Category How Apollo Flew to the Moon

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.

After Neil Armstrong and Buzz Aldrin had landed their LM Eagle on the Moon and while they were preparing for their foray onto the surface, Mike Collins made strenuous efforts to locate the tiny LM among the monotonous wastes of craters on Mare Tranquillitatis by aiming his sextant where mission control reckoned they were. Getting the optics around to face the lunar surface and back again involved carrying out a number of manoeuvres. It was during the manoeuvres after one such viewing opportunity that Collins got a call from Capcom Owen Garriott.

“Columbia, Houston. Over.”

“Columbia. Go,” replied Collins.

“We noticed you are manoeuvring very close to gimbal lock. I suggest you move back away.”

“Yes. I am going around it,” said Collins. “Doing this СМС-auto manoeuvres to the PAD values of roll 270, pitch 101, yaw 45.”

“Roger, Columbia,” said Garriott.

“How about sending me a fourth gimbal for Christmas,” commented Collins, showing his annoyance at the restriction imposed by gimbal lock. Garriott could not make him out. “Columbia, Houston. You were unreadable. Say again please.” Collins let it lie in the spirit of their triumph. “Disregard.”

What was rankling him was a weight-saving decision that had the downside of

substantially complicating some of the operational aspects of a mission because it limited the range of attitudes that the spacecraft could adopt. Because of this, the crew and flight controllers had to avoid orientating the spacecraft in certain directions with respect to the guidance platform.

This characteristic was inherent in the system as designed by the MIT team who had settled on a three-gimbal mounting for the platform, similar to the system they had designed for the Polaris missile, and unlike the four gimbals employed in the Saturn V instrument unit and the Gemini spacecraft. Collins was a veteran of Gemini, and knew the advantage given by the fourth gimbal. But there were solid reasons for implementing only three gimbals. As well as saving the weight of a heavy outer gimbal, trade-offs included greater accuracy and a reduced tendency for the platform to drift in its orientation. However, the three-gimbal arrangement had this unfortunate side effect whereby, if the gimbals were moved in a particular fashion, the assembly lost its ability to maintain the platform’s alignment – a condition termed gimbal lock, and one that meant that the system had lost all knowledge of the direction in which the spacecraft was pointing. Having a fourth gimbal would have avoided this problem. As a result, care had to be taken during the flight-planning process, and throughout the flight itself, to avoid risking gimbal lock.

If gimbal lock did occur, it was a time-consuming procedure to fully realign the platform, possibly with the loss of important operational work. Even worse, if it occurred in the run up to a time-critical man­oeuvre where good platform align­ment was important, there would be no time available to take corrective action. To help crews to steer clear of it, two areas on the 8-ball’s surface were marked in red – it was these red spots that prompted the reference to the Pool ball. Manoeuvring the spacecraft in a manner that would bring either of these spots towards the centre of the display meant risking gimbal lock.

The mechanism that causes gimbal lock is not easy to describe. As previously discussed, the platform was mounted within three nested gimbals. Each had a rotation axis which was arranged 90 degrees away from the axis of the adjacent gim­bals). In normal circumstances, this

arrangement allowed three degrees of freedom because the axes were pointing in three different directions. The problem arose when an attitude was adopted that allowed the axes of the outer and inner gimbals to line up. When this condition was approached, the gimbal system lost its ability to isolate the platform from the spacecraft’s rotations because there were now only two degrees of freedom. All the gimbal axes were now on a single plane, so any rotation of the spacecraft around an axis outside that plane could not be accommodated by any of the gimbal axes. Since the region that flirted with gimbal lock was defined by the current REFSMMAT. it followed that whenever the spacecraft needed to manoeuvre to an attitude that might approach gimbal lock mission control had to give the crew a new REFSMMAT. The platform could then be realigned so as to allow the otherwise awkward attitude to be adopted.

Of course, all this was worked out during mission planning. As many as eight REFSMMATs might be used during a mission, switching as the operational requirements changed. Each Lime the REFSMMAT changed, the platform would be duly realigned. But the avoidance of gimbal lock w as only one reason for changing the REFSMMAT. A more important reason was to aid the monitoring of critical events, such as launch, re-entry, and the major manoeuvres that required long engine burns or where the correct attitude of the spacecraft was paramount. By aligning the guidance platform to an appropriate REFSMMAT that matched the required attitude for the manoeuvre, the crew would find the 8-ball display easier to interpret when the spacecraft was pointing in the correct direction. Attitude errors, which must be avoided during an engine burn, could therefore be easily spotted and corrected.

When Apollo 8 made the first manned flight to the Moon, only three REFSMMATs were required. The purpose of the mission was simple – get to the Moon, orbit it ten Limes, and get back. There was little reason for the spacecraft to adopt widely varying attitudes. For the journey to the Moon, the platform was aligned to the launch pad REFSMMAT. This represented the launch pad’s attitude in space at the moment of launch, as determined with respect to the stars. This orientation made it easy for the crew? to monitor the progress of their ascent from Earth’s surface into orbit and during the translunar injection burn. Later, as they approached the Moon, they realigned their platform to a new REFSMMAT which coincided with their ideal attitude for the engine burns that Look them into lunar orbit. Choosing such an orientation for their platform made it much easier for them to monitor their attitude on the spacecraft’s displays. Once they had left the Moon, Jim Lovell realigned Apollo 8’s platform to a suitable REFSMMAT for re-entry into Earth’s atmosphere, again to make it easier to monitor this critical event.

As missions progressed, the number of REFSMMATs increased to facilitate a more sophisticated use of the hardware. Apollos 12 and 14 had six REFSMMATs while for the advanced J-missions that concluded the programme there were eight. The start of the journey began with the platform aligned with the launch pad. as with Apollo 8. Coasting to the Moon required the spacecraft to be turned slowly to evenly distribute heat around its surface. As this rotation had to avoid gimbal lock, a special REFSMMAT was invented. Each of the three major manoeuvres by the

CSM at the Moon had its own REFSMMAT in order to simplify crew monitoring. Two additional REESMMATs were defined to aid the lunar landing and lift-olT. each representing the orientation of the landing site at the times of these events. Finally, as with Apollo 8, a REFSMMAT was defined for re-entry.

After the loss of power on board Apollo 13. its crew found themselves in the uncomfortable situation of discovering what happens to the cabin temperature of a spacecraft after a power cut. With no electricity running through the systems of the CSM and very little in the LM. hardly any heat was being generated – heat that the crew’ depended on for warmth and comfort. Despite the unfiltered rays of the Sun falling on the ship, a chill permeated the cabin until an equilibrium temperature of only 6: C was reached.

In a properly functioning Apollo spacecraft, the substantial amount of electronic gear that it contained generated copious quantities of heat and. for the designer, the problem was to keep the spacecraft cool. Heaters w’ere only installed for items of peripheral equipment that felt either the chill of space or the chill of the cryogenic gases. To control internal temperatures, the CSM had a sophisticated cooling system that took heat from where it was not wanted, sent some of it to where it was wanted, and rejected the rest into space.

The electronic boxes in the command module were mounted on metal plates, known as cold plates. These w’ere cooled by pipes that contained a mixture of w’ater and glycol the same mixture used in the radiator of a car to cool the engine block. By the time it had passed through all the cold plates, the coolant was quite warm

and, if required, could be used to heat the cabin air, which again is something similar to the system in a typical automobile (at least one without air conditioning).

The warm liquid was then pumped to the service module where it was passed to one of two large radiators built into the spacecraft’s skin. Normally, one of these radiators would be basking in the full heat of the Sun while the other was being chilled by the cold of deep space. Automatic controls fed the coolant to whichever radiator was colder and the heat from the command module was released through radiation. For the sake of redundancy, the spacecraft had two independent parallel radiator circuits in case one developed a leak or became blocked. Automatic systems monitored the outlet temperature of these radiators to keep them from freezing. The cold water/glycol mixture was then returned to the command module where it could absorb more heat from the spacecraft’s electronics.

These radiator panels were not designed to lose all of the command module’s heat but they provided a simple, passive method of dealing with most of it. A second, much more active system was built into the command module to take care of peaks in the spacecraft’s heat output – for example, during preparation for a burn when most of the spacecraft’s systems were powered. This was the evaporator, often referred to by the crew as a ’boiler’, which worked because energy is required to convert a liquid to a gas.

When water evaporates, it takes heat from its surroundings, which is why we sweat when we are too warm. The evaporator used the same principle, but by introducing the water to the vacuum of space the evaporation was much more vigorous, making it a very efficient cooling system. In the spacecraft’s evaporator, spare water generated by the fuel cells was fed through metal plates that contained many tiny holes. Beyond the plates, the water encountered a mass of porous stainless steel called a wick, the other side of which was exposed to space. The evaporation of water from the wick kept it cold. Pipes from the coolant system were passed through this assembly and the water glycol within them gave up its heat to the vaporisation process.

The water vapour from the evaporator was led to space through a duct, called the steam duet, which exited from a port just below the crew’s left-most window. A valve in the duct controlled the loss of vapour to ensure that the wick remained wet and did not freeze. A frozen evaporator was considered a danger because there was a risk that the expanding ice could breach the spacecraft’s pressure hull. Redundancy dictated that there should be two evaporators, one each for the primary and secondary cooling systems.

If the mission had Lo be aborted before the LOI burn. Retro’s response would attempt to achieve two things. It would ensure that the spacecraft was set on an accurate path, not only to Earth but also to a landing site, usually in the mid-Pacific Ocean, where a recovery fleet would be on station. In addition his solution would strive to increase the speed of the spacecraft slightly, so that it would return home 24 hours (one Earth axial rotation) earlier than would occur without intervention. On Apollo 8, Retro had planned to use two separate burns to achieve these goals: & flyby manoeuvre that would have been carried out just before the spacecraft disappeared around the far side of the Moon; and a pericynthion plus 2 manoeuvre, or ‘PC — 2′ for short, to he made Lw’o hours after their closest approach to the Moon. On later missions, both of these functions were combined into a single planned abort contingency.

The PC —2 abort burn was actually used on one oeeasion as part of the effort to get the ailing Apollo 13 back to Earth. On this mission. Retro had to calculate the burn using the descent engine of the lunar module, the SPS engine being unusable owing to the loss of power in the CSM.

Apollo was conceived as a two-part spacecraft. The three-man crew occupied the conical re-entry section, from which they controlled the mission. This command module (CM) carried much of the equipment the crew needed for their flight, and everything they needed for re-entry. Most of their consumables (air, water, power) and their chief means of propulsion and cooling were carried in a cylindrical section attached behind the command module’s aft heatshield. This service module (SM) remained attached to the CM for most of the flight, the two sections acting as one spacecraft under the acronym CSM, for command and service modules. On the return journey the SM was discarded shortly prior to re-entry into Earth’s atmosphere. This distinctive cone-and-cylinder arrangement, with a nozzle sticking out of its aft end, became the archetypal spacecraft in the minds of many children who grew up at this time, fascinated by space flight.

Early plans envisaged taking some arrangement of the CSM all the way to the Moon’s surface as part of a larger vehicle that would sport a set of landing legs to enable the combination to touch down. Although this would have been a rather unwieldy craft to land, the requirement to lift the CSM off the Moon dictated the thrust of the spacecraft’s large main engine.

NASA resumed Apollo operations on 9 November 1967 with Apollo 4. It was an А-mission to test the Saturn V launch vehicle. As so often happens with new, complex systems, getting this vehicle ready for flight proved to be a slow, difficult affair. Its S-II stage repeatedly exhibited cracks during in­spections, and the unmanned Block I spacecraft, CSM-017, tested modifica­tions called for by the investigation into the AS-204 fire.

The Saturn V launch vehicle turned the normal procedures of rocket devel­opment upside down. Traditionally, engineers undertook a careful, pro­gressive programme of testing a rocket stage to ensure that it worked before setting another stage on top, and testing that. To test the entire config­uration at once – so-called all-up testing – was deemed too risky. How­ever, when George Mueller became head of NASA’s Office of Manned Space Flight in 1963 he argued that the incremental approach to testing rocket stages not only wasted expensive

flight-capable stages, it also wasted precious time. He ordered that the engineering and ground testing of the rocket’s components should be of such a quality that all stages of the vehicle could be flight tested at the same time. Apollo 4 would prove to be a triumphant vindication of this strategy. The launch issued a noise like nothing that had ever been heard at the Kennedy Space Center, and this blew away much of the lingering pessimism from the spacecraft fire. As the acoustic and thermal energy was enough to cause substantial damage to the launch tower, NASA had subsequently to make modifications to the launch pads in order to suppress the extreme conditions.

As well as testing the entire rocket system, Apollo 4 placed its CSM payload into a high ballistic arc. From here, the SPS engine powered the command module into a high-speed dive into the atmosphere to test its heatshield by re-entering at the speed it would have if it were returning from the Moon. The CM was recovered from the Pacific Ocean after an 8 /4-hour flight that, in all important respects, was a complete success.

The soft-sounding term ‘launch pad’ belied the true nature of Pads A and В at Launch Complex 39. Each of these two massive, hard, angular structures consisted of a low concrete hill split in two by a trench whose base was level with the surrounding land, barely above sea level. This was to accommodate a wedge-shaped flame deflector of appropriately large dimensions that was wheeled beneath the rocket without descending below the local water table. The alignment of the trench ran along a line towards true north.

This was engineering audacity on an immense scale. The entire space vehicle with its launcher and transporter was substantially heavier than the Eiffel Tower. Yet all of its 8,400 tonnes were driven up a five per cent incline to the top of the 12-metre hill. As it climbed, the launcher was kept level by the crawler’s jacking system, which then gently set it down upon six piers astride the trench. After the crawler withdrew,
the flame deflector rolled beneath the cavity in the launch platfonn, ready to force the flames from the first – stage engines sideways along the trench in order to protect the vehicle from damage by reflected acoustic energy. All the surfaces directly fa­cing the 1,500°C exhaust had to be lined with a suitable refractory mate­rial.

Arranged around the pad’s central hill were ancillary buildings and equipment for storing and feeding propellants, gases, water and power to the vehicle, ponds for fuel spills, a hydrogen-burning pond and a net­work of roads.

Having installed the space vehicle on the pad, the crawler’s next task was to retrieve another huge tower from its parking site just off the crawlerway, and deliver it to the rocket. This mobile service structure (MSS) shielded the spacecraft from the weather and provided access all around it for final preparation. Weighing over 4,700 tonnes, this was yet another mobile engineering marvel among marvels.

The designers of the Apollo/Sa – turn launch facilities had been swept up in the optimism of the program­me’s early days, when the Earth-orbit rendezvous method of getting to the Moon implied a much higher launch rate than was ever realised in opera­tional use. Thus two pads were built with planning for a third having left a tell-tale kink in the crawlerway lead­ing to Pad B. The complex had been designed to process as many as three stacks simultaneously. Pad В was actually only ever used once during the Apollo programme, for Apollo

10. This was during the very peak of

activity, as the final push was being made for the Moon in 1969 and launches were occurring at bimonthly intervals.

At an altitude of about eight kilo­metres, the Saturn V attained the speed of sound, or Mach 1, and went supersonic. It was approaching a dangerous region of the ascent. As the stack rose, the density of the air around it gradually diminished, yet as the rocket gained speed, it con­tinued to ram air onto its forward­facing surfaces, thereby raising the aerodynamic pressure, especially at the conical sections, and increasing the stresses on the skin. At about 14 kilometres, this dynamic pressure, known as ‘Q’, reached its greatest extent, a point in the flight called hnax-Q’. Beyond this point, the rapidly thinning air reduced these aerodynamic stresses.

This was considered to be a risky phase of the launch and one that was always annunciated by the public affairs commentator in view of the risks it held, when any weakness in the structure would be revealed or when a slight deviation of the great length of the rocket in its true passage through the air at Mach 1.7 could result in the catastrophic break-up of the vehicle.

While the commander and LMP busied themselves with equipment checks, the third crewman prepared for his guidance role. When the stack was inserted into orbit, it did so with the apertures for the optical systems facing towards space. The command module pilot (CMP) could use the optics to take sightings on stars and thereby properly align their guidance platform, essentially refining the system’s sense of direction. Not only did this prepare their guidance system for the all-important engine burn to take them to the Moon, it also allowed the CMP to satisfy himself that the system was working well and that it could be trusted to enable the flight to proceed to the next stage.

The first task in the CMP’s alignment procedure was to jettison the covers that protected the exterior surfaces of the sextant and the telescope; two optical instruments on the spacecraft’s hull that were articulated and could be aimed to view

any object within the range of their movement. As he peered through the telescope to report what he saw. he pushed a control lever fully to the right to actuate the ejection mechanism. On Apollo 8, Jim Lovell w’as surprised at what appeared. ‘‘The optics cover jettison worked as advertised; however. when they are first ejected, there is so much debris ejected with them (little sparkles and floating objects in front of the optics) it is hard to tell exactly what occurred." A problem faced by the CMP was that the spacecraft was usually bathed in full sunlight yet he was expected to sight on relatively faint stars through complex optical systems. The tiny points of light he was trying to see were many magnitudes dimmer than the nearby Sun. When additional floating particles were illuminated by the Sun, it only made the task trickier. "It is very difficult at first to see stars through the optics because of the jettisoning of the covers and the putting out of quite a bit of dust with them. As a matter of fact, during the entire mission some of this dust would come out every time w;e rotated the shaft [of the instrument]."

Unsurprisingly, it became standard practice to align the guidance system while the spacecraft passed over the night hemisphere of Earth. Then the particles, although present, would not be lit up by the Sun, giving the CMP a better chance of finding his way around the constellations. Richard Gordon w’as particularly busy when Apollo 12 entered Earth’s shadow for the first time. The guidance platform on board Yankee Clipper had been completely knocked out of alignment by a lightning strike on the spacecraft soon after lift-off. This meant that Gordon not only had to carry out a fine alignment as per routine, but he first had to align the platform from the beginning and this coarse alignment proved troublesome. “When I looked in the telescope I couldn’t see anything," he later explained. "There was no light or anything coming from there. I thought it must be because I’m not dark-adapted and probably this was correct."

It generally takes half an hour for a person’s vision to adapt to dark surroundings. As stars are so dim, and as there was a substantial loss of light through the complex optical system, the CMP needed some help to know’ which star he was pointing at. In the normal course of things, the guidance system itself could point the optics at where it believed the star to be and even if this was a bit off, it was usually enough for the CMP to finesse the aim. On this occasion, the guidance system was completely misaligned and it could give no assistance.

"Fortunately Л1 [Bean] was helping me with this. He was looking out his window’ and could see Orion coming up on his side. So, I just waited until it came into the field of view of the optics." Orion, one of the best-known constellations, w’as of assistance to Gordon because it not only contains Lw’o bright stars, Betelgeuse and Rigel. but is also near to Sirius, the brightest star in the sky excluding our Sun. Usefully, Orion’s belt points roughly towards Sirius. "I saw’ the belt of Orion dimly in the very edge, and then 1 could pick up Rigel and Sirius. Once I had picked up Rigel, I could find Sirius. They were the only stars I could see in the entire field of view." Once he had aimed the optics at known stars, he used Program 51 in the computer to roughly align the guidance platform. Now’ the job became easier because the computer could aim the optics to approximately the right direction for a particular star and Gordon could then use Program 52 for the all-important fine alignment.

“The pressure was on and fortu­nately those two stars were the only ones I ever did recognize,” said Gordon. “They were Rigel and Sir­ius. They were just barely in the field of view. I grabbed those two quickly and got a P51 and did a quick P52. I think that one of the stars [that the P52] came up with was Acamar. I wouldn’t have been able to find that in any circumstances.”

Having aligned the platform dur­ing their first night-time pass over Australia, Gordon repeated the P52 exercise on the second revolution to check that the platform alignment was not drifting excessively. “The second P52 over Carnarvon [West Australia], just before TLI, indicated that we had a good platform. Drift angles were very low. Everybody breathed a sigh of relief that we had our platform back again.”

On 3 September 2002, astronomer Bill Yeung discovered a faint, 16th magnitude object that was orbiting Earth.1 Initial excitement about this apparent asteroid, designated J002E3, centred on the remote possibility that it might, one day. impact Earth. As more data on its orbit was gathered, analysis showed that it could not have been in Earth’s vicinity for long and had probably been in a heliocentric orbit before being captured by Earth. Additionally, spectroscopic studies revealed that its surface colour was consistent with titanium oxide, the pigment in white paint. It was no asteroid.

Projecting the orbit ОҐ. Г002ЕЗ around the Sun backwards in time showed that it had previously been in the Earth-Moon vicinity in 1971, around the time of the Apollo 14 mission. However, since all of the components of that mission had been accounted for. it could not have come from Alan Shepard’s flight. Suspicion shifted to the Apollo 12 S-IVB.

After Richard Gordon had completed his TD&E exercise, the two Apollo 12 spacecraft. Intrepid and Yankee Clipper, continued on their path to the Moon in November 1969. NASA intended that Apollo 12’s S-IVB should go the same way as the previous Moon-bound third stages by having its residual propulsion slowr it dowm sufficiently to pass the Moon’s trailing limb and be slung into heliocentric orbit. Unfortunately, a guidance error by mission control resulted in a burn that lasted too long and the stage was slowed more than intended. It therefore passed too far from the Moon to achieve a proper slingshot and instead entered a large Earth orbit from which, owing to a later encounter with the Moon, it subsequently escaped. As far as anyone can tell, it was this S-IVB that had returned for Bill Yeung to catch in his telescope that September night.