Category How Apollo Flew to the Moon

With the docking successfully completed, Worden pressurised the tunnel between Endeavour and Falcon, then removed the forward hatch and docking equipment to inspect the 12 docking latches. Meanwhile, Irwin copied down a P30 PAD from mission control for a burn that would eventually Lake the jettisoned LM out of lunar orbit to crash on the Moon.

Once the LM’s overhead hatch had been opened, Worden sent the vacuum cleaner through the tunnel to help the LM crew to deal with the dust on their spacesuits. Scott and Irwin then began to transfer all required items to the CSM, with a list in the flight plan indicating where each item should be stored. The list included film magazines, rock and soil samples, food, used urine and faecal bags and one of the oxygen purge system (OPS) packages from the surface. The OPS. w’hich had been mounted on top of one of the PLSSs during the moonw’alks. w’ould be needed by Worden during the coast home to Earth, for his spacewalk to retrieve film magazines from the cameras in the SIM bay. It contained high-pressure oxygen bottles that would provide emergency air to a suited crewman in case of a problem with their primary umbilical air supply.

Items not required by Endeavour for the remainder of its mission, such as used lithium hydroxide canisters, a second OPS and the now-useless docking probe and drogue, were left in the LM to be jettisoned with it. In the light of the Soyuz 11 incident, this jettison was to occur with the crew fully suited up. As Irwin w:as the last to leave Falcon’s cabin, he closed its overhead hatch behind him. Once everyone was inside the command module, the forward hatch was installed and the cabin checked for leaks. At this point. Scott had to deal with a slight pressure leak in his suit. “Okay, we are going to be a few minutes here. We’ve got to pul some LCG plugs in our suits and it’s going to take probably about 10 or 15 minutes to gel all that done.”

This communication was the start of a confused episode which involved checks of the suit and hatch for pressure integrity. Scott’s boss, Deke Slayton, came on to the communications loop, betraying management’s concern at the crew’s deviation from the flight plan. Scott’s use of the plugs in his liquid cooled garment (LCG) w:as a minor remedy for a leak that was probably brought on by the wear and tear from the tenacious and abrasive lunar dust.

“Hey, one quick question. How come you guys need plugs for those suits?’’ asked Slayton.

“Well, because, apparently, the LCG connection on the inside won’t hold an air seal,’’ replied Scott. “So we’re getting them taken care of with these extra little blue plugs we got that are airtight on the inside.”

“Roger. We thought those plugs only were required w’hen the LCG was not on. We’re trying to crack that one for you down here, Dave. There’s something screwy here.’’

“Okay. Well, we’ll put these plugs in and run another pressure integrity cheek and see how it works.’’

“Roger.”

Scott’s subsequent successful suit integrity cheek pul the crew slightly behind their timeline, but Slayton’s intervention displayed the start of jitteriness in mission control about the crew and their tiredness when a slightly abnormal situation arose. Then, with only a few minutes to go before LM jettison, another pressure integrity problem became evident when Worden reported the pressure difference between the cabin and the tunnel. “LM/CM dcha-P is 2.5… 2.0, excuse me.”

“Copy, 2.0,” confirmed Bob Parker at the Capcom console.

The crew had used the tunnel vent valve to bleed air out into space from between the two spacecraft. Had it been completely evacuated, this pressure reading, given in pounds per square inch (psi), would show between five and six psi because it indicated the pressure difference across the forward hatch. With a good vacuum in the tunnel, the reading would be essentially the absolute cabin pressure. Their procedures called for the reading to be at least three psi prior to jettison. The fact that it was only two psi, having earlier read three psi, strongly suggested that air was entering the tunnel through the hatch of one or other spacecraft. Compounding the jitters in the MOCR was the knowledge that, on the way to the Moon, there had been confusion between Scott and the MOCR about the settings of this valve, which could either vent the tunnel or allow the crew- to monitor the pressure but not do both.

“Okay, the LM/CM delta-P doesn’t look exactly right to us. What do you think?” asked Scott.

“We’d like to get another pound [per square inch of pressure] out of there.” replied Parker. “We’re showing about 3.5 in there.” But mission control were not reading this directly. They had deduced this figure by subtracting the reading they had been given from the measured cabin pressure (5.5-2.0 = 3.5).

“Okay.” said Scott, as he and his crew looked for answers. “We had a suspicion that possibly the LM overhead dump valve was open, and it might be.” That is, it was possible Irwin had inadvertently left it open a little when he left the LM. Scott tried venting the tunnel further. "It’s up to about 2.3 now,” he reported.

The flight controllers in the MOCR discussed the readings with Scott a bit longer, before reaching a conclusion that was an extreme rarity in the history of flight control a mistaken conclusion. Parker radioed up. “Dave, we think that the increase in the cabin pressure during the suit integrity check could have raised it from your side.” However, adding more air to the cabin by inflating the suits for Scott’s pressure test would have had the opposite effect, increasing the pressure difference across the hatch.

Then Parker let slip about how the ground and the spacecraft had got out of sync with each other. "Stand by. Dave; confusion reigns down here.” In the light of this, mission control decided to hold off on the jettison, back out of the situation they were in, and have the crew disarm the pyrotechnic devices that were about to cut loose the LM. If the crew’ were to remove the hatch to inspect its seal, an accidental detonation of the armed LM jettison explosives would be catastrophic.

Scott and his crew brought the tunnel back up to the same pressure as the cabin, then removed the hatch but found nothing untoward. In any case, it was perfectly possible that contamination to the seal, perhaps from lunar dust, could have been blown off as the hatch was removed. Now that they had an extra two hours before the next jettison attempt, because it had to occur at a specific point in the orbit, mission control decided to use the Lime to test the hatch seal thoroughly. The crew reduced the pressure in the tunnel low enough to give a reading of 3.5 psi and Parker asked them to hold it there throughout their next far-side pass to see whether it had changed when they reappeared 45 minutes later. Scott and his crew were thinking about food and wanted to take their helmets and gloves off to eat: "I guess in that case, we’ll probably break the suits down and then run another suit check before we see you around the corner.”

“Okay, we’ll buy that," replied Parker.

“It’s about time for dinner.’’ said Scott.

“I knew there was a reason.”

By this time, it was 18 hours since Scott and Irwin had suited up for their gruelling final day on the lunar surface. They had not eaten for eight hours, and had been fully suited for much of the time since before launch from the Moon 6 lA hours earlier. The problems with their suit and hatch integrity were compounding their tiredness and they were going to be a further two hours behind. They were keen to get settled down to a much-needed meal break.

“Okay, we’re about 3.2 [psi] now on the delta-P,” reported Scott. “We’ll leave LM [meaning tunnel] in Vent.”

“Roger.” replied Parker. “I understand; 3.2 and still venting.”

The confusion was being compounded. Mission control had asked for the tunnel pressure to be held around the far side, but SeoiL had understood that he was to leave it venting. Then the managers worried whether the crew’ should remove their helmets and gloves in order to eat. Breaking open their suits w’ould necessitate another check of their pressure integrity before LM jettison. Despite having earlier concurred with the request from the crew to do precisely this, the suit integrity check would pump air into the cabin and affect the reading on their pressure gauge, so Parker notified them of a compromise: "You are permitted to break the suits down, but do not do the suit integrity check until you come back around the other side; wfe can Lake another look at that tunnel.”

Once the crew’ reappeared from behind the Moon, Parker quizzed them. “How’ did the hatch integrity check go?’’

‘"Well, we’ve just had it in Tunnel Vent all the way around the back side as I think you suggested," replied Scott.

“Did you have a look at holding it in delta-P to see how it was holding on that?’’ queried Parker.

“No, we just left it in Tunnel Vent all the way around the back side,” reported Scott. “That’s what we’d thought you’d said to do. We can check it now.”

By now’, Glynn Lunney. the flight director on this shift, w’as becoming frustrated at the difficulty his team were having in getting this crew put to bed. Parker called up, “15, why don’t you bring it up to 3.5. and let us watch it for a w’hile. I think w’e garbled something there.’’ Lvcryone was keen that they jettison the LM only when the seal on the forward hatch w’as good.

Although Apollo occurred in the first decade of manned space flight, doctors had already begun to test the body’s reaction to weightlessness during the Gemini programme and had noticed how muscle tone and bone mass were lost after only a few days. Bxcrcisc was believed to be the key to mitigating these effects but this was next to impossible in the cramped confines of a Gemini spacecraft – the exerciser was an elasticated strap, and the astronaut would loop one end around a foot and then pull against the tension. The greater volume afforded by an Apollo cabin permitted some limited exercise, especially when the couches were folded away. Every Apollo flight therefore carried an ‘Exer-genic’ or ‘Exergym’ exerciser, a commercial gadget consisting of a rope with handles that passed through a cylinder. The resistance to pulling the rope could be adjusted.

’’We all did a little bit of exercise almost every day." said Armstrong after his flight. "We used either isometrics or callisthenics in place, or the Exer-genie. It got a little hot and stored a lot of heat, but it was acceptable.’’

Collins elaborated on how their little gadget was dealing with the heat from friction. ’If you got a good workout on the Exer-gcnie, it got so hot that you couldn’t really touch it.”

As military test pilots for the most part, these men tended to take their exercise seriously in life outside NASA. Collins did daily runs, and Scott and Irwin often played handball. Armstrong was the exception when it came to exercising for its owm sake. As strong, fit individuals, they felt the need to exercise hard, even using the spacecraft’s structure, as the Apollo 12 crew related. "The thing we had for exercise,” said Gordon, "other than just moving around using the struts and the flat areas in the LEB for doing pushups and armpulls or whatever you wanted to do. is the Exergym. We all used it on the way out a couple of times a day for maybe a half hour each time. I didn’t use it at all coming back. Л1 didn’t use it coming back because the Exergym rope was frayed. Pete was using it on the wray back when he noticed that fibres were coming loose. So we elected not to use the exerciser at all on the way back.”

Surface crews found that the demands of working on the lunar surface was a hard exercise in itself. The CMPs. on the other hand, needed as much extra workout time as they could get, as Worden did on Apollo 15. "The Exergym is good for keeping some muscle tone,” he said after the flight, "but I found that there was just no way I could get a heart rate established and keep it going. I finally decided on a combination of two exercises. I used the Exergym a little bit. just to keep my shoulders and arms loned, and I ran in place. I took the centre couch out and flailed away with my legs, just like running in place as a matter of fact.’’

Crews regularly wore biomedical sensors on their skin that allowed the Surgeon in mission control to monitor their normal heart rate and breathing, and also while they were exercising. "I didn’t say anything to the ground.” continued Worden, ‘but the doctors watching the biomeds called up and said, ’Hey. you must be exercising. We can see your heart rate going up.’ And they kept me advised of what my heart rate was. It worked out very nicely. I thought, because they could tell you that you’re up to 130. going up to 140 (beats per minute). Then 1 would exercise a little bit harder, and true, even though I wasn’t exerting any pressure on anything, just moving the mass of your legs around really gets your heart going. As a matter of fact, I thought I’d strained some muscles that I had never used before because I was just free wheeling my legs and wasn’t exerting any pressure on anything. I found out that with the centre couch out, there’s just almost the right amount of room. In fact, the same thing could be done up in the tunnel area. You don’t need a whole lot of space.”

Irwin added, "We strained against the struts, against the bulkhead, and against the straps. This was kind of an isometric form of exercise. I think it’s almost as good as the Exergym.”

Ken Mattingly was not a huge fan of the exercise they had from a practical standpoint. “I just can’t believe that the amount of exercise 1 had justified 30 minutes [of my time],” he said after Apollo 16. ‘T really think I’d have been just as well off to just forget the whole thing.”

When it came to the CSM, Mattingly was regarded as an expert and he felt that the spacecraft’s environmental control system (ECS) might not handle the extra heat of someone who was really working out: “If you go out there and work up a sweat, really do exercise like you ought to. the ECS will not handle that kind of a load. The ECS is marginal. It’s designed for three marshmallows laying there. It isn’t designed for you to go out and do any exercise. The other thing I worried about was lying there and banging into things, because you can’t do any reasonable exercise and maintain your body position."

Sometimes crewmen exercised so vigorously that the entire spacecraft felt it. "Bob, this is Jack," called Schmitt to Bob Overmyer at the Capcom position. "I’m going to try to get a little exercise. I’d be interested to know how high I can get my heart rate just fooling around up here."

"Okay, we’ll keep you posted. Jack."

As Schmitt started exercising. Cernan noticed that the CSM’s barbecue roll was deviating. "I just figured out what happened on my PTC. here.” he told Overmyer. "With his exercises. Jack is shaking all of America in all three axes."

"Roger. He finally got to 115 on the heart rate," said Overmyer.

"Yes, the rate needles are bouncing back and forth a half a degree," laughed Schmitt as he watched his movements show on the FDAI needles that indicated rate of rotation.

Even EECOM. watching the spacecraft’s tanks, could see the effects.

17, we’ve got a serious one here.” joked Overmyer. "You might be interested. ЛИ that exercise banging around in there has destratified tank three 02. so it stirred it all up good.” The movement of the spacecraft had achieved the same effect that an internal fan had prior to Apollo 13’s explosion. It had disturbed the unwanted separation of density layers in the tank.

”Yes, glad we brought him along then." returned Schmitt’s colleagues. "We found some use for him.”

As the mission entered its final hour, one chore for the astronaut in the right couch was to install a 16-millimetre movie camera in a bracket next to his rendezvous window. This would record the view from the window looking backwards along their glowing wake. The camera did not have a direct line of sight, but rather was mounted off to one side and used a small 45-degree mirror to see out.

In the meantime, a final few items were stowed away for the re-entry. These included the ORDbAL box, the COAS optical sight, the chlorine injector and gas separator of the water squirt gun. An important aspect of stowage for re-entry was to ensure that objects were not only well secured but that their weight, soon to rise more than six times their earthly weight, and their edges and points, did not strike a crew member or cause damage, especially to the aft hull. Additionally, items above the crew had to withstand the sudden shock of the spacecraft’s impact with the ocean’s surface.

With 50 minutes to go, tasks leading up to their meeting with entry interface were coming thick and fast. The heaters that were preheating the CM thrusters were switched off, and a check was made of the two batteries that would fire the pyrotechnic devices. These were separate from the spacecraft’s three main batteries.

If either battery indicated less than 35 volts, extra energy was taken from the main supply to ensure operation. The third of the CM’s other three batteries was connected across both of the main power busses. The batteries would become the spacecraft’s primary electricity supply after the fuel cells were cut adrift with the service module.

Л check was made to see that their backup attitude reference, the GDC. was not drifting excessively. If it was, then two instruments that were relying on its output had to be treated as suspect: the right-hand FDAI and the RSI, the latter being the instrument that showed the direction of their lift vector and therefore a key item on a manual re-entry.

As ever, there was a backup system for the PCNS, although in this case the philosophy was a little unusual because, in the event of failure, it was not meant to replace the PCNS in order to allow the mission to continue. As its name indicated, the abort guidance system (AGS pronounced biggs’) was intended to be used only in ease of an abort.

Given the limited capabilities of the lunar module, it was considered to be almost impossible to accomplish a landing without a working guidance system. The highly optimised nature of the approach trajectory and the complexities of keeping the spacecraft balanced on top of the descent engine’s thrust meant that there was very little room for error. A fully functioning backup system would have been excessively heavy. Yet there were reasonable concerns about the possibility of the PGNS failing while two men were descending to the rocky surface of a hostile world. Its systems were complex, exotic and very new. It was decided, therefore, that if the PGNS did fail, the descent to the surface should simply be aborted, the descent stage should be jettisoned, and the ascent stage should fire its engine to return to orbit. To achieve this, designers added a separate pared-down guidance system, the abort electronics assembly, which included a computer at its heart, the AGS, which was even simpler than that in the PGNS. Instead of having its own heavy IMU, the AGS received its attitude reference from a set of body-mounted gyros and accelerometers. ‘These were intrinsically less accurate and more prone to

drift than a full IMU, but they would only be required for a short period while the abort took place.

Throughout a normal descent, the lunar module pilot closely monitored the AGS to ensure that its knowledge of velocity and position kept track of the PGNS. At regular intervals, he fed it updates from the more accurate system and then watched how the two compared. Then, if the crew lost the PGNS, the AGS was ready to take over and automatically guide them to a safe orbit, from which the CSM could rescue them.

The LMP worked with the AGS using an interface that was basic even compared to the DSKY, the data entry and display assembly (DEDA). It had one single 5-digit display and a simplified keyboard. Since it had little in the way of a user-friendly interface, he had to get down to its machine level to use it. For example, to access its memory he had to supply the address where a value was stored in a manner that will be familiar to people who used the very early microprocessor machines of the 1970s. In order to achieve high functionality, he had to understand it well and be slick at interrogating it. It could keep an LMP very busy. By Apollo 17, Jack Schmitt and the engineers he worked with on simulations had done so much with the AGS that they believed they could have used it to continue to a landing had the PGNS failed.

While Alan Shepard and Ed Mitchell were activating Antares on Apollo 14, flight controllers noticed that a single digital bit they were monitoring was being intermittently set. This bit reflected the state of the Abort pushbutton and appeared to indicate the button had been pushed, which it had not. Fred Haise, the Capcom,

passed on the news to the crew: "Antares. we’re showing the abort bit set, and we’re working on a procedure to reset it.”

‘’Okay. That’ll be great, thank you," said Mitchell. "We’re pressing on with the DPS pressurisation.”

A Tew minutes later as mission control watched telemetry, Haisc asked Mitchell to help with a little troubleshooting. "We’d like to do a Verb 11. Noun 10, Enter; 30 Enter; and look at that bit again."

This dialogue with the computer asked it to display a digital word which included the suspect bit on the DSKY. The crew now had a visual indication of wiiich way the bit in question was set.

"While we’ve got that display up. Ed.’! said Haise. "could you tap on the panel around the Abort pushbutton and see if we can shake something loose?’’

Mitchell tapped around the pushbutton and quickly saw how the bit’s state responded. "Yes, Houston, it just changed while I was tapping there.”

"You sure tap nicely.’’ said Haise.

"I’m pretty good at that,” replied Mitchell.

Without a LM to disassemble after the mission, engineers managed to work out that the problem was a short circuit caused by a metallic object that had been inadvertently sealed within the Abort pushbutton itself on its manufacture. This, and the similar problem that beset Apollo 15’s SPS, meant that NASA and its contractors began to x-ray all their switches for internal contamination.

Apollo 14‘s problem was that if the bit were to be set at the moment of PDI, then instead of commencing the descent, the computer w’ould use the DPS to abort the mission and return to a safe orbit. As Antares passed around the Moon’s far side, a team from Mi l’ led by Don Eyles figured out a workaround. It required Mitchell to feed instructions to the computer just before ignition so that PDI could occur automatically and the abort bit would be ignored. ‘I he procedure also required them to manually raise the engine’s thrust to maximum at 26 seconds, and then punch in more instructions to allow P63 to continue with the bit being ignored. Mitchell managed to enter all the verbs, nouns and values as required, saving a S500 million mission from w’hat was probably no more than a rogue blob of solder.

When President Kennedy gave the United States his lunar challenge, he never stipulated that the crew should go outside. Land on the Moon and return safely to Earth; that was the challenge. Yet it was simply assumed from the outset that extra vehicular activity (EVA) on the surface would be part of the show. Right or wrong, a walk on the Moon would be the climax of the mission. And in the minds of most people, the Apollo 11 moonwalk would climax the entire program.

POSTLANDING

Once on the Moon, it took a while for the LM’s two-man crew to transition from the role of pilots to that of explorers. Their ship was still fully powered and configured for flight. It was particularly important that the crew and mission control be ready for lift-off in case some problem with the spacecraft was identified.

Apollo 11, again riding its luck as the first landing, came astonishingly close to invoking this scenario. As soon as the landing had been achieved and the engine shut down, the flow of fuel through the heat exchanger also stopped. This heat exchanger had been using the warmth in the fuel to heat the extremely cold helium being used to pressurise the propellant tanks. The contents of the supercritical helium tank were then vented, which unintentionally froze a slug of fuel in the fuel line. Engine heat warmed the rest of the line and caused its internal pressure to rise beyond the limit of the sensor. Flight controllers and managers began to confer, working towards a decision to lift-off, or at least to burp the engine before the line could burst and spray hydrazine onto hot components. As they deliberated, the heat eventually worked its way to the frozen slug and melted it. The pressure in the line fell dramatically, and so did the tension in mission control.

As illustrated by this tale, the moments after a landing were tense ones for people in Houston as well as the crew. The final drop to the surface had ended in a minor jolt that, though not seen as serious, had nevertheless applied a deceleration as large as any since the LM had been powered. This was a profound transition between modes. If something were to go wrong – perhaps damage to a tank or an electrical

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

DOI 10.1007/978-1-4419-7179-1 11. © Springer Science+Business Media. LLC 2011

connection shaken loose – then it was more likely to be a problem at that moment, just as on Earth the cheering and plaudits dared to begin.

Go/no-Go decisions had punctuated the flight thus far and now the flight director wanted his controllers to make another, this time on whether the surface phase of the mission should continue – but he wasn’t going to call it ‘Go/no-Go’. It had been pointed out by Bill Tindall that in the heat of an emergency, ‘Go’ could easily be construed as advice to get out of there as much as an instruction to continue with the planned mission and stay on the surface. Therefore this call was ‘Stay/no-Stay’.

Three opportunities were set aside for a possible lift-off soon after landing: T-l was immediate, with the intention to catch up with the CSM on its current orbit. There were only a few minutes available for the Stay/no-Stay decision at T-l to be reached. It would be based on ‘first impressions’. The next opportunity, T-2, would also catch up with the CSM on this orbit but the price of a little more decision time on the surface was a modified rendezvous arrangement. It would be based on a more detailed examination of the telemetry. A third opportunity had to wait two hours while the CSM came back around the Moon so the T-3 decision to Stay/no-Stay could be a little more leisurely. On Apollo 11, the crew began a simulated countdown towards lift-off at T-3 to keep them on top of the procedures, given that they had not practised them for some time. With the operational familiarity gained from Apollo 11, future crews felt such a procedure was not necessary and dispensed with it.

Pete Conrad became a little irritated at the time it was taking for mission control to come up with a decision on T-2. When he prompted them, he raised a little mirth. "Okay, Houston. Are we Go or Stay?”

“Intrepid, Houston," replied Capcom Gerry Carr. “You’re Slay; and if you’d like to recycle and try it again, we’ll talk to Sims."

"No!" laughed Conrad and Bean in unison.

"No, not this time." said Conrad.

The crew and the mission control team had carried out many simulations, usually with difficult problems thrown in. After each shot at simulating a landing, it was common practice to ‘recycle’ and try again immediately. In some respects, their landing had been like a tame simulation but during the launch from Earth, when they had been hil by lightning. Conrad had compared that experience to a particularly tricky simulation. With this in mind, Bean threw a friendly brickbat at the Sim Supervisor. "Yeah. We’re still mad at him for earlier in the week."

Crews did not vent the propellants in the descent stage’s tanks. To do so would have contaminated the surrounding area with noxious chemicals. Only helium was vented to avoid the heal of the lunar day raising the internal pressures of the helium tanks. Then with the LM’s oxygen supply set to feed the cabin instead of the suits, they could remove their helmets and gloves to permit greater freedom to talk and operate the systems.

The next flurry of activity surrounded the guidance system. The platform had to be realigned and to accommodate it, window shades were put in place so their eyes could adapt to view stars through the alignment telescope. The dish of the rendezvous radar, which sat just in front of the telescope’s external optics, was parked face down so it would not obscure the field of view. After the platform had been aligned, the commander would reposition the antenna to face upwards for the remainder of their slay. Rather than use two stars as in a conventional realignment, the crew used the accelerometers in the guidance platform to deduce the direction of gravity. With that vector and a sighting on one star, the alignment of the platform could be restored.

On some missions, after the platform had been aligned, Houston would take control of the guidance system lo perform a little science that would take advantage of their Moon-bound situation. When the spacecraft was in powered flight, the accelerometers in the guidance system measured how much acceleration was being imparted by the engines. But now they were on the Moon, the engines were off, and yet they could still feel acceleration – the gravitational acceleration of the Moon. Without a specialised gravimeter, something that would be added Lo later missions, the accelerometers were a neat means of gaining a local measurement of its strength. Ed Mitchell remembered this from the Apollo 14 flight. "One of the things they did with the platform was to torque [it] to calibrate the accelerometer on each axis in the gravitational field. And, by comparing that with the known calibration of the accelerometers, they could come up with some sort of estimate of the gravitational field. Then they returned the platform to its initial configuration that wc [had] aligned it in as a result of the star sighting."

The next task was to configure the batteries.

Before a traverse, the rover had to be loaded with all the items the crewmen would need. The rear chassis panel had a fixture for a pallet of tools. This was loaded with items such as hammer, tongs, rake, shovel, core tubes and sample bags. There were bags under the seats for cameras, film magazines, rock samples and other ancillary items. A bag containing a hose was hung from the seat backs to help a crewman in case of an emergency. This buddy secondary life support system (BSLSS) allowed the two men to share cooling water in case the cooling system on one PLSS failed. If it had to be used, it would mean the immediate end to the EVA and the crew would return to the LM. There was no need to share oxygen because each crewman had a spare supply of this in their OPS.

Apollo is very unusual in the history of planetary science, lor although it carried the kind of instruments that most probes to the Moon and planets would sport, it had one extra resource – a human. Therefore, w’hile the instruments of the SIM bay were looking down at the Moon, the command module pilot, if he was not too busy, could also peer out of a window and report and photograph what he saw.

Coming as they did from the test pilot fraternity, none of the Apollo CMPs w7as a career scientist. However, like most of their colleagues exploring the surface, their profession made them very skilled observers, adept at perceiving, remembering and describing details of what they saw7. Moreover, compared to the photographic films used throughout the Apollo programme for image capture, the dynamic range of the human eye. and its ability to discern subtle hues, made it more able – especially when coupled with a curious mind – to scan intelligently for interesting detail.

The increasing scientific focus of the later Apollo missions meant that it was not only the surface crews who were trained intensively in geology. The CMPs also received instruction in the subject from Farouk El-Baz. an enthusiastic teacher who focused on the interpretation of a landscape from an aerial perspective. In exercises prior to their missions, they were taken up in small aircraft to fly over the types of terrain on Earth that u’ere considered likely to assist them in interpreting the lunar terrain. This often meant flying above volcanic landscapes in the western deserts of the United States and Hawaii. In lunar orbit, the CMP could then seek features that might be of further interest to El-Baz and his colleagues. Since the photography from the cameras in the SIM bay w7ould not be seen until they had been processed after the flight, the CMP could help scientists to plan further photographic sorties while the mission was still in progress. An example of this occurred during A1 Worden’s solo tenure in Endeavour as he coasted over western Mare Imbrium. The Sun had just risen across this basaltic expanse and the lighting was so shallow that it brought out the more subtle undulations in the surface, as he explained to Capcom Karl Ilenize.

“.At this low7 Sun angle, I can very clearly see some lava flow’s coming out of what appears to be a ridge, extending in both directions from the ridge. And I wasn’t set up this time to take a picture of it, but it might be interesting on the next pass if we could get a PAD to take a picture of that."

"Very interesting. Which window7 are you looking out?”

“I’m looking out window 3." This was the circular window on the main hatch.

“Thank you,” replied Henize. “Sounds like an interesting observation, and I’m sure the guys down below will be sending you up more work to do as a result. Be careful there, now.”

The scientists duly passed up instructions for Worden to use his Hasselblad and the mapping camera to photograph these features. The extremely thin flows he saw were compelling evidence that areas like Mare Imbrium had been filled by lava in a sequence of small eruptions over a long period of time. He talked about them after the flight.

“I get the impression that there are just hundreds of flows that filled up the basin. They all look like, for example, you’d take a pail of water and sluice it out into a skating rink and let it freeze in place; then, if you do that 15 times around the same area, you would get this overlapping mixed up ice. All the flows were very thin and appeared as if they came out and froze in place.”

Worden’s flight path took him directly over Mare Serenitatis, another roughly circular sea of frozen lava that had filled an impact basin. On the west side of this 700-kilometre plain stood an impressive range of rounded mountains, the Apennines, beyond which, his colleagues were exploring a magnificent embayment cut through by the meanders of Hadley Rille. There was another range on the eastern side of Serenilatis that was rather less majestic, known as the Taurus Mountains. Within this highland area, south of the crater Liu row. stood a cluster of fine hills between which were a series of valleys whose floors were as dark as any place on the Moon. Worden regularly observed this area and closely studied how the hues of the Serenitatis lavas changed towards the mare shore. On his third viewing opportunity, he looked more closely at the dark valley floors.

“Okay, fm looking right down on Littrow now. and a very interesting thing. I see the whole area around Littrow. particularly in the area of Littrow where we’ve noticed the darker deposits, there are a whole series of small, almost irregular shaped cones, and they have a very distinct dark mantling just around those cones. It looks like a whole field of small cinder cones down there. And they look well, I say cinder cones, because they’re somewhat irregular in shape. They’re not all round. They are positive features, and they have a very dark halo, which is mostly symmetric, but not always, around them individually."

“Beautiful, Al,” replied his Capeom Bob Parker.

This report of cinder cones, along with Worden’s earlier descriptions of distinct colourations in the region, became one of the major reasons for sending Apollo 17 into one of these valleys 17 months later to seek evidence of recent lunar volcanism and determine whether the dark mantling was pyroclastic in origin. The pull of volcanics was sufficient to counter arguments from other quarters that to land at the edge of another major mare would essentially be a repeat of Apollo 15. even to the extent that the ground track would cover much the same landscape. In turn, this latter point prompted the decision to assign Apollo 17‘s SIM bay a different set of instruments in order to further study that track.

It has been said that because the CMPs on the J-missions had been trained to look for volcanics, that is exactly what they found. Worden’s ‘cinder cones’ observation is a case in point. One of these cones was later named Shorty crater by the Apollo 17 crew. When they visited it, they were astonished to discover deposits of bright orange soil on the rim of what was obviously an impact crater, not a volcanic cone. As so often happened on Apollo, and with any true exploration, theories proved lacking and had to be replaced with new interpretations based on ground truth.

The twist in the story of Shorty was that although this crater was of impact origin, as shown by its nature, its orange soil did turn out to be related to volcanic processes. The soil consists of Liny orange glass beads that have been dated at 3.64 billion years old when, as molten rock, they were sprayed from a ‘fire fountain’ to rise perhaps hundreds of kilometres into the lunar sky before falling into the valley, soon to be buried by a lava flow. The dark mantling across the whole valley was a mixture of ancient orange and black pyroclastic glass. At one end. light-toned avalanche deposits had been laid on Lop and the impact that created Shorty had simply punched through to excavate the ancient volcanic deposits as an ejecta blanket of dark material around the crater.

The integrity check was successful and the crew proceeded with the jettison. It was timed to occur w’hcn the stack, which was holding its attitude constant with respect to the stars, had the LM on the side of the CSM that was facing the Moon. This occurred only once per orbit. Л crewmember pressed a guarded push-button to send a signal to the pyrotechnic circuits. This detonated an explosive cord around the circumference of the tunnel to cut it cleanly.

“And, it’s aw’ay clean. Houston.” said Worden as the remaining air within the tunnel gave the LM a mild push away from the CSM. along with the tunnel and the discarded items in the cabin.

“Roger, copy,” empathised Parker. “Hope you let her go gently. She was a nice one.”

“Oh, she w’as at that,” agreed Worden.

But the trials of Apollo 15’s rendezvous day were not over. The procedures called on the crew to make an RCS burn to open the distance belw’een them and the LM, details of which had been entered into the computer earlier. Scott was then to use P41 to execute this burn.

“Houston, 15,” called Scott. “Question on the separation manoeuvre. Do you want us to burn residuals in P41, or just make 1-foot-per-second burn?”

“Roger. Dave,” replied Parker. "Burn them in P41. please.”

Scott looked at the DSK Y and was not happy with what it was telling them. The magnitude of the burn in the three orthogonal axes was displayed in front of him, and one component was telling him that the burn would take them forward, towards the very object they were trying to avoid. Additionally, the delayed jettison meant that it was difficult to keep a check on the LM because the discarded spacecraft was nearly in line of sight to the Sun.

“Houston, P41 says seven-tenths forward,” pointed out Scott. “Yes. seven-tenths forward, seven-tenths up.”

“Roger. Dave,” confirmed Parker.

“And forw’ard takes us right back to the LM,” reminded Scott.

”Stand by, Dave.’- said Parker, the MOCR’s only point of contact with the crew.

"We’re looking into that, of course."

‘’Okay. We got about a minute and 15 seconds or so.”

‘■Roger.”

Having pointed out the inconsistency. Scott continued with preparations for the burn, trusting that the flight controllers would know what was best. After a pause, he announced, “Average g is on.” The computer had begun to measure acceleration and was about to begin the burn.

‘’Ah, hold the burn, Dave.”

“Okay, we ll hold the burn,” said Scott.

The confusion bciween the MOCR and the spacecraft continued as each party began to use differing terminology to describe the position of the LM with respect to the CSM. Terms such as ‘in front of, ‘dead ahead’ and ‘trailing’ can have multiple meanings in the three-dimensional regime of space. Therefore when mission control suggested that Scott should simply point towards the LM and fire the thrusters to move away from it, Parker compounded the confusion by saying, “We need you behind him and then a firing of retrograde.” Unfortunately, the w’ord ‘retrograde’ has a precise meaning in orbital mechanics: opposite the velocity vector. Since they were leading the LM around the Moon at this point, the instruction’s strict meaning required that they manoeuvre the CSM to be trailing it. then slow’ down their orbital motion slightly in order to increase the separation, which was not what was intended. It wns an example of vehicle-based and orbital-based references being mixed. The MOCR eventually tightened up its language.

“Okay, Dave,” called Parker. “How about 2-foot-per-second posigrade, as long as you’re in front of him. Understand?"

”Okay; so that’ll be a minus-.v dclta-v for two feel per second at our present attitude, right?” checked Scott.

“Roger. That affirm. Dave."

‘’Okay. We’re all in the same frequency. We’ll do that.”

Between the Moon and Harth, there came a point where the gravity of the approaching body became stronger than that of the receding body. When this point of gravitational equality was reached, it was customary for mission control, and especially those concerned with flight dynamics, to switch their frame of reference from one world to another. However, because the Moon itself w’as in motion around Harth. the numbers representing the spacecraft’s speed and position appeared to jump. Journalists, more used to figuring out the trajectories of political figures rather than those of spacecraft, found it difficult to make sense of this change in the velocity figures being fed to them by the NASA public affairs people, and some got the impression that a ‘harrier’ was being crossed and that this must surely be felt by the crew.

Mike Collins later related how Phil Shaffer, one of the flight dynamics controllers in the MOCR struggled to explain the truth to reporters as Apollo 8 entered the lunar sphere of influence: ’’Never has the gulf between the noil-technical journalist and the non-journalistic technician been more apparent. The harder Phil tried to dispel the notion, the more he convinced some of the reporters that the spacecraft actually w’ould jiggle or jump as it passed into the lunar sphere. The rest of us smirked and tittered as poor Phil puffed and laboured, and thereafter we tried to discuss the lunar sphere of influence with Phil as often as w’e could, especially when outsiders w’ere present.”

As a homeward-hound Apollo 11 crossed the imaginary line between the gravitational spheres of influence of the tw’o worlds. Capcom Bruce McCandless called the spacecraft to inform the crew: "Apollo 11. this is Houston. Stand by for a ’mark’ leaving the lunar sphere of influence.” He then indicated the moment’s passing, "Mark. You’re leaving the lunar sphere of influence. Over.”

Collins saw; a chance for some mischief. "Roger. Is Phil Shaffer down there?”

The FIDO console w’as being manned by Dave Reed rather than Shaffer. "Negative,” said McCandless. "but w’e’ve got a highly qualified team on in his stead.”

"Roger. I wanted to hear him explain it again to the press conference.” Leased Collins, ’’’fell him the spacecraft [definitely] gave a little jump as it went through the [equigravisphere]. ’ ’

"Okay. I’ll pass it on to him. Thanks a lot." said McCandless, "and Dave Reed is sort of burying his head in his arms right now.”

Crews continued to play with this confusion throughout the programme. As Endeavour headed home. Capcom Joe Allen let Apollo 15‘s crew know they had entered Earth’s sphere of influence. "Be advised at my mark, you are leaving the sphere of lunar influence; and it’s downhill from here on in… Mark!”

‘■Roger. Thank you, Joe,” replied Scott. "That’s nice to know.”

"Did you notice anything there. Dave? Discontinuity in velocity or anything like that?” Leased Allen.

"Well, Joe," returned Scott. "That’s one of the mysteries that we’ll probably have to keep to ourselves.”

"I was afraid of that,” replied Allen.