Category How Apollo Flew to the Moon

The docking system was one of the many engineering wonders of the Apollo programme and one whose importance is perhaps underplayed. It was an ingenious, compact, pneumatic and mechanical arrangement that managed to elegantly fulfil a number of tasks: it self-centred the two spacecraft as they contacted; it absorbed the shock of that contact to achieve a soft-dock; and, finally, it pulled the two craft together to achieve hard dock and straightened their axes as it did so. It was then collapsible and removable from either the LM or CM side and could be stowed when not required. Years later, Apollo 15 commander David Scott, who was also the first CMP to use the Apollo docking system on Apollo 9, wrote about how crucial it was. "It is really quite important to the whole scheme of the Apollo concept – a very complex apparatus and one of the few single-point failures in the entire system. But at the end of the day, it was probably one of the more brilliant mechanical devices of the programme.”

Like so many plug/socket combinations in the electrical and electronics world, it was a sexed affair with the CSM carrying the male docking probe and the LM providing the receptacle into which the probe was inserted. The movie Apollo 13 played up the suggestive nature of this arrangement when the character of Jack Swigert, who would be the CMP on the Apollo 13 mission and was a bachelor with a reputation as a ladies’ man, was shown using a glass and bottle to demonstrate the Apollo docking system to a beautiful young woman. But the male/female nature of the system limited its future, and later spacecraft instead used androgynous designs which would allow any pair of suitably equipped vehicles to dock. However, despite

Top. An engineering model of the probe and drogue docking mechanism. Bottom. A test of the docking mechanism for Apollo 14 where Ant ares was turned upside down to perform a docking with Kitty Hawk. (NASA)

this inherent inflexibility, the probe and drogue arrangement was well suited to the needs of Apollo.

On the CM side, the probe consisted of an articulated tip mounted on the end of a retractable rod. Around this rod were three arms with shock absorbers in their elbow joints. The whole probe assembly could be mounted within the docking ring which itself was bolted to the apex of the command module. This ring carried 12 automatic latches around its circumference that engaged with the LM’s docking ring when the two were brought together by the retraction of the probe.

The LM’s side of the affair was much simpler. The drogue was really just a concave cone with a carefully sized hole in its centre. The purpose of the cone was to gently shepherd the tip of the probe into the hole. Three small spring-loaded capture latches built into the probe’s tip then caught the edge of the hole. This was the ‘soft –

dock’ condition. When commanded, one of four small bottles of nitrogen gas inside the probe energised the retraction mechanism to pull the spacecraft together and as it did so. three pitch arms ensured that both spacecraft were aligned by their contact with the drogue’s conical surface.

When the CSM was manoeuvred towards the LM, use of the docking target and the COAS helped to ensure both spacecraft tvere aligned in pitch, yaw and roll. Remaining pitch and yaw errors were removed by the shock absorbers in the pitch arms as the retraction took place. The roll error was usually small because the COAS and docking target were displaced well away from the centre-line of the docking system. At a later stage of the mission, the LM’s guidance system would be given an approximate alignment by the crew manually reading the appropriate numbers from the command module’s guidance system and passing them across to the LM. These alignments would have to be adjusted to account for the difference in the orientation of the coordinate systems of the two spacecraft. This calculation also meant taking into account any angular misalignment between the two vehicles at docking. To facilitate this, the docking tunnel included markings that allowed the docking index angle to be read off.

The set of numbers that defined the desired orientation of the platform had their own peculiar abbreviation – the REFSMMAT, a remarkably simple concept couched in very opaque terms. Not only was this acronym extraordinary in its size, it was also ubiquitous, being peppered throughout the crews’ conversations with the ground and in their documentation. It stood for reference to a stable member matrix, an incomprehensible jumble of jargon; but it was simply a numerical definition of an orientation in space, one to which the platform could be aligned. Being an inertial orientation, it was defined with respect to the stars.

Whether or not the absence of the Sun renders them visible, the stars are constantly moving across Earth’s sky. They rise in the east and set in the west but only because Earth is rotating in the opposite direction. Remove Earth from the scene and the vista of stars can be thought of as an essentially static sphere with the observer at its centre. Onto this sphere, astronomers have drawn an imaginary spherical coordinate system against which they measure the positions of the stars. If wc then place a З-axis coordinate system at the centre of this celestial sphere and we project its axes out to the sphere, the axes will be aimed at particular angles on that sphere. We can see that the orientation of the three axes can be defined as angular positions against the sphere. This is the basis of the REFSMMAT. The platform can then be orientated so that its coordinate system is aligned to that of the REFSMMAT. To do this requires that sightings be taken on the stars with the
scanning telescope and sextant so that the computer can gain direct knowledge of the celestial sphere.

Ed Pavelka was one of the flight controllers who occupied the FIDO console in The Trench at mission control. As a way to cement the esprit de corps among the flight dynamics team, he invented a fictional character called Captain REFSMMAT who represented the ideal flight controller. Urged on by one of his bosses – the tough but sensitive Eugene Kranz – Pa­velka imagined a figure of mili­tary stature with a radar in his helmet, and drew a series of posters depicting Captain RE­FSMMAT and his arch enemy, Victor Vector. During the Apol – One of Ed Pavelka’s drawings of Captain lo yearSi pe0ple in the MOCR

REFSMMAT. (Courtesy of Chuck Deiterich.) scribbled little comments on

these posters, often sarcastic, to let off a little steam.

A cliche that has become firmly set in the public’s mind since the space age began is that space food is a bland, dehydrated mush that comes in a tube. Certainly, for the earliest flights, this was true. However, on Apollo, things began to change a little.

Some of the food taken on Apollo w as dehydrated, for good reason. Water makes up a substantial component of soups and juices, and makes them heavy. Since spare water was plentiful anyway as a by-product of the fuel cells, it made little sense to carry more from Earth. Instead, some food was free/.e-dried, packed into plastic bags and vacuum-sealed to save space. When required, it was retrieved from its storage locker and water was injected through an orifice in the bag. It was then kneaded and left for a few minutes to he fully absorbed. When ready, the corner was cut off with scissors and the contents squeezed out into the mouth.

The Apollo spacecraft had one feature that made eating soups somewhat more pleasurable than on previous spacecraft – hot water. Because the fuel cells had to constantly generate electricity, designers could afford to add a small water heater that could then he used for making coffee and soup. Unfortunately, the limited power available on the lunar module meant that there could be no hot water, and its crews had to spend their lime on the surfaee eating cold food.

On most flights, main meals w’ere similar to modern ready meals, set out in aluminium trays with peel-back lids. Some were kept in a freezer, others in the food stow-age lockers. As a small eleetrie food warmer was provided in the command module, these packages could be heated before consumption. Each meal was planned before the mission, with eaeh crewman choosing what he would like from an available range. Enough food was packed on board to provide each crewman with 2.500 calories daily. For Pete Conrad, the menu for his second day in space w’ent like this: For breakfast, he had apricot pieces, rehydratable sausage patties and scrambled eggs and he finished it off with tw’O rehydratable drinks, grapefruit juice and coffee. At lunchlimc, he heated a tray of turkey with gravy, ate it with four cheese crackers, and downed it with rehydrated orange and grapefruit drink. His evening meal consisted of pork and potatoes which had to be rehydrated, a slice of bread with spread and some sweeties, all washed down with rehydratable cocoa and an orange drink.

On Apollo 8. the crew found an extra treat for Christmas 1968. "It appears that we did a grave injustice to the food people.” said Jim Lovell to Mike Collins in Houston. ‘ Just after our TV show’. Santa Claus brought us a TV dinner each, w’hich was delicious, turkey and gravy, cranberry sauce, grape punch; outstanding.’’ These foil-w’rapped dinners became the norm for Apollo 10 onw’ards. Additionally, the Apollo 8 crew’ found that three small bottles of brandy had been packed among their Christmas food rations. Borman, however, pulled rank and said they could not partake of the brandy until they got home. Being one of the early Apollo flights, almost all their food was in rehydratable form.

’’The food has generally been good.” commented Bill Anders while making audio notes into the onboard tape recorder. "Particularly the last meal: butterscotch pudding, beef stew, grapefruit drink and chicken soup.”

"Well, Bill, you might mention the hot water makes a big improvement, too.” added Lovell. He and Borman had already experienced the longest space mission to date, having spent two weeks in the Gemini 7 spacecraft. Compared to its cramped accommodation, the Apollo cabin wus relatively luxurious, especially the supply of hot water.

Later, during a TV showy Borman and Anders prepared a drink for the camera. "Well, here w-e have some cocoa,” said Anders. "Should be good. I’ll be adding about five ounces of hot water to that. These are little sugar cookies, some orange juice, corn chowder, chicken and gravy, and a little napkin to wipe your hands when you’re done. I’ll prepare some orange juice here.”

Borman picked up the narration. "Okay. You can see that he’s taking his scissors and cutting the plastic end olT a little no/./.le that he’s going to insert the water gun into. The water gun dispenses a half-ounce burst of water per click. Here we go; Bill has it in now, and the water is going in. I hope that you all had better Christmas dinners today than us. but nevertheless, we thought you might be interested in how we eat.”

"Roger.” said Collins at the Capeom console. "I haven’t heard any complaints down here, Frank. We’ll bring you up to speed on your food when you get back. Looks like a happy home you’ve got up there.”

Borman continued. "Ordinarily, we let these drinks settle for five or ten minutes, but Bill’s going to drink it right now. He cuts open another flap, and you’ll see a little tube comes out…”

"This is not a commercial." interjected Lovell.

"… and he drinks his delicious orange drink,” continued Borman. "Maybe 1 should say he drinks his orange drink. He’s usually not that fast. Bill is really in a hurry today. Well, that’s what we eat. Now’ another very important part of the spacecraft is the navigation station or the optics panel. And wc – just a minute; Bill wants to say something.”

“Thai’s good.” said Anders, “but not quite as good as good old California orange juice.”

As Gemini veterans. Pete Conrad and Dick Gordon appreciated the improved culinary features of the Apollo spacecraft. But as they neared the Moon on Apollo

12. A1 Bean had a question for Don Lind, Capeom in mission control. "How about asking the food experts down there, we had a can of tuna fish spread salad last night, and there’s about a half a can left today, and that stuff is still good to eat. isn’t it?”

"We’ll check,” said Lind. "I’ll be right back with you.”

In a moment, the medical doctor occupying the Surgeon console had passed his opinion to Lind w’ho told the crew. "The Surgeon suggests you try a new’ one."

"Well, Dick has this one in his hot hand.” said Bean, "and we just opened it last night. You sure that one isn’t all right?”

The w’heels of mission control w’ere starting to crank up. "We’re still checking with some people down here whether there’s any problem over that tuna fish,” said Lind, "but why don’t you hold off eating it until w’e get a better answ er for you?”

With the flight otherwise proceeding smoothly, managers and backroom people suddenly had a concern and all were keen to come to the correct decision.

"Apollo 12. Houston,” called Lind after 10 minutes had passed.

"Go ahead,” replied Conrad.

"You can’t imagine what consternation your tuna fish question has raised dow? n here. We have a wide diversity of opinion."

Gordon had also been thinking about it. "I decided it was okay,” he said.

"Well, w’e have a vote..said Lind. "The majority says throw’ it aw’ay; there’s a minority report that says everybody can cai ii except Dick Gordon.”

“Okay. That’s done.” said Conrad.

“Roger, d hey recommend that you probably throw it away.” said Lind.

‘•Okay.” * *

Perhaps Gordon got to enjoy his Luna. It is difficult to know. Perhaps he was the butt of inflight banter about his only exercise being between the couch and the food compartment. But the problem was very real. Gordon had trained more than either of the other two crewmen to fly the spacecraft back through the atmosphere at the end of the flight. Had he become ill through bad food, the re-entry would have had to be flown by less experienced crew, and while a normal re-entry w ould have been something Conrad could easily have handled, he simply had not practised for the range of possible abnormal situations that could arise. Л possibly dodgy can of tuna could not be allowed to threaten the mission. They had enough risks to contend with.

The food and drink provided was thought to give the crews everything they w ould need for a flight, but the demands placed on the final three crews showed that this was not so. From Apollo 15 onwards, crews were expected to work for up to seven hours per day on the lunar surface. In preparation, they were intensively schooled in the methods of geology and their missions had much more activity packed into all phases of the flight, ranging from onboard science experiments and advanced photographic mapping operations, to the careful documenting of every rock sample lifted from the dust.

To achieve these enhanced demands, the lunar module crews repeatedly practised the tasks that they would fulfil during their precious few hours on the Moon. As the date of launch approached, much of this training was carried out in the heat of the Florida sun. Apollo 15 w as launched at the height of summer and in the days leading up to its launch, David Scott and Jim Irwin laboured for hours inside their training suits, simulating the techniques that would make their work on the Moon as efficient as possible. Since the cooling systems they would use on the lunar surface could not function in Earth’s atmosphere, this work was hot and demanding. Both men sweated copiously and both drank as much juice as they needed to compensate. On the Moon, as they worked on the plain at Hadley, their heart rhythms were radioed back to the doctor on the Surgeon console at mission control. Towards the end of their lunar stay, he noticed that their hearts occasionally gave an abnormal beat. This was somewhat alarming but the mission objectives had been met and an emergency return would not have been any faster than letting the crew proceed as planned. After their return, further investigation showed that their bodies were lacking in potassium. It had been leached out of their systems by their profuse sweating and imbibing prior to the flight and this had upset their electrolyte balance. It was decided that future lunar module crews would compensate by taking fruit drinks laced with potassium.

On Apollo 16, John Young, who had adopted Florida as his home state, got a little tired of the quantity of potassium-laced orange juice he w as being expected to drink – and the flatulence it was causing. lie began to complain to Charlie Duke about it after their first moonwalk. However, as he spoke, an electronic fault meant that his voice was unexpectedly being transmitted to Earth.

“I have the farts, again,” he moaned. ”1 got them again, Charlie. I don’t know what the hell gives them to me. I think it’s acid stomach. I really do.”

“It probably is,” said Duke.

“I mean, I haven’t eaten this much citrus fruit in 20 years!” laughed Young. “And I’ll tell you one thing, in another 12 fucking days, I ain’t never eating any more. And if they offer to supplement me potassium with my breakfast, I’m going to throw up!” He continued, laughing: “I like an occasional orange. Really do. But I’ll be durned if I’m going to be buried in oranges.”

Apollo 17, like other flights, found that they tended not to eat very much during the coasting phases. The relative inactivity and the weightless environment reduced their calorie needs and their appetite. When mission control asked for an update on what they had eaten, it was partly to enable John Zieglschmid at the Surgeon console to check that the crew could maintain a proper balance of electrolytes in their system in the light of Apollo 15’s problems.

“And are you ready for the trotting gourmet’s report?” asked Jack Schmitt. “Roger,” replied Bob Parker. “Everybody’s here with all ears.”

“Okay,” started Schmitt. “The commander today had scrambled eggs and three bacon squares and a can of peaches and pineapple drink for breakfast. And then later on in the day he had peanut butter, jelly and bread with a chocolate bar and some dried apricots. The LMP had scrambled eggs and four bacon squares, an orange drink, and cocoa for breakfast, and potato soup, two peanut butter and jelly sandwiches, and a cherry bar and an orange drink.” Schmitt then went on to relate what Ron Evans, who had been making a TV broadcast earlier, had eaten. “And that hero of the matinee, the matinee idol of Spaceship America, had scrambled eggs, bacon squares, peaches, cinnamon toast, orange juice and cocoa for breakfast. That’s how he keeps his form. And, for lunch, he had a peanut butter sandwich and citrus beverage. And that’s it, since there’s nobody else up here.”

“Jack, we appreciate all your information,” said Parker, “and we’d like to just pass on some recommendations here from the ground that we’d like you to keep on with your regular menu as much as possible. And, if you do cut anything off, we’d like you to concentrate on eating the meats, the juices and the fruitcake, which are the most effective for maintaining your electrolyte balance.”

Eugene Cernan then piped up. “Okay, Bob. We understand what you’re saying, ft’s just a lot of food, that’s all.”

“Roger. We understand, Gene,” replied Parker. “Also, on that group of foods, peanut butter’s great for the electrolyte balance, also; so you’re doing okay.”

“I knew it was good for something,” said Cernan. “It couldn’t be that good without being good for something.”

Suit food

Imagine it. You spend two hours getting into a spacesuit, you go outside into the hardest vacuum possible for seven hours’ hard labour and you need another hour or so to get back out of the suit on your return. While your helmet is on, there is no way to get so much as a hand to your mouth, never mind taking a meal. This was the scenario faced by the J-mission crews, so to ease their inevitable hunger and to provide extra energy for the exertions of working outside, a bar of food was placed inside the neck ring of their suits. Then when the urge took them, they could crane their necks down and chew on it.

Additionally, they had about a litre of water stored in a bag attached to the neck ring of their suits. As he worked outside, a crew­man could slake his thirst by sipping through a short tube placed within reach of his mouth.

Apollo 14 used these first, but on Apollo 15,

Irwin’s tube failed, leaving him dehydrated after their first moonwalk. On his subsequent A suited Jim Irwin during training, outings he tried to compensate by drinking His drinking tube can be seen inside

more before and after their time outside. the neck ring. (NASA)

As Apollo w7as being planned, detailed studies were made of how: best to perform lunar orbit rendezvous – the technique that brought two spacecraft together around the Moon, one of which had come up from the surface. As this w as then considered to be difficult and dangerous, much effort was devoted to understanding and then

Пои not to crash into the Moon 229

optimising all the variables that affected the operation. Initially, it was assumed that when the LM lifted off the Moon it would rendezvous with a CSM in circular orbit at 148 kilometres. As planners continued to refine the trade-offs between operational concerns and vehicle capabilities, they came to the conclusion that the CSM should be in an orbit 1K.) kilometres above the Moon. This lower orbit was chosen to reflect the limited propellant budget of the LM’s ascent stage. Planners decided that it was acceptable to expect the ascent stage to get off the Moon within the resulting short launch windows.

This decision meant that every Moon-bound Apollo mission was targeted to make a pass around the far side with a minimum altitude of 110 kilometres. This point of closest approach was called pericynthion a term from celestial mechanics meaning the lowest point in a lunar orbit made by a craft arriving from another body (the highest point being apocynthion) The words are derived from Cynthia, an alternative name for the Greek Moon goddess Artemis. It was around pericynthion that the LOl burn was made. These two terms are rather unwieldy and refer to the particular case of an orbit achieved by a craft from outside the Moon’s vicinity. It is more common to use a shorter pair of terms, perihme and apohme. which arc more general in their use and mean more or less the same thing.

In April 1970. after Apollo 11 (the "G” mission) and Apollo 12 (the first of the “H” missions), the most dramatic and hazardous halt to the program occurred with the near-fatal loss of Apollo 13. But four months later, in August, NASA made one of its boldest decisions. In the face of that near disaster in space, dwindling public support, and a rapidly declining budget, it decided to skip the final "IF’ type mission, press on with upgrading the total ‘system” (hardware, software, science, and operations) and finish the program with three full-up ".)” missions to the most significant scientific sites on the Moon. This upgrade from "IF’ to ’T’ included, in particular, the lunar roving vehicle, which in turn greatly increased the exploration capability, especially to investigate several different geological areas miles away from the LM in different directions, significantly more scientific equipment and experiments, and importantly, a mobile TV camera to view and record the distant activities of the crew so that MCC (and the public) could participate in the exploration to an unprecedented degree. As a result, a single ".I” mission that used an LRV to investigate multiple geological areas at a particularly worthy landing site became almost equivalent to sending a series of “II" missions to individual sites. Consequently, the ".I” mission erews became very proficient in "planetary field

geology”.

Of the thirty original astronauts, none had any formal geology training NASA had to teach pilots how to be proficient planetary field geologists; adding science to engineering as a primary discipline. Again, the training was superb; and because of their previous spaceflight experienee, the mission commanders played a major role in planning the training for their crew. After many hours of practical and effective geology training (classroom, laboratory, and field), the results justified the process, because it can be argued that during the “F‘ missions the performance of the eight "pilot-geologists” (in orbit and on the surface) was equal to the performance of the only "geologist-pilot” who reached the lunar surface on Apollo 17. which was the final mission of the program.

But this commitment to the "F‘ missions was surely one of the most rewarding decisions of the Apollo programme. It would have been a lot easier, safer, and cheaper to have finished up with the final two "H” missions as scheduled, because if one of the final missions had failed then the programme would surely have been brought to an end and "Apollo’’ would have passed into history as a "failure’’. In this regard, the lunar roving vehicle was the final element in the overall configuration of a complete "system” for human planetary exploration. For the future of Apollo and for human planetary exploration in general, in August 1970 NASA management truly made the “right” decision!

But as time passes, hardware for lunar exploration will come and go; software will eomc and go; and astronauts, cosmonauts, and the staff who support them in training and in flight will come and go. Although the future will see more automation and robotics, the manner in which manned spaceships fly to the Moon (and return!), like wheels rolling the roads and ships "sailing” the seas, will be the same for most likely decades to come. This exceptional book describes "how” for those who contemplate, for those who plan, and for those who fly; and also for the historical record.

David R. Scott Commander, Apollo 15 Los Angeles, California January IS, 2011

1

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.”