THE ROUTE TO THE MOON Translunar injection
Flying to the Moon, when you don't have a lot of propellant to hose around, is like a stone throw - a ballistic lob across 400,000 kilometres of space between two worlds. The impulse for this 'throw' came from the S-IVB stage of the Saturn V which added an additional 3 kilometres per second to their speed with a burn nearly 6 minutes long. As this translunar injection TLI burn progressed, it modified the spacecraft's circular orbit into an increasingly long, stretched elliptical orbit whose...
New Knowledge Apollo
The scientific feast continued with Apollo 16, launched on 14 April 1972 to explore what were believed to be 'highland volcanics' within the rugged hills near the crater Descartes towards the centre of the Moon's disk. Its crew of John Young, Charlie Duke and Ken Mattingly nearly had to abort their mission some hours before landing, when the main engine on board the CSM Casper began to wobble when Mattingly tried to test its back up steering system preparatory to a scheduled burn. Once this...
Lunar Orbit Rendezvous
Any journey in space is heavily influenced by the propellant available to achieve it. At the same time, the amount of propellant required is largely determined by the mass of the object that is to make the journey and how quickly the journey has to be undertaken. The alternative scheme, known as lunar orbit rendezvous LOR sought to limit the amount of mass that had to be propelled at any stage of the journey. A reduction in the quantity of propellant required for the Apollo spacecraft would...
Xray fluorescence spectrometer
Having essentially no atmosphere, the Moon has little protection from the Sun's constant output of x-rays that wash over its day-lit surface and strike whatever gets in their way. When they strike certain elements, particularly those at the lighter end of the Periodic Table, they cause the atoms to re-emit or fluoresce x-rays in certain well-defined energies. Therefore, by comparing the spectral make-up of x-rays from the Sun with x-rays from the sunlit lunar surface, scientists could determine...
Heatshield sacrificial surface
Heatshield designs for Apollo originated in the re-entry vehicles that were developed in the 1950s for nuclear warheads. These weapons were launched on ballistic arcs out into space by large rockets to increase their speed and minimise delivery times, but as their elaborate mechanisms had to negotiate the great temperatures generated by reentry, they were protected inside a vehicle whose outer wall included some form of heatshield. Initially heat sinks were used, but development of this Cold...
DOI with the LM
For Apollo 10's rehearsal and for the first two landings, the CSM remained in its 110-kilometre orbit, leaving the LM to enter the descent orbit itself with a DOI burn. On Apollo 11, this was a 30-second burn, 15 seconds with 10 per cent throttle and the remainder with the throttle set to 40 per cent. Having a period of time at a low thrust setting allowed the gimbal mechanism, on which the descent engine was mounted, to align the engine's thrust with the spacecraft's centre-of-gravity. This...
Looking out of the window
Responsibilities in the LM were tightly defined, especially during the approach and final phase. The commander wanted to keep his eyes out of the window, watching where the spacecraft was going. The LMP, on the other hand, generally had to keep his attention inside the cabin. His responsibility was to vocally feed whatever relevant information the commander would require at a given point in the descent. The details of this were worked out by each crew individually over the months of training...
Contents
xxiii 1 Apollo an extraordinary The meaning of Dreaming of the The Apollo Which Lunar orbit Swords to ploughshares von Braun's rockets 17 2 The Apollo flights a brief An alphabet of Failure of Back in the saddle Apollo The lunar module flies Apollo 5 29 The Saturn balks Apollo Testing Block II Apollo Gutsy decisions Apollo A complete system test Apollo 9 34 A dress rehearsal Apollo Task accomplished Apollo Lightning strikes Apollo The successful failure Apollo Try again Apollo Exploration at...
TRANSPOSITION DOCKING AND EXTRACTION Preparations
The first step in the whole process was to ensure that the command module's cabin was pressurised with air up to its maximum extent, about two-fifths of an atmosphere. This was in preparation for later when, to save the LM's scarce resources, its initial air supply would be drawn from the CM cabin air. Valves on each side of a tunnel that would eventually connect the two spacecraft would then allow air to be exchanged between them. While the crew worked through the TD amp E checklist, the APS...
Freereturn
Even before Kennedy's challenge, the lunar free-return trajectory had been recognised as a safe and efficient means by which a spacecraft could make the journey. This was a wonderful solution to the problem, one whose propellant needs were within the capabilities of the Saturn V, that could get a crew to the Moon within three days and allow the entire mission to be carried out within 14 days, well within the duration for which the Apollo spacecraft was being designed. Furthermore, if something...
Cleanliness
Just as there was no conventional toilet, the spacecraft contained no shower or basin. On a flight lasting less than two weeks, simpler regime. Washing was performed by just having a wipe with one of the available cleansing cloths. Two types were available wet and dry each about 10 by 10 centimetres, with the wet cloths containing a germicide. These were specifically intended for general cleansing after food and defecation. Afterwards, the skin was dried with tissues from one of seven...
Dead band
The next stage of the LM checks required the crew to think about the concept of the dead band, which is another of those curious terms in spaceflight where a simple concept lay behind opaque jargon. Apollo was one of the first applications of a digital fly-by-wire system whereby control of a vehicle was placed in the hands of a computer. In the Apollo guidance computer, programmers included a series of algorithms that would fire the RCS jets as necessary to bring the spacecraft to a desired...
Redundancy in control
The designers of the Apollo spacecraft were always careful to build redundancy into their systems to ensure that a single point failure could not jeopardise the crew - a philosophy that extended to the guidance and navigation system. The designers were very aware that any of its exotic components could fail at any point in the mission. To this end, the command module had a second control system which, although it shared many components with the G amp N system, could operate entirely separately....
Entry monitor system
The crew's next task was to put the entry monitor system EMS through a series of tests to verify that it could be trusted in its role, which was, as the name implied, to monitor the progress of the re-entry. This bit of kit on the main display console came into its own in the final minutes of the mission, but its weight wasn't carried for 2 weeks without it having to work for its passage. NASA's engineers saved weight by having systems share their components where possible, so throughout the...
Plummet
At 18 kilometres altitude, the cabin pressure relief valve was set for entry. In this mode, the valve held the cabin pressure at its nominal value until the outside pressure rose to a slightly higher level, at which point outside air would begin to flow into the cabin. On the main display console in front of the CMP and commander was a small altimeter whose needle now responded to the rising air pressure outside, allowing the crew to use its information to check the progress of the descent. In...
Mascons a lumpy Moon
Over a one-year period between 1966 and 1967, five Lunar Orbiter spacecraft were dispatched to the Moon to carry out comprehensive photo-reconnaissance of its surface, largely in support of the Apollo programme. It was mostly through this programme that engineers gained the skills necessary to accurately track an object around the Moon and control its flight path. Controllers were surprised to discover that, unlike orbits around Earth where the gravity field is nearly uniform, the orbits of...
Rendezvous Techniques
Once NASA had accepted LOR as the Apollo mission mode, they had to work out how rendezvous, whether in Earth or in lunar orbit, should be accomplished. The problem is far from straightforward, and the solution did not spring forth from the mind of some brilliant engineer. Rather, it evolved from 1964 right through to the first landing and continued to evolve throughout the programme. The problems were many. Some of the major factors with which they had to contend were how accurately would the...
Braking And Stationkeeping
The final major manoeuvre of the rendezvous was braking. Since the TPI burn, the LM had been coasting on an intercept trajectory that was essentially part of an orbit. The apolune of that orbit was a kilometre or more higher than the altitude of the CSM and, without braking, the LM would have sailed by in front of its target. Starting from a distance of nearly 3 kilometres, the commander executed a series of manoeuvres to reduce the closing speed of the two spacecraft. Each was pre-planned to...
THIRD STAGE The second staging event
It was only when the S-II tanks had run dry and a signal had been sent to shut down its engines, that the Saturn's computer could begin the next stage of the ascent - the staging event that discarded the spent S-II and ignited the S-IVB for the first of its two burns. The same signal began Timebase 4 in the instrument unit to choreograph everything that had to occur. Unlike the dual-plane separation between the first and second stages, this cut was made across a single plane at the top of the...
Final preparations
Over the final few hours before entering lunar orbit, the Apollo crews began an exhaustive series of checks and adjustments, interrogating their spacecraft's systems about their ability to sustain life while in the Moon's clutches, and on the engine's readiness to do its job properly. Another important task in the build-up to LOI was to change the spacecraft's knowledge of which way was 'up'. During the 5 or 6 minutes of the burn, the crew wanted to avoid any appreciable errors in the direction...
Descent propulsion system
Most of the LM's descent stage was taken up with the descent propulsion system DPS . In the parlance of Apollo, the DPS was always pronounced 'dips'. The designers had come up with a simple cruciform structure for the descent stage which held a propellant tank in each of the four box-shaped bays around a central space where the engine was mounted. This engine was remarkable for its time for being able to be throttled, i.e. its thrust was variable, which was a major technical achievement. The...
How Apollo Flew to the Moon
Editor - Apollo Flight Journal NASA web resource SPRINGER-PRAXIS BOOKS IN SPACE EXPLORATION SUBJECT ADVISORY EDITOR John Mason B.Sc., M.Sc., Ph.D. ISBN 978-0-387-71675-6 Springer Berlin Heidelberg New York Springer is a part of Springer Science Business Media springer.com Library of Congress Control Number 2007932412 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication...
Door jettison
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 crewmates explored the lunar surface. Hidden as it was behind the external skin of the service module, the SIM bay...
A Walk Outside Eva
On the day after TEI, the command module pilot of the J-missions took centre stage. The cameras of the SIM bay had photographed their images onto long lengths of photographic film stored in large circular magazines, which were now sitting in the service module, itself to be discarded in a few days time when it would burn up and be destroyed in Earth's atmosphere. The film therefore had to be brought into the command module's cabin, the only part of the spacecraft that would survive reentry. To...
Subsatellite
In an effort to get around the terribly short period of time that an Apollo CSM orbited the Moon, barely a week at most, scientists added a small, 35.6-kilogram subsatellite to the SIM bays of Apollos 15 and 16. This was ejected just before the crew headed home. Its function was to investigate the various particles and fields in the lunar environment. 'Particles and fields' is an expression used within the planetary science community for the investigation of planets and their environments...
Getting the height right
The spacecraft's design had assumed that the windows would face forward during the final approach to give the crew a view of their landing site, and that it would pitch into this attitude from a windows-up attitude. If the windows were facing up, and given that the landing radar had to face downwards, then its antenna had to be mounted on the base of the descent stage on the side opposite the windows. Intrepid, Houston,'' called Carr to Conrad and Bean. You're looking good at three minutes .''...
The circularisation manoeuvre
In all instances, the two spacecraft were allowed to separate once the LM was well into the checkout of its systems and no problems were being encountered. For the later missions, Apollo 14 onwards, mission control read up a PAD with which the CMP could make his circularisation burn. In truth, the orbit resulting from this burn was not really circular but was made deliberately elliptical. This reflected the fact that FIDO was compensating for the perturbation of the CSM's trajectory by the...
Program alarms part II
Apollo 11 had already had a brief encounter with the computer throwing out program alarms during the braking phase. As Armstrong and Aldrin brought Eagle through the approach phase, the computer began to play up again. Eagle, Houston. You're Go for landing,'' said Duke in the Capcom chair. Roger. Understand. Go for landing. 3,000 feet,'' returned Aldrin, as they passed 1,000 metres altitude. Just then, Aldrin made a call that the computer was acting up yet again. Program alarm. 1201.'' 1201,...
LM abort modes
In the continuing spirit of NASA's defence-in-depth philosophy, a series of PADs were read up to the crew that not only told them exactly when they were going to start their descent to the surface, but also what to do in the event of an abort being necessary at various times before, during and after the descent - in case the radio link were to fail. As the flights progressed, these PADs increased in complexity as planners learned from previous missions and made their procedures more elaborate....
Landing site REFSMMAT
The landing site REFSMMAT was another of the many frames of reference used during an Apollo flight. It was carefully chosen to aid a landing crew by having their attitude displays, the FDAIs, or 8-ball, give readings that made sense to a pilot approaching the lunar surface. This frame of reference was defined as being the attitude of the landing site with respect to the stars at the predicted time of landing. The actual orientation of the landing site, of course, continuously changed as the...
Ptc Spacecraft On A Spit
Space is a strange place for those of us who are used to the warmth of Earth. Here on our planet, the air around us, the oceans and the land absorb the heat from the Sun and, as a result, temperatures are moderated. 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 the...
Transearth Injection
The NASA-ese term for the manoeuvre that brought the spacecraft out of lunar orbit and homeward to Earth was trans-Earth injection TEI . In simple terms, it was very similar to the TLI manoeuvre that sent the crew moonward in the first place in that its task was to add more speed to the spacecraft in order to raise the high point of its orbit sufficiently to take it from one world to another. To achieve this, their orbital velocity had to be raised by nearly 1 kilometre per second. With only...
Saturns guidance
At T-20 seconds, swing arm 2 was retracted from its position connected to the top of the S-IC. As it arced back to the tower, the guidance system on the Saturn was finally set for the flight. In the instrument unit above the S-IVB stage, there was a conventional gimbal-mounted guidance platform - the type that can hold its orientation while the vehicle around it rotates. As the Earth turned with the Saturn V on the pad, the platform kept its alignment with respect to the stars. If an onlooker...
Landing point designator
In the LPD, the computer's programmers had devised a simple but powerful way to tell the commander where P64 was taking them. It was as simple a device as you could hope to find in a high-tech spacecraft, though its operation depended on what was then one of the world's most sophisticated small computers. It consisted of nothing more than lines carefully scribed onto the inner and outer panes of the commander's forward-facing window that marked his line of sight, measured from a line directly...
A Long Day
For their pioneering journey to the surface of the Moon, Armstrong and Aldrin made only a single foray onto the surface before attempting to get some sleep in the uncomfortable confines of the LM. The rendezvous and docking next day were therefore carried out by a crew that were hopefully rested to some extent. As each successive flight became more ambitious and the LM was trusted with a crew for longer periods, the rendezvous and docking day grew increasingly packed. At first, 4-hour, and...
Crossing the equigravisphere
Between the Moon and Earth, there came a point where the gravity of the approaching body became stronger than that of the receding body. When this point of gravitational equality was reached, it was customary for mission control, and especially those concerned with flight dynamics, to switch their frame of reference from one world to another. However, because the Moon itself was in motion around Earth, the numbers representing the spacecraft's speed and position appeared to jump. Journalists...
Landing radar
On Earth, an aircraft's altitude is conventionally determined by measuring the outside air pressure making use of the fact that the atmosphere gradually thins in a well-understood manner as altitude is gained. On the Moon there is essentially no atmosphere so another method had to be devised to determine how high the LM was above the surface. This was particularly important given the fact that there are few clues a pilot can use to determine speed or altitude by eye. There are no trees, roads...
The launch escape system
When the spacecraft was sitting on top of the Saturn V, it included one extra element of the Apollo system that everyone hoped would never be used. If it had, it would have been a particularly bad day for all involved. Attached to the tip of the CM was a truss structure upon which was mounted a thin, pencil-like tower which included a Computer rendering of the LM ascent stage. Image courtesy of Scott Sullivan. Computer rendering of the LM ascent stage. Image courtesy of Scott Sullivan. Diagram...
The Apollo lander
The CSM was a streamlined and sturdy craft, designed to ascend through the atmosphere of Earth, and, in the case of the command module, withstand a punishing re-entry. In complete contrast, the lunar lander was a true spacecraft because it was entirely incapable of flight in an atmosphere. Known as the lunar module LM , its construction was entrusted to the Grumman Aircraft Engineering Corporation. This was a truly exotic ship in which every aspect of its major systems pushed the know-how of...
The Apollo spacecraft
The command module was a stubby, conical craft almost entirely covered with a heatshield that was thickest across its base to sustain most of the punishment of re-entry. The outer rim of the cone was packed with small tanks, thrusters, various antennae and two small ports for the ejection of waste water and urine. The apex of the cone had a removable probe mechanism to enable it to dock with the Apollo lander and a tunnel through which the crew could transfer between the two spacecraft....
Command module RCS
Having heated the command module's thrusters, the rest of its reaction control system could be primed, ready for use. Throughout the mission, all small-scale manoeuvres were carried out using the RCS thrusters on the service module. The command module's RCS was a simpler system primarily because there was no need to perform translation manoeuvres. It controlled the command module as re-entry began, presenting it to the atmosphere in its naturally stable, aft-first attitude until aerodynamic...
Entering lunar orbit the LOI manoeuvre
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 an utterly inhospitable lunar surface unless a small rocket engine worked properly to get them off and begin 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...
The restaurant at the edge of the universe
One of the cliches that has become firmly set in the public's mind since the space age began 50 years ago is that space food is a bland, dehydrated mush that comes in a tube. Certainly, for the earliest flights, this was true. However, on Apollo, things began to change a little. Some of the food taken on Apollo was dehydrated, for good reason. Water makes up a substantial component of soups and juices, and makes them heavy. Since spare water was plentiful anyway as a by-product of the fuel...
Probe and drogue spacecraft sex
The docking system was one of the many engineering wonders of the Apollo programme and one whose importance is perhaps underplayed. The docking system was an ingenious, compact, pneumatic and mechanical arrangement that managed to elegantly fulfil an enormous range of tasks it self-centred the two spacecraft as they contacted it absorbed the shock of that contact to achieve a soft-dock and, finally, it pulled the two craft together to achieve hard dock and straightened their axes as it did so....
Splashdown
Finally, after a journey lasting up to 13 days, and having taken men further from Earth than they would go for at least another two generations, Apollo's mission to the Moon ended with a hefty thump on the surface of the ocean. With luck, the spacecraft would catch the tip of the descending swell, softening its impact. Not so for the crew of Apollo 12. Luck went against them, and especially against the skull of LMP Al Bean when rough waves and bad timing created a very hard impact, as Conrad...
The midcourse correction
The purpose of determining the state vector was to see if their course to the Moon was true and, if not, to 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...
LOS and AOS out of sight
Apollo missions were intensively monitored from Earth. Because they had deep technical visibility into the spacecraft's systems through telemetry, and huge computing and personnel resources on hand in case of problems, mission control became accustomed to nursing its crews and machines over the days of the coast to the Moon. It was then a bit of a wrench when some of the most critical events in an Apollo flight, particularly the entry into and departure from lunar orbit, had to occur with a...
Lunar whiskers
Shaving was optional. Many lunar explorers returned to Earth with two weeks' growth proudly displayed as they stepped off the helicopter following their recovery. Others chose to shave even though it could be difficult. Mike Collins did a bit of both, returning to Earth with a decent moustache. Although these normally fastidious men tolerated such limitations to their personal hygiene for the duration of a mission, many began to be irritated by them towards the end and were only too glad to get...
Power the fuel cell
Buried within the pie-shaped structure of the service module were originally two later three tanks each of oxygen and hydrogen. Although these two substances are excellent propellants for rocket engines, propulsion was not their purpose in the Apollo design. A common notion is that spacecraft usually derive their electrical power from the Sun via large arrays of solar cells. While this is generally true for automatic spacecraft in the inner solar system and for the international space station,...
The state vector
In order to describe a flight path in space, the trajectory experts simply need to know two things where the spacecraft is and how fast it is going at any particular time in the flight. But before they can express these two concepts they must have some frame of reference against which to measure them. If I were throwing a stone across my back garden and wished to define its path -assuming I had access to the necessary measuring equipment - I might be able to state that 1 second into its flight,...