Category How Apollo Flew to the Moon

American companies learned a lot from building the Saturn; it was experience that was applied to the other fleets of rockets they built – the advanced versions of the Atlas, Delta and Titan families. However, it took over 30 years for these expendable rockets to match even the thrust of the Saturn IB, itself only as powerful as a single F-l engine on the base of a Saturn V. After Apollo, America’s heavy lift capability was entrusted to the Space Shuttle, which could match the lift-off thrust of the Saturn V but only by the dangerous expedient of employing massive solid-fuelled boosters that tragically constrained the spacecraft’s safety during ascent.

It is debatable whether the Shuttle system was a more cost-effective means of lifting large payloads to orbit. However, not only did the Saturn never kill anyone as it roared into space, it also gave crews survivable options to escape from a serious mishap at every stage of its flight. Yet, despite its spectacular success, the remaining Saturn V stages now hang as museum pieces or as lawn ornaments at various NASA centres while exquisitely built F-l and J-2 engines sit out in the Florida rain to be poked and prodded by curious tourists. One day soon they will be joined by the retired Shuttles.

Apollo’s final lunar mission took advantage of behind-the-scenes lobbying by the lunar science community to have a professional geologist visit the Moon. Many of the astronauts, whose backgrounds were usually in the fighter-pilot/test-pilot milieu, believed that a dangerous environment such as an experimental spacecraft in the vicinity of the Moon was just not the place to take someone who was not already inculcated in the philosophies surrounding aviation. Indeed, it was a requirement for the five scientist/astronauts recruited by NASA in 1965 that they learn to fly jets. Only one of them, Harrison ‘Jack’ Schmitt, was a geologist, and he proved a worthy representative when he flew with Eugene Cernan and Ron Evans on the Apollo 17 mission to explore a region of unusually dark soils in a valley near the shores of Mare Serenitatis.

The interest in this site was stirred by A1 Worden’s observations during Apollo 15 of dark halo craters on the floor of the valley which looked like a possible source of continuing lunar volcanism. Apollo 17’s launch on 7 December 1972 was notable by

being the only night launch in the programme, with the Saturn V’s fire rising like an artificial sun to illuminate the eastern coast of Florida. To reach the landing site, the spacecraft had to adopt a Moon-bound trajectory that took longer than any previous mission. The subsequent orbital dance around the Moon was the most involved of all the missions. Having landed, Cernan and Schmitt immediately began preparations to exit the LM Challenger, deploy their rover and set up their ALSEP science station. As had Scott on Apollo 15, Cernan had difficulty extracting the deep core drill from the ground, despite having a special jack to aid him in the task. The extra time taken meant that a planned drive to a nearby crater had to be curtailed.

On their second day, during a moonwalk that lasted over 7 ‘A hours, they drove over seven kilometres west to the base of a mountain. Here they sampled boulders whose tracks indicated that they were from outcrops further uphill, thereby enabling the astronauts to collect rock from sites that were well beyond the rover’s reach. On the way back they stopped at a crater that was later named ’Ballet’ because Schmitt lost his footing while sampling, and performed wild gyrations in an attempt to regain his balance.

A frisson passed through those conducting the mission, both on Earth and Moon,

when deposits of orange soil were found on the rim of one of Worden’s dark halo craters. Nothing like it had ever been seen on previous missions, and its colour suggested iron oxidation or rusting, something that normally requires water – a substance notable by its apparent absence on the Moon. Subsequent analysis of the material showed that it was certainly due to volcanism, but of an ancient variety when spectacular fire fountains had sprayed droplets of molten rock hundreds of kilometres into the sky some three billion years ago. It had simply been excavated by the impact that made the crater.

A productive range of stops on the final moonwalk of the Apollo era included a visit by Cernan and Schmitt to another mountain where a split boulder had come to rest. Schmitt’s expert eye spotted the signs of alteration that showed how more than one massive impact had worked and reworked the Moon, and by implication, Earth during their infancy.

Evans, working in the CSM America, was not idle either. The complement of instruments built into the side of his service module had been changed compared to what Apollo 15 carried because its orbit would repeat much of Endeavour s swathe. As with the two previous missions, thousands of high-resolution images of the Moon were taken on giant rolls of film that Evans retrieved during the coast back to Earth by exiting the hatch and manoeuvring hand-over hand along the SM.

The visit of Apollo 17 to a site nearly as grand as Hadley was the peak of a spectacular mission that brought the initial human exploration of the Moon to a highly successful close.

The Saturn V took care of its own guidance and, assuming everything went
smoothly with the ascent, the crew had little to do except to keep a careful watch over it by running Program 11 (PI 1) on their computer, which displayed their speed, height and how rapidly that height was changing. Pll also drove their displays to show what their attitude should be through­out the ascent, so that any deviation could be seen. Should the commander have to take over control of the Saturn, he would fly it by following the cues given by Pll.

Eugene Cernan, who commanded the only mission to launch at night, later spoke about having trained to fly his Saturn V to orbit manually, a task no commander wished upon their mission, yet one which appealed to their test-pilot credo. "The launches – both from the Earth and from the Moon – were the only truly automatic phases of the mission, but we could take over and fly it manually to orbit. Aborting during Earth launch was the last thing I wanted to do, so I trained and planned. It was a lot more difficult at night than in the daytime because you didn’t have horizons and things to look at; you had to look at the stars. We had several modes of failure that could have degraded systems. The worst would have been for all the guidance to fail so that you literally had to fly it by the stars.

Now, I can never prove that I could have done it. But I did it a lot of times in simulators and really did – and still do – believe that I could have flown that Saturn V to orbit. It’s one of those things where you say T hope it never happens; but I dare you. I’ll show you. If you do fail, you just watch.’ You had to have that attitude; and I think that attitude is reflected across the cockpit. You develop confidence in each other, and, from that, the teamwork evolves.”

Making certain that a rocket gets to where it needs to go is a significant part of what is commonly referred to as ’rocket science’, although it would be better described as rocket engineering as, like all engineering, it is merely underpinned by science. Though the bedrock of rocket guidance is mathematics and physics, the basic concepts behind it are not so difficult to understand. What a space rocket is usually trying to achieve is to reach a point above most of Earth’s atmosphere at a defined time, and to be travelling at a certain speed and in a particular direction

when it gets there. Fulfilling these criteria should result in the rocket and its payload travelling in the desired orbit around Barth.[2]

The Saturn V. and many other launch vehicles after it, handled its guidance in two distinct and separate ways: one dumb, the other smart. It started off dumb, switching to smart once it was beyond the majority of the atmosphere. The dumb technique went something like this. "I don’t care where I am.’- says the rocket’s computer. ‘Tin just going to manoeuvre myself upwards through the air. tilling over in a fashion that’s been programmed into me. and I’ll see where I get to at the end.’’ This is termed open-loop control because information about the effect of a steering command was not fed back to influence subsequent commands. Engineers began the flight with this guidance philosophy because it was considered unwise to have the Saturn potentially make large steering turns while it was travelling at high speed through the denser regions of the atmosphere. For the first three minutes or so. the rocket flew according to a pre-programmed tilt sequence, a series of manoeuvres designed to ensure that its structure endured minimal sideways aerodynamic forces. This tilt sequence consisted of four major manoeuvres.

The first such manoeuvre was the 1.25-degree yaw that tended to scare onlookers during the first few seconds of ascent as it steered the Saturn V away from the launch umbilical tower. Once clear of the tower and upright again, it then made its second manoeuvre, rolling around its long axis to align the minus-г axis, the cast-facing axis, with the flight azimuth. Remember that, when sitting on the pad. the launch umbilical tower was to the north and the spacecraft’s hatch faced cast; the minus-z axis also pointed directly east and in that position the vehicle’s azimuth was 90 degrees. The roll manoeuvre’s job was to aim this axis in the direction they wanted to go so that thereafter the whole space vehicle would only need to make a simple tilting manoeuvre around its у axis, and start picking up horizontal speed. For most Apollo missions, the flight azimuth was around 72 degrees, a direction around cast- northeast which allowed for the most efficient path to a highly desirable free-return lunar trajectory that the early Moon missions would take. Apollo 15 and Apollo 17 had flight azimuths very near due east which helped them to access the northerly lunar sites that they had to reach.

Once the rocket had aligned its own coordinate system with its flight azimuth, the third and largest manoeuvre of the tilt sequence began; a very slow pitch-over to take them from a vertical attitude towards the horizontal as they began to accelerate not just upwards, but along the flight azimuth. The whole of the S-IC’s flight was carried out in dumb mode. The smart mode of rocket guidance came later.

The concepts of orbits and weightlessness are often misunderstood by laypeople who harbour the mistaken idea that there is literally no gravity in space. Nothing could be
further from the truth, as gravity binds all matter and light in the universe. To understand how objects move in space, otherwise known as celestial mechanics, one has first to grasp the concept of freefall, because, for much of the time, that is the condition of everything in space. Our communications, weather and TV satellites are in constant freefall around Earth, as is the Moon. Earth itself, along with the other planets, is in a permanent state of freefall around the Sun, which itself freefalls around our galaxy. Even the immense Milky Way galaxy that we inhabit is freefalling along with a collection of others in our local group of galaxies in an eternal gravitational dance that is essentially no different to the freefall experienced by a stone dropped off a bridge into a river.

The crucial ingredient that transforms freefall from a short-term descent that ends in a messy impact, into the essential element of an orbit, is speed, very high horizontal speed. A common thought experiment that explains the concept of the orbit is one that invokes a perfectly smooth, airless Earth with an imaginary tower. At the top of the tower is our intrepid imaginary experimenter, presumably wearing an imaginary spacesuit, whose task is to fling an object to the ground and watch how

it travels before it impacts Earth’s surface. Let us imagine that this object is a box containing beads, so that the effects of weightlessness can be observed, at least from the perspective of our mind’s eye.

In this scenario of the mind, our experi­menter begins by simply dropping the box from the tower. The box accelerates by gravity’s pull until it hits the ground. The beads within the box experience an identical acceleration such that not only is the box falling, but so are the beads. In our mind’s eye, looking within the box, the beads can be seen freely floating around between the walls of the box and so they appear to be weightless. Viewed from outside, however, they are falling with the box until they both meet their end directly below the point from which they were dropped.

The next incarnation of the thought experiment deals with what happens when, instead of just dropping the box, our experi­menter throws it horizontally. For the few hundredths of a second that the throw is being executed, the beads are pushed against the back of the rapidly accelerating box and they experience whatever g-forces the experi – The dynamics of falling objects in a menter’s arm can achieve until the throw is thought experiment. complete. Once the box has left the thrower’s

hand and is coasting, it follows a curved path to the ground that can be resolved into two components: horizontal and vertical motion. Following the first law of motion devised by Isaac Newton, once horizontal velocity has been imparted by the throw, it is maintained until something causes it to change; and there is nothing in our thought experiment to do that because we have exorcised the effects of the atmosphere. In the vertical direction, however, the gravitational effect of Earth exerts the same force on the box as it did in the previous scenario, pulling the box and its beads to their untimely end on our imaginary airless surface. By combining these two velocities, we arrive at a curved path as the acceleration of gravity takes our subjects to their doom. Inside the box, the beads float around, apparently weightless and unaware of their fate. Although the box now follows a longer distance in its curved path to the surface, the time taken to reach the surface is essentially the same as if it had been dropped.

The next case for our thought experiment above our idealised Earth is where arrangements are made to throw the box at a far greater speed than is achievable by a human arm; say something of the order of a few thousand kilometres per hour. Traditionally in these kinds of mind games, this can be achieved by an immense, imaginary cannon. Once the cannon has done its rather violent job of quickly accelerating the box, we see the same two influences affect the box’s flight. Gravity accelerates the box and its beads down to Earth while the constant horizontal speed takes it away towards the horizon. Again the result is a curved path to the surface. Once the beads within the box have recovered from their sudden acceleration, they are once more seen to float freely and exhibit what we call weightlessness. However, on this occasion, the flight lasts rather longer than in the previous cases. The box’s horizontal speed is so great, and so much distance is being gained as it drops, that by the time it has fallen the height of the tower, the curvature of Earth has dropped the surface level a little, and so the box has further to fall to reach the surface.

In successive versions of our thought experiment, we increase the power of the cannon higher and higher, reaching ever greater starting velocities. As we do so, we find that the effect of Earth’s curvature be­comes ever greater, increasing the time that the box coasts in freefall until impact. In every case, the beads gaily float around inside the box and appear to be weightless to anyone who could look.

Eventually our thought experi­ment reaches a special case where the horizontal velocity of the box is so high that it manages to fall in a
great ballistic arc all the way to the opposite side of our perfectly smooth, imaginary Earth without hitting it. It might be expected that it would simply travel a little further before meeting its doom but we run thought experiments to illustrate when nature does not act as we expect. By the time the box has reached the opposite side of the planet, the antipode, it not only has the horizontal velocity imparted by the cannon, but has also gained additional momentum by virtue of the speed of its fall towards Earth. This means that the box not only continues around Earth, but also climbs back up to the altitude from which it was launched, much like a pendulum that, having fallen to the lowest point in its arc, has the momentum to continue to the top again. There is no case where the horizontally-fired box will impact the surface beyond the antipodal point. In our idealised scenario, our experimenter had better watch out, because about 90 minutes after he fired it from his cannon, his box will come whizzing by at the same speed, about 28,300 kilometres per hour, that it had when it was first set on its journey. In all this thought experimentation, we must, of course, not only ignore the effect of the atmosphere, we must also forget for the moment that Earth is rotating. The box has completed an orbit of Earth during which the beads within it experience the same weightless effects of freefall that they experienced in all the previous cases.

Having achieved an orbit, there are three further cases of orbital travel we can look at. The basic orbit just illustrated has two important features that are typical of nearly all orbits where a small body revolves around a much larger one. At the point where it just missed the surface on the opposite side of the planet, it was at its lowest altitude. For an orbit around Earth, this is termed the perigee. The point at which it was launched was, in this case, the highest point in its Earthly orbit, which of course is the height of the tower on which the cannon was fitted, and is termed the apogee. This lop-sided trajectory around a large body is called an elliptical orbit.

Continuing with our thought ex­periment, there is a specific case with a slightly higher starting speed than the previous example, where the box maintains a constant altitude. The curvature of Earth’s surface is falling away in exact sympathy with the box’s path, making the two con­centric and the orbit becomes circu­lar at the height of the tower. Again, the beads float around weightless within the box, and again, our space – suited experimenter needs to keep his head down as the box will whizz by in about 90 minutes.

Finally, we need to look at what happens when the experimenter adds The orbit in a thought experiment is extended. even more charge to his hypothetical
cannon and fires the box at an even higher starting velocity. In this situation, the box has more impetus than is needed for a circular orbit and this extra momentum straightens out the flight path a little, causing it to rise from Earth as it moves away from our imaginary tower. However. like a ball thrown vertically into the air. the box slows down as it rises away from the planet until it gets to the opposite side of Earth where it reaches an apogee. The box’s vertical travel, i. e. its movement away from Earth’s surface, has come to a stop and it gains no more height. Once its remaining horizontal speed has taken it past apogee, it continues on its path, descending all the time and regaining all the speed it began with until, at the tower. it reaches its perigee at the height of the tower, ready to repeat its elliptical orbit. In this, as in all the previous cases, the beads within our box float around in the same state of apparent weightlessness that they experienced when on their way to destruction in our first example. The orbit is simply a special case of freefall in a universe where gravity is king.

Applying this rather fun analysis to real life, the Saturn launch vehicle was both our cannon and our tower. It lifted our box. the Apollo spacecraft, to an altitude beyond the sensible atmosphere where the air could not impede it. and accelerated it horizontally until it had enough speed to fall all the way around Earth. Instead of beads, we have three crewmen who found themselves weightless and able to float around in their cabin until another force pushed them back in their scats.

The elliptical nature of orbits was first w’orked out by Johannes Kepler in the early seventeenth century. His first law of planetary motion states that all planets move in ellipses with the Sun at one of the tw;o foci of their ellipse. The same holds true for spacecraft orbits with Earth, the Moon or other planet at one focus. And although the crew are still subject to gravity, they are weightless.

Stu Roosa was the command module pilot on the Apollo 14 mission and it was his job to guide the CSM Kitty Hawk towards the LM Airfares stowed atop the S-IVB.

Lunar module pilot Edgar Mitchell gave the television viewers a running commentary of their view of the approaching LM. “Okay, I’ll chat for a minute,” he began. “The S-IVB is surrounded here by typically thousands, or millions of panicles that came out when we separated. They look like little winking stars, floating around in a very random pattern. The sunlight is shining very strongly off the top of the lunar module as we drift into it. Stu’s doing an excellent job of sliding in here very slowly. As you can see, our approach speed is a few tenths of a foot per second, probably. And the LM is starting to get very large in our field of view; starting to cover the window. And the LM and the S-IVB are bore-sighted right out our, y axis.” The x axis of the CSM ran out through the apex of the command module and therefore the spacecraft and probe were aimed directly at their quarry. The approach to the captive LM was carried out in such a slow, careful manner that it hardly appeared to move on the TV. A viewer’s attention had to be taken away for a moment to realise, when looking back, that they had actually edged closer to the LM. * *

Mitchell continued as the final distance was closed. "We can see all of the orange, yellow thermal protection around the LM. The colours stand out very nicely. And Houston; we’re about to dock. We’re probably a foot or 18 inches to two feet out now.”

The probe contacted the drogue’s conical surface and scraped its way down to the central hole. As it nestled into the apex of the drogue, he called out, "And we docked."

But they had not docked. The capture latches had failed to engage with the drogue, and Roosa found that his spacecraft was gently rebounding away from the LM. He immediately tried again.

A minute later, he radioed his failure to achieve soft-dock. “Okay, Houston. We hit it twice. Sure looks like we’re closing fast enough. I’m going to back out here and try it again.”

Over the next minute, Roosa made a third attempt, giving the CSM an extra push home by continuing to fire the RCS thrusters after the probe settled home. Again the latches failed to work.

“Man, we’d better back off here and think about this one, Houston. We’re unable to get a capture,” Roosa concluded.

For the next five minutes, Capcom in mission control had Roosa check the spacecraft’s configuration, verifying that everything appeared to be just as it should. For a fourth time, he manoeuvred the spacecraft towards the LM.

“Okay, Houston. I hit it pretty good and held four seconds on contact and we did

The crew could see the scratches on the drogue’s surface where the probe had been guided into the hole but there was no obvious reason why the two ships were not holding. As they waited for the controllers and engineers in Houston to assess the situation, they were treated to a spectacular display of countless li­quid droplets shimmering before them as the S-IVB began a planned dump of some of its residual propel­lant. Mitchell enthused about the sight as they drifted among the particles of propellant all around them. “Of course, it’s the source of another ten million particles floating out in front of us.”

Over an hour passed as possibili­ties were weighed and engineering minutiae were discussed. Meanwhile, the two large spacecraft flew away from Earth in exquisite formation for a distance greater than the diameter of the planet. Then Capcom made another call. “Okay, we’d like to essentially try the docking again with the normal procedures rather than going to more drastic alternate pro­
cedures. Make your closing rate on this not fast, not slow, just a normal closing rate.”

‘’Okay," replied Roosa. "We’ll try it. I thought that’s what I had the first time, but we’ll give it a go.”

fid Mitchell picked up on the commentary again. "Okay. Houston, we’re starting to close on it now.”

”14, Houston. Roger.”

’’About four feet on it, Houston.”

"Roger. Ed.”

"Here it comes,” continued Mitchell as the probe homed in on its quarry for the fifth time, resulting in another disappointed call.

"No latch.’’

"No latch. Houston.’’ echoed Stu Roosa. His commander, Alan Shepard voiced what was on his mind. "I’m sure you’re thinking about the possibility of going hard – suit and bringing the probe inside to look at, as wc are. ‘

Mission control was thinking of this possibility, where the crewmen would seal themselves in their suits, depressurise the cabin, open the forward hatch and remove the probe to enable it to be inspected. But first they had one more suggestion that would avoid this cumbersome procedure. The backup commander Eugene Cernan. who had been working with the people analysing the situation, Look the Capcom console.

"Okay. We got one more idea down here, before doing any hard-suit work. Wc’rc thinking of attempting to dock actually without the aid of the probe.”

Their idea was to use the probe only as a way of aligning the docking rings of the two spacecraft. In a normal docking, once the probe had latched onto the hole in the drogue, it was pneumatically retracted to pull the docking rings of the wo spacecraft together so that the twelve strong docking latches could engage. Ccrnan’s suggestion was for Roosa to manoeuvre the probe back to the centre of the drogue for a sixth time and then, while Roosa continued to use the thrusters to push forw ard. Shepard would retract the probe. The hope was that the alignment of the docking rings would be maintained as they came together and the docking latches would engage cleanly. But having had one unexplained malfunction in the system, mission control could not be sure that the probe would retract as commanded. Once again, Mitchell picked up the commentary for the TV viewers.

"Okay, Houston. We’re about 12 to 15 feet away.”

"Roger. Ed,” replied Capcom. "We got a very good picture.”

Again the probe was guided to the hole at the centre of the drogue. Once it seemed to have settled in, Shepard retracted the probe. "We got some. Houston. I believe..Shepard was cut off as the loud bang-bang-bang of the engaging docking latches rippled through the cabin. Stu Roosa triumphantly exclaimed. "Wc got a hard dock, Houston.”

"Outstanding,” came the relieved reply from Houston. "Super job. Stu.”

After the crew had folded up the docking equipment and retrieved it for inspection, they could find no fault in its mechanism, and it was used successfully for the crucial docking in lunar orbit after Shepard and Mitchell returned from their exploration of the lunar surface. Usually, the probe was discarded with the LM in lunar orbit, but Apollo 14‘s was returned to Earth for examination. No fault could be found and the engineers could only surmise that some unknown foreign debris, possibly water ice, had temporarily jammed the mechanism.

During a normal docking, after the capture latches had gripped around the edge of the drogue’s central hole, the crew would have waited a while to allow any swinging motion of the two spacecraft to damp down. The probe Lip was gimballcd to facilitate this rotation and it included springs to make it self-centre. Once everything had settled, the probe would be retracted as normal to bring the docking rings together and engage the twelve docking latches around the circumference of the tunnel.

A1 Worden on Apollo 15 found that the capture latches appeared not to engage when he brought the CSM Endeavour up to the drogue in the LM Falcon. With memories of Apollo 14’s difficulties still fresh, he then made sure of a positive engagement by a little extra forward push on the thrusters. This extra thruster firing, combined with the rotation given to the CSM by the probe being shepherded towards the centre of the drogue, contributed to a misalignment of the two vehicles and, as a result, the two docking rings did not meet face on when the probe was retracted, imposing an undesirable stress on the tunnel’s structure.

On Apollo 16, Ken Mattingly tried to ensure that the two craft were better aligned before retracting the probe. However, having engaged the capture latches, he found the spacecraft remarkably difficult to manoeuvre. “Whatever gas we used during TD&E, we used after I hit in trying to get it re-centred.’’ Mattingly was trying to make sure that the long axes of the two craft were aligned before he pulled them together with the probe retraction. “They [management] busted the [Apollo] 15 guys about forcing it in. I tried to centre it up, and that is a pretty expensive operation. It’s very inefficient when you have your nose hooked to something you’re trying to push. I was using the translation controller and I was really surprised. Either the friction on the probe head or something is a lot more than I expected. It was very ineffective.’’

With all the thruster activity he was generating around the two spacecraft, Mattingly became aware of an unexpected noise from the thrusters. “I didn’t hear any RCS sounds when I got off the S-IVB. I didn’t hear any sounds during the turnaround; and, I didn’t hear anything on closure until I got in real close. I would swear – I know it’s not possible – but I’d swear 1 could hear the jets impinge on the LM before w’e docked.” This was a surprise to him. Sound cannot travel in a vacuum, yet he seemed to be hearing the gas from the thrusters washing over the LM. He thought that perhaps the exhaust was forming a temporary local atmosphere around the spacecraft through w’hich sound waves might carry.

He continued, “And you could certainly see it. Maybe I was visually seeing the skin of the LM kind of flutter and I knew’ that should make a noise. I heard the same noises every time w’e fired the engines after that. I don’t know’ if there could be enough local atmosphere or whether you can get a reflected shock that you could hear. I don’t know’ how’ it is. but. I know I could hear reflections off the LM before we docked.” The mission’s commander John Young supported his pilot. ”1 think

that is possible, Ken, with the gas going out and coming back and bouncing off your vehicle. There are a lot of particles in there.”

Although the IMU was finely engineered, the platform inevitably drifted very slowly out of perfect alignment with the REFSMMAT, and had to be realigned at regular intervals. Naturally, the CMP turned to the spacecraft’s optical system to take sightings of the stars. Because this task was carried out in conjunction with the computer using Program 52, it was simply known as doing a P52, another ubiquitous term in Apollo jargon. If the crew needed to perform any kind of propulsive burn, which always required accurate aiming of the spacecraft’s engines, then a P52 was perfonned beforehand as a matter of standard procedure. It was also carried out if some time had elapsed since the previous P52 because many other operations, such as the aiming of cameras and cislunar navigation, depended on a properly aligned platform. In any case, engineers were keen to monitor the rate of drift of the platform as an indicator of the IMU’s overall health.

With two stars, a P52 could determine the orientation of the entire universe around the spacecraft. With the spacecraft held in a steady attitude, the sextant’s movable line of sight was pointed towards a specified star. Once the star was accurately aligned in the eyepiece graticule, a button was pressed to tell the computer to note the star’s apparent position with respect to the slightly misaligned platform.

The sextant was then aimed at a second star, where another mark was taken. The computer now knew where the stars appeared to be and. from its internal knowledge of where they really were, could calculate the amount by which the platform had drifted since its previous realignment. These angles were usually very small, and were expressed to an accuracy of thousandths of a degree. Their values were displayed on the DSKY to be passed on to the controllers in Houston, and they indicated by how much the gimbals needed to be rotated, or torqued. to bring the platform back into accurate alignment.

As in every aspect of their work, the command module pilots were competitive about aligning the platform well, and the P52 procedure included a measurement of their sighting accuracy so as to let them gauge their performance. From its internal tables, the computer knew what the angles between pairs of stars should be. Once the CMP had made the two sightings, the computer also knew what the measured angle between them w’as and could display the difference betw een these two angles to hundredths of a degree. If the pilot had made a perfect P52, the /его difference would be displayed on the DSKY as a row of five noughts, 00000, which the crew’ gleefully referred to as ’all balls’. А /его figure was commonplace, as was Tour balls one’ – an error of only one hundredth of a degree. Only occasionally was the error as large as 0.02 degrees. Of course, a well-aligned platform was as important for an accurate determination of the state vector as it was for the crews’ bragging rights.

The concept behind the P52 became familiar to amateur astronomers of the generation after Apollo as powerful computers became small and cheap enough to build into backyard telescopes. By aligning these inexpensive instruments on two stars in succession, their computers learned the orientation of the universe around them and could thereafter quickly and easily aim themselves at any desired celestial object in a manner greatly reminiscent of the Apollo G&N system.

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

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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.