Category How Apollo Flew to the Moon

Apollo 11 departed the Kennedy Space Center in the early morning of 16 July 1969 on a mission that would culminate in an attempt to land on the lunar surface. It is widely quoted that over a million people gathered in the vicinity of Cape Canaveral to witness the start of what promised to be a defining event in human history. For the first four days, its crew of Neil Armstrong as commander, lunar module pilot Edwin ‘Buzz’ Aldrin and the command module pilot Michael Collins followed a path

blazed by their predecessors. They even took time out to give viewers to the TV networks an extended tour of their lunar module, Eagle, with an improved colour camera.

On the fourth day, Armstrong and Aldrin left the command module, Columbia, in the charge of Collins, undocked, and fired Eagle’s descent engine to enter the descent orbit around the Moon. As communications proved to be somewhat troublesome, Armstrong reorientated the LM slightly in order to improve reception. On approaching the point where they were to reignite the engine for the landing phase, Armstrong timed the passage of landmarks to determine whether their trajectory was as it should be, and saw that they seemed to be a little ahead. The engine was ignited on time, and after several minutes of continuing to monitor the passage of the landscape below they rotated the LM to allow its radar to take altitude and velocity measurements.

At this point, things became hair-raising, especially for the flight controllers in Houston who lacked the crew’s situational awareness. Thanks to a subtle flaw in the spacecraft’s electronic systems, the computer began to complain of being overloaded, ft displayed debugging codes that were never meant to be seen during a flight and which most people at mission control, as well as the two men in the spacecraft, had little knowledge of. However, just two weeks before the mission, the LM computer experts had studied a large number of such codes, including those that the crew were seeing. Given that the vehicle was otherwise operating normally, they recommended that the descent continue.

Armstrong was able to monitor where on the lunar landscape the computer was guiding them as Aldrin read out relevant numbers. When he saw that their destination appeared to be a boulder field near a large crater, he put himself in the control loop earlier than planned, and manoeuvred to smoother ground 300 metres further along the flight path. Meanwhile, mission control began to worry about a shortage of propellant. When only 15 seconds remained before mission control would have advised the crew to abort the landing attempt, Eagle successfully realised John F. Kennedy’s goal on 20 July 1969 by touching down in the southwest comer of Mare Tranquillitatis.

In the minds of the crew the difficult part of Apollo’s goal had been achieved, yet the public was more eager to witness an event whose scale was much more human and personal. This was the moment when a man made a boot impression in the lunar dust. Armstrong later pointed out that the moonwalk carried far fewer dangers than manoeuvring seven tonnes of flimsy spacecraft loaded with explosive propellants down onto an unknown rocky surface on the end of a rocket flame, while surrounded by a hard vacuum. Nonetheless, it was inconceivable that a crew would land on the Moon and not walk on the surface!

Over the subsequent hours, in one of the most memorable television events in human history, Armstrong and then Aldrin descended the ladder onto the lunar surface. Observed by a black-and-white television camera whose mode of operation gave them a ghostly appearance, they took photographs, collected samples and set up three simple scientific experiments: a small seismometer, a laser reflector and a solar wind collector. The social significance was not forgotten when the flag of the United States was raised on behalf of the nation that had paid for the venture. Additionally, a plaque was unveiled to inform any future visitors to Tranquillity Base that its first visitors "came in peace for all mankind” and the two explorers took a telephone call from President Richard Nixon. After 2 V2 hours, the moonwalk ended. Armstrong and Aldrin took their exposed film and a box of lunar samples up to the ascent stage, repressurised the cabin and tried to get some fitful sleep before

performing lift-off for the second time in less than a week. Their return to Collins in Columbia and the trip back to Earth were uneventful, concluding with a landing in the Pacific Ocean on 24 July.

The Apollo programme had been designed to be aggressive from the outset, with launch facilities at KSC constructed for multiple or closely spaced launches. Now, with the moonlanding successfully accomplished, and America’s spending on the Vietnam War draining the nation’s purse, the scale of lunar exploration was cut back by Congress. Nevertheless, the sheer momentum of the programme brought another landing attempt only four months later.

At T-20 seconds, swing arm 2 was retracted from its position connected to the top of the S-IC. As it arced back to the tower, the guidance system on the Saturn was finally set for the flight. In the instrument unit above the S-IVB stage, there was a conventional gimbal-mounted guidance platform – the type that can hold its orientation while the vehicle around it rotates. As the Earth turned with the Saturn V on the pad, the platform kept its alignment with respect to the stars. If an onlooker could have watched it over a few hours, it would have appeared to rotate, making one full turn each day. Both CM and LM contained similar devices, and these will be discussed more fully later in the book.

The Saturn’s guidance platform provided two important pieces of information needed to guide the space vehicle to the required orbit. One was knowledge of the direction in which the rocket was pointed. This was derived from the platform’s property of maintaining its orientation and thereby provide a reference against which the vehicle’s orientation (normally referred to as its attitude) could be measured. The second came from a set of accelerometers mounted on the platform
with which the instrument unit’s computer could sense the movement of the rocket, and hence, its three­dimensional path from Earth into orbit and later the manoeuvre to head for the Moon.

The orientation of the Saturn as it sat on the pad, and indeed the orientation of the pad itself, was not haphazard. It had been carefully thought out prior to being built. Each pad was aligned to the cardinal points of direction, with the flame trench aligned exactly north-south. The launch vehicle was brought to it with its umbilical tower to the north. From here, the most efficient head­ing was to fly directly to the east, so the rocket was presented with the spacecraft’s hatch also facing east. This way, when the rocket ascended, tilted over and entered orbit, it did so with the spacecraft windows essentially facing Earth and its navigation optics facing out into space.

At this point, it is worth outlining the vehicle’s coordinate system. The Saturn V’s plus-.v axis ran along the length of the rocket and out through the top of the escape tower. It plus-у axis ran through the vehicle towards the umbilical tower and therefore was pointed north. The plus-2 axis ran through the vehicle to point west. As the crew lay on their couches, their heads aimed east and therefore towards the minus-2 axis.

Most Apollos did not fly directly east but on a heading a little north or south of east to ensure that they reached the spot over the Pacific Ocean where the burn for the Moon would be made. The heading taken by the launch vehicle was known as its flight azimuth, a figure quoted as degrees from true north where a heading due east was said to have an azimuth of 90 degrees. The azimuth was directly related to the groundtrack of the vehicle and the inclination of the subsequent orbit. As KSC was at a latitude of 28°, an easterly azimuth would lead to an orbit whose inclination would also be 28°. A smaller azimuth of say 72°, would produce a steeper inclination.

For the flight, the orientation of the platform had to be aligned to match the flight azimuth, but this could only be done a few seconds prior to lift-off. Had the platform been aligned early on and left uncorrected, Earth’s rotation would have rendered the alignment invalid by the time lift-off occurred.

What was done on the Saturn V was to align its orientation with respect to a theodolite that was mounted some way from the pad between the crawlerway tracks. A small window in the side of the instrument unit was provided for this purpose. The

Diagram to explain the effect of flight azimuth on resultant orbital inclination.

platform’s alignment was then held rigid until T-17 seconds, the time of guidance reference release when it was set free. From then on, it held its orientation with respect to the stars. This moment has been immortalised in the recordings from that era when the NASA public affairs officer announced to the world, "Guidance is internal”, ff the countdown were stopped after T-17 seconds, a new flight azimuth would have to be calculated and the platform realigned to it.

As has been said herein repeatedly, the Saturn V was a big vehicle and its length helped to contribute to one of the most uncomfortable sensations most crews had to tolerate during their ascent to space – pogo. This was named after a stick-like toy of the 1960s on which children could bounce along, aided by a large spring that stored the energy of each jump. Engineers found that many rockets, not least the Saturn V, were prone to severe longitudinal vibrations which they called pogo for the obvious reason. Such vibrations could, and sometimes did, cause serious damage to vehicles. Like all structures, the Saturn V could resonate at particular frequencies if excited by an appropriate mechanical stimulus. As it happened, it was not short of such stimuli for it operated in a highly dynamic environment where as many as five huge engines pushed forward and liquids by the tonne flowed to the rear; all of which made the vehicle especially susceptible to vibrations along its length. Ugly mechanisms took hold whereby small, perfectly normal variations in thrust affected the pressure of the propellant lines. This resulted in further thrust variations that interfered with the flow of large volumes of propellant coming down the pipes, inducing ever larger surges. The natural resonance of the rocket’s structure sometimes reinforced these vibrations. Worse, the resonances constantly changed as the tanks emptied, sweeping through a substantial range of frequencies. To further complicate matters, payloads and mass distributions were altered from mission to mission, w’hich changed the nature of the pogo vibrations and made it difficult to design the problem out of the structure. Contrary to popular misconception, pogo was not related to the tendency of liquid propellant to slosh about in the tanks, although this phenomenon also had to be suppressed by the installation of anti-slosh baffles within the tanks.

The second unmanned test flight of the Saturn V (Apollo 6) suffered a spell of pogo in its first stage that would have nearly shaken a crew senseless had there been

anyone on board. Engineers suppressed the S-IC pogo problem by pumping helium into cavities in the propellant lines to make them act like shock absorbers, but it was never completely eliminated and affected most flights to some degree.

As Apollo 8 rode its S-II, Frank Borman relayed his impressions. “Okay. The first stage was very smooth. And this one is smoother.’’ Perhaps he was trying to keep the flight controllers from worrying, because his crew and others on the early Saturn V launches had noticed that pogo was especially strong towards the end of the second stage. According to his post-flight debrief, it bothered Borman. ‘’Quite frankly." he said, “it concerned me for a while, and I was glad to see S-II staging.”

By Apollo 10, engineers had decided that the easiest way to avoid pogo in the S – II would be to shut down its centre engine early, but when Apollo 13 ascended on its second stage, the pogo vibrations became so severe that switches designed to detect improper thrust in its central J-2 engine were inadvertently activated and the engine shut itself down earlier still. Jim Lovell was in command: "Houston, what’s the story on engine 5?” Capcom Joe Kcrwin in mission control didn’t know why the centre, or inboard, engine had quit but he was being told that the other engines were doing a good job. “Jim, Houston. We don’t have a story on why the inboard – out was early, but the other engines are Go and you’re Go.’’ Fred Haise was monitoring the rate at which their height was changing, a quantity known as h-dot. and immediately saw that they weren’t gaining height as rapidly as expected. “Okay. We’re a little bit low on h-dot now, but that’s to be expected." The loss of the centre engine was not as problematic as might be expected, because the other four engines continued to give a balanced thrust and the instrument unit compensated to some extent by burning them for longer, using up the remaining propellant. The crew continued monitoring.

“Didn’t like that inboard [shutting dow n early].1’ said Lovell as the S-II drove on with four engines, but his CMP Jack Swigert gave him comforting news. “Okay, we’re 1,400 feet a second low? on V|. That’s not too bad.’’ The quantity > q was their inertial velocity. Swigert realised that although they were 430 metres per second slower than they should have been, the Saturn had enough in reserve to make up the shortfall. “Watch the trajectory closely, Jack.’’ urged Lovell.

“You’re S-IVB-to-orbit capability now.” announced Swigert eight minutes into the mission. If the S-II gave up completely, the S-IVB third stage would have enough power to take them into Earth orbit. Mission control reassured them that the Saturn wasn’t defeated yet.

“Thirteen, Houston. Looking good at eight minutes."

“Roger.” replied Lovell before asking Haise. "How’s those systems. Fred? Are there any…” His lunar module pilot was quick to reassure, “They’re looking good." Swigert continued his analysis. "Okay, now. h-dot is low?. Jim, [but the] S – 1VB ought to pick you up.’’ The S-II was not meant to Lake Apollo to orbit anyway and the final burst of speed was provided by a short burn by the S-IVB. Lovell was concerned that if the S-IVB had to make up more speed to compensate for his ailing S-II, it might not have enough propellant left over to send Apollo 13 to the Moon, but it reached orbit with sufficient propellant for its lunar mission. After diagnosing the premature shutdown on this flight. NASA altered the pipeline feeding LOX to the centre engine to make sure that this particular source of pogo was suppressed in future flights.

Once in Earth orbit. Lovell summed up the experience: ‘‘There’s nothing like an interesting launch.” he said, not knowing how ‘interesting’ Apollo 13 was to become.

After only 90 minutes in space, the Apollo stack on top of the S-IVB had made one revolution of Earth and was coasting over United States territory where it had near­continuous communication from Hawaii to the Atlantic. The most important task during this 20-minute opportunity was for Capcom to read up to the spacecraft three huge lists of numbers, called PADs (short for pre-advisory data)} Each list gave pertinent details of an engine bum relevant to the next few hours. One of these, the TL1 PAD, would almost definitely be used by the crew. The other two were for bums they hoped they would never have to make, because they were contingencies to abort the mission.

Throughout every mission, NASA implemented strategies that would attempt to

1 See Chapter 8 for a fuller explanation of the PAD, including a worked example.

make any reasonable technical failure snrvivable. Sometimes this was by providing redundant systems. Another strategy was to lay down procedures so that the crew and the flight controllers already knew what to do at any point in the mission, should a problem make a return advisable. The strength of these approaches was dramatically and successfully vindicated on Apollo IS when they overcame a failure that was both crippling to the spacecraft and completely unforeseen.

One proeedure was based on the premise that the crew might lose communica­tions with Earth while on their way to the Moon, or in lunar orbit. In case this happened, mission control always ensured that while they could still talk with the erew, they would keep them updated with enough data to enable them to return home as safely and as quickly as was appropriate. This was the function of the two contingency PADs read up while passing over Hawaii. They gave the crew all the information they would need if. for any reason, they had to return home soon after TLI without the help of mission control.

The first was calculated on the basis of an ignition time 90 minutes after TLI and was therefore called the ‘TLI – 90′ PAD. It would have required the CSM to burn its main engine for more than five minutes against their momentum away from Earth. For the early Apollo flights, the second was known as the "TLI — 4 hours’ PAD, but this became a TLI – 5 hour’ burn on Apollo 11. For the remainder of the missions, it was calculated on a time relative to lift-off, usually eight hours after lift­off. Once the crew had the two abort PADs copied down onto paper forms, they could concentrate on the Lranslunar injection PAD and the preparations for the burn itself.

The second ground-based tracking system determined the range or distance to the spacecraft by measuring delay. Most people are familiar with the annoying delay introduced into television interviews carried out over satellite links. It takes light, and therefore radio about one and a quarter seconds to travel from the Moon to Earth, so the return travel time for a signal to a spacecraft at the Moon is about two and a half seconds. Engineers used this delay to measure range by putting a marker onto the radio signal which the spacecraft preserved and returned to Earth. The marker consisted of a digital code called pseudo-random noise, essentially a very large random number carefully chosen not to add undesirable artefacts to the radio spectrum. When the spacecraft synthesised the dowmlink carrier using the 240/221 relationship, it preserved this code, and sent it back to Earth. Engineers recovered the code and compared it with the transmitted code, ‘sliding’ one over
the other until they matched. The amount of ‘slide’ yielded a time for the round trip, and hence, knowing the speed of light, which is fixed, the distance. This technique was powerful enough to measure a spacecraft’s distance to an accuracy of better than 30 metres, and it could do so to a distance of nearly a million kilometres. For all of these ground-based systems, the movement of the ground station due to the rotation of Earth had to be taken into account before deriving measurements of the state vector.

The fuel cells were not the only source of power in the spacecraft. A collection of batteries were included and. despite their weight, there were good reasons for their inclusion. The fuel cells had a limited range of output power. They could not deliver more than 1.4 kilowatts at any one time, yet their power output had to be maintained above 400 watts at all times. The spacecraft’s requirements were much more variable, especially when motors had to operate. For example, the SPS engine had sizeable motors that gimballed its nozzle from side to side during a burn, and these placed heavy drains on the spacecraft’s electrical system. Batteries w ere a way of smoothing out the load on the fuel cells because they could supply extra power during the peaks in demand. At other times, their need to be recharged provided a convenient load for the fuel cells. At the end of the mission, after the fuel cells had departed along with the rest of the service module, the batteries were all that remained to power the command module as it streaked through the atmosphere during re-entry. They were therefore essential!

The CM carried a total of five silver oxide-zinc batteries mounted in the lower equipment bay below the navigation instruments. This battery technology had the highest energy to weight ratio at the time. Two of them were never recharged after launch. Their only use was to provide energy for the various pyrotechnic devices around the spacecraft. These devices performed a range of critical tasks; they separated the launch escape tower, the S-IVB and. at the end of its mission, jettisoned the lunar module. At re-entry, they separated the CM and the SM, jettisoned the upper heat shield from around the spacecraft’s apex and deployed the parachutes. Their health w’as checked regularly throughout the mission.

A further three batteries, each rated at 40 amp-hours, provided supplementary power during busy periods, but they became the sole source of power through re­entry, splashdown and post-landing operations. It was these that were recharged at times when the load on the fuel cells was low’. All five batteries were installed in separate pressure cases which, in case the batteries were to emit gases through failure or improper operation, could be vented to space to ensure that the gases did not enter the cabin. An additional 400 amp-hour non-recharged battery was added to the service module after the Apollo 13 incident.

In general, the batteries gave very little trouble. Only once, during the Apollo 7 Earth-orbital flight, were problems encountered when Walt Cunningham discovered that the batteries were recharging more slowly than expected. Then when the CM separated from the SM for re-entry, the voltage delivered by the batteries fell low’ enough to make the caution and warning lights "glow: yellow’ the rest of the w ay", as Cunningham put it. “This was a slightly traumatic experience at this point because we hadn’t expected anything like it,” he added. How’ever. the spacecraft’s systems operated satisfactorily with the slightly low operating voltage. Conversely, Apollo 12
relied on the CM batteries when its lightning strike incident took the fuel cells offline for most of the ascent to orbit.

During Apollo, colour television was still in its infancy and was still viewed as notoriously complicated technology. Conventional colour TV cameras of the time used at least three imaging tubes to generate simultaneous images in red, blue and green. The cameras were therefore large, heavy and required constant attention to keep the three images aligned in the final camera output. A simpler system was required and designers turned to a derivative of one of the earliest methods of gen­erating colour TV, the colour wheel.

CBS, one of the United States’ three major TV companies at the time, initially developed the colour wheel camera in the days before a rival system was adopted for general use. The colour wheel camera had one great advantage that lent itself to use in space. Since the colour scans were expressed sequentially instead of simultaneously, only a single imaging tube was required and the camera could be made much smaller than conventional colour cameras of the time.

With only a single tube, the Apollo 12’s troublesome colour TV camera on

Apollo colour camera produced its tripod on the Moon. (NASA).

what was essentially a standard black-and-white signal at 60 fields per second, 262.5 lines per field, with about 200 useful lines per field. Directly in front of the imaging tube, between it and the lens, was the colour wheel. This had six filters as two sets each of red, blue and green. It was spun at 10 revolutions per second such that each field from the camera was an analysis of the image in red, then blue, then green, over and over. If viewed on a black-and-white monitor, the image would display a pronounced 20-Hz flicker because the field that represented green was brighter than the other two, but would only come around 20 times per second. The bandwidth given over to this television signal was increased to 2 MHz which overlapped other components in the Apollo S-band radio signal. Consequently, careful filtering was required to remove these from the TV image.

The flickering black-and-white signal received from the spacecraft, or from the Moon’s surface, had to undergo extensive processing at Houston. In television studios of the Apollo era, it was crucial that the timing of the TV signal was extremely accurate and stable. In other words, the pulses within the signal that define the start of a line or field should occur with extreme regularity and precision. In addition, all equipment dealing with the signal had to agree when the lines and fields began – that is, they all had to be synchronised. This was a problem for Apollo because there was no provision to send synchronising pulses to the camera. In fact, there would have been no point incorporating such pulses because the Doppler shift caused by the changing velocity of the spacecraft or of the landing site with respect to

the receiver on the turning Earth constantly altered the timing of the received TV signal anyway.

This was in the days before mass digital storage made the task of synchronising video simple. The engineers’ solution used two large videotape recorders to correct the signal’s timing. The first machine recorded the pictures coming from space and synchronised itself with the pulses that were built into the incoming television signal. However, instead of the tape going onto a take-up reel, it was passed directly to a second videotape machine which replayed its contents. This second machine took its timing reference from the local electronics so that when it reproduced the signal, it did so with the timing pulses synchronised with the TV station.

Once the timing had been sorted, a colour signal had to be derived from the three separate, sequential fields that represented red, blue and green. To achieve this, a magnetic disk recorder spinning at 3,600 rpm (once every 60th of a second) recorded the red, blue and green fields separately onto six tracks. From this disk, the appropriate fields could be read out simultaneously using multiple heads and combined conventionally to produce a standard colour television signal. Overall, the time required to undertake the processing put the image about 10 seconds behind the associated audio.

Apollo 10 proved that a colour camera worked within the overall Apollo system though Tom Stafford had to battle against a conservative NASA bureaucracy to get it there. On Apollo 12, colour TV was transmitted from the lunar surface for the first time – or at least it was until the camera was inadvertently aimed at the Sun. This destroyed part of the sensitive imaging tube and gave the commercial TV networks a headache while they scrambled for something to show the viewers!

The cameras for Apollos 11, 12 and 14 were merely placed on stands near the LM, which was acceptable as long as activity was centred around the lander, but when the Apollo 14 crew set off for their geological traverse they walked out of shot and left the audience watching an unchanging scene for several hours. It was clear that when lunar exploration stepped up a gear for the J-missions, the TV camera would have to be mounted on the lunar rover.

Early on the morning of 26 July 1971. the crew of Apollo 15 in the good ship Endeavour with its cargo (the lunar module. Falcon, and Lunar Rover-1) departed Earth-space for the Hadley-Apennine landing site on the Moon.

The expedition had actually begun 20 months previously and required more than 100.000 people to prepare the launch vehicle, prepare the three vehicles, prepare the spacesuits. gather up equipment, provisions, and instruments, and generally plan the three-day exploration of the mountains of the Moon.

Just over ten years had passed since May 1961. when President John F. Kennedy committed the United States to "landing a man on the Moon and returning him safely to Earth". During this period, tw’enty five US manned space missions had been flown (Mercury, Gemini and Apollo) nineteen in Earth orbit, three around the Moon, and three to the lunar surface.

The crew of Apollo 15 was now embarking on the next phase, the first extended scientific exploration of the Moon. NASA termed it "[one of] the most complex and carefully planned expeditions in the history of exploration." Only two more such missions were to follow, then there would be a hiatus lasting several decades, maybe even longer, before humans would onec again set foot on the Moon.

I was the commander of the Apollo 15 mission. Jim Irwin accompanied me down to the lunar surface in Falcon while A1 Worden looked after Endeavour in orbit. The planning and preparation for our mission had been so thorough that there was no doubt in our minds that we really knew "how to fly to the Moon" and to do so in any conceivable situation. But as "we” (all 400.000 people working on the Apollo program) had learned during the many preceding missions, flying to the Moon and returning to Earth (successfully, that is) is very, very difficult. So, just how did we actually plan and prepare for this extraordinary adventure – how was our Apollo to fly to the Moon?

lire Apollo program was implemented through five sequential tasks that evolved during two overlapping phases perhaps the "ABCs" of how to fly to the Moon:

Phase 1

A. Adopt a method by which men could fly to the Moon and return safely.

B. Build the spacecraft and ground facilities to implement the method.

C. Develop the techniques and procedures to accomplish the mission.

D. Select and train the astronaut crews (the vital link between В and C).

Phase 2

E. Upgrade the capabilities of the entire system to maximize the technical and scientific results of the Apollo phase of human lunar exploration.

In 1967 mission planners at NASA introduced an alphabetic nomenclature by which to describe where individual flights fitted into the overall scheme. This started at "A" with unmanned tests of the Saturn V launch vehicle and worked through a scries of missions of progressively greater operational capability, finally reaching "G", which was the Apollo 11 lunar landing, and "П" lor a number of follow-on missions. These constituted Phase 1. Missions flown during Phase 2 were intended to maximize the science objectives, and were designated "J“. Apollo 15 was the first such mission.

While the F-l used conventional kerosene-type fuel for brute force, the J-2 achieved almost double the efficiency through the use of relatively exotic liquid hydrogen. However, despite being more efficient, it could not match the raw power levels attained by the F-l, which made it more suitable for an upper stage. A single engine could balance over 100 tonnes and it could be restarted in space. It traced its origins to work done in the 1950s to create a hydrogen-burning rocket engine, but its development funding came solely from NASA who wanted the inherent benefits of hydrogen applied to its Saturn vehicles.

By concentrating almost single-mindedly on the goal of a manned lunar landing, secondary considerations like landing accuracy and science had taken a back seat. In the event. Apollo 11 had landed about seven kilometres beyond its planned site and for some time, no one knew exactly where they were. Not even Mike Collins had been able to see Eagle through his sextant – a powerful optical instrument built into Columbia’s hull. The science payload had been severely limited by mass constraints and lack of time. Future missions would make amends because the United States had invested heavily in the infrastructure to support Apollo and wanted to see results. It also demanded justification for the continuing costs. Fittingly, science became that justification.

To gain knowledge from the Moon. NASA had to go to sites where Earth-based and orbital imagery suggested that answers to questions might lie. However, given the limited walking range of an astronaut on the lunar surface, the ability to land "on target’ became paramount. Although Apollo 12 was not sent anywhere of particular geological importance, it was given a very small target to aim for. Specifically, it was to land within walking distance of Surveyor 3. a small robotic lander that NASA had sent to Occanus Procellar urn in April 1967.

The mission courted disaster in its first minute when the vehicle flew through a rain cloud and invoked a lightning strike. Regardless, the crew’ continued to the Moon amid fears that their command module may have been damaged by the surge of power that had passed through it. In the event, the CSM Yankee Clipper proved to be unharmed, and on 24 November 1969 Charles ‘Pete’ Conrad and Alan Bean landed their LM Intrepid some 1.500 kilometres west of where Eagle had landed and a mere 200 metres from Surveyor 3. This demonstrated that ground controllers and crew could bring a lunar module down exactly where they wished. Richard Gordon, orbiting overhead, confirmed their position by spotting both the LM and the Surveyor on the surface through his sextant.

Since Apollo 12 was an II-mission, Conrad and Bean made two moonwalks. On the first they laid out an ALSEP which was an autonomous scientific station that operated on the lunar surface for many years after they left. The next day they hustled across the surface taking a circular route of over a kilometre, pausing at preplanned points of interest on the way to visit the Surveyor probe. After examining

and photographing the probe, they removed pieces to enable researchers to study how well the hardware had survived 31 months of exposure to the lunar environment. In terms of public relations, the low point for this fun-loving crew was when their television camera was ruined early in the first moonwalk by being inadvertently pointed at the Sun. TV networks struggled to provide a visual accompaniment to the crew’s voice communication and audiences quickly became bored of listening to indistinct and often arcane yakking by the two guys on the surface. Nonetheless, like every crew after them, Conrad’s and Bean’s two joyous forays out on the surface yielded samples of greater bulk than the previous mission, and the scientists were more than happy with what they brought back. In particular, tiny grains of a very slightly radioactive rock type began to lift the lid on important aspects of the Moon’s early history.

Despite concern that it may have been damaged during launch, Yankee Clipper’s successful splashdown concluded a successful, if charmed 10-day mission that was marred only by the loss of the TV coverage.