destroyed, but when this occurred is disputed. Although Ptolemy’s book was lost, an Arabic translation survived as the Almagest. He accepted Earth to be centrally located, celestial objects to be travelling in circles, Aristotle’s belief in the reality of concentric celestial spheres, and also Hipparchus’s endorsement of the deferents and epicycles as the reason for the anomalous motions. The Church of Rome accepted Aristotle’s philosophy, and so, despite its contrived nature, the ‘Ptolemaic system’ – as it became known, even although Ptolemy had not invented it – survived for over 1,000 years.

In March 1958 Major General John B. Medaris of the Army Ballistic Missile Agency requested JPL to compute the payload that could be dispatched into deep space by a configuration of the Jupiter launch vehicle that would later be named the Juno IV.

The result prompted W. H. Pickering to ask Daniel Schneiderman, head of a payload design group that included James Burke, to study preliminary concepts for a spacecraft capable of a flyby of Mars. They outlined a З-axis stabilised vehicle that would face flat arrays of transducer cells to the Sun for power and maintain a high – gain antenna pointing at Earth. It was decided the craft would require a small rocket engine to correct a modest trajectory error inherited from the launcher. These points were accepted by a review in June. When the Juno IV was cancelled in October, JPL proposed that the Atlas-Vega be developed with the capability to dispatch 265 kg to the Moon or 200 kg to either Venus or Mars. To reduce the development costs and improve reliability, JPL decided that all deep-space missions should use a common ‘bus’ to provide not only the main structure but also electrical power, command and control functions, communications, З-axis attitude control and midcourse correc­tion. Peripheral structures would be held against the bus for launch, and be deployed in space.

When in July 1959 NASA told JPL to focus on the Moon in the short-term, the laboratory decided to stick with the bus concept so as to exploit this development to prepare for planetary missions in 1962. This made Ranger much more sophisticated than strictly required for a flight to impact on the Moon. Although recognised to be a high-risk venture in the short term, this strategy was expected to pay off in the long term. The preliminary outline was submitted to NASA on 1 August. The scientific payload for Ranger was to be specified by the Office of Space Flight Programs, and Silverstein delegated this task to Homer Newell. By the autumn, Newell’s working groups and JPL had agreed on a rough priority for experiments to be carried on six Vega-launched lunar flights. The first two spacecraft, designated Block I, would not be sent towards the Moon, but would test the basic spacecraft systems in the deep – space environment by using Earth orbits with apogees significantly beyond the orbit of the Moon. The spacecraft engineers had argued for not carrying any experiments, in order to increase the mass available to provide redundancy in key systems until their reliability could be determined, but Newell insisted that such orbits provided an excellent opportunity to study particles and fields in space. The Block II spacecraft would be devoted exclusively to studying the Moon. However, then the Vega was cancelled and Silverstein directed JPL to prepare a five-flight series for the Atlas – Agena B. On 28 December 1959 Pickering proposed that the bus it had planned for the Vega-launched spacecraft be revised to suit the Agena B, and NASA concurred. Once again, the first two missions would be test flights carrying particles and fields payloads.

Daniel Schneiderman issued the design concept for Ranger on 1 February 1960. Reflecting the fact that the frame of the third stage of the Atlas-Vega was to have been hexagonal, the bus was a hexagonal disk 1.5 metres in diameter. The systems would be contained in rectangular boxes on its sides. For the test flights, a ‘tower’ was to be mounted on top of the hexagon with a platform to support the experiments and a fixed low-gain antenna on the tip. It would not, however, have the midcourse engine. On the underside would be a wider hexagonal frame scaled to mate with the Agena, and this would have a pair of solar panels that would be held against the bus for launch and hinged out in space, and a 1.2-metre-diameter high-gain antenna dish

ELECTRONICS

BAY VI

Details of the Block I Ranger spacecraft.

that would be stowed directly beneath the bus for launch and gimballed out in space. The Systems Division at JPL completed the design of the Block I in May I960, and Burke froze it. The design was then split up in terms of functions and the individual tasks assigned to the various divisions. These missions were to provide data on flight performance in space that could not be gained by testing on the ground – at least not with the facilities then in existence.

The Block II spacecraft would have the same hexagonal frame, solar panels and high-gain antenna, but include the midcourse engine and a structure to accommodate a rough landing package. The operational flights were to activate a TV camera and a gamma-ray spectrometer during the terminal approach and,

OMNI ANTENNA

MAGNETOMETER

ION CHAMBER

LYMAN ALPHA TELESCOPE

COSMIC DUST DETECTOR

ELECTROSTATIC ANALYZER
PITCH & ROLL JETS

VELA HOTEL EXPERIMENT

EARTH SENSOR

ANTENNA GEAR BOX

YAW JETS

ELECTROSTATIC

ANALYZER

FRICTION EXPERIMENT

SUN SENSOR

SOLAR PANEL

HIGH-GAIN ANTENNA

ELECTOSTATIC ANALYZER

The configuration of the Block I Ranger spacecraft.

shortly prior to impact, eject the landing package that contained a single-axis seismometer. Conceived at a time when America’s only experience in deep space was the Pioneer probes, this was an extremely ambitious design.

JPL contracted out the development of the surface package. It was an experiment, and as such represented a distraction to the spacecraft engineers since it would not directly contribute to the exploitation of the bus for planetary missions. In February I960 JPL issued three competitive contracts. It received the proposals on 15 April, and on 25 April selected the one submitted by the Aeronutronic Division of the Ford Motor Company. The design mounted the spherical capsule above a solid-propellant
retro-rocket (later revised to a liquid engine) and at an appropriate height above the Moon a pulse-type radar altimeter dish antenna would command separation from the bus. At burnout, the retro-rocket would be jettisoned. A crushable shell of balsa would protect the fibreglass capsule from the impact, and the scientific payload would be immersed in high-viscosity fluid. Once the capsule had come to rest, the offset centre of mass of the payload would allow it to adopt an upright orientation within the fluid. Including its support structure, the surface package subsystem had a mass budget of 136 kg. The propulsion was contracted to the Hercules Powder Company, and the altimeter to the Ryan Aeronautical Company. The contract for the battery powered single-axis seismometer had been placed in July 1959 with Frank Press at the Seismological Laboratory at Caltech and Maurice Ewing at the Lamont-Doherty Geological Observatory at Columbia University. It was a magnet suspended in a coil by a spring, and restrained radially so that it would respond only to motion parallel to its axis. It weighed 3.6 kg, and by floating it in a viscous fluid inside the ‘survival shell’ of the 44-kg capsule it could withstand the deceleration force of 3,000 times Earth gravity on hitting the ground at 60 m/s. Aeronutronic’s contract called for the first surface subsystem to be delivered by September 1961. The company formed a Lunar Systems group headed by Frank G. Denison specifically for the project, and he was to report to Burke at JPL.

The Ranger spacecraft would require 100 to 150 watts of power when fully active, which was to be generated by a pair of solar panels. Attitude determination would be by photocells and gyroscopes. Attitude control would be by thrusters squirting cold nitrogen gas. After being released by the Agena, the spacecraft would deploy its solar panels and orient itself to face its longitudinal axis towards the Sun for power generation, then aim its high-gain antenna at Earth. Later, it would have to adopt the attitude required for the midcourse manoeuvre, then re-establish its cruise attitude. This burn would be made by a hydrazine monopropellant rocket engine. Because the engine was installed beneath the hexagonal framework, it could not be fired until the high-gain antenna had swung clear. The autopilot would hold the vehicle’s attitude during the manoeuvre using vanes in the rocket exhaust. For the Block I, a simple ‘alarm clock’ would prompt a sequencer to perform the various actions of deploying the solar panels, locking onto the Sun and deploying the high – gain antenna. For the more demanding Block II, a ‘computer’ would drive the sequencer – but the attitude for the midcourse manoeuvre and the magnitude of the burn would be specified by Earth. The low-gain antenna was for use after the craft was released by the Agena and before it adopted cruise attitude, and later for the midcourse manoeuvre during which the high-gain antenna would not attempt to hold its ‘lock’ on Earth. The high-gain antenna would send telemetry while cruising, and scientific data (including TV) during the terminal approach. On the Block II, a boom would swing the low-gain antenna away from its initial position above the surface package shortly prior to the terminal approach – by which time the high-gain antenna would have locked on – in order to clear the way for the separation of the surface package, which would occur when the radar altimeter indicated that the slant range had reduced to 24 km.

The Vega-launched Ranger had been allocated a launch mass of 364 kg in order to match the predicted performance of the three-stage Atlas-Vega. NASA’s decision to switch to the Agena B for deep-space missions was based on the expectation that the performance of the Atlas-Agena B would almost match this. But whereas the Air Force’s Agena payloads operated in Earth orbit, NASA wanted the Agena to remain in ‘parking orbit’ only briefly before reigniting its engine to head for deep space. On 11 July I960 Lockheed announced a cut in its estimate of the Agena B’s capability in this role by 34 kg to 330 kg. This did not affect the 307-kg Block I, but the design of the Block II had started out as 364 kg – including the 136-kg surface package subsystem. The issue of the Block II mass remained in doubt through the remainder of the year, with the Agena B Coordinating Board failing to achieve a resolution. Meanwhile, James Burke told Harris Schurmeier’s Space Division to do all it could to lighten the Block II, short of deleting equipment. But by the end of 1960 the mass of the Block II design still exceeded 330 kg. Worse, Aeronutronic warned that their subsystem may well exceed its mass limit. On 14 December the Space Technology Laboratories were asked to re-evaluate the capacity of the Agena B by combining Lockheed’s data for launch to translunar injection and JPL’s data for the remainder of the mission. The calculation would take several months to perform.

In early 1961, awaiting this report, Burke faced a dilemma. To match the overall project timescale of 36 months specified by Silverstein, the schedule called for the test

flights in July and October 1961, and the lunar flights in January, April and July 1962. To achieve this, he would have to commit the Block II to a mass heavier than the currently projected capability of the Atlas-Agena B. Alternatively, he could let the schedule slip until he had a definitive mass figure. Part of NASA’s rationale for Ranger was to steal a march on the Soviets. However, on 12 February 1961 they dispatched a 454-kg spacecraft on an interplanetary trajectory towards Venus. It was З-axis stabilised, had solar panels and a high-gain antenna, and utilised the parking orbit technique rather than direct ascent – all of which JPL had hoped Ranger would pioneer.[14] Under pressure, on 16 February Burke told Schurmeier that the Systems Division “must begin removing items’’ from the Block II in order to lighten it. He also told Aeronutronic that if their subsystem exceeded its allotted mass it would not be carried.[15] The deletions that Burke specified would cut the mass of the Block II to ЗЗ2 kg, which was still marginally greater than Lockheed’s revised estimate. The design of the Block II was frozen in April 1961 at this mass. Ironically, in late May 1961 the Space Technology Laboratories reported that the Agena B would be able to place З82 kg on the Block II trajectory, which was even more than the Vega figure! Rather than introduce a further delay by trying to exploit this situation, Burke let the development proceed. If the actual capability of the Atlas-Agena B in this role had been known when JPL drew up the specifications for the Block II in early 1960, a significant degree of redundancy would have been built into the spacecraft. In fact, the mass-saving exercise had deleted those redundant systems that existed, making it even more technologically risky than initially envisaged. In effect, the design of the Block II was predicated on the assumption that all of its systems would work, which in turn put it at risk of loss if a single system were to fail.

In January 1958 Joshua Lederberg, a geneticist at the University of Wisconsin, warned the National Academy of Sciences that if a spacecraft transported terrestrial microbes to another body of the solar system, this would preclude a later experiment to determine whether life independently originated there. The International Council of Scientific Unions established an ad hoc committee to consider the issue, and then urged all nations to sterilise their spacecraft. On 15 October 1959, with the approval of Keith Glennan, Abe Silverstein directed that any NASA “payloads which might impact a celestial body must be sterilised before launching’’.

The case for such a precaution on planetary missions was self-evident, because at that time the seasonal variation of the dark areas on Mars was widely believed to be due to vegetation, and although the atmosphere of Venus was permanently cloudy, one idea was that conditions on the surface might resemble the carboniferous period of Earth’s past. As regards the Moon, one theory (not widely held, but impossible to falsify with the data available) posited there might be water ice at a shallow depth beneath the surface, and this environment might be conducive to microbial life that would not be able to survive on the surface. It was therefore decided that spacecraft destined for the Moon must be sterilised.

JPL soon decided that NASA’s recommendation of immersing the spacecraft in lethal gaseous ethylene oxide would have to be augmented by ‘dry heat’ treatment. In April I960 George L. Hobby, a research biologist in the Space Sciences Division, was assigned to work with James Burke to draw up sterilisation procedures for the Block II spacecraft. The first task was to define the term ‘sterile’ – which basically was an issue of deciding how efficient the process had to be. Ideally all components and subassemblies would be subjected to a temperature of 125°C for a period of 24 hours, but this proved impractical owing to its deleterious effects on the electronics, and one by one waivers were issued to protect particularly sensitive items. Once the spacecraft had been fully assembled (using the sterilised subassemblies) it would be thoroughly cleaned with alcohol. It would be transported to the Cape in a controlled environment. After the spacecraft had been installed on its launcher and passed its final checks, the aerodynamic shroud would be sealed and gaseous ethylene oxide pumped in for a time to complete the sterilisation process. On 26 June 1961 Robert Seamans approved these procedures.

As a matter of policy, the choice of experiments for space missions was made by Homer Newell’s Space Sciences Steering Committee. Abe Silverstein retained the final approval. Experimenters therefore submitted proposals to NASA headquarters, and, if successful, worked with a field centre to implement the experiment. In the case of JPL, this was the Space Sciences Division. While James Burke concentrated on the spacecraft, the launch vehicle and its support systems, Albert Hibbs prepared the scientific experiments to be carried. The particles and fields experiments did not require much development because they were by now being flown widely, but a lot of care was required to integrate them into the spacecraft. The final list of scientific experiments for the Block I was a solar plasma detector, a magnetometer, a trapped – radiation detector, an ion chamber, a cosmic-ray telescope, a Lyman-alpha detector, a micrometeoroid detector and the Vela Hotel package. The Vela Hotel provided by the Atomic Energy Commission was a late addition which Silverstein approved on 29 June 1960. A network of satellites were to carry X-ray and gamma-ray sensors to detect above-ground nuclear tests. But if the Sun issued microsecond-duration bursts of X-rays, then these might cause the satellites to report false detections. The highly elliptical orbits of the Ranger test flights would have their apogees above the van Allen belts, and the 3-axis-stabilised spacecraft would enable the Vela Hotel sensor to ‘stare’ at the Sun to determine whether it produced such emissions.

The in-flight experiments for Block II consisted of a TV camera and a gamma-ray spectrometer. The TV camera was to be activated by command from Earth when the spacecraft was within 4,000 km of the Moon. The Astro-Electronic Division of the Radio Corporation of America in Hightstown, New Jersey, which had supplied the TV system for the Tiros meteorological satellites, was hired to provide a slow-scan vidicon imaging tube and related electronics. The Space Sciences Division at JPL built the optical element, which was essentially a telescope with a focal length of 1

metre and an aperture ratio of f/6. The image scanned off the vidicon tube would have 200 ‘lines’. The plan was for the camera to provide about 100 pictures during the terminal approach, with the transmission terminating when the separation of the surface package perturbed the attitude of the bus and the high-gain antenna lost its lock. In excellent ‘seeing’, the best telescopes had a lunar surface resolution of about 300 metres. An image taken by this camera at an altitude of 50 km was expected to provide a resolution 100 times better. On 16 October 1961 Newell’s Space Sciences Steering Committee named Gerard Kuiper, Gene Shoemaker and Harold Urey as the experimenters who would receive and interpret the pictures transmitted by this camera.6

The gamma-ray spectrometer experiment was led by James R. Arnold, a chemist at the University of California at San Diego. Its scintillation counter was to detect the natural radioactivity originating from the uppermost layer of the lunar surface. In particular, it would detect gamma rays issued by the decay of uranium, thorium and potassium. If these large-ion lithophile elements were widespread, this would imply that the interior of the Moon had undergone significant thermal differentia­tion. The instrument was mounted on an 18-metre-long boom that would be deployed after the midcourse manoeuvre in order to determine the ‘background’ from the spacecraft itself and from celestial sources. It would operate until the high- gain antenna lost its lock. In fact though, such a study would be better done from a polar orbit in order to obtain global coverage.

On 27 March 1961 Walter E. Brown, head of the Data Automation Systems Group of JPL’s Space Sciences Division, pointed out that if the signal from the radar altimeter were to be telemetered to Earth, the radar echo could be correlated with the imagery to gain insight into the density, conductivity and thickness of the material at the surface – in particular its dustiness. This information would be of use to the team planning the soft lander. On 28 April, after it was established that this modification would not adversely affect operations, James Burke authorised the modification. The Space Sciences Steering Committee in Washington duly designated Brown as the investigator for the radar reflectivity experiment.

THE SECOND GENERATION

After the success of Luna 3, the Soviets developed a new spacecraft designed to deliver a capsule to the lunar surface using the rough landing technique. Luna 4 was launched at 08:16 GMT on 2 April 1962, and after cruising in parking orbit it set off for the Moon. After an ineffective midcourse manoeuvre, the 1,422-kg vehicle made a flyby at 13:25 on 5 April at a range of 8,500 km and passed into solar orbit. After several further failures, the Soviet Union conducted a deliberate flyby mission.

FILLING THE GAP

Zond 3 lifted off at 14:38 GMT on 18 July 1965. After parking orbit, it was sent on a trajectory to pass by the illuminated leading limb of the Moon. Imaging began at 01:24 on 20 July at an altitude of 11,570 km and ended at 02:32 at 9,960 km, with the closest point of approach at 9,220 km. It had been intended to launch this probe in 1964 as a companion to Zond 2 on a mission to Mars, but it was held back. The pictures were not transmitted until the narrow-beam of the high-gain antenna was able to lock onto Earth, which occurred on 29 July at a range of 2.2 million km. The objective of this flight was to test deep-space communications for an interplanetary mission, and the Moon was merely a convenient photographic target. It transmitted two dozen pictures of Oceanus Procellarum and around onto the far-side to view the area which had not been visible to Luna 3.

The results indicated that although there were few maria on the far-side, and those were small, there were multiple-ring structures which for some reason had not been flooded by lava. The Orientale basin was seen in its entirety for the first time, since even at the most favourable libration barely half of it was observable in reprojected telescopic pictures. In addition to the concentric rings, there were radial patterns in evidence. There was a small patch of mare material inside the central ring, and small patches between the rings, but otherwise the entire structure was ‘on display’ in its

magnificence. It boggled the mind that Earth must once have been disfigured by such structures!

The successful mission of Surveyor 6 completed all requirements established for the project in direct support of Apollo landing site selection. Nevertheless, the Office of Space Sciences and Applications decided to fly the final mission. The target was hotly contested. It was decided that the most important objective was to investigate a site as different as possible from the maria already visited, and preferably a site that offered the greatest likelihood of being different in terms of geology and chemistry. Harold Urey had proposed that the Moon was ‘pristine’ material condensed from the solar nebula and therefore must have an ultrabasic composition, but several lines of evidence implied that the maria were volcanic lava of a basaltic composition. H. H. Nininger proposed in 1936 that ‘tektites’ were ejected by impacts on the Moon and had acquired their aerodynamic shape and a glassy skin during hypersonic entry into the Earth’s atmosphere. But their acidic composition posed a problem. The viscosity of an acidic magma such as granite is several orders of magnitude greater than that of basalt. If the tektites originated from the Moon, they must therefore represent the highlands.[39]

The 85-km-diameter crater Tycho in the southern highlands was widely believed to be the result of a hypervelocity impact but Jack Green thought it was a volcanic caldera, and there were a variety of intermediate theories speculating that an impact promoted volcanism. Because the prominent system of bright rays indicated it to be the youngest crater of its size on the near-side of the Moon, it ought to be relatively uncontaminated by ejecta from elsewhere. Infrared observations made during a lunar eclipse on 19 December 1964 had shown Tycho to be one of the most striking of the thermal ‘anomalies’, implying that there would be lots of rocks on the surface out to a distance of one crater’s diameter beyond the rim crest. It was also bright at radar wavelengths, which also implied rockiness. Lunar Orbiters 4 and 5 had photographed the crater and its immediate environs from an overhead perspective at high resolution. It was decided to aim for a point 30 km north of the rim crest. But a

‘target’ was a circle within which the vehicle had a given probability of landing, and in such rough terrain it proved necessary to trim the diameter of the circle from 60 km to 20 km, which offered barely 10 per cent of the area and would require an extremely accurate trajectory.

It was decided to select a backup target at a similar longitude in order to have the same illumination for surface operations, and make the choice of which target to aim for in-flight by the accuracy of the translunar injection. If the trajectory was unlikely to yield the accuracy required for Tycho, the spacecraft would be diverted to a site in the Fra Mauro Formation. Although this blanket of ejecta lying peripheral to the Imbrium basin would be hummocky and heavily cratered, it ought to be much less demanding than Tycho, and a landing there offered the prospect of determining the composition of material excavated from many tens of kilometres beneath the surface – perhaps even subcrustal material whose chemistry would provide valuable insight into the interior of the Moon. But because the Fra Mauro Formation was ‘ancient’, it was probably contaminated by ejecta from elsewhere. The target was at 13°W, 5°S, just northeast of the 95-km-diameter crater Fra Mauro, and the target circle was the usual 60 km in diameter.

Surveyor 7 was launched at 06:30:01 GMT from Pad 36A on 7 January 1968. For the first time in the series, Gene Shoemaker went to watch the launch. The Centaur achieved orbit at 06:39:54. Owing to the predawn launch, the vehicle emerged from the Earth’s shadow at 06:50:19. It reignited at 07:02:15, shut down at 07:04:15, and released the spacecraft at 07:05:16. Because the decision about the target was to be delayed until after the performance of the Centaur had been ascertained, the nominal aim point for the translunar injection was Hipparchus, near the centre of the disk. It was decided to aim for Tycho. The midcourse manoeuvre at 23:30:09 on 7 January lasted 11.4 seconds, and the change in velocity of 36.4 ft/sec placed the interception point within the target circle. The trajectory was so accurate that an optional second refinement was cancelled.

A study of Tycho and its immediate environs had been made using the medium – resolution pictures taken by Lunar Orbiter 5. On average the rim crest stood 2.5 km above the surrounding highlands, but this was difficult to specify since there was no level plain for reference. The floor of the crater was 4.5 km below the rim crest. The prominent central peak rose over 2 km above the floor, and had hills nestled close alongside it. The theory of impact crater formation implied the central peak complex was a mass of rock thrust up from a great depth by the ‘rebound’ in the final stage of the process. The interior wall was a series of terraces produced when large blocks of material slumped on steeply inclined concentric faults. The high-resolution pictures from Lunar Orbiter 5 revealed the presence of flow features in low-lying areas of the wall terracing, and on the crater’s floor. The exterior was an annular belt 80-100 km wide that could readily be subdivided by albedo and texture into several geological facies.[40]

The innermost of the concentric rings extended from near the crest of the rim out to about 10-15 km, was asymmetric, widest on the northern side of the crater, and comprised irregular hills and intervening depressions which presented a hummocky texture. It contained many well-developed flow features, some as long as 8 km. The second ring, extending from 15 km out to 35-40 km, comprised subradial ridges and valleys, with the ridges typically 2-5 km in length and 0.5-1 km in width, etched on broad undulations 5-20 km across that were recognisable as craters swamped by the ejecta from Tycho. The inner ring had an albedo of 16-17 per cent, and the second was darker at 13-14 per cent.5 Most parts of the rim and the inner two rings were broken by closely spaced radial, arcuate and circumferential faults. Displacements on the radial faults had produced many small radial ridges and troughs interpreted as horsts and grabens respectively. Next was a ring of closely spaced craters ranging from one to several kilometres in diameter that were made by the fall of individual blocks of ejecta from Tycho. Beyond, out about as far as 100 km – a little over one crater’s diameter – the ejecta was discontinuous and transitioned into the system of rays composed of smaller craters which were much less closely spaced. The pictures from Ranger 7 showed a ray from Tycho crossing Mare Nubium to comprise craters ranging in size from 100 metres to 1 km. The thickness of the ejecta was expected to range from several hundred metres near the rim crest, where the ‘hinge flap’ placed the material excavated from the deepest point, to only a few metres in the peripheral zone. At Surveyor 7’s target, on the second ring, the ejecta was expected to average several tens of metres in thickness.

The pre-retro manoeuvre in which the spacecraft departed from its cruise attitude involved starting a roll of +80.5 degrees at 00:27:17 on 10 January, a yaw of +96.1 degrees at 00:35:52 and a roll of-16.5 degrees at 00:41:09. The initial approach was at 34.8 degrees to the local vertical. The altitude marking radar was enabled at 01:00:33.7, and it issued its 100-km slant-range mark at 01:02:11.892. The delay to the initiation of the braking manoeuvre was specified as 2.775 seconds.

The verniers ignited precisely on time, and the retro-rocket 1.1 seconds later. At that time the vehicle was travelling at 8,580 ft/sec. The RADVS was activated at 01:02:15.752. The acceleration switch noted the peak thrust of 9,200 pounds fall to 3,500 pounds at 01:02:58.973, giving a burn duration of 42.9 seconds. The verniers were throttled up to their maximum thrust at 01:03:09.250 for 2 seconds while the motor was jettisoned. At burnout, the angle between the vehicle’s thrust vector and velocity vector was 19 degrees. The RADVS-controlled phase of the flight began at 01:03:13.090, when the slant range was 51,259 feet (and because the velocity vector at burnout was offset to vertical, the altitude was 41,510 feet) and the total velocity was 452 ft/sec (and since the vehicle had maintained its thrust along the velocity vector extant at the time of retro ignition, the longitudinal rate was 428 ft/sec). The vehicle immediately aligned the thrust axis along the velocity vector extant at retro burnout

and flew with the verniers at 0.9 lunar gravity, very slowly accelerating as it descended. When the altimeter locked on at 01:03:17.649, at a slant range of 41,673 feet, attitude control was switched from inertial to radar and the thrust axis was swung in line with the instantaneous velocity vector to initiate the gravity turn. On intercepting the ‘descent contour’ at 01:04:03.018, the slant range was 20,246 feet and the speed was 464 ft/sec. By the 1,000-foot mark at 01:05:13.285, the vehicle was descending very nearly vertically at 102.5 ft/sec. The 10-ft/sec mark was issued at 01:05:30.184 at a height of 46 feet.

The verniers were cut off at 01:05:36.284, and after falling freely the vehicle touched down at 01:05:37.620 with a vertical rate of 12.5 ft/sec and a lateral rate of 0.3 ft/sec. Leg no. 1 was the first to make contact, followed rapidly by legs no. 2 and 3 in that order. There had been a fair chance that the vehicle would be disabled on trying to land in such rough terrain, so its survival gave rise to wild applause in the Space Flight Operations Facility.

The camera was of the type introduced by Surveyor 6 – the hood was of the boxy configuration, the elevation range of the mirror was 70 degrees, and it had polarising filters. The first 200-line picture was sent at 01:47. After 15 pictures had been taken for a preliminary study, the solar panel and high-gain antenna scanned for the Sun and Earth respectively, locking on by 03:21. The first 600-line picture was taken at 03:42. The foot pads had displaced as the legs rebounded on contact, but overlapped their original imprints. Pad no. 2 had nudged aside a rock that was about 18 cm long and at least 10 cm high. Pad no. 3 landed partially on top of a semi-buried rock, and in the process suffered localised deformation and tearing. The pads had penetrated to a depth of 4 cm and displaced clods to a radius of about 40 cm, but there was barely any lunar material on their upper surfaces. As on the maria, the disturbed material was darker than the undisturbed surface. The orientation of the lander put the camera on the north-facing side. To the east, south and west the horizon was less than 200 metres away, but because the local surface sloped down to the north the view in that direction was spectacular, with a succession of ridges on the horizon. Despite being the roughest-looking target to date, the landscape still bore little resemblance to the depictions of the lunar surface in contemporary popular fiction. The slope on which the lander stood was about 3 degrees. Most of the landscape on view was no steeper than 10 degrees. The steepest flank of a ridge on the horizon was 34 degrees, and the summit was rounded.

It turned out that Surveyor 7’s trajectory was very accurate and it landed a mere 2.5 km from the aim point. The coordinates were difficult to determine because the selenographic grid presumed the Moon to be spherical, which was not the case. For points above the mean sphere and situated some distance from the centre of the lunar disk, the measured coordinates were greater than the actual coordinates. Also, at this location the latitudinal circles were significantly curved. This complicated the drawing of a local grid. Instead, features on frame M-128 from Lunar Orbiter 5 were identified on a picture taken in 1919 by the 100-inch telescope at the Mount Wilson Observatory, and the site pin-pointed on M-128 was transferred first to the telescopic picture and then to the coordinate system of the relevant sheet of the Orthographic Atlas of the Moon (based on that picture) which had been issued by D. W.G. Arthur and E. A. Whitaker in 1961 as a supplement to the Photographic Lunar Atlas produced by Gerard Kuiper.

A number of geological units were identified in the high-resolution pictures taken by Lunar Orbiter 5. The most widespread unit was described as ‘patterned debris’. This was the major unit of the second ring of ejecta deposits. The size-frequency distribution of craters exceeding 8 metres in diameter was the highest of all the units in the ejecta debris.

To the lander, the patterned debris extended several tens of kilometres to the west, north and northeast, and the large craters had raised rims which, in many cases, were relatively smooth. This was well demonstrated by a crater about 650 metres to the north that was 60 metres in diameter. Although it was 10 metres deep, its rim was smooth. It was apparent that the patterned debris was a blanket of unconsolidated material. The crater contained a few large blocks, but they were no more numerous than were lying around between the craters. The absence of strewn fields associated with craters on the patterned debris indicated it to be at least 20 metres thick, which

The northward-looking portion of a panorama taken by Surveyor 7. The outline shows the area covered by the next illustration. (Courtesy of Philip J. Stooke, adapted from International Atlas of Lunar Exploration, 2007)

Three ridges at successively greater distances to the north of the Surveyor 7 lander. The letters are explained in a subsequent Lunar Orbiter illustration. (Courtesy of Philip J. Stooke, adapted from International Atlas of Lunar Exploration, 2007)

was consistent with expectation. Surveyor 7 actually set down about 50 metres from the western margin of a ‘patterned flow’, beyond which was the dominant patterned debris. There was no relief at the contact between the two – the difference evident in overhead imagery was only a distinction in the surface texture. The patterned flow extended to the north and east, but most of it was to the south of the lander and hence beyond the near horizon, which was only a few hundred metres off. In the Lunar Orbiter pictures, the surface of the flow comprised low hills and depressions ranging up to several hundred metres across. But superimposed on these broad irregularities was a pattern of north-trending low ridges and grooves similar to those on the patterned debris (but less well defined) with swarms of fissures running along the ridges which suggested they had undergone slumping. There were a great variety of rock fragments in the vicinity of the lander, ranging up to 1 metre in size. Two craters to the southwest of the lander – one 20 metres in diameter and the other 30 metres – had rims littered by coarse blocks up to 75 cm in size. They were on the patterned flow, and had excavated these rocks. There was an irregular crater about 3 metres in diameter 5 metres north of the lander that contained coarse blocks up to 60 cm in size and issued a strewn field extending to the northwest, but this crater

was undoubtedly made by the fall of ejecta from another event, and the blocks were the debris of the secondary projectile.

The lander could also observe an area of‘smooth patch material’ to the northeast. Such units occurred in enclosed depressions several hundred metres across and – in addition to being smooth – were relatively dark. The fact that the smallest crater on this material to have a blocky rim was only 5 metres in diameter indicated a source of rocks at a depth of about 2 metres. As this particular smooth patch material was superimposed on the patterned flow, the craters had undoubtedly punched through to the patterned flow. This in turn indicated that this particular spot of smooth patch material was a thin veneer. On all three types of terrain, most of the craters with diameters in the range 8 to 16 metres were elongated with their major axes radial to Tycho.

The principal difference between the patterned debris and the patterned flow appeared to be that whereas the patterned debris material rapidly settled on being ballistically deposited, the patterned flow gained its distinctive texture by flowing for distances ranging between several tens and several hundreds of metres.

In the immediate vicinity of Surveyor 7, small craters were as abundant as on the maria, but the size-frequency distribution of those exceeding 10 metres across was significantly less. There was a greater variety of rock types than at any of the maria sites, and they varied in albedo up to 22 per cent. Some blocks were plain, but others were spotted. The spots were of various sizes, had irregular margins, and appeared to be surface protrusions. One particularly striking rock 2 metres away had spots that ranged in size from less than 1 mm to about 30 mm and covered about 30 per cent of the visible face. It was speculated that the spots were fragments of light-toned rock assimilated into a dark matrix – a mechanically assembled conglomerate known as a breccia. Some rocks had well-developed linear structures, and others appeared to be vesicular – both of which were suggestive of lava.

The maria were lava flows that solidified as coherent rock and were subsequently progressively pulverised by meteoroid bombardment to accumulate a regolith which matured over time into ever finer fragments. Although the excavation of Tycho laid down a blanket of ejecta, it did so essentially instantaneously. Such material would contain blocks of all sizes with a size-frequency distribution different to a regolith. Some blocks would have come to rest on the surface as the ejecta was laid down, but most would have been buried. Some would later be excavated and tossed around. If (as the superposition relationships indicated) Tycho was formed recently, then there could not have been much time for the rain of meteoroids to produce a true regolith on top of the ejecta blanket. A theoretical study which incorporated all that had been learned to date about the rates of small impactors, predicted that the regolith at this site ought to be about 10 cm thick on average.

In early 1967 the plan was to fly the soil mechanics surface sampler on Surveyors 3 and 4, and then the alpha-scattering instrument on the remaining missions. But it had been decided that Surveyor 7 should have both. The intention was to conduct an elemental analysis of undisturbed surface, then activate the sampler and use this to reposition the sensor head to analyse subsurface material excavated by the arm. The alpha-scattering instrument was powered up at 09:28 on 10 January. The

MAGNET AND CONTROL BAR

The configuration of the Surveyor 7 lander.

standard sample was measured between 09:28 and 15:29, yielding 5.2 hours of data. At 15:49 the standard sample was removed to enable the head to measure the background, and 4.8 hours of data was obtained between 16:13 and 21:59. The auxiliary mirror on leg no. 1 orientated to provide the camera with a line of sight beneath the vehicle in order to investigate where the head of the alpha-scattering instrument would take its first sample showed a uniform grey; evidently during the landing it had been completely coated with fine-grained material! There was a partial coating on the mirror for viewing crushable block no. 2, but it was still possible to establish that there was an imprint. The area beneath block no. 3 was in the lander’s shadow for most of the time. The command to release the head was issued at 22:01 on 10 January. The instrument’s counts were monitored in real-time for 6 minutes, awaiting the increase that would confirm that the head was on the surface; but there was no change. The command was reissued at 22:09 and the counts monitored for 10 minutes – again with no increase. A series of pictures taken between 22:41 and 23:44 of the head and the deployment mechanism showed that the squib had fired, the pin had been pulled and the door of the cable compartment was open. However, the head had not moved. It was concluded that the escapement mechanism for the nylon cord had either failed to function or the cord had become stuck in the mechanism. It was decided to activate the arm and try to use this to lower the sensor head.

The soil mechanics surface sampler was powered up at 01:00 on 11 January, then exercised to verify its functionality. To enable the arm to manipulate the head of the alpha-scattering instrument, its mounting structure had been redesigned to draw the arc of its azimuth range to the left; but this was at the expense of the other end of its range, with the result that it could no longer reach foot pad no. 2. On Surveyor 3, an

attempt had been made to measure the force that was applied by the arm but the time-resolution of the motor current telemetry had been insufficient to provide an accurate measure. Originally, the motor current readout had allowed a maximum of eight current samples for a 2-second motor actuation. The upgraded system provided samples at 50-millisecond intervals. In a static bearing test the arm would lower the flat face of the scoop’s door over the selected spot using a series of either 0.5 or 2.0- second commands until the elevation motor stalled, indicating the force against the surface. When driving the scoop into the surface with its door open for trenching, it would be possible to measure bearing strength as a function of depth.

After the arm had made two bearing tests well clear of where the alpha-scattering instrument was to sample – in the process obtaining readings very similar to those at the Surveyor 3 site, where an identical test had been made – the arm began its efforts to deploy the balky instrument. Between 07:23 and 08:09 the arm was manipulated until it rested its scoop on the base plate of the head, and then from 08:15 to 08:50 it applied a series of light taps to the plate. It had been hoped that this would cause the head to unreel all the way down to the surface, but TV pictures showed that it swayed on its cable without unreeling. It had not, in fact, been possible to impart much downward force because with the head dangling freely on its cord a force applied to one side of the plate simply caused the head to tilt and swing away. Further pictures were taken between 23:14 and 23:41 to inspect the escapement mechanism.

On 12 January the arm began its day with another three bearing tests, and then manoeuvred to pick up a rounded rock (Rock ‘A’) that was about 5 cm in size, with

the motor current being monitored to estimate the mass of the rock. Between 05:48 and 07:33 the arm was first positioned alongside the right-hand side of the head and then manipulated using a procedure that had been tested on an engineering model to jam the head against the helium tank to the left, to prevent it from swinging when a downward force was then applied. In driving the head down by several centimetres, sufficient room was gained to position the scoop directly above the head, near the eye-bolt to which the cable was attached. This was achieved by 08:01, and between 09:11 and 10:05 a downward force was applied to drive the head against the tension of the fouled cord all the way down to the surface. During the hiatus, the instrument had obtained an additional 7.2 hours of background data. There were a number of fairly large fragments on the surface close to where the head deployed, and in fact not only was there a rock some 4 cm in size under the inboard side of the base plate that was tilting the head, there was also a fragment of about 1.5 cm in the aperture at the centre. The analysis of sample 1 started at 16:42 on 12 January, and 6.2 hours of data had been acquired by the end of the day.

On 13 January the arm made an attempt to lift Rock ‘B’, but this proved to be just out of reach. Instead, Rock ‘C’ was scooped up, but when the arm was elevated to weigh the rock it fell out of the scoop. Trench 1 was made at the extreme right of the arm’s operating area. This was foiled by a subsurface obstacle at a depth of 2.5 cm which proved able to resist the retraction motor on two scrapes, with the result that the penetration was limited to 5 cm. This obstacle proved to be a buried rock with an irregular upper surface. The alpha-scattering instrument had to be switched off early on 13 January when the head exceeded its maximum operating temperature of 50°C, but data-taking resumed at 10:55 after the arm positioned its scoop to shade the head and allow it to cool off. There was a hiatus between 20:21 and 22:36 while the scoop again provided shade, and operations ended at 23:33. The arm devoted the whole of 14 January to Rock ‘D’. At first sight this appeared as a rounded knob poking out of the surface and sufficiently small to fit into the scoop for weighing, but when it was excavated it proved to be too large. The angular shape of the buried portion of the rock was an indication of the efficiency of the erosional process that had rounded off its exposed face.

Some alpha-scattering data was obtained on 14 January, but for most of the time the head exceeded its maximum operating temperature. When the lander arrived, 30 hours after sunrise, the Sun was at an elevation of 13 degrees. At the equatorial sites visited by previous missions the Sun passed close to the zenith at noon, but at this site its maximum elevation was 48 degrees above the northern horizon. A pre-flight study indicated that the surface temperature at noon would be approximately 100°C, as opposed to 127°C on the equator, but the analysis presumed a smooth surface and did not take account of local influences such as slopes, craters and blocks that could not be predicted in detail. Although the incident heat would be less harsh at this site, the fact that the Sun did not pass near the zenith meant that the shadow of the mast – mounted panels never fell on the vehicle. As a result, the scientific payload, which faced north, grew hotter during the mid-morning, noon and mid-afternoon than at any previous site, and both the head of the alpha-scattering instrument and the electronics of the sampling arm exceeded their maximum operating temperatures.

For the three days during the mid-day period, therefore, the arm only manoeuvred to maintain the shadow of its scoop on the head in an effort to keep this below its ‘survival limit’ of 75°C – which was only just achieved. The thermal stress on the camera was worse than on earlier missions, as at noon the Sun shone on the side of the cylinder rather than down upon its top. It was rotated in azimuth away from the Sun to minimise the solar absorption by the black interior of the hood. During the 5- day period near local noon its use was severely restricted – at worst to only 5 minutes per hour.

Arm work resumed on 19 January by re-weighing Rock ‘A’. A flat 22×60-cm mirror just below the upper collar of the mast allowed the camera to view a roughly triangular area of about 0.25 square metres lying between 1.7 and 3 metres from the camera, a portion of which was accessible to the sampling arm. Carrying the rock, the arm swung into the field of view of the mirror and stereoscopic pictures were taken to enable the volume of the rock to be estimated and, in turn, the density. With a density in the range 2.4 to 3.1 g/cm3 – the most likely value being in the range 2.8 to 2.9 g/cm3 – the rock could not be very porous. The arm was then elevated to drop the rock from a height of about 60 cm – after making a small indent in the surface, it bounced or rolled about 12 cm. The strength of this rock was tested by having the scoop squeeze it, but it did not break. The arm then retrieved the rock and deposited it closer to the head of the alpha-scattering instrument – in preparation for possibly placing the head on top of the rock to determine its elemental abundance and further characterise it.

On 20 January the arm made trench 2 using four scrapes. A buried obstacle near the start of the trench deflected the scoop to the left. Once finished, the trench was 75 cm long and varied in depth between 15 and 18 centimetres. Trench 3 was placed close alongside as a single scrape. In scraping trench 4, the scoop’s door was kept closed in order to measure the ability of the surface to resist lateral force. In addition to having magnets on both foot pads no. 2 and 3, Surveyor 7 had a pair of horseshoe magnets embedded in the door of the scoop. In fact, the pads penetrated only 6 cm, which was insufficient to bring the magnets on their sides into contact with the lunar material. However, the magnets on the arm were able to test selected spots. As these magnets repeatedly came into contact with the lunar surface they attracted material with a granularity finer than the resolution of the camera, which was about 1 mm at that distance. As an experiment, the scoop was nudged against a chip of rock about

1.2 cm in size that had a smooth shape, a low albedo and a lustre. When the scoop was raised, the rock clung to the magnets on the door. Prior to being disturbed, this rock was partially embedded, with no evidence on the surface of it having landed or rolled into position. The fact that its exposed surface was much darker than most of the rocks in the arm’s operating area implied that it was atypical. Its strong magnetic susceptibility would have been consistent with a nickel-iron meteorite or a material rich in magnetite – it was not possible to say which (if either). Unfortunately, as the arm was manoeuvred to facilitate stereoscopic photography the acceleration caused the fragment to fall off.

The alpha-scattering instrument was reactivated at 21:14 on 20 January and found to have cooled down to 40°C, so data-taking was resumed. By 07:21 on 21 January it had accumulated a total 27.3 hours of data for its first sample. With two days remaining to sunset, it was decided to reposition the head. On previous missions the cord was attached to an eye-bolt installed directly on the head’s upper surface, but this time it was attached to a knob that had been designed to enable the arm to grasp the head. On 21 January, the scoop lifted the head. The motor current was monitored in order to provide a calibration check of this method of weighing rocks. The plan to analyse Rock ‘A’ had been rejected in favour of an undisturbed rock – the one selected was adjacent to Rock ‘D’. It was lighter in tone than its surroundings and about 5 x 7 cm in size. In manoeuvring the head the arm caused the rock to shake, which indicated that it was sitting on the surface rather than embedded in it. The arm engineers were delighted with the precision of its movements. At 12:30 the head was left perched on the rock. In fact, part of the rock protruded through the aperture into the cavity of the head. The instrument analysed the ‘exposed’ upper surface of the rock for 10 hours. Meanwhile, the arm scraped first trench 5 with the door open and then trench 6 with the door closed. On 22 January the arm excavated trench 7 in between the trenches scraped the previous day – again with the door closed. With three trenches in close proximity, there was a significant amount of debris piled up at their inner ends. The alpha-scattering instrument was moved onto this disturbed material and 6.7 hours of data was obtained between 12:06 on 22 January and 14:40 on 23 January, which was some 8.5 hours after sunset, and by the time it was switched off at 15:36 the head of the instrument had chilled down to -20°C and the associated electronics to -50°C.

While the alpha-scattering instrument was performing its third analysis, the arm made a series of bearing tests – one of which was adjacent to trench 2, with pictures being taken to look for any evidence of the wall of the trench collapsing in response to the pressure. Then it was decided to attempt to crack open a rock to obtain a fresh surface which could be photographed using the polarising filters to seek insight into its structure. The arm positioned the scoop directly above Rock ‘E’, raised the scoop to a height of about 35 centimetres and let it fall with its door open on the rock. The rock was about 5 cm in size, and the impact broke off a small piece – either because it was intrinsically weak or because it contained a fracture. While scraping trench 1, the arm had been fouled by a buried rock, so as a finale the scoop was lowered back into this trench and the arm retracted to re-engage the obstacle. Then after sunset on

23 January, exploiting the increased torque of the retraction motor as a result of it having chilled to -110°C, the arm tried to dislodge the rock. However, the fact that the applied force partially compressed the shock absorber on leg no. 2 indicated the rock to be firmly embedded! This final experiment over, the arm was switched off at 08:41 that same day.

Over a total of 36.3 hours of operation the arm made 4,397 mechanical motions. It made two impact tests, seven trenches, two of which used more than one scrape, and sixteen bearing tests, five of which were with the scoop door open. One of the trenches was directed by a command tape which took a picture between each action, and the frames were later compiled into a movie. There were fragments up to 10 cm

in size within the arm’s reach, most of which seemed to be dense coherent rock. The subsurface was predominantly fine-grained granular material but, as was revealed by the trenching, there were fairly large rocks at a shallow depth. As on the maria, the fine-grained material was slightly cohesive, partially compressible and consolidated with depth. The fact that the undisturbed surface was brighter than the subsurface on both the maria and in the highlands indicated that this was not simply a property of the maria but a universal weathering process. Whereas on the maria the albedo of the undisturbed surface was 7.2 to 8.2 per cent and the subsurface was 5.5 to 6.1 per cent, in this case the undisturbed surface was 13.4 per cent and the subsurface was 9.6 per cent. The fact that at this site the subsurface was slightly brighter than the undisturbed surface of the maria was probably a consequence of the highlands being generally brighter than the maria.

From the point of view of the alpha-scattering investigation, Surveyor 7 was the most productive mission, with the increase in yield being derived from collaboration with the sampler. In fact, fully 8.75 hours of the arm’s operating time was devoted to deploying and subsequently tending to the alpha-scattering instrument.

The high latitude and the increased elevation range of the camera’s mirror enabled narrow-angle pictures to be taken of Earth. On its first day of operation, the lander photographed Earth through polarising filters – the first time this had been done, and the highly polarised component was inferred to be specular reflection of sunlight by the ocean.

An experiment assigned to the first Apollo lunar landing mission was to emplace on the lunar surface an instrument that comprised an array of corner-cube reflectors designed to reflect a laser beam fired from Earth back towards its source, so that the intervening distance could be precisely measured to analyse the secular components of the Moon’s motion.6 To test the first stage in this process, Surveyor 7 was to take pictures of Earth while laser beams were being fired. Six sites were established, each with a laser directed through a telescope to reduce the divergence of the beam during its transit to the Moon. The first test on 14 January was a failure. After a pause while Earth and the Sun were close together in the lunar sky, the experiment resumed on 19, 20 and 21 January. The first clear detection was on 20 January, with the pictures simultaneously capturing the beams from the 60-inch McMath solar telescope of the Kitt Peak National Observatory, Tucson, Arizona, and the 24-inch telescope of the Table Mountain Observatory – the latter operated by JPL in Wrightwood, near Los Angeles, California. Although the power of the lasers was just 1 to 2 watts and they illuminated a footprint on the lunar surface that was about 3 km in diameter, which had the effect of diluting the energy across a wide area, to the lander’s camera they appeared against the dark part of the crescent Earth as points of light rivalling Sirius, the brightest star in the sky.

Because the Moon rotates once in the same time as it takes to pursue one orbit of

А З-second exposure taken by Surveyor 7’s camera at 09:06 GMT on 20 January 1968 recorded laser beams fired at it by two telescopes on Earth. The lasers were fired by the Kitt Peak National Observatory near Tucson, Arizona, and the Table Mountain Observatory near Los Angeles, California. They are indicated by black circles on the globe (left). Owing to the long-exposure required to detect the laser beams, the illuminated part of Earth is washed out.

Earth, our own globe remains more or less stationary in the lunar sky, rotating on its axis on a 24 hourly basis and waxing and waning in illumination over the period of a month. Starting at 17:11 on 22 January, the lander took sets of pictures of Earth through polarising filters at 2-3-hour intervals over a period of 26 hours. The goal was simply to determine what such observations could discern, starting with how the reflectance of the atmosphere varied as a function of the changing cloud distribution over one diurnal period.

It had been hoped to make at least one ‘hop’, and the predicted windows for this were when the elevation of the Sun was climbing between 23 and 31 degrees in the morning and falling between 23 and 16 degrees in the afternoon, but even at these times parts of the vernier propulsion system were too hot. Because leg no. 2 was on the north side of the vehicle, it suffered the longest period of direct illumination. The thrust chamber assembly of vernier no. 2 exceeded its pre-ignition temperature limit in the morning – in fact, it grew hotter than any engine on any previous vehicle. And before this engine could cool in the afternoon, vernier no. 3 had grown too hot. Only vernier no. 1, on the south side, remained usable in this respect. Furthermore, the temperature of the shock absorber on leg no. 1 plummetted to -53°C, well below the minimum temperature at which it could be expected to work properly during a hop. With leg no. 2 cooling in the afternoon, at 23:55 on 20 January the temperature of vernier no. 2 sharply dropped from 31°C to -18°C. At the same time there was an increase in the temperature of the fuel line indicating a flow from the tank, which was at 70°C. The engine was being chilled by the vaporisation of fuel leaking from the shutoff valve poppet. At 17:21 on 22 January the helium regulator automatically opened in a fruitless effort to re-establish the fuel pressure. The shock absorbers of the legs had not been locked following landing, but at 15:32 on 21 January, with no prospect of attempting a hop, they were commanded to lock. The squibs fired, but at sunset leg no. 2 deflected 2.4 degrees, indicating that it had failed to lock.

Sunset occurred at 06:06 on 23 January. Over the next 15 hours the camera took further pictures of the Earth, stars and the solar corona. Exposures of 20-30 minutes detected the corona out as far as 50 solar radii, which was about five times further out than was feasible for a solar eclipse viewed from Earth – sufficiently far, in fact, to study the hitherto unobservable transition zone between the solar corona and the inner zodiacal light zone. The pictures taken during the first 90 minutes after sunset provided further evidence of the ‘horizon glow’ discovered by Surveyor 6. When viewed from the equator the glow had remained due west, but for Surveyor 7, some 40 degrees south, the axis of the glow tended to migrate northward along the horizon with time. As for the cause of this phenomenon, it was concluded that electrostatic levitation of fine dust, if it occurred at all, would be minimal with insolation at a grazing angle. This left diffraction of the last rays from the upper limb of the solar disk approximating a point source on the horizon – as this geometry migrated beyond the local horizon the glow would persist for a time, with the pattern of the gaps in the line changing according to how the lunar surface features lying beyond the horizon cast their shadows onto the local horizon. Camera operations ceased at 21:10, having taken a total of 20,993 pictures.

Less post-sunset temperature data was obtained than hoped, once again owing to problems involving the bimetallically activated switches in the thermally controlled compartments, and the hibernation command was enacted at 14:12 on 26 January, 80 hours after sunset.

Surveyor 7 was reactivated at 19:01 on 12 February, some 120 hours after sunrise on its second lunar day. The shock absorber on leg no. 1 had compressed during the night, causing a deflection of 23.5 degrees – in effect completely collapsing the leg. Leg no. 2 had also compressed at sunset, but the fact that it recovered meant that its deflection had merely been the result of fluid contraction. In the case of leg no. 1, however, it appeared that high-pressure gas had leaked from the shock absorber. The alpha-scattering instrument resumed taking data on 13 February. The following day the arm was sent a single-step extension command, simply to verify that it was still operational. When the camera was activated, it proved unable to scan pictures in the 600-line mode due to an electrical fault. It was still functional in the 200-line mode, but a problem with the rechargeable battery limited its use. Indeed, after 45 frames the rate at which the camera could take pictures had decreased to one per hour and it was decided to cancel further operations. The arm test was successfully repeated on 20 February. By that time the power supply was so critical that the alpha-scattering instrument had to be switched off. The final communication from Surveyor 7 was at 00:24 on 21 February 1968 – there would not be another NASA transmission from the lunar surface until the first landing by an Apollo crew.

During the first lunar day the alpha-scattering instrument was operated for a total of 136.5 hours. This included 310 minutes of calibration using the standard sample, 727 minutes measuring the background (longer than planned, owing to the difficulty in deploying the sensor head) and 64 hours of science data – of which 44 hours was of sample material: 27.3 hours on the undisturbed surface, 10 hours on the rock and 6.7 hours on the subsurface that had been exposed by the arm. On the second lunar day the instrument provided another 34 hours of data for the third sample area over a 35-hour period, but only 20 hours of this were deemed to be usable owing to a low signal-to-noise ratio in the transmission. The total usable surface data was therefore 64 hours.

The main results of the alpha-scattering instrument were that for the fine-grained material the aluminium abundance was higher than measured at the maria sites, and the ‘iron group’ with atomic masses ranging from titanium to nickel were a factor of two less abundant. In the case of the relatively light-toned rock that was analysed the iron content was lower still. On seeing the elemental abundances, some people inferred that the lunar highlands must be an alumina-rich form of basalt, but Gene Shoemaker countered that the dominant rock in the Tycho ejecta – which was drawn from deep within the crust – was anorthositic gabbro. Such a feldspathic rock was a further indication that the Moon had undergone thermal differentiation. The lower iron content suggested that the highlands had a significantly lower density than the mare material. Later, John A. Wood would pick up on this and argue that the Moon had been so hot in the final stage of its accretion as to be molten to a considerable depth. In this ‘magma ocean’, the heavier elements sank to create a magnesium and iron silicate mantle whilst the lighter elements floated to the surface and cooled to create a crust. There was no evidence of the acidic rocks that would be required to
account for the tektites. Overall, the elemental analyses performed by the Surveyors strongly indicated that the Moon was not a pristine body of ultrabasic composition, and this, in turn, ruled against the hypothesis that the most abundant meteorites on Earth – known as chondrites – originated from the Moon.

The Surveyor project achieved its primary objective of yielding sufficient insight into the nature of the lunar surface to allow Apollo to proceed in confidence, free of concern that the lander might sink into a sea of dust or fall through a brittle surface into a subterranean cavity.

Table 14.1: Surveyor sites – selenographic coordinates

Spacecraft Longitude Latitude Description

As derived from Orthographic Atlas of the Moon issued by D. W.G. Arthur and E. A. Whitaker in 1961 as Supplement 1 to the Photographic Lunar Atlas.

Note – these are finalised figures from the Surveyor Program Results, SP-184, 1969, which states that it corrects figures in the individual mission reports.

ROVING PLANS

It had been hoped that Surveyor would advance beyond the Block I engineering model. Planning for the Block II was terminated on 13 December 1966. Each would have weighed about 100 kg more than the original model, and have carried a greater scientific payload. In April 1964 Bendix submitted to JPL the outcome of a 6-month study to assess the feasibility of having a Block III deliver a 45-kg Surveyor Lunar Roving Vehicle. The plan was for the rover to be remotely controlled from Earth as it conducted a systematic study of a site which had been short-listed on the basis of Lunar Orbiter imagery as an Apollo target, to provide the ‘ground truth’ required to inform a final decision. It would be equipped with a scanning and digitising camera

RF RANGING ANTENNA

OMNI ANTENNA

DIRECTIONAL ANTENNA

TRACTION DRIVE ASSEMBLY

Detail of the Surveyor Lunar Roving Vehicle proposed by the Bendix Corporation.

for stereoscopic imagery from which the local relief could be mapped on the scale of interest to the site selectors seeking ‘clear’ areas large enough to accommodate an Apollo lander. The rover would also have a penetrometer with which to measure the roughness and bearing strength of the surface along its route – something that could not be done from orbit. One survey method would involve an ever-widening spiral. It might make several such spirals, driving some distance cross-country in between, in total driving up to 25 km over an interval of several months – working during the lunar day and hibernating at night. There would be a trade-off between conducting a wide-area survey and certifying a given site for an advanced Apollo landing.7 It had been hoped to launch five such missions in the 1970s, but the development funding was never forthcoming.

Note that the plan presumed that an Apollo spacecraft would be able to set down precisely at a preselected point.

In 1330 AD the Italian scholar Francesco Petrarca coined the term ‘dark ages’ for the centuries of cultural decline in Europe after the fall of Rome in the fifth century. Intellectual development did not resume until the start of the Italian Renaissance in the fourteenth century. During this interregnum, the works of classical Greece and Rome were available only in Arabic translation. On being ‘rediscovered’, they were translated from Arabic into Latin.

In 1505 Leonardo da Vinci, who had exceptional eyesight, drew an impression of the face of the Moon. He interpreted the brighter part to be water, the dark areas as land, and believed that there were clouds. He was the first to explain the old-Moon-in-the-new-Moon’s-arms effect that occurs when the Moon is a narrow crescent. At such times the majority of the Earth’s disk in the lunar sky must be illuminated, and the dark part of the remainder of the lunar disk is dimly lit by sunlight reflecting off Earth. Late in the 13th century, it had been realised that light was bent by passing through a glass lens. The term ‘refraction’ was not invented until some time later. In 1490 da Vinci had speculated upon whether lenses could be used in combination to make an enlarged view of a distant object. In 1504 he conducted experiments, and by 1510 had the optical principle of the telescope.

After further experiments, three years later he described how a concave mirror could produce a magnified image.

As the Renaissance progressed, some of the ancient beliefs were questioned. By the Ptolemaic system, all celestial bodies travelled around Earth on a daily basis, but Nicolaus Copernicus, a Polish canon, realised that this was not entirely true. In his book De Revolutionibus Orbium Coelestium he revived the heliocentric system of Aristarchus of Samos. Copernicus said only the Moon travels around Earth, but he retained circular orbits, deferents and epicycles. The planets, including Earth, are in orbit of the Sun. But knowing that the Church of Rome would construe this to be heresy, he kept silent, and his book was not released until after he died in 1543. His caution was justified, as in 1600 Giordano Bruno was burned at the stake in Rome for arguing in favour of the heliocentric hypothesis.

Johann Kepler was born near Stuttgart in Germany in 1571. He went to Prague in 1600 to assist the Danish astronomer Tycho Brahe, who held the title of Imperial Mathematician to the Holy Roman Emperor Rudolph II. Over a period of 20 years Brahe had compiled a highly accurate catalogue of planetary motions. When Brahe died in 1601, Kepler inherited the title of Imperial Mathematician, together with the archive of observations, which he set about analysing – something that Brahe had never attempted. Brahe was convinced of the view that Earth was central, but Kepler found otherwise. In his book Astronomica Nova, published in 1609, he announced that a planet pursues an ellipse with the Sun at one focus and the other focus vacant. The same applies to the Moon, but with Earth at one of the foci instead of the Sun. Whilst this rendered obsolete the Ptolemaic system with its circular orbits, deferents and epicycles, the Church was reluctant to concede the point.

In fact, Kepler also realised that the speed of a body in its orbit is proportional to its distance from its primary. In the case of the Moon, with Earth at one focus of its orbit, it travels more rapidly at perigee than at apogee. As a result, whilst the rate at which the Moon turns on its axis is fixed and is synchronised with its orbital period, the Moon is sometimes leading and sometimes trailing the mean position of its orbit, at which times we can see a portion of the otherwise hidden hemisphere around first one equatorial limb and then the other. Similarly since the Moon’s orbit is inclined to the Earth’s equator, when the Moon is in the southern sky we can observe slightly beyond its north pole at a time when that is illuminated, and when the Moon is in the northern sky we can see beyond its south pole when that is illuminated. This effect is known as libration. As for the Moon as a body, Kepler introduced the terms ‘terrae’ and ‘maria’ to describe the light and dark areas respectively.

When the Advanced Research Projects Agency decided in 1958 that a series of probes should be launched towards the Moon, Eberhardt Rechtin led a team at JPL in the development of radio tracking, telemetry and command facilities. When W. H. Pickering created the Telecommunications Division, he made Rechtin its chief. JPL recognised early on that it would need a world-wide network of antennas to maintain contact with deep-space missions. In late 1958 NASA approved the proposal by JPL to develop the Deep Space Instrumentation Facility. To oversee this activity, Abe

Note that Kuiper, Shoemaker and Urey did not actually originate the experiment.

Silverstein appointed his assistant for Space Flight Operations, Edmond C. Buckley, who had experience of tracking and instrumentation at the rocket range on Wallops Island.7

As the Ranger project geared up in I960, Rechtin was given the additional role of Program Director for the Deep Space Instrumentation Facility. It was decided to build three stations located approximately 120 degrees apart in longitude to provide a continuous line of sight to a spacecraft in deep space. The main station was built near the Goldstone Dry Lake in the Mojave Desert of California, 160 km east of JPL and on the far side of a range of mountains which would shield the antenna from the ‘noise’ of the coastal cities. The other stations were at the Woomera Test Range in Australia and near Johannesburg in South Africa. Later, a fourth station was added near Madrid in Spain.

Because the antennas had to be both large and fully steerable, it was decided to adapt a radio-telescope design. Although the dish was mounted like a telescope, the steering system was designed to hold the antenna pointing precisely at a spacecraft travelling against the background of stars, rather than to maintain sidereal rate. This

In November 1961, James Webb introduced the Office of Tracking and Data Acquisition at NASA headquarters and made Buckley its Director.

was to be done by having the antenna lock onto the spacecraft’s radio transmission and maximise the received signal strength. A 26-metre-diameter dish was required to track the 3-watt transmitter of the Ranger spacecraft. In addition, a system was installed to enable the antenna to simultaneously send ‘uplink’ at one frequency and to receive ‘downlink’ at another. This allowed not only the position of the spacecraft in the sky to be determined, but also both its range and radial velocity along the line of sight. This data would enable the vehicle’s location and motion in space, together known as its state vector, to be monitored continuously in real-time.

Planning for the Space Flight Operations Centre at JPL began in May I960 and was finished in November I960. As it fell within the remit of the Systems Division, Harris Schurmeier appointed Marshall S. Johnson to supervise its construction in Building 125 of the campus. The Space Flight Operations Centre, together with the terrestrial communications network (initially by voice lines and teletype) to link it to the Deep Space Instrumentation Facility, were declared operational on 4 July 1961.

In February 1961 W. H. Pickering ordered a study of future requirements for flight operations, and the recommendation was to construct a new building specifically for this role. In July, NASA gave the go-ahead. This Space Flight Operations Facility entered service in the summer of 1964. Meanwhile, on 24 December 1963 the Deep Space Instrumentation Facility, the terrestrial commu­nications network and the JPL control centre were integrated under the umbrella of the Deep Space Network.8

Note that the Deep Space Network comprised the Deep Space Instrumentation Facility and Space Flight Operations Facility, it did not supersede them.

The Soviet effort to deliver a capsule to the lunar surface using the rough landing technique finally succeeded with Luna 9. This was launched at 11:42 GMT on 31 January 1966. Its mass was 1,538 kg, including the surface capsule. The midcourse manoeuvre was made at 19:29 on 1 February. As with the Block II Ranger, the inability to deal with a lateral velocity component in the descent limited targets to longitudes of about 64°W and fairly near the equator. In this case, the target was in Oceanus Procellarum, near Hevelius. At an altitude of 8,300 km, with about half an hour to go, the spacecraft aligned its main axis to local vertical. The radar altimeter initiated the retro manoeuvre at 18:44:42 on 3 February, at an altitude of 75 km. At 18:45:30, after slowing by 2.6 km/sec, the engine was cut off when a 5-metre-long probe made contact with the surface, and simultaneously the payload was ejected upward and to the side. The bus hit the ground at 6 m/s and its transmission ceased.

The 250-foot-diameter radio dish at Jodrell Bank in England was the largest fully steerable antenna in the world, and it was monitoring the transmission. When the signal ceased, Bernard Lovell, the head of the facility, wrote it off as another failed landing. But the shock-proof 58-cm-diameter spheroidal capsule rolled to a halt and, some 250 seconds after being released, initiated its own transmission. Four petals opened to right and stabilise the capsule and to expose its contents, which comprised a radiation detector and a line-scan TV camera that pointed upward and viewed the landscape using a nodding mirror that could rotate in azimuth.

Between 01:50 and 03:37 on 4 February a panoramic picture was built up line by line and the data transmitted in real-time. Jodrell Bank recorded the transmission. On a hunch, Bernard Lovell asked the local office of the Daily Express to provide a commercial wire-facsimile machine, and the signal was fed into it. Even before the Soviets announced their probe had transmitted a picture, the ‘scoop’ was published in Britain with the headline: From Luna 9 to Manchester – The Express Catches the Moon. Unfortunately, not knowing how to extract the aspect ratio of the image from the telemetry, they had guessed, and caused the horizontal scale to be compressed by a factor of 2.5, and since it was consistent with the popular expectation of the lunar surface, the resulting jagged landscape seemed ‘right’. The ruggedness was further emphasised by the fact that the Sun was just 7 degrees above the horizon and cast very long, very dark shadows. The surface looked like glassy scoriaceous lava that would be very treacherous for an astronaut to walk on – much like the ‘aa’ lava in Hawaii, so named because a person walking on it tends to cry that sound!

When the official version was issued later using the true aspect ratio, the jagged ‘spikes’ were seen to be just rocks resting on the surface, and the scene was rather less dramatic. The capsule had come to rest oriented 16.5 degrees off vertical. The field of view spanned 11 degrees above and 18 degrees below the perpendicular to the capsule’s axis, with a series of 6,000 vertical lines spanning a full 360 degrees of

azimuth. As the mirror was only 60 cm off the ground, the perspective was very low, with objects in the foreground appearing larger than they were, and the horizon was very close as a result of the capsule having landed in a shallow 25-metre-diameter crater. There was no sign of the bus.

Gerard Kuiper claimed that there were vesicles in the rocks, which supported his idea that the maria were volcanic. As meteors were particles of dust that penetrated

the Earth’s atmosphere, it seemed only reasonable that the airless Moon would have accumulated a blanket of such material, but this did not seem to be the case. Thomas Gold responded to the evident absence of dust (on this patch of mare, where it could reasonably have been expected to be very thick) by suggesting that the ‘rocks’ were not fragments of lava but fine powder which had adhered to form clods. The surface clearly had sufficient bearing strength to support the capsule’s 100-kg mass – but in the weak lunar gravity its weight was one sixth of this value. To the Apollo planners, this was the most significant result of the mission. Gold argued that the capsule was spreading this load across the four deployed panels, and in time it would sink from sight. The geologists of the Branch of Astrogeology inferred that the surface was (to use Harold Urey’s term) gardened by impacts. The site was on a dark geological unit that Jack McCauley, in making the Lunar Astronautical Chart for this area, had interpreted as a pyroclastic blanket with lava flows. Although there was nothing in the image to suggest pyroclastic, it did indeed look like a lava flow, and judging by the sharpness of the rocks and the absence of dust it was relatively young in terms of lunar history.

A second panorama was taken between 14:00 and 16:54 on 4 February, and this showed that the capsule had increased its tilt to an angle of 22.5 degrees, altering the angle of the horizon. Gold claimed this was evidence of the capsule sinking into the dust. The offset had the benefit of facilitating limited stereoscopic analysis. Before the battery expired on 6 February, further partial pans were made to observe how the illumination changed as the elevation of the Sun in the lunar sky increased, thereby demonstrating the value of repeatedly imaging a scene from a fixed vantage point.