Category How Apollo Flew to the Moon

What about the astronauts up top? Riding a Saturn V was never a relaxing experience for the crews, but a few usually those taking their second flight exhibited much lower heart rates than their rookie colleagues. Bill Anders, who flew to space only once, was part of the first crew’ to experience the rocket on Apollo 8. "The thing that impressed me about the early stages of lift-off w’as the very positive control during the gimballing of the S-IC engines. It was very positive."

In the initial moments of its flight, most of the w’eight of a Saturn V was at the bottom, particularly in the huge kerosene tank just above the engines of the first stage. The upper stages, although large, were taken up with huge tanks of relatively light hydrogen and, consequently, the centre of mass of the stack w’as quite low’, somewhere in the first stage. Anders therefore found himself on the end of a very long lever and w’as being jolted from side to side by the steering motions of the four outer engines of the first stage although they operated nearly 100 metres below him.

Steering of the first stage w’as achieved in all three axes by swivelling the four outer F-l engines in response to commands from the instrument unit’s computer. Roll manoeuvres w’ere made by moving opposite engines in opposite directions to give a slight screw effect to the vehicle. Moving them in the same direction at once allowed control for pitch and yaw manoeuvres, causing the vehicle to rotate about its centre of mass. Because the crew’ sat far aw’ay, on the opposite side of this point, they felt the vehicle’s rotation doubly as it shook them from side to side. Anders had expected this from rides the crew had taken in a simulator, one that was capable of moving and shaking them w’hile they practised their procedures but. as he noted, the simulation failed to live up to the real thing. “In fact, it felt to me on the first stage ride like an old freight train going down a bad track."

Later in the same mission, the commander, Frank Borman, gave his impressions of the very high noise levels at lift-off to a voice tape, the contents of which were later replayed to Earth on a separate channel. "The launch was nominal in almost every respect. There w’as no difficulty determining lift-off. Vibrations w’ere noticed before the thrust came up to commit to launch, and then when the hold-dowm arms released, the vibration went away." Anders by then had firmed up his impressions of the launch. “The thing w’as still rattling like a freight train as it became clear of the tow’er."

Ed Mitchell on Apollo 14 concurred with Anders’s observation. “Just can’t beat it, huh?" he told his crewmates. "Just like a railroad coach in this couch.” he added. In his post-mission debrief, Eugene Ccrnan on Apollo 17 even took the railway analogy right back to the start of the flight, “Yon could feel the ignition. You could feel the engines come up to speed. Ignition was like a big old freight train sort of starting to rumble and shake and rattle as she lifted off.”

The crew of Apollo 16 had similar recollections at their debrief as John Young brought up the next subject on the agenda: “S-1C ignition?”

“Wow!” was Charlie Duke’s instant reaction.

“Wow is right.” Young agreed. “There goes a train that is leaving. Lift-off – you can tell lift-off because everything is moving.” Duke elaborated further: “It is like an elevator slowly lilting off. It just kept shaking at the same frequency throughout the whole S-IC burn. You felt yourself going faster and faster and faster. I had the feeling it was a runaway freight train on a crooked track, swaying from side to side. That was all the way through the first stage.”

Soon after the centre engine had shut down as planned on Apollo 16. and as they approached the final minute of the S-II’s flight, the crew felt a slight, but expected drop in thrust.

“PIJ shift,’’ reported John Young, the mission’s commander.

‘’Sixteen. Houston. We saw the PU shift. Thrust looks good, and you’re Go for staging,” replied Gordon Fullerton, the launch Capcom.

What was shifting was a valve in eaeh engine that controlled the flow of LOX to the combustion chamber. This was the ■propellant utilisation valve and it was one of the strategies brought into play to ensure that the propellants were utilised as fully as possible. These strategies were implemented by the engineers at North American as they struggled to squeeze as much impulse out of the stage as possible in the light of the narrowing weight limits to which they were constrained. Any quantity of cither Lib or LOX that remained in the tanks after shutdown was useless weight that had not only failed to contribute to the task required of that stage, it had also consumed useful propellant by being carried into space. Engineers were keen to balance the consumption of the two propellants in order to minimise the quantities that remained in the tanks at shutdown. However, small errors in the quantity of propellant loaded before the flight, and an imprecise knowledge of how fast the engines would consume it, made it difficult to plan for matched consumption. One method chosen to minimise wastage was to monitor the depletion of the propellants in the tanks and then to alter the mixture ratio at a point that would lead to simultaneous depletion.

This propellant utilisation valve had three settings; high, null and low, and these yielded mixture ratios of 5.5, 5.0 and 4.5 respectively. At its null setting, every kilogram of hydrogen was burned with five kilograms of LOX. When the S-II ignited, it did so with each engine’s valve in the null position. A few seconds later, the valve moved to its high position and stayed there for about two-thirds of the stage’s operation. This yielded the engine’s maximum thrust of 1.03 MN. The exact time at which the valve moved to its low’ position varied across the missions. For the early flights of the S-II. engineers used a so-called ’closed-loop’ arrangement. Sensors in the tanks determined how quickly the level of each of the propellants was falling. From this information, the computer in the instrument unit decided when to operate the valve and change the ratio. If the timing was correct, the two tanks could be made to empty almost simultaneously. Based on mathematical modelling, engineers opted for ‘open-loop’ control on the later flights, whereby the change to the low setting was made simply by the guidance system detecting that it had reached a specific velocity.

The resulting mixture ratio of 4.5 to 1 brought each engine’s thrust down to 0.77 MN. Although the thrust decreased, the efficiency of the engines rose, causing it to deliver more thrust per kilogram of propellant. This shift in mixture ratio occurred on every flight of the S-II, though not all the crews noticed the change like Young had. Twenty-five seconds later, another call came from mission control.

"You have level sense arm now.”

This cryptic call was related to another strategy to ensure that the stage’s propellant was fully utilised. The S-II was a high-energy stage and its designers wanted it to burn for as long as possible with the propellant it had available. In its role for the Apollo lunar flights, when its task was to achieve about 90 per cent of orbital speed, it was not required to shut down at a precise speed. Doing so would always hold the possibility that large quantities of wasted propellant would be left on board. Its job in its Apollo role was to add as much speed as its propellant could deliver. The final increment of speed for orbit would be supplied by the restartablc S – IVB engine. It was therefore important that shutdown occurred when the S-II’s tanks were as empty as possible and, for this, designers used the propellant levels themselves to initiate shutdown of the stage.

The two propellant tanks each contained five sensors that would indicate that the stage was nearing exhaustion. As soon as any two sensors within cither of the tanks indicated depletion, the instrument unit issued the engine cut-off signal to shut the stage down. Engineers had feared that these sensors might cause a false shutdown command, so they arranged for this system not to be armed until a separate gauging system had verified that the tanks were indeed nearing depletion. This was the point where the ‘level sense’ system was ‘armed’.

LEAVING EARTH

In the years that have elapsed since the Apollo programme, people have forgotten the scale of what the S-IVB was designed to achieve. There is little appreciation of the difference between low Earth orbit and the reaches of space into which this rocket stage took the Apollo crews. In any case, many fail to understand the relative scale of the Earth-Moon system. I once gave a talk to schoolchildren about the Moon and used the popular method of scaling the solar system down to what our minds can handle. As props, along with a model of the Saturn V launch vehicle and some good photographs, I took my own model of the Earth-Moon system. Earth was represented by a 20-centimetre globe that I had been given some years earlier. The Moon was represented by a lucky find I made during a visit to the holy grail of aerospace memorabilia: the National Air and Space Museum in Washington, DC, in the USA. While browsing the museum’s gift shop, I had come across a 5-centimetre – diameter foam ball, grey and pockmarked with craters, that perfectly matched the scale of my globe of Earth, as the Moon’s diameter is very nearly one-quarter that of Earth.

During the talk, I threw my foam Moon out among the schoolchildren and asked the boy who caught it to come forward and hold the Moon beside my Earth at what he thought would be its correct distance. Repeated attempts by various children suggested distances between a half and one metre. Of course, I had previously calculated the correct distance and cut a piece of string to length, which I had rolled up around a pencil. I asked the final child to place the foam Moon at the end of the string and walk back until I had fed out its full length. Back she went up the aisle between the rows of seated children towards their teacher who’s eyes widened in amazement as the schoolgirl took my Moon all the way up to where she was seated. On the scale of my little model, the mean distance between Earth and the Moon was represented by a piece of string six metres long. I then explained how every flight into space by humans since the end of the Apollo programme had risen above Earth between 300 and 600 kilometres, no more than the thickness of that girl’s little finger.

W. D. Woods, How Apollo Flew to the Moon, Springer Praxis Books,

DOI 10.1007/978-1-4419-7179-1 5. © Springer Science+Business Media. LLC 2011

It was by virtue of the power of the S-IVB that Apollo transcended any space exploration before or since, and took men into the realms of deep space.

Astronaut Michael Collins understood the significance of the ТІЛ burn very well and wrote about it in his autobiography, Carrying the Fire. He was at the Capcom console in the mission operations control room (MOCR) in Houston, usually called simply mission control, and acted as the intermediary between the crew of Apollo 8 and the huge team of people occupying the building with him. He realised that TLI was what made this first manned flight to the Moon different from all the flights that had preceded it, and from any journey ever made by humans. On his own flight, Apollo 11, he yearned for a deeper appreciation of what TLI really meant.

“The umbilical snipping ceremony carries about as much drama as asking for a second lump of sugar. ‘Apollo 11, this is Houston. You are Go for TLI.’ I answer, ‘Apollo 11. Thank you.’ There should be more to it.”

Only 30 minutes after the completion of the TLI burn, the stack was already approaching an altitude equivalent to Earth’s radius. The home planet no longer filled half the sky as it had when their spacecraft hugged the world in its parking orbit. Now the crew could see the planet as a globe and view entire continents in a single glance. “You could see all of the United States. If the pictures come out, there will really be some pictures.” This was praise indeed from the laconic John Young during the debriefing for Apollo 16. His CMP Ken Mattingly concurred. “The Earth was right there in the window. And centred right in the middle of the Earth was the United States, without a cloud over it.’’

‘’All the way from the Great Lakes to Brownsville." added Charlie Duke.

"Just as if you had drawn it and set it up so you could take a picture of it.” continued Mattingly.

Young then changed the subject. "Why don’t you talk about TD&E. Ken’.’”

Young w’as referring to transposition, docking and extraction. a typically NASA – ese piece of nomenclature that concerned their next task. The CSM would separate from the S-IVB. coast a short distance away, turn, come back, dock with the LM and then pull it aw-ay from the nearly spent stage. By Apollo 16, Mattingly was familiar with this series of tasks. "That’s got to be the simplest manoeuvre performed in space flight," he said afterwards. “Thai was exactly like the simulator.”

During the Gemini programme. NASA had learned how to safely dock two spacecraft together, in the knowledge that such a capability would be an important part of future operations in space. Once the Saturn launch vehicle had set an Apollo mission on course for ihc Moon, the crew put the techniques learned to good use and docking became a means to an end rather than an end in itself.

Within the stack of the Apollo/Saturn space vehicle, the lunar module sat below the command and service modules, hidden away in a conical shroud known as the SLA (pronounced ’slaw’) which took the vehicle’s diameter from the 6.6-metre-wide S-I VB to that of the 3.9-meire service module. The initials SLA variously stood for spacecraft or service module to lunar module adapter or even spacecraft to launcher adapter, and it was the CMP’s task to retrieve the LM from its embrace in the final intensive task that had to be completed before the crew could settle down to the translunar coast. It did not always go according to plan.

The guidance and navigation system on board the Apollo command module was not only used for cislunar navigation exercises. It also formed an entire control system in itself that, to list just a few of its abilities, could be used to manoeuvre the spacecraft, control its attitude and make calculations relevant to many operations that might be carried out in orbit or during cislunar coast. It could fire the SPS engine, calculate the size and shape of orbits, aim cameras and other instruments at any target or maintain a desired attitude.

The design of the G&N was one of the first contracts awarded by NASA after President Kennedy set his lunar challenge. It was given to MIT, which had gained much experience in this field by designing inertial navigation systems for the US military for use in submarines, aircraft and the Polaris missile system. The Apollo design was based around three tightly integrated systems that worked together to provide a large range of functions.

How can you get to the Moon with just that?

At the core of the G&N system was the Apollo guidance computer. Now seen as primitive in comparison to its successors, it was nevertheless one of the items in the Apollo programme that helped to drive forward important technologies in electronics and computing. It demanded compactness and low power consumption, allied with high computational power – capabilities that could only be performed by a new device that was just coming out of American research laboratories: the integrated circuit or ‘chip’. When production of onboard computers for the Apollo programme was at its peak, it consumed fully half of the world’s output of integrated circuits yet only 75 units were constructed between 1963 and 1969. This was not because they were all used in the final machines, but because NASA bought vast numbers of the tiny devices from the manufacturers and hammered them with a barrage of tests to force ever higher quality control.

It is common for the Apollo guidance computer to be compared with modern domestic computers. More often, people display incredulity that a task perceived to be as complex as a mission to the Moon could be achieved with a machine whose computational power was, they believed, comparable to a digital watch, pocket calculator or other lowly item of electronic hardware. This is to misunderstand the nature of computers and how they work. Though limited in resources, the Apollo computer was carefully programmed at the machine code level. It did not require huge resources because its functions were very narrowly defined. The layers of abstraction that go into modern programming, where a high-level language has to be translated to a lower level of coding, were largely unnecessary; and computing power was not required to support sophisticated ancillary devices such as video displays. There was no word processor, spreadsheet, or even a simple decimal calculator.

Furthermore, its front end was not a QWERTY keyboard. Rather than make comparisons with modern stand-alone computers, the Apollo machine is better thought of as being like an embedded controller, tightly integrated into the spacecraft systems around it.

In hardware terms. Loo, it can be difficult to directly compare then and now. There was no one-chip processor at the heart of the machine. The processing unit was a card full of simple chips whose processing rate was 80,000 cycles per second, seemingly meagre in today’s terms. The data moved about the machine arranged as 15-bit words (plus a parity bit to detect errors), whereas computers from later generations settled on 8, 16, 32 or even 64 bits. Its sparse memory was very carefully and efficiently programmed with an extensive range of routines to assist the crews with the operation of their spacecraft. There were a total of 44 programs in the case of Colossus III – which was the name given to the software loaded into Apollo 15’s command module computer and this was packed into the equivalent of about 64 kilobytes of computer memory. This programming was stored on hand-verified, machine-wired core rope, an archaic memory technology that is no longer in use.

The crew ’spoke’ to the machine in a language of programs, verbs and nouns. Programs were numbered in groups according to the broad field of operation with which they were concerned. For example, programs used for the spacecraft’s descent to a planet’s surface were numbered in the range 61 to 67. Four programs for aligning the guidance system were numbered from 51 to 54. The selection of these programs and the functions they offered w’ere not arrived at easily. As Apollo went through its gestation, engineers, planners and crew’s wanted the computer to handle an ever-increasing range of tasks but, faced with its limited resources, they soon ran into difficulties. When programmers complained that the meagre memory available to the computer was filling up, their managers established an elaborate bureaucracy to carefully define w’hich tasks were essential and how’ best to achieve them, and left the rest off the machine. In truth, the computer was always running a number of programs simultaneously in order to carry out background tasks such as updating the state vector, but one program wns dominant at any one time, and w;as knowm as the major mode. The crew could call up a program as appropriate, or in some cases one program could call up another.

The crew’ gave the computer instructions using numerical codes called verbs. For example. Verb 49 was an instruction to automatically manoeuvre the spacecraft to a new attitude, and Verb 06 instructed the computer to display a set of three requested values in decimal form. Any value that the crew’ might wish to access was given a name, called a noun. Each noun was a numerical code that led to a value or a set of values stored in the computer. For example, during launch, the crew ran Program 11 in order to monitor their ascent. They punched in Verb 06, Noun 62 which asked the computer to display, in decimal form, three values that told them their speed, their height and how rapidly that height was changing. Internally, the computer handled the spacecraft’s guidance and navigation with metric units but because the crews were used to English units by virtue of their aviation background, it converted all relevant numbers to fect-pcr-second, nautical miles, pounds, etc.

All interaction between the crew and the computer was by way of a dedicated display and keyboard, affectionately known as the DSKY and pronounced ‘diss-key’. This had ten numerical keys, a plus key, a minus key and seven other control keys that allowed the crew to engage in a dialogue with the computer. Above the keyboard were a cluster of lights to indicate the status of the machine and an arrangement of seven-segment displays, stacked vertically. Three of these displays, each with five digits, allowed the crew to see what data they were entering into the computer, or showed the result of the computer’s efforts. To keep the machine’s programming simple, there was no facility for the decimal point. Number entry and readout could be in octal (base-8) or decimal and was pre-scaled with the position of the decimal point assumed. It was left to smart astronauts to know where it should be.

Apollo crews came to respect the computer’s reliability and capability. David Scott said in 1982, "With its computational ability, [the computer] was a joy to operate – a tremendous machine. You could do a lot with it. It was so reliable, we never needed the backup systems. We never had a failure, and I think that is a remarkable achievement.”

This was not a stand-alone machine. It was tightly integrated into the spacecraft around it. It was linked to the optical systems and could both control and read the angles to which they were aimed; it could start and stop the engines; and it could

adjust the spacecraft’s attitude in relation to the reference that it gained from the gyroscopically stabilised guidance platform, i. e. its knowledge of which way was up.

The computer in the command module was called the CMC. for command. module computer. The lunar module had an essentially identical machine, the LGC or lunar – module guidance computer, which necessarily operated a different version of the software, named Luminary. Programming had to be specific to the tasks that were relevant to the spacecraft. For example, the LGC had to handle the lunar landing whereas the CMC needed routines for Earth re-entry. Also, the systems into which the computer was integrated were substantially different; for example, whereas the CMC only needed to start and stop the SPS engine, the LGC needed to control the throttle capability of the main engine for the descent to the Moon. They were not interchangeable.

The optics, described previously, formed the second part of the system in the command module. The sextant and telescope were not only useful for navigation, but being motorised they could also be commanded to sight on landmarks and track them to maintain the line of sight as the spacecraft passed overhead. The sextant’s optical power and tracking capability were such that a crewman in the command module could peer through its eyepiece and. if the coordinates were correct, see his colleagues’ landing craft on the lunar surface while passing more than 110 kilometres above at a speed of nearly 6.000 kilometres per hour. Moreover, he could Lake marks that allowed the computer to calculate the exact position of the lander.

The third major element of the guidance and navigation system defined which way w;as up.

Shaving was optional. Many lunar explorers returned to Earth with two weeks’ growth proudly displayed as they stepped off the helicopter following their recovery. Others chose to shave even though it could be difficult. Mike Collins did a bit of both and returned to Earth with a decent moustache. Although these normally fastidious men tolerated such limitations to their personal hygiene for the duration
of a mission, many began to be irritated by them towards the end and were only too glad to get back to Earth and cleanliness.

The crew of Apollo 10 tried using old-fashioned shaving cream and a razor instead of a mechanical shaver. ‘‘We’re in the process now of commencing scientific experiment Sugar Hotel Alpha Victor Echo [SHAVE],” joked Eugene Cernan, “and it’s going to be conducted like all normal human beings do it.”

Later, during a TV broadcast, Capcom Charlie Duke commented on the pictures coming down of commander Tom Stafford. “Okay, 10. I think we’re looking at Tom’s left shoulder there now, and the Sun coming in his window. Yes. There’s his old grinning face, clean shaven.”

“Roger,” said John Young. “This is a remarkable innovation. After spending a lot of money on mechanical shavers which always manage to leave the whiskers flying around in the atmosphere, somebody finally came out with the idea of using a straight razor and brushless shaving cream. You rub it on, it keeps the whiskers

when you shave it off, you put it in a towel and dispose of it, and you end up clean shaven.”

“That’s amazing, 10,” said Duke. “That’s what the space age does for you.” “I’ll tell you, Charlie,” said Cernan, “that’s one of the most refreshing things that’s happened in the last couple of days. That was really great. We were getting where we could barely stand ourselves there for a while.”

However, a continuing problem was dealing with the effects of weightlessness on fluids and the hairs that had been shaved off, as Neil Armstrong explained: “We did shaving on board, and didn’t have a lot of real good luck with that. For some reason or other, we let our whiskers get pretty long before we tried that and found out it was an hour’s job to shave.”

Aldrin elaborated: “It takes a lot more water than you’d think ahead of time, and getting water on your face is not too easy a task. You can get some to accumulate on your fingers in a thin film and then get it on your face, but invariably it’s going to start bubbling and get all over the cockpit in various places.”

“The only difficulty really was conditioning the beard for shaving,” continued Armstrong. “Handling the equipment was no problem and there was no problem with shaving cream getting away from you. It wasn’t that kind of a problem.”

“Well it did use up a fair number of tissues to keep wiping it off,” said Aldrin.

Collins shaved but let a mous­tache grow. “Now, in 1 g, what you do when you get all through shaving is to bend over the bowl, you take water, wipe it all over your face, and all the bits and pieces of hair go down the sink. But the way we were doing it, when you got through, they were all over your face; then you had to wipe each and every one off. It was sort of hard to get them off. For hours afterwards, they were scratch­ing and itching.”

The Apollo 15 crew decided not to bother with shaving throughout their mission. The increasing length of their beards became obvious just prior to a press conference on the penultimate day of the journey. Karl Henize was Capcom at the time:
“Hey, 15, we’re getting a beautiful picture coming through.”

“Yes,” confirmed David Scott. “Go ahead with your questions.”

“Roger. We’ll admire the beautiful pic­ture for a few minutes here,” complimented Henize.

The crew appeared on camera in a row. Scott was camera-left, A1 Worden in the middle and Jim Irwin on camera-right. Behind them was the lower equipment bay with the optics above Scott’s head and the DSKY between Scott and Worden. All were sporting over 10 days’ growth on their chins.

“Deke just passed out from the shock, incidentally,” joked Henize. They all laughed. Deke Slayton was the crew’s boss in Houston.

“Do we look that scroungy?” asked Irwin.

“No, we look so good,” quipped Scott. “He probably can’t believe it.”

“It’s just because we haven’t shaved in two weeks,” Irwin reminded them.

“Is that a fact?” said the laconic Worden.

Irwin: “Yes.”

By Apollo 16, John Young and his crew were still comparing wet shaving with mechanical shavers.

“I tried the windup,” said Mattingly, “and that worked great until you missed a day. If you miss a day, you’ve had it, because that thing feels like its pulling the whiskers out instead of shaving them off.”

Young had tried wet shaving again, with mixed results. “The Wilkinson worked okay if you’d taken that cream and made a lather out of it.”

“Well, you looked pretty bloody, John, the time you used it,” Duke reminded him.

“You wouldn’t have sold any blades, John,” said Mattingly.

“I really didn’t get too good, did I?” agreed Young. “Pretty bad.”

“Somehow we ought to be able to find a way to let you have a razor that you can open up like any other safely ra/.or and clean off.’’ suggested Mattingly. “That’s the big problem. You get that thing all crudded up and that’s it. There must be some way to do that without producing a free floating hazard.’’

After Apollo 17. Cernan said how important shaving was to the crew. “1 think it’s one of the most clean feelings a guy can get in the spacecraft.’’

Schmitt agreed. "It’s great. I could only shave about a third of the face at a Lime, maybe a fourth, so that’s the way you do it. You put a little bit on and shave that part off and start again. I’ve got a recommendation on the razors. And Gene didn’t have that problem. 1 guess my beard is a little thicker or something, but I couldn’t use a two-bladed razor. I could gel one scrape out of the thing and it was full. There is just no way to clean it out and it just wouldn’t cut anymore. The single-blade razor is the one that evidently has enough room in there. Even though it got plugged up with the shaving cream, it still worked okay."

The cylindrical form of the service module consisted of a long central tunnel, with the volume around this divided into six sectors shaped like pieces of a cake. The structure was designed to support the weight of the command module and the launch

W. D. Woods, How Apollo Flew to the Moon, Springer Praxis Books,

DOI 10.1007/978-1-4419-7179-1 8. © Springer Science+Business Media. LLC 2011

The external and internal layout of the service module. (Redrawn from NASA source.)

escape tower, a load that increased by a factor of four towards the end of the Saturn’s first stage of flight. Its strength came from the beams and trusses of its internal skeleton, and the panels that subdivided its volume and formed its external skin. These panels were formed from a sandwich of aluminium honeycomb bonded between aluminium sheets and were therefore largely hollow.

The sectors around the tunnel were numbered 1 to 6. The first was one of the smaller sectors which subtended only 50 degrees and which was left empty for the early Apollo missions apart from a load of ballast that served to keep the craft’s centre of mass within limits. After the Apollo 13 explosion, an additional oxygen tank was added to this sector for Apollo 14. For the J-series missions that followed, this sector gained another tank filled with hydrogen in order to help to supply the increased power needs of these more demanding flights. Another modification for these intensively scientific missions was the addition into this sector of a suite of remote-sensing instruments and cameras to study the Moon from orbit.

Sectors 2 and 3 occupied 70 degrees and 60 degrees respectively of the volume around the central tunnel. They accommodated two large cylindrical tanks that held oxidiser for the SPS engine. Both they and the fuel tanks opposite were fabricated from titanium. The electrical power supply for the CSM was contained in sector 4 which, like its opposite number, swept only 50 degrees of the available volume. Three fuel cells were mounted near the top of the sector, towards the command module. They produced electricity by the reaction of hydrogen and oxygen supplied from

The service module 227

four tanks located in the remainder of the sector. As with sectors 2 and 3. sectors 5 and 6 accommodated a pair of titanium tanks for the SPS engine, in this case for fuel. In the central tunnel, two tanks of helium provided gas to pressurise the fuel and oxidiser tanks.

This vast assembly of systems, subsystems, components, astronauts, flight controllers, support staff, and many others, had to be tightly integrated and they had to play in harmony just like a 100-piece orchestra. Everybody had to be on the same page, the same line, and the same note; or there would be no music. In preparing this orchestra to play the complete symphony, four concepts were key: (1) crew’ procedures, (2) mission techniques. (3) mission rules, and (4) the “flight plan.” Crew procedures. To fly the mission, the spacecraft had to be operated in a manner consistent with both the functions of its systems operation as w’ell as with the sequence of mission aeiiviiics. The crew procedures were developed for this purpose in the form of step-by-step checklists. Together they amounted to several volumes of switch-by-sw’itch procedures for each system, each spacecraft, and each phase of the mission, stating whether they were to be operated either in primary modes, backup modes, emergency modes, or trouble-shooting to determine the cause of a failure or an anomaly.

Procedures had to be developed, integrated, and tested, time and again in order to ensure that in flight every action was performed in precisely the correct, and verified, sequence. This involved countless hours of training in mission simulators, procedures trainers, part-task trainers, mock-ups, and other representations of actual hardware and software, and even a simulated lunar surface.

Mission techniques. These defined the manner in which the mission would be flown, or more specifically, the manner in which the spacecraft “trajectory’’ would be controlled. Once the mission objectives, the crew procedures, and the trajectory are defined, it becomes necessary to specify exactly how the various components of the guidance, navigation, and control systems, as well as the rocket engines, should be used during each phase of the mission to maintain the “trajectory” for that phase. The mission techniques development task was basically: how do you decide how to fly an Apollo mission? It required detailed planning on precisely how well the systems must work to achieve the mission, including all of the options for use and/or failure of primary or backup systems. This was also termed the "data priority” task, and its detailed planning was absolutely essential to success.

As an example, LOR was key to both mission success and crew safety. During the LOR phase, five first-class systems computed the rendezvous manoeuvres – two in the LM, one in the CSM, the MCC. and even some simple charts used by the crew. If all of these sources agreed, the solution was clear. But if there was disagreement, there had to be a rationale for deciding which one to use.

Mission rules were established as a combination of crew procedures and mission techniques whereby, if any failure or anomaly occurred, a “rule” defined the action to take. Mission rules essentially answered the “what if’ question. Even so, there were events during Apollo that had not been foreseen, and required thinking and action beyond mission rules – an excellent example being the oxygen tank explosion that aborted the Apollo 13 mission.

Flight plan. The flight plan was developed as an integrated time-line of events and activities to bring together the mission objectives, the mission techniques, and the crew procedures for each phase of the mission. It served many functions and included references to the particular technique to be used, an index to checklists, the equipment to be used, constraints on the use of spacecraf t systems, limitations on consumables, specific tasks for each member of the crew, ground tracking coverage, day-night cycles, and even eat and sleep periods. Alternate and contingency flight plans were also included.

The S-II (pronounced s-two) stage was the last of the Saturn’s three stages to be developed, and while the other two stages faced formidable engineering problems, neither caused the kind of headaches that the S-II gave managers at NASA and

Apollo 12’s S-IVB stage during transportation operations on a Super Guppy aircraft,

(NASA) " "

North American Aviation, the company that won the contract to build it. The stage not only had to carry cryogenic propellants, it was large. It matched the 10-metre diameter of the S-IC and was nearly 25 metres long. Additionally, because the other two stages were much further along in their design cycles, any demands for reductions in mass tended to be made of the S-П. The decreasing mass of the stage during development led to the inadvertent destruction of two stages in ground testing and, for a while, the S-II became the pacing item in the race for the Moon. Indeed, in the wake of the Apollo 1 tragedy, scathing reports on the management style of North American – which was also building the Apollo spacecraft – came close to ending the Apollo programme.

At first glance, the S-II is like a very large S-IVB, as both shared the same basic tank design utilising a common bulkhead. However, North American chose to save further weight by fabricating the tank walls from metal alloys that actually gained in strength when chilled by liquid hydrogen. This meant that insulation would be added to the outside and the adhesive had to work at 20 К. Initially, engineers used panels of honeycomb filled with polyurethane foam. They then found that gaps between the insulation and the tank wall caused the air within to freeze and the panels to loosen or fall off. Eventually, an arrangement of grooves within the insulation was implemented which was purged with helium (which would not freeze) while fuel was being loaded. This proved unsatisfactory, and starting with the S-II for Apollo 13, a spray-on foam was directly applied to the tank walls which not only provided improved insulation but also saved on weight and cost and eliminated the helium purge.

Power for the S-II came from five non-restartable J-2 engines which produced a

combined thrust that could balance 520 tonnes. As with the S-IC, the stage was steered by commands which swivelled the four outboard engines.

The final three flights of the programme took Apollo to new and worthy heights of exploration, science and discovery. Since the engineering had been largely proved, science became the driving force behind the choice of landing site and the equipment to be carried. Both the LM and CSM were upgraded to carry more supplies and

increase their endurance. To further facilitate this final push for knowledge, a small fold-up electric car was carried on the side of the lunar module and a suite of sensors and cameras were fitted into an empty bay of the service module. The capabilities of the Apollo system were pushed ever further by extending the J-missions to 12 days.

Scenically, Apollo 15 had everything. Its target was an embayment of a lunar plain bounded by the stunning mountains of the Apennine range and a meandering channel called Hadley Rille. It was well north of the equatorial band to which Apollo had heretofore been restricted, but the relaxation of operational constraints made such a mission viable. It was an enchanting site for exploration, where the story of the Moon’s most ancient time began to be revealed.

Apollo 15’s launch from Earth on 26 July 1971, while as spectacular as any, gave no surprises. The coast to the Moon was punctuated by a fault in the main engine’s control circuits and a leak in the CM’s water supply, both of which were dealt with successfully. Once they had landed at Hadley Base, the crew of the LM Falcon, David Scott and Jim Irwin, depressurised the cabin to allow Scott to survey the site by poking his head out of the top hatch of the lander. The following three days saw the two explorers carry out a relentless programme of exploration that sampled the rocks of both the mare beneath them and the adjacent mountains beside them. A
ground-controlled TV camera on their rover allowed their audience to accom­pany them as they visited landscapes that Capcom Joe Allen described as "absolutely unearthly”. The presence of the rover changed the rules of lunar exploration. Instead of working near the LM for the first part of a moon- walk, then going on an excursion, a rover-equipped crew jumped on board and made tracks as soon as they could so that, if it failed, they would have adequate reserves of oxygen to walk back to the safety of the LM.

Their first excursion took them on a drive to where Hadley Rille ran below Mount Hadley Delta. Scott said the vehicle was somewhat sporty to drive, but both crewmen benefited from the rest gained while driving between stops. Upon their return, they set up a third ALSEP science station and in trying to emplace sensors for a heat-flow experiment Scott had difficulty in drilling into the lunar soil. Although the material was an unconsolidated mass of powder and debris, over a period of billions of years it had become so compacted as to be as hard as rock. The drill had to be redesigned for the next mission.

In their second excursion they drove up the lower slopes of Mount Hadley Delta, where they hoped to find fragments of the original lunar crust. Near a fresh crater they collected a likely candidate which the press instantly dubbed the ‘Genesis Rock’ because scientists said they hoped the sample would yield insight into the Moon’s earliest era. Back at the LM, Scott battled once more with the balky drill. Although he managed to obtain a core that was more than two metres long, he found he could not pull it out of the ground. With the surface mission far behind the planned timeline, the third moonwalk was shortened. On their final outing, and with Irwin’s help, Scott managed finally to extract the deep core. Then they drove to the edge of Hadley Rille where they could see layers of lava exposed in the opposite wall. As a final flourish, this time in the name of science rather than golf, Scott carried out a simple experiment in which he simultaneously dropped a hammer and a falcon feather in order to prove the theories of Galileo and demonstrate that objects of differing mass fall at the same speed in the absence of air.

While the surface crew redefined lunar surface exploration at Hadley Base, Alfred Worden operated the apparatus built into CSM Endeavour. As it orbited the Moon, large swathes of terrain were photographed with modified reconnaissance cameras, and the surface was surveyed with instruments that could determine the composition of the lunar material. A laser altimeter measured the varying elevation of the ground passing beneath, obtaining data which quickly demonstrated the relationship between the highlands and lowlands and, along with how their composition differed, insight into the Moon’s history. Before departing for Earth, the crew deployed a

subsatellite that reported measurements of the Moon’s environment for seven months.

The knowledge gained from Apollo was beginning to tell a story of an ocean of molten rock whose surface cooled to form an aluminium-rich crust. This was then punctured by massive asteroid impacts whose wounds were later filled in as iron-rich lava welled up through deep fractures, ft was a story that would also tell of Earth’s earliest years.

By carrying out its Moon programme in the full glare of world publicity, NASA had been bound to do its best to ensure the safety of the crew. This was not to be the world of the test pilot from which most of the astronauts had come – a world where a great many gifted pilots died in obscurity at remote bases, wringing out the problems from capricious new aircraft for the military. The prestige of the Apollo programme. NASA and, indeed, of the United States, could not afford the public loss of a crew whose persona had been built up in the media during the weeks leading up to the launch. NASA’s leaders decided that, as far as could be envisioned, there should be no part of the flight where a single failure was not survivablc.

This policy was aggressively pursued during the incredibly dynamic ascent from Earth when prodigious amounts of carefully directed energy were expended from an assemblage of tanks filled with volatile fuel that pushed through the atmosphere at increasingly high speeds. There were so many things that could go wrong; and in the lower levels of the atmosphere, things could go wrong very quickly. Of particular concern was the possibility that engines might fail, especially during the first few moments of flight vehen the Saturn needed all five F-ls to w’ork just to get off the ground. Lor years, the mission planning team analysed and argued over the details of the ascent and eventually broke it down into sections. For each section, they defined an abort mode’ or appropriate get-out-of-there-quick plan that would whisk the crew away from an errant rocket to safety, to continue the flight into orbit if possible or to splash into the sea if not. To assist in these rescue scenarios, the tip of the command module sprouted the launch escape system (LES) with its powerful rocket, the LET, to pull the crew clear of the Saturn V. For each abort mode, the crew and equipment veere poised to react in a certain way in the event of a launch vehicle failure.