Lucy Rogers
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`|t’5 0 N |_Y
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`Rocket Science
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`An Introduction
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`{
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`Dr. Lucy Rogers
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`|t’s ONLY Rocket Science
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`An Introduction in Plain English
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`Q Springer
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`Space Exploration Technologies; NEW PETITION
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`Dr. Lucy Rogers Cling MIMechE FRAS
`Isle of Wight, UK.
`www.itsonlyrocketscience.com
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`
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`ISBN 978-0-387-75377-5
`D01: 10. 1007/978-0-387-75378-2
`
`e-ISBN 978-0-387-75378-2
`
`Library of Congress Control Number: 2007939660
`
`(9 2008 Springer Science+Business Media, LLC
`All rights reserved. This work may not be translated or copied in whole or in part without the written
`permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY
`10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection
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`i. Introduction
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`Non est ad astra mollis e terris Via
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`(There is no easy way from the Earth to the stars)
`Seneca, circa AD 50
`
`On October 4, 1957, Sputnik I became the first artificial satellite.
`It was launched into orbit by the former Soviet Union. The media
`coverage following the Soviet/s success meant that the general public
`quickly became aware that rocket science was a scientific endeav-
`our and no longer in the realms of science fiction. Rocket science
`has always been perceived as very challenging and the difficulties
`the Americans faced with their early launch failures reinforced this
`idea. Wernher von Braun, a major contributor to the development of
`rocket technology, both in Germany and later in the USA, said:
`
`It takes sixty-five thousand errors before you are qualified to make
`a rocket.
`
`After the success of Sput111'I< 1, the launch and operation of satellites
`became very politically sensitive and so the brightest scientists
`and engineers were often employed as rocket scientists. It there-
`fore became thought of as a subject only for the most intelligent.
`There are other fields of study that are arguably more challeng-
`ing than rocket science, but, other than brain surgery, none have
`entered the mainstream vocabulary as a difficult thinglto do.
`This book aims to explain, in everyday terms, just what is involved
`in launching something into space and exploring the universe outside
`of our own small planet. It provides an overview into what is required
`for a rnission, without the mathematical analysis of the fine detail.
`Such analysis is included in many good textbooks, SOI11€ of which are
`listed in the bibliography. The rest of this chapter explains and defines
`some of the fundarnental properties of space and rocket science that
`will be referred to throughout the book. The more technical aspects
`have been relegated to the Appendices, and, for sirnplicity, I have usu-
`ally referred to all spacefaring humans as astronauts, no matter their
`citizenship or the country from which they launched.
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`Tsiolkovsky calculated many astronautical principles and
`designed rockets, but he never built any. At about the same time as he
`was Working on his theoretical models, the American scientist Robert
`H. Goddard began to work seriously on rocket development, although
`neither knew of the other’s Work. Goddard was much more practical
`than Tsiolkovsky and by 19 15 Goddard had carried out his first experi~
`merits involving solid—fL1elled rockets. Both Goddard and Tsiolkovsky
`independently came to the conclusion that the solid fuels of the time
`would not be sufficient to power rockets to the height they believed
`would make it into space, but that liquid fuels Would. Liquid-fuelled
`rockets are a lot more complex than solid—fuelled ones and involve
`many parts. Goddard launched the first liquid—fue1led rocket in 1926
`and by the time he died in 1945 he had been granted many patents
`on various component rocket parts, including combustion chambers,
`nozzles, propellant feed systems and multistage launchers. Some of
`his patents still produce royalties for his estate. Goddard is regarded
`as the American Father of liquid-fuelled rockets.
`‘
`By the 1930s there were rocket enthusiasts and rocket clubs
`in many countries including Germany, the Soviet Union and the
`USA. The German Society for Space Travel (Verein fuer Raum—
`schiffahrt or VfR) was formed in 1927 with the Romanian born
`Hermann Oberth as one of its earliest members. In 1930 the VfR
`
`successfully tested a liquid-fuelled engine and by 1932 they were
`regularly flying rockets. Oberth wrote his doctoral thesis The
`Rocket into Interplanetary Space in 1922., but the University of
`Heidelberg rejected it and he was not given his doctorate. However,
`he believed in his ideas and published his thesis as Die Rakete zu
`den Planetenriiumen (By Rocket into Planetary Space), which he
`later expanded to become Wege zur Raumschiffahrt (The Way to
`Space Travel). Oberth is regarded as the German Father of rocketry
`and his books described, amongst other things, a space station and
`liquid—fuelled rocket designs. Oberth influenced many scientists
`including the young Wernher Von Braun. Von Braun joined the VfR
`as a teenager and assisted Oberth in his spare time.
`During the First World War, rockets powered by solid propel»
`lants were used as weapons. The Treaty of Versailles, the peace
`treaty that officially ended the First World War, forbade solid—fuel
`rocket research in Gerniany. Liquid—fuelled rbckets were not specifi~
`cally forbidden and, by 1932, the German Army began to take an
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`interest in the VfR’s efforts. The German Army Rocket Research
`Group was formed the same year, headed by Captain, later Major Gen
`eral, Walter Dornberger. Von Braun and most of the other members
`of the society eventually joined the military and the German Army
`Rocket Research Group. The group's main interest was to research the
`possibility of using liquid propellant rockets for military purposes.
`With the financial support and strict requirements of the army,
`the scientific research and development work on rockets progressed
`rapidly. Von Braun, who had been fascinated with the idea of space
`travel and earned his doctorate in physics by the age of 2.2, was the
`technical director. By 1934, a liquid propellant rocket, named the A2,
`had been launched and reached a maximum altitude of 2.2 kilometres.
`
`Due to the limited availability of materials and manpower, financial
`constraints and rivalry between the German services, the develop-
`ment of the next rockets, the A3 and the A4, progressed more slowly.
`In 1942, the A4 was successfully launched for the first time. During
`one of its test flights, it reached an altitude of 189 kilometres, and was
`the first rnan—rnade object to be launched into space.
`In his book, V2, Major General Walter Dornberger recalled
`that at the time he told his colleagues:
`
`We have invaded space with our rocket and for the first time
`— mark this well ~ have used space as a bridge between two
`
`points on the Earth; we have proved rocket propulsion practi-
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`cable for space travel.
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`He continued:
`
`This third day of October 1942, is the first of a new era of trans-
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`portation, that of space travel.
`
`The A4 was renarned the V2 or Vergcltungswaffe 2 (Reprisal
`weapon 2). It was the first successful long~range ballistic missile and
`had a range of about 300 kilometres and could carry a payload of about
`a tonne. The majority of the design of the engine is credited to Walter
`Thiel and the rocket itself to Von Braun. Dornberger says in his book:
`
`Any ambition to penetrate into space with liquid propellant rock-
`ets could bc no more than wishful thinking until general tech-
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`nological progress provided thc means for realisation. Essential
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`prerequisites were the smelting of light alloys on a large scale,
`
`the ability to produce, and store, liquid oxygen in quantity, or
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`alternatively to obtain big supplies of chemicals containing oxygen,
`and finally the development of electrical precision instruments.
`
`He added:
`
`I think it is probable that any genuine inventor, research worker,
`or engineer who had had the problem to deal with under identi-
`
`cal conditions and had worked painstakingly on scientific lines
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`would have achieved practically the same results.
`
`He continued:
`
`The time was ripe and the basic conditions were there.
`
`He also said:
`
`As so often before in the history of technology, necessity in Ger-
`many after the First World War had forced a great invention to
`proceed by way of Weapon development. Never would any private
`or public body have devoted hundreds of millions of Marks to the
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`development of long range rockets purely for scientific purposes.
`
`The first hostile V2 fell at 6:43 pm. on September 8, 1944, at
`Chiswick, near London, England. They continued to fall, mainly
`on London and Antwerp in Belgium, until March 27, 1945. It is
`estimated that the V2 bombs killed 10,000 civilians. The V23 were
`mass~produced using mainly labour camp inmates under atrocious
`conditions. Over 25,000 Workers died either directly or indirectly
`from the conditions and Work of producing the bombs. The manu-
`facture of the rocket produced more deaths than its deployment.
`After the war many of the scientists and engineers who had
`helped develop the V2 continued their rocket work for either the
`Soviet Union or the USA. Their expertise and the information gath-
`ered from unused V23 and other rocket parts contributed greatly to
`the development of the rockets that eventually launched satellites
`and Man into space.
`
`Rocket Basics
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`Multistaging
`
`It would be very useful if a rocket could take off from the Earth, go
`into orbit, come back to Earth, be refuelled and be ready to launch
`
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`into space again quickly, in a similar way to an aeroplane or a car
`continually travelling from one place to another. However, there
`are technical and financial restraints that mean that, although this
`is theoretically possible, we do not yet have the materials or tech-
`nology available to develop this type of rocket. The Ansari X~Prize,
`which is described in more detail in Chapter 1 1 — ”The Future”,
`was awarded to the first non-governmental organization to launch
`a reusable manned spacecraft into space twice within two weeks.
`As this was only required to enter space and not enter into an orbit,
`the winning design was only a fraction of the way to a fully reus-
`able orbital launch system.
`A technique that was utilized in the 16th century by a Ger-
`man firework manufacturer called Iohann Schrnidlap has been
`adopted for all current orbital space launches, although the rockets
`are not reusable. So that his fireworks could reach higher altitudes,
`Schmidlap attached smaller rockets to the top of the larger ones.
`When the large rocket ran out of fuel and began to fall back to the
`ground, the smaller one became detached, and, using its own fuel,
`climbed even higher. Schrnidlap called this a step rocket. Today
`this type of system is still used, but it is known as multistaging
`and was independently described by Kazimierz Siemienowicz,
`Konstantin Tsiolkovsky, Robert Goddard and Hermann Oberth.
`As the fuel is burnt, the propellant is expelled and the rocket is
`accelerated. The lighter the rocket, the less propellant is needed to
`accelerate it to the required speed to get into orbit. Or, conversely,
`the more propellant the rocket has onboard, the faster and further
`it can go. The Weight of the rocket, including the engines, fuel and
`payload, is too large for current propulsion systems to get into orbit
`in one stage. Rockets therefore usually consist of separate stages.
`Each. stage contains its own propellant, engines, instrumentation
`and airframe, so that it can function independently. By discarding
`the first stage, with its associated engine and fuel tank, the weight
`of the rocket is lighter and therefore the remaining stages can be
`more easily accelerated to the required speed.
`In most rockets, the stages are stacked one on top of the other,
`called serial staging. The Soyuz launch Vehicles use three serial
`stages, as did the Saturn V rockets that launched the Apollo rnis~
`sions. The stage at the bottom is called the first stage and is ignited
`first. The payload is usually in a protective nose cone at the very
`top of the stack. The first stage is the largest stage and requires the
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`most thrust, as it must lift all of the other stages and the payload,
`as well as itself, off the surface of the Earth. It must also counteract
`the drag caused by the atmosphere. Usually, the first stage burns
`only for a couple of minutes. After it has used all of its propellant,
`the empty propellant tank, engine, instrumentation and airframe
`are just dead Weight and are jettisoned and usually return to Earth.
`The second stage then ignites and further accelerates the rocket,
`which now has less mass.
`
`An alternative method of staging is parallel staging, where
`several solid propellant motor boosters are strapped onto the side
`of the rocket. They form a supplementary first stage and are usu-
`ally attached to the first stage. At launch, all of the rockets are
`ignited. The smaller rockets are sometime called the zero stages
`or boosters. When the strap-on rockets have used all of their pro-
`pellant, which is usually before the main or sustainer engine has,
`they are discarded and the sustainer engine continues to burn
`until it too runs out of propellant. The Space Shuttle uses parallel
`staging. The Titan III and Delta II rockets use a combination of
`both serial and parallel staging. The Space Shuttle’s booster rockets
`are salvaged after they land in the ocean and are reused, but for
`most other rockets, and for the Space Shuttle’s main sustainer
`engine, the fuel tank for the first stage usually crashes into the
`ocean and is not recovered. Most rockets’ later stages either burn
`up in the Earth's atmosphere or become pieces of space debris and
`orbit the Earth until their orbit decays and they too eventually
`burn up in the Earth's atmosphere.
`Rockets have been designed and launched with up to five
`stages. There are an optirnum number of stages for any rocket before
`adding more actually slows the rocket down. This is because the
`added inass and cornplexity of each subsequent stage counteracts
`the benefit of staging. As the complexity increases, the reliability
`decreases. It is cornrnon for rockets to use two or three stages. Each
`stage can incorporate many rocket engines, for different purposes.
`The more stages a rocket has and the heavier it is, the more expen-
`sive it is to launch. Smaller vehicles are therefore used for small
`
`payloads and low orbits. Larger ones usually have more stages,
`are heavier and are therefore more expensive, but can carry larger
`payloads or take them to higher orbits or even out of Earth orbit
`altogether.
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`third stage and the payload into a low Earth parking orbit. This is
`a temporary orbit, where the spacecraft can wait for the correct
`timing before the third stage fires and moves it into its final orbit
`or another trajectory. This waiting time, or coast period as it is
`l{D.OWfl, is usually between 30 minutes and an hour, but it can be
`longer depending on the mission. The propulsion system for this
`final manoeuvre may be integrated with the payload or it may be
`discarded when it is used.
`
`Once the launch vehicle has released its payload, it has no
`further useful purpose and remains circling the globe in tighter
`and tighter orbits until it eventually burns up in the Earth's atn1os~
`phere. In September 2006 there were over 6,500 spent rocket bod~
`ies and other pieces of debris orbiting the Earth.
`Once in orbit, the type of propulsion system can be changed.
`This is because leaving the Earth requires the rocket to be acceler~
`ated quickly through the atmosphere and around the planet before
`it falls back to it. Once in orbit, the pull of gravity from the Earth
`is balanced by the speed of the spacecraft around the planet, and
`the spacecraft does not fall back to Earth and so slower accelera-
`tions can be used to change the path of the trajectory. This allows
`the use of much more efficient motors that produce more thrust
`per quantity of propellant, such as ion drives. These are explained
`in Chapter 5 ~ ’’Propulsion Systems”.
`
`Launch Vehicles
`
`The launch Vehicle is the rocket, including all of the stages, that
`is used to launch a payload into space. The structure consists of
`the fuel or propellant tanks, a frame onto which the propulsion
`systems are inounted and an aerodynamic shroud, which provides
`a low—drag housing for the rocket and all of the components. It also
`contains all of the guidance and control systems that are needed
`to put the payload into the required orbit and the payload can—
`ister, Where the payload is stored during the launch until it has
`reached orbit. The part of the shroud protecting the payload can-
`ister is called the payload shroud, the payload fairing or the nose
`cone. The Whole rocket has tight weight limitations and therefore
`it is made with the least amount of material that will Withstand
`
`the severe stresses or loads encountered both on the ground and
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`spacecraft. This type of spacecraft usually needs an aeroshell, an
`aerodynamic braking heat shield, to slow them down and pro—
`tect them from the heat created by atmospheric friction during
`atmospheric entry. The use of an aeroshell is called aerobraking.
`After the aeroshell is jettisoned, these spacecraft need parachutes
`or retrorockets, rockets that are used to slow the motion of the
`craft, so that they can descend slowly. The scientific instruments
`onboard usually take measurements of the atmosphere’s composi-
`tion, temperature, pressure and density. Some atmospheric space—
`craft land on the surface and continue to send back data, and so can
`also be classified as landers.
`»
`
`Lander and Rover Spacecraft
`
`Lander spacecraft are designed to reach the surface of a planet and
`survive long enough to send the data back to Earth. The Soviet Venera
`landers in the 19603 managed to survive the harsh conditions on
`Venus long enough to carry out chemical composition analyses
`of the rocks and relay colour images. NASA’s Surveyor series of
`landers carried out similar experiments on the Earth's Moon, also
`in the 19603. Rover craft move about on the surface of the planet
`and gather more information. They are semi-autonomous as the
`delay in radio communication over interplanetary distances means
`they must be able to make some decisions on their own. They are
`usually used for taking images and analysing soil and rocks. The
`Mars Exploration Rovers, Spirit and Opportunity, which landed on
`Mars in 2004, are probably the most well-known rovers.
`
`Observatory Spacecraft
`
`These spacecraft do not travel to a destination to explore it. Instead,
`they observe distant targets from either an Earth or a solar orbit,
`without the obscuring and blurring effects of the Earth's atmosphere
`getting in the Way. Examples include the Hubble Space Telescope,
`the Chandra X~Ray Observatory and the Solar and Heliospheric
`Observatory, SOHO.
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`Penetrator Spacecraft and Irnpactors
`
`Spacecraft that have been designed to penetrate the surface of a body,
`such as a comet or asteroid, are called penetrators. Once they have
`survived the landing, they then ‘take readings of the properties of the
`object. This data is usually then sent to an orbiting spacecraft and
`relayed to the Earth. Impactor missions gather data by impacting the
`surface and analysing the results of the impact. In 2005, NASA’s Deep
`Impact was a fly-by spacecraft that fired an impactor into the interior
`of the comet Tempel 1, thus excavating debris from the interior. The
`fly-by spacecraft Deep Impact and the Earth orbiting Hubble Space
`Telescope, Spitzer Space Telescope and Chandra X-ray Observatory,
`all recorded the impact. The images showed the comet to be more
`dusty and less icy than expected. As the impact generated a large,
`bright dust cloud the irnpact crater was obscured from view. Also in
`2005, the Japanese Hayabusa spacecraft successfully landed a probe
`on asteroid Itokawa. Hopefully, it managed to take a sample of the
`asteroid, by firing a bullet or irnpactor into the asteroid and catching
`any debris that was thrown up. The probe then returned to its space-
`craft, which is now on its return journey to the Earth. However, there
`were a few technical problems and the sampler may not have been
`successful and communication with and control of the spacecraft
`
`has become difficult.
`
`Manned Spaceflight
`
`The first human carrying spacecraft was Vostok 1 on April 12.,
`1961. It carried the Soviet cosmonaut Yuri Gagarin once around
`the Earth. Since then over 2.00 spacecraft carrying humans have
`been launched. Most of these spacecraft have been either the Soyuz
`or the Space Shuttle. Spacecraft that carry a human crew and pas~
`sengers have more design constraints than unmanned spacecraft.
`It does not matter if the craft is 15,000 metres or 15,000 kilometres
`above the surface of the Earth, huinans need a sealed pressurized
`cabin containing an atmosphere that is approximately the same as
`normal conditions on the Earth. More details about living in space
`
`are included in Chapter 8 —- ”Humans in Space”.
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`the launch window can be shorter. However, for missions where the
`launch period is relatively short and will not occur again for a long
`time, such as a mission to Mars, a longer launch period is required to
`take account of adverse weather conditions or delays in the prepara-
`tion of the launch Vehicle. With this type of mission, lift~off is usu-
`ally planned for before the ideal launch day. The rest of the launch
`period is made up of a range of days after the ideal launch date. If the
`launch period is missed, the window of opportunity for a mission
`to Mars closes for another two years. Once the spacecraft has been
`launched, it is moved into the required orbit, as described in Chapter 4
`— ’’Movement in Three Dimensions”.
`
`Landing Sites
`
`Earth Landing Sites
`
`The type of spacecraft and its payload determines the type of land
`ing site required. Yuri Gagarin, the first man in space, ejected from
`his spacecraft Vostok 1 when it was in the Earth's atmosphere and
`parachuted to land. The Mercury, Gemini and Apollo astronauts
`stayed within their capsules, which were parachuted down into the
`ocean. The Space Shuttle glides in to land on a specially designed
`runway. Manned spacecraft need to land within easy access of recov~
`ery teams, whereas unmanned capsules can be left for a while before
`they are recovered. All astronauts and cosmonauts undergo eXten—
`sive survival training in case no rescue party can reach them quickly
`and they have to rely on themselves.
`
`Space Shuttle Landing
`
`Since the Space Shuttle is launched froin NASA’s Kennedy Space
`Centre (KSC) in Florida, it is also the preferred landing site. This
`saves time and money, as landing at any other site requires the Space
`Shuttle to be transferred back to KSC. This is done on top of the
`Shuttle Carrier Aircraft, which is a modified Boeing 747, as can be
`seen in Figure 3.2. The preferred backup landing site is at Edwards
`Air Force Base in California, where the Weather is more stable and
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`. ...—-n---a---'°""
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`.,,,,_..sgn-;-f.mma;; "'-H r'--'-'-‘-""""“" '
`
`FIGURE 3.2 Space Shuttle Discovery, on top of the Shuttle Carrier Aircraft,
`touches down at NASA Kennedy Space Centre.
`Image courtesy NASA/KSC
`
`predictable. The weather is a major factor in whether the landing
`is at KSC, Edwards Air Force Base or if it is postponed until a later
`orbit. The weather conditions include the amount and height of any
`cloud cover, the visibility, the wind speed and direction and if any
`thunderstorms are in the vicinity. The angle of the Sun is also con-
`sidered, in case it is in the pilot's eyes as they come in to land. The
`chosen landing site can be changed up to 90 minutes before landing.
`About an hour before landing a de-orbit burn slows the Space Shut-
`tle enough to begin its descent. There are other emergency landing
`sites around the world, which are covered later in this chapter.
`The Shuttle Landing Facility (SLF) at KSC is shown in Figure
`3.3. It was designed specifically for the returning Space Shuttle. It
`is over 4,500 metres long and about 90 metres wide, which is longer
`and wider than those at most commercial airports. In comparison,
`London Heathrow’s longest runway is just over 3,900 metres long
`and only 45 metres wide.
`The SLF runway is made of 40 centimetres thick concrete and
`slopes gently from the centre to the edges to help drainage. Although
`it is only a single landing strip, it is considered to be two runways as
`the Space Shuttle could approach from either the northwest or the
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`changed. Any atmosphere on the body will also influence the land-
`ing site as winds can affect where the lander finally comes to rest.
`The atmosphere or lack of one will also determine the method of
`landing, such as using aerobraking and parachutes or relying on
`retrorocket thrusters. Most landers are bespoke and are designed for
`certain mission and scientific requirements. They are also designed
`to withstand the environmental conditions they will encounter.
`
`Moon Landers
`
`The first spacecraft to make a soft landing on the Moon, rather than
`crash onto it, was the Soviet Union's Luna 9 in 1966. It landed in Ocea-
`nus Procellarurn or the Ocean of Storms. About five months later the
`American spacecraft Surveyor 1 also made a soft landing on the Moon.
`It landed in a flat area inside a lOOkilometre diameter crater to the
`north of Flamsteed crater in the southwest of Oceanus Procellarum.
`When the spacecraft reached an altitude of about 75 kilometres and a
`velocity of just over 2,600 metres per second, the main retrorockets
`fired and, after slowing the spacecraft to about 1 10metres per second
`and at an altitude of about 1 1 kilometres, they were then jettisoned.
`Small rocket engines continued to slow the descent until it was about
`3.4 metres above the surface after which the lander fell freely under
`the pull of the Moon's gravity. Both the Soviet and American lunar
`missions in the 1960s and 1970s were used to gather information
`about the Moon both for scientific purposes and also for the planning
`of possible future missions, including manned missions. The main
`landing site criteria were therefore sirnilar to those for the manned
`Moon landings, discussed below. Between 1976 and 1990 there were
`no rnissions to the Moon. In 1990 Iapan’s Hiten spacecraft first flew
`by, then orbited and then impacted on the Moon three years later. The
`primary reason for this mission was to test and verify technologies for
`future lunar and planetary missions. There has not been a soft landing
`on the Moon since 1976.
`A
`
`Manned Moon Landings
`
`The first landing site for a manned craft on the Moon was deter-
`mined mainly by safety and operational criteria. Any scientific
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`Space Exploration Technologies; NEW PETITION
`Exhibit 1110
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`Space Exploration Technologies; NEW PETITION
`Exhibit 1110
`Page 15 of 23
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`3 Space Missions
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`69
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`investigation was a secondary consideration although this did
`become more important in later missions when more was known
`about the practicalities of a Moon landing. The most important
`safety rule stated that the spacecraft must be on a free—return tra-
`jectory. This meant that if the main engine failed, and the space-
`craft could not be put into an orbit around the Moon, it would
`swing around the Moon under the influence of the Moon's gravity
`and head back towards the Earth. Apollo 13 used this free—return
`trajectory after an explosion onboard forced the landing mission
`to be abandoned. A free—return trajectory places the spacecraft in
`the equatorial region of the Moon and so the landing site had to be
`within a belt 5° north and 5° south of the Moon's equator.
`The timing of the first Apollo landing attempts was also
`important. The lunar module crew needed to View the landing area
`and choose a safe landing site. Therefore, the landing had to be
`not too long after lunar sunrise, when the Sun's height above the
`horizon was enough to highlight the surface, without producing
`long and confusing shadows, but not too high as to wash out all
`of the details. The launch from the Earth was chosen so that the
`
`lunar module would land when the solar illumination was near
`
`optimum. However, the launch time was constrained to daylight
`hours at the launch site, in case of an aborted launch and an emer-
`gency rescue operation was required.
`The angle of the Sun was also relevant after the lunar module
`had landed. As the Moon has no atmosphere, sunlight is not scat-
`tered as it is on the Earth and the shadows are completely black.
`Therefore if the Sun were too low, visual observations would have
`been difficult. If the Sun were too high, there would be no shadows
`for contrast, and again visual observations would be difficult. The
`temperature on the Moon also varies with the angle of the Sun.
`To protect the astronauts and the spacecraft, the landing site was
`specified to be when the Sun was between 15° and 45° above the
`horizon.
`
`If the launch were cancelled for any reason, it would take
`nearly 48 hours for the Saturn V launch vehicle to be ready for use
`again. Although a day on the Moon lasts just over 27 Earth days,
`and the angle of the Sun over the horizon changes slowly, a delay of
`48 hours would mean that the original landing site would be washed
`in sunlight and the fine detail shown up by the shadows would not
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`Space Exploration Technologies; NEW PETITION
`Exhibit 1110
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`Page 16 of 23
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`Space Exploration Technologies; NEW PETITION
`Exhibit 1110
`Page 16 of 23
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`It's ONLY Rocket Science
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`be visible to the lunar module crew. Therefore a backup landing
`site, that was more westerly than the original site, was needed.
`The launch period, which was just a few days per month for one
`landing site, was substantially increased when an alternate landing
`site could be used.
`The favoured landing sites were therefore on the eastern side of
`the Moon's visible face. The east and west bou