Senior Science
9.9 Space Science
Section 4
Rocket launch
and Reentry
Section 4 :: Rocket launch and Reentry
The components and materials used in the construction of rockets and shuttles
must withstand launch and re-entry conditions
9.9.4.a
Describe the functions of the components of the Space Transportation System
(STS), commonly called shuttle, including:
–
the orbiter
–
solid rocket boosters (SRB)
–
external tank
9.9.4.b
Identify some of the difficulties experienced during lift-off but not on re-entry into the
Earth’s atmosphere
9.9.4.c
Explain why a large booster rocket is required during lift-off but not on re-entry
9.9.4.d
Describe properties of materials used in the STS and relate the properties to
conditions experienced during lift off or re-entry
9.9.4.i
Gather and process secondary information to trace changes in the type of
systems that have been used in space travel and discuss the advantages and
disadvantages of using a shuttle
9.9.4.ii
Gather, process and present information from secondary sources on plans for
future space vehicles
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9.9.4.a
Describe the functions of the components of the Space Transportation
System (STS), commonly called shuttle, including:
–
the orbiter
–
solid rocket boosters (SRB)
–
external tank
THE SPACE SHUTTLE
The Space Transportation System (STS), commonly called the Shuttle, has three main
components:
 the orbiter
 the external tank and
 the solid booster rockets
THE ORBITER
The Orbiter looks much like an aeroplane and is 37 meters long, spans 24 meters across
the wingtips, and stands 17 meters tall on its landing gear. An important feature is its
payload bay, an area 4.6 meters in diameter and 18.3 meters long. The empty weight of
the orbiter is about 86,000 kilograms. The thrust of each of three main engines is up to
215,000 kilograms.
The orbiter performs a number of functions.
 It provides the living space for the astronauts.
 It provides the working space for the astronauts.
 Its engines provide the final thrust to allow the craft to reach orbit velocity
 It can be flown like a plane; it lands like a plane and it returns the astronauts to earth.
 It is the first reusable spacecraft.
 It carries and then positions the payload in space.
It functions like;
 a rocket during launch,
 orbits the Earth as a space craft,
 transports objects to and back from space like a truck
 returns to Earth like an unpowered aircraft or glider.
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Inside the orbiter Astronauts live and work in a two-level crew compartment at the front
of the Orbiter. This living section accommodates up to eight people (ten in an emergency).
The upper level houses the flight deck “cockpit” and a workstation, which controls the
payload bay operations. The mid-deck is used for sleeping, eating, storage and small
experiments; it also has an airlock that opens into the payload bay and allows access to
space. A lower deck below the mid-deck floor is the site of equipment such as water
pumps, and air purification systems.
In the center of the craft is a payload bay 18.3m long and 4.6m wide – about the size of a
tour bus. Up to 29,500kg of payload can be lifted into a low orbit; 14,500 kg into a polar
orbit. The Remote Manipulator System (RMS) is a mechanical arm that moves objects in
and out of the payload bay and can mount a work platform for astronauts. Two large
payload bay doors are opened to deploy satellites or to expose scientific instruments to
space. The doors also have radiators to dispose of heat produced by the electrical
equipment and the astronauts; these doors must be opened on flights to prevent the
shuttle from overheating. Electrical energy on shuttle flights is provided by fuel cells that
use oxygen and hydrogen.
The space Shuttle’s guidance, navigation and control depend on its five general purpose
computers. The Shuttle’s autopilot is one of the most advanced ever built, reacting many
thousands of times faster than any human being. One of the computers acts as a backup
during launch and reentry – the two most critical phases of the mission. The reliability of
the other four computers is extremely high – during critical phases, they serve as backup
for one another.
The external tank
The external tank, actually two tanks in one, carries liquid
hydrogen and oxygen for the three main engines. The tank’s
diameter is 8.4 meters, its height is 47 meters, and its empty
weight is 34,000 kilograms. The tank is covered with insulation to
protect the supercold fuel and oxidizer form the heat of even a
cold winter’s day. The external tank, made of light weight but
strong aluminium and titanium alloys, is the only part of the space
shuttle that is not reusable.
The purpose of the main tank is to provide continuous thrust for
the STS until just before the orbital speed is reached. As well,
the liquid fuel used in the external tank, allows the engines to be
throttled back during the lift-off phase. The tank remains attached
to the shuttle from lift-off until after main engine cut-off. The tank
is then separated and, because it has less than orbital speed,
falls back to earth.
The fuel and the oxidizer are stored in separate tanks. They are
pumped into the combustion chamber where they mix, ignite, and
burn to produce thrust. Some mixtures require igniters to start
the combustion process. Others, ignite immediately on contact
with each other and need no igniter. Because the flow of fuel can
be controlled, so can the thrust of the rocket. Liquid-propellant
engines can also be shut off and restarted, unlike most solidpropellant engines.
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Liquid-propellant rockets use a mixture of liquid fuel and liquid oxidizer as propellants.
Thus far, most rockets used in spaceflight, such as Saturn V and the main engines of the
Space Shuttle, have been liquid-propellant rockets. They are the most common kind used
in spaceflight because of their high energy in relation to their weight and the ability to
control their thrust. Common liquid fuels include alcohol, kerosene, liquid hydrogen, and
hydrazine. Common oxidizers include nitrogen tetroxide and liquid oxygen. Many of these
propellants are difficult or dangerous to handle, transport, or store.
The solid booster rockets
The purpose of the twin, solid rocket boosters is to give the shuttle 2
minutes of thrust to get it above the thickest layers the atmosphere.
This allows the 3 main engines (also firing from lift-off) to work most
efficiently. After burn-out, the boosters parachute into the ocean for
recovery and reuse. They are then refurbished for a later
mission.
A solid propellant is a compressed form of fuel and oxidizer that is
solid, not liquid or gas. The earliest rockets built by the Chinese,
used a solid propellant: gunpowder.
Today, solid-propellant
mixtures are much more powerful and complicated than gunpowder.
The boosters for the Space Shuttle, for example, use a mixture of
ammonium perchlorate, powdered aluminium and additives.
The shape of the solid block of propellant can affect its performance
because the thrust of a rocket depends on the amount of fuel
burning at one time. Solid propellants are usually prepared in liquid
form, then poured into a mold or the casing of the rocket itself, and
allowed to harden. The boosters for the Space Shuttle are made in
this way.
The advantages of solid propellants lie in their simplicity and reliability. They are easier to
store than liquid propellants, can withstand changes of temperature better, can be readied
for launch quickly, and can produce high thrust rapidly. Solid propellants are also less
expensive to produce. The major disadvantage is that once most solid-propellant rockets
are ignited, it is impossible to stop combustion. These rockets will burn until all the
propellant is consumed.
Each booster stands 43 meters tall and is 3.7 meters wide through the main body. Empty
weight is 87,000 kilograms, while lift-off weight is 590,000 kilograms.
The space shuttle is a very versatile spacecraft that is approximately 56 metres high when
fully assembled. The two rocket boosters which contain solid propellant consisting of:
 aluminium powder which is the fuel,
 ammonium perchlorate which is the oxidiser
 iron oxide which is the catalyst
 a polymer that binds them together to form a rubbery consistency.
© P Wilkinson 2002-04
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Notes Questions
1. Copy the diagram. Label the orbiter, external tank
solid booster rockets and Shuttle.
2. How big is the orbiter?
3. What is a payload?
4. How many engines does the orbiter have?
5. Outline three functions of the orbiter.
6. Where do astronauts eat and sleep?
7. What is the purpose of the remote manipulator
system?
8. What type of fuel is carried in the external tank?
9. How big is the external tank?
10. Name the materials used to make the external tank?
11. Does the external tank have any engines?
12. What is the purpose of the main tank?
13. Why can the thrust of the rocket be controlled when using liquid fuel rockets?
14. Name three common liquid fuels used in liquid propellant rockets.
15. What is the purpose of the solid booster rockets?
16. What happens when the solid booster rockets use all their fuel?
17. Name one example of a solid fuel.
18. What is the main disadvantage of solid fuels?
19. How big is a booster rocket?
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9.9.4.b
Identify some of the difficulties experienced during lift-off but not on re-entry into
the Earth’s atmosphere
LIFT OFF: GETTING INTO “SPACE”
Once the space craft has been designed and built, it must face the challenges of leaving
Earth and going into space. The account below describes the difficulties experienced by
the space shuttle during lift-off. Similar difficulties would be experienced during the launch
of all space craft.
Months before liftoff
To prepare for space flight, astronauts undergo years of
general preparation. In the months before lift-off the astronauts fly hundreds of launches
in flight simulators. Every possible chance of failure, every emergency is prepared for.
Just prior to lift-off, the crew is isolated in an effort to prevent exposure to colds and flu.
During isolation, the crew adjusts their circadian rhythms to the sleep-rest cycles planned
for the mission. They then receive final briefings on global weather conditions and the preflight status of the launch vehicle.
T minus 5 hours The crew is woken up about five hours before the scheduled launch.
Each crew member dresses in high-topped boots and a fire resistant flight suit. One by
one they are loaded into the orbiter and assisted into seats – helmet on, straps tight and
buckles secure, legs and feet in place. The crew members lie flat on their backs, the best
position in which to bear the forces of acceleration due to the launch.
T minus 1 hour
In the final hour before launch a series of pre-launch checks occurs.
T minus 8 seconds
Thousands of litres of water are released into the flame trench
at the base of the rockets. This is to absorb the sound energy from the engines. One
difficulty associated with launch is the huge noise produced. Reflections of the sound
energy can severely damage the orbiter’s wings and tail and fragile payload.
T minus 5 seconds
Another difficulty that must be overcome at all space launches
is producing enough thrust to carry the craft into space. The spacecraft must have a
propulsion system that provides enough prolonged thrust to deliver its payload, to its
destination. At T minus 5 seconds, the three main engines are ignited to produce a thrust
of 4.98 million newtons (0.509 million kilograms). These engines use liquid fuel and can
be shut down if a problem occurs.
T minus 2 seconds
The computers confirm that the main engines have ignited
properly. Then, the solid fuel in the two booster rockets is ignited. This produces a
combined thrust of 23 million newtons (2.36 million kilograms). The boosters ignite with an
incredible roar. Once in flame, they cannot be turned off or throttled back. For the
astronauts, it is like sitting on the top of a gigantic, controlled bomb.
Lift off
As the solids ignite, explosive charges release
eight bolts that hold the whole assembly onto the launch pad. Once
released the vehicle lifts off in the midst of an inferno of smoke, steam,
light and earth-quivering noise. To overcome the difficulty of the
precise sequencing that must occur prior to launch the process is
controlled by computer.
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Immediately after launch The astronauts face a number of difficulties immediately after
launch. Within seconds after the launch the astronauts experience a force of 3 G’s
(three times the force of earth’s gravity). The crew members are pushed back hard
against their seats; their bodies feel very heavy, and they can move their arms only with
deliberation. The vehicle vibrates widely, and in spite of their helmets, the cabin is
incredibly noisy. The space shuttle system must be engineered to withstand these
vibrations.
Lift off + 30 seconds
Within a span of 30 seconds, the blue sky outside the
orbiter'’ windows changes to a deep and solid black.
Lift off + 50 seconds
Another difficulty experienced during lift-off is the
increase in the air pressure on the shuttle. It is essential to prevent overstressing of the
orbiter’s windshield, wings, and the large vertical tail by the growing pressure of the
rushing air. As the vehicle approaches a speed of 1100 kilometres an hour, 50 seconds
into flight, the orbiter’s main engines are throttled back to about 65% of their potential
thrust. As the vehicle climbs and the atmosphere gets thinner, this pressure decreases
and the engines are throttled back up to full thrust.
Lift off + 2 minutes
Two minutes into the flight the solid-fuel rocket boosters have
burnt themselves out. They are released from the other sections with small explosions. At
this time the shuttle is travelling at about 4800 kilometres an hour and is 45 kilometres
above the earth.
Lift off + 6½ minutes
The shuttle is moving at 17700 kilometres an hour and is 130
kilometres above the earth’s surface.
Lift off + 8½ minutes
Two minutes later, the engines are again throttled back to 65%.
The shuttle is travelling at 27000 kilometres an hour, yet continues to accelerate. The
main engines are about to be shut down and the external tank released.
Lift off + 8minutes & 50 seconds
The orbiter is still travelling too slowly to
continue in orbit. The orbiter’s own engines now ignite to accelerate the craft to the
necessary speed to reach its orbital velocity. The journey from earth to orbit takes 8
minutes and 50 seconds.
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Today, launching a vehicle into space seems almost routine. In reality, launches will never
become routine and they remain extremely dangerous. They will always remain
technologically complex. The orbiter is the most complex machine ever built. Its operation
is almost entirely automated – controlled by five very powerful computers.
As well as the problems of the launch the space shuttle design must take into account all
aspects of the environment of space. The craft must carry enough fuel and supplies to
complete its mission and sustain its crew. Finally, some spacecraft must be able to reenter Earth’s atmosphere and land safely.
REENTRY: RETURNING (TO THE ATMOSPHERE) FROM SPACE
Re-entry has a different set of problems from those experienced by the space shuttle
during launch. The return from space involves:
 entering the atmosphere at the correct angle – too shallow an angle and the
space shuttle will skip off the atmosphere like a tossed pebble skimming across
smooth water – too great an angle and the space shuttle could burn up and cause
very high ‘g’ forces both of which could kill the astronauts.
 needing to slow down from hypersonic speeds ie Mach 26 (26 times greater
than sound) to subsonic speeds (less than the speed of sound) in order to land on a
small dot on Earth which is the landing site.
 an unpowered descent (ie no fuel required)– it simply falls through the
atmosphere approaching the runway at six times the angle of any passenger jet.
There is no second chance for the gliding orbiter that lands at a very fast 300
km/hour approximately.
 using the atmosphere as a braking system which, in turn, causes super-heating
from the friction as it falls to its destination.
 the intense heat of descent ionizes the surrounding air changing it to a flashing
glow of red, pink and orange. A communications blackout occurs at this time
preventing messages from being directly received. All communications must be
sent via satellites that redirect messages between the space shuttle and mission
control.
 increased ‘g’ forces are not an issue with launch or re-entry. Only 2 ½ - 3 g’s are
experienced at each time.
Unlike the launch, there is not very much vibration or sound which is only just noticeable
as the Orbiter drops below the speed of sound and reaches the thicker part of the air.
© P Wilkinson 2002-04
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Notes Questions
20. What sort of training do astronauts complete in the months before liftoff?
21. Name two important reasons why crews are isolated just prior to liftoff.
22. How long before lift off are crew strapped into position?
23. Explain why crew members lie on their backs for lift off.
24. What damage can be caused by noise at the launch?
25. How does the Space Shuttle produce enough thrust to reach space?
26. Which engines produce the greatest thrust – the three main engines or the solid
booster rockets?
27. Which propulsion system is started first – the three main engines or the solid booster
rockets?
28. How quickly after launch do astronauts experience a significant increase in g forces?
29. Why are the orbiter’s engines throttled back about 50 seconds after lift off?
30. How long does it take for the shuttle to rise to 45 kilometres above the earth?
31. How long does it take for the shuttle to rise to 130 kilometres above the earth?
32. How long does it take for the shuttle to reach orbital velocity?
33. What controls the launch process?
34. Identify five problems experienced by the space shuttle during re-entry.
Notes Questions (for the next page)
35. What speed is needed to achieve earth orbit?
36. What speed is needed to send a space craft to the moon?
[NB The extra speed is needed to escape from the earth’s gravitational pull]
37. From what part of the earth is it best to launch a space craft? Give a reason why.
38. Research
What is thrust?
39. Why does the orbiter need the help of the solid booster rockets?
40. Why does the orbiter need an external fuel tank?
41. How heavy is the Shuttle at liftoff?
42. Why does the Shuttle get lighter during launch?
© P Wilkinson 2002-04
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9.9.4.c
Explain why a large booster rocket is required during lift-off but not on re-entry
THE NEED FOR A BOOSTER ROCKET
Overcoming Earth’s gravity
Humans are bound to the Earth by gravity. Overcoming
gravity requires great speed. The velocity needed to achieve Earth orbit is about 27,350
km/hr. The velocity needed to escape the Earth’s gravity and send a space craft to the
Moon or another planet is about 40,200 km/hr.
One way to reduce the effect of gravity is to take off in an easterly direction from a position
close to the equator. This adds the Earth’s velocity to that produced by the rocket. From
Cape Canaveral this adds about 1,450 km/hr to the rocket’s speed.
Reaching orbit
For any rocket to launch successfully, it's thrust must:
 exceed its weight in order the rocket to rise from the launch pad,
 allow the rocket to move easily through the thickest part of the atmosphere,
 enable the rocket to reach orbit.
Why use the solid rocket boosters for the launch of a space shuttle?
Simply put, a large booster rocket is required during liftoff to provide sufficient thrust for the
STS to achieve orbit velocity.
 The orbiter's three main engines can lift the orbiter but there is not enough fuel in
the orbiter to reach orbit.
 Extra fuel must be added by means of the cryogenic hydrogen and oxygen in the
external tank but now the total weight exceeds the thrust capacity of the engines.
 The two solid rocket boosters provide that additional thrust. They are the most
powerful solid fuelled engines ever used. They can lift their own weight as well as
the combined weight of the orbiter and filled external tank. Yes, the solid rocket
boosters can lift the entire space shuttle without help from the main engines, but the
SRBs do not contain enough propellant to allow the shuttle to reach orbit. Hence
the need for the fuel in the external tank as well as the solid rocket boosters.
 Each booster produces nearly 15 million newtons of thrust at liftoff.
 The total thrust provided by the solid rocket boosters and the main engines exceeds
33 million newtons.
 The total weight of the space shuttle at liftoff is approximately 2 041 200 kg.
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9.9.4.d
Describe properties of materials used in the STS and relate the properties to
conditions experienced during lift off or re-entry
MATERIALS USED IN THE SPACE TRANSPORTATION SYSTEM
 The orbiter is made from aluminium. Its important properties are:
 lightness,
 resistance to corrosion,
 durability
 strength.
The majority of the fuselage structure (body) is welded aluminium covered with an
aluminium skin. The bulkhead is aluminium as are the wings and tail that are made
from honeycomb aluminium panels. This lightweight construction obviously reduces
weight for launch while still ensuring high-strength.
 Except for its windows, the orbiter’s aluminium skin is covered by surface insulation to
protect it from the heat generated during reentry. This insulation takes three forms:
 reinforced carbon-carbon fibre -used on leading edges like the wings and nose
cap as well as the lower area where the external tank is attached. The fibre is very
strong and can withstand the forces exerted in these positions as well as insulate
the craft.
 felt (or quartz fibre) blankets
 ceramic tiles. The black and white tiles are made from sand refined into pure
silica fibres. About 23,000 individual tiles are used to protect the underside of the
Orbiter. Here the heat from reentry is extreme, and the silica fiber tiles prevent the
Space Shuttle Orbiter from being incinerated over the course of dozens of reentries
During the fiery dive of reentry through the Earth’s atmosphere, the orbiter will
experience extreme heating that is sufficient to melt the orbiter’s aluminium cover.
The tiles that protect the orbiter from reentry overheating have a black glass
coating for efficient radiation of heat. Those tiles for lower temperature areas are
coated with a white silica compound to better reflect the heat of the Sun while in
orbit.
A tile’s effectiveness at preventing the orbiter’s aluminium structure from melting is
spectacularly shown by heating a tile until it is red hot. The tile sheds heat so
readily that the tile will be cool to the touch in only a few seconds while the tile’s
interior is still glowing red.

The strong windows of the orbiter are made from a thick glass of aluminosilicate
and fused silica. This glass is designed to withstand pressure and heat shock while
providing crystal clear views and high efficiency reflection of heat.

The external tank is made from very light but strong aluminium and titanium alloys
also to ensure the overall lightness of the space shuttle without compromising strength.
The solid rocket boosters are made of stainless steel for high-strength for launch
and splash down collision in the ocean, heat resistance and ease of refurbishment for
future use.

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Notes Questions
43. Identify the properties that make aluminium a useful material from which to build the
orbiter.
44. Name the three materials that are used to provide insulation for the orbiter.
45. When and how do the silica tiles protect the orbiter?
46. What material is used for the windows in the shuttle?
47. Why do the solid rocket boosters need to be made from a stronger material than the
external tank?
© P Wilkinson 2002-04
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9.9.4.i
Gather and process secondary information to trace changes in the type of
systems that have been used in space travel and discuss the advantages and
disadvantages of using a shuttle
CHANGES IN SYSTEMS USED IN SPACE TRAVEL
The Space Age began with the launching of Sputnik 1, a Russian satellite, in 1957. This
was a very small sphere 38cm in diameter. It circled the earth every 95 minutes for 90
days. To put this satellite into orbit, new technologies had to be developed. Major
advances in the various systems used in space travel were developing rockets powerful
enough to put the object into space [rocket technology].
The USSR (Russia and …) was the first nation to put an artificial satellite into orbit. Their
main aim was simply to put an object into space (size was not important).
Since the launching of the Sputnik advances in technology have allowed humans to do
more and more in space.
 The first man in space was Uri Gargarin in 1961 (USSR).
 The first woman in space was Valentina Teresnova in 1963 (USSR).
 The first man to step onto the moon was Neil Armstrong in 1969 (USA)
Both the Russian and American Space Programs underwent gradual change. The general
trend is summarised in the table below.
Significant feature of
Program
Unmanned
One astronaut
Two astronauts
Three astronaut
Reusable space craft
Extended stays in space
US Space Program
Program Mercury
Program Gemini
Program Apollo
Space Shuttle
Space Stations
Russian Space Program
Vostok
Voskhod
Soyuz
Salyut 1
For the first decade of manned space travel, improvements were swift and dramatic.
 The first systems used a non-reusable, multi-stage launch vehicle with strap on
boosters. The landing module descends through the atmosphere with the assistance
of a heat shield, parachute and a last minute blast from rockets situated in the base to
cushion the final touchdown. US launch vehicles include – Vanguard, Delta, Titan
Saturn V
 NASA developed a partially reusable launch vehicle in 1981(ie the American space
shuttle). This landed like a plane or glider.
 Today, many ideas & concepts, and technologies are being developed by several
organisations.
o Launch technologies include - RAMJET, SCRAMJET, X-38, X-43A, Plasma rockets
o Important organisations include the European Space Agency, China, Russia, NASA
o International Space Station uses contributions from many nations
o A manned mission to Mars is being considered
o Probes, unmanned craft are used to explore space (eg Voyager)
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The Task
Gather and process secondary information
 To trace changes in the type of systems that have been used in space travel and
 Discuss the advantages and disadvantages of using a shuttle
1. Outline changes in the types of systems used in space travel
[4 marks]

The focus of the timeline is technological or scientific changes

Present information as a mind map with a minimum of eight entries. The map has
been started for you

Each entry is to include an outline of the change (technological or scientific). See
example below
One astronaut
Project Mercury
Systems used in
Space Travel
Designed to solve basic
problems of space flight.
Eg Re entry – Heat
shield: ablation
Marking Criteria
2. Discuss the advantages and disadvantages of using a shuttle
Marking Criteria
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Marks
3-4
1-2
[6 marks]
Marks
3-4
1-2