Category How Apollo Flew to the Moon

It was only when the S-II’s tanks had run dry and a signal had been sent to shut down the engines, that the Saturn’s computer could begin the next part of the ascent – the staging event that discarded the spent S-1I and ignited the S-IVB for the first of its two burns. The same signal began Timebase 4 in the instrument unit to choreograph everything that had to occur.

Unlike the dual-plane separation between the first and second stages, this cut was made across a single plane at the top of the conical interstage that separated the S-II and S-IVB stages. Although it was discarded with the S-II, this structure was actually manufactured as part of the S-IVB. Within a second of S-II cut-off. solid-fuel retro rockets mounted around the interstage ignited, as did two ullage rockets at the base of the S-IVB. A pyrotechnic device then severed the tw o stages. Engineers were less worried about the possibility of accidental contact because the S-IVB carried only a single centrally mounted engine and its extraction from the interstage occurred well above the atmosphere.

Crew’s generally found this staging event much less violent than the first, as Dave Scott opined in test-pilot prose after his Apollo 15 flight. "The S-II to S-IVB staging w’as about a quarter to a fifth the force of the S-IC staging. It was again a positive kind of feeling, but it wasn’t a violent crash like we felt on the S-IC. " Eugene Cernan pointed out other differences: "On the S-II [shutdown], although it’s sharp and a very hard hit. you don’t unload the entire stack like you do when you’re on the S-IC." However. Ed Mitchell had been so keyed up for the S-IC separation on Apollo 14 that he tvas unprepared for the jolt the S-II staging delivered. "I thought the S-II cut-off was more dramatic than the S-IC. Maybe that’s because I had been thinking about the S-IC being the dramatic one and not thinking about the S-II.” On his Apollo 10 flight Cernan told Capcom Charlie Duke how a cloud of debris was produced on staging that moved with the stack. "Charlie, lots of stuff out the window – on staging. We’re catching up and passing it now."

The ullage motors at the base of the S-IVB continued to burn for about eight seconds and helped to push propellant down the pipes and into the turbopump, during which time, the single J-2 engine brought itself up to full power. They were then jettisoned from the stage to avoid their dead weight being carried to orbit. The start sequence of this engine was identical to the .1-2 engines used in the S-II. except that the fuel was allowed to How through the engine walls for a longer period before ignition. The dead S-II coasted to a watery impact in the Atlantic Ocean. 4,500 kilometres from the launch site. With a mixture ratio of 5.0 to 1. the S-IVB continued to drive for orbit with a burn that typically lasted 140 seconds.

The crews experienced an acceleration of only 0.5 g. which rose to 0.75 g as the burn progressed. When the Saturn’s guidance system sensed that the required speed had been achieved at the necessary altitude, it shut down the engine. This was also the signal to initiate Timebase 5. which sequenced all the tasks required to settle the stage and its spacecraft payload in their orbital coast. In only 11 Vi minutes, the Saturn V had accomplished one of the riskiest parts of the mission by achieving orbit about 180 kilometres above Earth.

During a post-flight debriefing, Eugene Ccrnan summed up the Saturn V in layman’s terms: “I think the S-IC acted and performed like some big, old, rugged, shaky monster. It has to be noisy, has lots of vibration and smoothed out somewhat after max-Q. but still was a rumbling bird. The S-II was a Cadillac: quiet, less than 1 g flight most of the time until we built up our g-load prior to staging. It was quiet, smooth, had very little noise, or feeling of rumbling or anything else. The S-IVB: a light little chugger. is probably the best way I can describe it. It just sort of rumbled on, not anywhere near the extent of the S-IC. but just sort of continued to rumble on through the burn."

The first step in the whole process was to ensure that the command module’s cabin was pressurised up to its maximum extent, about two-fifths of an atmosphere. This was in preparation for when valves on each side of the tunnel that would eventually connect the two spacecraft would let oxygen flow from the CM into the LM, thereby saving the lunar module’s scarce resources.

While the crew7 worked through the TD&E checklist, the APS modules at the aft end of the S-IVB, which controlled the stack’s attitude, fired to bring it to the correct orientation for the manoeuvres. Planners had calculated the most appropriate attitude for the S-I VB to adopt to preclude the CMP being blinded, cither by the Sun or by reflections from the lander’s metal surfaces, yet give good illumination of a docking target mounted on the LM that was to aid the alignment of the two craft as the CSM came in to dock.

The CMP could monitor the whole manoeuvre using the entry monitor system (EM’S), an example of a piece of equipment that was meant for one purpose being

pressed into service for another. The EMS was a unit built into the main console that was to monitor the spacecraft’s re-entry into Earth’s atmosphere at the end of a mission. One of its displays was a digital readout that would, during a re-entry, show how many nautical miles they still had to travel before landing on the ocean. When the crew were performing a rendezvous, it could be switched to display how many feet separated the CM and an approaching LM. For powered manoeuvres, it could display how their speed changed in response to the thrust produced by the engines. This versatile unit could also send a shut-down command to the engines once a preset change in speed had been accomplished. Most of these functions were for later, but for TD&E, the command module pilot was interested in knowing how his speed, or to be more precise, his velocity had changed – a quantity known as delta-v.

In space flight, and in physics in general, an important distinction is made between speed and velocity. Speed simply defines distance travelled over a set time, and no account is taken of the direction of travel. With velocity, direction becomes part of the equation. In the three-dimensional arena of space, it is customary to measure speed after resolving it into three components of velocity. Therefore some frame of reference or coordinate system has to be brought into play where the directions of left/right, up/down and backwards/forwards are defined, usually labelled л’, у and z. As an example of how this works, an object whose velocity is three metres per second along the a axis and four metres per second along the у axis is actually travelling at five metres per second in a direction somewhere between these two axes by simple application of the Pythagoras Theorem. At this stage, it is worth noting that spaceflight is full of coordinate systems. The one used for velocity is different to that used for the spacecraft’s body.

Unlike the spacecraft’s main guidance system, which resolved delta-v in three axes, the EMS measured it along one axis only – in this case, along the spacecraft’s longitudinal axis – and displayed it on the digital readout in feet per second. It had its own accelerometer (a device that measured velocity changes), whose sensitive axis was aligned parallel to the spacecraft’s long axis. The dclta-v display could therefore be used by the CMP to monitor how thruster firings were affecting the spacecraft’s velocity as he separated from and then manoeuvred relative to the S-IVB. Before separation, he could zero the display, then directly read off how his velocity had altered with respect to the stage. However, pilots on the early missions had noticed that the della-v display did not work well around the zero mark, so they began to preset it to read minus 100 feet per second, which gave better results and was easier to interpret. A step was eventually included in the checklist to this effect.

Bang!

The precise time for the CSM to separate from the rest of the stack was not critical but. as was NASA’s nature, they defined it as part of their carefully organised flight plan. The major constraint to this whole exercise was that the S-IVB had to be left with enough battery power for the final manoeuvres which would steer it away from the spacecraft’s flight path and to its ultimate doom.

In the cabin, a one-hour event timer had been preset to read 59:30. It was then started 30 seconds before the planned moment of separation. Counting up, it reached zero at the intended moment of separation and it helped the crew to coordinate activities with their checklist both before and after the key moment. The timer was often used in this way for critical events in the mission.

With only two seconds remaining, the CMP, sat in the left couch, eased the translation control in his left hand forwards, away from himself. At his command, rear-facing thrusters on the service module began to fire so that, as soon as the CSM became free, it would move away from the SLA. The separation itself was executed by a guarded pushbutton on the main display console. This switch was one of a group of eight such buttons that could be used to initiate pyrotechnic events, but it was the only one that was meant to be used during a normal mission; the others allowed backup manual control of events that normally occurred automatically.

Separation was a fast yet complex event. An explosively driven guillotine severed the electrical connections between the spacecraft and the S-IVB. Next, a complex train of explosive cord was detonated to cut the service module free and to slice the uppermost three-quarters of the SLA into four separate panels. These panels were not allowed to immediately drift free of the stage. Rather, each had two partial hinges mounted along its lower edge. The pyrotechnics also forced small pistons mounted in the lower section of the SLA to push on the outside edges of the panels, ensuring that they rotated away as desired. Once the panels had swung away about 45 degrees, the hinges disengaged and the panels departed, pushed away from the S-IVB by springs built into the hinge mechanism. Each continued on its own path away from Earth; perhaps to impact the Moon, more likely to be east by the Moon’s gravity into some chaotic orbit around Earth and

then be deflected by the Moon into solar orbit, to interact with the Earth-Moon system every few decades. Today there are as many as 36 such panels out there. They will drift aimlessly for perhaps thousands of years. In the fullness of time, some may re-enter the Earth’s atmosphere and bum up, while others may be thrown into the deeper reaches of our solar system for eternity.

NASA did not originally intend to jettison the panels. During Apollo 7, the crew attempted a partial simulation of the TD&E manoeuvre for the first time. There was no LM occupying the SLA and partial hinges were not used for the panels, engineers having originally chosen to keep them attached. As the CSM returned to the S-IVB to manoeuvre near their mock docking target, the commander Wally Schirra observed how one of the panels had not properly deployed and was instead flexing uncomfortably close to where they intended to practise. His CMP Donn Eisele described the scene to mission control: “The SLA panel at the top, left and bottom are opened at [what] I would guess to be about a 45-degree angle, and the SLA panel on the right is just opened maybe 30 degrees at the very best.” Schirra elaborated: “Except for that one panel, everything looks like it’s just as you’d expect it to be on that S-IVB SLA deployment.” Schirra invoked the commander’s prerogative and cancelled the docking practice. He elected instead to station-keep with the S-IVB. “We’re a little worried to get backed up in there with that one cocked panel.” Next day, when they rendezvoused once again with the S-IVB, the panel was found to have fully deployed, but the practice approach was not attempted.

CSM turnaround

Having separated from the Saturn, the CMP continued thrusting forward, controlling with the translation hand control, until the EMS indicated that he had gained a speed of half a foot per second. Then, once enough time had elapsed to ensure that the CSM w as well clear of the third stage, he pulled back on the rotation control in his right hand. A different pattern of thrusters fired to pitch up the nose of the spacecraft for a half-turn that would point the CSM at the lunar module, now exposed atop the S-IVB.

One reason for using the EMS was because the crew could not see whether the spacecraft had cleared the third stage, and it was felt safer to rely on empirical measurement rather than guesswork. Not all the crews agreed with this approach. In his post-flight debrief. Richard Gordon of Apollo 12 felt the EMS got in the way. "If I’d been smart and used my head, I’d have taken these TD&E procedures and scratched all reference to the EMS whatsoever."

Both he and his commander Pete Conrad felt that it would have been enough simply to fire the thrusters for a set period of time, thereby simplifying the procedures. “That’s exaetly what 1 would have done," continued Gordon. "1 would have separated from the SLA. I‘d have thrust forward for the time to get 0.8 feet per second. I’d have counted to 15. and I would have backed off thrusting for a couple more seconds. And that’s all you need." An additional problem using the EMS was that it could not track the delta-v very well if the CSM was rotating, or was subjected to shock, both of which were happening in this task. Having set the display to read minus 100. Gordon found it had jumped to read minus 98 when he was expecting a reading over 100. "So I had no idea how much velocity I’d put in to the thing and I jusi continued thrusting forward for a few seconds, probably being conservative because I wanted to make sure I got far enough away from the booster before we did the turnaround."

On turnaround, many Apollo crews discovered that a lot of debris could be generated when the pyrotechnics fired to separate the CSM from the launch vehicle and cut the SLA into four. Even before America, Apollo 17‘s CSM, had turned around to face the LM Challenger. Ron Evans, exclaimed. “My gosh, look at that junk!"

By the time of this final Moon mission, the procedures for separation were well rehearsed. Evans let the CSM drift out for a few’ seconds. "Okay; there’s 15 seconds. Pitch her up.’’ As the spacecraft came around to view’ the S-IVB, Eugene Ccrnan spotted the debris surrounding it, “Houston, we’re right in the middle of a snowstorm."

“Roger." confirmed Capcom Bob Parker. “And we’d like Omni Delta." The rotation of the CSM meant that the omnidirectional antenna they had been using was no longer well placed and they needed to switch to another one to maintain a clear line of sight. Parker didn’t seem particularly interested in the debris.

"And there goes one of the SLA panels," called Cernan.

“Yes," agreed Evans as they continued rotating. “We’re not there yet. Longways to go yet."

“There goes another SLA panel, Houston, going the other way," said Ccrnan.

Jack Schmitt had his own windows to look out of. "Hey, there’s the booster!” he yelled as the S-IVB came into view of his forward-facing window.

"Roger,” said Parker. "Bet you never saw the SLA panels on the simulator.”

Cernan agreed. "No, but we’ve got the booster and is she pretty! Challenger’s just sitting in her nest.”

"Roger. We’d like Omni Bravo, now, Jack,” requested Parker.

Cernan had been watching the particles that were floating outside his window. "And, Houston, some of the particles going by the window fairly obviously seem to be paint.”

Once the CSM had turned around to face the LM, its rotation was stopped. Then, by pushing on the translation controller, the CMP could kill the drift away from the third stage and start to approach. The LM’s docking port was on the roof of the lander, while the CSM’s was built into the apex of the command module. As the two spacecraft slowly came together, he had to keep them aligned. As an aid, he had an optical device, known as the crewman optical alignment sight (COAS), which was rather like a gun sight. It was mounted in the forward-facing window on the left and it gave him a consistent line of sight. A stand-off target was mounted on the LM, appropriately positioned so that the combination of the COAS and the docking target allowed him to adjust for left/right, up/down and angle of approach to bring the two spacecraft accurately together.

Ken Mattingly was surprised at how easy this manoeuvre proved to be – a testament to the fidelity of the simulations prior to the flight. "When we pitched over, the crosshairs on the COAS were almost exactly centred on the target. It was just a matter of pushing it, sitting there, and waiting for the two to come together. I made one lateral correction and one vertical correction. We didn’t do another thing until contact.”

Here on Earth, we know, to the depths of our being, which way is up because gravity affects just about every action we Lake. In a spacecraft, any sense of direction that the crew– has is artificially imposed by their personal knowledge of the cabin, its layout and their view from the windows. Beyond that, there is no up or down in space. However, to get to a destination, the crew – must aim their engine correctly so that its thrust will act in the required direction. To achieve this, there must be some measurable definition of which way is w-hich; up. down, left, right, back, forward. In fact, there were many operations on board the Apollo spacecraft that needed some sense of direction – although not the same sense in all cases. Engineers had to provide a reference against which the spacecraft’s current orientation could be measured. Once again, the answer was in the stars.

Earth, the Moon and the rest of the solar system are, along with the other stars that make up the Milky Way galaxy, wheeling around the galactic centre at speeds that are literally out of this world, but it takes 250 million years to make one revolution. Although all these stars mostly move in roughly the same direction, each follows an independent path because it is tugged and pulled by the gravity of the stars around it. However, the galaxy’s size is immense; it takes many Lens of thousands of years for a light beam to travel across the galactic disk, and on the scale

of humans and our meagre range of travel, the stars appear to be fixed points. Their distance is so huge and their apparent motion so slow that over a human lifetime even the closest ones hardly appear to move. Throughout the centuries of human exploration their seemingly static display has provided a useful ‘fixed’ reference against which progress across the surface of Earth could be metered. Apollo continued a long tradition of employing the stars for navigation.

We have already seen how the angular relationship between a star and a planet could be used to pin down a spacecraft’s position and velocity. The stars contributed in another essential way by helping to define direction. The magnitude of an engine burn was not the only important parameter to its success. It had to be fired with its nozzle (and hence the spacecraft) aimed in the right direction. Any appreciable misalignment during a burn would take the spacecraft off its intended course. Correcting for such an error would be wasteful of precious propellant and might put

the crew in jeopardy. The orientation of a spacecraft in space is known as its attitude (not to be confused with altitude) and, in an Apollo spacecraft, measuring attitude was the role of the inertial measurement unit (IMU).

Encased in a spherical housing a little larger than a soccer ball, the IMU consisted of three nested gimbals that supported a platform at their centre. Their arrangement isolated the platform from the spacecraft’s structure in such a way that the spacecraft could freely rotate up to a point and the platform would maintain its orientation in space. The platform carried three gyroscopes mounted orthogonally (at 90 degrees to each other). If a change in orientation was detected, the gyroscopes signalled motors to return the platform to its previous orientation. This arrangement ensured that as the spacecraft rotated this way and that, the orientation of the platform would remain the same, at least for a few hours. Encoders built into the axes of the gimbals could measure the attitude of the spacecraft relative to the platform’s orientation. These yielded three angles that told the computer in which direction the spacecraft was pointing.

The spacecraft attitude angles were displayed to the crew using the elegant (and elegantly named) flight director)attitude indicator (FDAI) which was more usually referred to as the ‘8-ball’. It was two instruments in one package, hence the dual name, and it is best to think of this as the spacecraft’s equivalent of the artificial horizon display found in the instrument panel of almost every aircraft. Its inclusion reflected the aviation background of the crews that flew Apollo. Usually, the ball at the centre of the display was driven to match the orientation of the platform. This was the ‘attitude indicator’ part of the instrument and if the spacecraft rotated, it would appear to do so around the 8-ball, mimicking the way it actually rotated around the stable platform. Graduations marked on the ball’s surface then allowed

the crew to read their current attitude off the display as degrees of pitch, roll and yaw. Needles in front of the ball formed the ‘flight director’ by indicating to the pilot which way he must rotate the spacecraft to attain an ideal attitude. Further meters and needles built around the 8-ball informed the crew how fast they were rotating. The reason for calling it an “8-ball” was a red disk on either side of the ball that gave it a superficial resemblance to the balls used in a game of Pool. This disk represented a range of attitudes that the spacecraft must avoid, of which more later.

Each spacecraft had two FDAIs on its instrument panel at the insistence of the crews, as David Scott recalled. “The thing we fly by, as pilots, is the attitude gyro – the 8-ball. And there was only one in Block I. And that’s key to what you do in all sorts of situations, and they didn’t want to put two 8-balls in Block II. We wanted a backup attitude gyro. As I recall, [James] McDivitt finally had to go to the [Apollo Spacecraft] Program Manager on behalf of the [Astronaut] Office, and say, ‘without two attitude gyros on the Block II spacecraft, we’re not going to fly it! That’s all. Want to put two in or not?’ And we got two 8-balls, which could not be justified technically – No way! – because they were reliable and there were other things to look at. But, from a pilot’s perspective, those were key.”

The IMU had another important function. As well as providing a reference against which the spacecraft’s attitude could be determined, its stable platform also provided an excellent base for the measurement of acceleration. Mounted alongside the gyroscopes on the platform were three accelerometers that detected changes in velocity along the three axes of the platform. Measurement of acceleration allowed the computer to calculate the effect of an engine burn.

The idea runs like this. Another way to think of velocity is that is it a measure of how fast you are changing position – it is your rate of change of position. Similarly, acceleration is a measure of how fast you are changing velocity. So if you start from a known point in space, measuring your acceleration will tell you how much your velocity has changed. Knowledge of your velocity will allow you to calculate how your position has changed, and position is an important element of the state vector. The IMU’s ability to measure acceleration accurately allowed the G&N system to update the state vector on an ongoing basis, and especially during engine bums. During a period of coasting, the state vector would be periodically determined by the ground or the crew.

In the realm of guidance and navigation, the IMlJ’s measurements only made sense if the computer knew which way the platform was orientated in space, i. e. which way was up, and this required some kind of external fixed reference. Neither Harth nor the Moon could be used because invariably the spacecraft was moving substantially with respect to both of these bodies. This was where the stars came in as the platform’s orientation was defined against a frame of reference for which they were the fixed points.

Although the Apollo crews w ere drawm from a pool of very fit men, each of whom had undergone an exhaustive medical examination before being hired and again before the flight, they were nonetheless human and ended up suffering the normal range of minor illnesses and conditions during their flights that one would expect from any sample of healthy people. One perennial problem that afflicted the early flights was the common cold. It made life much harder for the Apollo 7 crew when the commander, Wally Schirra contracted a cold early in the 11-day flight. As LMP Walt Cunninghan later recounted, “When Wally had a cold, everybody had to be miserable.” A bout of sniffles and congested noses caused the launch of Apollo 9 to be delayed for three days to enable its crew to recover. Their susceptibility was attributed to their high work rate prior to launch, which sapped their immune system, and to the large numbers of people with whom they came into contact in those final w’eeks and days. Aftenvards. NASA began to quarantine crews to reduce the likelihood of their catching colds.

Of some surprise and initial concern to the doctors was the prevalence of motion – related sickness as experienced by Frank Borman on Apollo 8 and Rusty Schweickart on Apollo 9. Motion sickness had not been a problem during the Mercury and Gemini flights, and nor had it shown up on Apollo 7; so when Borman began vomiting within a day of Apollo 8’s launch, doctors and managers feared for the mission. Borman was unwilling to mention how’ ill he felt over the normal communications channel, so he left a message on the voice track of the spacecraft’s tape recorder. This recorder was intended to record voice and data while the spacecraft was out of sight behind the Moon. Its contents would be transmitted, or ‘dumped’ to Earth on a secondary communications channel within the S-band signal once a radio link wras re-established. As they had not yet reached the Moon, Borman disguised his desire for mission control to listen to the tape by treating it as an engineering test.

“How’s the voice quality been?”

“It’s been very good, Frank.” replied Mike Collins at the Capcom console.

“Okay,” said Borman. “We’ll send you something down here shortly.”

After Borman had recorded his message, Anders began to nudge mission control to give it a listen.

“Г11 go ahead and dump this. You might want to listen to it in real time to evaluate the voice.”

“Okay,” replied Collins. “We’ll do that as soon as we can.”

When mission control eventually decided that there was something to listen to, they learned of Borman’s condition and arranged to have a private conversation with him from another control room in the Mission Control Center building. Their diagnosis was that Borman must have contracted a viral infection, though by that time he had recovered. With hindsight, his condition was attributed to motion sickness. After Schwcickarl suffered similar symptoms, NASA had its crews try to condition themselves to extremes of motion by performing aerobatic manoeuvres in the T-38 aircraft that were made available to them.

The problem seemed to stem from the greater space available to the crew in the Apollo cabin. Mercury and Gemini spacecraft were very small and a crewman could do little more than sit in his couch. In the Apollo command module things were different, especially with the centre couch folded away. There was sufficient room to do weightless spins and somersaults. Some crewmen found the disturbance to their vestibular system upsetting. The longer term history of spaceflight has shown that a proportion of space travellers simply have to overcome an initial adjustment to weightlessness.

To try to mitigate the effects of so-called space adaptation syndrome, the crew’ could dip into a medical kit that had been included in the cabin. There wasn’t room for much, but doctors had tried to cover most of the minor ailments from which an otherwise healthy man might suffer. On Apollo 11 the kit carried ointments, eye­drops, sprays, bandages and a thermometer. It included an assortment of pills, such as antibiotics, anti-nausea tablets, analgesics and stimulants. There w? ere aspirins, decongestants, anti-diarrhoea pills and sleeping pills. There w’as also a selection of injectors for pain suppression and motion sickness. A smaller kit was kept in the lunar module.

“It was pretty clear that the medical kits were not carefully packed.” said Armstrong during Apollo 11‘s debrief. ‘The pill containers blew’ up as if they had been packed at atmospheric pressure. The entire box was overstuffed and swollen. It was almost impossible to get it out of the medical kit container.”

“I ripped the handle off as a matter of fact, trying to pull it out.” added Collins.

“That w’as even after we cut one side off the medical kit,” said Armstrong, “so it would be less bulky and we would be able to put it in the slot."

The SPS engine was mounted at the rear of the central tunnel, below the helium tanks. From the point of view of crew safety, this was the one major engine in the Apollo system that had to be capable of being regularly restarted. Failure to operate at its first major firing to enter lunar orbit could be tolerated, because the spacecraft would loop behind the Moon and return to Earth’s vicinity and it would be possible for other engines to restore a trajectory home. However, a spacecraft already in lunar orbit was completely dependent on the successful restarting of that engine to bring the crew home.

With maximum reliability in mind, engineers endowed the engine with two of just about everything: two control systems, two sets of plumbing, two ways to pressurise the propellant tanks. In fact, except for the injector plate and combustion chamber and bell, the SPS engine was really two engines in one, with the crew having entirely separate control of either. Even pumps were banished from its systems in order to avoid having to rely on the moving parts that they contained. Instead, helium gas provided the pressure needed to push the propellants through the piping and into the combustion chamber with sufficient force. This helium was stored at extremely high pressure and passed through regulators which reduced its pressure to that required by the large propellant tanks. Reliability was further assured by the use of a hypergolic fuel and oxidiser combination. This meant that these substances – hydrazine as a fuel and nitrogen teiroxide as an oxidiser – merely had to mix to spontaneously ignite, unlike the engines on the Saturn V’s three stages which required igniters to begin their conflagration. On the Apollo stack, every engine within the two spacecraft used these propellants. To start the SPS engine, one had only to open valves and permit these exotic propellants to spray into the combustion chamber through hundreds of holes across the face of the injector. As they met. they burned fiercely to generate an almost invisible but powerful flame.

For the SPS to operate without pumps, the pressure with which the propellants were injected had to be sufficient to overcome the combustion pressure in the chamber where they met. which was 690 kPa (100 psi). To enable the propellant to reach the injector the tanks were pressurised at 760 kPa (110 psi). The engine valves could be operated manually by the crew via two prominent switches on their main console, or the computer could send a signal to achieve an automatic burn based on preloadcd information and the results of its computations. In fact, this engine was so intensively designed to ignite in response to a wide range of command sources, that on occasions when faults afflicted its control systems, the problem became one of ensuring it would not fire inadvertently.

Soon after the crew of Apollo 15 had extracted their LM and were about to settle into their long coast to the Moon, its commander David Scott reported to

mission control: "Okay; that all went fairly nominally, and the only different thing wc’vc noticed is the SPS Thrust light is now on. And wc don’t know when it came on; somewhere in the process here.” This light was mounted right in front of the left-seat occupant on Panel 1 of the main display console, an indication of its importance. It was there to indicate that the SPS engine valves were open and that the engine ought therefore to be firing. The light was energised, although the engine clearly was not.

‘■Roger. I understand the SPS Thrust light is on.’’ checked Gordon Fullerton, the Capcom in Houston.

”And all the switches are off," added Scott, ominously. He knew that one way to operate the engine was to throw one of two large, prominent, guarded switches in the middle of that panel. They allowed the crew to manually start the engine if automatic control was unavailable. Scott wanted to make clear to mission control that they had not been thrown and that there was obviously an electrical fault.

After an initial analysis, flight controllers asked the crow to open all the circuit breakers that could energise the engine’s propellant valves. They realised that if electricity had reached that light, then it could also reach the valves merely by arming the control system, which would cause the engine to fire immediately rather than on command. Apollo 15 was the first mission to have TLI not establish a frce-rcLurn trajectory in order to reach its northerly landing site. If the SPS were declared unusable, a large manoeuvre by the LM would be required to get home. Further careful diagnosis suggested that there was an electrical short in the vicinity of one of the two manual switches for the SPS. which Scott confirmed the next day by slowly manipulating the suspected switch to see how it made the light came on.

This fault was no show-stopper, as long as it was understood. Mission control drew up revised procedures for the rest of the mission and the crew operated the SPS using the redundant system whenever possible in order to prevent an inadvertent firing. After the flight, when the spacecraft’s anomalies were analysed, a tiny sliver of wire was found to have been trapped inside one of the two manual switches for the SPS during manufacture.

This was an occasion where the duplication of nearly every part of the engine allowed the faulty system to be isolated. The two separate halves of the engine’s control and plumbing were termed the A and В banks. The Apollo 15 crew could start and end all their burns accurately using the good В bank, and bring the A bank in and out manually only during long burns when it was desirable for the engine to keep running should either bank fail. When both banks operated, slightly more propellant reached the injector and the engine achieved a slightly higher thrust.

The 12-ycar Apollo lunar exploration program (1961 through 1972) occurred during the second half of a transformational period between the end of WW-II (1945) and the demise of the Soviet Union in 1991, a period of major technological, political, economic, and cultural dynamics. Technologically, the digital computer was in its infancy, yet automation and robotics were clearly imminent. The Apollo astronauts were required to bridge this gap, as humans capable of using a computer to assist in manually operating the vast array of systems, techniques, and procedures necessary to explore the surface of the Moon. The crew had to operate the hardware manually because computers did not yet have the reliability or capability necessary to operate autonomously and by the nature of the design strategy MCC did not really "control” the spacecraft.

And at any point in the mission, the crew had to be prepared to operate on their own without any contact from Earth, using only the equipment and computers on board, together with pre-calculated manoeuvre data. For. among the many potential emergencies that could occur on such a voyage, one of the most serious was loss of communications with MCC; whereby the crew and their spaceship would be alone in the ocean of space, perhaps even on the surface of the Moon and miles from the lunar module.

During each Apollo lunar exploration mission the three astronauts were obliged to be qualified and certified in essentially seven crew’ positions;

• The CSM had three crew positions: (1) Pilot (launch, major manoeuvres, rendezvous and re-entry); (2) Navigator (inertial navigation and rendezvous); and (3) Systems Engineer (all systems including fuel cells and propulsion).

• The LM had a crew of tw o: (4) Pilot (landing, launch, and rendezvous); (5) Systems Engineer (two computers, oxygen, electrical, thermal and water management)

• The surface exploration required a crew of two: (6) Lead geologist (also LRV driver); and (7) Geologist, systems engineer (for LRV. the suits and the backpack).

NASA training for the astronaut crews was superb – every aspect of the mission was covered by expert teachers and experienced professionals. Every spacecraft and all equipment and software were tested and verified by the astronaut crews (including flight spacecraft and spacesuits in vacuum chambers). In addition to the sophisticated (for that Lime) CSM and LM simulators, training w’as received in spacecraft systems, fundamental astronautics (navigation and rendezvous), and the operations of MCC. Commanders were qualified in helicopters and the Lunar Landing Training Vehicle. All astronauts maintained flight currency in T-38 jets, received SCUBA diving (for underwater weightless training), and jungle, desert, and water survival. And for the M" missions in particular, crews had extensive geology training with many hours of classroom and laboratory work, and field exercises.

By late 1963, the first thirty astronauts had been selected – all wrere experienced pilots in high-performance jets (twenty-four w’ere Lest pilots); all had engineering degrees (twelve also had graduate degrees); and all had been trained by the military (Air Force, Navy and Marines). This group would eventually command all tw’enty – nine US manned space missions (Mercury, Gemini, and Apollo) through the end of Apollo lunar exploration in 1972. But seven died during training or flight; and eleven more w’ho were selected in later groups flew’ Apollo lunar missions.

The basic design of the lunar module had been frozen in mid-1963, but systems integration, test and checkout had not yet commenced. Apollo simulators had not yet been developed. One of the major challenges for these first astronauts (and their operational support teams) was to develop and verify the procedures by which spacecraft would be operated. This required the integration and confirmation of the delicate sequence of operating the electrical, mechanical, computer, propulsion, life – support and other systems and Apollo was far more complex than Mercury and Gemini, and certainly any contemporary aircraft. And in developing procedures, they also necessarily became major contributors to the development of mission techniques (data priority). And because of their experience and involvement in the evolution of the Apollo program, these original thirty astronauts participated in and contributed to major management and programmatic decisions at the highest level.

One of the fortuitous design choices made by the Apollo/Saturn engineers was that the rocket ought to depend, in the first instance, on its own guidance system rather than being controlled by the one in the spacecraft. All the equipment required to autonomously steer the vehicle was mounted on the inside of a 6.6- metre annular ring positioned atop the S-IVB that extended the height of the launch vehicle by one metre. This was the instrument unit, and examples were installed on both the Saturn IB and Saturn V. The unit included a digital computer, a stabilised guidance platform, sequencers and other kit to control the entire launch, the ascent to orbit and the burn to the Moon. However, arrangements were also made to allow the Apollo spacecraft to control the Saturn V in case of an instrument unit failure.

The Apollo 12 flight of November 1969 vindicated the engineers’ decision when

lightning hit the ascending vehicle shortly after launch. The guidance system in the command module was temporarily knocked out by the surge of current, yet the Saturn continued on its way under the control of its instrument unit, giving mission control and the crew time to recover from the disruption. Had the spacecraft’s systems been in control, the vehicle would have strayed off course and the mission would surely have been aborted by firing the LES motor.

The scientific feast continued with Apollo 16, launched on 14 April 1972 to explore what were believed to be ‘highland volcanics’ within the rugged hills near the crater Descartes towards the centre of the Moon’s disk. Its crew of John Young, Charlie Duke and Ken Mattingly nearly had to abort their mission some hours before landing. When Mattingly tried to test the back up steering system of the main engine on board the CSM Casper preparatory to a scheduled burn, it began to wobble violently. Once this glitch had been overcome, Young and Duke made a successful landing six hours late in their LM Orion.

After a night’s sleep, they stepped onto the surface, immediately prepared their rover, and set up their ALSEP science station. Although Duke had no difficulty drilling into the surface for the heat-flow experiment, Young inadvertently disabled the instrument by tripping over its cable. Their first traverse was a short one to craters where they only found breccia or ‘instant rock’, made in the high-energy environment of an impact event when fragments were bound together by the melting of powdered rock. Their second and third days also concentrated on traverses, seeking signs of the expected volcanism but finding only beat-up rocks of a vast

ejecta blanket. In orbit, Mattingly continued the same type of observations that Apollo 15 had made, but over a largely different swathe of terrain.

The surface crew returned to the CSM and then, in view of the problem with their engine’s steering, departed lunar orbit a day early. Apart from being unable to release their subsatellite into the correct orbit, this curtailment of the Apollo 16 flight barely impinged on the quantity and quality of its results.

It was an example of classic scientific research. A hypothesis had been proposed by geologists to explain the origin of light-toned plains that were visible across some areas of the lunar highlands. Part of Apollo 16’s brief was to test this hypothesis, and with samples and observations to hand, the theories were proved wrong. However, this is how scientific progress is made, because it prompted a new hypothesis and a better understanding of the Moon’s evolution as a planetary body.

The first 42 seconds of the flight up to a height of about three kilometres was flown in abort mode one-alpha. This meant that in an abort, the escape tower above the command module would fire its large solid-fuelled motor to quickly pull the CM up and away from the service module and the rest of the stack below. The LHT included a small sideways-firing rocket motor at the Lop, called the pitch control motor, whose function was to steer the CM eastward out over the ocean to ensure that it would not subsequently descend into the conflagration caused by the destruction of its launch vehicle. Safely clear, the CM would dump its manoeuvring fuel (nasty, toxic, highly corrosive stuff that would otherwise present a danger to the recovery forces), jettison the complete escape system both Lower and boost protective cover – followed by the forward heatshield in order to deploy its parachutes and make a normal landing in the ocean.

At the centre of the decision to abort was the commander. From the launch pad to orbit, he closely monitored various lights and displays on the panel that supplied him with whatever information was relevant to making that decision. All the equipment that fed these displays, and which sensed whether an emergency was imminent, was called the emergency detection system (EDS). It was decided that he would not react to a single cue. lest it be spurious; but if two cues from the EDS called for an abort, this was sufficient indication for him to twist the T-handle in his left hand counterclockwise to activate the appropriate sequence to abandon the malfunctioning launch vehicle. There was also a set of conditions that could initiate an automatic abort. The idea of ending a half-billion-dollar mission at the behest of a few’ bits of hardware necessitated detection systems that were triple-redundant and which were required to ‘vote’ electronically for an abort. The automatic portion of the EDS was switched off once the rocket was out of the densest part of the atmosphere. Once aerodynamic forces were left behind, situations could not develop so rapidly.

The EDS was responsible for lighting a cluster of indicators that showed whether each engine was running at full thrust, whether the rocket was veering Loo fast and whether the Saturn’s guidance system really knew which way was up. In the latter case, from Apollo 11 onwards, if the commander saw that the Saturn was incapable of guiding itself, he had the option of twisting the T-handle clockwise to pass control of the entire rocket to the spacecraft’s computer, and if that was also failing then he could manually guide it to orbit. Another prominent light informed him when launch control in Florida, or the range safety officer, also in Florida, or mission control in Houston, believed an abort was advised. A gauge that normally showed the state of the spacecraft’s main engine for the rest of the mission was pressed into service by the EDS to show the rocket’s angle-of-attack; that is. whether it was moving cleanly through the air with no tendency to slip sideways – a condition that could impose such aerodynamic stress as to cause the break-up of the vehicle’s structure.

SETTLING INTO ORBIT

In only 11V2 minutes, the Saturn V had accelerated the Apollo spacecraft to nearly eight kilometres per second. The length of the stack had been reduced by two-thirds and the remaining stage, along with the spacecraft, had been lifted to an altitude of between 170 and 185 kilometres above Earth and above the vast majority of the atmosphere, though by no means out of it completely.

It was in orbit and the crew were experiencing weightlessness. They had almost three hours in which to give their ship a thorough checkout before setting off for the Moon with an engine burn called transhmar injection (TLI), and no one was keen to ignite it unless they knew it would be sending a good ship. In that time, they would make not quite two orbits of Earth although, if required, there was a contingency for an extra orbit.

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

DOI 10.1007/978-1-4419-7179-1 4. © Springer Science+Business Media. LLC 2011

As soon as the J-2 engine at the rear end of the S-IVB third stage had shut down, a pair of Liny auxiliary rocket engines at the base of the stage’s outer skin burned for a minute or so in an effort to keep the propellants settled at the bottom of their tanks. Other small manoeuvring engines began to operate to ensure that the stage would always point in the direction of travel with the spacecraft’s optical systems facing the stars. Once everything had settled down, a pair of aft-facing valves were opened to allow; hydrogen gas from the S-IVB‘s supercold fuel tank to safely vent to space as heat leaked in and caused the fuel to boil. This venting acted like a very weak rocket thruster and provided a Liny propulsive force that continued to keep the propellants settled at the bottom of their tanks long after the auxiliary thrusters had stopped.

Microgravity

Weightlessness is the common term for what is usually known in the space industry as microgravity though it is arguable which is the more accurate term. Microgravity implies a virtual lack of gravity which reinforces a common misconception that space is notable for the absence of this universal force. At the altitude the spacecraft was coasting, the force of Earth’s gravity was almost as much as it was down on the surface, yet the crew and all the loose objects in the cabin w’ere floating.

The body reacts to microgravity in ways that are now quite well understood. But when Apollo began to fly. no one had been in space for more than two weeks, and that had been in a claustrophobic Gemini cabin. After their Apollo 16 flight, veteran astronaut John Young and rookie Charlie Duke described their reactions to it. “It’s really neat; beats work," was Young’s opinion. Duke noticed how, with the cardiovascular system no longer having to work against gravity, the body’s fluids tended to go Low-ards the head. "For the first rest period, I had that fullness in the head that a lot of people have experienced. More of a pulsing in the temples, really than a fullness in the head.” Young had attempted to anticipate the effects. "I tried to outguess it by standing on my head for five minutes a night a couple of weeks before launch. Standing on your head is a heck of a lot harder."

Like a lot of crewmen, and taking note of the nausea experienced during earlier flights. Alan Bean took his time when he moved around the cabin at first. "I think we were all pretty careful and I had the feeling that if I had moved around a lot. I could have gotten dizzy. But I never did. Everyone was pretty careful and after about a day. it didn’t make any difference. We were doing anything we wanted." Bean also noted the way fluids gathered in the head: ‘ Your head shape changes. I looked over at Dick [Gordon] and Pete [Conrad] about two hours after insertion [into Earth orbit] and their heads looked as if they had gained about 20 pounds.”