Category How Apollo Flew to the Moon

THE SECOND ARRIV AL BURN

Having established the spacecraft in its initial trajectory around the Moon. FIDO in mission control could begin working on his next move: a short burn by the SPS that would be carried out about four hours later, after two complete orbits, in order to get the Apollo stack into its operational orbit. This burn would be very carefully monitored to ensure that it had exactly the required effect.

The details of this burn depended on the flight in question. For Apollos 8 to 12. a relatively short burn, known as LOI-2, brought the apolune down from 300 kilometres to 110 kilometres and made the orbit circular. Apollo 8. without the mass of a lunar module, required only a 9-second burn to achieve this. On the next three flights, the extra 16 tonnes or more of the LM meant that their burns had to be somewhat longer. On Apollo 10 the lunar module lacked a full propellant load and the LOI-2 burn was 14 seconds, but the full LM tanks on the next two flights extended the burn to 17 seconds. On these early flights, the CSM never left its 110- kilometre circular orbit, and come landing day, the LM would have to do all the work of manoeuvring down to the surface. The first part of this would be the descent orbit insertion (DOI) burn to place the LM in an orbit with a low point of only 15.000 metres. This was the descent orbit, so called because this perilune was the point from which the LM would begin its final descent to the surface.

After Apollo 12 the strategy changed. Planners were keen to increase the capability of the Apollo system, and analysis had shown that the LM’s payload capacity to the lunar surface would be maximised by having the CSM make the DOI burn to take the LM into the descent orbit, thereby saving its propellant for the Final descent. Later, once the LM was released and inspected, the CSM would make another burn to circularise its orbit at 110 kilometres to undertake a programme of lunar reconnaissance while the LM was on the surface. This also placed the CSM in a suitable orbit for the rendezvous when the LM returned.

Owing to its unforeseen circumstances, Apollo 13 never got as far as carrying out this burn. On Apollo 14, which was first to perform this manoeuvre, the burn Look 21 seconds, which was four seconds longer than Apollo 12’s LOI-2 burn, reflecting the fact that, in this case, the near-side altitude was being dropped all the way down to 17 kilometres. As the mass of the stack increased for the final three J-missions. the duration of the DOI burn stretched to 24 seconds.

“Going to two,” replied Armstrong. "Coming up on eight minutes.’’ “HEY, THERE IT IS!": PITCIIOVER AND P64

After about nine minutes, when P63 had delivered the LM to high gate, typically only 2,200 metres up and 7.5 kilometres from landing, control was passed to Program 64, whose role it was to guide the LM through the approach phase to a point just above the landing site. Many aspects of the descent changed at this point. In particular. P64 did not continue the effort by P63 to reach a point below the surface. Prior to high gate, the crew’s windows had been facing into space, so one of P64’s first actions was to give the crew a chance to see where it was taking them. It fired the RCS thrusters to pitch the spacecraft forward sufficiently to enable the crew to view the horizon ahead – a manoeuvre called pilchover. This change in attitude with respect to the ground meant that the antenna for the landing radar had to rotate to its second position so as to continue to face roughly downwards. Meanwhile, P64 continually rode the engine’s throttle setting to aim for a point 30 metres above and five metres short of where it thought the final landing site was located.

As Pete Conrad waited for P64 to begin, he strained at his window to look for a familiar pattern of craters towards which he had trained to fly. Careful correlation of photographs taken two years earlier by a Lunar Orbiter mission with surface pictures taken by the Surveyor 3 unmanned spacecraft had shown that it had landed within a 200-metrc-diameLer crater that formed the torso of a distinctive pattern of five craters known as the Snowman. Planners had decided that this would make a good target to prove the pinpoint landing capabilities of the Apollo system.

“Standing by for P64.” he told Л1 Bean standing beside him. “I’m trying to cheat and look out there. I think 1 see my crater.” He was the shortest of the astronauts, and was straining against the harness restraint to see the lunar surface in the bottom corner of his triangular window. He had not yet seen his crater.

“Coming through 7,” said Bean as they passed 7,000 feet or 2,150 metres. “P64 Pete.”

“P64,” confirmed Conrad.

“Pitching over,” said Bean as the LM began to tip forward.

“That’s it; there’s LPD,” said Conrad as he brought up the angle display of the landing point designator.

AI. SEP

All subsequent Apollo landings included time to deploy a full ALSEP, each consisting of a varying set of instruments cabled to a central station, all of it powered by a radioisotope thermoelectric generator (RTG). This was an early example of the type of power supply that would energise a generation of probes to the outer planets.

The Apollo RTGs used the radioactive decay of plutonium-238 to generate heat which was directly converted to electricity by an array of thermocouples. The presence of plutonium on the spacecraft had certain repercussions. It could not travel to the Moon in the RTG for fear of contamination if there were to be an accident near Barth. Instead, it was packaged into a fuel element or capsule which was transported to the Moon inside a graphite cask mounted vertically on the outside of the descent stage where it could radiate its heat. This cask was strong enough to withstand re-entry through Barth’s atmosphere and, thanks to this ability, the Apollo 13 plutonium now lies at the bottom of the Tonga trench in the Pacific Ocean.

Once on the Moon, it was the LMP’s task to remove the plutonium fuel capsule from its cask and insert it into the body of the generator. Alan Bean w as the first to try this and ran into problems when reality failed to match any Barth-bound trials. First he hinged the cask down to gain access to the removable dome at one end. then he removed it with a special tool.

’’There you go,” said Pete Conrad encouragingly.

”It came off beautifully.” said Bean. ‘ [I’ll] put the tool and the dome aside.”

This had started well. Next he had to engage the capsule removal tool. “Go ahead,” said Conrad.

“There you go.” commented Bean. “Sliding right in there. Okay. [I’ll] tighten up the lock.”

With the tool firmly engaged, Bean pulled on the capsule, only to discover that it wasn’t going anywhere. “You got to be kidding,” he exclaimed.

“Make sure it’s screwed all the way down,’’ suggested Conrad.

Bean was caught between wanting to give it a good yank but not wanting to break the mechanism that attached the tool to the capsule. Gear that w? ent to the Moon was built as light as possible. There wouldn’t be much strength in reserve.

“Thai could make a guy mad. you know it?” moaned Bean.

“Yup,” replied his commander.

“Let me undo it a minute, and try it a different way.”

“Yup.”

“It can really get you mad."

AI. SEP

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The graphite cask that held the plutonium fuel capsule for Apollo 17’s RTG, seen here attached to Challenger inside the SLA before launch. (NASA)

 

Подпись:Bean reinserted the tool with its prongs rotated to use different slots.

"You guys got any suggestions?” asked Conrad of the folks in Hous­ton.

"I just get the feeling that it’s hot and swelled in there or something,” Bean said as he tried again to extract the capsule. "Doesn’t want to come out. I can sure feel the heat, though, on my hands. Come out of there! Rascal.”

The capsule was seated within two steel rings that held it away from the graphite cask. It seemed that, with it giving off 1.5 kilowatts of heat, the expansion of the arrangement was holding it snug on the rings.

"You know, everything operates just exactly like it does in the training mock-ups and up at GE (General

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Alan Bean attempts to extract the fuel capsule from Intrepid’s cask. Beside him is the black-finned RTG ready to take the capsule. (NASA)

Electric Corporation). The only problem is, it just won’t come out of the cask. I am suspicious that it’s just swollen in there or something and friction’s holding it in. But it’s such a delicate tool, I really hate to pull on it too hard.”

Unfortunately engineers had not fully taken account of the length of time that the capsule would sit in its cask from Florida to the Moon, its 700°C heat soaking the steel mounts.

Bean piped up. “Go get that hammer and bang on the side of it.”

“No. I got a better idea,” said Conrad. “Where’s the hammer?”

“That’s what I said.”

“No, no. But I want to try and put the back end in under that lip there and pry her out. Let me go get the hammer. Be right back.” Conrad’s idea was to use the hammer’s blade to lever the capsule out.

“Let me get the tool off,” said Bean as he felt the capsule’s heat move along the handle. “It’s starting to warm up.” He disengaged the tool as Conrad went around the LM. They were not unduly bothered by the radiation from the capsule. It was alpha radiation and as such, was stopped by a small amount of material. They would not be exposed to it for long anyway. Their real concern was that the thermally hot capsule might damage their suits. They had to use the tool to extract it. Once Conrad had retrieved the hammer. Bean re-engaged the tool with the element. They were both leaning towards a little percussive persuasion.

Bean spoke first. "Now, my recommendation would be pound on the cask.” He preferred that Conrad not use the hammer’s blade on the capsule. As Bean pulled on the tool, Conrad began to repeatedly hit the side of the cask with the hammer.

”Hey, that’s doing it!” yelled Bean excitedly as the cask began to yield its contents. "Give it a few more pounds. Got to beat harder than that. Keep going. It’s coming out. It’s coming out! Pound harder/’

“Keep going/’ commanded Conrad to the balky capsule.

‘’Come on, Conrad!” laughed Bean.

"Keep going, baby."

“Thai hammer’s a universal tool.”

“You better believe it/’ cheered Conrad.

With every thump, the capsule edged out until, after a few centimetres, it came away easily. To Conrad’s giggles. Bean swung it over to the RTG unit.

"That’s beautiful. That’s Loo much.” said Bean.

“Well done, troops/’ congratulated Ed Gibson, Capeom in Houston.

“We got it, babe!" explained Bean. “It fits in the RTG real well! It’s just the cask was holding in on the side. Don’t come to the Moon without a hammer.” He brought the hammer home to Earth and now uses it to texture his paintings in his post-Apollo life as an artist.

Deployment of the ALSEP required a reasonably flat site a few hundred metres from the LM. The complete kit was mounted on two pallets and stored on rails in the LM’s descent stage. Once lowered to the ground by pulleys, the packages were hung on a bar bell and carried to the site. The layout was roughly star-shaped with ribbon cables that radiated out from the central station to the various instruments. Each cable was on a reel which fed out both ends simultaneously. There were often stringent constraints on the placement of each instrument, requiring care to avoid interference between instruments and to minimise heat conduction with the ground. For example, the magnetometer had to be clear of other instruments that contained magnets. Also, the seismometer was mounted on a stool surrounded by a reflective Mylar skirt that kept the Sun from heating the ground because the expansion and contraction from the heating cycles w’ould have added noise to the instrument’s output. However, the skirt itself routinely added unwanted signals each morning when the Sun first hit it and caused it to flex and buckle in the heat.

Prior to deployment, the various instruments were attached to their pallet by ‘Boyd bolts’, spring-loaded fasteners that required a crewman to insert the end of their universal hand tool (UHT) and give a fifth of a turn to release them. To help the crew7, each bolt had a collar that guided the tool to the bolt. In general, the bolts worked well but on some occasions, what had seemed simple on Earth became much more difficult in the dust and light gravity of the Moon.

“Another one of those beautiful Boyd bolts is all full of dust,” muttered Shepard

Подпись: 370 Exploration at its greatest

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Assembled panorama of Apollo 17’s ALSEP after deployment. RTG is on the left, central station to the right with its antenna aimed E <i+hward. (NASA)

sardonically as he tried to release a small instrument, the supra thermal ion detector, from its pallet.

‘’Yep,” agreed Mitchell. "’Everything else is going to be full of dust before long. Be filthy as pigs."

Shepard first tried the obvious solution. "Tm going to have to lift it up and shake the dust out of that Boyd bolt; I can’t get it otherwise. Let’s just turn it upside down and shake it.’’

As they lifted it. parts fell away. "Well, there’s a lot of Boyd bolts falling off,’’ said Mitchell, referring to the parts of the bolts that Shepard had already unfastened.

"Yeah, but them’s not the ones we’ve got the problems with. Okay, flop it over a minute."

‘"That’ll do it?" asked Mitchell hopefully.

"No, it’s still not clear.’’

Shepard was having problems on three levels. Lunar dust gets everywhere and having found its way into the Boyd bolt, its cohesive nature in the vacuum helped it to stay there. Additionally, the weakness of the lunar gravity gave little assistance in clearing the bolt’s sleeve, even when Shepard turned it upside down. The situation was exacerbated by the bolt being relatively inaccessible and, as Mitchell would later explain, it was difficult to see what was happening. “On the lunar surface, there’s no air to refract the light in there. So, it’s either shadow or it’s light and, unless you’ve got a direct sunlight on it, there’s no way in hell you can see anything. That’s an amazing phenomenon on an airless planet. It’s amazing how much we count on reflected and refracted light here. But there, unless you had it directly in sunlight, it was just pitch black. And that’s what he was wrestling with, there. The dirt was packed in around it and, besides that, he couldn’t see dowm in there unless we picked it up, physically, and twisted it and held it so we could get it in the sunlight."

That one bolt cost Shepard nearly ten minutes before he finally got it loose. David Scott later discussed how important it was for something that small to work correctly. "In a training context, especially [as Apollo 12 backup commander]. I remember trying to get the Boyd bolts to work, and they would hang up. One would hang up, and you couldn’t deploy the ALSEP. Or, the UIIT’s hexagonal probe that goes into the socket w’ould sort of strip and get w’orn and you couldn’t turn it. And, if you turned it too hard, you’d strip the edges. The Boyd bolts were challenges. I think all ours w’orked just fine. But the UIIT and the Boyd bolts w’ere a big deal; because, if it didn’t work, then you didn’t get that piece of the ALSEP up. And there were a lot of Boyd bolts."

Across the six missions that landed, crew’s deployed a large number of instruments as part of the ALSLP or as standalone experiments. Seismology was a popular topic, with passive seismometers being carried on most missions. Some missions included active seismometry. with small explosive charges being set up to provide calibrated shockwraves that w’ould help to profile the local subsurface. Magnetometers sensed the local magnetic held which, on the Moon, was dominated by its monthly passage through Earth’s magnetotail. However, because some of the Apollo 11 rocks proved

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The magnetometer experiment of the Apollo 16 ALSEP. (NASA)

to be magnetic, some later missions included a portable magnetometer to measure remanent magnetic fields at points along a traverse. Many experiments tried to sense and characterise the various particles that comprised what little atmosphere the Moon possessed. Most of these were from the solar wind or from the rocket exhaust of the spacecraft, but there was also the question of whether the change from night to day, and the resulting rise in ultraviolet exposure caused tiny particles of charged dust to levitate for a while.

There were experiments on the mechanics of the lunar soil which acted in ways that were not foreseen. Though the top layer was extremely loose and powdery, its characteristics changed markedly just a few centimetres below the surface. Millions of years of slow settlement had caused it to become extremely tightly packed and crews sometimes found it difficult to drive in items like flagpoles and the solar wind collector. Trenching experiments showed that the vacuum and the very finely ground nature of the powder made it remarkably cohesive and able to support steep sides. Even Buzz Aldrin’s famous bootprint photograph showed how well the powder could hold an impression.

There was an ultraviolet telescope on Apollo 16, a device for measuring the local gravitational field mounted on Apollo 17’s rover, and experiments to determine the electrical properties of the lunar surface. Add to all this the intense expeditions to photograph, document, sample and generally geologise across their site, this feast of science kept all the Apollo surface crews extremely busy for their precious hours walking on the Moon. One particular ill-starred experiment served to teach everyone about the difficulties of trying to carry out science in a vacuum, under an unfiltered Sun into a poorly understood, extremely dusty and abrasive soil while wearing in an awkward pressure suit with limited visibility. This was the heat-flow experiment.

Drill problems and the heat-flow experiment

Geophysicist Marcus Langseth was good at taking Earth’s temperature and now he had a chance to take the Moon’s. More specifically, he wanted to accurately

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Left, John Young with Apollo 16’s UY telescope. Right, UV image of Earth. (NASA)

measure the temperature of the lunar soil at various depths. From these measurements, he hoped to calculate how much heat was flowing out of the Moon’s interior and infer whether its core is still molten. He designed an experiment for Apollo 13’s ALSEP that would place temperature probes into drill holes. The equipment burned up in Earth’s atmosphere after that mission’s LM had served as a lifeboat for its crew.

Langseth had to wait over a year for the Apollo 15 crew to try again. Using the father of the cordless drill, the experiment required two holes, each nearly three metres deep into which the probes would be inserted. Separate from the experiment, the drill would also be used to extract a deep core of material that would give geologists a record of the depositional layering of the soil potentially going back hundreds of millions of years.

Scott quickly found the drilling to be hard going and could only get the first hole down to 1.6 metres. He tried putting his weight on the drill but in the Moon’s weak gravity, this provided little push and, if anything actually worked against the design of the drill stems and their helical external flutes. At any rate, the designers had not taken sufficient account of the nature of the Moon’s surface. Although the Moon is draped in a blanket of finely ground-up rock – the regolith – which is many metres deep at the landing sites, the highly compacted nature of all but the uppermost few centimetres made it more like hard rock. Worse, the flutes at the joins of the drill stems had been narrowed to strengthen those joins but, with the dust unable to go anywhere else, it caused the stems to jam. Mission control agreed that Scott should place the probes in the existing hole even though it compromised the quality of the experiment. The second hole fared worse and at one metre, they decided to revisit it the next day. On returning to the site, Scott tried to lift the drill and rotate it to help clear the flutes but unbeknownst to him this actually caused the bit to disengage

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David Scott sets down the drill during operations to emplace the heat-flow experiment. (NASA) "

from the stem above. Subsequent drilling with the hollow upper stem merely created a core running down alongside and when Scott inserted the probes they penetrated no further than about one metre.

With the heat-flow probes less than ideally placed, Scott began to drill a deep core sample using hollow stems which meant the material in the hole would be kept rather than pushed aside. Also, the flutes were of uniform depth and much faster progress was made. Scott readily reached 2.4 metres in depth, much deeper than the other two holes but by this time, they needed to return to the LM and leave the extraction to the final day. Much time and frustration had already been expended on the drilling.

On the final day, Scott learned that extraction of the deep core was to take precedence over their final drive to Hadley Rille and a feature known as the North Complex, a possibly volcanic site of some interest to Scott and the geologists. Usually rover drives came first so the crews would have more consumables available in case they had to walk back from a stalled vehicle. The decision to favour the drill meant that there would be no visit to the North Complex. However, when they tried to remove the core, it proved difficult to budge. Both Scott and Irwin had to work to extract the core, first by pulling hard on the drill’s handles, and eventually putting their shoulders under the handles and shoving so hard that Scott managed to injure his shoulder. It was a measure of the confidence that the crews had in their suits that they felt they could expend maximum physical effort without fear of a rip dumping their air.

"It shows how tough and durable the things were,” remembered Scott when reviewing the incident years later. "I’m really surprised that somebody in the back row in Houston didn’t get real squeamish about all of this. I’m surprised some boss didn’t just say. ’Hey, just knock that off.’ because they could hear us grunting and groaning – two guys on the Moon in pressure suits doing this kind of stuff. In retrospect, not smart, from a safety point of view.”

How ever, their suits included systems to warn of problems with the air pressure or cooling. ‘’Only if a tone comes on do you do something.” continued Scott. “As long as there are no tones, you work as you would work on the Earth and you never really think about [the dangers], Houston, that’s their job. To sort of pace us and guide us, because once we’re out in the suits, boy, it’s very comfortable."

Eventually, Scott and Irwin extracted the deep core but Scott’s troubles were not over and he was getting frustrated at the time being spent on it. "Joe, I haven’t heard you say yet you really want this that bad.” Joe Allen was the tactful Capcom in mission control. As part of his job, he acted as a go-between for the crew and the geology team in the science back room. ‘’Tell me you really want it this bad.” implored Scott. “It’s hard for me to say. Dave," was Allen’s wistful reply.

The six-part core stem, including a treadle that had helped guide the stem into the soil, all had to be taken apart for return to Earth. To help, a simple wrench vice that gripped in one direction was on the rover. Scott was having difficulty getting it to work. ‘‘This vice just won’t hold. There’s something wrong with it." They needed that wrench because a suited hand does not have much grip. It is already working against the suit pressure trying to straighten it “My hand wrench works okay. The one on the back of the [rover] doesn’t seem to want to work for some reason. It may just be because of the threads on the stems. I just can’t get them broken apart!” As Scott struggled with the stem in the vice, it dawned on him what the problem was. "I hate to tell you. Jim, but that… Oh boy! This vice is on… I swear it’s on backwards.” In fact, a reversed diagram in the assembly manual had thwarted them. The wrench had indeed been mounted back to front.

With Irwin’s help. Scott managed to separate half of the segments, even though it meant gripping the stem’s sharp flutes, yet the final three refused to come apart.

“We might be able to return it just like that.” suggested Irwin. Although it was 1.5 metres long, they would be able to get it in the LM.

“I don’t know where we’re going to put it in the command module.” said Scott. "I guess we ought to take it back. There’s more time invested in that than anything we’ve done.”

When the deep core reached Earth, it was immediately x-rayed which revealed 58 distinct layers within the core. Grant Heiken, a scientist who painstakingly analysed each layer, grain by grain, described it as the most valuable sample returned from the Moon.

The Apollo 15 heat-flow experiment gave good results despite its problems and created enough interest in Langseth’s experiment for another to be taken on Apollo 16. All the lessons from Scott’s battle with the drill and wrench had been learned. Using redesigned drill stems, Duke had no problem drilling the holes and inserting the temperature probes.

“Mark has his first one. announced Duke. "All the way in to the red mark [on the rammer] on the Cayley Plain.”

“Outstanding!” replied Tony England. “The first one in the highlands.”

Moments later, John Young lifted a package away from the central station and as he walked, his feci got caught up with the cable leading to the heat-flow electronics package.

“Charlie."

“What?"

“Something happened here."

“What happened?"

“I don’t know." said Young. “Here’s a line that pulled loose."

“That’s the heat-flow," Duke informed. “You’ve pulled it off."

“God almighty." Young’s spirits dropped like a stone as he went to examine the damage closely. The wires at the end of the cable had been torn from its connector where it was plugged into the central station.

“Well, I’m wasting my time," said Duke as he realised there was no point in drilling the second hole for the heat-flow probes.

“I’m sorry. I didn’t even know, said Young. "Agh; it’s sure gone."

“Okay, we copy," said England in Houston as the engineering back rooms began to crank up in a futile effort to resurrect the experiment. “I guess we can forget the rest of that heat flow."

“Yeah," replied Duke. “I’ll go do the [deep core]. Oh. rats!"

In fact, it was surprising there were not more accidents like this. Having the RCU mounted on his chest afforded the astronaut almost no visibility of his feet and the numerous layers in the suit’s construction severely attenuated any sense of touch. He constantly had to work against the internal pressure and its tendency to return the suit to one stance. This made it difficult for Young to have seen or even to have felt the snagging cable. Additionally, in lunar gravity cables tended not to lie as flat as they would on Earth and they ’remembered’ their coiled-up shape to form numerous loops spiralling across the lunar dust.

After more than 2 ‘/■ years. Marcus Langseth finally triumphed when his heat – flow experiment was fully installed at Taurus-Littrow by the Apollo 17 surface crew. The measurements from the two sites where emplacement was successful showed that the Moon has little residual heat of its own. What heat it has is produced by radioactive decay in the topmost few hundred kilometres but it is insufficient to cause substantial melting of the lunar mantle.

COLM I’iG DOWM TO THU BURN

"What’s the time?” asked Aldrin from Columbia’s right-hand couch. The crew of Apollo 11 had made their attitude checks prior to TEI. and were verifying that the engine bell was swivelling on its gimbal correctly in response to steering commands. Preparations were going smoothly and there was a light mood in the cabin as their incredible flight began to look as if it might actually come off.

“We have 12 minutes to go.” replied Collins, occupying the left couch.

Aldrin had been wondering what they should do once TEI w as completed: “You going to pitch up after the burn?”

“Sounds like a good idea,” agreed Collins. “Let’s look at the Moon after the burn. That’ll give us high-gain, right?”

“Cheek,” concurred Aldrin. Since they needed the spacecraft’s high-gain antenna to face Earth and it was positioned on the opposite side from their windows, it made sense to point the spacecraft down to have the high-gain in a favourable position for Earth and. meantime, watch the Moon recede.

“Okay, 10 minutes until Tig,” called Armstrong. ‘Tig’ was the ‘Time of ignition’ and everything they did worked towards it being on time and as flawless as possible. As they were over the far side of the Moon, where it also happened to be lunar night, neither the Sun nor Earth was shining across the landscape, and the only way to see the Moon’s position was by looking at a huge void where there were no stars. The spacecraft had to be travelling with its apex forward to enable the engine at the rear to accelerate them out of lunar orbit, and Collins was straining at the window for some kind of confirmation of this fact.

“I see a horizon,” he laughed. “It looks like we are going forward.”

“Shades of Gemini.” reminded Armstrong.

“It is most important that we be going forward,” stated Collins.

Aldrin began gently mocking his crewmate. “Let’s see. The motors point this way and the gases escape that way. therefore imparting a thrust that-a-way.” They all laughed.

This was a chance to pause and reflect during their preparations, and to look for the horizon that they were supposed to check in a few; minutes.

“Beautiful looking horizon." said Armstrong. “It’s hard to describe."

“God, it has an eerie look to it,” added Aldrin. “It’s not a horizon, it’s just a band.”

Collins and Aldrin could sec directly forward through their rendezvous windows

along the plus-.v axis and towards the sunrise. Armstrong’s view from the middle couch was limited to the hatch window just above his head.

‘’It was really eerie when it first came/’ said Armstrong as the Sun rose and the terminator came into view. "And the way the terminator is, you don’t see the whole Moon at all."

"I know.” said Collins. "I was looking at it upside down for a while.”

"Yes, and then that scares you,” added Armstrong, "because that says you’re going retrograde, right? Well, let’s see. if it’s upside down, you’re going backwards/’ Collins brought them back to their checklist. "Alright, we’re coming up on bus tie time; we’ve got a little over 6 [minutes] 50 [seconds] until fig.”

The crew returned to the protocol of challenge and response, with Armstrong reading out a line from the checklist and Collins repealing it once he had carried out the instruction. Once they had dealt with the internal configuration of the spacecraft it was time for another external check.

"Two minutes to get our horizon check at 10 degrees.’’ Armstrong had little option but to have his head in the checklist.

"Yes, and sneaking up on there, looks pretty darn good.” said Aldrin. "Looks like we’re darn near right.” The spacecraft was holding a steady attitude with respect to the stars so, in a sense, the Moon appeared like a great, rounded hill and they were in a helicopter approaching the summit, ‘fhe Moon’s horizon crept down Collins’s window towards the 10-degree mark. Aldrin’s window did not have that mark but he could infer it. "Okay, coming up on two minutes.” he eallcd, "and this damn horizon check is going to be. would you believe, perfect?”

"I hope so,” said Armstrong.

"fantastic,” enthused Aldrin. "First lime we ever got a perfect horizon check. Spent too many hours in the simulator looking for an unreal horizon. Alright, horizon check passes.”

"Beautiful,” agreed Collins, who armed one of the engine’s control banks then proceeded with Armstrong through the final lines of the checklist.

"Okay, stand by for 35 seconds,” announced Collins. "Mark it. DSK. Y blanks; EMS is in Normal.” The guidance system had begun to measure their acceleration. Aldrin came back, "Check.”

"Coming up on 15 seconds,” said Collins.

Armstrong readied himself at the computer keyboard for when the display w ould start flashing ’99’ at him, asking for permission to light the engine. "Okay. I’ll get the 99.” – – –

"Okay,” said Collins. "Stand by for ullage. Ullage.’’

"Cot the ullage,” reported Aldrin. Two rearward-facing thrusters lit up, gently pushing the spacecraft forward and bringing the weightless propellant to the bottom of the tanks as the crew counted down.

"Burn!” shouted Collins as the SPS engine lit. "A good one. Nice.”

"I got two balls,” called Aldrin.

As planned, only two of the four ball valves on the propellant feed lines had been opened by the computer.

"Okay, here comes ihc other two.” said Collins as he threw the switch to bring in the second control bank and bring the engine to its maximum thrust. “Man, that feels like g, doesn’t it?"

When they fired the SPS engine on arrival at the Moon, the tanks in the service module had been full and the LM was attached to their nose. Now the CSM was by itself and its tanks were only one-third full, giving the SPS the ability to accelerate the spacecraft towards 1 g.

Collins was closely monitoring the displays in front of him. "Pressures are good. Busy in steering, but it’s holding right in there.’’

“Hotv is it. Mike’.’" asked Aldrin from the right.

"It’s really busy in roll," replied Collins, "but it’s holding in its dead band. Looks like it’s holding instead of plus or minus five, more like plus or minus eight [degrees]. It’s possible that we have a roll-thruster problem, but if we have, it’s taking it out. No point in worrying about it. Okay, coming up on one minute. Mark it, one minute. Chamber pressure’s holding right on 100 psi."

"Looks good," agreed Aldrin.

Collins continued with his commentary. "Gimbals look good: total attitude looks good. Rates are damped out. Still a little busy."

There was no problem with the roll thruster, but the sloshing propellant could have a significant effect on the spacecraft’s attitude which was corrected by the thrusters and the engine gimbals.

"Two minutes. Mark it," continued Collins. "When it hits the end of that roll dead band, it really comes crisply back." Collins was describing how well the computer was able to deal with the CSM’s tendency to drift off in attitude.

“Okay, chamber pressure’s falling off a little bit." Collins had one eye on the gauge that showed the pressure within the combustion chamber. "Now it’s going back up; chamber pressure’s oscillating just a tad."

Armstrong called out. “Ten seconds left.”

"We don’t care about the chamber pressure," said Collins. "Brace yourself. Standing by for engine off."

The 2 minutes 28 seconds that mission control had predicted for the burn came and went, but the engine was still firing.

“It should be shut down now’," said Armstrong.

Collins queried him, "Okay?"

“Shutdown," called out Armstrong.

Collins stopped the engine at the same time as the computer. It had burned for 3.4 seconds longer than predicted because its thrust during the LOI burn had been slightly high and mission control had used that data when planning TEI. In the event, a slight change in mixture ratio lowered the thrust and so it burned a little longer to achieve the same change in velocity.

"Let’s look at what we got," said Collins as they brought up the residual velocity components. "Beautiful," he commented, “,v and r, 0.2." A burn that had changed their velocity by 1,000 metres per second was showing an error of only six centimetres per second. "SPS, I love you," he exulted. "You are a jewel! Whoosh!"

As with the LOI burn, no one knew anything of this in the MOCR or anywhere else on planet Earth. Any communication with Columbia was blocked by a 3.476- kilometre ball of rock. What they did know in mission control, down to the second, were the limes when the CSM would come back into view if the burn had worked, and if it had not. The increase in velocity would dramatically shorten how long it was out of sight.

Breathing fumes

It was around this point in the descent that the last Apollo command module to enter space ran into problems. During their return from the first international link­up in Earth orbit, the Apollo-Soyuz Test Project, the crew failed to switch on the Earth landing system at the right time. This episode illustrates how quickly an otherwise nominal mission can be derailed by a small operational error. Vance Brand was flying in the left couch with ‘l orn Stafford in command occupying the centre couch and working through the checklist with him. Somehow, they missed the step where the Earth landing system should have been powered and. all too quickly, they realised that the apex cover was still attached when it should have already departed. Brand punched the button to manually jettison it, and did the same for the drogue chutes. Unfortunately, in the rush, the RCS jets were not disabled, and when the drogue deployment caused the spacecraft to sway, the RCS jets began to lire to damp out these motions. By this Lime, the cabin pressure relief valve had begun to admit air from outside and, as it did so. exhaust from the jets, including a fraction of unburnt propellant, entered the cabin where the highly noxious chemical irritated the skin and eyes of the crew and caused them to cough. After struggling through the remainder of the descent and a hard landing that left the spacecraft upside-down. Stafford found Brand to be hanging in his straps unconscious. He struggled to get oxygen masks on his crewmates and gain control of the ship.

CONTINUING PREPARATIONS

While the commander was Lending to the LM’s guidance needs, the LMP continued his checks with the activation of the communications system. Communications to the CSM were handled by two VHF antennae mounted fore and aft. Communica­tions to Earth, as well as the same ranging and tracking functions as found on the CSM, used either of two low-gain S-band antennae, also mounted fore and aft. For higher data rates, a steerable, high-gain dish was mounted high on the right-hand side of the ascent stage and it included systems to keep itself aimed towards Earth.

For the descent, the electrical power for the LM came from batteries mounted in the descent stage. Originally, the lunar module’s manufacturer, Grumman, had intended to power it with fuel cells, in a manner similar to the CSM and most of the Gemini spacecraft. Managerial and technical difficulties, mostly concerned with the interdependence of the power system with other systems in the already exotic LM, conspired with the race to get the spacecraft ready on time to force a switch to using batteries as the power source. Though heavy, batteries had the enormous advantage of simplicity, and since the LM was intended to be powered for only a few days, their weight penalty was no worse than the fuel cells. As part of the checkout of the LM, their health was closely studied, as were the extra set required for the ascent stage. The ascent stage carried a separate small set of batteries because it had to operate on its own for only a few hours for the trip from the surface of the Moon up to the CSM.

Another major item in the LMP’s checklist was the cooling system. Whereas the CSM used radiators and evaporators to lose heat from a water/glycol coolant, the LM relied on a sublimator to achieve the same task. These devices cooled by having ice directly sublimate to waiter vapour in a vacuum, in the process taking heat away from the coolant. The lunar spacesuits used the same cooling technique. Because the LM had no source of water available as a by-product of fuel cell operation, a large water tank was included in the descent stage, with a smaller supply in the ascent stage. The water/glycol coolant was pumped between the LM’s electronics and the sublimator by redundant sets of pumps. The pressures delivered by these pumps were checked before committing the LM to the surface.

Manoeuvring the LM was effected by a set of thrusters similar to the RCS jets mounted on the service module. Where each cluster of jets on the service module had independent propellant supplies, those on the lunar module had a common propellant system that, if the need arose, could be topped up from the propellant used by the ascent stage’s main rocket engine. As a further difference, the service module’s RCS quads w’ere mounted on the spacecraft axes, while those for the LM were set at the corners of a square around the spacecraft to keep the windows and hatchway clear. Before it could be used, the propellant system had to be pressurised. An explosively operated valve was opened to allow helium gas into the propellant tanks, at which point the crew and mission control could verify that the pressures within the system were as expected.

To rest or not to rest

When Armstrong and Aldrin arrived at Tranquillity Base, their flight plan gave them a rest period before they were to embark on their historic moonwalk. NASA’s operational conservatism had not wanted to load them up with too much in one day. But many believed that the crew would be too keyed up to rest at that point and there were tentative plans to bring their EVA forward. One hour after landing. Armstrong announced his decision. “Our recommendation at this point is planning an EVA, with your concurrence, starting about eight o’clock this evening. Houston time. That is about three hours from now. We will give you some lime to think about that."

Charlie Duke promptly gave Houston’s reply. “We thought about it; wre will support it. We’re Go at that time.’’

Aflcr the mission, Armstrong explained their thinking. “There were two factors that we thought might influence that decision. One was the spacecraft systems and any abnormalities that we might have that we’d want to work on; and the second was our adaptation to one-sixth g and whether we thought more time in one-sixth g before starting the EVA would be advantageous or disadvantageous at that point. Basically, my personal feeling was that the adaptation to one-sixth g was very rapid and [it] was very pleasant, easy to work in. and I thought at the time that we were ready to go right ahead into the surface work and [so I] recommended that."

For the most part, crews had their first surface EVA on the day of landing. Apollo 16 was one exception. The 6-hour delay in its landing had changed mission control’s view. “You probably gathered that we want y’all to sleep first," said Jim Irwin in Houston.

“That suits us," said Duke, not entirely honestly. “Jim. I feel exactly like I thought I was [going to feel], I really want to get out, hut I think that discretion is the better part of the valour here.’’

Decades later. Duke regretted the decision. “As a hindsight observation, it wasn’t a good idea. I think we should have gotten out first. I had a tough time getting to sleep. My mind wras just racing and I wanted to get out. I was thinking about all that was coming up; and the excitement had just passed; and. you know, my mind was just whirling. 1 think wn had so much adrenaline pumping we could have gone, probably two days – forty-eight hours – without any problem. So, looking back, I think we made a mistake. But it’s done."

The other exception to EVA on landing day was Apollo 15. They had a SEVA!

SEVA

David Scott’s flight was the first J-mission, the first to have a rover and the first where science defined the mission. Back in 1964, when geology training began for the prospective lunar explorers, Scott’s teachers spotted that, more than the other jet – jockeys that passed through their hands, he possessed a mind that was receptive to scientific enquiry. When his Moon mission came up. his enthusiasm and excitement for Apollo’s scientific quest easily transferred to the other members of his crew, and to those subsequent members of the J-mission crews who, like him, came from a test – pilot background. Don Wilhelms, who played a major part in transforming Apollo into a hunt for geological answers, described Scott, Jim Irwin and Л1 Worden as "the geologic crew”.

Scott had been impressed by the teachings of geologists like Caltech professor Lee Silver and USGS staffer Gordon Swann who had been brought in to give the crews training in field geology, as distinct from the previous classroom instruction. When approaching a new’ geological site, one of Silver’s techniques was to find a high spot, even the vehicle that had brought them there if needs be, to gain an overview of the site before digging into the detail of stones and bedrock. This site survey gave the bigger picture; what the major rock exposures were, what type of rocks they held and at w’hat angle the layers of rock dipped. Scott decided that since there were no plans for an EVA on the day of their landing, he w’ould make a stand-up extravehicular activity (SEVA) instead.

The arguments to convince managers that a SEVA was worthwhile included a need to maintain the crew’s circadian rhythm. At the time, it was felt that a full 7- hour EVA after landing would have meant an excessively long day. Yet. to sleep so soon after arrival would lead to a shorter than normal day. The SEVA would fill the gap and help to release the excitement they would naturally feel at having landed on the Moon. Also, Apollo 15 s northerly site had not been well mapped by the Lunar Orbiter probes whose high-resolution imagery had been expended near the equator. In particular, no one really knew w’hether Iladley provided a suitable surface for the rover, and if significant problems became visible from up top then his descriptions would be useful in revising the planned drives.

From Scott’s point of view, the best reason for the SEVA was the science, as he later recalled. "To be able to stand there and just look at all that stuff. I mean, that was just a mindblower to be able to just stand up there and gaze around and report what you saw% knowing full w’ell that Lee Silver and Gordon Sw’ann and the guys in the Backroom are listening to every word.”

As well as the SEVA, Scott and the geologists wanted to take a telephoto lens. "We spent a lot of time and energy justifying the 500-mm lens,” remembered Scott. "And the final trade-off was in abort propellant. They reduced the amount of abort propellant on the landing by witatever the mass of the telephoto lens w’as. There was a lot of scepticism on whether it would be useful at all. But, gosh, you go out in the field with a bunch of geologists and you can’t get to the mountain and it becomes obvious that a telephoto picture is a lot better than nothing.”

Once he had got his head out of the overhead hatch. Scott began to photograph the virgin site using a 60-mrn lens to take an all-round panorama and then his telephoto lens to capture features of special interest. With that out of the way, he began what, according to Wilhelms, ranked as "the best geological description by an astronaut on the Moon.”

"All of the features around here are very smooth,” reported Scott. "The tops of the mountains are rounded off. There are no sharp jagged peaks or no large boulders apparent anywhere.”

image182

Silver Spur, as photographed by David Scott during his SEVA using a 500-mrn lens. (NASA) " " "

That was good news. They would have little difficulty driving the rover across the landscape as planned. Scott worked his way around the view, describing everything he saw while giving clock-face references with respect to the LM’s west-facing aspect. "As I look on down to my seven o’clock, I guess I see Index Crater here [in] the near field. But, back up on Hadley Delta, to the east [at Silver Spur], why, again I can see a smooth surface. However, I can see lineaments. I’ll take a picture for you.”

The Moon’s immense antiquity drapes almost all its bedrock with a thick blanket of beat-up, pulverised rock. Since bedrock is what geologists like the most, by virtue of it being in situ, any sign of it on the lunar surface gets their attention, especially when they see layering. Scott’s lineaments, on the feature they had happily named Silver Spur for their geological mentor, appeared to be such layering.

"There appear to be lineaments or lineations dipping to the northeast, parallel [to each other]. And they appear to be, maybe, three per cent to four per cent of the total elevation of the mountain, almost uniform [spacing]. I can’t tell whether it’s structure or internal stratigraphy or what. But there are definite linear features there, dipping to the northeast, at about, oh, I’d say 30 degrees.”

Silver Spur was too far away to visit, but with his telephoto lens Scott was able to gain clear images of the structures for the geologists.

For the two later missions, the justifications for a SEVA lessened and it was dropped. Scott would be the only commander to look out of the top of his LM in what Jim Irwin likened to Desert Fox in his Panzer.

SUITING UP

If a crew intended to leave the lunar module soon after landing, their preparations were reduced by virtue of being already suited. In fact, for the first three landings, suits were never removed while on the Moon. Their task primarily involved changing over from the LM’s oxygen and coolant water to that supplied from their back pack, the portable life support system (PLSS, pronounced ‘plies’). Once they had put their helmets and gloves back on, there were a large number of checks to be made.

The LM provided very little room for two crewmen wearing suits with PLSSs attached, so one of the first tasks was to lay out all the items they would need at positions where they could get to them without undue difficulty. They checked their zippers, the double locks that would hold their gloves and helmets in place, then positioned themselves to put their back packs on. The sequence of steps in the process was very carefully choreographed. Among all the unstowing of cameras, boots and other paraphernalia was one important task; to deploy a VHF antenna on the outside of the LM by turning a crank. One of the crew had to manoeuvre to the back of the cabin to get at it. When crews had eight hours or more hard work outside while sealed inside a suit, some food was welcome while an occasional drink was essential, so for the later missions, bags of water and a food bar would be installed within the neckring. Then coatings of anti-fog treatment would be applied to the inside of their helmets.

image183

A PLSS with its covers removed. (NASA)

image184

Buzz Aldrin carries science equipment across the lunar surface. On his back is his OPS (with the US flag) and PLSS (the larger unit below the OPS). (NASA)

Before they added their oxygen purge system (OPS) to the top of the back packs, a check was made of the pressure in the oxygen tanks within. Each OPS had two spherical tanks with the gas inside stored at an extremely high pressure. A small gauge was provided to check its value. Depending on how a crewman’s PLSS or suit had failed, the OPS would provide at least 30 minutes of emergency oxygen and cooling by the regulated discharge of the contents of its tanks. In fact, the OPS carried more than three times as much oxygen as did the PLSS itself but the latter was merely recycling the gas in a loop and topping it up as necessary as it was consumed.

As the Apollo 14 crew worked through their suiting up procedures, they reached the point where they had to don the PLSS. Mission control had them call out where in the checklist they were. “Okay, Houston,” called Ed Mitchell. “We’re at that point where we hand the real PLSS out and get the lightweight one.”

Once again, the crews could not help but compare their amazing experience on the surface of the Moon with the endless rehearsals they had put in before the flight. During their training exercises or when they had checked out Ant ares itself, they had used a real PLSS up to the point of donning it, but the back packs were uncomfortably heavy in Earth’s gravity and unwieldy in the tight space of the LM cabin. To avoid damaging flight hardware, the real PLSS would be exchanged for a lightweight mock-up. Ron Blevins was an instructor who would typically make the exchange.

“Roger,” laughed Capcom Bruce McCandless. “I’ll have Ron come on up the ladder.”

Crews did find the LM cabin to be a much more pleasant environment when the one-sixth-g of the Moon ruled the physics of their work. “The only time I found the lunar module really confining was when we started moving the PLSSs around,” remembered Charlie Duke. “We move one of the PLSSs on the floor between us, and we pick it up and put it somewhere else. We’d done that in training and John just struggled to get that thing up, because it was heavy! You know, 155 pounds [70 kg]. They had a lightweight mock-up which 1 think was a little bit lighter. But up there, in that one-sixth g, boy, he just picked it up with one hand. It was just tremendous. It made you feel like Superman.”

With the OPS attached to the top of the PLSS, connections were made between the two, including a feed to the antenna on top through which the crew would keep in touch with each other and Earth. Then they would don the PLSS. “Getting the PLSSs on was very difficult,” recalled Gene Cernan. “It was a two-man operation. The PLSSs were strapped to the side walls, at working height, and you had to back up against yours and the other guy would then unhook it from the wall and help you get it strapped to your back. The LM was so small that it was a very difficult operation, even in soft (unpressurised) suits.”

To control and monitor most of the functions of the suit, a remote control unit (RCU) was attached to the chest. It had a quantity gauge for oxygen; switches that controlled their water pump and fan assembly, and their communications; and there were flags that indicated the status of the back pack. These gave warnings for oxygen, water and carbon dioxide as well as for the suit’s pressure. On the front was a bracket upon which a crewman could attach his Hasselblad camera. Once the suit’s systems had been connected up, it was time for checks of the communications

image185

Remote control unit for the PLSS. (Training unit at the Smithsonian Institution’s Garber Facility, 2006. Photo courtesy Ulrich Lotzmann.)

between each other and with mission control. That’s when Conrad and Bean came unstuck.

Подпись:The checklists the crews used were very thorough. Every connection and every switch position was detailed for the men to check, and the procedures were practised repeatedly before the mission. The problem for the Apollo 12 crew was that they had done this so many times that they thought they knew it. More importantly, they were used to their training hardware. A1 Bean explained: ‘’The gear used down at the Cape [for training] have the comm switches on them but you don’t have to use them at all for comm.” Hence they did not have to actually operate the switch during training, as Conrad pointed out, “fn training, we always just read it in the checklist and kept on going.”

“Here’s an example of the gear we’re using [on the Moon] not being configured precisely like the gear we use in practice; and that cost us,” recalled Bean. In fact it cost them nearly 20 minutes in a machine whose operational lifetime was measured in hours. Differences between training and flight hardware would bite them again when their TV camera was damaged by being inadvertently aimed at the Sun. The crew had only ever practised with an inert mock-up and had no appreciation of the flight unit’s susceptibility to direct sunlight.

With the final oxygen connections made from the OPS to the PLSS, each crewman took a last long drink from the LM’s water supply before they sealed themselves off by donning their helmets and gloves. Care was taken to ensure their microphones were properly positioned as there would be no opportunity to reposition them once outside. They then transferred the suit’s oxygen and cooling water hoses from the LM to the PLSS and put on their hard-wearing outer gloves. Because they would get no cooling from the PLSS until they were in a vacuum, crews from Apollo 12 onwards made sure to give themselves an extra shot of cooling water from the LM through their liquid-cooled garment before this changeover.

The next step was to make sure the leakage from their suits was acceptable. Rather than build suits that were completely airtight, engineers accepted a slight leak rate in the knowledge that the PLSS supply would be adequate to make up for the loss across the duration of the EVA. This ‘pressure integrity’ check required the suits to be inflated above cabin pressure until the gauges on their cuffs indicated 3.7
to four psi. The oxygen supply was then turned off and the gauge watched for a minute. Their check­list stipulated that they should not observe a drop greater than 0.3 psi, some of which was merely due to them breathing the oxygen or the gas getting into all the nooks and cran­nies within the suit.

image187Lost air

Once everyone was happy, it came time to let the air out of the cabin, or depressurise, to use the parlance. There were two valves the crew could use to achieve this; one on the forward hatch that led out to the ladder, and the other on the overhead hatch that would lead to the tunnel and the CSM once they redocked. The handles for these dump valves had three positions; open, closed and an intermediate position called ‘automatic’ which was its normal setting in which the valve acted to protect the spacecraft against excessive internal pressure. It remained closed until the cabin’s pressure reached a threshold of about one third of nonnal Earth atmospheric pressure with respect to the outside. It then opened to vent air until the pressure dropped below the threshold.

The procedure for depressurisation was to set the dump valve in its open position and drop the cabin pressure from its normal reading of about five psi until it indicated 3.5 psi and then stop. They then monitored their suits to ensure that they were also dropping to maintain the correct relative pressure. If all was well, the dump valve was returned to the open position until the cabin was evacuated enough that the forward hatch could be opened. When sensors indicated less than 3.5 psi, the EVA was deemed to have begun and Houston would begin to time the crew’s progress.

On Apollo 11, the depressurisation proved to be a lengthy procedure. Unlike subsequent missions, Eagle’s forward dump valve had been fitted with a bacterial filter which halved the rate at which air could depart the cabin. As the amount of air within the LM decreased, so did the pressure that was pushing it through the depress valve and thus the rate of evacuation tailed off. It took about three minutes for the cabin pressure to indicate only 0.2 psi but even this was too high for a crewman to directly open the hatch. It had to get nearer to 0.1 psi. Yet at such low pressures, the cabin began to be replenished by internal sources that further slowed the depressurisation, as Armstrong explained after the flight. “It took a very long time to depressurise the LM through the bacteria filter with the PLSS adding gases to the cockpit environment or something adding some cabin pressure. The second was that

image188

Detail of the overhead hatch with latch handle on the left and overhead dump valve on the right. (Courtesy, Frank O’Brien)

we weren’t familiar with how long it would take to start a sublimator in this condition. It seemed to take a very long time to get through this sequence of getting the cabin pressure down to the point where we could open the hatch, getting the water turned on in the PLSS, getting the ice cake to form in the sublimator, and getting the water alarm flag to clear so that we could continue. It seemed like it took us about a half hour to get through this depressurisation sequence.” To speed up the process on subsequent flights, not only was the filter dropped, crews took to grabbing the corner of the hatch and peeling it open.

The sublimator that Armstrong was referring to was the central element of the PLSS’s cooling system. Water was fed directly to the vacuum where its evaporation and eventual sublimation from ice to a gas cooled a separate water circuit that cooled the crewman. This emission of vapour was the reason that later crews pre­cooled themselves before disconnecting their water from the LM. It was better not to start the sublimators until the hatch was open and a vacuum had been established in the LM.

Once the hatch was fully open, the commander manoeuvred himself onto the floor, kneeling with his feet towards the open hatch. Guided by his LMP, he crawled backwards through the hatch onto the porch, a small platform between the hatchway and the top of the ladder. When Neil Armstrong got onto the porch, he reached to his left and pulled a nearby D-ring which allowed one of the side panels of the descent stage to hinge open. A small TV camera was mounted upside down on the panel and strategically aimed to document his descent into the history books. On

image189

Alan Bean manoeuvring through Intrepid’& hatch. (NASA)

Earth, TV converters at the ground stations had circuitry to flip the image the right way up.

In the expectation that a descending LM was likely to deform the crushable interior of the landing legs and compress them, the lowest step of the ladder was set the best part of a metre above the footpad. However, on all missions, there was little appreciable compression of the gear, necessitating a gentle leap from the bottom step to the footpad in the low lunar gravity. Only then could a boot print be made in the lunar surface.

THE MOON AFTER APOLLO

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.

Re-entry

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

Next stop: the Moon “GO FOR THE PRO”: THE LANDING BEGINS

By July of 1969, NASA had done about as much as they could to prepare for the Moon landing. On the flight of Apollo 10 two months earlier, Tom Stafford and Eugene Cernan had taken their LM Snoopy into the descent orbit but had gone no further before returning to John Young in the CSM Charlie Brown.

Where Snoopy had feared to wander, Eagle swooped in. Although the first landing attempt, flown by Neil Armstrong and Buzz Aldrin, would be ultimately successful, it was by no means a straightforward descent. Landing on the Moon was a 12-minute rocket ride from orbit with a starting speed of nearly 6,000 kilometres per hour leading to a gentle touchdown on a terrain where no prepared ground awaited the LM. In that short time, a plethora of problems were served up to the crew of Eagle that would have curled the toes of everyone involved had it merely been a simulation. The fact that they all occurred on the actual landing attempt in full view of the world, yet were successfully handled by the mission control team and the crew, is testament to their professionalism, and to the power of exhaustive simulation as a means of properly preparing people for the challenges they may face.

Programs and phases

Planners broke the descent into three parts with each controlled by a dedicated program in the computer. The first was the braking phase, when most of the spacecraft’s orbital speed was countered by the thrust of the descent engine. This was the domain of Program 63 which began 10 minutes before the powered descent. It included the engine’s ignition and continued for the first nine minutes or so of the nominally 12-minute burn while the computer worked to take the crew to a point in space known as high gate, typically 2,200 metres in altitude and about seven kilometres from the landing site. At the start of the braking phase, the LM flew with its engine pointing against the direction of travel. Then as the burn

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

DOI 10.1007/978-1-4419-7179-1 10. © Springer Science+Business Media. LLC 2011

Подпись: Perilune & PDI. 500 km and 11.5 minutes to landing Landing site Diagram to show how Program 63 began nearly 1,000 kilometres before PDI.

progressed, the spacecraft gradually tilted a little more upright. At high gate, P64 took over.

P64 handled the approach phase of the descent. When the program assumed control, its first action was to pitch the LM further towards an upright attitude in order to enable the crew to see the landscape ahead. The point to which the computer was taking them was just on the near side of the horizon. They then flew in a manner roughly similar to a helicopter, but with the LM carefully balanced on top of the engine’s exhaust with the computer still in full control of where it was going. P64 included a method of informing the commander of where the computer was taking them, but if he deemed this to be unsuitable, then with a nudge of his controls he could instruct the computer to move the aim point. P64 was targeted to take the LM to a point about 30 metres above the surface and about five metres from the landing site. Prior to reaching this point, the crew would reach low gate, about 200 metres altitude and 600 metres short of landing.

As low gate approached, the commander was faced with a range of options. If he was completely satisfied with the job the computer was doing, he could allow it to automatically move on to P65, which could complete the landing. No commander ever allowed that, although it is said that Jim Lovell had intended to if Apollo 13 had reached this point. These competitive ex-test pilots, many of them experienced at landing on aircraft carriers, were happier to have some degree of control and steer the LM, and they all selected P66 before reaching low gate. P66 continuously throttled the engine to control their rate of descent, and the commander could adjust this rate as conditions warranted. At the same time, he assumed manual control of the LM’s attitude, which allowed him to steer the ship to a site of his own choosing. One other program, P67, was available to the commander, which gave him full manual control of the spacecraft, both the attitude and the throttle setting, but this

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“Go for the pro”: the landing begins 287

option was never used. Both P65 and P67 were dropped from later versions of the LM software.