Category How Apollo Flew to the Moon

The early Apollo service modules carried two tanks that supplied oxygen for the crew to breathe and also feedstock for the fuel cells, but after an overpressured tank burst on Apollo 13 and caused the contents of both tanks to be lost, a third tank was added. This tank was isolated from the other two, both physically and by the routeing of its plumbing. It is a common misconception that this tank was added in direct response to the Apollo 13 incident, but it was already planned as one of the upgrades to the spacecraft to support the extended operations of the J-missions and was therefore just brought forward to the final H-mission. The command module had a surge tank and three small oxygen storage tanks to support periods of high demand, loss of cabin integrity, cabin repressurisation; and to sustain the crew through re-entry.

The decision on the type of air to use in an Apollo cabin was not arrived at easily, and was tied up with the tragedy of the Apollo 1 fire. The difficulty was not in choosing the air supply for space. The problem arose because the air supply on the ground, prior to flight, proved to be a lethal mix of high-pressure oxygen and excessively flammable materials spread throughout the cabin, including nylon netting and excessive amounts of Velcro.

The rationale for the cabin atmosphere to use in space was simple enough. On Earth, we experience air pressure at about 1,000 millibars. Since about 20 per cent of that air is oxygen, we say that the partial pressure of oxygen is about 200 millibars. To simplify the design of the Apollo spacecraft and to save weight, NASA decided to use a single gas for all stages of the flight. By having pure oxygen, there was no need to engineer the spacecraft’s hull to hold sea-level pressure against the vacuum of

space, or to carry apparatus to store nitrogen and to regulate the gas mixture. Instead, the spacecraft designers set the cabin pressure so that the concentration of oxygen molecules presented within the lung, where gases are exchanged to and from the blood, was similar to what would be found on Earth. This was achieved by regulating the oxygen atmosphere within the cabin at around 250 millibars. By adopting this lower pressure, the hull could be lighter, since it only had to hold two – fifths of sea-level pressure at most.

The problem with this arrangement arose on the ground. The early version of the Apollo spacecraft. Block I. had no facilities whatsoever for a two-gas atmosphere, even at the launch pad. Once the crew were sealed in, the system that supplied them with oxygen had no option but to maintain it at the full sea-level pressure of 1.000 millibars because the hull was not designed to withstand high pressure from the outside. Worse, when the spacecraft was being tested for leaks, the internal pressure was pumped even higher, despite being pure oxygen. Right through the Mercury and Gemini programmes which preceded Apollo, spacecraft tests on the ground were carried out with the cabin pressurised at about 10 per cent above the ambient pressure. But on 27 January 1967 the complexity of the Apollo spacecraft and the rush to launch it caught up with this flawed policy. Three weeks before the planned launch of Apollo 1, during a countdown rehearsal atop an unfuelled Saturn IB, an unknown ignition source set the interior of spacecraft 012 alight. Fed by high-pressure oxygen, the cabin burned intensely with the resultant deaths of the three crewmen on board: Virgil I. Grissom, Edward H. White II and Roger B. Chaffee.

In the light of this tragedy, the Block II spacecraft was redesigned to have a two- gas atmosphere while on the ground with a mix of oxygen and nitrogen at a 60/40 ratio at a pressure of 1,000 millibars. Although this ratio wras relatively rich in oxygen when compared to normal air, it suppressed flammability while minimising the time required to flush nitrogen out of the cabin after launch. During ascent, the cabin was maintained at sea-level pressure until the outside pressure had dropped by 400 millibars, then the pressure relief valve began to bleed the nitrogen/oxygen air out of the spacecraft to maintain a 400-millibar difference across the hull. During this time, the crew were sealed in their suits breathing only oxygen from the suit circuit. The pressure in their suits was kept slightly high so that the excess gas would help to Hush the nitrogen out of the cabin air. Like passengers in an aeroplane, they could feel the drop in pressure make their ears pop.

Because the total reduction in pressure during the ascent was quite large and occurred over a relatively short space of time, the crew had to condition their blood beforehand. A diver who rises to the surface too quickly can consequently suffer from the bends a debilitating and painful condition, so-named because it makes the victim curl up tightly. Similarly, an Apollo crewman who Look no precautions would also get the bends as the nitrogen gas that was dissolved in his bloodstream came out of solution as the pressure dropped, just like the bubbles produced by a fizzy drink bottle when opened. To prevent this occurring, the crew breathed pure oxygen from the time they suited up three or more hours prior to launch in order to Hush dissolved nitrogen out of their blood.

By the time they reached orbit, the cabin pressure had settled at around 350 millibars and most of the nitrogen was gone. The crew could break open their suits by removing their helmets and gloves and begin to prepare their ship for the Moon. Later, they removed their suits completely and worked in a shirtsleeves environment until a situation arose that required the suits to be donned again.

For Apollo to enter lunar orbit the crew simply burned the SPS engine at perilune to slow down sufficiently to ensure that the two joined spacecraft did not have enough momentum to escape the Moon’s vicinity. If the burn was timed right, they would instead enter a close orbit around it. If the burn failed to occur at all. the crew were left in the fail-safe scenario of returning by default to the vicinity of Earth, with only a tweak of their trajectory by the RCS thrusters required to bring them to a safe splashdown. However, in between the two scenarios of’no burn’ and ‘a burn of the required duration’, there were a range of possible outcomes that depended on exactly how much the engine had managed to slow the spacecraft prior to some kind of failure, and some of these were potentially lethal. The flight plan included notes on how these should be handled.

In the scenario of a very short burn, the stack would come around the Moon and begin to head towards Earth. However, its trajectory would be far from ideal and would require a major engine burn, perhaps from the LM’s descent engine, to restore a successful interception with the atmosphere.

A somewhat longer burn could leave the spacecraft with insufficient momentum to leave the Moon’s gravity. This scenario was inherently unstable as it would leave the spacecraft languishing in a region above the Moon’s near side for some time and return to the Moon’s vicinity. However, owing to perturbations from Earth’s gravity, and the fact that the Moon was still travelling in its orbit, the stack could either pass the Moon’s trailing edge to be slung out into the depths of the solar system, or it could impact the Moon’s surface. In this case, the crew would wait until

the spacecraft was high above the near side and then burn the descent engine to effect a return to Earth.

If the LOI burn lasted long enough prior to SPS failure, the stack would enter an elliptical lunar orbit with a perilune of about 110 kilometres over the far side, and an apolune over the near side whose altitude depended on the length of the burn. A longer burn resulted in lower altitude at apolune. Л typical get-out from this predicament would have been to complete one orbit and burn the descent engine to return to Earth. Additional power was available from the LM’s ascent engine if required.

In truth, if the SPS engine managed to start, there was very little likelihood that it would stop until commanded. What w:as of far greater concern was the possibility that it might continue to burn after the required shut-down Lime – another lethal scenario.

Part II

With a sufficiently long burn at LOI. the altitude of the resulting orbit’s apolune would match that of perilune, 110 kilometres, and the orbit would therefore be circular. For Apollo, the burn to achieve circular lunar orbit was between five and 6 /2 minutes long, depending on the mass of the spacecraft and the precise thrust of the SPS engine. However, to make an LOI manoeuvre for a circular orbit at the first attempt raised great dangers for an Apollo crew. If the engine were to slow them down Loo much, either by over-performance or perhaps through failure of the control equipment, the altitude of their orbit over the near side could drop so low as to become a negative value. Put less euphemistically, the spacecraft would descend until it augured into the lunar surface at great speed. Given the imprecise knowledge of the Moon’s shape at the time of the early missions, this was considered to be a very real danger.

The situation was even more extreme for the crews from Apollo 14 onwards. Rather than targeting for a circular parking orbit, they deliberately brought the altitude of their final orbit over the near side right down to only about 17 kilometres, with the low point conveniently located to enable the lander to subsequently descend to the surface. To put this into perspective, consider that for Apollo 15. every second that the SPS engine burned dropped the near-side altitude by about 11 kilometres. An overburn of only two seconds would wipe out their near-side altitude and have them impact the surface.

To avoid the possibility of impact, the Apollo SPS took two bites at the task. An initial huge burn was made that was slightly shorter in duration than that which would be expected to produce a circular orbit. This first burn was called LOI-1 on the early missions, or just LOI on the later missions. It placed the spacecraft in an elliptical orbit with a perilune of 110 km around the far side, and an apolune over the near side that was typically around 300 km altitude. After two orbits, which was more than adequate time for the shape of the orbit to be precisely measured by radio tracking from Earth, an additional short burn was made at perilune in order to lower the near-side altitude to the required height. This was called the LOI-2 burn on the early missions. Its name was changed to DOI on the later missions for descent orbit insertion.

When the crew monitored these long burns, duration was not the only value that interested them. Although the thrust from the SPS was accurately calibrated, there were always small variations in its power that made the length of the burn less reliable as an indicator. What was more important was delta-v, the change in velocity brought about by the engine. Throughout a burn, this value was measured by the guidance system and displayed in front of the crew’. If all was proceeding normally, the burn would be stopped automatically by the computer once it had achieved the required delta-v. If that w’ere to fail, there was a backup system that independently measured and displayed delta-v and which could also shut the engine down at the right time, f inally, there w ere three pairs of eyes that eagerly looked at both delta-v displays, their owners ready to reach out and manually cut the SPS engine if it seemed to be burning for too long.

THE MEANING OF APOLLO

The Apollo programme was not just a Cold War stunt, though many correctly saw it as such. Neither was it just an example of superpower posturing, though it most certainly was that too.

As is the nature of so many decisions in the human realm, America’s plan to go to the Moon in the middle of the twentieth century had repercussions that were barely conceivable when the President’s advisers steered him towards his historic challenge. In a speech on 25 May 1961, to a Joint Session of Congress on "Urgent National Needs”, President John Fitzgerald Kennedy justified his goal by stating that ".. .no single space project in this period will be more impressive…”. Was he right? Probably. It was certainly a magnificent example of how a state-run command system can successfully fund and manage a megaproject given a conducive political environment. Ironically, this central direction characterised elements of the Soviet system that America was trying to upstage when it went to the Moon; perhaps a demonstration that people are more similar than they are different.

As the programme came to its successful climax with Apollo 11 on July 1969 the media were filled with commentators proclaiming that such a wondrous achievement was bound to bring humanity closer together. There was a sense that this was the obvious culmination of a rising drive towards peaceful endeavours by an increasingly enlightened western society. In an interview for British television on the day after Apollo 11 reached the Moon, NASA Administrator Thomas O. Paine asked: "Why aren’t our political institutions more tuned in to bringing to people around the world this great common aspiration that we all have: world peace, freedom from hunger and ignorance and disease? Why can’t we do better in many of these other areas as we reach out and touch the Moon?”

In the short term, the media lost a measure of its cynicism and adopted an almost reverential tone. During the coverage of the launch of Apollo 11, veteran BBC commentator Michael Charlton spoke to the British audience while Neil Armstrong, Michael Collins and Edwin ‘Buzz’ Aldrin boarded the van that would take them out

W. D. Woods, How Apollo Flew to the Moon, Springer Praxis Books, 1

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

to their space vehicle. In solemn, awed tones, he commented. “They take with them, this morning, the good wishes and the admiration of a world of people, as Man. a species born and who has lived all his life on Earth, moves, with this journey, out into the solar system. And so. presumably begins, with this journey, his dispersal in other places out in the Universe.’’

In a documentary made for the 25th anniversary of Apollo 1 I s achievement, one of the men on the front line of the Apollo programme, f rank Borman, who orbited the Moon on Apollo 8, pointed out how the pragmatic President Kennedy, in his bid to end the Cold War, had used his ability as a word smith to sell a voyage to the Moon as a great endeavour for exploration, “fiddlesticks.’’ exclaimed Borman. "We did it to beat the Russians.’’ In the same documentary, Armstrong’s introduction suggested that as well as national posturing, other forces and impulses within the minds of the participants were driving the quest to the Moon with equal force: "The dream of venturing beyond our own planet was too powerful to resist. We w anted to explore the unknown. We wanted to push the limits of space flight."

Perhaps Apollo could become whatever its detractors or protagonists wished. To those scientists whose unmanned missions were shelved or commandeered for the sake of Apollo, it was a wasteful enterprise; spending vast sums where similar knowledge could be gained robotically for much less cost. Others from the scientific community bought into the programme for the opportunities it offered. They claimed that the presence of humans would greatly increase the science yield. Historian Lewis Mumford dismissed Apollo as "an escapist expedition" from a world beset by problems of malice and irrationality. In the view of economist Barbara Ward, it was a sign that humanity’s destiny could be outside this planet and that the view of the Earth from space could change the thrust of human imagination to one that would lead humans to coexist better.

Apollo is undoubtedly NASA’s greatest achievement, but in its very success it became a burden. NASA’s funding came directly from the US government, annually allocated according to the political whims of a fickle Congress. When the political imperative behind the programme faded. NASA naturally looked around for projects that would allow it to continue to exist in the manner to which it had become accustomed as would any maturing government bureaucracy. But there was no project that could come anywhere near Apollo’s grandeur, scale and expense, let alone maintain the political momentum needed to fund it. In the post-Apollo era. therefore, NASA sold the Space Shuttle to the American taxpayer as a new reusable spacecraft that would provide cheaper access to the new frontier. In the process, they ended up with a versatile yet expensive ’space truck’. But the Shuttle was also fragile, and it threatened the agency’s very existence each time it killed a crew, which it did twice. Apollo was a very difficult act to follow.

One of the ways NASA tried to justify its continued funding was to point out the technological spin-offs derived from the research and development that supported the quest for the Moon. Certainly. American industry learned much from Apollo in a very wide range of fields: from metallurgy to computer simulation, from electronics to fluid valve design. But the problem for those who would use spin-offs to justify further space exploration was that most of these advancements were as much tied up

with the larger defence and aerospace effort being undertaken by the United States at the time, as they were with Apollo per sc. On close inspection, it was difficult to disentangle a new technique, material or system from parallel developments in ballistic missiles or aircraft design or reconnaissance satellites. From an economic and industrial standpoint, it would be more accurate to say that a primary benefit of the billions spent on Apollo was the cash injection it gave to the US aerospace industry and the jobs and know-how that resulted. Indeed, this was part of Kennedy’s motivation in setting the lunar goal.

However, unlike the shadowy exploits of the US defence community, Apollo was carried out in the open. It was a difficult feat of fantastic vision executed in full view of the world for its propaganda benefits, even though such a stance left NASA exposed at every failure of machine or management, or every lime a crew was killed. One effect of this openness was to inspire vast numbers of young people to take up careers in science and technology. On 4 October 2004. a small oddlv-shaped spacecraft won the X-prize. a SlO-million sum offered to the first privately financed three-man ship to rise above the internationally agreed threshold of space at an altitude of 100 kilomeires. although on this occasion ballast replaced the weight of two passengers. Despite the substantial prize, no profit was made from this early effort in commercial space transport, as it relied on a S20-million investment by Paul Allen, whose fortune derives from the fact that in the mid-1970s he eo-founded the software giant Microsoft. As a boy. he avidly watched the progress of the Mercury, Gemini and Apollo missions. “I really got enthralled [by the early space efforts of the USA], and probably more than most kids." He is just one of a collection of multimillionaire entrepreneurs from the computer and internet industries who were brought up on ihc dreams of Apollo and who later expressed their interest in space by investing in start-up commercial space efforts that may make that dream a reality for many others.

During their voyages to the Moon. Apollo crews would sometimes look out of their spacecraft windows, see Earth in the distance and take a photograph. Some have claimed that the resulting extraordinary imagery was directly responsible for the modern environmental movement, when people who were concerned about the state of the planet’s biosphere pounced on images of the jewel-like Earth rising above the barren limb of the Moon, or a full-Earth image captured en route between the two worlds. These images have been reproduced endlessly as symbols of the fragility of our planet. They served as the opening line of the green movement’s clarion call, and are heavily used by corporations to display their environmental credentials. In truth, and somewhat ironically, although much was indeed learned about the Moon, the most profound thing we discovered through Apollo was Earth itself.

In some ways, the Apollo programme was the ultimate adventure for the American people because it fed into the frontier spirit that imbues much of their society, and gave the astronauts of that era an almost god-like status. In his book, The Right Stuff, author Tom Wolfe described the early American space programme and its crews in terms of single combat whereby, in some ancient civilisations, battles would be pre-empted by one-on-one combat between the best warrior from each side. In the Cold War. tribal heroics between the two superpowers on Earth were

being enacted, not by knights on horseback, but by men who, for the most part, came from the fighter-pilot fraternity – afterburner jet-jockeys who were willing to risk their lives for their country’s prestige. These were warriors who wanted to rise to the peak of their profession’s ziggurat, a pyramid of ever faster, jet – and rocket – propelled aircraft reaching ever greater heights and speeds – the dangerous world of the test pilot. In this arena, where it was accepted that men would die for a worthy goal, the dawning of the space age had introduced a new pinnacle to entice the need-for-speed hot-shots and it seemed more dangerous than ever. Through television broadcasts of early unsuccessful space attempts, the American public had witnessed the unreliability of the early rockets. They became steadfast in their admiration for men who would strap themselves to the top of these jittery, controlled bombs and be blasted into space to demonstrate their country’s prowess. In Ron Howard’s movie, Apollo 13, there is an iconic sequence leading up to a superbly rendered dramatisation of a Saturn V launch. It is no coincidence that

James Horner’s score for this scene is strongly reminiscent of a regal coronation. These men were being anointed – prepared to be sent to the realm of the gods for the glory of a nation.

The Moon landings eventually came to be the ultimate expression of technical competence; to the extent that a cliche entered the language: If we can land a man on the Moon, why can’t we…? Seen as solely a demonstration of technical prowess, Apollo became a yardstick against which the stuttering progress of the western world in other fields was judged. In the light of such a dazzling display of what humans could do. why did real-world achievements appear tarnished, tardy and piecemeal? In truth, the world moved on to other preoccupations that tested human ingenuity in other ways; in particular, the rising power of the computer, increasingly fluid communications and information flow via the internet and mobile telephony. To a world that was beginning to look in on itself, the outward-looking achievements of Apollo appeared outlandish, superficial and almost naive.

In many ways, Apollo was an aberration, a sample of twenty-first-century exploration brought forward by perhaps two generations by political circumstance and pushed through by the dreams and technical inventiveness of the thousands who took part – using the technology of the 1960s.

AN ALPHABET OF MISSIONS

Owen Maynard, one of the engineers who had been designing manned spacecraft for NASA from the beginning, reduced the task of reaching the Moon to a series of missions that, one by one, would push Apollo’s capability all the way to the lunar surface. These missions were assigned letters of the alphabet: А, В, C, etc. Managers believed that if the lunar goal was to be realised, each mission would have to be accomplished, with some missions possibly involving more than one flight.

• An А-mission would be an unmanned test of the Saturn V rocket to rate it for manned flight and test the ability of the Apollo command module to re-enter Earth’s atmosphere safely.

• A В-mission would take an unmanned lunar module up into space for a workout. It would be launched by a Saturn IB launch vehicle.

• A C-mission would be an Earth orbital test of the CSM with a crew, again using the Saturn IB.

• A D-mission would be a full manned test in Earth orbit of the CSM and LM Apollo system, launched by a Saturn V.

• An E-Mission would see NASA move away from the Earth with another full test of both spacecraft, this time in an orbit that would reach much higher than any manned spacecraft had previously flown, in order to test the combination away from Earth where navigation, thermal control and communications would be different.

• An F-mission would be a full dress rehearsal of a flight to the Moon, carrying out every manoeuvre except the actual landing. This would give crews in the spacecraft and the people in mission control their first operational experience of lunar orbit.

• The G-mission would attempt to land on the Moon. Its goal would not extend much beyond the landing itself, as the two-man crew of the lander would take only one short walk on the lunar surface.

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

DOI 10.1007/978-1-4419-7179-1 2. © Springer Science+Business Media. LLC 2011

This was the plan, but circumstances altered the manner in which these mission were achieved. Three further mission types were later envisaged by the planners.

• An H-mission would maximise the capabilities of the basic lander to enable a crew to make two forays outside their craft on foot, and to deploy a suite of science instruments on the surface.

• An I-mission would have used only the CSM for a month-long stay in an orbit whose ground track would include the lunar poles. Cameras and other remote-sensing instruments built cither into the side of the service module, or aboard an instrumented module docked onto the CSM. would have mapped the entire Moon. However, no such mission was ever flown.

• A J-mission was the final type to enter the planners’ lexicon and would use an uprated Saturn V and LM to extend surface operations to three days. In the event, the CSM included remote-sensing instruments and the LM delivered a little electric car to enable its crew to venture much further around the landing site and explore areas with multiple scientific objectives.

When Kennedy’s challenge was made. NASA had barely dipped its toe into space with the Mercury programme. Before an advanced spacecraft like Apollo could head for the Moon, the agency had to address a lot of basic questions about how to fly in space. The Gemini programme was its classroom. Across two hectic years of 1965 and 1966, ten increasingly ambitious flights were launched at bi-monthly intervals to test techniques for Apollo; in particular controlled re-entry, rendezvous, docking, spacewalking and long-duration flights. Its achievements placed America ahead in the space race for the first time, and as ‘Go-fever’ gripped the agency, NASA looked forward to getting the Apollo programme flying in the new year of 1967.

The bulk of this book deals with the steps involved in flying to the Moon rather than the sequence of the flights themselves. However, to give the reader a historical perspective the following is a resume of what each flight achieved.

Although Apollo 17 ended the lunar phase of the Apollo programme, America’s investment in its hardware and infrastructure continued to pay back for three more years. A spare S-IVB stage became an orbital workshop called Skylab. This massive 77-tonne space station was launched by a Saturn V on 14 May 1973 and serviced by three crews riding modified Apollo CSMs launched by Saturn IBs. The crews stayed on board for one, two and three months respectively. The final Apollo flight was also to Earth orbit as part of the Apollo-Soyuz Test Project in 1975. again using a Saturn IB, when an American Apollo and a Soviet Soyu/ spacecraft met and docked in space as a political act of detente, thereby ending the ‘space race’ amicably. The two remaining Saturn Vs were turned into lawn ornaments.

The decision to control the Saturn V from its own instrument unit instead of using the capabilities of the command module’s guidance system was primarily driven by the expectation that the vehicle would one day be called upon to carry payloads
other than the Apollo spacecraft. It was dramatically shown to be a fortuitous decision when the Apollo 12 stack was struck by lightning only 36 seconds after it lifted into overcast cloud on 14 November 1969. Although the nearest natural lightning was many kilometres away, the exhaust of the rocket left a trail of ionised gas that acted like a giant conductor and enabled the cloud’s static charge to reach the ground.

"What the hell was that?” called Dick Gordon after the interior of the cabin was flooded by a flash of white light. Gordon, the CMP for this mission, and his commander Pete Conrad were carefully watch­ing the main display console. "I lost a whole bunch of stuff,” yelled Gordon. Directly in front of him, the caution and warning panel “was a sight to behold” as Conrad would later recount.

Sixteen seconds later, another strike hit the vehicle during a cloud-to-cloud discharge. “Okay, we just lost the platform, gang. I don’t know what happened here; we had everything in the world drop out.” Conrad continued to inform them that the fuel cells that powered the spacecraft were no longer doing so, and that the guidance platform in the command module had tumbled out of alignment. The platform was now useless as a tool to guide anything, never mind the giant rocket that was currently powering them to space. Below them, the Saturn V had been entirely unaffected by the electrical catastrophe that had befallen its payload and it continued its programmed ascent without missing a beat. The crew rode their Saturn on into orbit, where they were able to bring the spacecraft’s power back on line, align their guidance platform and continue successfully to the Moon.

Pete Conrad was one of the most colourful characters among the astronauts and was never short of a quip. “I think we need to do a little more all-weather testing. That’s one of the better sims, believe me,” he joked, comparing this real-life drama to the many simulated dramas they had practised endlessly prior to the mission. Capcom at that time, Gerry Carr, wasn’t short of a line of his own, “We’ve had a couple of cardiac arrests down here, too, Pete,” to which Apollo 12’s commander replied, “There wasn’t any time for that up here.”

Later in the mission, Conrad laughed about the experience. “The launch was almost as good as me getting to fly the Saturn V into orbit.” His was only the second Saturn equipped to allow the commander to fly manually to orbit – a contingency
that, while never called upon, would have been welcomed by the hot-shot commanders within the astronaut corps.

Gordon continued the quips as he spoke with Carr. “That’s a terrible way to break A1 Bean into space flight, I’ll tell you.”

At this stage, having achieved an orbit, it is worth considering what a spacecraft does to change it. Our box of beads has no means of propulsion and once released into its orbit, it is doomed to revolve around our imaginary Earth to the end of time. Of course, real life isn’t like that. Spacecraft usually have some kind of rocket motor, especially human-carrying ships that must return to the home planet.

Imagine, then, that our box of beads is a spacecraft w’ith an engine. Let us assume that, having entered a circular orbit, we want to reach a higher orbit. To do so. we must increase our speed further by firing the engine, its nozzle aimed rearwards. This would straighten out the flight path a little and cause the spacecraft to enter an elliptical orbit in which it would coast to an apogee on the other side of the planet. The point at which the burn w’as made becomes a perigee, and if the duration of the burn is appropriately timed, the spacecraft can be made to ascend to any desired apogee altitude. Half an orbit later, having slowed down considerably (just like any object tossed upward in a gravity field), it arrives at apogee but does not have enough momentum to stay at that altitude and will fall back to its perigee as it continues around the planet. Apogee then becomes a good place to adjust the altitude of the orbit’s perigee. By adding yet more speed at apogee with another burn, the flight path is straightened out further, so that the spacecraft does not fall

quite so far as it descends to perigee. If enough extra speed is applied at apogee, the shape of the orbit can be made circular again, this time at the higher altitude. This method of transferring from one orbit to another involving a pair of burns perfonned 180 degrees apart is known as the Hohmann transfer orbit and was formulated in the early part of the twentieth century by Walter Hohmann, a member of the same German rocketry club as Wernher von Braun.

Now comes the counter-intuitive bit. Although our imaginary spacecraft’s speed had been increased on two occasions, it ended up travelling much more slowly than when it was in the lower orbit. Its speed had been traded for height, a situation that will be familiar to all fighter pilots. There are all sorts of ramifications to this in terms of spaceflight operations, especially for Apollo. For example, if one spacecraft wanted to catch up with another that was ahead in the same orbit, the wrong thing to do would be to aim towards the target, light the rockets and try to fly directly towards the quarry. This would make its orbit more elliptical, raise it to a higher apogee and it would therefore travel more slowly, thereby opening the range, which is exactly the opposite of the desired effect. The right thing to do would be to turn the craft around and fire to slow down, thereby making the orbit elliptical with a lower perigee. This increases the spacecraft’s speed and closes the range. Then, to effect a rendezvous the spacecraft would need to turn around yet again and make another burn to rise back up to the target’s orbit at just the right time.

Clearly, making large manoeuvres in space has to be done with careful forethought. Computers and radars are also indispensable tools. This was especially true during an Apollo flight where the success of the mission depended on the ability of two spacecraft to rendezvous successfully. It was also true from the point of view

of their next major manoeuvre; the burn to set them on a path to the Moon, itself essentially a Hohmann transfer.

Immediately after the Apollo/Saturn stack had achieved orbit, Earth-based radars began to track the vehicle to determine its trajectory as precisely as they could. From these measurements, computers at mission control calculated a suitable Moon – bound trajectory and the details of a burn that would achieve it. given the constraints of what the S-IVB could manage. These details were transmitted to the computer within the instrument unit. Whatever information was relevant to the crew was passed on to them also in the form of a list of numbers manually read up by the Capcom. Based on these calculations, and after a little more than 2’/2 hours orbiting Earth, the S-IVB stage reignited and set the Apollo spacecraft on its path to the Moon.

The final stage of the TD&E process was the ejection of the lunar module from the S – IVB, which was not simply a process of throwing a switch and then watching it happen. Throwing the switch would come at the end, but first they had to feed the signal from the switch in the CM down past the LM to the pyrotechnically-fired spring thrusters on the SLA that would push the LM free. That meant that the CMP had to connect two umbilical cables to feed power and signals between the two spacecraft. However, to do that he had to get into the tunnel, which is a short void between the command module’s forward hatch and the lunar module’s overhead hatch. Immediately after the docking, the space within the tunnel was still a vacuum so the CMP had therefore to bleed oxygen from the CM into the void and, in doing so, he also fed it into the LM cabin. Prior to launch, the dump valve in the LM’s overhead hatch was left open in order that, as the Saturn V lofted both spacecraft to orbit, the mixed atmosphere within the LM was gradually exhausted, leaving the interior essentially a vacuum, ready to be filled with oxygen. By docking with the LM, the tunnel had been placed over the hatch and its dump valve. Once the pressure on both sides of the forward hatch had equalised, the hatch itself could be removed, the umbilicals could be connected to feed power to the pyrotechnic devices for freeing the LM, and a check could be made to ensure that all twelve latches had properly engaged. Finally, the switch could be thrown to eject the LM from the S – IVB and allow the Apollo stack to continue its journey to the Moon.

None of these steps were simple, as each had its own checklist of items that had to be set or verified to ensure that the crew did not configure the spacecraft in a way that might endanger their lives. The process was carried out in a slow, methodical fashion of checks, verification and cross-checks: forty minutes work to allow them finally to throw one switch.

A catalogue of 37 stars distributed across the sky was programmed into the rope memory of the onboard computer. There w’ere some quite faint stars in the list, but this w’as only because the brightest stars are unevenly distributed across the sky. Planners had w’anted to ensure that irrespective of the direction in which the fixed line of sight of the optics was pointed, the crew7 would find a star sufficiently bright within the range of the movable line of sight to view through the sextant. Haeh star had a numerical code in base eight (octal) so that the crewman could tell the computer which star he wished to use. or in other cases the computer w’ould indicate the star that it had chosen for a specific operation.

Some of the objects in the Apollo star list were not stars at all. Three numbers were set aside so that the Sun. Moon and Harth could be referenced by the crewman for other tasks, and there w’as also a code that allowed a ‘planet’ to be defined if needed. In fact this could be any celestial object and in some cases, this ’planet’ was actually a star, just not one that the computer knew about.

Three of the fainter stars in this list have unconventional names that were added as a practical joke by the crew of the ill-fated Apollo 1 during their training. Star 03,

Navi, is the middle name of Gus Grissom (Ivan) spelled backwards. Likewise, his two crewmates added oblique references to themselves among the Apollo star list: Star 17, Regor, is the first name of Roger Chaffee spelled backwards; and Edward White II gave his generational suffix to the prank by spelling ‘second’ backwards as Dnoces and applying it to Star 20. The people of Apollo kept these names in their literature as a mark of respect to a fallen crew and they have been known to appear in a few star atlases and books in succeeding years.

Soon after the crew of Apollo 8 had begun their coast to the Moon, they removed their suits and never put them back on for the rest of the flight. After all, there were no plans for a spacewalk or any undocking event to pose a risk to the integrity of the cabin’s pressure hull. After the flight, Frank Borman wondered whether they had been required at all. “I would not have hesitated to launch on Apollo 8 without pressure suits,” he said at the debriefing after the mission. He continued, "We wore them for about three hours and stowed them for 141 hours. I see no reason to include the pressure suits on a spacecraft that’s been through an altitude chamber.” However, suits were needed for the ascent to allow the crew to breathe pure oxygen, and for the whole flight in case the spacecraft’s hull was breached for some reason.

All subsequent flights did require the crews to suit up regularly, either for operational reasons (a walk on the Moon is an obvious example) or as a precaution when pyrotechnic charges were cutting pieces from the spacecraft. For example, the final jettison of the lunar module required an explosive cord to cut through the

tunnel wall just in front of the forward hatch.

In some ways, a spacesuit can be seen as the ultimate in extreme out­door gear. Just as a climber on the peak of Mount Everest has to dress up appropriately, an Apollo astro­naut had to protect himself from the conditions he was about to encoun­ter. Like the mountaineer, he had a supply of oxygen as well as protec­tion from the cold and the heat in the rays of the Sun. Two distinct types of suit were produced for Apollo. The CMP had a simpler suit while the surface crews’ suits were designed to support a back pack that allowed them to work on the lunar surface. The following refers to the surface suit.

Air to breathe was fed into the suit either from the back pack, called the

portable life support system (PLSS,

pronounced ‘pliss’), or from the spacecraft via hoses. A fine network of water-filled tubes worn next to the skin kept control of the suit’s internal temperature as the crewman worked. The main part of the suit had an airtight bladder with layers of Dacron fibre, Mylar foil and woven Teflon cloth to protect against heat and cold. The outermost of the suit’s 18 layers was white Teflon cloth that helped to protect against abrasion.

Instead of sunglasses or goggles, a polycarbonate helmet was worn over the head that allowed almost all-round vision. An additional cover, which was worn over the helmet, included a visor that was thinly plated with gold to reflect light and infra-red radiation. It also had a set of pull-down shades at the top and to each side that the crewman could deploy to protect his eyes from the intense lunar sunlight.

When inflated to a pressure of 250 millibars, the suits ballooned and stiffened, which made them difficult to bend and hold in a set position. To counter this, flexible joints were built into various parts of the suit and a network of cables within the layers allowed a posture to be adopted and held. The gloves contained thermal insulation and the fingertips were made from silicone rubber to help to improve the astronaut’s sense of touch. On Apollo 15, David Scott arranged to have his fingertips up against the end of his gloves with the result that, over the course of his 18 hours on the surface, his bruised fingernails had begun to lift from his fingers.

The PLSS carried batteries to power the pumps and communications gear, high – pressure oxygen for breathing, a lithium hydroxide canister for removing carbon dioxide from the suit’s air, and a supply of water for cooling. The cooling element was a clever piece of kit called a sublimator. Water was fed through a porous metal plate where, on reaching a vacuum, it evaporated, thereby removing heat to form ice. From that point on, the ice would continue to sublimate to space and take heat with it as long as more water was fed to replace the lost ice. This cooled the separate water circuit that went around the crewman’s skin.

By the end of a J-mission’s lunar stay, a crewman’s suit was a heavily abused item of clothing that had undergone 20 hours of intense work in the hostile environment of the Moon. Often a crewman would accidentally fall and cover himself in dirt, or the guards over the w’heels of the rover would break off and the crew would be sprayed with dust as they drove. The suit’s outer layer was therefore heavily ingrained with dirt and its locking rings around the neck and wrists w ould threaten to seize owing to the highly abrasive nature of the all-pervasive lunar dust. These multimillion-dollar wonders of engineering are now museum fodder.