Category How Apollo Flew to the Moon

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.

Up to the moment of launch, the entire weight of the space vehicle had been resting on four hold-down arms mounted around the edge of a 14-metre hole in the launch platform through which the engines could belch their fire down onto the deflector. These arms included strong pincers with mechanical linkages that firmly held the base of the first stage to the platform against the thrust of the engines. When the computers that controlled the launch had decided that all the engines were up to full thrust, the four hold-down arms were opened by their linkages being pneumatically collapsed. Simultaneously, three small tail service masts that had supplied fuel and other services to the bottom of the S-IC disconnected and swung up­wards. Protective hoods, some ac­tuated by cords attached to the rocket itself, fell over both the arms and masts before the vehicle rose enough to subject them to the full blast of its exhaust.

The release of the Saturn V was not instantaneous: it was once de­scribed as more of an ooze-off rather than lift-off. This was in part due to a number of tapered pins mounted to the hold-down arms, which were pulled through dies affixed to the bottom of the S-IC.

This controlled release mechanism limited the acceleration of the rocket for the first 15 centimetres of its ascent.

As soon as the immensely heavy vehicle began to rise, it could not safely return to the pad, so for the first 30 seconds of flight, intentional shutdown of the engines was explicitly inhibited. In reaction to this change in circumstances, five access arms that had continued to service the vehicle up to the moment of launch now had to quickly swing clear, their motion triggered by the first two centimetres of travel. As part of that action, all the umbilicals connected to the vehicle had to drop away, and their disconnection marked the starting point for the first of seven ‘timebases’ which orchestrated the control of the Saturn V. Timebase 1 would operate through most of the first-stage burn.

As 3,000 tonnes of metal and volatile propellant rose past the umbilical tower, it could be seen to lean disconcertingly to one side as though it were about to go out of

control. This was an entirely planned yaw rotation designed to manoeuvre the rocket away from the launch tower as a precaution against a failed swing arm or a gust of wind that might push the vehicle back towards the unyielding tower.

It took about 10 seconds for the entire length of the space vehicle to clear the tower, at which point re­sponsibility for the mission passed from the Launch Control Center in Florida to the Mission Operations Control Room (MOCR) on the out­skirts of Houston, Texas.

Twenty seconds after lift-off, the four outboard engines canted away from the vehicle’s centreline so that if one of them were to fail, the thrust of the others would be directed to act nearer to its centre of mass and thereby improve the chances of the instrument unit continuing to steer the rocket successfully.

The first two minutes of the Saturn V’s flight was a spectacular affair attracting many hundreds of thou­sands of sightseers to the roads and beaches around KSC to witness each launch. Over a million people are believed to have gathered for the launch of Apollo 11. At Apollo 4’s lift-off, which was the first time a Saturn V had flown, TV presenter

Walter Cronkite was bemused to find pieces of the ceiling coming down around him as the roar from the five F-l engines shook the temporary CBS studio from five kilometres away as millions of viewers looked on. Until then, few had appreciated the intensity of sound from five of these engines in free air. Once the acoustic energy finally reached them, people described how they didn’t so much hear the rocket as feel it. The slow’ rate of this leviathan’s majestic rise only served to lengthen its assault on the human body.

By six minutes into the mission, the S-II had worked long enough that, were it to fail, it could be jettisoned and both the S-1VB and the service module’s engine would allow the spacecraft to reach orbit. This was essentially abort mode three but the scenario was more often known as contingency orbit insertion (COl). However, had it been invoked, the spacecraft would have had insufficient propulsion remaining to take it to the Moon. Instead, it would have had to embark on a planned for. but never implemented. Earth orbit mission to make the best of a poor situation.

Haulin’ the mail

Pogo problems notwithstanding, crews generally found that if the S-II wasn’t buzzing and rattling, it gave them a smooth ride after the thrash and fury of the S­IC, Whereas the first stage had given them a good squeeze over a couple of minutes, the S-II’s acceleration rose smoothly over 6 ‘A minutes from less than 1 g to a little below 2 g – a peak less than half that of the first stage. Charlie Duke gave his impressions of the S-II during his Apollo 16 debrief: "I thought the S-II was very smooth and very quid. 1 had the sensation of very low acceleration or g’s and no noise at all that I could tell. I felt like we were almost floating at that time.’’

To reach a valid orbit, the space vehicle had to achieve a speed of 7.4 kilometres per second with respect to the Earth below. The S-IC provided about 30 per cent of this and the S-II Look it up to 90 per cent. The final 10 per cent was provided by the S-IVB stage in the first of its Lwo burns. However, once a rocket has left Earth’s atmosphere there is no longer a need to quote its speed with respect to the surface of the home planet. In space, the rocket’s physics is only dictated by the gravitational pull of Earth. It Teels’ no effect from the fact that the planet is revolving below. Instead, its speed in space is quoted with respect to some wider frame of reference, usually referred to as inertial space, but more easily grasped as being with respect to

the stars. In this inertial frame of reference, Earth had itself supplied an initial 0.4 kilomcirc-pcr-second boost as a consequence of its axial rotation. In total therefore, the stack had to be travelling at 7.8 kilometres per second to maintain a useful orbit. Around the 6-minute point in the ascent, the stack had more or less reached its orbital altitude. From then on, the S-II’s main task was to add additional horizontal velocity to help achieve orbit.

One second prior to ignition, the central light in the indicator cluster came on to tell the crew that the J-2 was about to spring into life. When it did. the crew felt an acceleration of about 0.5 g that gently rose to about 1.5 g over the duration of the burn as the tanks in the third stage emptied. Translunar injection typically lasted just under six minutes and it increased their speed from 7.8 to 10.8 kilometres per second. As soon as the burn began, the position at which it occurred became the perigee of the stack’s new elliptical orbit. Then as the burn proceeded and as they continued to orbit around Earth. their height began to rise; slowly at first, but at an increasing rate as the apogee of their orbit was drawn out. Although the crew monitored their instruments in case the S-fVB showed signs of trouble, they were not averse to taking a look out of the window and enjoying the view. As Eugene Cernan described on Apollo 17, "As the S-IVB manoeuvred, we flew through a sunrise during TLI. which in itself was very interesting, very spectacular.’’

Like the burn of the S-II stage, the S-IVB’s engine changed its mixture ratio during this burn. However, the effect of the change and the strategy behind it were very different. For the S-II. the change lowered the thrust and increased the stage’s efficiency to ensure simultaneous depletion of propellant and maximum possible impulse from the stage. For the S-IVB‘s second burn, the change brought an increase in thrust. Maximum use of the propellant was still desirable but of greater importance was that the shutdown should occur as soon as a precise velocity had been attained. Moreover, the loading of propellants had to take account of the constant boil-off of hydrogen fuel in Earth orbit and of the fact that there was a contingency for TLI to be made on the third rather than the second orbit, by which time a substantial quantity of hydrogen would have been lost. Therefore hydrogen had to be held in reserve for a delayed TLI. This meant that if the burn occurred at the first opportunity there would be an excess of the stuff. So for approximately 100 seconds of an on-time TLI the engine burned with a fuel-rich mixture to use up this excess and then the remainder was burned using a normal, more efficient mixture ratio. A delayed TLI was never performed, but if it had then the time required for the fuel-rich burn would have been very short, and if the boil-off of hydrogen had been greater than expected the engine would have moved into a fuel – lean regime.

к was common for commentators of the day to say that the I’Ll burn accelerated Apollo to Earth escape velocity. This statement implied that when the S-IVB finished its work, the slack was travelling so fast that it would never return to Earth’s vicinity without intervention, whether by the Moon or a rocket engine. Strictly speaking, this was not true, as the stack’s long elliptical orbit around Earth would have eventually returned them to perigee if the Moon had not intervened. Nevertheless, it was well within the capability of the S-IVB to add the few extra metres per second in order to escape into solar orbit.

With respect to the ground, the stack’s new trajectory took it less and less parallel to Earth’s surface, and instead more and more perpendicular to it as it pulled away from the planet. As it did so, its horizontal speed across the ground diminished; so much so. in fact, that the rotation of the planet began to catch up with the spacecraft, with the result that the ground track, which had been towards the cast, slowed, halted and began to travel towards the west, which kept the spacecraft in view of the United States for a few hours.

For a few minutes, as they raced away at about 10 kilometres per second, the crew passed through the van Allen belts, where they received a small dose of radiation. The Apollo flights represent the only example of human spaceflight through and beyond the van Allen radiation belts into interplanetary space. These belts consist of diffuse toroidal volumes around Earth’s equator within which radiation levels arc elevated by the planet’s magnetic field trapping energetic particles from the Sun. There is an inner torus populated by energetic protons, which the spacecraft passed through in a matter of minutes, and against which the spacecraft’s skin was an effective shield. The spacecraft took about an hour and a half to traverse the more extensive outer torus, but this region has mainly low – cncrgy electrons and so was less of a worry to mission planners. Also, the inclination of the trajectory, being in the plane of the Moon’s orbit, avoided the strongest regions of the belts near the equator.

Over a complete mission, including exposure to very energetic particles encountered in the solar wind environment beyond Earth’s magnetosphere and relativistic cosmic-ray particles, crews w-erc believed to have sustained a dose of a similar magnitude to that allowed annually for workers in the nuclear industry. There were additional dangers from occasional explosive events on the Sun when huge quantities of radiation were spewed out in coronal mass ejections and flares, but the Apollo programme simply ran the gauntlet of these events, accepting such risks along with the many other risks already inherent in an Apollo mission. Astronauts came from the test-pilot milieu where danger was a given and risks had to be weighed against the gains of mission success.

The purpose of determining the state vector was to see if their course to the Moon was true. If it w’as not, they could do something about it. With this in mind, seven occasions were set aside in the flight plan for possible trajectory corrections; four on the way out and three for the return trip.

Having determined the state vector and calculated the current trajectory, FIDO the controller primarily concerned with planning the spacecraft’s trajectory – then brought the RTCC computers to bear on the task of working out the magnitude and direction of a mid-course correction burn, a manoeuvre that would restore their current path to the ideal. If the mid-course correction was small, as it usually was, it could be made using the RCS thrusters on the side of the service module; otherwise the SPS engine was used. On some occasions, the flight controllers deliberately started the crew’ on a trajectory that w’as slightly off the ideal in order to allow’ them to correct it using the SPS. thereby providing an opportunity to exercise the big engine and see how well it worked. Everyone knew how’ crucial this engine was, and even a short burn lasting a second or tw’o little more than a burp generated reams of engineering data.

Having w’orked out the details of any required burn and checked them carefully. FIDO wrote all the information onto a standard form where about six copies would be made using carbonless copy paper. Capcom read the top copy up lo the spacecraft as pre-advisory data (PAD) – a list of numbers abbreviated down Lo barely the digits with units and decimal points omitted. Accuracy and interpretation was much easier when the PAD was laid out on a standard form. On board, the list was copied, usually by the LMP, onto an identical form and read back Lo Harth as a check of their accuracy. As the time for the burn approached, the data from the PAD was entered into the first of a series of programs on the computer that automatically controlled the burn. The PAD included three items that were crucial for the burn: when it should occur; the amount by which it should change the spacecraft’s velocity; and the direction in which the spacecraft should be pointing at the time of the burn. The PAD also included supplementary data: some was for the computer and its control routines; some was Lo improve the safely of the burn by offering details of backup methods of shutting down the engine; and some was to ensure that the attitude of the spacecraft was correct.

When flying in space, and especially when firing engines, it is of paramount importance to know in which direction a spacecraft is pointing. Three methods of cheeking this could be included in a typical PAD. A crewman could look through the sextant, having previously aimed it to a given angle, where he would expect a specific star to be centred in the eyepiece. A second check came from sighting another star with the COAS, having first mounted this sight in a window aimed in a known direction. However, their primary method of attitude determination relied on one of the major systems on board the spacecraft; the guidance and navigation (G&N) system with its inertial measurement unit (IMU) – a gyroscopically stabilised platform built into the spacecraft’s lower equipment bay below the optical systems. With the spacecraft aimed correctly and the PAD data entered into the computer, the burn could be controlled automatically or manually, as desired, with its results displayed for the crew Lo monitor.

Just as there w’as no conventional toilet, the spacecraft contained no show’er or basin. On a flight lasting less than tw’o w’eeks. personal hygiene had lo be demoted lo a simpler regime. Washing was performed by having a wipe down with one of the available cleansing cloths. Two types were available: wet and dry: each about 10 by 10 centimetres, with germicide added to the wet cloths. These were specifically intended for general cleansing after food and defecation. Afterwards, the skin was dried with tissues from one of seven dispensers available for the flight.

To clean their teeth, crews had a choice of either chewing gum that could be
swallowed, or using a brush and edible toothpaste to save them from having to rinse out their mouths. After Apollo 12, Pete Conrad spoke about brushing teeth en route to the Moon. “I guess everybody used his tooth­brush to one degree or another. I didn’t use it as much because my mouth doesn’t get that bad in 100 per cent oxygen. I did use the dental floss. I guess we all did. We all used the toothpaste.”

"I liked the toothpaste,” said Alan Bean.

“I don’t know where the rest of the guys kept their toothbrushes,” said Conrad, ‘‘but I just put mine back in my pocket after I cleaned it. I think everybody did.”

‘‘We found that once a day we liked to strip down,” said Dick Gordon. ‘‘We’d strip down completely and use the hot water with those towels that we did have on board. We’d completely sponge down and give ourselves a bath. I don’t think enough can be said for this type of thing and for the way you feel. We wanted to shave and bathe daily, on a regular basis, but we simply didn’t have the equipment on board to do it.”

One of the essentials missing on earlier flights was soap, as Conrad explained. “The potable water was used for personal hygiene, and I’d also like to have some soap along for personal hygiene and just to get clean after lunar surface operation – just to get the dirt off. That’s another reason we wanted more towels. We all stripped down all the way and washed down with the water and our towels several times during the flight.”

Lunar soil was a pervasive substance that covered everything after a crew had been on the surface. As Jack Schmitt related, the soap taken on later flights helped washing arrangements to work well. “I washed several times with soap, and, post­rendezvous, I actually washed [my] hair quite adequately by putting a lot of water on a towel and wetting the hair quite well. Then, just in a normal terrestrial way, I rubbed soap into it and then washed the soap out again with a couple of wet towels. The soap on board seemed to be quite good. It did a good job of cleaning but also was not overly sudsy and seemed to wipe off or wash off very well. It did not leave any noticeable residue that was uncomfortable.”

On the journey to the Moon, two events symbolised the crew’s daring and acceptance of risk more than any other. One was the landing itself, which committed two crewmen to stay forever on an utterly inhospitable lunar surface unless a small rocket engine worked properly to get them off and start their journey home to Earth. The other was lunar orbit insertion (LOI), the point in the journey when Apollo crews committed themselves to the gravity of the Moon. After LOI, there was no possibility of a return to Earth except by the success­ful operation of one major system within the service module. This was the service propulsion system (SPS), whose most obvious component was a large bell that protruded from the engine at the rear of the module. This engine, and the tanks that fed it, took up the bulk of the service module’s volume and mass, and its require­ments largely defined the module’s layout and construction.

Eight different “vehicles" were designed and built: three stages of the giant Saturn V launch vehicle: four spacecraft modules (command module [CM], service module [SM], together forming the CSM; and the lunar module (LM) with its descent stage

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and ascent stage); and on the lunar surface, the lunar roving vehicle (LRV). the spaccsuit, and its backpack with oxygen, cooling and communications. They were all required to perform an advanced Apollo lunar surface mission.

To provide operations, support, and supply, each of the four spacecraft modules required several major systems, including specific combinations of guidance and navigation, electrical, communications, control (rockets), environmental, sequential (pyrotechnics), and consumables (propellant, water, cooling). Of course each system itself consisted of several subsystems and a myriad of components. These essential systems had twenty-five modes of operation (automatic, semi-automatic, and manual for both prime and backup systems).

Additionally, Apollo was the first flight vehicle to be controlled through a digital computer (a “digital autopilot’-, or DAP). ‘I’his remarkable advance in computers would soon propagate through both government and industry as an essential element of both spacecraft and aircraft. At the time of Apollo, of course, the capability of the DAP was relatively meagre because each of the identical computers in the CM and the LM had only 38,000 words of memory (a mobile phone today can have over two billion words!) and what happened was that the spacecraft would be flown by the astronauts using the DAP as their main interface with operating systems.

And simultaneously with the spacecraft, the ground “systems– were designed and built, including a worldwide network of tracking and communications and especially the Mission Control Center (MCC) in Houston. In its broader sense the very complex and capable MCC was like a spider web in that it consisted of a central hub with ever expanding sequential “rings– and connected through nodes like spokes on a wheel. Each node was. in its own way. a “mission control center’’, and was manned by the true experts in that particular discipline.

The smallest stage of the Saturn V was the S-IVB (pronounced s-lour-b). and it was the earliest to fly. McDonnell Douglas had already been building them as the second stage of the Saturn IB rocket and little modification was needed to make it w ork with the rest of the Saturn V stack. It used the high-energy combination of liquid hydrogen and oxygen burning in a single restartable J-2 engine.

Liquid hydrogen is another cryogenic propellant, although in this case to become liquid it had to be brought down to minus 253’C. or 20 K; a mere 20 degrees above absolute zero. Rather than having two separate tanks that would require a heavy support structure between them, substantial mass was saved by fabricating one huge tank for both cryogenic propellants with an insulated bulkhead separating the lower, ellipsoidal compartment containing LOX from the liquid hydrogen in the larger upper section. As materials can have odd properties at these extremely low temperatures, insulation was painstakingly applied to the tank’s interior in the form of carefully machined polyurethane foam blocks to protect the adhesive and the tank’s aluminium skin. Including the conical interstage that joined it to the two low’er stages, the overall length of the stage was 18 metres with a 6.6-metre-diameter tank section.

With Apollo 13, NASA had dodged a bullet. The flight had very nearly killed its crew and, as always happens when it is hit by traumatic events, NASA needed a hiatus to investigate and understand what had disrupted Odyssey’s service module. Although there were calls from both inside and outside the administration to end Apollo before anyone else got killed, its managers kept faith with it. The programme of exploration which they instituted, now almost forgotten, visited immensely beautiful sites with spectacular vistas. Hnhaneed equipment allowed crews to explore further from the LM, and although the results from these missions had little political impact, their scientific findings now underpin our understanding of the early history of the solar system.

Apollo 14 returned the programme to the Moon to achieve what its predecessor had set out to do: visit the Fra Mauro area to gain insight into the formation of the Imbrium Basin. The precise target for the lunar module Am ares was near a relatively fresh impact feature dubbed Cone Crater. The scientists’ interest in Cone arose from a useful property of crater formation whereby, w’hen an impactor hits the ground, it removes the target rock in such a way that the most deeply excavated material ends up at the rim of the crater and material from successively shallower depths is deposited at increasing distances in an ejecta blanket. By having the surface crew of Alan Shepard and Edgar Mitchell radially sample this blanket as they walked towards its rim, geologists hoped to use Cone Crater as a convenient 25-million-year – old ‘drill hole’ to sample down through the ejecta blanket of the Imbrium Basin impact itself, which is now thought to have occurred 3.91 billion years ago.

The launch from Earth on 31 January 1971 was successful, and once they were on course for the Moon command module pilot Stu Roosa separated CSM Kitty Hawk from the S-IVB, turned around and attempted to dock with the LM Ant ares. For reasons that have never been clear, the docking was unsuccessful, and five further attempts were required to capture the lander. At the Moon, just before Antares was due to begin its powered descent to the surface, an intermittent short circuit threatened to abort the mission as soon as its engine ignited. A virtuoso engineering effort between mission control and the crew1 reprogrammed the computer, instruction by instruction, to work around the problem.

Being the last of the H-missions, the surface crew were scheduled two excursions

outside. On their first day, Shepard and Mitchell set up a second ALSEP science station and explored their locale. On their second day they were to undertake a trek of over a kilometre across the hummocky plain and up a shallow ridge to approach the 370-metre-diameter Cone Crater. The climb proved to be tiring and, as they neared the summit, they experienced difficulty in locating the crater. They had come 400,000 kilometres to get to this rim but were reaching the safe limits of their oxygen supply. With time running out, they collected a clutch of samples and turned back. Analysis later showed that they had navigated to within 30 metres of the rim, which was near enough for their samples to represent material from deep within the Imbrium ejecta.

Back at the LM, Shepard pulled off a famous stunt by attaching a genuine golf club head to the shaft of one of his tools and hitting golf balls he had smuggled to the Moon. Meanwhile, in lunar orbit, Roosa had planned an aggressive campaign of orbital photography with a high-resolution mapping camera attached to the hatch window. When the instrument failed early on, he was able to accomplish some of his photographic assignments by clever flying and using handheld cameras.

Apollo 14 was a highly successful mission that restored NASA’s confidence and prepared it for the triumphs of exploration and science to come. It was also the last time lunar explorers were required to undergo a period of biological isolation after landing on Earth. The returned rocks allowed geologists to probe the nature of the ejecta from the formation of the Imbrium Basin. They could apply the principle of superposition, whereby one feature can be seen to overlie another, to distinguish between pre-Imbrium and post-Imbrium landforms.