Category How Apollo Flew to the Moon

By concentrating almost single-mindedly on the goal of a manned lunar landing, secondary considerations like landing accuracy and science had taken a back seat. In the event. Apollo 11 had landed about seven kilometres beyond its planned site and for some time, no one knew exactly where they were. Not even Mike Collins had been able to see Eagle through his sextant – a powerful optical instrument built into Columbia’s hull. The science payload had been severely limited by mass constraints and lack of time. Future missions would make amends because the United States had invested heavily in the infrastructure to support Apollo and wanted to see results. It also demanded justification for the continuing costs. Fittingly, science became that justification.

To gain knowledge from the Moon. NASA had to go to sites where Earth-based and orbital imagery suggested that answers to questions might lie. However, given the limited walking range of an astronaut on the lunar surface, the ability to land "on target’ became paramount. Although Apollo 12 was not sent anywhere of particular geological importance, it was given a very small target to aim for. Specifically, it was to land within walking distance of Surveyor 3. a small robotic lander that NASA had sent to Occanus Procellar urn in April 1967.

The mission courted disaster in its first minute when the vehicle flew through a rain cloud and invoked a lightning strike. Regardless, the crew’ continued to the Moon amid fears that their command module may have been damaged by the surge of power that had passed through it. In the event, the CSM Yankee Clipper proved to be unharmed, and on 24 November 1969 Charles ‘Pete’ Conrad and Alan Bean landed their LM Intrepid some 1.500 kilometres west of where Eagle had landed and a mere 200 metres from Surveyor 3. This demonstrated that ground controllers and crew could bring a lunar module down exactly where they wished. Richard Gordon, orbiting overhead, confirmed their position by spotting both the LM and the Surveyor on the surface through his sextant.

Since Apollo 12 was an II-mission, Conrad and Bean made two moonwalks. On the first they laid out an ALSEP which was an autonomous scientific station that operated on the lunar surface for many years after they left. The next day they hustled across the surface taking a circular route of over a kilometre, pausing at preplanned points of interest on the way to visit the Surveyor probe. After examining

and photographing the probe, they removed pieces to enable researchers to study how well the hardware had survived 31 months of exposure to the lunar environment. In terms of public relations, the low point for this fun-loving crew was when their television camera was ruined early in the first moonwalk by being inadvertently pointed at the Sun. TV networks struggled to provide a visual accompaniment to the crew’s voice communication and audiences quickly became bored of listening to indistinct and often arcane yakking by the two guys on the surface. Nonetheless, like every crew after them, Conrad’s and Bean’s two joyous forays out on the surface yielded samples of greater bulk than the previous mission, and the scientists were more than happy with what they brought back. In particular, tiny grains of a very slightly radioactive rock type began to lift the lid on important aspects of the Moon’s early history.

Despite concern that it may have been damaged during launch, Yankee Clipper’s successful splashdown concluded a successful, if charmed 10-day mission that was marred only by the loss of the TV coverage.

At 8.9 seconds to lift-off, a command was sent to the Saturn V to begin the ignition sequence for the five F-l engines at the base of the first stage. The Saturn’s instrument unit then sent start commands to each engine, their timing slightly staggered in order to prevent a single jarring ignition transient being imposed on the launch vehicle. First to be commanded was the centre engine, followed at quarter-second intervals by diagonally opposed pairs of engines. Each engine then went though an elaborate sequence that was carefully choreographed to minimise rough starting, with, if all went well, all engines attaining full thrust by T-l second.

A description of the astonishing F-l engine is necessary before going through its ignition sequence. The most prominent component of the engine was the bell or nozzle, usually seen with an extension added to improve its performance. This tapered to the throat and a cylindrical space, not quite a metre across, called the combustion chamber. At the far end of the chamber was a thick steel injector plate with hundreds of slightly angled holes like a giant shower head. Alternate rings of these holes sprayed jets of fuel or oxidiser that impinged and burned together. The walls of the chamber and nozzle were constructed of piping through which the

kerosene fuel was circulated to cool the structure, prior to it being sprayed through the injector plate.

As is to be expected for any fluid system, the propellants arrived at the engines with a pressure that depended on the height of the fluid above – its head – and any added by the pressure of the gas in the top of the tank. This was not nearly enough to inject fuel and oxidiser directly into the chamber. The huge internal pressures from their combustion would simply have forced the propellants back through the holes in the injector plate. Each engine was therefore provided with a high-pressure pump arrangement to force propellants into the combustion chamber. This dual turbopump was mounted to the side of the combustion chamber and was driven by burning some of the propellants. In an action somewhat similar to that in a jet engine, the hot gases from this combustion forced a turbine to spin a shaft which drove the pumps. The final task for the turbopump’s exhaust gases was to be expelled at the join between the engine bell and the nozzle extension via a large wrap­around manifold. Although the turbopump exhaust was hot, the combustion gases coming from the chamber were far hotter and by forming a thin film of relatively cool gas, it served to protect the extension from erosion. Four pipes, two each for fuel and LOX, led from the pumps to the injector via valves that controlled the engine.

The ignition sequence for the F-l began with firework-like igniters going off, some of which burned to ignite the turbine propellants, others to ignite its fuel-rich exhaust gases when they reached the engine bell. They also burned through electrical links to provide a signal to begin to open the LOX valves and pour LOX into the combustion chamber. This in turn, caused another valve to open to send propellant

to power the turbopump. As the turbopump accelerated, the pressure in the fuel lines rose and burst a cartridge of hypergolic[1] fluid. As its contents were injected into the chamber followed by fuel, engine start-up was ensured by its spontaneous ignition with the LOX already in the bell. When combustion was detected in the chamber, the fuel valves opened, flushing ethylene glycol out from the cooling pipework and into the chamber where it helped to soften the thrust build-up as the engine strove to assume its steady-state condition.

For about a second after full thrust had been achieved, great flames roared from below the static spire of the Saturn V while sensors measured each engine’s perfonnance. In that second, and every subsequent second of the S-IC’s powered flight, each engine consumed nearly one tonne of kerosene and almost two tonnes of LOX – 13 Vi tonnes across all five engines – as the vehicle sat at full power, waiting

Graph of thrust build-up of the five F-l engines on Apollo 8’s S-IC. Note the staggered start of the engines and the hiccup as the four outboard engines ingested helium from the pogo suppression system. (Redrawn from NASA source.)

Diagram of the linkage arrangement of a hold-down arm. (NASA)

for the confirmatory signal that they had achieved the required thrust and the Saturn V could be released.

A sense of the prodigious power that was being expressed by this machine can be gained from a little maths. One of the most basic equations in physics is that for kinetic energy. A mass that is moving has a quantity of energy that would be expressed if it hits something stationary – think of a car hitting a wall. While carefully avoiding an equation in this book, kinetic energy can be worked out by taking half the mass and multiplying it by the square of the velocity. To apply this to the Saturn V, during each second of operation, the energetic chemical reaction in the combustion chambers of the five F-l engines made 13.4 tonnes of mass leave the engine at almost three kilometres per second. Therefore we multiply 13,400 by 0.5 and further multiply it by 3,000 squared. The answer we get is 60 billion joules of energy. If we express that as energy per second, in other words, power, then we find the output power of the Saturn first stage was 60 gigawatts. This happens to be very similar to the peak electricity demand of the United Kingdom.

As soon as the escape Lower was jettisoned, the rules changed again on what to do in the case of emergency. The vehicle was now being flown in abort mode two, which took account of the fact that, to all intents and purposes, the remaining stack was in space and catastrophic break-up from aerodynamic forces was no longer a concern. This abort scenario called for the CSM to detach itself from the rest of the stack and use either the service module’s main engine or its small RCS thrusters to increase its distance from the failing launch vehicle. Once clear, the CM would detach from the SM and descend on parachutes to a normal splashdown in the Atlantic at some point downrangc. These abort rules applied until the S-II was spent.

As the stack passed over NASA’s network of communication stations around the world, its orbit was carefully measured and intensive calculations were performed to enable FIDO to choose exactly when and how the TLI burn should be made. This information was radioed up to the Saturn’s instrument unit, which would control that burn. In particular, the computed lime of ignition was back-timed to a moment 9 minutes and 38 seconds earlier, when the instrument unit needed to begin Timebase 6. a choreographed sequence of events that would lead up to ignition and through the burn.

The start of Timebase 6 was indicated to the crew when a lamp on their panel came on for 10 seconds. This was one of the cluster of lamps that had informed them of the status of the launch vehicle throughout its flight. At this point, the Saturn’s computer checked the state of a switch in the CM to verify that the crew really did still want to go to the Moon. This switch was provided so that further preparations for ignition could be terminated if a problem surfaced that necessitated cancelling the lunar phase of the mission. If all was progressing well, valves were closed to stop the S-IVB’s tanks from venting, and a burner was ignited to heat helium gas that would repressurise the tanks, to prepare them for operation.

At 100 seconds before ignition, the computer display blanked to let the crew know that the guidance system had begun to measure whatever acceleration the S-IVB was about to imparl. With 80 seconds to go before ignition, the aft-facing ullage motors within the APS modules filed to push the fuel and oxidiser to the base of their tanks in order to settle them and provide a little head of pressure into the engine. The crew still had options to stop the S-IVB from starting up. If the)’ did so earlier than 18 seconds prior to ignition, the inhibit switch would work; otherwise, an adjacent switch, one which normally made the second and third stages of the Saturn separate, would have to he used.

At eight seconds prior to ignition, valves were opened to route hydrogen fuel through the engine to chill its pipes and ducts. As this was a restartable engine, the ‘start’ tank had been refilled with hydrogen during the first burn. At the calculated time of ignition, the contents of this tank were discharged through the pump turbines, spinning them up and increasing propellant pressures in the pipes that led to the core of the engine. The propellant valves, which had been cracked open slightly at this point, then began to fully open, allowing a rush of fuel and oxidiser into the combustion chamber where an ASI initiated full combustion and the engine brought itself up to full thrust.

An entirely different technique to determine position and velocity was brought to bear in the spacecraft which relied on sightings of the stars, Earth and the Moon. It was designed by MIT under the direction of Charles Stark Draper. To reinforce his faith that his team could successfully come up with an accurate system to navigate to the Moon and back, and somewhat to the mirth of folks at NASA, he put himself forward as an astronaut candidate. The MIT system was based on a computer, an inertial platform, and optical devices; one of which was directly descended from an instrument used by generations of sailors to navigate across the world.

Set into the hull of the command module, opposite the hatch, were two apertures that accommodated the spacecraft’s optics. The smaller was for a so-called telescope, although it hardly justified the name as it had only a ‘times-one’ magnification. Neil Armstrong later quipped, “NASA is probably the only organisation in history that’s been sold a one-power telescope.” Its function was to give the CMP a wide-angle overview of the constellations visible at that side of the spacecraft to assist in aiming the other instrument, the sextant.

The second aperture in the hull was a disk and slit affair that accommodated the

objective optic of the sextant, a 28-power device used by the CMP to measure angles. Like a mariner’s sextant, it had two lines of sight with the ability to move one with respect to the other. The version used by marine naviga­tors for hundreds of years works by viewing the horizon through a small telescope mounted on an arc which sweeps through one – sixth of a circle (hence the name ‘sextant’). A mirror arrangement on a radial arm permits the image of a celestial body (the Sun, Moon or a star) to be aligned with the view of the horizon. The

Apollo 16 command module Casper in lunar orbit showing the exterior apertures of the sextant and telescope. (NASA)

Line of to horizon

angle between the two could then be read off a scale at the circumference of the arc. If carried out when the Sun was at its highest point, this measurement would yield the ship’s latitude.

The role of the sextant on the Apollo spacecraft was similarly to measure angles, and it worked in much the same way, but with major refinements. It also had two lines of sight – one fixed, the other movable – both of which peered through the slitted disk in the spacecraft’s hull. The fixed line of sight, also called the landmark line of sight (LLOS), had to be aimed by controlling the attitude of the entire spacecraft. A dense filter was placed in its light path so that the relatively bright horizons of Earth or the Moon would not swamp the stars with which they were to be compared. The movable line of sight was usually aimed at a star, and was thus called the star line of sight (SLOS). It could be swung up to 57 degrees away from the fixed line of sight to bring the image of a star into alignment with the image of the horizon. It was important that the star image be placed on that part of the horizon that was nearest to or furthest away from the star, depending on which horizon was illuminated by the Sun. Because the computer was closely integrated with the optics, the angle between the two lines of sight could be directly fed to it and used in its calculations of the state vector. The entire optical head could be rotated about the fixed line of sight and, as it did so, the disk on the outer surface of the spacecraft also turned to accommodate it. A crude sextant had been tested during the Gemini programme with mixed results. Mike Collins had tried using two hand-held models without success on Gemini 10. Later on Gemini 12, Buzz Aldrin brought one into play to help with angular measurements during a rendezvous after the spacecraft’s radar had failed.

This ability to measure the angle between a planet’s horizon and a star was what enabled onboard determination of the state vector to work. As a spacecraft coasts from one world to another, the apparent position of either orb against the stars will change, and this change will reflect the progress of the craft along its trajectory. The angle between the planet and the star at a particular time can only be valid for a single trajectory given the laws of celestial mechanics and the layout of our solar system. It can therefore be used by an onboard computer to calculate their current state vector. Repeated measurements could be used to refine the state vector. Because Program 23 in the computer was being used for this task, crews referred to their navigation task as doing a ‘P23’.

During the system’s development, experiments carried out on Gemini flights revealed difficulties of knowing exactly where Earth’s horizon was. First, having selected a star, there was a 50:50 chance that the nearest point of a planet’s horizon would be in darkness. To work around this, the CMP had to tell the computer whether he was using the nearest point or, if it was dark, the furthest point of the horizon relative to the star he was using. The second problem was that optical navigation was most sensitive when the spacecraft was near the planet on whose horizon the CMP was trying to sight. Unfortunately, the nearer they were to Earth or to the Moon, the less well-defined was the horizon. Earth’s atmosphere blurred the precise edge of its limb and the Moon’s rough terrain could make its limb decidedly knobbly when observed up close. Based on the pioneering work of Jim Lovell, who gave the onboard guidance system a workout dur­ing Apollo 8, MIT set up a simulator to train the astronauts how to choose an appropriate horizon when trying to mark on a nearby Earth or Moon.

During the flights, the CMPs made it a matter of pride to excel in their navigation exercises, even though, in most cases, their results were only meant as a backup in case communications were lost. Nevertheless, a friendly rivalry existed between some crews and the trajectory experts on Earth as to whose evaluation of the state vector was the most accurate. When Lovell put the onboard navigation system through its paces for the first time, there was a lot of interest in his results. Two days out from Earth on Apollo 8, and one day

from the Moon, Lovell informed mission control of his progress with the P23 navigation work. *Tt might be interesting to note that after sightings, we ran out P21, and we got a pericynthion of 66.8 [nautical] miles.”

What Lovell had done was to use P21 in the spacecraft’s computer. This program’s task was to deter­mine the spacecraft’s path across a planetary surface. If the crewman entered a time, it used the current state vector to return three values; the spacecraft’s latitude and long­itude directly below the ship at that time and its altitude, also at that time. As he knew roughly when they should arrive, he tried entering times at 10-minute intervals around their expected closest approach. With each advancing time entered, he noted how their predicted alti­tude above the lunar surface dropped, reached a minimum value, and then began to rise again. The point where it reached a minimum was their pericynthion – the spacecraft’s closest approach to the Moon. What Lovell was saying was that his predicted value for the pericynthion was very near the ideal of 60 nautical miles (110 kilometres). Bill Anders’s wit intervened. "I knew if he did it long enough, he’d finally get one that was close.”

Lovell continued to make P23 measurements and checked his resultant state vector once again with P21. Frank Borman informed Mike Collins in Houston of his results. ‘‘Mike, we ran the latest state vector we have through the P21, and it showed the pericynthion at 69.7 [nautical] miles. We’ve got the navigator, par excellence.” This may have been a gentle dig at Collins, who had been CMP on the Apollo 8 crew before standing down to undergo surgery. Nevertheless, the flight controllers were impressed. “You can tell Jim he is getting pretty ham-handed with that P21,” congratulated Collins. “He got a perilune altitude three-tenths of a mile off what we are predicting down here. Apparently, he got 69.7 [nautical miles], and the RTCC says 70.” The RTCC was the real-time computer complex, a bank of huge IBM-360 mainframe computers at mission control that were processing the radio tracking data.

Thus, at the first test of the Apollo navigation system, two entirely different systems were coming up with determinations of the spacecraft’s position that agreed to within 500 metres at a range of 300,000 kilometres out from Earth. It was a huge

confidence boost, proving that the engineers had done their work well. Procedure dictated that Lovell’s determination would be noted, but the crew would be instructed to place a switch into the correct position to accept data uplinked from the ground, w’hereby the Earth-based solution w’ould be sent up by radio and loaded directly into the onboard computer’s memory, supplanting Lovell’s effort. Apollo 8’s navigator saw the opportunity for a little one-upmanship.

“Houston, Apollo 8,’’ called Lovell.

“Apollo 8. Houston,’’ replied Collins.

Lovell then jokingly reversed the usual procedure. "Roger. If you put your [telemetry switch] to Accept, we will send you our state vector.’’ Mission control had no such switch and the request was in jest. But Lovell knew’ his state vector was as good as theirs and Collins knew’ it too. “Touche.’’ Collins responded.

Later, as Apollo 8 coasted back towards Earth, Lovell continued his P23 navigation exercises. As he did, mission control still found it hard to say w’hether his solution or the one from Earth was better. Gerry Carr informed the commander: “Frank. Let him know the state vectors have converged. They are very, very close now.”

“Is that right, Gerry?’’ replied Borman. “Okay. I’ll tell him. Thank you.”

“Don’t let his head get big. though," suggested Carr.

“You guys arc going to make it impossible to live with him.” moaned Borman. “It always was pretty hard.”

A day later. Lovell was doing even better. Carr brought the bad news. “I hate to tell you this, Frank, but that last set of marks put your state vector right on top of the [ground’s] state vector.” Borman returned with a mock plea. "Come off that, Gerry. Come on; you promised.”

When humans are cooped up in a spacecraft for a week or two, they pose a potential waste and hygiene problem that has to be dealt with, just as much as guidance, propulsion or power. In the Apollo era, individual astronauts who were not on a specific flight assignment were regularly sent to do the public-relations rounds on NASA’s behalf to show the American taxpayer how their money was being spent. Mike Collins, the CMP for Apollo 11, reported that the all-time favourite question asked of the astronauts by the public was, "How do you go to the bathroom in space?” He answered the question in his autobiography by detailing the 20 steps a crewman had to accomplish to urinate during the Gemini 7 flight by Borman and Lovell.

On Apollo, a crewman had multiple ways to urinate depending on whether he was suited or not and whether he preferred to simultaneously dump the urine into space.

If he was suited, urine would be collected by a device worn under the suit which filled until the crewman had an opportunity to dump its contents overboard; a valve in the suit enabled the bag to be drained while suited. However, wearing a suit was not the norm over the span of a mission. Instead, the crew spent most of the coasting period wearing at least their constant-wear garments, and perhaps some coveralls. Urina­tion then required the use of a roll­over tube and a short hose that led to a bag. The contents of this bag could be dumped later, or be dumped even as the crewman was filling it, with a bypass valve to protect him from the direct vacuum of space. The exterior of the command module sported two nozzles, one each for the dumping of waste water or urine, both heated to prevent the formation of ice which would block the orifices. When the liquid was dumped into space, it sprayed into a gleaming cascade of ice crystals that sparkled in the

sunshine. At a press conference. Wally Schirra dubbed this starry display, the "Constellation IJrion". a play on Orion.

Whereas urine could be expelled from the spacecraft, faeces had to be kept on board and returned to Earth for analysis. Defecation was carried out into a bag whose adhesive flange allowed the crewman to attach it to his buttocks. Having finished his motion, the bag was removed and a germicidal sachet added. Once the bag was sealed, the sachet was ruptured and mixed with the contents by kneading. However, this degree of seal was considered inadequate because the bag contained air at cabin pressure and there was every chance the cabin might be depressurised. Indeed, a spacew alk out of the command module’s hatch was planned on the final three missions. Therefore the faecal bag was placed in an outer bag with double seals to ensure that the contents would, hopefully, remain there, even when the cabin was exposed to vacuum. However, the Apollo 16 crew’ had their doubts.

"Our concern was that with cabin depressurisation. the bag w’ould blow7 up." said Ken Mattingly during their debriefing.

John Young agreed. “Boy, would that have been a mess!"

This crew had placed their double-sealed faecal bags into a large black bag to keep them contained, but Mattingly wanted to get as much air out of the bag as possible. "I vented the bag to make sure that the big bag didn’t burst. That had nothing to do with the little bags. As far as 1 know-, none of them burst. I didn’t open the bag to find out either!"

"fortunately, you can’t really get an airtight seal on those faecal bags." said Charlie Duke. "That probably saved us. I’m sure they went down. We filled up that black bag.”

The truth was that this crew, and probably others, did not particularly like carrying their solid waste around with them in the command module. At least the LM crew’ had to lighten their ship by jettisoning their waste, including any faeces. Mattingly continued. "I guess the rationale for using the supplementary bag first was a holdover from the desire to be able to throw it aw’ay. which we weren’t allowed to do for other reasons, but I really think that’s what you should do.’’

"You should have been in the LM when we got rid of it." said Young.

"I just don’t think you ought to carry that stuff around, if you can avoid it. I think it’s a health problem if you ever get some of that stuff loose in there."

In fact. Apollo 16 was given some preliminary research to do in support of the upcoming Skylab programme. Duke was first to try one of these experiments. “The first time I had to go was right after w aking up on the first day. Ken broke out one of those Skylab bags, and I tried that the first time. I thought it w orked pretty good. Once you performed the task, the clean up was still as horrendous as ever."

While on his own in lunar orbit. Mattingly got the task of dealing with human bodily functions down to a fine art. When his crcwmatcs returned, he told them all about it. "Man. one of the feats of my existence the other day was, in 42 minutes. I strapped on a bag. went out of both ends, and ate lunch," he laughed, "by doing it all at one time."

"Fantastic," said Duke. "That’s a record!"

"I had this bag on the front end. a plastic bag on my rear, and a juice bag in my mouth,” laughed Mattingly. “That’s the only chance I had all day; with one backside pass.”

Mattingly’s mirth continued. ‘T used to want to be the first man to Mars. This has convinced me that, if we got to go on Apollo. I ain’t interested.”

The bags used on Apollo were the same as used on the Gemini spacecraft. Their design included a moulded finger tube. The theory was that the crewman could use it to help dislodge any faeees adhering to their skin. Young and his crew did not like it. "I still don’t see any use for that finger in the bag,” he said during their debriefing.

“That was one thing I w’as going to add.” said Duke. “You want to get that finger out of there.”

“Get the finger out of there to keep the faeces from hanging up.” affirmed Young, "which it does every lime the finger’s in the way. All that’s going to do is give you a bigger cleanup problem than you already got.”

Mattingly agreed: “I tried doing it the w’ay they suggested pulling the finger thing out first and then use it afterwards. All that does is smear. Absolutely no advantage to it. It looks to me like you could simplify the bag and remove one more potential weak spot in it by just deleting that whole [finger] thing.”

Frankly, doing a ’number two’ on Apollo was no joke. According to Duke, “Our technique w’as to abandon the [lower equipment bay] to whoever had to go. get naked, and go. Thai was about a 30- to 45-minute task.”

Apollo ll’s Buzz Aldrin had come to a similar conclusion after his flight. ”It certainly is messy and it’s distasteful for everybody involved to do it in that particular fashion.”

On the later, longer flights, the crew’s were Finding that towards the end. they were becoming more prone to bowel problems. Apollo 17‘s Jack Schmitt pointed out the dangers. ’’The best thing you can do is to work out some prevention of loose stools rather than trying to handle them. Loose stools is one of the major hygiene, sanitary and operational problems that you can have on a flight. I can’t emphasise that more. If it happened on a daily basis, you would eventually cut the efficiency of the crew’ member as much as 30 per cent. I think it’s important to try to understand why Apollo 17 was different than Apollo 16 in the delay of the problem ofloose stools till about the eleventh or twelfth day."

Faecal bags were stored in a container on the right-hand side of the cabin. In case of leakage or burst bags, there w’as a vent with which any odorous air could be expelled overboard.

During the coast out to the Moon, the crews lived in the command module to preserve the LM’s consumables. At least once during the coast, they took time to open up the tunnel between the two spacecraft and make a preliminary inspection of the lander. No one had seen the inside of the LM since it was on the launch pad and no one knew how well it had survived the rigours of launch. As Armstrong and Aldrin prepared to enter Eagle for the first time on their third day in space, Collins powered up Columbia’s colour television camera and gave mission control, and anyone else watching, a TV show.

“Apollo 11, Houston." said Capcom Charlie Duke. "We’re getting the TV at Goldstone. We’re not quite configured here at Houston for the transmission. We’ll be up in a couple of minutes. Over."

Collins had got the camera working early, an hour or so in advance of a planned TV show-, which caused technicians to hustle to get the signal from California to Houston by landline and convert it to colour.

"Roger. 1’his is just for free.’’ he said. " This isn’t what we had in mind.’’

"It’s a pretty good show’ here," said Duke, watching their progress on the huge Eidophor projection TV screen at the front of the MOCR. “It looks like you almost got the probe out.’’

The crew’ had earlier pressurised the LM cabin with air from the command module. When the pressures on both sides of the forward hatch had equalised, the hatch could be removed and the tunnel cleared of the docking equipment: first the probe, then the drogue. Once Armstrong got the probe out. he inspected its tip for signs of damage from the impact with the drogue during Collins’s docking.

"Mike must have done a smooth job in that docking,’’ he told Duke. "There isn’t a dent or a mark on the probe.”

"Roger.” replied Duke. "We’re really getting a great picture here, 11. With a 12- foot cable, we estimate you should have about five to six feet excess when you get the camera into the LM.” During their training, they had discovered that they were to be supplied with a short cable that would not have reached into the LM, and so they arranged a longer substitute.

With the tunnel cleared, one of the crew’ could read off the docking index angle. "We w’ent up in the tunnel checking the roll angle. Charlie, and it’s 2.05 degrees.” called Collins. "And that’s a plus,” he added. When he had docked the two spacecraft tw’o days earlier, he used visual aids to help him to line up. In a perfect docking, the angle between the coordinate systems of the tw’o vehicles would be 60 degrees. Any slight deviation from this was read off a calibrated scale in the tunnel between the two craft. The measurement was later factored into calculations when the orientation of the CSM’s guidance platform was transferred to the LM.

Access to the LM was finally gained by opening the hatch at the top of its cabin. Typically, crew’s w’ould discover small items of detritus floating around that had been left over from the LM’s manufacture. In the factory, these items would have fallen dowrn into some inaccessible corner but they could now float freely in the weightless environment of space. Often crews would see a lonely washer gently floating around the cabin. ‘ There wasn’t very much debris in the command module or the LM.’’ said Aldrin as he moved about Eagle’s cabin. "We found very few loose particles of bolts, nuts and screws and lint and things. Very few in each spacecraft. They were very clean."

The Apollo 15 crew found something a little bit different floating around Falcon’s cabin. Unlike all the earlier flights, it had been decided that Scott and Irwin should inspect their LM a day earlier, on the second flight day. "One little problem we ought to discuss with you before we go on," said Scott as he looked around. “It seems that somewhere along the way. the outer pane of glass on the tapemeter has been shattered. About 70 per cent of the glass is gone. The inner pane of glass seems to be okay. There’s no apparent damage to the tapemeter itself. 1 found one piece that’s almost an inch in size, and there’s some small ones around. We’ll try to pick it up with the [sticky] tape, and then get the vacuum cleaner later on to get it all up."

Spaceflight has a knack of taking what, on Larth, appears to be a trivial problem and make its possible consequences very profound. First, the shards of glass did not fall to the floor. They were floating about the cabin, being wafted by any passing air current, which meant that they could easily be breathed in by the crew. There was little experience of what would happen w hen sharp glass shards entered a human’s respiratory system and certainly no one wanted them to enter an eye.

Second, the tapemeter was an important instrument. It told the commander how far away something was – be it the ground during a landing, or the CSM during rendezvous and it told him how fast the object was approaching or departing. Its manufacturers had filled it with helium gas to minimise corrosion of its parts, and sealed it at sea-level pressure. Immediately Scott reported the broken glass, NASA realised that this gas had been lost, and arranged to have an identical instrument tested to see how’ well it operated with an oxygen atmosphere at one third of its design pressure, and indeed in a vacuum (as it would experience while the LM was depressurised during the moonwalks). Mechanical devices can suffer from various problems when operated in a vacuum. Lubricants can evaporate and, without a film of air to separate them, close-fitting surfaces can stick together by a process knowm as vacuum welding.

As Scott had suggested, sticky tape and their vacuum cleaner dealt successfully with the glass, and lesis showed no problems with operating the tapemeter in non­optimal conditions. By having the crew enter the LM a day early. NASA had given themselves an extra day to examine problems such as these.

While they were in the LM. some of its systems were powered up to allow’ mission control to examine the telemetry coming from them. As an aid for this, the crew’s checklists included diagrams of the spacecraft’s circuit breaker panels. Those breakers that had to be closed were black, the others white, making it easier for the LMP to match the patterns and know he had operated the correct breakers. The LM’s power budget was tight, and no one wanted to draw upon the batteries more than necessary. Just as the backup CMP had checked all the command module switches and knobs prior to launch, this was an opportunity for the LMP to check that everything was properly set for landing day it was a ‘get-ahead’ exercise. Readings were taken on the pressures in their emergency oxygen supplies and the voltages of the LM’s batteries. Checks were also made of the communications systems. Could they talk with mission control using S-band’.’ Could they talk to the CSM using VH K? Was spacecraft telemetry getting through to mission control along with the data from their biomedical sensors?

Checks complete, the LM crew powered the spacecraft down and returned to the CSM. The hatch to the LM was closed in case a meteor strike to the thinly-skinned lander dumped its atmosphere. On later flights, a second check was made of the LM on the third day.

To pursue President Kennedy’s challenge, NASA defined three methods of achieving a lunar landing and safe return: (1) direct ascent from the surface of the Earth to the surface of the Moon; (2) rendezvous of all of the mission elements in Earth orbit and then proceed directly to the lunar surface (EOR); and (3) fly into lunar orbit and send down a specialised lander while the mothership remained in space, then rendezvous upon lifting off from the Moon (LOR). In June 1962 it was decided to use LOR. Thus "rendezvous" became the key to the method. Actually, at that lime LOR was seen as the most hazardous option – we had not yet attempted a rendezvous of any type, even in Earth orbit (the first would not be for another 3 Vi years), much less around the Moon, 240,000 miles away, where, on the far side, there was no ground tracking nor any contact with the engineers in the Mission Control Center. But LOR drove the design of the entire lunar landing ‘‘system" – spacecraft (hardware and software); ground facilities, and in particular the resulting complex flight operations, techniques, and procedures.

To illustrate the necessary complexity of this method, ten distinct phases of a lunar surface mission were defined, each operating in a different domain: (1) launch from Earth; (2) Earth orbit; (3) translunar (and later trans-Earth); (4) entry into lunar orbit (and later departure from lunar orbit); (5) operations in lunar orbit; (6) descent to the surface and landing; (7) surface operations; (8) lunar ascent. (9) lunar rendezvous; and (10) Earth re-entry.

Engineers at Marshall worked through a series of potential configurations before they finally arrived at a super-booster that would have the capability to complete an Earth-orbital-rendezvous mission with two launches, or a lunar-orbital-rendezvous mission with only one – the Saturn V. Including the Apollo spacecraft and launch escape system on top, it was a 110-metre-tall behemoth. After an often acrimonious tendering process the manufacture of each of its three stages was assigned to a different company, and every part of the production was carefully monitored by NASA’s engineers. Each stage differed in size and power and each presented unique difficulties for its designers.

The first stage: S-IC – Raw power

Although the S-IC (pronounced s-onc-e) was the largest of the Saturn V stages, its manufacturer, Boeing, had relatively few problems constructing it. The design was conservative and largely a straightforward stretch of then-current technologies. To lift the Saturn V’s 3,000 tonnes, five F-l engines were clustered at the base. Steering was provided by mounting the four outer engines on gimbals. The onboard guidance system pointed them very precisely to direct their great force in the direction required to send the space vehicle where it was intended to go. The rest of the stage’s 42-metre length comprised two huge tanks, each 10 metres across, stacked one above the other. Over 800.000 litres of refined kerosene fuel called RP-1, similar to that used in jet aircraft, sat in the lower tank, while the upper tank carried 1.3 million litres of very cold liquid oxygen (LOX) – a cryogenic propellant whose temperature had to be less than minus 183 C to render it liquid. Although the LOX tank was huge, reputedly not as much as the residue from a fingerprint was permitted to be left on its interior, lest this cause an explosion when LOX was pumped in. Live enormous insulated ducts from the LOX tank ran down through the fuel tank to feed oxidiser to the engines.

Despite its dominance of the Saturn V’s profile, the S-IC’s contribution to an Apollo flight lasted a little over 2 Vi minutes. Then it was cast away to fall into the Atlantic Ocean 650 kilometres from the launch pad. where 13 examples now litter the sea floor.

Now that NASA knew how to land accurately on the Moon, it could pursue its science goals with increased vigour with a view to finding out how the Moon formed

although whether the tax-paying American public wanted to know this information is a moot point. Lunar studies before Apollo had focused upon one large feature as perhaps being a key to understanding much of the visible lunar landscape. This was Mare Imbrium. a lunar ‘sea’ that is readily visible from Earth. In reality, it is a vast circular structure, fully 1,300 kilometres in diameter, that was formed by the impact of an asteroid early in lunar history. The resultant depression was subsequently filled with dark lava. Like any impact structure, the Imbrium Basin would have been surrounded by a blanket of material ejected during its formation. The cadre of lunar scientists involved in Apollo believed that much could he learned by sampling this ejecta blanket, which appeared to dominate the near side. To sample it, they proposed a landing site for Apollo 13 in hummocky terrain just north of the crater Fra Mauro, and Apollo 12 took pictures to assist in planning.

Apollo 13’s first problem occurred several days before its 11 April 1970 launch, when command module pilot Ken Mattingly had to be replaced by his backup. Jack Swigcrt, owing to a possible exposure to rubella. The glitches continued soon after launch when one of the five engines in the second stage of the Saturn V shut down prematurely. However, these issues were as nothing compared to what occurred almost 56 hours into the mission. When Swigert operated fans to stir the contents of an oxygen tank in response to a request from mission control, the tank violently burst. The resultant shock blew out one of the skin panels of Odyssey’s service module and damaged its oxygen system sufficiently to cause most of the spacecraft’s supply of this vital gas to leak out to space. At that time, Apollo 13 was.328,300 kilometres from Earth and 90 per cent of the way to the Moon.

This traumatic event deprived the spacecraft of electrical power and began a four- day feat of dedication, ingenuity and endurance by the crew, the flight control team and thousands of support staff to effect a safe return to Earth. Every system in the SM was rendered inoperable by the blast itself, by the lack of power, or by concern that it may have been damaged and represented part of the problem rather than part of the solution. The CM had to be powered down very quickly to save its remaining consumables, as they would be needed for re-entry into Earth’s atmosphere. This left the LM Aquarius as the only means of sustaining the crew while the two joined ships flew7 around the Moon for a slingshot back to Earth. It also became the sole means of manoeuvring to speed up the return trajectory and control the accuracy of its arrival.

Without power, the interior of the spacecraft soon cooled to around 6 C. In these uncomfortably low temperatures, the crew grew increasingly exhausted as they took refuge in the LM while nursing their dead CSM to the safety of Earth, its command module being the only way to pass through the atmosphere. During the long fall to Earth, they had to construct devices to remove toxic carbon dioxide from their air, w ork through complex checklists to fire the LM’s main engine, and also improvise a means of firing it for the correct duration while ensuring that it was correctly pointed. They found themselves carrying out difficult and often completely new procedures without having slept for days.

In the flight’s final moments on 17 April as it re-entered Earth’s atmosphere, the world was gripped by the tension of not knowing whether Odyssey’s heatshield had been damaged by the blast. A safe splashdown in the Pacific Ocean ended a failed

mission that became perhaps the finest hour for a spacecraft’s crew, its ground control team and their supporting organisations. It showed that in spaceflight, and in the face of terrible odds, toughness and competence could win through.

Despite the superstition that surrounds the flight number, and knowing with hindsight that the spacecraft left tiarih with a flaw on board. Apollo 13‘s oxygen tank rupture occurred at just about the most opportune time. Much earlier and their coast to the Moon and back would have been too long for the LM to sustain them. Much later, and they might not have had a LM available to act as a lifeboat. In fact, it was a case of lucky 13.