Category How Apollo Flew to the Moon

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.

As the design of the G&N system was being finalised in the early 1960s, a eonllict arose between those who designed the equipment and those who would fly with it. The designers at the Instrumentation Laboratory at MIT led the field of applying mathematics to the problems of guidance, whether in a submarine, an aircraft, a nuclear-tipped missile or the exploration of space. They saw the problem from a wide perspective in which all guidance could be reduced to equations that modelled the solar system as it sat surrounded by the stars. Their fundamental point of view’ was an inertial one. which was expressed during Apollo’s gestation by an intention that the spacecraft’s attitude should be displayed as a set of numbers with respect to inertial space. The crews, on the other hand, w’ere pilots, and pilots see flight largely in terms of movement with respect to the horizon of wTiatever planet (usually Earth) they are flying over. Their point of view’ dealt with a local frame of reference that stayed aligned with the ground beneath their spacecraft, even as they flew around a curved planet.

These two viewpoints on spacecraft control influenced the Apollo guidance and navigation system as it evolved at a tremendous pace during its development; the inertial point of view’ dictating its fundamental structure, but w’ith the astronauts’ preferences heavily influencing the final mode of operation because they had experience on their side. They had cut their teeth on the Gemini flights of 1965 and 1966 during which NASA learned how to fly in space. They pointed out that most manoeuvres needed to be carried out with respect to the ground below, especially the all-important rendezvous manoeuvres on which the Moon-bound flights relied. As the design of the Apollo G&N system had been largely settled by the Lime this operational experience w-as gained, both hardware and software modifications had to be made to meet the expectations of the crews. These included the ‘8-ball‘ display and the ORDEAL add-on to turn it into an artificial horizon that the pilots preferred.

Space is a strange place for those of us who are used to the warmth of Earth. Here on our planet, the air. the oceans and the land absorb the heat from the Sun and give it up at night, thereby moderating temperatures. We know instinctively the importance of air in the transportation of heat, whether it is between the sea and land, within the rooms of our houses or inside the equipment we possess. In space, things are very different.

Imagine placing an object in cislunar space, not too near Earth, sitting motionless. The side facing the Sun will become warm. How much depends on its characteristics but as it gradually warms, it also radiates heat. The warmer it gets, the more heat it radiates until it reaches a point where it radiates as much heat as it receives. At this point, it is at thermal equilibrium and its surface temperature, probably quite high, is constant. The side of the object opposite the Sun will also radiate whatever heat it had. but this will not be replenished. The surface temperature will gradually fall until the minimal sources of heat available to it become comparable to the heat it is losing. Given time, and assuming that little heat leaks through the object from the sunward side, this area will become extremely cold. These extremes of temperature easily coexist in an environment where there is no air to transport heat.

In the Apollo spacecraft, there were various reasons why it was undesirable to allow these temperature extremes to exist for long. For example, tests had shown that the heaishicld material around the command module would crack and flake if it were allowed to become too cold, while the tanks for the RCS thrusters had to be kept at moderate temperatures at all times to prevent freezing or overpressurisation. The simple solution was to rotate the spacecraft gently around its long axis, side-on to the Sun. This technique was formally known as passive thermal control (PTC) but for many commentators, a far more descriptive term was the ‘barbecue’ mode.

Apollo 8 was the first to try to set up a PTC roll. Mission control gave Frank Borman an initial altitude that would place the spacecraft side-on to the Sun whilst avoiding gimbal lock and maintaining good communications. Once aligned, he began a constant, slow roll about the spacecraft’s longitudinal axis of only 0.1 degree per second which Look an hour to make a full rotation. However, physics abhors such a rotation, at least in the long term, and especially when large quantities of fluid are involved. With Lime, the rotation axis itself began to rotate so that the long axis sw’ept out a cone with an ever-increasing angle – a motion appropriately known as coning.

It was soon found that this simple method of initiating and maintaining PTC would not be appropriate for later missions. The addition of a lunar module would lengthen the stack further and make the simple roll manoeuvre even more difficult to maintain. Instead, use was made of the tracking programs in the command module’s computer to carefully control the overall attitude as the rotation progressed. Another change for later missions was to generate a reference orientation for the platform, a REFSMMAT, which was particularly suited to the manoeuvre.

The final three Moon-bound Apollo missions. Apollos 15 to 17, had one special task to perform prior to arrival in lunar orbit. Sector 1 of their service modules contained a scientific instrument module, or SIM bay for short. It housed a variety of cameras and instruments to investigate the Moon and its environment, and would be operated by the CMP during his lonely vigil while his crew-mates explored the lunar surface.

Hidden as it was behind the external skin of the service module, the SIM bay had to be exposed to space by removing one of the spacecraft’s panels. Rather than implementing door-like mechanisms with latches and hinges, engineers decided that a more reliable solution was to jettison the bolt-on panel by blowing it clear with pyrotechnic charges. This occurred before the spacecraft entered lunar orbit in order

that the jettisoned door would not enter lunar orbit and become a possible collision hazard. Explosive cord had been laid within a groove around the door’s edge. This was detonated to cleanly cut the aluminium skin, while further charges were set off to push the severed door clear. While the spacecraft then eased itself into lunar orbit, the door coasted around the Moon to emerge on a trajectory which would return it to the vicinity of Earth and. in all likelihood, eventually enable it to slip into an independent solar orbit.

Apollo 15 provided the first occasion for the detonation of these fireworks and Capcorn Joe Allen made light of the situation: “By the way. is that the manoeuvre where the SIM bay door jettisons the spacecraft?’’

In the Newtonian environment of space, it was as valid to say that the door was jettisoning the spacecraft as the other way around. A1 Worden agreed: "It has been variously known as that kind of a manoeuvre, yes.”

In fact, just as the spacecraft had pushed the door away, the door also pushed the spacecraft away, and engineers on Earth could detect this tiny trajectory change in their tracking. “15, just out of interest, we saw a good healthy jolt in our Doppler data down here during jcLL time," informed Allen.

“Gee, that’s very interesting,” replied David Scott, “because I would say that the jolt in here was very minor.”

As a precaution, the crew of Apollo 15 put their suits on in ease the shock of the explosives caused a breach in the cabin for some reason. This reflected wariness by programme managers following a Soviet space tragedy. A month earlier. Soyuz. 11 had departed the first Salyut space station. The shock of the pyrotechnic charges that jettisoned the orbital and service modules of the spacecraft immediately following the de-orbit manoeuvre had inadvertently opened a ventilation valve intended for use in the atmosphere, enabling the air to escape and quickly asphyxiating the crew’. Although the automatic systems brought the capsule to a pinpoint landing on Earth, the ground personnel found that the crew were dead when the hatch was opened. It was decided that in future Soyuz crews would be provided with pressure suits to be worn for launch and entry.