Category How Apollo Flew to the Moon

The final stage of the TD&E process was the ejection of the lunar module from the S – IVB, which was not simply a process of throwing a switch and then watching it happen. Throwing the switch would come at the end, but first they had to feed the signal from the switch in the CM down past the LM to the pyrotechnically-fired spring thrusters on the SLA that would push the LM free. That meant that the CMP had to connect two umbilical cables to feed power and signals between the two spacecraft. However, to do that he had to get into the tunnel, which is a short void between the command module’s forward hatch and the lunar module’s overhead hatch. Immediately after the docking, the space within the tunnel was still a vacuum so the CMP had therefore to bleed oxygen from the CM into the void and, in doing so, he also fed it into the LM cabin. Prior to launch, the dump valve in the LM’s overhead hatch was left open in order that, as the Saturn V lofted both spacecraft to orbit, the mixed atmosphere within the LM was gradually exhausted, leaving the interior essentially a vacuum, ready to be filled with oxygen. By docking with the LM, the tunnel had been placed over the hatch and its dump valve. Once the pressure on both sides of the forward hatch had equalised, the hatch itself could be removed, the umbilicals could be connected to feed power to the pyrotechnic devices for freeing the LM, and a check could be made to ensure that all twelve latches had properly engaged. Finally, the switch could be thrown to eject the LM from the S – IVB and allow the Apollo stack to continue its journey to the Moon.

None of these steps were simple, as each had its own checklist of items that had to be set or verified to ensure that the crew did not configure the spacecraft in a way that might endanger their lives. The process was carried out in a slow, methodical fashion of checks, verification and cross-checks: forty minutes work to allow them finally to throw one switch.

A catalogue of 37 stars distributed across the sky was programmed into the rope memory of the onboard computer. There w’ere some quite faint stars in the list, but this w’as only because the brightest stars are unevenly distributed across the sky. Planners had w’anted to ensure that irrespective of the direction in which the fixed line of sight of the optics was pointed, the crew7 would find a star sufficiently bright within the range of the movable line of sight to view through the sextant. Haeh star had a numerical code in base eight (octal) so that the crewman could tell the computer which star he wished to use. or in other cases the computer w’ould indicate the star that it had chosen for a specific operation.

Some of the objects in the Apollo star list were not stars at all. Three numbers were set aside so that the Sun. Moon and Harth could be referenced by the crewman for other tasks, and there w’as also a code that allowed a ‘planet’ to be defined if needed. In fact this could be any celestial object and in some cases, this ’planet’ was actually a star, just not one that the computer knew about.

Three of the fainter stars in this list have unconventional names that were added as a practical joke by the crew of the ill-fated Apollo 1 during their training. Star 03,

Navi, is the middle name of Gus Grissom (Ivan) spelled backwards. Likewise, his two crewmates added oblique references to themselves among the Apollo star list: Star 17, Regor, is the first name of Roger Chaffee spelled backwards; and Edward White II gave his generational suffix to the prank by spelling ‘second’ backwards as Dnoces and applying it to Star 20. The people of Apollo kept these names in their literature as a mark of respect to a fallen crew and they have been known to appear in a few star atlases and books in succeeding years.

Soon after the crew of Apollo 8 had begun their coast to the Moon, they removed their suits and never put them back on for the rest of the flight. After all, there were no plans for a spacewalk or any undocking event to pose a risk to the integrity of the cabin’s pressure hull. After the flight, Frank Borman wondered whether they had been required at all. “I would not have hesitated to launch on Apollo 8 without pressure suits,” he said at the debriefing after the mission. He continued, "We wore them for about three hours and stowed them for 141 hours. I see no reason to include the pressure suits on a spacecraft that’s been through an altitude chamber.” However, suits were needed for the ascent to allow the crew to breathe pure oxygen, and for the whole flight in case the spacecraft’s hull was breached for some reason.

All subsequent flights did require the crews to suit up regularly, either for operational reasons (a walk on the Moon is an obvious example) or as a precaution when pyrotechnic charges were cutting pieces from the spacecraft. For example, the final jettison of the lunar module required an explosive cord to cut through the

tunnel wall just in front of the forward hatch.

In some ways, a spacesuit can be seen as the ultimate in extreme out­door gear. Just as a climber on the peak of Mount Everest has to dress up appropriately, an Apollo astro­naut had to protect himself from the conditions he was about to encoun­ter. Like the mountaineer, he had a supply of oxygen as well as protec­tion from the cold and the heat in the rays of the Sun. Two distinct types of suit were produced for Apollo. The CMP had a simpler suit while the surface crews’ suits were designed to support a back pack that allowed them to work on the lunar surface. The following refers to the surface suit.

Air to breathe was fed into the suit either from the back pack, called the

portable life support system (PLSS,

pronounced ‘pliss’), or from the spacecraft via hoses. A fine network of water-filled tubes worn next to the skin kept control of the suit’s internal temperature as the crewman worked. The main part of the suit had an airtight bladder with layers of Dacron fibre, Mylar foil and woven Teflon cloth to protect against heat and cold. The outermost of the suit’s 18 layers was white Teflon cloth that helped to protect against abrasion.

Instead of sunglasses or goggles, a polycarbonate helmet was worn over the head that allowed almost all-round vision. An additional cover, which was worn over the helmet, included a visor that was thinly plated with gold to reflect light and infra-red radiation. It also had a set of pull-down shades at the top and to each side that the crewman could deploy to protect his eyes from the intense lunar sunlight.

When inflated to a pressure of 250 millibars, the suits ballooned and stiffened, which made them difficult to bend and hold in a set position. To counter this, flexible joints were built into various parts of the suit and a network of cables within the layers allowed a posture to be adopted and held. The gloves contained thermal insulation and the fingertips were made from silicone rubber to help to improve the astronaut’s sense of touch. On Apollo 15, David Scott arranged to have his fingertips up against the end of his gloves with the result that, over the course of his 18 hours on the surface, his bruised fingernails had begun to lift from his fingers.

The PLSS carried batteries to power the pumps and communications gear, high – pressure oxygen for breathing, a lithium hydroxide canister for removing carbon dioxide from the suit’s air, and a supply of water for cooling. The cooling element was a clever piece of kit called a sublimator. Water was fed through a porous metal plate where, on reaching a vacuum, it evaporated, thereby removing heat to form ice. From that point on, the ice would continue to sublimate to space and take heat with it as long as more water was fed to replace the lost ice. This cooled the separate water circuit that went around the crewman’s skin.

By the end of a J-mission’s lunar stay, a crewman’s suit was a heavily abused item of clothing that had undergone 20 hours of intense work in the hostile environment of the Moon. Often a crewman would accidentally fall and cover himself in dirt, or the guards over the w’heels of the rover would break off and the crew would be sprayed with dust as they drove. The suit’s outer layer was therefore heavily ingrained with dirt and its locking rings around the neck and wrists w ould threaten to seize owing to the highly abrasive nature of the all-pervasive lunar dust. These multimillion-dollar wonders of engineering are now museum fodder.

After they woke up on the final day of their coast to the Moon, a crew would set about their usual post-sleep chores of reporting their condition to mission control and preparing their breakfast. Normally the spacecraft w’as slowly turning around in its barbecue roll, spreading the heat of the Sun across its surface. While the crew slept, engineers at the ground stations on Earth had taken precise measurements of the spacecraft’s position and velocity to accurately monitor its trajectory. Using this data, FIDO, the flight dynamics flight controller in the MOCR, calculated the amount by which the approach to the Moon needed to be adjusted, if at all. Was the spacecraft coming in too quickly or Loo slowly to pass around the far side at the correct altitude? Was it within the correct orbital plane to pass over the desired landscape? Based on the results of overnight radio tracking, and with the help of the big computers in the real-time computer complex (RTCC), FIDO calculated the details of a burn to be carried out at the fourth opportunity for a mid-course correction, usually scheduled to occur five hours prior to entry into lunar orbit. The details of this corrective burn w’ere read up to the crew1, along with the results of calculations by the Retro flight controller.

While FIDO had been deciding w’here they wanted the spacecraft to fly. Retro was busily working out what to do if something w’ent w’rong. He had Lw’o scenarios to consider: the first was if something were to prevent or impair the LOI burn; and the second was for the situation in w’hich the LOI burn w’as completed successfully but the crew7 were required Lo return Lo Earth at the earliest opportunity. Having decided the manoeuvres that the crew’ should make in these scenarios, it was then important that the details be passed up to the spacecraft while it w’as still in communication with Earth. The mantra was that they should always have the data necessary to get home without further assistance from mission control, in case communications w’ere lost.

In the years after World War II. in the bowels of America’s aeronautical research facilities, a few remarkably gifted engineers were having ideas above their station. Thinking outside the box. as we now call it, they wondered how a manned spacecraft (women were never considered) that had been blasted outside Earth’s atmosphere, could possibly return without killing its crew. Two in particular, Max Fagct and Owen Maynard, were formulating a plan to bring together diverse technologies that were then maturing which might allow the dream of space travel to be realised. Many of these technologies were also concerned with the delivery of nuclear weaponry – the most prominent examples being the liquid-fuelled rocket, the ablative heatshield and the blunt-body re-entry vehicle.

Both the USA and the Soviet Union had been familiarising themselves with rocket technology gleaned from the defeated Germans of World War II. Having learned from rocket engineers who had worked for the Nazis, both superpowers had launched vehicles that had been either looted from central Europe or built locally on the basis of German experience. It soon became apparent that these rockets would be useful carriers for the newly developed nuclear warhead, able to dispatch these weapons across large distances in a short time. Both sides in the Cold War had nuclear armaments, and both realised that in the event of an exchange, early delivery of their warheads would be crucial to national survival.

Fast delivery of nuclear weapons required development of the intercontinental ballistic missile (ICBM) whose long, coasting flight could cross continents in half an hour. Though this class of missile was not required to go fast enough for orbital flight, much of its trajectory was spent in the vacuum of space and one of the chief problems encountered in this arrangement was dealing with the punishing heat the payload had to endure as it re-entered the atmosphere at hypersonic speeds.

After dispensing with solutions that tried to absorb the energy in a heat sink, engineers turned to the ablative heatshield. This was a layer of material on the outside of the warhead fabricated from materials that would ablate – that is, they would slowly char and burn away, carrying the heat and thereby protecting the bomb as it came hurtling back into the atmosphere. At the same time, the work of H. Julian Allen had shown that by forming the shape of a re-entering body into a blunt shield, the searing hot shockwave that always accompanied high-speed aerody­namics could be made to stand away from the fabric of the hull, and thus keep the hottest and most erosive gases clear of the vehicle.

Faget and Maynard investigated whether this technology could be arranged so that a person could sit inside the rocket’s payload instead of a warhead, enter space and return to Earth without being roasted, chilled, asphyxiated, crushed or drowned. An early implementation of their work was the one-man Mercury spacecraft, a relatively unsophisticated capsule that enabled America to log its first minutes and hours of manned space flight. Even before the first such flight was attempted, engineers had begun to consider the design of a successor that could sustain a three-

man crew for an extended flight in space and make a controlled descent through the atmosphere to land on the ocean. Although there was no specific mission for such a spacecraft, the engineers were intrigued by the possibility that it might be able to fly to the Moon.

The name for this spacecraft, Apollo, was coined in mid-1960 by the Director of NASA’s Office of Space Flight Programs, Abe Silverstein, who delved into Greek mythology for inspiration. Apollo was the son of Zeus and had associations with Helios the Sun god. In Silverstein’s mind, the idea of Apollo riding across the face of the Sun seemed an appropriate metaphor for the grand sweep of the programme that such a spacecraft might be able to undertake.

In May 1961, America had hardly dipped its toe in space with the 15-minute flight of Alan Shepard, when President Kennedy proclaimed a mission for this nascent spacecraft by challenging his nation to send a man to the Moon and return him safely to his home planet, and to do so within the eight and a half years still remaining of the 1960s. Kennedy’s early months as President had been troubled by a succession of ‘space firsts’ achieved by the Soviet Union, particularly on 12 April 1961 when Yuri Gagarin became the first person to fly in space by making a single orbit of Earth. Further trouble with an aborted invasion of Soviet-backed Cuba made Kennedy seek something that would raise America’s profile around the world. Landing men on the Moon, a goal that people within NASA were already thinking about, and carrying it out to a deadline, seemed like an enterprise at which his country could excel. The Apollo system would be pressed into this role.

As soon as the world learned of Sputnik’s launch, it was clear that the United States lagged behind the Soviet Union in the lifting capacity of their launch vehicles. But this was no failing of their designers. Rather, most rocket research to this point had been in support of both nations’ nuclear weapons programmes and because US designers were better at building smaller, lighter weapons their rockets were smaller. The Atlas missile used for the Mercury orbital flights and the Titan for the Gemini programme were really delivery systems for nuclear weapons, and struggled to lift their manned payloads. It became habitual for designers to minimise payload weight as they strove to maximise the capability of their spacecraft within the constraints of the available rockets. One decision to save weight would have tragic consequences for what was to have been the first manned Apollo mission.

On Earth, the atmosphere consists of four-fifths nitrogen and one fifth oxygen, the latter being the gas that sustains life. To save the substantial mass of the
equipment required to supply two gases in a manned spacecraft, NASA decided that the cabins of its space­craft would be filled with 100 per cent oxygen, but at a low pressure to ensure that the crew received only the concentration of oxygen mole­cules to which their lungs were accustomed. This single-gas arrange­ment worked well throughout the Mercury and Gemini programmes, and was a sound engineering deci­sion, but as the first Apollo crew were preparing their spacecraft for flight, this nearly ended the pro­gramme.

On 27 January 1967, the AS-204 mission was three weeks away from its planned launch. It was so desig­nated because it was to use the fourth vehicle in the Saturn IB series.

Informally, it was dubbed Apollo 1.

The Apollo spacecraft, CSM number 012, was a Block I type and was sitting on top of an unfuelled launch vehicle. Its crew of three were strapped in for a ‘plugs out’ countdown simulation in which the ability of the entire space vehicle to function on its own power would be tested. The cabin had been deliberately overpressurised with pure oxygen in order to test for leaks, as had been done in ground tests for the Mercury and Gemini programmes. Five and a half hours into a simulated countdown that had made only halting progress, a fire began near the commander’s feet. In the super-oxygenated environment, this quickly grew into an intense conflagration that ruptured the hull of the spacecraft and asphyxiated the three crewmen – Gus Grissom, Ed White and Roger Chaffee.

NASA sustained heavy criticism from the press and the political classes for this tragedy. Some was directed at the manufacturer, North American Aviation, with accusations of sloppy workmanship. North American rebutted, pointing out that as it tried to build the spacecraft, NASA had insisted on interfering with the process by ordering a multitude of changes. In congressional hearings on the fire, astronaut Frank Borman appealed for support from the lawmakers. “We are confident in our management, our engineering and ourselves. I think the question is: are you confident in us?”

NASA learned many lessons from this accident and applied them to the rest of the Apollo programme. Some commentators have argued, convincingly, that there was a very real possibility that, had the fire not occurred, NASA would never have realised

its lunar dream. They point out that the shock of the deaths spurred all those involved in the programme, especially at NASA and North American, to make the Block II spacecraft into the great spacefaring ship it became. Without the changes imposed by the tragedy, casualties may have occurred later in the programme, possibly in space. At the very least, the development problems of the Block I Apollo spacecraft would probably have crippled the programme at a later stage had they not been brought into sharp focus so early on.

Although NASA wanted to keep this unflown mission’s name as AS-204, it acceded to the widows’ requests that the name Apollo 1 be reserved for their dead husbands’ flight. Crews had been in training for Apollos 2 and 3, scheduled for later in 1967, but they were cancelled.

Meanwhile, a few months after the Apollo fire the Soviet Union grieved at its first loss of a cosmonaut during a test of the new Soyuz spacecraft. Both nations therefore had to cope with setbacks in their race to the Moon.

PREPARATIONS FOR LAUNCH Leaving the VAB

Final preparations for the launch of an Apollo mission began weeks in advance in one of the cavernous aisles of the 160-metre-tall vehicle assembly building (VAB). On a large steel platform, 49 by 40 metres, a complete but unfuelled Apollo/Saturn space vehicle, itself 110 metres tall, was stacked. ‘Space vehicle’ was a term for a combined launch vehicle and spacecraft. It started its journey when a 2,700-tonne diesel- powered crawler/transporter that employed tracked tractor units derived from heavy open-cast mining equipment jacked itself up underneath the platform and carried the combined load of 5,700 tonnes out through one of the massive doors and along a 5 V2 – kilometre crawlerway to one of two launch complexes, 39A or 39B, from which the rocket would make its fiery departure.

The crawler/transporter was one element of a mobile launch system that had been devised by members of Wernher von Braun’s rocket team. They had suggested that for a vehicle as large as an Apollo/Saturn V, the task of stacking its stages and installing the Apollo spacecraft on top would be best carried out inside a large hangar. The resulting VAB was a huge box-shaped building 52 storeys tall at the focus of Kennedy Space Center (KSC). In a sense, it was from here that a journey to the Moon began.

If the space vehicle had to be stacked indoors, a method had to be devised to get it out to the launch pad. Barges within dedicated canals were considered, as were great layouts of railway tracks, before the mobile launcher concept was decided. This called for a platform upon which the space vehicle would be fixed until the moment of launch. A tower even taller than the rocket sprouted from one end of the platform, which took the height of the whole affair to 136 metres. This launch umbilical tower (LUT) supplied the space vehicle with its essential services by way of nine huge arms that reached across from the tower. These tended the vehicle until they were swung away either prior to launch, or in some cases disconnecting and

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

DOI 10.1007/978-1-4419-7179-1 3. © Springer Science+Business Media. LLC 2011

pulling away only as the rocket began its flight. Though they weighed an average of 22 tonnes, these arms could quickly accelerate away from a rising rocket, and just as quickly brake to a halt close against the tower.

With the VAB doors open, the crawler/transporter lifted the platform clear of six supporting pillars and carted the entire assemblage away at about 1.5 kilometres per hour. To accommodate the pressure of the crawler’s 456 treads, each weighing nearly a tonne, a specialised roadway had to be constructed wherever it needed to go. A metre depth of support ballast fonned a bed for a layer of aggregate that bore the immense weight of the crawler and its load as they were steered along their journey to the launch pads.

After 42 seconds of flight, the rules of what would happen in case of an abort changed slightly to take account of the fact that the space vehicle had tilted over substantially and had also gained plenty of horizontal speed. The mission had moved into abort mode one-bravo which lasted until it reached an altitude of 30.5 kilometres. If an abort were to be called during this period, the escaping command module would no longer be in danger of falling into the Saturn’s debris, and the small motor intended to steer it out to sea would no longer be required. What was needed, however, was a way to ensure that the CM would turn to face the correct direction after being pulled from an aborting Saturn. This was because tests had shown that at hypersonic speeds, it was possible for the CM/escape tower combination to be stable in a nose-first attitude. The tower could not be safely jettisoned in this mode because the airflow would ram the boost protective cover onto the CM hull, which would not only prevent the tower pulling away but would also prevent the deployment of the parachutes.

Once the LES had pulled an aborting spacecraft free, two skin sections near the top of the tower, known as canards, would deploy after the escape motor had done its job. The drag they created would thereby force a turn-around manoeuvre, if one were needed, to face the heatshield in the direction of travel, and enable the tower to be jettisoned cleanly and the parachutes to be safely deployed.

One of the original concepts put forward for getting to the Moon was the direct ascent mode, whereby a rocket from Earth left the planet on a direct trajectory for the Moon. A major objection to this plan was that it included no opportunity to check whether the spacecraft had come through the stresses of launch unscathed before committing it and its human crew to a lengthy journey in deep space. The competing arrangements. Earth orbit rendezvous and the ultimately successful lunar orbit rendezvous concept, did include a period in parking orbit around Earth as part of their mission plan, giving time to make a comprehensive check of the spacecraft’s systems.

Earth orbit was an important staging point on Apollo’s lunar. journey. It was 2’A hours or so during which the crew and the flight controllers on the ground checked every system they could and prepared for the 5-minute translunar injection burn. For the first time in the flight, the spacecraft was being exposed to a true space environment after having endured the vibration and shock of launch and ascent. It was generally the task of the lunar module pilot (LMP) to work through a series of checklists to verify the status of every major system on board the spacecraft. In this, he was normally aided by the commander.

Careful checks were made of the environmental control system to ensure that the supply of oxygen to the crew was under proper control, that the system was capable of providing necessary cooling for the many electronic and mechanical systems, and that it would maintain the cabin at a comfortable temperature for the crew. Special attention was given to the radiator panels on the side of the service module, and the evaporators in the command module which supplemented the radiators when cooling needs increased. Pipes had been fabricated into the radiators to take the hot fluid from the spacecraft and cool it by radiation into space. If a leak had sprung in one of these panels, there would be no mission to the Moon.

Neither would a journey to the Moon be possible if a problem arose in one of the sets of thrusters arranged around the spacecraft. These small, low-thrust rockets were the business end of the reaction control system (RCS). There were two sets: one each in the command and the service modules. While the thrusters built into the command module would only be required upon re-entry, those on the service module were crucial to just about everything that happened; from simply aiming the spacecraft for the collection of science data to controlling its attitude for critical operations such as guidance sightings, engine burns and thermal control.

In some romantic sense, the S-IVB stage had the most bittersweet, almost tragic fate of all the Saturn components. These large, perhaps elegant stages had been faithful servants to their Apollo masters, who they dutifully sent onwards to the Moon. They were spared the ignominious crash into the sea that befell their larger brethren, the S­IC and the S-II. Instead, they were sent away from Earth to meet a celestial end. Of the ten manned Saturn V third stages – nine of which were Moon bound – half were sent to impact the Moon at high speed in the name of science and lunar seismometry, while the others coasted away from the Earth-Moon system to follow lonely orbits around the Sun, perhaps for all time.

After the departure of their Apollo payload, they became spacecraft in their own right, controlled from Karih or by the systems in the Saturn’s instrument unit until either their batteries ran out or the ground stations ceased to track the receding hulks. The people who controlled the S-IVB from Earth used what little residual propulsion the stage had remaining to achieve these final ends.

After translunar injection, both the S-IVB and the spacecraft were on very similar trajectories which were initially highly elliptical Earth orbits; but the intervening gravitational influence of the Moon would determine the final fate of both craft. While the Apollo spacecraft continued on a path to lunar orbit, the S-IVB was given one of two fates.

For the early lunar Apollo missions, a decision was made to ensure that the S-IVB would be taken well clear of the spacecraft and, in effect, dumped in solar orbit. To achieve this, its remaining propulsion was used to slow it down, so that while the spacecraft would pass the Moon’s leading hemisphere, the stage would be targeted to pass the Moon’s trailing hemisphere and receive a gravitational slingshot that would eject it from the Earth-Moon system. This was the fate of four of the Apollo S-IVB stages and they arc out there, drifting still. Although the Apollo 9 mission never went to the Moon, its S-IVB was nevertheless sent out of Earth orbit as a rehearsal and it, too. orbits the Sun. Like the others, it is slightly inside Earth’s orbit and periodically catches up with Earth.

As Apollo 17 headed out from the Moon, the crew saw something in the distance flashing at them regularly. Jack Schmitt had seen it earlier and Cernan had caught a glimpse of it. "Hey, Bob, I’m looking at what Jack was talking about,” said Cernan to Robert Parker, their Capcom. "It is a bright object, and it’s obviously rotating because it’s flashing. It’s way out in the distance. It’s apparently rotating in a very rhythmic fashion because the flashes come around almost on time.”

They discussed the idea of turning the spacecraft around to enable them to look at the object with their optics, which were mounted on the opposite side. What could be seen out of the windows could not be viewed through the optics any more than windows at the front of a house could be used to look around the back. Anyway, Schmitt was in the habit of using a 10-power monocular to view – Earth’s weather patterns and when he trained it on the object, he reckoned it to be their S-IVB, some way off.

"One unique thing about it. Bob. is that it’s got two flashes,” said Cernan. "As it comes around in rhythmic fashion, you get a very bright flash, and then you get a dull Hash. And then it’ll come around with a bright Hash, and then a dull flash.”

‘"That’s the side of the S-IVB.” said Schmitt, “and then the engine bell. Gene.”

Cernan didn’t believe him. "The commander doesn’t think that I can see the engine bell on that thing,” commented Schmitt.

‘"Roger, Jack. Is that w’ith the monocular you’re looking at it?” asked Parker.

“He couldn’t see the engine bell if he had ten monoculars.” said Cernan wryly.

‘’Bob, a couple of revolutions ago when I was looking at it, I had a much brighter view and I believe I was looking at it broadside.” said Schmitt. "It looks to me like it may be flashing more or less end-on now. But it’s not as bright now as it was a while ago. I just hadn’t put it together as maybe being the S-IVB. I thought it was just some other particle out there.”

”IIey. Bob,” said Cernan later. ‘’We got two of those flashers out there. They could be SLA panels. I don’t know. They’re alike in intensity and pretty regular in the bright and dim flashes they come out with, and they’re widely separated.”

We’ll never know whether Cernan and Schmitt were seeing the S-IVB stage or a couple of SLA panels. We do know that other crew saw flashes from discarded equipment. But as events transpired it was not the last meeting the human race would have with an Apollo cast-off.