Category Paving the Way for Apollo 11

In May 1961 Aeronutronic began to drop balsa encapsulated ‘survival capsules’
containing sterilised systems immersed in viscous fluid from aircraft flying over the Mojave Desert – with disappointing results: those that fell on rocky ground failed to operate. Further tests in October showed that even seismometers which survived the impact often suffered electronic issues. With the launch of Ranger 3 only months away, this was disconcerting. On 6 November 1961 Don B. Duncan replaced Frank Denison in charge of developing the capsule. NASA issued heat-treatment waivers for the most sensitive components of the radar altimeter, retro-rocket and capsule. In 1961 Albert Hibbs, Chief of the Space Sciences Division at JPL, appointed Harold W. Washburn as Ranger Project Scientist to liaise between the spacecraft engineers and the experimenters and coordinate their activities during a mission.2

Meanwhile, after the Ranger 3 bus was assembled at JPL in July 1961 it suffered much greater component failure rates than the case of the proof-test model, with the only difference between them being heat-sterilisation. NASA issued further waivers for the most sensitive components. ft was clear that the sterilisation process efficacy specified in 1960 was unattainable. On 15 November NASA formally accepted the repaired bus. ft was driven by truck in an environmentally regulated container, and arrived at the Cape on 20 November. On 6 December Oran Nicks opined to Edgar Cortright that one of the three Block ff flights would be successful, and one, perhaps two, of the four Block fff flights. This underscored the perceived technological risk of the venture. James Burke expected one of each to be a fully successful flight. On 2 January 1962 Clifford Cummings told Robert Seamans that it was “likely that the sterilization procedures have compromised spacecraft reliability”. However, when Lockheed announced that it had fixed the problem with the Agena B, NASA decided to try to launch Ranger 3 on schedule.

The major objectives for the mission were to perform the midcourse and terminal manoeuvres. Given the performance of its predecessors, it was fully expected that on being set free by the Agena, Ranger 3 would deploy its appendages and adopt cruise attitude. ff it flew to the Moon as planned, then Burke’s engineers would be content. ff the surface package functioned properly, this would constitute a bonus – if not, the package would have two more opportunities to achieve its scientific objectives.

Although it would be a considerable technical feat to reach the Moon at all, and in a sense anywhere would satisfy the mission, the trajectory was very limited. The fact that the retro-rocket of the surface package could not deal with a lateral velocity component meant the bus needed to make a vertical descent over the target. This, in turn, meant a site near the equator on the leading hemisphere. Prior to the space age, astronomers had defined lunar longitude in terms of how the Moon appeared in the terrestrial sky, with the leading limb (i. e. the one that faces the Moon’s direction of travel as it pursues its monthly orbit of Earth) being east. However, in August 1961 the fnternational Astronomical Union had redefined the system to match the point of view of an observer on the lunar surface, with east in the direction of sunrise; thus reversing the old scheme. For a Ranger Block ff the

fn 1963 Thomas Vrebalovich would succeed Washburn as Ranger Project Scientist at JPL.

target would therefore have to be in the western hemisphere. In fact, a vehicle launched from Florida would expend less energy in approaching Oceanus Procellarum between 10 and 50 degrees west of the meridian and within 16 degrees of the equator than it would for any other region. Because the Moon maintains one hemisphere facing towards Earth, at any given site Earth remains in a more or less fixed position in the sky. The target could not be so far towards the limb that at unfavourable librations the signal from the surface would be too weak to be read. Another constraint was that the timing had to be such that the Moon was visible to Goldstone when the bus transmitted its scientific data. The phase of the Moon would be ‘full’ on 20 January 1962 and ‘last quarter’ on 28 January. The window was set for 22-26 January. If Ranger 3 managed to lift off on the first day, it would make its approach on 25 January.

After Ranger 3 completed its final systems checks in Hangar AE, it was driven to Pad 12 on 18 January and installed on its launch vehicle. When kerosene was loaded into the Atlas on 19 January, a leak was discovered in the bulkhead between the fuel tank and the liquid oxygen tank. Over the next few days the Air Force removed the centre engine and built a wooden frame up through the exposed aperture at the base of the fuel tank in order to allow technicians wearing masks and oxygen cylinders to replace the ruptured bulkhead. This round-the-clock effort made the vehicle ready in time to attempt to launch on the last day of the window. Meanwhile, as this was the first mission of the project intended to reach the Moon, the spacecraft was sealed in the aerodynamic shroud atop the Agena and bathed in gaseous ethylene oxide for 11 hours as the final stage of the sterilisation process, then the shroud was purged with dry nitrogen passed in through a sterile filter.

The countdown on 26 January proceeded smoothly, and Ranger 3 was launched at 20:30 GMT. The Air Force tracked its ascent and calculated the steering commands, but when these were transmitted to the Atlas it failed to act on them. The autopilot flew on, ignorant of deviations from the planned trajectory. In particular, it was not possible to command the moment of shutdown to optimise the final velocity, and when the autopilot ordered this using its programmed parameters it was both higher and faster than required. As a result of this discrepancy, the parking orbit attained by the Agena was slightly different to that planned. The limited ability of the spacecraft to correct its trajectory meant that in making the translunar injection the Agena had to pass through a ‘key hole’ in the sky that was only 16 km wide, and attain a speed which differed from the desired 40,000 km/hour by no more than 25 km/hour. In the event, Woomera’s tracking indicated that the spacecraft would cross the orbit of the Moon at a point 32,000 km ahead of that body – a discrepancy which exceeded the spacecraft’s 44-m/s midcourse manoeuvre cap­ability. Nevertheless, engineers were encouraged that Ranger 3 had deployed its solar panels, locked onto the Sun, rolled to acquire Earth and then deployed its high – gain antenna. The flight would provide an opportunity to evaluate the spacecraft’s performance in deep space, essentially as had been intended for the Block I.

James Burke flew from the Cape to JPL to operate the spacecraft from the Space Flight Operations Center. It was decided to exercise all of the functions, including the midcourse and terminal manoeuvres. It was not possible to test the retro-rocket

Preparing the surface package subsystem of the Block II Ranger spacecraft.

of the surface package, since its separation from the bus could be triggered only by its own radar altimeter. On 27 January the sequence of commands was uplinked for a midcourse manoeuvre designed to reduce the flyby range. Ranger 3 executed the preliminary roll and pitch changes as specified, fired its engine, then resumed cruise attitude. However, tracking revealed that the burn was the opposite of that intended and had increased the miss distance to 36,750 km. The error was an inverted sign in the computer program used by JPL to calculate the burn. Regardless of the outcome, the engineers were delighted that the spacecraft had made a manoeuvre and resumed its cruise attitude. Shortly after this, the boom holding the gamma-ray experiment completed its deployment. It had hinged down after separation from the Agena, and now, as planned, a gas generator extended it in a telescopic manner. The instrument was able to calibrate the emissions by the spacecraft and then make the first direct measurement of the flux of gamma rays in space.

A plan had been devised to perform a terminal manoeuvre which would orient the spacecraft to enable it to photograph the Moon during the flyby – in much the same manner, in fact, as had been intended for some of the Pioneer probes. In this case, it would view the illuminated leading hemisphere, and reveal that portion of the far – side which was in darkness for Luna 3 in 1959. The unplanned trajectory meant that Ranger 3 drew close to the Moon on 28 January. The cover for the optics was commanded to open, and power was applied to warm up the TV system. Goldstone uplinked the commands for the terminal manoeuvre to turn the spacecraft in order to point the camera at the Moon. The inverted sign had been corrected prior to making the calculation. An hour later, the spacecraft was told to make the manoeuvre. It initiated the pitch change in the correct direction, but soon thereafter the downlink began to intermittently drop out – a computer/sequencer fault had denied the vehicle the use of its Earth and Sun sensors, the gyroscopes directing the turn did so in an uncontrolled manner and the spacecraft was left spinning. At the appointed time, the TV system took pictures. Some frames were received at a very weak signal strength, and the fact that it was possible to see the black reference marks on a pane of glass in front of the focal plane silhouetted against a soft glow of sunlight glinting off the structure of the spacecraft provided welcome confirmation to the engineers from the Radio Corporation of America that their system had worked. At 23:23 GMT, some 6 hours after the attempted manoeuvre, Ranger 3 crossed the orbit of the Moon and passed on into solar orbit.

On 8 February 1962 JPL informed Oran Nicks of the preliminary findings of its investigation into the loss of Ranger 3. It had been concluded that the malfunction of the computer/sequencer was a result of the heat treatment required for sterilisation. It would therefore be necessary to issue waivers for the components believed to have failed. Although the mission had not reached the Moon, it had nevertheless provided an opportunity for the flight control team to compute a deep-space trajectory and then uplink the commands for a midcourse manoeuvre, which the spacecraft – the most sophisticated American deep-space vehicle to date – had executed as directed. The engineers were therefore confident that the next mission would reach the Moon.

Meanwhile

Homer Newell’s Space Sciences Steering Committee decided on 1 December 1961 to consolidate the TV experiments of the Block II and Block III versions of Ranger. Previously, Gerard Kuiper, Gene Shoemaker and Harold Urey had been named to receive and interpret such pictures as were returned by the Block II flights – having played no part in the development of the camera. Now it was decided that they should form a team, together with Ray Heacock of the Space Sciences Division at JPL, and work with the Radio Corporation of America in the development of the high-resolution TV system for the Block III. In effect, Newell wished to integrate the engineers and scientists at the project level at JPL to match the recent integration at the program level in Washington, in the expectation that this would enhance the scientific results. Unfortunately for James Burke, in early 1962 Newell also sought to augment the Block III to recover some of the particles and fields research lost on the Block I flights. On 14 March 1962 the Steering Committee decided to add eight experiments to the Block III. Burke learned of this from Oran Nicks on 20 March. The solar panels of the Block I and Block II were triangular with truncated tips. It was necessary to fit larger rectangular panels to provide the power to operate all the additional Block III experiments.

RECONNAISSANCE FLIGHTS

Only 28 months elapsed between James Webb approving the Boeing contract for Lunar Orbiter and the first mission. It had been hoped to launch on 11 July 1966, but Eastman Kodak was late in delivering the photographic system and the launch was rescheduled for 9 August. At the Cape, the Air Force made available Hangar S for the project. The photographic system was installed on 1 August, and the next day the spacecraft was mated with its Atlas-Agena D on Pad 13. At this point, a Deep Space Network facility at the Cape verified the spacecraft’s communication system.

The countdown on 9 August was scrubbed at T-7 minutes owing to an anomaly with the Atlas, but liftoff occurred at 19:26:01 GMT on 10 August. The spacecraft’s launch mass was 387 kg – which was at the top end of the launcher’s capability for a deep-space mission. The Agena made a 154.5-second burn to achieve insertion into parking orbit at an altitude of 190 km at 19:34:44. It reignited at 20:02:35 to perform the 89-second translunar injection manoeuvre.

Following its release at 20:06:48, Lunar Orbiter 1 deployed its solar panels and antennas, then acquired the Sun for the first step towards adopting its cruise attitude. Some 6 hours into the translunar coast, the spacecraft was ordered to roll in order to locate the star Canopus, but it failed to lock on. The sensor was being distracted by sunlight reflecting off the vehicle’s structure – a possibility that really ought to have been ‘designed out’. The vehicle was commanded to turn to point the sensor at the Moon to provide a second point of reference to initialise the inertial system.

The midcourse manoeuvre of 38 m/s was achieved by a 32-second burn started at 00:00 on 12 August. When its interior began to overheat, the vehicle was instructed to swing its main axis 36 degrees off-Sun. This thermal problem came as a surprise, because Boeing had subjected the design to thorough testing in the vacuum chamber at its Kent Test Facility in Seattle. The Canopus sensor was finally able to lock on at 13:50 on 13 August.

The trajectory was so accurate that the vehicle arrived within 10 km of the desired

orbit insertion point. The command for the insertion manoeuvre was sent at 15:23 on 14 August, after a cruise of 92 hours as against 66 hours for Ranger. After adopting the requisite attitude, the spacecraft began the burn at 15:34, firing its engine for 579 seconds in order to slow down by 790 m/s and enter a 190 x 1,860-km orbit that was inclined at 12.2 degrees to the lunar equator and had a period of 3 hours 37 minutes. As viewed from an imaginary vantage point above the Moon’s north pole, the orbit was anticlockwise. Shortly after insertion, the vehicle disappeared around the Moon’s trailing limb.

On 15 August Lunar Orbiter 1 read out the pre-exposed test frames on the leader of its film strip. These had been read out during ground trials at Goldstone to verify the functionality of the scanning and communication system. This in-flight readout was to confirm that the entire apparatus, both in space and on Earth, was functioning properly. By now, the thermal problem had become acute. The paint on the base of the vehicle was meant to absorb heat while exposed to sunlight and radiate it back to space while in the shadow of the Moon, but it seemed the pigment was deteriorating. However, on 18 August an electrical issue had the beneficial side – effect of easing this overheating problem.

The phase of the Moon was ‘new’ on 16 August; ‘first quarter’ would occur on 23 August and ‘full’ on 31 August. As the alignment of the spacecraft’s perilune would remain fixed relative to the stars, the longitude of perilune would migrate westward at a rate of 12 degrees per 24 hours as the Moon travelled around Earth. This meant that the spacecraft could photograph a succession of sites along the equatorial zone with the Sun at essentially the same elevation in the sky. The Canopus sensor would routinely recalibrate the inertial system to ensure that the camera was accurately aimed.

After advancing the film to its start point, the camera snapped its first pictures on 18 August. It viewed Mare Smythii, near the equator on the eastern limb. Although outside the Apollo zone, this area was of interest for selecting landmarks to assist in Apollo orbital navigation. In this case, the spacecraft was at an altitude of 246 km, its velocity relative to the surface was 6,400 km/hour, the shutter setting was 1/50th second, and the frame pairs were taken at 10-second intervals. These frames were processed and 5 hours later were scanned travelling forward through the system. The M frames were of excellent quality, but it seemed that the focal-plane shutter of the narrow-angle optics was out of synchronisation with the V/H sensor, smearing the H frames. To investigate the problem, it was decided to take additional pictures using different shutter speeds, both with and without the V/H sensor operating. The results confirmed the sensor to be inoperative. A further test was made in which the output voltage of the sensor was increased in the hope of engaging the shutter, but this did not work. An analysis of the telemetry showed that the logic control circuitry of the focal-plane shutter was susceptible to electromagnetic interference that made it fire at the wrong point in the motion-compensation cycle, and this was a problem which could not be overcome in flight.

Since the H frames were essential to addressing Apollo’s requirements and they would not be able to be provided, Jack McCauley and Lawrence Rowan of the US Geological Survey recommended that the high perilune be retained in order to

206 The Apollo zone

Preparing to fit the aerodynamic shroud on the Lunar Orbiter 1 spacecraft, wrapped in its thermal blanket.

A press conference by Lunar Orbiter managers on 1 August 1966 in the run up to the first Lunar Orbiter mission.

The Lunar Orbiter 1 mission timeline.

obtain wide-area mapping at a resolution of about 25 metres, to improve coverage of the majority of the Apollo zone at a definition better than that of a telescope. Doing so would enable other candidate sites to be re-evaluated prior to drawing up the target lists for subsequent Lunar Orbiter missions. The Bellcomm advisors were in agreement. But Clifford Nelson, the Project Manager at Langley, and his Boeing counterpart, Robert Helberg, argued that if the perilune were lowered then the increased rate of motion presented to the V/H scanner might induce the shutter to synchronise, in which case the mission would be able to proceed as planned. And so it was decided to make a 22.4-second, 40-m/s burn at 09:50 on 21 August to lower the perilune to 58 km.

As the spacecraft was approaching apolune, shortly prior to the perilune – lowering manoeuvre, it took a picture of the far-side. At an altitude of 1,497 km there was no need for V/H motion compensation, and when the H frame was read out it proved to be of excellent quality, confirming that the optics were correct. At this point, it was discovered that the Bimat strip was sticking to the processing drum. The plan had been to obviate this problem by not letting the Bimat remain immobile for more than 15 hours, and to shoot a frame-pair once every four orbits with the thermal door shut if no target was scheduled. The remedy was to reduce the time that the Bimat was immobile. The increased number of frames for this maintenance task meant revising the photographic mission. The most important targets would still receive the planned 16-exposure blocks, but others would get only half this number.

Lunar Orbiter 1 was to photograph nine primary targets in the southern part of the Apollo zone, seven secondary targets and the far-side from high altitude. At this stage in the reconnaissance process, however, each primary target spanned an area in which there might prove to be tracts which could be nominated as potential Apollo landing sites.

The primary targets were labelled by Roman numeral ‘I’ (for the first mission), ‘P’ for primary, and an Arabic number in a sequence progressing generally from east to west. In this scheme, the Mare Smythii area was I-P-0.

In terms of classifications:

I, mare

A, average mare

B, dark mare

C, ridged mare

D, rayed mare

II, upland

A, highland basins

B, subdued uplands

C, upland plains

D, sculptured highlands

III, craters

A, well formed

B, subdued

A map of the near-side of the Moon on a scale of 1:5,000,000 derived from imagery produced by the Lunar Orbiter missions.

The Apollo zone annotated with the primary photographic targets assigned to the Lunar Orbiter 1 mission.

IV, structural features

A, ridges

B, domes

C, rilles

the planners had the following to say about the primary sites:

Site I-P-1 (0.9°S, 42.3°E)

This site is within the lowlands of the western extreme of Mare Foecunditatis, and a portion of the eastern extremity of the central highlands. The inclusion of dark mare, moderately light mare and uplands makes this a valuable terrain calibration area. The 1-metre relative roughness of the two mare types is of special interest. The possible detection of generic relationships in the contact between the uplands and dark mare is of particular importance scientifically. The mare units are potential Apollo landing sites. (Rating A)

Site I-P-2 (0.2°S, 36.0°E)

A highland site bordering the southeast part of Mare Tranquillitatis. Significant terrain calibration data is expected for the mare and upland units II-A and II-B. Potential Apollo landing sites may be revealed here. (Rating B)

Site I-P-3 (0.3°N, 24.9°E)

This site in southwestern Mare Tranquillitatis is crossed by a ray. Data on the small-scale roughness and morphology of this area should be obtained. It is a potential Surveyor and Apollo landing site. (Rating B)

Site I-P-4 (0.0°, 12.9°E)

This site is located in the central highlands between Mare Tranquillitatis and Sinus Medii. High-resolution photography of terrain units II-A, II-B, II-C and II-D will provide data to define the 1-metre-resolution roughness of the upland areas. This is a potential Surveyor and Apollo landing site. (Rating A)

Site I-P-5 (0.4°S, 1.3°W)

Located in the southwestern portion of Sinus Medii, this is an especially good example of a smooth mare with low subdued ridges, which are important in the evaluation of the mare origin and development. This has high potentiality as a Surveyor and Apollo landing site. (Rating B)

Site I-P-6 (4.0°S, 2.9°W)

This area in the northern sector of the central highlands is important to terrain calibration by offering high-resolution photography of upland unit II-D as well as the deformed crater floor that is a previously selected Surveyor landing site. It is expected that this coverage will be valuable when bearing-strength data becomes available for the major terrain types. (Rating A)

Site I-P-7 (3.8°S, 22.8°W)

This site located between the craters Fra Mauro and Lansberg is a moderately good example of a mare with low sinuous ridges, small craters and a light ray. It should provide important information regarding the development of older mare surfaces, and their characteristic morphology. It is a previously selected Surveyor landing site. (Rating B)

Site I-P-8.1 (3.0°S, 36.5°W)

This site in the southeast part of Oceanus Procellarum is a superior example of a relatively straight mare ridge, and is of particular importance in the definition of 1-metre-resolution roughness. It is an opportunity to investigate the generic processes concerned with the development of this mare morphology. It is a highly rated Surveyor landing site. (Rating A)

Site I-P-9.1 (2.3°S, 43.4°W)

This is the Surveyor 1 landing site. The location was changed on the basis of later refinement of the position of the lander, relabelled I-P-9.2a and I-P-9.2b, and scheduled for two successive orbits.

The first photography of a site in the Apollo zone was a 16-exposure sequence of I-P-1 taken on 22 August. The possibility of photographing Earth on the limb of the Moon had been discussed a year before the spacecraft was launched, but it was not made a mission requirement. On 22 August NASA representatives suggested that it be attempted, even though it would require the vehicle to adopt an unusual attitude. Robert Helberg, the Boeing manager, considered the impromptu manoeuvre to be an unnecessary risk because immediately after taking the picture the vehicle would pass beyond the limb and would have to re-establish its normal attitude out of contact with Earth. The company was understandably reluctant, because a large part of the bonus of its ‘incentive’ contract depended on completing the primary mission. Floyd Thompson, Clifford Nelson and Lee Scherer were in favour. Boeing relented when NASA agreed to compensate it if the vehicle were lost as a result of the experiment. At an altitude of 1,198 km, climbing towards apolune on 23 August, Lunar Orbiter 1 approached the trailing limb of the Moon as viewed from Earth. It turned to point its main engine perpendicular to the line of the limb, and then rolled until the camera’s oblong H frame paralleled the limb. The shutter was fired at 16:36:28.6 GMT. The wide-angle view showed Earth as a tiny crescent against the limb, and also provided a magnificent view of the far-side crater Tsiolkovsky. The H – frame was much more dramatic, showing ‘Earth set’ against the cratered lunarscape. This was prominently featured by newspapers. A somewhat less impressive picture of Earth was taken at 07:15:00.9 on 25 August.

A 3-second, 5.4-m/s burn at 16:01 on 25 August lowered the perilune to 40 km to increase the motion of the image across the narrow-angle shutter, but the V/H sensor remained inoperative. At 13:23 on 29 August the spacecraft began the photographic sequence for I-P-9.2b, the final target on its list. The Bimat strip was cut at 18:14 on 30 August, and the full readout by rewinding the film began at 20:42. This process was finished at 21:18 on 16 September. Of the total of 205 frame-pairs, 38 had been obtained in the initial orbit. All nine primary targets had been photographed at lower altitude. Despite the loss of the high-resolution pictures of the primary targets, the mission was judged a successful engineering test of a new spacecraft which had produced some useful imagery.

On 23 August 1966 Lunar Orbiter 1 took this picture of Earth about to set behind the limb of the Moon. As the first view of our planet from lunar distance it was a sensation.

The geometry of Lunar Orbiter 1’s historic picture of Earth near the Moon’s limb. (Courtesy of the Lunar Orbiter Image Recovery Project, Ames Research Center, 2008)

Its primary mission over, Lunar Orbiter 1 flew on to gather additional selenodesy, micrometeoroid and radiation data – all eagerly sought by the Apollo planners. The radio tracking of the spacecraft also served to certify the facilities and procedures of the Manned Space Flight Network at lunar distance.[31] By 28 October the condition of the vehicle had deteriorated – its battery was failing as a consequence of persistent overheating, its transponder was dropping out intermittently, its inertial reference unit was becoming unreliable, and the nitrogen for its attitude control thrusters was almost exhausted. To lose control of the communications system would risk radio interference with its successor, so on 29 October Lunar Orbiter 1 was deliberately crashed onto the far-side. In its 8 weeks in space, the micrometeoroid experiment had reported no hits at all. Because of the persistent thermal problems, the white paint for the base of the vehicle was modified for the next mission.

The Lunar Orbiter Photo Data Screening Group of specialists from JPL, Langley, the Manned Spacecraft Center, Boeing, Bellcomm, the Army Map Service, the Air Force Chart and Information Center, NASA headquarters and the US Geological Survey studied Lunar Orbiter 1’s M frames to test the hypothesis that terrain which appeared smooth at the resolution of a telescope was probably smooth in finer detail. They also estimated the cratering of the different types of terrain, first by counting the craters down to the limiting resolution and thereafter using the photogrammetry technique. And, of course, photoclinometry was used to measure slopes. With Gene Shoemaker busy with Surveyor, the analysis at the US Geological Survey was led by Jack McCauley. For a spacecraft making a powered descent directly from translunar trajectory the target was a 60-km-diameter circle, but an Apollo lander descending from lunar orbit was expected to be able to be more accurate. But because pin-point accuracy could not presumed, at least not for the early missions, Apollo targets were ellipses with their major axes aligned along the line of approach. The US Geological Survey produced terrain and geological maps for smooth-looking areas which were large enough to accommodate ellipses of sizes corresponding to differing degrees of landing accuracy.

Taking into account the ‘ground truth’ provided by Surveyor 1 at I-P-9.2, the nine primary targets were rated in terms of increasing roughness as follows:

I-P-9.2

I-P-3

I-P-1

I-P-7

I-P-8.1

I-P-5

I-P-6

I-P-4

I-P-2

Table 11.1 – Lunar Orbiter 1 orbital manoeuvres and photography Date Event/Site Frames 14 August Orbit insertion 18 August I-P-0 22 (5-24) 19 August far-side 1 (28) 20 August far-side 1 (30) 21 August Perilune cut to 58 km 22 August B-2 2 (48-49) 22 August I-P-1 16 (52-67) 22 August I-P-2 16 (68-83) 23 August I-P-3 16 (85-100) 23 August Earth 1 (102) 23 August B-5 1 (103) 24 August I-P-4 8 (105-112) 24 August B-7 2 (113-114) 25 August B-5 2 (115-116) 25 August Earth 1 (117) 25 August I-P-5 16 (118-133) 25 August Perilune cut to 40 km 25 August B-8 2 (134-135) 26 August I-P-6 8 (141-148) 27 August B-9 1 (149) 27 August B-10 2 (150-151) 27 August B-11 4 (153-156) 28 August I-P-7 16 (157-172) 29 August I-P-8.1 8 (176-183) 29 August I-P-9.2a 16 (184-199) 29 August I-P-9.2b 16 (200-215) 30 August Cut Bimat and start full readout 16 September Finish readout Notes: (1) Engineering exposures have been omitted. (2) The В-sites were previews of targets being considered for the forthcoming ‘В’ mission.

On 6 May 1966 representatives of Lunar Orbiter, Surveyor, Apollo and Bellcomm had met at Langley in order to plan the ‘B’ mission. Whereas the inclination of the first spacecraft’s orbit was chosen to facilitate vertical photography of targets in the Apollo zone south of the equator, the inclination of the second spacecraft’s orbit was to inspect targets north of the equator. As planning for this mission began before the first mission flew, the targets were drawn from those chosen by the Surveyor/Orbiter Utilisation Committee from the list submitted by Jack McCauley in August 1965 on the basis of telescopic studies. A total of 13 primary and 17 secondary targets were selected, each of which was to receive one pass. The secondary areas were not under consideration for the early Apollo landings, but were considered to be of ‘scientific interest’. The photographic system had to advance at regular intervals to prevent the Bimat from sticking. In accordance with Boeing’s procedure, for Lunar Orbiter 1 the film had been advanced with the thermal door closed. But Tom Young at Langley and Ellis Levin at Boeing had devised a procedure for doing this with the door open, and a schedule had been written to allow this maintenance function to provide useful pictures. The ‘B’ plan was approved by the Surveyor/Orbiter Utilisation Committee on 1 June.

In late September, however, the planners convened to review the target list in the light of the results of the first mission. One factor that influenced Apollo planning was Ranger 7’s pictures of bright rays from Copernicus and Tycho crossing Mare Nubium. If (as was suspected) all rays were highly cratered, then this would argue against such areas being considered as landing sites. To test this hypothesis, Lunar Orbiter 1 had imaged a faint ray crossing Mare Tranquillitatis that originated from Theophilus, a prominent crater in the highlands to the south. There was no H frame coverage to confirm it, but the M frame suggested that the cratering was insufficient to rule out this site (I-P-3) as a potential Apollo site. It was decided to revise the ‘B’ mission to further study this issue by inspecting rays crossing Oceanus Procellarum between the craters Copernicus and Kepler. On 29 September the Surveyor/Orbiter Utilisation Committee, having reviewed the crater densities and slopes derived from Lunar Orbiter 1’s M frames, recommended that eight areas be carried over to Lunar Orbiter 2 for study at higher resolution. Apart from the deletion of the high-perilune photography of the eastern limb, in purely operational terms the ‘B’ mission was to be a repeat of its predecessor.

After serving as the backup for the first mission, Lunar Orbiter 2 had been stored. Once modified, it was mated with its launch vehicle on 31 October and a countdown test that concluded on 3 November certified it ready for flight.

Lunar Orbiter 2 was launched at 23:21 GMT on 6 November 1966. After coasting in parking orbit for 14 minutes, the Agena performed the translunar injection burn. Parts of the spacecraft’s surface had been painted black to reduce the opportunity for reflected sunlight to dazzle the Canopus sensor, and at 08:21 on 7 November this locked on without incident. At 19:30 on 8 November the spacecraft fired its engine for 18 seconds for a 21-m/s midcourse manoeuvre. The modified paint on the base of the vehicle eliminated the thermal problem that had marred the first mission. The 612-second, 830-m/s burn at 20:26 on 10 November put the spacecraft into an initial orbit of 196 x 1,871 km that was inclined at 12.2 degrees to the lunar equator and had a period of 3 hours 38 minutes. At 22:58 on 15 November a 17.4-second 28-m/s burn lowered the perilune to 50 km. The photography began on 18 November. The phase of the Moon was ‘new’ on 12 November; ‘first quarter’ would occur on 20 November and ‘full’ on 28 November.

Several modifications had been made to the photographic system. In particular, an integrating circuit had been added to the focal-plane shutter control logic to ensure that an output signal was not an electrical transient but a genuine command pulse; and a filter had been added to the 20-volt power line in order to minimise electromagnetic interference and spurious triggering of the circuits. An early check showed that the V/H sensor was operating correctly. As the spacecraft’s perilune migrated west with the terminator, on 20 November it photographed site II-P-5 in Mare Tranquillitatis in search of Ranger 8’s impact point. On the next revolution it

The Apollo zone annotated with the primary photographic targets assigned to the Lunar Orbiter 2 mission.

inspected the nearby I-P-3 target that had been rated highly on the basis of Lunar Orbiter 1’sM frames, thereby obtaining the H frames which would be required for a more detailed evaluation.

The most striking image of any mission to date was taken on 24 November as one of the maintenance exposures. Douglas Lloyd of Bellcomm had suggested early in planning that at this point the opportunity should be taken to obtain an oblique view of Copernicus, and this had been agreed as II-S-12. The vehicle was at an altitude of 46 km, and the 100-km-diameter crater was some 240 km away to the north of the ground track. The illumination was ideal for discerning the nature of the local topography – on the horizon beyond the crater was a section of the Carpathian Mountains, whose peaks stand 1,000 metres above the surrounding terrain. This was the first view to present the Moon as it would be seen by an astronaut in low orbit. When the picture was issued to the press, the New York Times journalist Walter Sullivan described it as “one of the greatest pictures of the century”.

Another such maintenance exposure, II-S-15, was an oblique of the Marius Hills in the western portion of Oceanus Procellarum, which gave the impression of being volcanic domes.

The photography concluded on 25 November, after all 30 of the specified targets had been documented. The high-gain transmitter failed on 6 December, one day before the readout was to end. Although this resulted in the loss of three M and two H frames of target II-S-1 in the eastern part of Mare Tranquillitatis, these had been taken at the start of the mission and their loss was not serious because some of them had been read out as part of the verification process as the film was running forward. The mission provided a number of high-quality pictures of the far-side. As regards the rays crossing the maria, while the results showed these were not always heavily cratered, II-S-11 located between Copernicus and Kepler was certainly ruled out for Apollo. The micrometeoroid experiment reported three hits. As the first mission had reported no hits, it was speculated that Lunar Orbiter 2 had been exposed to the annual Leonid meteor shower.

On 8 December Lunar Orbiter 2 fired its engine for 62 seconds to increase the inclination of its orbit to 17.5 degrees in order to improve the selenodesy coverage. A 3-second burn on 14 April 1967 reduced the period of the orbit by 65 seconds in order to minimise the time the vehicle would spend in darkness as the Moon passed through the Earth’s shadow on 24 April. After providing almost a year’s worth of selenodesy, on 11 October 1967 Lunar Orbiter 2 was deliberately crashed on the far – side.

The mission provided 184 frames of the 13 primary targets. The screening team reconvened at Langley on 5 December 1966 to assess the results. After the M frames had been examined to identify the terrain units in terms of the regional geology, the H frames were used to make a detailed characterisation in terms of crater densities, slope frequency distributions, blockiness etc.

When the Apollo Site Selection Board convened on 15 December, it was able to discuss the pictures from the first two Lunar Orbiter missions. Shallow pits (‘dimple craters’) on Ranger pictures had been interpreted by some people as having formed by loose material draining into subterranean cavities, with chains of pits indicating

A portion of the picture taken by Lunar Orbiter 2 on 24 November 1966 showing the central peak complex and terraced wall of Copernicus, with a mountain range beyond. This unprecedented oblique view was described as “one of the greatest pictures of the century’’.

An oblique view taken by Lunar Orbiter 2 on 25 November 1966 showing the hills and flow fronts in western Oceanus Procellarum near the crater Marius.

Table 11.2 – Lunar Orbiter 2 orbital manoeuvres and photography Date Event/Site Frames 10 November 15 November Orbit insertion Perilune cut to 50 km 18 November II-P-1 16 (5-20) 18 November II-S-1 4 (21-24) 18 November II-S-2a 4 (25-28) 18 November II-S-2b 4 (29-32) 19 November II-S-3 1 (33) 19 November II-S-4 1 (34) 19 November II-P-2 8 (35-42) 19 November II-P-3a 8 (43-50) 19 November II-P-3b 8 (51-58) 19 November II-P-4 8 (59-66) 20 November II-P-5 8 (67-74) 20 November II-S-5 1 (75) 20 November II-P-6a 8 (76-83) 20 November II-P-6b 8 (84-91) 21 November II-S-6 1 (92) 21 November II-S-7 1 (93) 21 November II-S-8 1 (94) 21 November II-S-9 1 (95) 22 November II-P-7a 8 (96-103) 22 November II-P-7b 8 (104-111) 22 November II-S-10 1 (112) 22 November II-P-8a 8 (113-120) 22 November II-P-8b 8 (121-128) 22 November II-P-8c 8 (129-1З6) 23 November II-S-11 1 (137) 23 November II-P-9 8 (138-145) 23 November II-P-10a 8 (146-153) 23 November II-P-10b 8 (154-161) 24 November II-S-12 1 (162) 24 November II-P-11a 8 (163-170) 24 November II-P-11b 8 (171-178) 24 November II-P-12a 8 (179-186) 24 November II-P-12b 8 (187-194) 25 November II-S-13 1 (195) 25 November II-S-14 1 (196) 25 November II-P-13a 8 (197-204) 25 November II-P-13b 8 (205-212) 25 November II-S-15 1 (213) 25 November II-S-16 1 (214) 25 November 26 November 6 December II-S-17 Cut Bimat and start full readout Readout halted 1 (215)

fractures. There was concern that if the maria were lava flows, then by terrestrial analogy they might contain lava tubes which could collapse under the weight of an Apollo lander. Lawrence Rowan of the US Geological Survey ventured that in this respect younger-looking mare areas (such as II-P-2) appeared to pose a greater risk than older-looking mare areas (such as II-P-6). It had been possible to fit 23 Apollo target ellipses into clear-looking patches in the Lunar Orbiter pictures to date. After these had been screened by counting small craters and measuring slopes, eight were selected for further study.

On 5 January 1967 the Surveyor/Orbiter Utilisation Committee approved the plan for the third mission. As its predecessors had reconnoitred all the assigned targets, Lunar Orbiter 3 was to provide additional data for those which the screening process had deemed to be the most promising. The spacecraft was identical, but the operational plan was more sophisticated. At the western end of the Apollo zone, launches at different times of year favoured passing either north or south of the equator. In the case of the first mission, the orbit was inclined at 12 degrees to the lunar equator in order to photograph sites lying south of the equator from a vertical perspective, and for the second mission the orbit was inclined the other way for sites north of the equator. To enable Lunar Orbiter 3 to cover the entire latitude range, its orbit was to be inclined at an angle of 21 degrees. It was given 12 primary and 32 secondary targets. It was to obtain H frames of the best-looking areas that had been imaged by Lunar Orbiter 1 as M frames but not by Lunar Orbiter 2 as H frames. In particular, it was to provide pictures to facilitate stereoscopic analysis to compile terrain maps with 3-metre contours, in order to chart the topography on the line of approach from the east over which an Apollo lander would pass during its powered descent to a target.[32] This marked a switch from reconnoitring areas to certifying specific targets. Some of the secondary frames were oblique views of Apollo sites, taken looking west to show them as they would appear to astronauts preparing to make a descent. It was felt that three Lunar Orbiter missions in the equatorial zone should be sufficient to select targets for the first few Apollo landings. The Manned Spacecraft Center also wanted further radio tracking in lunar orbit to investigate anomalous gravitational effects which had been revealed by tracking the first two missions.

Lunar Orbiter 3 was launched at 01:17:01 GMT on 5 February 1967. Translunar injection was at 01:36:56. The spacecraft was released at 01:39:40 and deployed its appendages. Some 7 hours into the flight, it locked onto Canopus to adopt its cruise attitude. At 15:00 on 6 February the spacecraft executed a 4.3-second, 5.1-m/s midcourse manoeuvre to achieve the orbit insertion point for the desired inclination. At 04:20 on 7 February, an optional refinement was deleted. At 21:54:19 on 8 February the spacecraft began the 542-second burn to enter an initial orbit of

The Apollo zone annotated with the primary photographic targets assigned to the Lunar Orbiter 3 mission.

210 x 1,850 km inclined at 21 degrees to the lunar equator with a period of 3 hours 25 minutes. As Lunar Orbiter 2 was still providing selenodesy data, the Deep Space Network tracked both spacecraft to enable the Manned Space Flight Network to obtain experience of simultaneously monitoring two vehicles in lunar orbit, as it would for an Apollo mission.

At 18:13:26 on 12 February, Lunar Orbiter 3 lowered its perilune to 55 km. The photographic mission started on 15 February – the first sequence was of the Apollo target in eastern Tranquillitatis. The phase of the Moon was ‘new’ on 9 February; ‘first quarter’ would occur on 17 February and ‘full’ on 24 February.

When the mechanism that advanced the film started to behave erratically, it was decided to cancel an oblique picture of Grimaldi (III-S-32) in order to start the read out process a day early. Accordingly, at 06:36 GMT on 23 February the spacecraft was told to cut the Bimat strip. But film transport continued to be problematic, and when the motor burned out on 4 March only 182 of the 211 frame-pairs had been transmitted; some of the earliest were lost.3

On 12 April the orbit was revised to minimise the time the spacecraft would spend in darkness during the lunar eclipse of 24 April. On 30 August it made a 125-second burn to circularise its orbit at 160 km, in order to provide experience for the Manned Space Flight Network in tracking a spacecraft in an orbit similar to that which would be used by Apollo. On 9 October 1967 Lunar Orbiter 3 was deliberately crashed on the far-side – two days before its predecessor was commanded to do likewise.

The photographs of III-P-12 were to locate Surveyor 1, and were accumulated in four overlapping blocks on successive revolutions. The lander had oriented its two mast-mounted panels to maximise its shadow and hence improve its visibility on the surface. After it was pin-pointed on an H frame, it was able to be located on one of

Table 11.3 – Lunar Orbiter 3 orbital manoeuvres and photography Date Event/Site Frames 8 February Orbit insertion 12 February Perilune cut to 55 km 15 February III-P-1 16 (5-20) 15 February III-S-1 4 (21-24) 15 February III-P-2a 8 (25-32) 15 February III-P-2b 4 (33-36) 15 February III-S-2 1 (37) 15 February III-S-3 1 (38) 16 February III-S-4 1 (39) 16 February III-P-3 4 (40-43) 16 February III-P-4 8 (44-51) 16 February III-P-5a 8 (52-59) 3 The lost frames degraded the coverage of III-P-3, III-] P-4, III-P- 5 and III-P-6.

Table 11.3 cont. Date Event/Site Frames 16 February III-P-5b 8 (60-67) 16 February III-P-6 4 (68-71) 17 February III-S-5 1 (72) 17 February III-S-6 1 (73) 17 February III-S-7 4 (74-77) 17 February III-S-8 1 (78) 17 February III-S-9 1 (79) 17 February III-S-10 4 (80-83) 18 February III-S-11 1 (84) 18 February III-S-13 1 (85) 18 February III-P-7a 8 (86-93) 18 February III-P-7b 8 (94-101) 18 February III-S-14 1 (102) 18 February III-S-15 4 (103-106) 19 February III-S-16 1 (107) 19 February III-S-17 4 (108-111) 19 February III-S-18 4 (112-115) 19 February III-S-19 4 (116-119) 19 February III-S-21 1 (120) 19 February III-S-21.5 1 (121) 19 February III-S-22 1 (122) 20 February III-S-20 1 (123) 20 February III-P-8 8 (124-131) 20 February III-S-23 4 (132-135) 20 February III-S-24 1 (136) 20 February III-P-9a 8 (137-144) 20 February III-P-9b 8 (145-152) 20 February III-P-9c 8 (153-160) 21 February III-S-25 1 (161) 21 February III-S-26 1 (162) 21 February III-P-10 8 (163-170) 21 February III-S-27 1 (171) 21 February III-S-28 1 (172) 21 February III-P-11 8 (173-180) 22 February III-P-12b.2 4 (181-184) 22 February III-P-12a 16 (185-200) 22 February III-P-12b.1 4 (201-204) 22 February III-P-12c 8 (205-212) 22 February III-S-29 1 (213) 22 February III-S-30 1 (214) 23 February 23 February 4 March III-S-31 Cut Bimat and start full readout Readout interrupted 1 (215)

Hyginus Rille by Lunar Orbiter 3.

Table 11.4 –	Apollo site reconnaissance
Mission	No. sites	No. exposures
LO-1	9	136
LO-2	13	184
LO-3	18	162
Total	40	482

Note: Some sites were assigned to more than one mission.

the M frames taken by Lunar Orbiter 1 – although only in hindsight. The scientific targets included oblique perspectives of the 32-km-diameter crater Kepler (III-S-26) in Oceanus Procellarum and the 11-km-diameter crater Hyginus in Sinus Medii and the associated rille (III-S-6) that was suspected by some people of being of volcanic origin and was under consideration as a site for an advanced Apollo mission.

As soon as the Lunar Orbiter 3 readout ended, the screening team reconvened at Langley to assess the results. Now that the Surveyor 1 site was known, the landscape observed by that vehicle provided the ‘ground truth’ needed to test the validity of the process of interpreting overhead pictures – this was a major part of the rationale for devoting so many frames to seeking the lander.

As a result of the first three Lunar Orbiter missions 32 individual sites clustered in eleven groups in the Apollo zone had been comprehensively photographed. These, and nine less intensively imaged sites, were designated ‘Set A’ for the selection of the early Apollo landings sites.

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256 The Apollo zone

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By design, the ellipses selected as potential targets for the first Apollo landing were bland areas.

Apollo site short-list 285

The 1966 schedule had called for the first Saturn V launch early in 1967 but few people believed that this would be feasible owing to problems with the S-II, which had become the ‘pacing item’. In fact, the delivery of the first ‘live’ S-II to the Cape had already slipped from July to October 1966, and on its arrival at the Mississippi Test Facility on 13 August the inspectors found a number of cracks which delayed the start of its acceptance test firings. In November 1966 Sam Phillips revised the schedule to require the S-II for AS-501 to arrive at the Cape on 9 January 1967 for launch in April.

Meanwhile, the S-IC stage had been erected upon a mobile launch platform in the VAB on 27 October. So as not to delay the checkout of the vehicle, a bobbin-shaped ‘spacer’ was stacked in place of the S-II to support the S-IVB, and on 12 January 1967 the spacecraft comprising CSM-017 and LTA-10R in the SLA was added for its own checkout.

When the S-II arrived on 21 January 1967, several faults were found. By now the launch had slipped into May. On 14 February the spacecraft was transferred to the Operations and Checkout Building for examination as part of the investigation of the Apollo 1 fire, and so many wiring discrepancies were identified that repairs ran into June. In the meantime the S-IVB was de-mated, and on 23 February the spacer was replaced by the S-II. But when factory inspectors discovered cracks in another S – II being prepared for shipment, the S-II was destacked on 24 May for inspection and not restacked until mid-June. Once the S-IVB had been added, the revised spacecraft was installed on 20 June. CSM-017 was a Block I with some Block II modifications for certification, including a heat shield with a simulated unified crew hatch and the

CSM-101 was to fly the Saturn IB and manned CSM evaluation, and CSM-102 was to be retained by North American Aviation as a ground test article.

AS-501 is transported to Pad 39A in readiness for the Apollo 4 mission.

As Apollo 4 soars into the sky it is trailed by a 1,000-foot long plume.

umbilical which crossed the rim of the basal shield from the command module to the service module. The crawler transported AS-501 to Pad 39A on 26 August. The plan was to start the 6-day countdown demonstration test on 20 September but it slipped to 27 September and a variety of issues delayed its completion to 13 October. To be fair, however, this was the first Saturn V, it was vastly more complex than any other space vehicle, and the launch operations team was on a learning curve.

The countdown for Apollo 4 began on 6 November, ran smoothly, and the vehicle lifted off on time at 12:00:01 GMT on 9 November 1967.

For the crowds, the first indication that a launch was in progress was a light at the base of the vehicle. A jet of flame passed through a hole in the launch platform to a wedge-shaped deflector, which split and vented it horizontally north and south. The water which was pumped onto the pad to diminish the acoustic reflection from the concrete was vaporised and blasted out with the flame as a roiling white cloud. It was almost inconceivable that a vehicle that weighed 6.5 million pounds could rise from the ground, but the five F-1 engines generated a total of 7.5 million pounds of thrust and as it slowly lifted from the pad the brilliance of the flame rivalled the early morning Sun. Since the Saturn V was so much more powerful than its predecessors, nobody really knew what to expect. At first it was like a silent movie, because the thunderous roar of ignition took fully 15 seconds to reach the facilities for the public and press, which were 3.5 miles from the pad because this had been computed to be as far as an exploding vehicle could hurl a 100-pound fragment. Deafening as this roar was, as the vehicle rose it was enhanced by a staccato pop and crackle that was more felt than heard. The ground shook sufficiently to register on remote seismic sensors. The effect not only rattled the tin roof of the VIP bleacher alarmingly but also threatened to collapse the lightweight booth from which Walter Cronkite was providing TV commentary. It was incredible to think that one day soon men would ride such a rocket.

During the first 10 seconds of the ascent the 363-foot-tall vehicle performed a yaw manoeuvre to ‘side step’ away from the launch umbilical tower, in order both to preclude a collision with any swing arm that might be tardy in rotating clear and to resist any wind gusts that might otherwise cause it to drift towards the 400-foot-tall structure. Liftoff was on a pad azimuth of 90°E of N, but once clear of the tower it initiated a roll to align its inertial guidance system with the flight azimuth of 72°E and then it pitched over. It achieved Mach 1 at T + 61.4 seconds. Then at T + 78.4, at an altitude of 37,700 feet and a wind speed of 50 knots, it passed through the region of maximum dynamic pressure. The central engine of the S-IC was shut down by a timer at T+ 135.52, and the outer engines were cut off by liquid oxygen depletion at T+ 150.77. The separation proceeded in two phases. Firstly, at T+ 151.43, the S-IC separated from the interstage, or ‘skirt’, that extended down over the engines of the S-II; then at T+ 152.12 the S-II ignited its five J-2 engines and at T+ 181.44 the skirt was jettisoned. This scheme was designed to ensure that the S-IC could not damage the engines projecting from the base of the S-II as it separated. A small solid rocket motor on the launch escape system fired at T+ 187.13 to draw this structure clear of the spacecraft. The S-II shut down at T+519.76 and was jettisoned at T+520.53. A pair of solid rockets on the periphery of the S-IVB settled the liquid propellants prior to J-2 ignition and were then jettisoned. The vehicle attained a near-circular parking orbit at an altitude of 100 nautical miles, and the continuous-vent system maintained ullage pressure in the propellant tanks during the coast phase. At 003:11:26.6,[49] after essentially two revolutions with its longitudinal axis in the orbital plane and parallel to the local horizon, it reignited for a simulated translunar injection, although in this case the burn of almost 5 minutes was to create an elliptical atmosphere-intersecting ‘waiting orbit’ with an apogee of 9,292 nautical miles.

CSM-017 was released at 003:26:28.2, and at 003:28:06.6 the service propulsion system was briefly fired to demonstrate its ability to ignite in the zero-g environment without an ullage impulse to settle its propellants. This burn had the effect of raising the apogee to 9,769 nautical miles. The vehicle then aligned itself with its main axis perpendicular to the Sun and its hatch on the sunny side. It maintained this attitude for about 4.5 hours to induce circumferential thermal stresses and distortions on the command module and its ablator prior to entry. At 005:46:49.5 the vehicle attained its high apogee. During this coast, an automated 70-mm camera took a total of 715 high-resolution pictures of Earth at 10.6-second intervals. At 008:10:54.8 the service propulsion system was reignited to accelerate and set up an atmospheric entry which would subject the heat shield to the most severe operational conditions that a return from the Moon might impose. An inertial velocity of 34,816 ft/sec was intended, but a slight over-burn owing to the manoeuvre being controlled from the ground yielded 35,115 ft/sec.

The command module separated 2 minutes 27 seconds later, and used its thrusters to adopt entry attitude. The entry interface (an altitude 400,000 feet, by definition) occurred at 008:29:28.5 while travelling at an inertial velocity of 36,639 ft/sec and a flight path angle of-6.93 degrees. As a result of the longer than planned final burn of the service propulsion system the conditions at the entry interface were 210 ft/sec faster than nominal and the flight path angle 0.20 degrees shallower, yet still within the desired ‘corridor’. Due to the change in the entry conditions, the dynamic load of 7.27 g was less than the predicted 8.3 g. This did not affect the performance of the guidance system in achieving the target, however. The lift-to-drag ratio was 0.365 ( + 0.015) compared with the predicted 0.350. The command module splashed into the Pacific 10 nautical miles from the aim point at 008:37:09.2, and was soon recovered by USS Bennington.

With the spectacular success of this ‘all up’ demonstration flight, there was a real prospect of achieving Kennedy’s challenge of landing a man on the Moon before the decade was out. Indeed, on 20 November 1967 NASA publicly revealed that James McDivitt, David Scott and Rusty Schweickart, who had been trained to fly the dual launch version of the ‘D’ mission using the Saturn IB, were to be launched on the first manned Saturn V. They were to be backed up by Pete Conrad, Dick Gordon and Al Bean – the latter replacing Clifton Williams, who was killed in an air accident on 5 October 1967. Frank Borman, Michael Collins and Bill Anders, backed up by

Neil Armstrong, James Lovell and Buzz Aldrin, would still perform the high-apogee ‘E’ mission, but would ride the second manned Saturn V. If the lunar orbit ‘F’ mission were deleted, then the next crew would attempt a lunar landing.

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

Whence the Moon? 31

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

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

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

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

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

Ranger 4 arrived at the Cape on 26 February 1962. The countdown ran smoothly to liftoff at 20:50 GMT on 23 April. The Atlas performed satisfactorily, the Agena achieved the desired parking orbit and then made the translunar injection manoeuvre as planned. But when the spacecraft appeared above the horizon at Johannesburg it was transmitting a carrier signal without encoded telemetry, which meant that it was not possible to determine the state of the systems. Unable to lock onto the Sun, the initial instabilities imparted by separation from the spent stage caused the spacecraft to tumble. It was concluded that the master clock in the computer/sequencer must have failed. Ranger 4 had transmitted telemetry during the ascent, but the clock had stopped at some point in the gap in coverage between the vehicle passing beyond the final station of the Eastern Test Range and its coming into range of Johannesburg. In effect, the Agena had released a lobotomised robot. Ironically, the radar tracking by Woomera showed that the slight discrepancy in the trajectory would have been well within the capacity of the spacecraft to correct.

The target for Ranger 4 was the same as for its predecessor. The Moon was ‘full’ on 20 April and would be ‘last quarter’ on 27 April. James Webb, W. H. Pickering, Oran Nicks, Clifford Cummings and James Burke congregated at Goldstone on 26 April as the spacecraft approached the Moon. Without solar power, the battery had expired, terminating the carrier wave from the main transmitter, but the fact that the independently powered surface package was transmitting enabled radio tracking to continue. At 12:47 GMT, some 64 hours after launch, the spacecraft passed behind the leading limb of the Moon. Calculations showed that it impacted 2 minutes later.

For the first time, American hardware had hit the Moon, marking a success for

On 23 April 1962 an Atlas-Agena lifts off with the Ranger 4 spacecraft.

the launch vehicle – but this was little consolation for the spacecraft engineers, and the scientists gained nothing. On the one hand, in the original concept of the Block II it was deemed that three flights would be necessary to have a reasonable probability of achieving a fully successful flight that would deliver the scientific objectives of the project. However, the scientists appeared to think that every flight should succeed! It was difficult to precisely determine why Ranger 4’s clock had stopped, because the failure occurred when out of communication and it prevented the transmission of telemetry. But because the telemetry was present when the spacecraft was last seen on the Agena and absent following its release, attention focused on the separation procedure – in particular, when the umbilical plug was withdrawn from the bus and the onboard computer/sequencer issued the power-up command to the systems. It was inferred that there must have been a short circuit at this time, and the obvious root cause was the heat sterilisation process. Additional waivers were issued, but the computer/sequencer for Ranger 5 had already been treated. With mass no longer an issue for the Block II, it was decided to install a backup clock in order to ensure that telemetry would be produced in the event of the computer/sequencer being disabled.

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

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

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

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

In mid-1966 Sam Phillips had hoped that AS-206 would be able to launch LM-1 in April 1967, and Kurt Debus, estimating that it would take 6 months to check out the spacecraft, had asked Grumman to send it to the Cape in September 1966. But it was delayed by manufacturing issues and combustion instabilities in the ascent engine. Nevertheless, AS-206 was erected on Pad 37 in January 1967 in the expectation of launching in April. However, because the AS-204 launch vehicle on Pad 34 had not been damaged by the fire that destroyed the Apollo 1 spacecraft, on 20 March it was reassigned to LM-1. Accordingly, by 11 April AS-206 had been returned to storage and AS-204R – as this was redesignated – erected in its place. In the absence of the spacecraft, Grumman built a plywood mockup on the pad for facilities verification.

On 12 May George Low confided to headquarters that although Grumman had promised to deliver LM-1 in June, he was sceptical. John J. Williams headed a 400- man operations team at the Cape. After the arrival of the ascent and descent stages on 23 June, LM-1 was mated on 27 June. However, the initial examination identified a significant number of departures from specification. On 26 July Carroll Bolender was reassigned to Houston as ASPO’s LM Manager. LM-1 was de-mated in August to repair leaks in the ascent stage. After another leak developed in September, it was de-mated and a number of items extracted for return to Grumman. After the testing was finally completed, the spacecraft, minus its legs, was mechanically mated to the launch vehicle on 19 November and a nose cone fitted in place of the absent CSM. The flight readiness tests were finished in late December. The cabin closeout was on 18 January 1968, during the countdown demonstration test. Loading the hypergolic propellants into LM-1 was delayed by procedural issues, but the ensuing tests ended on 19 January.

The terminal countdown began on 21 January, at T-10 hours 30 minutes. The spacecraft went onto internal power at T-42 minutes and, several hours later than planned, AS-206 lifted off as Apollo 5 at 22:48:08 GMT on 22 January 1968.

The S-IVB achieved an orbit ranging between 88 and 120 nautical miles, shed the nose cone and then splayed the four SLA panels. LM-1 was released at 000:53:50. After manoeuvring clear using its attitude control thrusters, the LM adopted a ‘cold – soak’ orientation, which its guidance system successfully maintained with a minimal engine duty cycle.

The mission plan called for two descent propulsion system manoeuvres, an abort staging, and an ascent propulsion system manoeuvre. The first manoeuvre was to occur on the third revolution and last 38 seconds. It would run at 10 per cent throttle for the first 26 seconds, then be concluded at full throttle. The thrust profile of the second manoeuvre was to be representative of flying a lunar landing, involving five phases over a total of 734 seconds. The abort staging sequence would be initiated at

Installing LM-1 for the Apollo 5 mission.

full throttle, and was to include descent propulsion system shutdown and a ‘fire in the hole’ 5-second burn by the ascent propulsion system. The final burn was to run to propellant depletion and end the primary mission. The guidance system initiated the first descent propulsion system firing at 003:59:42 but the buildup of thrust did not satisfy the programmed velocity-time criteria, and the guidance system, sensing that the spacecraft was not accelerating as rapidly as expected, aborted the burn after just 4 seconds. In fact, this was a design feature, since on a manned mission it would allow the crew time to analyse the situation and decide whether to restart the engine to continue. In normal circumstances the engine would have fired with full tank pressurisation and achieved the desired thrust in 4 seconds, but in this case the tanks were only partially pressurised and it would have taken 6 seconds to build up thrust. The premature cutoff was merely the result of inadequate coordination between the guidance and propulsion teams, not a problem with the spacecraft. Mission Control sent a command to deactivate the guidance system in order to permit the remainder of the mission to be controlled from Earth using a preplanned sequence which would address the minimum requirements of the mission.

At 006:10:00 the onboard automatic sequencer initiated this program. It began by using the backup control system to control the vehicle’s attitude. In performing two burns in this mode, the descent engine gimballed properly and responded smoothly to throttle commands. But the short duration of the three descent propulsion system firings precluded a full evaluation of the thermal aspects of the supercritical helium pressurisation system. In abort staging, all system operations and vehicle dynamics were satisfactory for manned flight. The primary control system was then reselected to control the vehicle’s attitudes and rates. However, as this had been off during the abort staging sequence its computer program did not know of the change of mass resulting from this action and its computed thruster firing times were based on the mass of the two-stage vehicle and caused an extremely high rate of propellant usage. The final ascent propulsion system firing started at 007:44:13 and ran to thrust decay at 007:50:03. Since the attitude control system had by that time exhausted its own propellants, this burn was initiated with the thrusters drawing from the tanks of the ascent propulsion system. This continued until the sequencer automatically closed the interconnect valves, whereupon, with the thrusters starved and the ascent engine still firing, the vehicle started to tumble. The rates were soon of such a magnitude as to impede the flow of propellants to the engine, and helium ingestion induced thrust decay prior to propellant depletion. The vehicle had been in a retrograde orientation during the controlled portion of its final manoeuvre, and calculations indicated that it entered the atmosphere over the Pacific Ocean.

On 26 January the LM-2 flight requirements meeting determined that: (1) apart from minor anomalies, LM-1 had achieved all its flight objectives; (2) it should be possible to achieve the objectives for LM-2 either by additional ground testing or on a manned mission; and (3) it was not necessary to undertake additional unmanned flights to ‘man rate’ the LM. Grumman’s own view was that there should be two test flights, but the company relented after the review of the LM-1 data by the Manned Space Flight Management Council on 6 February. On 6 March NASA cancelled the shipment of LM-2 to the Cape. If AS-502 repeated the success of its predecessor, then AS-503 would indeed be manned, and hopefully be launched before the end of the year with CSM-103 and LM-3.

MISSILES AND SPACE

When a team of German rocket experts surrendered to the US Army in May 1945 and General Holger ‘Ludy’ Toftoy, an artillery officer serving as Chief of Ordnance Technical Intelligence in Europe, set out to arrange their relocation to the USA, the V-2 missile was seen as an important military technology. However, this perception changed with the introduction of the atomic bomb in August against Japan. In the immediate post-war years the US military felt that strategic aircraft carrying atomic bombs would enable it to defeat any enemy. In this context, a ballistic missile which could fly only several hundred kilometres to deliver about 1,000 kg of conventional explosive was insignificant. Consequently, upon being settled in El Paso, Texas, the German team led by Wernher von Braun found themselves with little to do.

Although the ballistic missile had seemingly become obsolete as a weapon, it held out the prospect of serving a more benign role, and in November 1945 the US Navy recommended the development of a satellite. The Army Air Force agreed. However, each service felt that it alone should be assigned this task.

In 1946 the RAND Corporation, created as a ‘think tank’ for the Army Air Force, said: ‘‘The achievement of a satellite craft by the United States would inflame the imagination of mankind, and would probably produce repercussions in the world comparable to the explosion of the atomic bomb. […] Since mastery of the elements is a reliable index of material progress, the nation which first makes significant achievements in space travel will be acknowledged as the world leader in both military and scientific techniques. To visualise the impact on the world, one can imagine the consternation and admiration that would be felt here if the US were to discover suddenly that some other nation had already put up a successful satellite.’’

Meanwhile, von Braun was showing the Army how to assemble, prepare and fire V-2 missiles at the White Sands Proving Grounds in New Mexico. They were made from parts either recovered from Germany or manufactured to his specifications in America. In 1948, while in Texas, von Braun wrote a book, Das Marsprojekt, in which he outlined how an expedition to explore Mars might be undertaken. It was a

‘grand design’ which left the details to be developed in due course. He set out “more or less to project the technology that existed then’’ to motivate young engineers. He argued that a mission would be feasible ‘‘in 15 to 20 years’’ if a nuclear-powered ion engine could be created. The expedition would involve ten space ships with a crew totalling around 70 people. The ships were to be assembled in Earth orbit, with three carrying ‘landing boats’ for Mars. Later in 1948, von Braun’s team was relocated to the Redstone Arsenal of the Army Ordnance Corps in Huntsville, Alabama. It was a new establishment on the site of facilities used by the Chemical Corps in the Second World War, and was to undertake research and development of rockets and missiles.

In September 1949 the Soviets exploded an atomic bomb – at least 3 years earlier than the US had expected. Although the Soviet bomb was not yet a weapon, it was evident that America would soon lose its monopoly. In early 1950 President Harry S. Truman authorised the hydrogen bomb. In 1951 funding was made available for preliminary work for what would become the Atlas intercontinental-range ballistic missile. The hydrogen bomb test at Eniwetok Atoll on 1 November 1952 was not a viable weapon, because it weighed 60 tonnes. But as the bomb’s weight was reduced for carriage by aircraft it was realised that if it were to prove possible to make the device even smaller, it might become feasible to develop a ballistic missile capable of delivering it. The Air Force (which had gained its independence from the Army in 1947) created a committee chaired by physicist John von Neumann. This was asked to predict the trend in weight-to-yield ratio of hydrogen bomb development, estimate the warhead that a ballistic missile might deliver over intercontinental range by the end of the decade, and assess whether the probable accuracy would make a warhead of that yield a viable weapon. In February 1954 the committee reported that progress with warheads would make missiles viable. The RAND Corporation endorsed this conclusion. Although the Air Force responded by assigning the development of an intercontinental-range ballistic missile ‘top priority’, Secretary of Defense Charles E. Wilson, who was in tune with the ‘economic conservatism’ of the administration of President Dwight D. Eisenhower deliberated on the matter for over 12 months until informed in 1955 that a recently established radar intelligence station in Turkey that was operated by the US had discovered that the Soviets were well advanced in the development of their own intercontinental-range ballistic missile – test flights were launched from a site east of the Black Sea and passed across Soviet territory to fall near the Kamchatka Peninsula. America had felt safe because the USSR had no strategic bombers, but a ballistic missile would be able to circumvent America’s air defences. The risk was that when the Soviet missile entered service with a nuclear warhead it would be able to wipe out the US bomber bases in a ‘first strike’ which would prevent retaliation against the Soviet Union. The US therefore simply had to have its own fleet of missiles.

On 15 June 1962 Brainerd Holmes issued Requirements for Data in Support of Project Apollo, in which he called for three types of information about the Moon as a matter of priority, certainly within the next few years. First, environmental data on particles and fields in space near the Moon to assist in the design of manned spacecraft and assure the safety of crews both in flight and on the Moon. Second, information on the physical properties of the lunar surface in order to confirm the design of the Apollo landing gear. Third, photo-reconnaissance and topographical data in order to facilitate early selection of Apollo landing sites. Holmes had not consulted Homer Newell in drawing up this list of requirements, he simply expected that since Apollo was the agency’s pre-eminent program Newell would arrange for the information to be provided as soon as possible – and pay the bill out of his own office’s budget. But Newell’s Space Sciences Steering Committee had its own priorities.

Holmes supported the unmanned lunar projects which would provide information for Apollo, but opposed those intended to undertake tasks which astronauts would soon be able to do. He therefore opposed Prospector, which was to collect and return lunar samples to Earth. Accepting this logic, Newell set out to ensure that astronauts performed useful science while on the Moon.[21] Soon after being appointed Director of the new Office of Space Sciences, Newell arranged for the Space Science Board of the National Academy of Sciences, now chaired by the Princeton geologist Harry H. Hess, to arrange a series of joint workshops to discuss the best way to undertake space science. The first Summer Study was held at the University of Iowa between 17 June and 10 August 1962, with over 100 representatives of NASA, academia and industry. The aim was to evaluate past and current programs, and recommend future

programs. Afterwards, the Space Science Board issued a summary report, A Review of Space Research, in which it acknowledged that Apollo would start off as “an engineering effort”, but expressed the hope that “scientific investigations will later become the primary goals”.

In September 1962 Gene Shoemaker began a 12-month secondment to NASA to assist the Office of Space Sciences. His motivation for taking this post was partly to increase his chances of becoming one of the astronauts who would have the good fortune to undertake field geology on the Moon. Don Elston served as Acting Chief of the Branch of Astrogeology in Shoemaker’s absence.

On 11 October 1962 Robert Seamans called in Homer Newell, Brainerd Holmes, W. H. Pickering and Oran Nicks, and told the Office of Manned Space Flight and the Office of Space Sciences to coordinate their lunar activities. Newell was told that his priority was to support Apollo’s requirement for data about the Moon. Nicks was to coordinate, and report how unmanned missions could best contribute to Apollo. In particular, could further Rangers provide some of this data by delivering a surface package incorporating a penetrometer to measure the strength of the lunar surface. When on 15 October Newell publicly announced five additional Rangers for 1964 equipped with the high-resolution TV system, he emphasised they “would increase the probability of obtaining lunar surface detail information that could be used in the manned landing system’’. Newell was also considering another series for 1965 which would deliver surface capsules. If these rough landers were funded, they would be primarily for scientific research. For these, Newell asked the Aeronutronic Division of Ford, which had developed the seismometer, to investigate a small TV camera capable of being delivered to the lunar surface in a capsule. On 22 October Holmes and Newell announced that a Joint Working Group would be formed, composed of representatives of their two offices. Chaired by Gene Shoemaker, at least during his period of secondment to NASA, it would be responsible for recommending to the Office of Manned Space Flight “a detailed program of scientific exploration’’ and for recommending to the Office of Space Sciences “a program of data acquisition to assure a timely flow of environmental information into planning for manned projects’’. It would also be responsible “for establishing and maintaining close liaison with field centers, government agencies and universities in the development of an integrated scientific program for manned space flights’’.

Seamans’s directive that the Office of Space Sciences fly lunar missions primarily in support of Apollo, rather than for purely scientific purposes, renewed Newell’s determination to ensure that Apollo crews conducted proper science whilst orbiting the Moon and on its surface – the Manned Spacecraft Center, being fully occupied with the engineering challenge of sending men to the Moon, was slow to pursue this aspect of the program.

A BOUNCY LANDING

The 6-month hiatus after Surveyor 2 was not due to concern over the loss of that spacecraft, but to the wait for the restartable version of the Centaur. The two-burn configuration traded payload capacity against the hardware to restart the engines and the cryo-propellants that would be vented while coasting in parking orbit, but it offered Surveyor launches in winter months,[33] considerably lengthened the launch windows, and increased the flexibility in selecting the arrival time for optimal illumination at the landing site. The Centaur stage demonstrated its restart capability by a launch on 26 October 1966, thereby completing its test program.

The target for Surveyor 3 was a 60-km-diameter circle in the southeastern part of Oceanus Procellarum, centred 120 km southeast of the crater Lansberg. Its attraction was that although it was crossed by a ray from Copernicus 370 km to the north, at telescopic resolution it was sparsely cratered. The smooth patch of mare material was broken about 20 km to the west by rough hummocky terrain and isolated hills, and was bounded to the east by low ridges. It had been photographed at medium resolution by Lunar Orbiter 1 as target I-P-7, and at high resolution by Lunar Orbiter 3 as III-P-9c. These pictures revealed the presence of sub-telescopic craters in the target circle – with one, just over 1 km in diameter, situated very near the aim point. As a smooth-looking patch of Oceanus Procellarum, it bore a similarity to the Surveyor 1 landing site in the Flamsteed Ring, some 650 km to the west.

Surveyor 3 lifted off from Pad 36B at 07:05:01 GMT on 17 April 1967. The Atlas jettisoned its booster section at T+ 142 seconds and the sustainer engine shut down at T + 238. Once free of the Atlas, the Centaur established the desired circular parking orbit at an altitude of 160 km – with insertion at T+569 seconds. The coasting phase would vary between 4 minutes and 25 minutes, depending on the geometry of the translunar injection – in this case it was to be 22 minutes 9 seconds. While coasting, the Centaur first fired two 50-pound-thrust hydrogen peroxide thrusters to settle the remaining propellants in their tanks, then continuously fired two 3-pound thrusters to maintain this condition. It had two clusters of 3.5 and 6- pound thrusters to control its attitude, and while maintaining its longitudinal axis to the local horizontal it rolled at a rate of 0.17 degree per second in order to even out solar heating of its payload and vented any propellant boil-off.

Owing to the predawn launch, the Centaur emerged from the Earth’s shadow at 07:21:25. About 40 seconds prior to the translunar injection, the 50-pound thrusters fired again to guarantee that the propellants would enter their feed pipes. The main engines were shut down when the inertial guidance system sensed that the requisite velocity had been achieved – in this case at 07:38:49, after a 108-second burn. As on earlier missions, after it had configured and released the spacecraft, the spent stage performed the separation manoeuvre. Once free, Surveyor 3 stabilised itself and then adopted its cruise attitude. The midcourse manoeuvre at 05:00:03 on 18 April lasted 4.3 seconds and the 13.8-ft/sec change in velocity was entirely devoted to achieving the ‘critical component’ required to reduce the divergence from the centre of the target circle from the initial 480 km down to a mere 5 km.

The pre-retro manoeuvre in which the spacecraft departed from its cruise attitude involved starting a yaw of-158 degrees at 23:23:30 on 19 April and a pitch of-76.8 degrees at 23:30:17 to align the thrust axis with the velocity vector. The final roll of -64 degrees initiated at 23:34:35 was to optimise the RADVS. The initial approach was at 23.6 degrees to the local vertical. This would require a significant gravity turn during the vernier phase of the descent to force the trajectory to vertical.

The altitude marking radar was enabled at 23:59:33, and issued its 100-km slant – range mark at 00:01:12.829 on 20 April. The delay to the initiation of the braking manoeuvre was specified as 5.090 seconds. The verniers ignited precisely on time, and the new ‘high-impulse’ retro-rocket 1.1 seconds later – at which time the vehicle was travelling at 8,618 ft/sec. The acceleration switch noted the peak thrust of 9,550 pounds fall to 3,500 pounds at 00:02:00.587, giving a burn duration of 40.0 seconds. After allowing the thrust to tail off, the casing was jettisoned at 00:02:12.429. At burnout, the angle between the vehicle’s thrust vector and velocity vector was 21.1 degrees.

When the RADVS-controlled phase of the flight began at 00:02:14.642, the slant range was 36,158 feet (and because the velocity vector at burnout was offset to vertical, the altitude was 32,900 feet) and the total velocity was 483 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 462 ft/sec). The altimeter had locked on at a slant range of 43,700 feet, only to drop out again. So when the RADVS was given control it aligned the thrust axis along the velocity vector extant at retro burnout

The descent of the Surveyor 3 spacecraft depicted in two sections, one for slant ranges above 1,000 feet and the other below 1,000 feet.

and flew with the verniers at 0.9 lunar gravity, very slowly accelerating as it descended. When the altimeter locked on again at 00:02:15.786, 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 00:02:33.816, the slant range was 22,300 feet and the speed was 495 ft/sec. By the 1,000-foot mark at 00:03:53.023, the vehicle was descending almost vertically with a sink rate of 103.3 ft/sec. When the 10-ft/sec mark was issued at a height of 46 feet at 00:04:10:623, it seemed to be home and dry.

But at 00:04:13.275, at a height of 30 feet, one of the three angled radar beams lost its lock on the surface. As the flow of data to the closed-loop computer abruptly ceased at 00:04:13.387, the control system reverted to its inertial guidance system to maintain its attitude and throttled the verniers to cancel out 0.9 of lunar gravity. But because the RADVS was no longer operative, it was unable to issue the 14-foot mark intended to cut off the verniers!

At 00:04:18.050 the vehicle touched down with a vertical rate of about 6 ft/sec. Although it was level at this time, the ground was sloping down to the west, causing leg no. 2 to make contact first. In response to the tilt induced by the other two legs touching down, the flight control system – which was in attitude-hold mode and did not realise that it was on the ground – increased the thrust of

The axial forces on the shock absorbers of the three landing legs of Surveyor 3 from first touchdown to finally coming to rest.

verniers no. 1 and 3 to re-establish a level attitude, and this additional thrust caused the vehicle to lift off.

After peaking at about 38 feet, the vehicle made second contact at 00:04:42.030 some 50 feet west of the initial point, this time at a vertical rate of 4 ft/sec. Just as previously, the slope caused leg no. 2 to touch down first and in its effort to hold its attitude the vehicle lifted off again. The engines were cut off by a command from Earth at 00:04:53.907 – at which time the vehicle had peaked at a height of 11 feet and was at 3 feet and falling. Since a portion of the thrust had been aimed laterally at each liftoff, this had built up a horizontal component, with the result that when the vehicle struck the surface its vertical rate was only 1.5 ft/sec but it had a horizontal rate of 3 ft/sec. The elasticity in its legs caused it to rebound several inches and hop another 18 inches further downslope before it settled at 00:04:54.420, some 36 feet west of its second point of contact. The gyroscopes indicated the lander to be tilted towards the west at an angle of about 12.5 degrees from vertical.

An investigation concluded that the most likely cause of the RADVS dropping out as it neared the surface was that its logic ordered a ‘break lock’ as one of the beams crossed a field of rocks – to a microwave radar, angular rocks would have appeared much as broken mirror fragments would to a searchlight. The circuitry was designed to make the radar tracking circuits select the strongest signal if several were present. It was essential to ignore antenna ‘side lobes’ when the radar was preparing for the gravity turn. As Surveyor 3 made the final vertical descent, the scintillating side lobe had obliged the system’s logic to break its lock. As the probability of losing lock on the main beam during the vertical phase of the descent was negligible, it was decided that this problem would be eliminated on future missions by having the flight control system inhibit this side-lobe rejection logic upon receiving the 1,000- foot mark.

The first 200-line picture was received 58 minutes after landing, and a total of 55 wide-angle pictures were obtained in this mode. For this mission, a small visor had been added to the hood of the camera to prevent direct sunlight from penetrating the optical train in the hope of reducing the glare that had afflicted Surveyor 1 when the Sun was above 45 degrees of elevation. Surveyor 3 arrived approximately 23 hours after local sunrise, and in the orientation in which the vehicle landed the camera was on the eastern side with the Sun 11 degrees above the horizon. There was therefore surprise that many of the preliminary pictures were partially or completely obscured by a veiling glare. It was concluded that either engine efflux or fine particles stirred up by the engines during the ‘hot’ landings had coated part of the camera’s mirror such that when that part of the mirror was directly illuminated by sunlight the view of the lunar surface was obscured. In addition, any scene that included terrain which strongly reflected sunlight was similarly degraded. Later, intermittent sticking of the mirror in both its azimuth and elevation motions implied that dust had penetrated its mechanism. The hood rotated in azimuth with the mirror, and the mirror could be rotated in elevation to seal the hood, but the engineers had been reluctant to start off in that configuration in case the mirror failed to open. A better hood was already in development. As events would show, the camera’s operational issues would impair the imaging schedule and the glare would degrade the results. A telemetry problem meant that scanning for the Sun and Earth could not start until 06:32. This issue had appeared at the time of the second contact in the protracted arrival. It proved to be a signal processing failure. The fact that the inoperative RADVS lost its high-voltage supply at the same time implied that the signal processing problem was the result of an electrical arc. After a detailed study of the performance of the system identified a number of short circuits, a work-around was devised to minimise the impact on the surface activities. Meanwhile, the Sun and Earth acquisition was completed at 08:15, and the first 600-line picture was taken at 08:42. By handing over in succession, the Deep Space Network stations at Goldstone in California, Canberra in Australia and Madrid in Spain maintained continuous communication with the lander.

An analysis of the early pictures determined that the horizon was 5 degrees higher than it would have been if the lander were on a level plain – indicating that it was in a shallow depression. From the tilt, it was inferred to be on the eastern interior wall of a medium-sized crater.

In-flight tracking could locate the landing site only to within a few kilometres, but the crater in which the vehicle had settled was able to be identified by comparing the landscape observed at ground level with the overhead view of frame H-154 taken by Lunar Orbiter 3 – although obviously the lander was not present at the time that this picture was taken. This showed that Surveyor 3 was within 2.8 km of the aim point. The area was in frame H-125 taken by Lunar Orbiter 4 in May 1967, but because that mission was mapping from high altitude the resolution was insufficient to show the lander – nevertheless, the resulting refinement of the selenodetic grid enabled the coordinates of the site to be measured to an accuracy of better than +0.01 degree in each ordinate.

Once the crater in which Surveyor 3 landed had been found in overhead imagery, its diameter was measured at about 200 metres. It was actually the largest of a tight cluster of craters arranged in a pattern which would later be dubbed the Snowman. Photoclinometry of H-154 suggested that the crater was about 20 metres deep, that there was a smooth transition from the concave floor, that the slopes of the interior walls averaged 10 to 15 degrees, and that the rim was low and gently convex. There was an inflection in the profile from concave to convex about half way between the centre and the rim crest, in both radial and vertical directions. The ‘ground truth’ of Surveyor 3 offered a means of checking the automated photoclinometry of overhead imagery – in particular, the depth of 20 metres was seen to have been overestimated by about 5 metres.

The overhead view resolved about 100 small craters scattered over the floor, inner slopes and rim of the main crater. These ranged in size from 25 metres down to the effective limiting resolution of 1 metre. Most had gentle interior slopes and rounded rims, but a few had steep interior slopes and sharp rims. Since blocks were of higher albedo than the surface material it was possible to discern blocks down to half a metre in size, and it was evident that most were related to three of the largest craters superimposed on the main crater. By taking bearings on features and relating these to the overhead perspective, the location of the lander could be pin-pointed to within 0.5 metre – it was almost half way between the centre and the rim crest. Because it was at the inflection of the slope, its foot pads were about 7 metres below the rim

A photograph by the 61-inch reflector of the Lunar and Planetary Laboratory of the University of Arizona showing the part of Oceanus Procellarum to the southeast of Lansberg (top left corner) to which Surveyor 3 was assigned. Note the hummocky terrain to the west and the wrinkle ridges to the east. The outline shows the area covered by the next illustration.

crest and about 7 metres above the centre of the cavity. In fact, the eastern rim of the crater proved to be beyond the camera’s horizon in the upslope perspective. In an exercise analogous to field surveying, the wealth of detail within the crater enabled a topographic chart of its interior to be compiled – it was an excellent example of how lunar orbiters and landers could work together. The tilt of the lander was measured by a variety of methods and estimated at 12 degrees, inclined almost due west. The fact that this was several degrees steeper than the local slope of 10 degrees was the result of foot pad no. 1, which was on the downslope side, having come to rest in a small depression.

Whereas Surveyor 1’s verniers had cut off as intended at a height of 12 feet and – as hoped – had not disturbed the surface, the fact that Surveyor 3’s verniers had kept firing through two touchdowns offered an opportunity to investigate how an intense gaseous plume affected the lunar surface material. Although the imprints of the first contact were unidentifiable owing to the highly foreshortened view of the rim of the crater and the problem with the camera made it difficult to look for erosional effects beneath the lander, the site of the second contact was conveniently positioned about

A close up of Lunar Orbiter 3 frame H-154 showing the crater in which Surveyor 3 landed, with the inferred position of the lander indicated by the arrow. (The lander was not present at the time, however.)

A contour map of the crater in which Surveyor 3 landed. The contours were drawn by interpolating between control points derived by the photographic trigonometry method. The probable vertical accuracy is +0.5 metre.

“less than 0.5 mm” which was made by tilting the camera’s mirror to view almost directly downward and taking high-resolution pictures of the surface beneath the camera.

After the success of Surveyor 1, it was decided to introduce the soil mechanics surface sampler that had been intended for later Surveyors, possibly for carriage by a rover. The original design included sensors for direct measurement of position, force and acceleration, but because the telemetry and commanding capability of the initial form of the lander could not support this complexity the position measuring system, strain gauges and accelerometers were deleted. Instead, the actions of the arm would have to be monitored by observing it using the camera, and a limited amount of data would be able to be inferred from measuring the current that the motors drew whilst in operation. The experiment comprised the articulation mechanism, the electronics compartment and their supporting structures and electrical cabling. The mechanism was mounted on the space frame immediately to the left of leg no. 2, in the position formerly occupied by the approach TV camera. The electronics compartment was at the same level and almost midway between legs no. 2 and 3. The electromechanical mechanism comprised an arm and a scoop. The arm consisted of tubular aluminium cross members which could be extended and retracted in a pantograph fashion. The scoop was a container about 13 cm long and 5 cm wide, was rigidly affixed to the arm and its door was opened and closed using an electric motor. Three electrical motors operated through drive trains to extend and retract the arm and to rotate it independently in azimuth and elevation. It was spring-loaded, extended by having an electric motor unreel a metal tape, and retracted by reeling in the tape. The arm had a maximum extension of about 1.5 metres, but was unable to access the ground immediately below its mount. It could be elevated to raise the scoop about 1 metre off the ground. On this mission the azimuth arc of the mechanism subtended 112 degrees, ranging from the left edge of pad no. 2 towards pad no. 3 – although because the legs were spaced at 120-degree intervals it stopped short of pad no. 3. In all, the sampler had an arcuate operating area of 2.2 square metres. It was controlled from Earth, but because there was no onboard memory for complex sequences it had to be operated one command at a time. The fact that it used the same radio channel as the camera meant their use had to be interleaved. The principal investigator was Ronald F. Scott, an engineer at Caltech who had worked on the Surveyor rover proposal, but the hardware had been designed and built by Hughes. Of the overall mass of 15 pounds, the mechanical assembly accounted for 8.4 pounds.

The soil mechanics surface sampler, which was also referred to as the ‘scratcher’, could manipulate the lunar surface material in a number of ways. A trench could be made by opening the door of the scoop to expose its blade, driving the scoop into the ground and retracting the arm. The scoop could hold up to 100 cubic centimetres of loose granular material, or a small rock fragment. The mechanism was designed to dig to a depth of 0.45 metre, providing that the material permitted this. An impact test involved raising the scoop and disengaging the elevation motor by releasing the clutch to allow a torsional spring to assist lunar gravity in drawing the scoop down to disturb the surface. If dropped on top of a rock, the scoop’s blade could serve as a rudimentary geological hammer. There was a 2.5 x 5.1-cm strip on the lower edge of

TV TARGET

FOOTPAD г

The configuration of the Surveyor 3 lander.

the door in order to place a flat face on the lunar surface. A static bearing test would involve placing the scoop, door closed, directly above the target and then driving the scoop down until the motor stalled, with the current providing a measure of the force applied. The arm could also be manipulated to push rocks aside in order to inspect either the underside of the rock or its imprint on the surface.

The checkout of the soil mechanics surface sampler started at 10:00 on 21 April, shortly before the end of Goldstone’s second session. After a pyrotechnic was fired to release the mechanism, JPL engineer Floyd I. Roberson commanded the arm to extend. The picture taken to confirm this showed that the arm had not advanced as far as expected. The command sequence was repeated, and the next picture showed that the arm was in the desired position. He then put it through a series of actions to verify that it could move in azimuth and elevation, checking its progress at each step by TV. This done, the arm was drawn back.

On 22 April the arm was swung to the middle of its operating area, and at 05:15 made its first bearing test of the lunar surface. The scoop was raised, the arm was swung to the right, and the scoop, door open, was driven into the surface at 09:14, after which the arm was retracted in order to scrape its first trench. Next the arm was swung left, beyond the bearing test position. After making a shallow scrape, it was raised and repositioned to make a second scrape on the same line. This time the motor stalled after just 10 cm – evidently it was more difficult to scrape an already existing trench. Meanwhile, the camera had suffered a difficulty moving in azimuth

A model of the soil mechanics surface sampler carried by Surveyor 3.

that limited its ability to support the sampling activity. Work on the second trench resumed on 23 April with a third scrape being made along the same line. Arm work was suspended on 24 and 25 April owing to the heat. Because the latitude of the site was 3 degrees, the maximum solar elevation was 87 degrees. The arm had been left at the inner end of the second trench. Having noticed what appeared to be a rock at that position, the team decided to scoop it up on 26 April, but in the process of doing so the object crumbled. The arm was swung as far right as it could traverse and the sample was deposited on the upper surface of foot pad no. 2 so that the camera could inspect the clump of fine-grained material in colour at high resolution.

On 27 April the arm swung slightly left, away from foot pad no. 2, and conducted a second and third bearing test. It then moved a little further left and scraped a third trench involving 26 retraction steps, with a wide-angle picture being taken after each step and later sequenced to produce a ‘stop-motion’ movie. On 28 April the scoop picked up a small bright object from near the most recently made trench. This was added to the material dumped onto foot pad no. 2 for inspection, but there was loose material in the scoop from the trench and on falling from the scoop this covered the white object. When the scoop was dragged across the pile to expose the object of interest, it was observed to have darkened. Next, the arm made two parallel scrapes

The operating area available to Surveyor 3’s soil mechanics surface sampler.

A picture taken by Surveyor 3 on 28 April 1967 showing the soil mechanics surface sampler positioned between trenches no. 1 and 2.

successively offset to the left of the third trench in order to widen it, and then a bearing test was performed on its floor. On 29 April half a dozen impact tests were conducted in an arc beyond the recent trench, with the scoop being released from a variety of heights in order to vary the force of the impact. The arm was swung to the left of its operating area on 30 April and the scoop manipulated to draw a partially buried bright object onto the surface – it proved to be a fragment of hard rock, and it was photographed in colour. On 1 May two additional scrapes were made to deepen the second trench and then the scoop was dropped four times with its door open to loosen the floor prior to a final scrape. With the Sun sinking in the west the lander’s shadow masked ever more of the arm’s operating area, so on 2 May the arm ended its operations by swinging over to the right to scrape a short fourth trench alongside the broad third trench.

The results of the arm operations indicated that the material was fine-grained and had sufficient cohesion to create loose aggregations up to several centimetres in size, although such ‘clods’ readily fell apart. When the scoop was pressed on the surface for a bearing-strength test, it left a smooth imprint which had a raised ridge of lumpy

V ‘MPACT □ BEARING О CONTACT

material around the edge. This implied that although the material was compressible, it was only moderately so, and after a certain compression the vertical force tended to displace material sideways. Impact tests were performed, but the ‘spring constant’ of the torsional spring proved insufficient to determine the density in this manner. In general, the first scrape of a trench excavated to a depth of about 7.5 cm, and each successive scrape on the same line gained an additional 5 cm – with the arm having to work harder to achieve this. Bearing tests on the floor of a trench showed that the strength of the material increased significantly at a depth of several centimetres. The deepest excavation achieved was about 18 cm, which was less than half of that for which the arm’s range of operation had been designed. Nevertheless, it provided a valuable insight into the third dimension of the enigmatic fragmental debris layer. There was no indication of textural layering in the walls of the trenches. If there was any change in the grain size, this was on a scale finer than the camera’s resolution. It simply seemed that the upper few centimetres were porous, and hence compressible, whereas the essentially similar material below was more consolidated. Its cohesivity was confirmed by the fact that the trench walls did not collapse. As in the case of the material disturbed by the foot pads, the subsurface was significantly darker than the undisturbed surface – in retrospect, it was more as if the uppermost few millimetres had somehow been lightened. From the fact that no bright angular fragments were uncovered in trenching, it was speculated that while buried they became coated with dark fine-grained material and in this darkened condition were difficult to see in a trench. By implication, it seemed that after a rock had been exposed on the surface for a time it was ‘cleaned off’ by some form of weathering. There were only a few rocks within the arm’s operating area. Most were small and partially buried. The arm picked up one rock for a close examination, but it was too small for its mass to be measured. The jaws of the scoop picked up a small white rock which was about 1.2 cm in size – a task involving 90 minutes of careful remote-control manipulation. The 100-psi pressure which the scoop exerted would have crushed a weak terrestrial rock such as a siltstone or friable sandstone, but the lunar rock remained intact.

The lesson for Apollo was that whilst the lunar material was very fine-grained, it was moderately cohesive and its bearing strength increased significantly at shallow depth.

Surveyor 3’s view was confined to the 200-metre-diameter crater in which it had landed – it could not see the plain beyond. The craters in view ranged in size from 10 cm up to 25 metres. Most of the craters that were less than 3 metres in diameter were fairly shallow, and either had very subdued raised rims or were rimless. Most of the craters between 3 metres and 12 metres in diameter were subdued, but 25 per cent had raised rims and relatively steep walls. It was apparent that most of the small craters had not penetrated beneath the fragmental debris layer within the main crater, and had merely redistributed the material that was already exposed at the surface. The size-frequency distribution was similar to that for this size range seen on the maria by Rangers 7 and 8.

The angular-to-rounded fragments ranged in size from tiny grains up to blocks of about 1.5 metres. The albedo of the undisturbed surface was 8.5 (±2) per cent, and in some cases the albedo of the blocks was one-third brighter. Although the camera

operated most effectively when the Sun was high in the sky, in such illumination the absence of shadows made subtle terrain relief almost impossible to discern – but on the other hand in such illumination it was straightforward to chart the distribution of blocks. Most blocks were relatively angular, with many wedge-shaped and some even tabular. Some of the angular rocks were partially buried, but most of the well – rounded fragments were fairly deeply buried.

In addition to the sparse and random litter of blocks, there were two prominent ‘strewn fields’ of coarse blocks. One was clearly associated with a sharp raised-rim crater about 13 metres in diameter that was embedded in the northeastern rim of the main crater, some 80 metres from the lander. The other was associated with a pair of subdued craters that were located high on the southern wall. The line of sight provided a view inside the northeastern crater, revealing its interior to be full of similar blocks. Exterior to the rim, there were radial lines of blocks. The blocks associated with this crater were the largest, coarsest and most angular in the lander’s field of view. It was evident that they were ejected by the impact that created the crater, and derived from material at a depth of 2 or 3 metres beneath the rim of the main crater. Some of the blocks had almost planar faces, as though they had broken along pre-existing joints. The tabular ones displayed grooves and ridges on their narrowest sides suggestive of lamination parallel to their longest dimension, such as would be produced in flow-banded lavas. The blocks associated with the southern craters were of similar size, but were more rounded and tended to be more deeply buried. Their source was probably the larger of the two craters there, which was 15 metres in diameter. These observations suggested that large blocks associated with subdued craters tended to be more rounded than those associated with sharp raised-rim craters, and those around subdued craters were more buried than those of sharp raised-rim craters. This suggested that freshly exposed blocks were not only eroded by the rain of meteoritic material, but also tended to be reburied as material accumulated – either by the arrival of further ejecta or as a result of downslope motion of loose debris. The fact that the rounded blocks had a pitted texture whereas the angular ones did not, implied that the pitting was caused by the same process that rounded off the angular blocks.

It was also apparent that the surface on the interior of a sizeable shallow crater on a mare plain was similar to that on a relatively level area between such craters. The 200-metre crater in which Surveyor 3 landed had probably been partially filled in by the downslope motion of material on its interior walls, thickening the debris towards the centre. Loose material piled up against the upslope sides of the larger blocks was interpreted as evidence of this process. The strewn fields of coarse blocks associated with 13-15-metre-diameter craters on or near the rim of the main crater implied that the fragmental debris layer was about 2 metres thick there. In contrast, the fact that a 20-metre crater near the centre of the main crater had not excavated blocks served to confirm that the layer there had been thickened. When the main crater was created, its floor would have been several tens of metres deeper and its rim several metres higher and sharper than it is today. By the ‘hinge-flap’ effect of an impact, the debris that formed the rim would have been excavated from the deepest point. In effect, a blocky crater on the rim of a larger crater serves as a ‘drill hole’. The crater on the

A northward-looking section of a panorama taken by Surveyor 3. The outline shows the area covered by the next illustration. (Courtesy of Philip J. Stooke, adapted from International Atlas of Lunar Exploration, 2007)

A portion of the previous illustration featuring a strewn field of boulders around a small crater on the northeastern rim of the crater in which Surveyor 3 landed. (Courtesy of Philip J. Stooke, adapted from International Atlas of Lunar Exploration, 2007)

northeastern rim would offer visiting astronauts an opportunity to recover material excavated from beneath the fragmental debris layer.2

After a detailed analysis of the Surveyor 3 imagery, Gene Shoemaker introduced the term ‘regolith’ to lunar science. This was familiar to terrestrial geologists as the collective name for the rock wastes of whatever origin and however transported that rest on bedrock and nearly everywhere form the surface of the land. On Earth, there are many erosional processes and the regolith includes volcanic ash, glacial drift, alluvial deposits, eolian deposits and soils rich in humus. On the Moon, the primary erosional process was meteoritic impact. Harold Urey had introduced ‘gardening’ for the manner in which the poorly sorted fragmental debris layer was turned over by impacts. The pictures from the two Oceanus Procellarum landing sites hinted that the thickness of the layer increased with age. To start with, the surface would have been bare rock. Any significant impact would have been capable of breaking up and scattering the material. This ejecta would have been progressively eroded by the rain of smaller projectiles. Over time, the layer of debris would have thickened, requiring ever larger impacts to reach the substrate. An important aspect of this process was that it would yield a continuous distribution of fragment sizes, which was expressed by saying that the lunar regolith was seriate.

One scientific task for Surveyor 3 was to monitor the Moon’s passage through the Earth’s shadow. With the Moon at ‘full’ phase and the Earth masking the Sun, this was a lunar eclipse to a terrestrial observer and a solar eclipse to the lander. It was the first opportunity to observe the thermal effects of such an event from the lunar surface and assess inferences drawn from telescopic studies. In particular, Surveyor science team member John M. Saari had been involved in infrared scanning of the Moon’s disk during the lunar eclipse of 19 December 1964, the data from which was processed into isothermal contours that indicated the presence of many ‘anomalies’, mostly associated with craters, where the heat that had been absorbed while the Sun was shining at lunar noon was radiated again at the onset of the eclipse. In addition to monitoring the temperature, Surveyor 3 gave the scientists a bonus: the mirror of its TV camera had the same 35-degree elevation limit as previously, but because the lander was west of the meridian and inclined due west at an angle of 12 degrees by virtue of having settled on a slope, the field of view of the wide-angle frame was just able to include Earth, east of the zenith. Optical observations of the eclipse would yield the first direct measurement of the distribution of the refracted sunlight which weakly illuminates the lunar disk at such times.

Fortunately, the eclipse on 24 April occurred during a period when the Moon was still just above Goldstone’s horizon. A total of 20 images were taken in two sets: the first at 11:24 and the second 37 minutes later. They were taken at two iris apertures, and with several exposures for each of the three colour filters. In the first set, an arc along the northwestern limb of Earth refracted light that varied greatly in brightness, and with a fainter glow at each end containing bright ‘beads’. In the second set, the

And in fact Apollo 12 would do so at precisely this spot.

• INFRARED ANOMALIES

The locations of lunar transient events reported over the years by various observers and infrared ‘hot spot’ anomalies measured during a lunar eclipse on 19 December 1964. (Courtesy of John M. Saari and R. W. Shortfall, Isothermal and Isophotic Atlas of the Moon, NASA, 1967)

brightest refraction had migrated to the northeastern limb. To assess the distribution of cloud on the limb, the geographic coordinates of the ‘beads’ were later calculated and compared to pictures taken by the ESSA 3 meteorological satellite in low polar orbit on the day prior to the eclipse. In some areas cloud in the troposphere occulted some of the refracted sunlight, but the bright ‘beads’ occurred where sunlight passed through regions free of cloud. Of course, the refracted sunlight made it impossible to view the much fainter solar corona.[34]

The thermal properties of the lunar surface inferred from the lander’s temperature data differed from inferences made from telescopic studies, in that the in-situ data showed a higher thermal inertia. However, the data was provided by sensors in place to monitor the thermally controlled compartments, not by instruments specifically designed to study the thermal properties of the lunar surface, and therefore was too crude to draw definitive conclusions.

The plan had called for attempting a ‘liftoff and translation’ manoeuvre by firing the verniers, but this was ruled out by thermal factors. The decision rested upon the temperatures of the thrust chambers of the engines, the flight control electronics, the helium tank, the shock absorbers and the roll control actuator on vernier no. 1 – all of which depended upon solar heating and shadowing in the orientation in which the vehicle came to rest. The key issue was the temperatures of the engines. Irrespective of the orientation, by the time the elevation of the Sun reached about 35 degrees one or other of the engines was sure to exceed its permitted pre-ignition temperature of 105°C. Hence, any attempt to lift off had to be made either early in the morning or late in the afternoon. For Surveyor 3, the thermal situation was complicated by the fact that the lander was on a slope, which significantly altered the manner in which shadows were cast. To preserve the option of this experiment, the helium tank had not been vented. Also, given that at no time during the protracted landing had the forces on the shock absorbers imparted even half the load endured by Surveyor 1, it had been decided not to lock the legs. Whilst the helium was significantly depleted, as the tank absorbed solar heat its pressure increased to 2,735 psia.[35] By the time of the eclipse, however, it had been decided not to attempt to fire the verniers. The legs were monitored to determine whether the rapid decline in temperature at the onset of the eclipse prompted the shock absorbers to leak, but they retained their integrity. At 20:36 on 24 April, the helium tank was finally vented.

Surveyor 3 had two flat beryllium mirrors situated to enhance the camera’s view of the underside of the vehicle. That is, the camera was between legs no. 2 and 3 and the mirrors were affixed to leg no. 1. One mirror was 35 x 22 cm and gave a view of the lower portion of crushable block no. 3 and the area beneath vernier no. 3. The other mirror was 9 x 33 cm and viewed the area beneath vernier no. 2. The fact that the verniers were cut off at a height of only 3 feet suggested there might be signs of surface erosion, but since the vertical velocity at the third contact was only 1.5 ft/sec the crushable blocks probably did not strike the surface. Unfortunately, the hopes of viewing beneath the lander were foiled by the fact that when the Sun was low in the sky the pictures were ‘washed out’ by the glare from the coating on the main mirror of the camera, and when the Sun was high in the sky the area of interest was in the lander’s shadow! It had been hoped to fire the downward-pointing cold-gas thruster on leg no. 2 to follow up on Surveyor 1’s surface erosion experiment, but this time obtaining good ‘before’ and ‘after’ pictures of the test area. However, pictures taken when the Sun was low in the east were washed out by glare, pictures taken when the Sun was high lacked the shadows required to highlight the minute changes likely to result from such a weak thrust, and in the late afternoon the area was in the lander’s shadow – so the test had to be cancelled.

Between 10:29 and 11:06 on 30 April, Surveyor 3 snapped wide-angle pictures of Earth illuminated as a crescent with the dawn terminator running the length of South America. These were the first colour pictures of Earth taken from deep space.[36] The filters had been revised to provide an improved spectral match to standard colorimetry functions.

Following sunset at 18:38 on 3 May Surveyor 3 monitored the rate at which the temperature fell, and at 00:02 on 4 May was commanded to hibernate.

In total, the camera took 6,326 pictures. Owing to the glare from contamination of the main mirror, usable images could be obtained only over a limited azimuth range during the early morning and late afternoon. This glare, combined with the difficulties in moving the mirror, made it impossible to obtain all of the systematic surveys of the landscape which had been planned. About 8 per cent of the pictures were taken at wide-angle to provide panoramas at specific illumination phases. The glare impaired detailed photometry, but the colorimetry confirmed that the surface was essentially grey. The glare precluded photographing the stars for use as celestial references to precisely determine the orientation of the camera, and hence the true orientation of the lander, but on one occasion it did manage to photograph Venus, which helped to some extent.

Although Surveyor 3 was unable to view the plain surrounding the crater in which it landed, scientists were delighted to have the opportunity to survey the interior of a medium-sized crater on a mare! In effect, therefore, its observations complemented those by Surveyor 1 of the open plain. In general, the character of the lunar surface material appeared to be similar at the two sites. The soil mechanics surface sampler was active for a total of 18.3 hours. It executed 5,879 commands, during which it made seven bearing-strength tests, thirteen impact tests and four trenches to provide data on the strength, texture and structure of the lunar material to a depth of 18 cm. In particular, it found that the bearing strength of the material increased with depth, even although there was no discernible change in the grain size – it was just that the uppermost few centimetres were more porous. Although sequences of commands to enable the sampler to perform complex operations had been stored on magnetic tape for step-by-step uplinking, for much of the time it was actually operated in real-time and monitored by TV.

Surveyor 3 evidently succumbed to the chill of the lunar night, because attempts to reactivate it after sunrise were unsuccessful.