Category How Apollo Flew to the Moon

The Apollo programme left behind an archive of data and over a third of a tonne of samples, which, to repeat the publicist’s mantra, really did keep scientists "busy for years” and they have formed the bedrock on which theories of planetary formation and evolution have been built. Prior to the space age, planetary science was in the doldrums, with only blurred photographic evidence to feed scientific curiosity. With Apollo’s scientific harvest, planetary science entered an age in which ground truth – actual rocks gathered in situ could inform new theories and help to sort the wheat from the chaff.

Our current understanding of how the Moon was formed first gained acceptance at a eonferenee in Hawaii in 1984. This idea, chiefly proposed by William Hartmann and Alistair Cameron, has yet to be toppled. It is a story of birth rising out of incomprehensible violence.

Our solar system formed about 4,600 million years ago out of a coalescing cloud of dust and gas known as the solar nebula. Most material ended up in the Sun, but some formed a disk out of which the planets gradually grew, or accreted – a process whereby gravity causes loose material in space to gradually gather into ever larger bodies. The light pressure and solar wind from the new star tended to push lighter substances out to the further reaches of the system while heavier substances tended to remain in the Sun’s vicinity. This created predominantly rocky planets near the Sun. gaseous giants further out, and frozen worlds beyond the point at which even gases become liquid or solid.

About 40 million years after the solar system’s birth, two nascent planets were orbiting the new Sun at similar distances and it was only a matter of time before they met. The larger body, our proto-Earth, received an off-centre impact by a body half its diameter in a tremendous cataclysm. The iron cores of the two worlds merged and a large amount of mantle material was ejected to form a giant cloud of debris around what was now Earth.

In a relatively short Lime, some accounts suggest within only a year, this ejected material had itself coalesced to form a new, smaller world – the Moon. As it did so, the huge energy of its fast accretion melted its outer layer to form an ocean of molten rock, or magma, that lasted long enough to fractionate – like a salad dressing that has been left in a cupboard for too long. As the lighter components rose to the Lop. they cooled and crystallised to form a solid crust. They were typically light-coloured and rich in aluminium. Below the crust, in the mantle, the rocks were heavier and richer in iron. The regions that were last to solidify gathered up those elements that had difficulty fitting into the crystal lattice, leading to them being described as KREEPy.

The solar system was still a mass of debris for the first 800 million years of its existence and large impacts were commonplace on all the planets. The Moon retains the scars of this bombardment in the form of large craters, often overlapping one another, all over its lighter-toned surface. During this time, it sustained a particularly large collision when an object gouged out the South Pole-Aitken Basin, a 2.500- kilometre depression on the Moon’s far side. About four billion years ago, the

impact of large objects seems to have peaked before tailing off suddenly. The dark patches wc now see on the Moon’s near side were mostly formed within huge circular basins that were formed by the largest of these impact events. Of particular interest to the lunar science community was the Imbrium Basin, which was dated to 3.91 billion years ago from Apollo samples. Scars from its formation can be traced across much of the near side and therefore its age provides an important benchmark for the relative ages of other superimposed features. As noted, the formation of this basin excavated rock from deep within the Moon that had KREEPy characteristics.

About half a billion years later, prodigious quantities of lava, rich in iron and magnesium, were erupted through the fractured crust. It filled the basins and other low-lying areas to form enormous smooth basalt plains to which we applied romantic names like Mare 1 ranquilliiatis, Mare Serenitatis and Oeeanus Proccllar – um. The last gasps of this activity probably died out ‘only’ about a billion years ago but its peak was around 3.3 billion years ago. Since then, little has changed on the Moon. The material from the bottom of the Apollo 15 deep core had lain undisturbed for 500 million years. Every few tens of millions of years, there is a very large impact that produces a spectacular fresh crater and sprays the landscape with a new layer of rubble and dust. Apart from that, the occasional large object and a slow but incessant barrage of hypervelocity grains of dust sandblasts the top layer of the surface. Across the eons, the topography becomes rounded off and the landscape is draped with a thickening blanket of ground-up rock, the lunar regolith.

This is the kind of profound knowledge produced by careful, focused exploration. As later generations of probes extended our reach into the depths of the solar system, their new data has elaborated on the story of planetary genesis gleaned by men who explored a new w orld in person and applied the power of human intelligence.

MISSION ACCOMPLISHED… NEARLY

With their exploration to the lunar surface finished, their rock samples stowed and the orbital science programme completed, it was time to return to the home planet. At this point, the Apollo spacecraft consisted of just the CSM, the LM ascent stage having been jettisoned and, in some cases, made to crash on the Moon for the benefit of the seismometers emplaced by the crews.

Return to Earth was achieved by the last major firing of the SPS engine. This burn had terrified managers for years, and amply fed the hunger of newspaper and television journalists for riveting speculation about doomed astronauts marooned in their cocoon of failed technology around a forbidding, desolate planet while waiting for a time when their own exhalations would begin to asphyxiate them even as they heroically struggled to repair their flawed ship. The terror and hyperbole was driven by the knowledge that, while a failure to enter lunar orbit would have resulted in a return to Earth, failure of the burn to leave lunar orbit would, by all analyses, have led to the deaths of the crew. As no fail-safe system existed, the SPS had to be totally reliable.

A FIERY RETURN

Arguably the most audacious feature of an Apollo flight was to have the crew re­enter Earth’s atmosphere in the manner that they did. In the final minutes of a mission, a lump of metal and plastic, three crewmen and a few dozen kilograms of moonrock, altogether weighing nearly six tonnes, came barrelling in from outer space at speeds approaching 11 kilometres per second as Earth’s gravity hauled them in. As it entered, the air in front of the blunt end of the command module was brutally compressed in a shock wave that generated temperatures approaching 3,000°C. All that stood in the way of the crew being incinerated by this extraordinary heat was a coating of resin and fibreglass that NASA’s engineers reckoned could withstand the punishment.

In truth, the heatshield that surrounded the Apollo command module was very conservatively engineered for two main reasons. When the spacecraft’s design was frozen, engineers still had a poor knowledge of how the superheated air of re-entry would flow around the upper walls of the spacecraft. Although this surface did not bear the brunt of the heat, they decided to cover almost all of the hull with the heatshield material. Additionally, the original specifications had required that the shield should tolerate a much longer passage through the atmosphere, 6,500 kilometres, than ever proved necessary. The command modules that returned from the Moon typically flew for only about 2,200 kilometres through the atmosphere, which nearly halved the overall amount of heat the shield had to endure. In practice, although the heatshield took a lot of punishment across its curved aft section, much of its conical surface was barely singed by re-entry. Even the reflective Kapton tape that had been glued to the spacecraft’s exterior for thermal control in space was usually found to be still adhering to much of the hull. On recovery, pieces of Kapton were occasionally peeled off by those in attendance and kept as souvenirs.

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

DOI 10.1007/978-1-4419-7179-1 15. © Springer Science+Business Media. LLC 2011

"Well. men. wc’rc getting close." said Frank Borman as Apollo 8 neared the planet to make the programme’s first lunar return.

“There’s no turning back now’." added Bill Anders.

Jim Lovell continued their obsession of stating the obvious. “Old mother Earth has us," he said.

As they waited for the first stage of the re-entry, the computer moved onto P63. This program wns purely to initialise the upcoming sequence and start calculating the re-entry parameters. It maintained their attitude and w’aited for the accelerometers to sense 0.05 g. The crew had little to do but to look out of their windows, which wnre facing backwards along the flight path, affording a view’ of the Moon setting behind Earth’s bulk at a precisely known Lime. On Apollo 12. Pete Conrad became almost lyrical about the scene as Yankee Clipper coasted over the Western Pacific.

“Hey, there’s the horizon. Hot damn. Hello, w’orld! I ley, you’re going to get Moonset right on the schnocker!"

“Yes," agreed Gordon.

“It’s coming pretty fast,” enthused Conrad. "We is flat smoking the biscuit. God damn! We’re going! Whooce!”

"’We’re going 35,000 feet per second,” said Gordon, keeping an eye on the DSKY as they edged towards 11 kilometres per second.

“Were hauling ass is right,” said Bean. ”Goi some high clouds and some low clouds down there. Got a lot of ocean.”

‘"You’re going to have Moonsct pretty quick,” said Conrad. Right on lime, the Moon seemed to descend into the murk of Earth’s atmosphere.

“Hey, that’s something else. Look at that. I wish I had a picture of that.”

""Where is it?” asked Bean.

"‘Right out the centre hatch," said Conrad. Since he was occupying the centre couch, it was the hatch window that gave him his view outside.

"’Hey, Al. turn your camera on,” called Gordon, knowing that Bean had the movie camera set up in the window7. “Maybe you can get a picture of it for a couple of seconds.”

"’The camera’s going this way. and that’s up that way,” replied Bean. It was not in the field on view.

"’Too far away, huh?” said Gordon.

After the flight, Conrad spoke of the impression the view7 left on him. “Moonset really w-as spectacular. It’s too bad we didn’t have a camera to photograph that. It was a full Moon; and it was exactly aligned in the yaw plane behind us. Just wntching that thing settle behind a beautiful, lit daylight horizon, with clouds above the Pacific, was phenomenal.”

The Apollo 15 crew7 were so engaged with the view of the blue planet speeding by that they missed Moonset.

"’Oh, man. are w’e moving, too!” said Al Worden. "Son of a gun! Sheeoo!”

""Yes, indeedy,” said David Scott, who had made an Apollo re-entry before, albeit from a slower speed in Earth orbit. "You ought to be able to see it out the hatch window.”

""Oh my. I sure can,” said Worden. "‘Sure a lot of mountains down there. How about that!”

“Shit. I think that’s Alaska out there. That would be right, wouldn’t it?” said Irwin.

“Yes,” said Worden. "Keep an eye out for the Moon.”

""Yes, keep an eye out for the Moon.” agreed Scott.

"’We’ve done it. Oh. we’ve missed it." said Worden. ‘"We were too busy watching the Earth.”

"T’m not sure there’s much you could do about it to correct it anyway,” said Scott. Indeed there was nothing since the CM possessed no propulsion.

Being an arbitrary construct, entry interface passed with little more than a mention from the public affairs announcer. Of greater importance to the crew7 was when P63 sensed 0.05 g. about 30 seconds later, at w’hich point it triggered the EMS to begin monitoring their entry. Its scroll began moving to the left as their velocity decreased, and its range, velocity display showed either how7 far across the ground they had still to fly or how7 much velocity they still had to lose. Simultaneously, the computer was automatically advanced to P64 to fly the initial part of the re-entry flight path. There was no fixed altitude at which 0.05 g occurred, because it depended completely on their velocity, now 11 kilometres per second, the shape of the spacecraft and the local atmospheric conditions.

In the Christmas season of 1968, with a little over two hours to go before they entered lunar orbit, the CMP of Apollo 8, Jim Lovell, pointed out that despite their pioneering journey, something was missing.

“As a matter of interest, we have as yet to see the Moon.”

“Roger,” came the reply from Capcom Gerry Carr. He pondered this point for a few moments then sought a degree of elaboration.

“Apollo 8. Houston. What else are you seeing?"’

The acerbic reply from LMP Bill Anders shed new light on the truth of the astronauts’ great adventure.

“Nothing. It’s like being on the inside of a submarine.”

“Roger."’ was all Carr could say, for Anders’s comment was so true.

Despite being nearer to the Moon than any human in history, and with the exception of some sightings that Lovell had made through the spacecraft’s optics, this crew had yet to view their quarry. This was partly because their three large windows had fogged up owing to a design problem with the sealant around them. Additionally, they had spent most of their time during the coast broadside to the Sun. twirling slowly in the barbecue mode. In this attitude their two good windows, which looked along the direction the craft was pointed, viewed only deep space.

As with many of the Moon-shots, Apollo 8 arrived over the western side of the lunar disk at the same time as the Sun was rising over the eastern side. The nearer they got to the Moon, the closer it came into line with the Sun until, in the final few hours before arrival, the spacecraft entered the Moon’s shadow’ and plunged the crew into darkness. Apollo 10 arrived at the Moon under similar lighting conditions and its commander Tom Stafford still gained no view’ of the approaching planet.

“fust tried looking out as far as 1 can. out the top hatch window-, and still can’t see the Moon; but we’ll take your word that it’s there.’’ By ‘top hatch’. Stafford meant the round window in the side hatch, though as they lay in their couches, it was above their heads.

“Roger. 10. That’s guaranteed; it’s there,” said Charlie Duke in mission control. Stafford’s LMP Lugcnc Ccrnan couldn’t catch a glimpse of it cither, but the next time he journeyed to the Moon as the commander of Apollo 17, he got an eyeful.

“Boy. is it big! We’re coming right down on lop of it!” he shouted. “I’ll tell you, when you get out here, it’s a big mamou.”

Cernan was one of the few’ Apollo astronauts who had a natural ability to convey to the lay person some of the emotion and depth of the Moon-flight experience. Although he had been there before, the approach of this serene orb stunned him. and in his memoirs he expanded on this first glimpse.

“Looking at the Moon from our vantage point w’as quite unlike seeing it from Earth, w’hen it is so distant. Now’ it was gigantic, a world of its ow’n. and it forced me to question what I was really seeing. Such scenes existed only in science fiction, for not even the simulators could impart the reality of such a moment. We plummeted tow’ards it, faster and faster, and the closer w’e got. the bigger it grew-.’’

Cernan w’as also struck at how this extraordinary initial scene even managed to mute his LMP. geologist/astronaut and incessant talker. Jack Schmitt.

“Dr Rock was also stunned by the sheer size of the planetoid lhai he had spent a lifetime studying. Never in his wildest dreams had Jack imagined such a sight, and he momentarily lost his ability to even speak. The Sun illuminated the high peaks and mountains, and the rims of giant craters and surface details emerged, bathed in gold or hidden in deep shadow-.”

Apollo 11 was the first flight to afford an approaching crew a view of the Moon.

They did not require a final mid-course correction, and this gave them the time and opportunity to turn the spacecraft around and for the first time see the Sun-blasted world they were about to explore loom in front of them. Mike Collins wrote about the shock he felt at what he saw.

“The change in its appearance is dramatic, spectacular and electrifying. The Moon I have known all my life, that two-dimensional, small yellow disk in the sky, has gone away somewhere, to be replaced by the most awesome sphere I have ever seen.”

This astronaut, one of the more poetic among the Apollo crewmen, had managed to glimpse the Moon at an opportune moment, just as they were about to enter its shadow. They then flew over an eerie landscape: the near side was dimly illuminated by Earthshine and a part of the far side which, owing to their vantage point was visible to them as a crescent, was as black as could be.

“To add to the dramatic effect, we find we can see the stars again. We are in the shadow of the Moon now. in darkness for the first time in three days, and the elusive stars have reappeared as if called especially for this occasion. The 360-degree disk of the Moon, brilliantly illuminated around its rim by the hidden rays of the Sun, divides itself into two distinct central regions. One is nearly black, while the other basks in tt whitish light reflected from the surface of the Earth/’

Collins was struck by the interplay of the three lighting effects on the Moon; the Sun’s corona, the dim light from Earth and the deep black of the star-peppered sky, combining to gently illuminate the lunar surface below’ with a bluish light.

“This cool, magnificent sphere hangs there ominously/’ he wrote in his autobiography, “a formidable presence without sound or motion, issuing us no invitation to invade its domain. Neil sums it up: ‘It’s a view’ worth the price of the trip.’ And somewhat scary too. although no one says that.’’

The next stage of the LM checks required the crew to think about the concept of the dead band, which is another of those curious terms in spaceflight where a simple concept lay behind opaque jargon.

Apollo was one of the first applications of a digital Пу-by-wirc system whereby control of a vehicle was placed in the hands of a computer. In the Apollo guidance computer, programmers included a scries of algorithms that would fire the RCS jets as necessary to bring the spacecraft to a desired attitude with respect to the IMU platform, and hold it there. These algorithms were called the digital autopilot (DAP). However, the gimbals around the platform were able to measure angular errors in the spacecraft’s attitude to an accuracy of hundredths of a degree, and to have constantly corrected the slightest drift to such a Light tolerance would have made the spacecraft seesaw backwards and forwards as the jets incessantly fought to maintain the ideal attitude, wasting propellant in the process. Instead, a range of attitude error around the ideal was deemed acceptable and the thrusters did not fire within this band; they were said to be ’dead’. This error band, the dead band, could be set to be cither a half or five degrees from ideal, depending on how accurately the spacecraft had to be pointed. A narrow er dead band used more RCS fuel, because the thrusters tended to fire more often when the spacecraft drifted beyond the permissible deviation.

While still docked, the commander gave the LM’s RCS system a checkout, first by using the computer to Lest that the hand controls were producing the commands expected of them, the so-called ‘cold-fire’ checks; and then by firing all 16 thrusters for short periods in a ‘hot-fire’ test. Prior to carrying out these tests, he had to ensure that his crcwmatc in the command module had the CSM’s digital autopilot set for a wide, five-degree dead band. That is, although overall the thruster firings – fore aft, left/right. etc. should be neutral, they would briefly rotate the entire CSM/LM stack by a few degrees, and it would have been a waste of propellant if the thrusters on the service module had to battle to restore attitude.

The commander also ensured that telemetry from the LM was being sent to mission control at a high bit rate. This maximised the number of engineering parameters that could be received while the health of the RCS was checked.

Almost like a third eye on the forehead of the LM’s face, another dish sprouted from the ungainly LM cabin, preferring a direction that faced forward. This was the antenna for the rendezvous radar, one of the subsystems that allowed the ascent stage to seek, find and follow the CSM as it chased the mothership around the Moon during the rendezvous. The radar operated in conjunction with a transponder on board the CSM so that the LM’s computer could tell how far apart they w ere, and in which direction. As the commander put it through a self-test routine, the final steps towards undocking were completed.

Breaking the link

Perhaps il was a bitter sweet moment for the command module pilot as he watched his crewmates leave for the Moon. There would probably be some relief that the mission had reached this point, and increasingly looked like it was going to be successful. At the same time, there might have been a deep longing for an opportunity to take a ride to the surface knowing that there were only a few kilometres between him and a moonwalk. But for all the CMPs, there was terror in the knowledge that it required only one or two of many possible failures to occur, and he might have to light his SPS engine and return to Earth alone, as a marked man, having left his crewmates on the Moon.

Alan Bean found Dick Gordon’s reaction to sending his crewmates away on Apollo 12 remarkably sanguine. Gordon and Conrad had flown together on Gemini 11, although their friendship went back to Patuxent River Naval Air Station where they were both test pilots and good buddies. Although Gordon’s friendship with the likeable and super-competent Conrad had helped to seal his place on Gemini, the experience subsequently gained prevented him from taking a ride to the Moon’s surface. Deke Slayton, who decided Apollo’s crewing arrangements, generally gave command to the most experienced in a crew, and that was Conrad. At the Lime, he preferred the astronaut in charge of the command module Lo have had experience of rendezvous in ease the CSM had to rescue an ailing LM. Thus Gordon got to fly the CSM solo. That left Bean, the rookie and the third member of this friendly crew-, with a ride to the moondust. Twenty-three years later. Bean completed a painting that imagined Gordon being down on the surface with his two buddies. In his notes on that work, Bean stated. "Dick was the more experienced astronaut, yet I got the prize assignment. In the three years of training preceding our mission, he never once said. Tt’s not fair, I wish I could w? alk on the Moon too.’ 1 do not have his unwavering discipline or strength of character.”

Having just dealt with a shorted abort switch. Apollo 14 ran into more technical problems when they reached a point where they expected the landing radar to begin feeding data to the computer. Typically, crews expected the all-important radar to be working by 10,000 metres altitude, but as Aniares passed this point, the computer was still receiving no radar data from the antenna.

“Come on radar,’’ implored Ld Mitchell, the LMP, but the two lights on the DSKY stayed stubbornly illuminated. “Come on radar!”

A minute passed and Fred Haise in Houston informed them of when they could expect P63 to begin throttling the engine. "Okay, 6 plus 40 is throttle down, Aniares.”

“Roger. Houston,’’ said Mitchell. “We still have altitude and velocity lights.’’

By 7.000 metres, there was still no valid data coming from the landing radar and the two crewmen frantically tried to make it work, knowing that if they still had no success by 3.000 metres, they were bound to abort the mission, separate the ascent stage, and return to the CSM.

“Antares, Houston,” said Haise. “We’d like you to cycle the landing radar breaker.”

Mitchell pulled one of the little aviation-type circuit breakers to remove power from the radar, then pushed it in again. Quite often in electronics, a power-down, power-up cycle is all that is required to clear an abnormal operating condition and the earlier manual patch to the computer to deal with the abort switch short had created such a state. “Okay.” said Shepard. “Been cycled.”

“Come on in!” Mitchell urged, then. ’’Okay!” as the lights went out and the radar began to function normally at only 5,500 metres. “How’s it look, Houston?” called Shepard.

Shepard, at 47, was the oldest of the Moon-bound crews and the only Mercury astronaut to go to the Moon. Many have wondered whether he would have attempted a landing without the radar. Most believe that if he had tried, the narrow’ margins of propellant w ould have obliged him to abort further down.

In contrast to Apollo 14‘s late acquisition of radar data, Young and Duke got a pleasant surprise when Orton s landing radar began to deliver data much earlier than expected on Apollo 16. Compared to the other landing flights, Orion’s descent began at a much higher altitude over 20.000 metres, probably due to some over­compensation made for the influence of the mascons on Apollo 1 5. They were then surprised when their landing radar started to work while they were still 15,000 metres or 50,000 feet up. w’hich was 50 per cent higher than expected.

“Look at that!” exclaimed Young. “Altitude and velocity lights are out at 50k!“

“Isn’t that amazing," agreed Duke.

“Look at that data, Houston,” said Young. "When do you want to accept it?”

“Okay, you have a Go to accept.” said Jim Irwin once the flight controllers had passed on their agreement.

”Okay,” replied Duke. "It’s in.”

"Tm at the foot of the ladder.” Neil Armstrong brought a quiet coolness to the moments before he took humankind’s first step on the Moon. "The LM footpads are only depressed in the surface about one or two inches, although the surface appears to be very, very fine grained, as you get close to it. It’s almost like a powder. [The] ground mass is very fine.”

Armstrong was not telling science anything it did not already know. Previous unmanned probes and objective theorising by lunar geologists had established that the lunar surface would be finely powdered, beat up from an incessant rain of objects over extremely long time periods. But, first and foremost, Armstrong was an engineer and test pilot and one of the best in the business. What test pilots do is observe and describe in physical terms, and that was exactly what he was going to bring to this endeavour.

“I’m going to step off the LM now.”

With his right hand holding onto the ladder. Armstrong placed his left foot onto the dust of Marc Tranquillitatis. "That’s one small step for [a] man; one giant leap for mankind.’’

With the moment appropriately marked, Armstrong continued onto the surface and tentatively began to adapt to moving around in the weak gravity field. He also returned to his descriptive roots. "Yes. the surface is fine and powdery. I can kick it up loosely with my toe. It does adhere in fine layers, like powdered charcoal, to the sole and sides of my boots.”

In the years leading up to this moment, one scientist had attracted the attention of the press, ever hungry for a story, by suggesting that the LM or an astronaut would be swallowed up by a great depth of dust which, he theorised, would have taken on a Tairy-castlc’ structure. Thomas Gold’s theory was based on interpretations of radar observations which showed that the surface consisted of very loose material, which is indeed an accurate description of the Lop few millimetres. However. Gold took this observation and wove it into a tale of great seas filled with electrostatically supported dust. In fact, the large size of the LM footpads is attributed to his influence. Gold continued to provide reporters with a yarn of possible catastrophe even after unmanned Surveyor landing craft had successfully touched down using footpads designed to impart the same pressure as the LM pads. These spacecraft also returned images of boulders resting on the surface and orbiting spacecraft had imaged great swathes of ejected blocks from large craters that had clearly not sunk into the dust. But of this period, geologist Don Wilhelms wrote, "One would think that the presence of all this dust-free blocky material would have weakened the Gold-dust theory, but no amount of data can shake a theoretician deeply committed to his ideas.”

Armstrong was demolishing such worries once and for all. "I only go in a small fraction of an inch, maybe an eighth of an inch, but I can see the footprints of my boots and the treads in the fine, sandy particles."

Always aware that a problem could cause the EVA to be terminated at any Lime, Armstrong’s initial moments on the surface were carefully planned. He had a short moment to ensure he would have no difficulty moving around, then he and Aldrin used a looped strap to send a Hasselblad camera down from the cabin. The hmar equipment conveyor (LEC) was NASA’s reply to a fear that it might be difficult and time-consuming to carry items up and down the ladder, particularly boxes of rock samples. The LEC w-as discarded after Apollo 12 as crews came to better understand the ease with which heavy loads could be handled on the Moon. With the camera attached to a bracket on his chest mounted RCU. Armstrong proceeded to take a series of overlapping pictures that could later be merged into a panoramic view of the landing gear. Then, after a reminder from Bruce McCandless in Houston, he used a scoop to gather a contingency sample of the soil near Eagle.

"Looks like it’s a little difficult to dig through the initial crust,” noted Aldrin from Eagle’s cabin.

"This is very interesting,” said Armstrong. "It’s a very soft surface, but here and there where I plug with the contingency sample collector, I run into a very hard surface. But it appears to be a very cohesive material of the same sort.” Armstrong

had discovered what is, to people used to Earth, an odd property of the soil. This part of Mare Tranquillitatis had seen essentially no volcanic activity for well in excess of three billion years. The only large scale processing of the rock had been by countless impacts, and the vast majority of these were small. Each had helped to pulverise the surface into a layer of dust and boulders about five metres thick called the regolith and each had served to shake the subsoil until it became extremely well compacted yet unconsolidated material. So while the top few centimetres were loose, the subsurface seemed hard and unyielding.

It was then Aldrin’s opportunity to climb down the ladder as Armstrong photographed him. “Now I want to back up and partially close the hatch, making sure not to lock it on my way out.”

“A particularly good thought,” laughed Armstrong.

“That’s our home for the next couple of hours and we want to take good care of it.” The checklist had called for the hatch to be partially closed, probably to prevent the shaded interior radiating its heat into space.

Ever the test pilot, Aldrin continued to narrate his descent of the ladder. “It’s a very simple matter to hop down from one step to the next.”

“Yes. I found I could be very comfortable, and walking is also very comfortable. You’ve got three more steps and then a long one.”

Aldrin practised leaping between the ladder and the footpad, then, before he stepped onto the surface, he turned to take in the landscape.

“Beautiful view!”

‘‘Isn’t that something!” said Armstrong. “Magnificent sight out here.”

“Magnificent desolation.”

Snow on the Moon

As A1 Bean waited to follow’ Pete Conrad out of Intrepid’s cabin, he moved to his window to adjust a movie camera that would record their work on the surface. Just after Conrad had taken a contingency sample of lunar soil, both men heard a warning in their headsets.

“Uh-oh, did I hear a tone?” said Conrad as he tested his mobility on the surface.

“Yeah; I’ve got an H20 A,” said Bean.

“You do?”

“Yeah. I wonder why?”

The ‘A’ flag and tone was telling Bean that his cooling system wras failing. For a few’ minutes he tried to troubleshoot the balky PLSS as Conrad got started on tasks around the LM.

“Okay. I think I know what happened. Houston.” said Bean as he spotted the cause. After the flight, he explained the circumstances: "1 happened to glance down and noticed the door was closed. I realised what had happened. The outgassing of my sublimator had closed the door, with the result that I didn’t have a good vacuum inside the cabin anymore. I quickly dove to the floor and threw back the hatch. The minute I did. a lot of ice and snow went out the hatch.”

“What did you just do, Al?” asked Conrad when he saw’ resultant display.

“Man, I just figured it out.”

“You sure did. You just blew water out the front of the cabin.” Then correcting himself, “Ice crystals.”

“That’s what had happened to the PLSS. The door had swung shut, […] and probably bothered the sublimator. ‘cause it wasn’t in a good vacuum anymore. So 1 opened the door and it’s probably going to start working in a minute.”

“I should hope so. laughed Conrad. "When you opened the door, that thing shot iceballs straight out the hatch.”

The first time David Scott opened Falcon s forward hatch, he treated Jitn Irwin to a similar display of ice particles visible out of his window. “It’s blowing ice crystals out the front hatch,” laughed Irwin. “It’s really beautiful. You should see the trajectory on them.”

“I bet they’re Паї, aren’t they, Jim?” asked Capeom Joe Allen. “The trajectories?” Allen wras a scientist by training and as soon as he heard about the flying crystals, he immediately began to think about how they would move.

“Very flat. Joe,” answered Irwin to Allen’s query.

For the first traverse with a rover on the Moon, Scott and Irwin headed southwest towards a spot where Hadley Rille took a sharp turn below the flank of Mount Hadley Delta. "Well, I can see I’m going to have to keep my eye on the road,” commented Scott as he negotiated the undulating terrain of the plain. "Boy, it’s really rolling hills, Joe. Just like [Apollo] 14. Up and down we go.”

The chaotic nature of the landscape kept him busy as he worked the rear-wheel steering to avoid fresh, steep-walled craters and occasional rocks large enough to be hazards.

"We’re going to have to do some fancy manoeuvring here,” remarked Scott. "Okay, Joe, the rover handles quite well. We’re moving at an average of about eight kilometres an hour. It’s got very low damping compared to the one-g rover, but the stability is about the same. It negotiates small craters quite well, although there’s a lot of roll. It feels like we need the seat belts, doesn’t it, Jim?”

“Yeah, really do,” agreed his LMP.

“The steering is quite responsive even with only the rear steering,” continued Scott. “I can manoeuvre pretty well with the thing. If I need to make a turn sharply, why, it responds quite well. There’s no accumulation of dirt in the wire wheels.”

“Just like in the owner’s manual, Dave,” said Allen.

The speed that Scott could maintain was typical for the rover and though it may not appear to be very fast, the combination of the heavily cratered surface and the light lunar gravity made the vehicle pitch and roll enough to take the wheels off the ground. “Man, this is really a rocking-rolling ride, isn’t it?” laughed Scott.

Irwin concurred. “Never been on a ride like this before.”

“Boy, oh, boy! I’m glad they’ve got this great suspension system on this thing.”

Young and Duke’s first traverse took them west for a short distance away from the LM. “Man, this is the only way to go, riding this rover,” said Duke.

But a disadvantage of driving west was that the Sun was behind them and so there were few shadows in front of Young to help him judge the terrain ahead. Essentially, all objects directly ahead were hiding their own shadows. Worse, at the point directly opposite the Sun, the so-called zero-phase point, the backscattered reflection from the tiny crystals in the regolith became particularly bright to the point of being dazzling. It limited their speed as Young fought to discern the obstacles ahead in the glare.

“Driving down-Sun in zero phase is murder,” moaned Young. “It’s really bad.” He elaborated further during his post-flight debrief. “Man, I’ll tell you, that is really

grim. I was scared to go more than four or five kilometres an hour. Going out there, looking dead ahead. I couldn’t see the craters. I could see the blocks alright and avoid them. But I couldn’t see craters. I couldn’t see benches. I was scared to go more than four or five clicks. Maybe some times I got up to six or seven, but I ran through a couple of craters because I flat missed [seeing] them until I was on top of them.”

The speed record for driving a rover probably goes to Gene Cernan on his second lunar EVA when he and Schmitt were driving down a scarp that crossed their valley floor. On the Moon, slopes tend to be smoother than level ground because the gradient tends to make particles move preferentially downhill with every micrometeoroid hit and the constant downslope movement smooths out the features. "What was it. 17’A or 18 clicks we hit coming down the Scarp. Jack?" claimed Cernan nonchalantly. Schmitt merely laughed at the suggestion.

Л record that Apollo 17 s rover can claim is to have taken its crew furthest from the LM. On EVA 2’s outbound leg. Cernan drove 9.1 kilometres to a site at the foot of the South Massif, fully 7.4 kilometres distant from Challenger, its safety and a ticket home to Earth.

John Young took his rover to its own record – the highest point up a hillside reached by any crew at 170 metres. The rover’s easy glide up Stone Mountain was in stark contrast to the labour-intensive struggle Shepard and Mitchell had climbing 85 metres up a much shallower slope in an effort to reach Cone Crater. At the Cincos craters. Young came to a stop and looked around to see the view. Duke was the first to speak up and tell Tony England about it. "Tony, you can’t believe it, this view looking back. We can see the old lunar module! Look at that, John.” But Young was too busy getting the rover parked in a position where it would not begin to slide back downhill. He had the experience of Apollo 15 to draw from.

On their second traverse. Scott and Irw’in had taken their rover onto the lower slopes of Mount Hadley Delta. Among their goals, they wanted to find anorthosite, a white crystalline rock that geologists believed would be a sample of the Moon’s primordial crust. The mountain was thought to be a block of that crust and the hope was that by driving a short distance up the hill, they would find a sample that had been dislodged from further up. Scott generally tried to park inside the lower rim of a crater as this tended to be a relatively level spot on the otherwise sloping ground. However, at one point, he was attracted to a boulder in which Irwin had spotted a hint of green in its dusty surface. On giving up on one parking spot above the boulder because the slope was too steep, Scott found that as he went to dismount at a spot below the boulder, he could feel the vehicle slide. In fact, the rover was sitting with one of its wheels off the ground. To keep it in place, he had to ask Irwin to stand below it and hold onto it while he investigated and sampled the green boulder.

Getting off the Moon and returning to the relative safety of the command module was a feat that literally defined the mission plan. NASA even named it lunar orbit rendezvous (LOR) in view of the important benefits the technique promised in overall weight savings, including that of the launch vehicle. Yet, to many in NASA in the early 1960s, it seemed suicidal for one tiny spacecraft to launch and attempt to pull up alongside another tiny spacecraft, each whizzing along at some 5,800 kilometres per hour, around another world nearly half a million kilometres away. At that time, no one had even attempted rendezvous in the relative safety of Earth orbit in spacecraft that could at least return to the ground if things went awry. Space navigation techniques were rudimentry at best. There were no GPS satellites around Earth and even spaceborne radar techniques were merely theoretical. It was a measure of the managers’ faith in their engineers and scientists that they felt confident to march ahead with an apparently hare-brained scheme which, if it were to go wrong, would doom two men to certain death in lunar orbit.

Once LOR had been chosen as the preferred mission mode, NASA needed to practise the techniques of rendezvous around Earth. Through 1965 and 1966, the ten missions of the Gemini programme turned rendezvous from a frightening unknown manoeuvre into a routine operation. Appropriate procedures were learned through successive flights beginning with simple tasks:

• Could the manoeuvrable Gemini spacecraft station-keep with its spent upper rocket stage?

• Could two independently launched spacecraft rendezvous and station-keep?

• Could a spacecraft rendezvous and then dock with an unmanned target?

• Could it achieve the same feat within a single orbit?

All these lessons built NASA’s confidence in its procedures, and were directly applicable to Apollo’s need to rendezvous and dock around the Moon. The Gemini programme is often overlooked by writers eager to tell the story of how NASA prepared to venture to the Moon. But without it, Apollo could never have succeeded within President Kennedy’s deadline. Years later, David Scott, Gemini 8 pilot and veteran of Apollos 9 and 15, reflected: "You go away back, it was a big mystery

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

DOI 10.1007/978-1-4419-7179-1 13. © Springer Science+Business Media. LLC 2011
doing a rendezvous. Magic mysterious stuff! Now it’s just straight off – choof, bang.”