Rockets and missiles solved question bank - academic purpose only

VINAYAKA MISSIONS UNIVERSITY
VINAYAKA MISSIONS KIRUPANANDA VARIYAR ENGINEERING COLLEGE
QUESTION BANK
ROCKETS AND MISSILES
SCHOOL OF MECHANICAL SCIENCES
DEPARTMENT OF AERONAUTICAL ENGINEERING
VMKV ENGINEERING COLLEGE
NH-47, SANKARI MAIN ROAD
PERIYA SEERAGAPADI
SALEM – 636 308

IV YEAR VIII SEMESTER
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UNIT - I
PART ‘A’
1. What do you mean by ignition system?
Ans. An ignition system usually operates electrically and which ensures availability of
sufficient heat for smooth combustion of fuel and oxidiser mixture.
2. What are the types of igniters used in rocket?
Ans. Two types: Pyrotechnic and Pyrogen.
3. What is pyrotechnic?
Ans. Pyrotechnic is an explosive mixture of various chemical combinations used for initiation
of ignition system and subsequently ignites the main charge.
4. What is pyrogen?
Ans. Pyrogen is a tiny rocket motor complete in all respect including CD nozzle, hot exhaust
gases of which is used for ignition of main charge of main rotor.
5. What do you mean by specific impulse of a rocket?
Ans. The specific impulse is the total impulse per unit weight of the propellent. It is an
important figure of merit of the performance of a rocket propulsion system. A higher number
means better performance.erformance.
6. What is a rocket?
Ans. A rocket is a non – airbreathing aerial vehicle which travels at hypersonic speed and used
for some specific missions.
7. Classify rockets on the basis of propellants used.
Ans. (a) Solid Propellant
(b) Liquid Propellant
(c) Hybrid Propellant
8. What is a motor in rocket terminology?
Ans. A solid propellant rocket is generally termed as a motor in rocket terminology.
9. What do you mean by engine in rocket terminology?
Ans. A liquid propellant rocket is generally termed as an engine in rocket terminology.
10. What do you mean by squib?
Ans. A small amount of sensitive powdered pyrotechnic housed within the initiator,
commonly called the squib or the primer charge. ; next, the booster charge is ignited by heat
released from the squib; and finally, the main ignition charge propellants are ignited..
11. What is booster charge?
Ans. The charge ignited by heat released from the squib is called booster charge.
12. Write down the composition of main charge of a solid propellant.
Ans. The main charge consists of 24% boron, 71% potassium perchlorate, and 5% binder.
13. Write down the various types of mounting options for igniters.
Ans. Forward Internal, Aft Internal, Forward External, and Aft External
14. What do you mean by safe and arm device?
Ans. Safe and arm device safeguards against motor misfires, or inadvertent motor ignition.
15. What is a sheet igniter?
Ans. An igniter which has its initiator included within a sandwich of flat sheets and the layer
touching the grain is the main charge of pyrotechnic. This form of igniter is used with multi
pulse motors with two or more end-burning grains.

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16. How can an unintentional ignition or disaster occur?
Ans. Energy for unintentional ignition--usually a disaster when it happens--can be
(1) Static electricity,
(2) Induced current from electromagnetic radiation, such as radar,
(3) Induced electrical currents from ground test equipment, communication
apparatus, or nearby electrical circuits in the flight vehicle, and
(4) Heat, vibration, or shock from handling and operations.
17. What do you mean by an exploding bridge wire?
Ans. The exploding bridge wire is a type of electric initiator design which employs a small
bridge wire (0.02 to 0.10 mm) of low-resistance material, usually platinum or gold, that is
exploded by application of a high voltage discharge.
18. What are the materials used for manufacturing case of rockets?
Ans. Three classes of materials have been used: high-strength metals (such as steel,
aluminum, or titanium alloys), wound-filament reinforced plastics, and a combination of these in
which a metal case has externally wound filaments for extra strength. High-strength alloy steels
have been the most common case metals, but others, like aluminum, titanium, and nickel alloys,
are also used for manufacturing case of rockets.
19. How does the ignition take place in a rocket engine?
Ans. Electric initiators in motor igniters which are also called squibs, glow plugs, primers, and
sometimes headers which constitute the initial element in the ignition train is used for ignition in
a rocket engine.
20. What are the methods of feeding propellants in combustion chamber?
Ans. Gravity feed and Pressure feed (Turbo Pump) in case for liquid propellant.
21. What do you mean by an ablative material?
Ans. An ablative material is a composite material of high-temperature organic or inorganic
high strength fibers, namely high silica glass, aramids (Kevlar), or carbon fibers, impregnated
with organic plastic materials such as phenolic or epoxy resin.
22. What are the types of loads and stresses a motor case is subjected to during its operation?
Ans. (1) Temperature (internal heating, aerodynamic heating, temperature cycling during
storage, or thermal stresses and strains);
(2) Corrosion (moisture/chemical, galvanic, stress corrosion, or hydrogen
embrittlement);
(3) Space conditions: vacuum or radiation.
23. What are case segments?
Ans. For very large and long motors both the propellant grain and the motor case are made in
sections which are called case segments and are mechanically attached and sealed to each other
at the launch site.
24. What are the specific characteristics of maraging steels?
Ans. The maraging steels have strengths up to approximately 300,000 psi in combination with
high fracture toughness. The term maraging is derived from the fact that these alloys exist as
relative soft low-carbon martensites in the annealed condition and gain high strength from aging
at relatively low
temperatures.
25. What are the various attachments a rocket case should have?
Ans. The case design has to provide means for attaching a nozzle (rarely more than one
nozzle), for attaching it to the vehicle, igniters, and provisions for loading the grain. Sometimes

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there are also attached aerodynamic surfaces (fins), sensing instruments, a raceway (external
conduit for electrical wires), handling hooks, and thrust vector control actuators with their power
supply. For upper stages of ballistic missiles the case can also include blow-out ports or thrust
termination devices. Typical methods for attaching these items include tapered or straight
multiple pins, snap rings, or bolts, Gaskets and/or O-ring seals. prevent gas leaks.
PART ‘B’
1. Describe the types of igniters used in rockets.
Ans. Igniters are the devices that start the combustion of the rocket propellant in the motor.
When electricity from the launch controller passes through the igniter, it heats up and bursts into
flame. This flame then starts the propellant burning. When choosing an igniter, first see the
recommendation of the rocket motor. Each motor takes a certain type of igniter. They vary in
size, and how much electrical current it takes to set them ablaze.
Pyrotechnic Igniter
A pyrotechnic igniter which was used for igniting the B-200, C-400 and similar sugar-
propellant rocket motors. It consists of a length of polyethylene plastic drinking straw filled as
shown with a charge of Ignition Powder, and as such, is often referred to as a "straw igniter".
The igniter is sealed at both ends with polyethylene "hot-melt glue". The nichrome
(nickel-chromium, high resistance) wire serves as the heating filament (bridgewire), and is
soldered to the ends of the copper wire leads using solder. Nichrome wire is quite inexpensive
(about $0.20 /ft.). Alternatively, a strand (or two) of coarse "steel wool" may be used in place of
nichrome wire, or even a strand of fine copper "speaker" wire.
Ignition Powder
The Ignition Powder that is used is a modified Black Powder mixture, and consists
of 80% Potassium Nitrate and 20% Charcoal, by weight. Sulphur is not added to this mixture.
The function of sulphur in conventional Black Powder is mainly to facilitate easy ignition. This
is great for flintlock guns, but for safety reasons, it is not such a good feature for rocket motor
igniters, nor is it really necessary.
Pyrogen Igniter
A pyrogen igniter is basically a small rocket motor that is used to ignite a larger rocket
motor. The pyrogen is not designed to produce thrust. All use one or more nozzle orifices, both
sonic and supersonic types, and most use conventional rocket motor grain formulations and
design technology.
2. Explain the designs of initiators with neat diagrams.
Ans.
(a) Internal Diaphragm Type
In the integral diaphragm type the initial ignition energy is passed in the form of a
shock wave through the diaphragm activating the acceptor charge, with the
diaphragm remaining integral. This same principle is also used to transmit a shock
wave through a metal case wall or a metal insert in a filament-wound case; the case
would not need to be penetrated and sealed.

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(b) The header type
The header type resembles a simple glow plug with two high-resistance bridgewires
buried in the initiator charge.
(c) The exploding bridgewire
The exploding bridgewire design employs a small bridgewire (0.02 to 0.10 mm) of
low-resistance material, usually platinum or gold, that is exploded by application of a
highvoltage discharge.
3. Discuss the types of loads and stresses a rocket motor is subjected to.
Ans. Rocket motor case loads
4. Explain the constructional aspects of motor case with respect to material selection.
Ans. Metal cases have several advantages compared to filament-reinforced plastic cases:
They are rugged and will take considerable rough handling (required in many tactical
missile applications), are usually reasonably ductile and can yield before failure, can be heated
to a relatively high temperature (700 to 1000°C or 1292 to 1832°F and higher with some special
materials), and thus require less insulation. They will not deteriorate significantly with time or
weather exposure and are easily adapted to take concentrated loads, if made thicker at a flange
or boss. Since the metal case has much higher density and less insulation, it occupies less
volume than does a fiber-reinforced plastic case; therefore, for the same external envelope it can
contain somewhat more propellant.
High-strength alloy steels have been the most common case metals, but others, like
aluminum, titanium, and nickel alloys, have also been used. Extensive knowledge exists for
designing and fabricating motor cases with low-alloy steels with strength levels to 240,000 psi.
The maraging steels have strengths up to approximately 300,000 psi in combination
with high fracture toughness. The term maraging is derived from the fact that these alloys exist
as relative soft low-carbon martensites in the annealed condition and gain high strength from
aging at relatively low temperatures.
The HY steels (newer than the maraging steels) are attractive because of their toughness
and resistance to tearing, a property important to motor cases and other pressure vessels because
failures are less catastrophic. This toughness characteristic enables a "leak before failure" to

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occur, at least during hydrostatic proof testing. The HY steels have strengths between 180,000
and 300,000 psi (depending on heat treatment and additives).
5. Explain about filament wound reinforced plastic cases.
Ans. Wound-Filament-Reinforced Plastic Cases
Filament-reinforced cases use continuous filaments of strong fibers wound in precise
patterns and bonded together with a plastic, usually an epoxy resin. Their principal advantage is
their lower weight. Most plastics soften when they are heated above about 180°C or 355°F; they
need inserts or reinforcements to allow fastening or assembly of other components and to accept
concentrated loads. The thermal expansion of reinforced plastics is often higher than that of
metal and the thermal conductivity is much lower, causing a higher temperature gradient.
Typical fiber materials are, in the order of increasing strength, glass, aramids (Kevlar),
and carbon. The inert mass of a case made of carbon fiber is about 50% of a case made with
glass fibers and around 67% of a case mass made with Kevlar fibers. Individual fibers are very
strong in tension (2400 to 6800 MPa or 350,000 to 1,000,000 psi).
The fibers are held in place by a plastic binder of relatively low density; it prevents fibers
slipping and thus weakening in shear or bending. In a filament-wound composite (with tension,
hoop, and bending stresses) the filaments are not always oriented along the direction of
maximum stress and the material includes a low-strength plastic; therefore, the composite
strength is reduced by a factor of 3 to 5 compared to the strength of the filament itself. The
plastic binder is usually a thermosetting epoxy material, which limits the maximum temperature
to between 100 to 180°C or about 212 to 355°F.
6. Describe briefly about turbopump and its operation.
Ans. The principal components of a rocket engine is turbopump system. Here the propellants
are pressurized by means of pumps, which in turn are driven by turbines. These turbines derive
their power from the expansion of hot gases. Engines with turbopumps are preferred for booster
and sustainer stages of space launch vehicles, long-range missiles, and in the past also for
aircraft performance augmentation. They are usually lighter than other types for these high
thrust, long duration applications. The inert hardware mass of the rocket engine (without tanks)
is essentially independent of duration. For aircraft performance augmentation the rocket pump
can be driven directly by the jet engine. .
7. Explain the operation of a liquid propellant rocket with a neat diagram.
Ans. A liquid-propellant rocket or a liquid rocket is a rocket engine that uses propellants in
liquid form. Liquids are desirable because their reasonably high density allows the volume of the
propellant tanks to be relatively low, and it is possible to use lightweight centrifugal turbopumps
to pump the propellant from the tanks into the combustion chamber, which means that the
propellants can be kept under low pressure. This permits the use of low-mass propellant tanks,
resulting in a high mass ratio for the rocket.
All liquid rocket engines have tankage and pipes to store and transfer propellant, an
injector system, a combustion chamber which is very typically cylindrical, and one (sometimes

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two or more) rocket nozzles. Liquid systems enable higher specific impulse than solids and
hybrid rocket engines and can provide very high tankage efficiency.
Unlike gases, a typical liquid propellant has a density similar to water, approximately
0.7-1.4g/cm³ (except liquid hydrogen which has a much lower density), while requiring only
relatively modest pressure to prevent vapourisation. This combination of density and low
pressure permits very lightweight tankage; approximately 1% of the contents for dense
propellants and around 10% for liquid hydrogen (due to its low density and the mass of the
required insulation).
For injection into the combustion chamber the propellant pressure at the injectors needs
to be greater than the chamber pressure; this can be achieved with a pump. Suitable pumps
usually use centrifugal turbopumps due to their high power and light weight, although
reciprocating pumps have been employed in the past. Turbopumps are usually extremely
lightweight and can give excellent performance; with an on-Earth weight well under 1% of the
thrust. Indeed, overall rocket engine thrust to weight ratios including a turbopump have been as
high as 133:1 with the Soviet NK-33 rocket engine.
Alternatively, instead of pumps, a heavy tank of a high-pressure inert gas such as helium
can be used, and the pump forgone; but the delta-v that the stage can achieve is often much
lower due to the extra mass of the tankage, reducing performance; but for high altitude or
vacuum use the tankage mass can be acceptable.
8. What are cryogenic propellants? Discuss.
Ans. Cryogenic propellants are fuels that require storage at extremely low temperatures in
order to maintain them in a liquid state. These fuels are used in the machinery that operate in
space (For example - Rocket ships, Satellites, etc.) because ordinary fuel cannot be used there,
due to absence of environment that supports combustion (on earth, oxygen is abundant in the
atmosphere, whereas in human explorable space, oxygen is virtually non-existent). Cryogenic
fuels most often constitute liquefied gases such as liquid hydrogen.
Some rocket engines use regenerative cooling, the practice of circulating their cryogenic
fuel around the nozzles before the fuel is pumped into the combustion chamber and ignited. This
arrangement was first suggested by Eugen Sänger in the 1940s. The Saturn V rocket that sent the
first manned missions to the moon used this design element, which is still in use today.
Liquid oxygen is mistakenly called cryogenic "fuel", though it is actually an oxidizer and
not a fuel.
Russian aircraft manufacturer Tupolev developed a version of its popular Tu-154 design
but with a cryogenic fuel system, designated the Tu-155. Using a fuel referred to as liquefied
natural gas (LNG), its first flight was in 1989.
9. Name four oxidizers and fuels used in a rocket engine. Explain their characteristics.
Ans. Rocket propellant is a material used by a rocket as, or to produce in a chemical reaction,
the reaction mass (propulsive mass) that is ejected, typically with very high speed, from a rocket
engine to produce thrust, and thus provide spacecraft propulsion. In a chemical rocket
propellants undergo exothermic chemical reactions to produce hot gas. There may be a single
propellant, or multiple propellants; in the latter case one can distinguish fuel and oxidizer. The
gases produced expand and push on a nozzle, which accelerates them until they rush out of the
back of the rocket at extremely high speed.

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Oxidizers
(a) Liquid oxygen has a pale blue color and is strongly paramagnetic; it can be
suspended between the poles of a powerful horseshoe magnet. Because of its
cryogenic nature, liquid oxygen can cause the materials it touches to become
extremely brittle. Liquid oxygen is also a very powerful oxidizing agent: organic
materials will burn rapidly and energetically in liquid oxygen. Further, if soaked in
liquid oxygen, some materials such as coal briquettes, carbon black, etc., can
detonate unpredictably from sources of ignition such as flames, sparks or impact
from light blows. Petrochemicals, including asphalt, often exhibit this behavior.
(b) Dinitrogen tetroxide (nitrogen tetroxide) is the chemical compound N2O4. It is a
useful reagent in chemical synthesis. It forms an equilibrium mixture with nitrogen
dioxide; some call this mixture dinitrogen tetroxide, while some call it nitrogen
dioxide. Dinitrogen tetroxide is a powerful oxidizer. N2O4 is hypergolic with various
forms of hydrazine, i.e., they burn on contact without a separate ignition source,
making them popular bipropellant rocket fuels.
(c) Nitrous oxide, commonly known as laughing gas is a chemical compound with the
formula N2O. It is an oxide of nitrogen. At room temperature, it is a colourless, non-
flammable gas, with a slightly sweet odour and taste. It is used in surgery and
dentistry for its anaesthetic and analgesic effects. It is known as "laughing gas" due
to the euphoric effects of inhaling it, a property that has led to its recreational use as a
dissociative anaesthetic. It is also used as an oxidizer in rocketry and in motor racing
to increase the power output of engines. At elevated temperatures, nitrous oxide is a
powerful oxidizer similar to molecular oxygen.
(d) Hydrogen peroxide (H2O2) is the simplest peroxide (a compound with an oxygen-
oxygen single bond). It is also a strong oxidizer. Hydrogen peroxide is a clear liquid,
slightly more viscous than water. In dilute solution, it appears colorless. Due to its
oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent.
The oxidizing capacity of hydrogen peroxide is so strong that it is considered a
highly reactive oxygen species.
Concentrated hydrogen peroxide, or 'high-test peroxide', is therefore used as a
propellant in rocketry. Organisms also naturally produce hydrogen peroxide as a by-
product of oxidative metabolism.
Fuels
(a) Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen.
Hydrogen is found naturally in the molecular H2 form. To exist as a liquid, H2 must
be cooled below hydrogen's critical point of 33 K. However, for hydrogen to be in a
full liquid state without evaporating at atmospheric pressure, it needs to be cooled to
20.28 K (−423.17 °F/−252.87°C). One common method of obtaining liquid hydrogen
involves a compressor resembling a jet engine in both appearance and principle.
Liquid hydrogen is typically used as a concentrated form of hydrogen storage. As in
any gas, storing it as liquid takes less space than storing it as a gas at normal
temperature and pressure. However, the liquid density is very low compared to other
common fuels. Once liquefied, it can be maintained as a liquid in pressurized and
thermally insulated containers.

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(b) Unsymmetrical dimethylhydrazine (UDMH) (1,1-Dimethylhydrazine) is a
chemical compound with the formula H2N2(CH3)2. It is a colourless liquid, with a
sharp, fishy, ammoniacal smell typical for organic amines. Samples turn yellowish
on exposure to air and absorb oxygen and carbon dioxide. It mixes completely with
water, ethanol, and kerosene. In concentration between 2.5% and 95% in air, its
vapors are flammable. It is not sensitive to shock. Symmetrical dimethylhydrazine
(CH3NHNH(CH3)) is also known but is not as useful.
(c) Hydrazine (also called diazane) is an inorganic compound with the formula N2H4. It
is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly
toxic and dangerously unstable unless handled in solution. Hydrazine is mainly used
as a foaming agent in preparing polymer foams, but significant applications also
include its uses as a precursor to polymerization catalysts and pharmaceuticals.
Hydrazine is used in various rocket fuels and to prepare the gas precursors used in air
bags. Hydrazine is used within both nuclear and conventional electrical power plant
steam cycles as an oxygen scavenger to control concentrations of dissolved oxygen
in an effort to reduce corrosion.
(d) Kerosene is a combustible hydrocarbon liquid. Kerosene is usually called paraffin in
the UK, Ireland, Southeast Asia and South Africa. A more viscous paraffin oil is used
as a laxative. A waxy solid extracted from petroleum is called paraffin wax.
Kerosene is widely used to power jet engines of aircraft (jet fuel) and some rocket
engines, but is also commonly used as a cooking and lighting fuel and for fire toys.
In parts of Asia, where the price of kerosene is subsidized, it fuels outboard motors
on small fishing boats.
10. Describe briefly about gas generators and preburners.
Ans. In the gas generator cycle the turbine inlet gas comes from a separate gas generator. Its
propellants can be supplied from separate propellant tanks or can be bled off the main propellant
feed system. This cycle is relatively simple; the pressures in the liquid pipes and pumps are
relatively low (which reduces inert engine mass). It has less engine-specific impulse than an
expander cycle or a staged combustion cycle.
There are several ways to obtain the hot gas for the turbines. The Saturn V used a “gas
generator cycle.” It tapped off small quantities of fuel and liquid oxygen, burning these
propellants in a small chamber to produce the hot gas. After driving the turbines, this gas simply
went overboard and did no further work.
The Space Shuttle uses the more demanding “staged combustion cycle.” It uses “pre-
burners,” which amount to rocket engines in their own right. Hydrogen fuel burns with a limited
supply of oxygen within a pre-burner, producing a hot fuel-rich flow of gas that drives the
turbines. But this gas does not go overboard. Instead it goes into the engine's main combustion
chamber, where it burns with the rest of the oxygen to produce the engine's thrust. When
hydrogen burns with oxygen, it produces very hot steam. The Space Shuttle's rocket engines
thus amount to high-tech steam engines.

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UNIT – II
1. What do you mean by propellant mass fraction?
Ans. The propellant mass fraction indicates the fraction of propellant mass mp and initial mass
m0. It can be applied to a vehicle, a stage of a vehicle or to a rocket propulsion system.
2. What are the forces acting on a vehicle in the earth’s atmosphere?
Ans. The external forces commonly acting on vehicles flying in the earth's atmosphere are
thrust, aerodynamic forces, and gravitational attractions. Other forces, such as wind or solar
radiation pressure, are small and generally can be neglected for many simple calculations.
3. Define thrust.
Ans. The thrust is the force produced by the power plant, such as a propeller or a rocket. It
usually acts in the direction of the axis of the power plant, that is, along the propeller shaft axis
or the rocket nozzle axis.
4. Define drag and explain its expression.
Ans. The drag D is the aerodynamic force in a direction opposite to the flight path due to the
resistance of the body to motion in a fluid. It is expressed as functions of the flight speed u, the
mass density of the fluid in which the vehicle moves p, and a typical surface area A.
5. Define lift and explain its expression.
Ans. The lift L is the aerodynamic force acting in a direction normal to the flight path. It is
expressed as functions of the flight speed u, the mass density of the fluid in which the vehicle
moves p, and a typical surface area A.
6. What do you mean by ballistic?
Ans. Ballistic is a branch of science which deals with the study of projectile behavior in its
trajectory.
7. What are the types of ballistics?
Ans. (a) Internal Ballistics
(b) External Ballistics
(c) Terminal Ballistics
(d) Forensic Ballistics
8. Briefly explain gravitational attraction.
Ans. Gravitational attraction is exerted upon a flying space vehicle by all planets, stars, the
moon, and the sun. Gravity forces pull the vehicle in the direction of the center of mass of the
attracting body. Within the immediate vicinity of the earth, the attraction of other planets and
bodies is negligibly small compared to the earth's gravitational force. This force is the weight.
9. Draw a free body force diagram for vehicle without wings or fins.
Ans.

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10. What do you mean by a force vector diagram?
Ans. A force vector diagram shows the net force (by adding thrust, drag and gravity vectors)
to be at an angle to the flight path, which will be curved. These types of diagram form the basis
for iterative trajectory numerical solutions.
11. What is the effect of effective exhaust velocity on rockets flight performance?
Ans. The effective exhaust velocity c or the specific impulse is usually have a direct effect on
the vehicle's flight performance. For example, the vehicle final velocity increment Au can be
increased by a higher Is. This can be done by using a more energetic propellant by a higher
chamber pressure and, for upper stages operating at high altitudes, also by a larger nozzle area
ratio.
12. What is the effect of mass ratio on rockets flight performance?
Ans. The mass ratio mo/mf has a logarithmic effect. It can be increased in several ways. One
way is by reducing the final mass mf, which consists of the inert hardware plus the non-usable,
residual propellant mass. Reducing the inert mass implies lighter structures, smaller payloads,
lighter guidance/control devices, or less unavailable residual propellant; this means going to
stronger structural materials at higher stresses, more efficient power supplies, or smaller
electronic packages.
13. What is the effect of reduced burning time on rockets flight performance?
Ans. Reducing the burning time (i.e., increasing the thrust level) will reduce the gravitational
loss. However, the higher acceleration usually requires more structural and propulsion system
mass, which in turn causes the mass ratio to be less favorable.
14. What are the various components of drag a rocket experience?
Ans. The drag has several components:
(a) The form drag depends on the aerodynamic shape. A slender pointed nose or
sharp, thin
leading edges of fins or wings have less drag than a stubby, blunt shape.
(b) A vehicle with a small cross-sectional area has less drag. A propulsion design
that can be packaged in a long, thin shape will be preferred. The drag is proportional to
the cross-sectional or frontal vehicle area. A higher propellant density will decrease the
propellant volume and therefore will allow a smaller cross section.
(c) The skin drag is caused by the friction of the air flowing over all the vehicle's
outer surfaces. A smooth contour and a polished surface are usually better. The skin drag
is also influenced by the propellant density, because it gives a smaller volume and thus a
lower surface area.
(e) The base drag is the fourth component; it is a function of the local ambient air
pressure acting over the surface of the vehicle's base or bottom plate. It is influenced by
the nozzle exit
design (exit pressure) and the geometry of the vehicle base design.
15. What is earth’s magnetic field?
Ans. The earth's magnetic field and any magnetic moment within the satellite interact to
produce torque. The earth's magnetic field precesses about the earth's axis but is very weak (0.63
and 0.31gauss at poles and equator, respectively). This field is continually fluctuating in
direction and intensity because of magnetic storms and other influences. Since the field strength
decreases with 1/R3
with the orbital
altitude, magnetic field forces are often neglected in the preliminary design of satellites.

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16. What do you mean by a flight maneuvers?
Ans. Different Attitudes of a space vehicle during its mission journey is called flight
maneuvers.
17. Categorise the types of maneuvers.
Ans. The three categories of maneuvers are:
(a) In translation maneuvers the rocket propulsion thrust vector goes through the
center of gravity of the vehicle. The vehicle momentum is changed in the direction of the
flight velocity. An example of several powered (translational maneuvers) and unpowered
(coasting) segments of a complex space flight trajectory. To date, most maneuvers have
used chemical propulsion systems.
(b) In truly rotational maneuvers there is no net thrust acting on the vehicle. These
are true couples that apply only torque. It requires four thrusters to be able to rotate the
vehicle in either direction about any one axis (two thrusters apart, firing simultaneously,
but in opposite directions). These types of maneuver are usually provided by reaction
control systems. Most have used multiple liquid propellant thrusters, but in recent years
many space missions have used electrical propulsion.
(c) A combination of categories (a) and (b), such as a large misaligned thrust vector
that does not go exactly through the center of gravity of the vehicle. The misalignment
can be corrected by changing the vector direction of the main propulsion system (thrust
vector control) during powered flight or by applying a simultaneous compensating torque
from a separate reaction control system.
18. What is an orbit injection?
Ans. Orbit injection or transferring from one orbit to another requires accurately
predetermined total impulses. It can be performed by the main propulsion system of the top
stage of the launch vehicle. More often it is done by a separate propulsion system at lower thrust
levels than the upper stages. Orbit injection can be a single thrust operation after ascent from an
earth launch station.
19. Define docking.
Ans. Docking (sometimes called lock-on) is the linking up of two spacecraft and requires a
gradual gentle approach (low thrust, pulsing node thrusters) so as not to damage the spacecraft.
20. What is LEO?
Ans. A single stage to orbit is generally referred as low earth orbit and in this type of mission,
multi-stage vehicles are not employed.
21. What are the advantages of multistage rocket vehicles?
Ans. Multistep or multistage rocket vehicles permit higher vehicle velocities, more payload for
space vehicles, and improved performance for long-range ballistic missiles. After the useful
propellant is fully consumed in a particular stage, the remaining empty mass of that expended
stage is dropped from the vehicle and the operation of the propulsion system of the next step or
stage is started. The last or top stage, which is usually the smallest, carries the payload.
22. Which stage is called a booster stage?
Ans. Usually the first or lowest stage, often called a booster stage, is the largest and it requires
the largest thrust and largest total impulse.
23. What is a missile?
Ans. A missile is a chemical rocket used preferably for military purpose.

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24. Differentiate between tactical and strategic missiles.
Ans. A tactical missile is used for attacking or defending ground troops, nearby military or
strategic installations, military aircraft, or war missiles.
Strategic missiles with a range of 3000 km or more have been two- or three stage
surface-to-surface rocket-propelled missiles. Early designs used liquid propellant rocket engines
and some are still in service.
25. What are guided missiles?
Ans. When missiles are launched from an aircraft at a relatively high initial velocity, or when
projectiles are given stability by spinning them on their axis, their accuracy of reaching a target
is increased two- to ten-fold, compared to a simple fin-stabilized rocket launched from rest.
These are called guided missiles. In guided air-to-air and surface-to-air rocket-propelled
missiles the time of flight to a given target, usually called the time to target tt, is an important
flight performance parameter.
PART ‘B’
1. Explain briefly what is meant by
(a) Monopropellants (b) Hypergolic propellants
(c) Bipropellants (d) UDMH
(e) RFNA (f) JATO
Ans. (a) Monopropellants are propellants consisting of chemicals that do not require an
oxidizer to release their stored chemical energy. While stable under defined storage conditions,
they decompose very rapidly under certain other conditions to produce a large volume of
energetic (hot) gases for the performance of mechanical work. Although solid deflagrants such
as nitrocellulose, the most commonly used propellant in firearms, and ammonium
perchlorate/aluminum/synthetic rubber, widely used in military and spacecraft boosters, could
be thought of as monopropellants, the term is usually reserved for liquids in engineering
literature.
Monopropellants release their energy through exothermic chemical decomposition. The
molecular bond energy of the monopellant is released usually through use of a catalyst. This can
be contrasted with bipropellants that release energy through the chemical reaction between an
oxidizer and a fuel. Example : Hydrazine, Ethylene Oxide, Hydrogen Peroxide etc.
(b) A hypergolic rocket propellant combination used in a rocket engine is one where
the propellants spontaneously ignite when they come into contact with each other. The two
propellant components usually consist of a fuel and an oxidizer. Although hypergolic propellants
tend to be difficult to handle because of their extreme toxicity and/or corrosiveness, they can
typically be stored as liquids at room temperature and hypergolic engines are easy to ignite
reliably and repeatedly. In contemporary usage, the terms "hypergol" or "hypergolic propellant"
usually mean the most common such propellant combination, dinitrogen tetroxide plus
hydrazine and/or its relatives monomethyl hydrazine and unsymmetrical dimethylhydrazine.
(c) Bipropellant liquid rockets generally use a liquid fuel and a liquid oxidizer, such
as liquid hydrogen or a hydrocarbon fuel such as RP-1, and liquid oxygen. The engine may be a
cryogenic rocket engine, where the fuel and oxidizer, such as hydrogen and oxygen, are gases
which have been liquefied at very low temperatures.
(d) Unsymmetrical dimethylhydrazine (UDMH) (1,1-Dimethylhydrazine) is a
chemical compound with the formula H2NN(CH3)2. It is a colourless liquid, with a sharp, fishy,

Page 14 of 41
ammoniacal smell typical for organic amines. Samples turn yellowish on exposure to air and
absorb oxygen and carbon dioxide. It mixes completely with water, ethanol, and kerosene.
(e) Red fuming nitric acid (RFNA) is a storable oxidizer used as a rocket propellant.
It consists of 84% nitric acid (HNO3), 13% dinitrogen tetroxide and 1–2% water.
[1] The color of red fuming nitric acid is due to the dinitrogen tetroxide, which
breaks down partially to form nitrogen dioxide. The nitrogen dioxide dissolves until the
liquid is saturated, and evaporates off into fumes with a suffocating odor. RFNA
increases the flammability of combustible materials and is highly exothermic when
reacting with water.
It is usually used with an inhibitor (with various, sometimes secret, substances, including
hydrogen fluoride;
[2] any such combination is called "inhibited RFNA" IRFNA) because nitric acid
attacks most container materials.
It can also be a component of a monopropellant; with substances like amine nitrates
dissolved in it, it can be used as the sole fuel in a rocket. It is not normally used this way
however.
(f) JATO is an acronym for jet assisted take off. It is a system for helping overloaded
aircraft into the air by providing additional thrust in the form of small rockets. The term is used
interchangeably with the (more specific) term RATO, for Rocket-Assisted Take Off (or, in RAF
parlance, RATOG for Rocket-Assisted Take Off Gear).
2. What are the methods of cooling employed in rockets? Explain regenerative heating of a
propellant in a liquid propellant rocket?
Ans. (a) Regenerative cooling
(b) Radiation cooling
(c) Heat Sink cooling
(d) Film cooling and special insulation
(e) Ablative Cooling
(f) Ceramic Insulation Cooling
Regenerative cooling is done by building a cooling jacket around the thrust chamber and
circulating one of the liquid propellants (usually the fuel) through it before it is fed to the
injector. This cooling technique is used primarily with bipropellant chambers of medium to large
thrust. It has been effective in applications with high chamber pressure and high heat transfer
rates. Also, most injectors use regenerative cooling.
3. What is the purpose of injectors in rocket engines? Describe an injector with the aid of a
sketch.
Ans. The functions of the injector are similar to those of a carburetor of an internal
combustion engine. The injector has to introduce and meter the flow of liquid propellants to the
combustion chamber, cause the liquids to be broken up into small droplets (a process called
atomization), and distribute and mix the propellants in such a manner that a correctly
proportioned mixture of fuel and oxidizer will result, with uniform propellant mass flow and
composition over the chamber cross section. This has been accomplished with different types of
injector designs and elements.
Types: (a) Impinging-stream-type, multiple-hole injectors.
(b) Non-impinging or Shower head.
(c) Coaxial Hollow Post Injector.

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Impinging-stream-type, multiple-hole injectors are commonly used with oxygen-
hydrocarbon and storable propellants. For unlike doublet patterns the propellants are injected
through a number of separate small holes in such a manner that the fuel and oxidizer streams
impinge upon each other. Impingement forms thin liquid fans and aids atomization of the liquids
into droplets, also aiding distribution. Impinging hole injectors are also used for like-on-like or
self-impinging patterns (fuel-on-fuel and oxidizer-on-oxidizer). The two liquid streams then
form a fan which breaks up into droplets. Unlike doublets work best when the hole size (more
exactly, the volume flow) of the fuel is about equal to that of the oxidizer and the ignition delay
is long enough to allow the formation of fans. For uneven volume flow the triplet pattern seems
to be more effective.
4. What are the various methods of ignition employed in liquid propellant rockets?
Ans. By using Hypergolic fluid for a short time
Ignition by spark plug
Pyrotechnic ignition
5. Describe the events leading to pressure oscillations in a rocket combustor.
Ans. Chugging
Chugging, the first type of combustion instability stems mostly from the elastic nature of
the feed systems and structures of vehicles or the imposition of propulsion forces upon
the vehicle. Chugging of an engine or thrust chamber assembly can occur in a test
facility, especially with low chamber pressure engines (100 to 500 psia), because of
propellant pump cavitation, gas entrapment in propellant flow, tank pressurization
control fluctuations, and vibration of engine supports and propellant lines. It can be
caused by resonances in the engine feed system (such as an oscillating bellows inducing
a periodic flow fluctuation) or a coupling of structural and feed system frequencies.
Buzzing
Buzzing, the intermediate type of instability, seldom represents pressure perturbations
greater than 5% of the mean in the combustion chamber and usually is not accompanied
by large vibratory energy. It often is more noisy and annoying than damaging, although
the occurrence of buzzing may initiate high-frequency instability. Often it is
characteristic of coupling between the combustion process and flow in a portion of the
propellant feed system.
Screeching or Screaming
screeching or screaming, has high frequency and is most perplexing and most common in
the development of new engines. Both liquid and solid propellant rockets commonly
experience high-frequency instability during their development phase. Since energy
content increases with frequency, this type is the most destructive, capable of destroying
an engine in much less than 1 sec. Once encountered, it is the type for which it is most

Page 16 of 41
difficult to prove that the incorporated "fixes" or improvements render the engine
"stable" under all launch and flight conditions. It can be treated as a phenomenon isolated
to the combustion chamber and not generally influenced by feed system or structure.
6. How does the development of thrust in a rocket engine differ from that in a turbojet
engine? Explain briefly.
Ans. Rocket thrust is the reaction force produced by expelling particles at high
velocity from a nozzle opening. These expelled particles may be solid, liquid, gaseous, or
even bundles of radiant energy. The engine's ability to produce thrust will endure only so
long as the supply of particles, or working fluid, holds out. Expulsion of material is the
essence of the thrust production, and without material to expel no thrust can be produced,
regardless of how much energy is available.
Jet engines, known as gas turbines or turbo fans, ingest atmospheric air as their
source of oxygen. The benefit of not carrying a supply of oxygen is also a handicap.
These engines suffer from oxygen starvation at high altitudes and reduced performance
in hot weather. The fuel, normally JP-4, is really a type of kerosene that contains very
little water contamination and is relatively economical. Although very expensive, jet
engines are quite simple and incredibly reliable. The spinning blades on those monstrous
GE and Rolls Royce engines are the first stage of the compressor. These blades ingest
massive quantities of air and hurl it back into the next compressor section. Each stage
being smaller, the air pressure and temperature increases dramatically. This hot air
combines with fuel in the burning chamber, exits as extremely hot gas, and spins
additional sets of blades on its way out. These blades turn the front compressors,
perpetuating the process. Tens of thousands of pounds of thrust can be produced. Some
of a jet engine's thrust is from the kinetic energy of exiting hot gasses. The turbo fans,
however, produce most of the thrust.
7. What are the forces acting on a vehicle in the atmosphere? Explain briefly.
Ans. In flight, a rocket is subjected to four forces;
Weight, Thrust, and the aerodynamic forces, Lift and Drag.
The magnitude of the weight depends on the mass of all of the parts of the rocket.
The weight force is always directed towards the center of the earth and acts through the
center of gravity, the yellow dot on the figure.
The magnitude of the thrust depends on the mass flow rate through the engine
and the velocity and pressure at the exit of the nozzle. The thrust force normally acts
along the longitudinal axis of the rocket and therefore acts through the center of gravity.
Some full scale rockets can move, or gimbal, their nozzles to produce a force which is
not aligned with the center of gravity. The resulting torque about the center of gravity
can be used to maneuver the rocket.
The magnitude of the aerodynamic forces depends on the shape, size, and
velocity of the rocket and on properties of the atmosphere. The aerodynamic forces act
through the center of pressure, the black and yellow dot on the figure. Aerodynamic
forces are very important for model rockets, but may not be as important for full scale
rockets, depending on the mission of the rocket. Full scale boosters usually spend only a
short amount of time in the atmosphere.
Although the same four forces act on a rocket as on an airplane, there are some
important differences in the application of the forces:

Page 17 of 41
(a) On an airplane, the lift force (the aerodynamic force perpendicular to the
flight direction) is used to overcome the weight. On a rocket, thrust is used in opposition
to weight. On many rockets, lift is used to stabilize and control the direction of flight.
(b) On an airplane, most of the aerodynamic forces are generated by the
wings and the tail surfaces. For a rocket, the aerodynamic forces are generated by the
fins, nose cone, and body tube. For both airplane and rocket, the aerodynamic forces act
through the center of pressure (the yellow dot with the black center on the figure) while
the weight acts through the center of gravity (the yellow dot on the figure).
(c) While most airplanes have a high lift to drag ratio, the drag of a rocket is
usually much greater than the lift.
(d) While the magnitude and direction of the forces remain fairly constant
for an airplane, the magnitude and direction of the forces acting on a rocket change
dramatically during a typical flight.
8. Calculate the orbital and escape velocities of a rocket at mean sea level and an altitude of
300 km from the following data:
Radius of earth at mean sea level = 6341.6 km
Acceleration due to gravity at mean sea level = 9.809 m/s2
.
Ans. At Z = 0 , Uorb = (g0R0)1/2
= (9.8 X 6341.6 X 1000)1/2
= 7887m/s
U esc = √2 Uorb = √2 X 7887 = 11,154 m/s
At Z = 300 km, R = R0 + Z = 6341.6 + 300 = 6641.6 km
Uorb = R0 [g0 / (R0 + Z)]1/2
= 7706.8 m/s
U esc = √2 Uorb = √2 X 7706.8 = 10.889.96 m/s
9. A rocket has the following data.
Propellants flow rate =5Kg/s, Nozzle exit diameter=10cm, Nozzle exit pressure=1.02
bar, Ambient pressure=1.013bar, Thrust chamber pressure=20bar, Thrust=7 KN.
(a) Determine the effective jet velocity, actual jet velocity, Specific impulse and
Specific Propellant consumption.
(b) Recalculate the values of thrust and specific impulse for an altitude where the
ambient pressure is 10 mbar.
Ans. Specific Impulse Is = F/wp = 7000/5 X 9.81 = 142.71seconds.
Effective jet Velocity = F / mp = 7000 / 5 = 1400 m/s
Ae = Aj = π d2
/ 4 = 3.41X 100 /4 = 78.54 cm2
F = mpce + (pe – pa) A e , 7000 = 5 X ce + (1.02 – 1.013) X 105
X 78.54 X 10-4
Ce = 1398.9 m/s, SPC = 1/Is = 1/142.71 = 0.007s-1
Thrust due to decrease in ambient pressure increases.
F = mpce + (pe – pa) A e , 7000 = 5 X 1398.9 + (1.02 – 0.01) X 105
X 78.54 X 10-4
=
7787 N, Is = 158.77 seconds.

Page 18 of 41
10. Determine the maximum velocity of a rocket and the altitude attained from the following
data:
Mass Ratio = 0.15
Burnout Time = 75 s
Effective Jet velocity = 2500 m/s
What are the values of the velocity and altitude losses due to gravity? Ignore drag
and assume vertical trajectory.
Ans. Difficult to type manually due to formulas and symbols involved. Will be explained
physically.

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UNIT – III
PART ‘A’
1. Define specific propellant consumption.
Ans. The weight flow rate of the propellant required to produce a thrust of one Newton is
known as the specific propellant consumption (SPC). This is given by
SPC = wp / F = 1/Is
2. What do you mean by weight flow coefficient?
Ans. This is the ratio of the gas or propellant flow rate and the force term p0A*
. This is not a
dimensionless quantity. It has the same unit as SPC.
3. What is thrust coefficient?
Ans. This is the ratio of thrust and the force term p0A*
. This is a dimensionless quantity. It is
used for determining the thrust with known values of the combustion pressure and the nozzle
thrust area.
4. Define characteristic velocity.
Ans. Rocket performance is frequently expressed in terms of characteristic velocity which is
defined as ratio of effective jet velocity and thrust coefficient.
5. What are the various efficiencies in rocket propulsion?
Ans. (a) Propulsive efficiency = Propulsion or thrust Power / Engine output power
= F.u / ½ (u2
+ cj
2
)
(b) Thermal efficiency = Engine output power / Power input through fuel
= ½ (u2
+ cj
2
) / mpQR
(c) Overall efficiency = Propulsion or thrust Power / Power input through fuel
= F.u / mpQR
6. Define propulsive efficiency of a rocket.
Ans. This is defined as the ratio of propulsion or thrust power and engine output power.
Propulsive efficiency ( ηp) = Propulsion or thrust Power / Engine output power
= F.u / ½ (u2
+ cj
2
)
7. Define thermal efficiency of a rocket.
Ans. This is the energy conversion efficiency of the rocket engine and takes into account the
thermal losses.
Thermal efficiency ( ηth) = Engine output power / Power input through fuel
= ½ (u2
+ cj
2
) / mpQR
8. Define overall efficiency of a rocket.
Ans. The overall efficiency is given by
Overall efficiency ( ηo) = Propulsion or thrust Power / Power input through
fuel
= F.u / mpQR
9. What are the forces a vehicle or satellite has to overcome when passing through the
atmosphere?
Ans. Drag and gravity.
10. What is a booster stage?
Ans. The first stage lifts off the entire rocket vehicle system, therefore it is the most powerful
stage and is known as the booster stage.
11. What are retro rockets?

Page 20 of 41
Ans. Retro rockets are small rockets fired in the direction of motion of the space vehicle to
achieve braking or deceleration.
12. What do you mean by sustainer?
Ans. The last stage of the rocket which is generally the smallest is called sustainer.
13. What are the purposes of small rockets used with rocket vehicle system?
Ans. Small rockets are used on the way for various minor operations such as trajectory
correction, attitude control and stage separation.
14. What are sounding rockets?
Ans. Rockets meant for taking instruments to high altitudes for meteorological measurements
are called sounding rockets.
15. Define mass ratio.
Ans. It is the ratio of final mass of the rocket after burnout and total mass of the rocket at take-
off.
16. What is propellant mass fraction?
Ans. This is defined as the ratio of propellant mass at take- off and total mass of the rocket at
take-off.
17. Define ‘burnout’.
Ans. The thrust becomes zero after propellant consumption which is called burnout.
18. Explain briefly the meaning of earth satellite.
Ans. Rockets are used to launch space stations or satellites into earth’s orbit; they revolve
round the earth at an altitude beyond the earth’s atmosphere where the drag force is absent.
Therefore, such satellites can remain in the orbit forever without any expenditure of energy.
Earth satellites are used for several scientific and technological programmes such as
observations of space phenomena, study of weather, military missions and communication.
19. What do you mean by stationary satellite?
Ans. If the orbital velocity of an earth satellite is equal to the angular velocity of the earth it
has zero velocity relative to the earth. Such a satellite is known as a stationary satellite which
can be usefully employed for several purposes.
20. What is coasting?
Ans. The behavior of rocket after the burnout condition and when thrust becomes zero is
termed as coasting.
21. Define total impulse and write down the formula and unit.
Ans. The total impulse It is the thrust force F (which can vary with time) integrated over the
burning time t.
For constant thrust and negligible start and stop transients this reduces to
It is proportional to the total energy released by all the propellant in a propulsion system.
It’s unit is Ns.
22. What is escape velocity?
Ans. A rocket vehicle system destined to travel in the outer space to other planets or their
orbits must escape from the earth’s gravitational field. The thrust should be able to accelerate the

Page 21 of 41
rocket to a velocity at which its kinetic energy equals the work required to overcome
gravitational force.
The escape velocity at the earth’s surface is about 11.2 km/s.
U esc = √2 Uorb
23. Show graphically the variation of acceleration due to gravity with altitude.
Ans.
24. What do you mean by orbital velocity?
Ans. The orbital velocity of the satellite can be found by equating the centrifugal force acting
on it to the gravitational pull. The velocity of the satellite is uorb at a radius R from the centre of
the earth.
At Z = 0 , Uorb = (g0R0)1/2
At Z = x km, R = R0 + x
Uorb = R0 [g0 / (R0 + x)]1/2
25. Show graphically the variation of thrust coefficient vs exhaust nozzle pressure ratio,
P0/Pe.
Ans.
PART ‘B’
1. Derive an expression for the velocity of a rocket vehicle at the end of the powered flight.
Ans. CFPS Book Page No. 436
2. What is the effect of mass ratio, specific impulse and burnout time on the maximum
velocity attained by the rocket vehicle?

Page 22 of 41
Ans. CFPS Book Page No. 437 and 438
3. Calculate thrust, specific impulse, propulsive, thermal and overall efficiencies of a rocket
engine from the following data:
Effective jet velocity : 1250 m/s
Flight to jet speed ratio : 0.80
Oxidiser flow rate : 3.5 kg/s
Fuel flow rate : 1.0 kg/s
Heat of reaction per kg of the exhaust gases : 2500 kj/kg
Ans. F = mp vj = (3.5 + 1) X 1250 = 5625 N
Is = F / mp g = 127.55 s
uj / vj = 0.80 , uj = 1250 X 0.80 = 1000 m/s
( ηp) = 0.975
( ηth) = 0.51
( ηo) = 0.50
4. A rocket nozzle has a throat area of 18 cm2
and combustion chamber pressure of 25 bar.
If the specific impulse is 127.42 seconds and weight flow rate 44.145 N/s. Determine:
(a) The thrust coefficient (b) Propellant weight flow coefficient
(c) Specific propellant consumption, and (d) The characteristic velocity.
Ans. The thrust coefficient = 1.25 , Propellant weight flow coefficient = 0.00981
Specific propellant consumption = 0.007848 , The characteristic velocity = effective jet
velocity / 1.25 = F / mp / 1.25 = 1250 / 1.25 = 1000 m/s.
5. Define orbital and escape velocities of a rocket vehicle. Derive the following relation:
Uesc = √2uorb = R0 {2g0 / (R0 + Z)}1/2
Ans. CFPS Book Page No. 447
6. Depict graphically the variations of orbital and escape velocities with altitude.
7. The diameter of earth at the mean sea level is 12,683.2 km and the acceleration due to
gravity 9.809 m/s2
; determine the values of the orbital and escape velocities of a rocket
propelled spacecraft at an altitude of 500 km.
Ans. 7.593 km/s , 10.739 km/s
8. Derive an expression for the final velocity of a rocket vehicle after complete burnout or
the operation of the nth stage.
Ans. CFPS Book Page No. 438 and 439.
9. Write a short note on gravity free and drag free space flight.
Ans. This simple rocket flight analysis applies to an outer space environment, where there is
no air (thus no drag) and essentially no significant gravitational attraction. The flight direction is
the same as the thrust direction (along the axis of the nozzle), namely, a one-dimensional,
straight-line acceleration path; the propellant mass flow rate, and thus the thrust F, remain
constant for the propellant burning duration tp. For a constant propellant flow the flow rate is
mp/tp, where mp is the total usable propellant mass. From Newton's second law and for an
instantaneous vehicle mass m and a vehicle velocity u,

Page 23 of 41
For a rocket where the propellant flow rate is constant the instantaneous mass of the
vehicle m can be expressed as a function of the initial mass of the full vehicle mo, mp, tp, and the
instantaneous time t.
10. Describe briefly about perturbations.
Ans. The disturbing torques and forces cause perturbations or deviations from any space flight
path or satellite's flight trajectory. A system is needed to measure the satellite's position and
deviation from the intended flight path, to determine the needed periodic correction maneuver
and then to counteract, control, and correct them. Typically, the corrections are performed by a
set of small reaction control thrusters which provide predetermined total impulses into the
desired directions. These corrections are needed throughout the life of the spacecraft (for 1 to 20
years) to overcome the effects of the disturbances and maintain the intended flight regime.
Perturbations can be cateogirzed as short-term and long-term. The daily or orbital period
oscillating forces are called diurnal and those with long periods are called secular.
High-altitude each satellites (36,000 km and higher) experience perturbing forces
primarily as gravitational pull from the sun and the moon, with the forces acting in different
directions as the satellite flies around the earth.
Medium- and low-altitude satellites (500 to 35,000 km) experience perturbations because
of the earth's oblateness. The earth bulges in the vicinity of the equator and a cross section
through the poles is not entirely circular. Depending on the inclination of the orbital plane to the
earth equator and the altitude of the satellite orbit, two perturbations result:
(1) the regression of the nodes, and
(2) shifting of the apsides line (major axis).
Regression of the nodes can be shown as a rotation of the plane of the orbit in space, and
it can be as high as 9 ° per day at relatively low altitudes. Theoretically, regression does not occur
in equatorial orbits.

Page 24 of 41
UNIT – IV
PART ‘A’
1. What is thrust vector control?
Ans. In a rocket, the rocket engine or motor not only provides the propulsive force but also the
means of controlling its flight path by redirecting the thrust vector to provide directional control
for the vehicle’s flight path. This is known as thrust vector control (TVC).
2. Name the various methods of vector control of liquid rockets.
Ans. Gimbaled Engines – Some liquid propellant rockets use an engine swivel or gimbal
arrangement to point the entire engine assembly. This arrangement requires flexible propellant
lines, but produces negligible thrust losses for small deflection angles. This method is relatively
common.
Vernier Rockets - Vernier rockets are small auxiliary rocket engines. These engines can
provide all attitude control, or just roll control for single engine stages during the main engine
burn, and a means of controlling the rocket after the main engine has shut off.
Jet Vanes - Jet vanes are small airfoils located in the exhaust flow behind the nozzle exit
plane. They act like ailerons or elevators on an aircraft and cause the vehicle to change direction
by redirecting the rocket. Jet vanes are made of heat-resistant materials like carbon-carbon and
other refractory substances. Unfortunately, this control system causes a two to three percent loss
of thrust, and erosion of the vanes is also a major problem.
3. Name the various methods of vector control of solid rockets.
Ans. Rotating Nozzle - The rotating nozzle has no throat movement. These nozzles work in
pairs and are slant-cut to create an area of under expansion of exhaust gases on one side of the
nozzle. This creates an unbalanced side load and the inner wall of the longer side of the nozzle.
Rotation of the nozzles moves this side load to any point desired and provides roll, yaw and
pitch control. This system is simple but produces slow changes in the velocity vector. Rotating
nozzles are usually supplemented with some other form of TVC.
Swiveled Nozzle - The swiveled nozzle changes the direction of the throat and nozzle. It
is similar to gambaling in liquid propellant engines. The main drawback in using this method is
the difficulty in fabricating the seal joint of the swivel since this joint is exposed to extremely
high pressures and temperatures.
Movable Control Surfaces - Movable Control Surfaces physically deflect the exhaust or
create voids in the exhaust plume to divert the thrust vector. This method includes jet vanes, jet
tabs, and mechanical probes. These TVC approaches are all based on proven technology with
low actuator power
required. They suffer from erosion and cause thrust loss with any deflection. A similar system is
the jetavator, a slipring or collar at the nozzle exit which creates an under expansion region.
The jetavator is a movable surface which allows the under expanded region to be moved 360
degrees around the rocket nozzle to produce pitch and yaw control. This system was developed
for the Polaris SLBM.
4. What is a gimbaled engine?
Ans. Gimbaled Engines – Some liquid propellant rockets use an engine swivel or gimbal
arrangement to point the entire engine assembly. This arrangement requires flexible propellant
lines, but produces negligible thrust losses for small deflection angles. This method is relatively
common.

Page 25 of 41
5. Define vernier rocket.
Ans. Vernier Rockets - Vernier rockets are small auxiliary rocket engines. These engines can
provide all attitude control, or just roll control for single engine stages during the main engine
burn, and a means of controlling the rocket after the main engine has shut off.
6. How are the movable control surfaces used for TVC?
Ans. Movable Control Surfaces - Movable Control Surfaces physically deflect the exhaust or
create voids in the exhaust plume to divert the thrust vector. This method includes jet vanes, jet
tabs, and mechanical probes.
7. What do you mean by staging?
Ans. Currently, the only practical method we have for launching satellites is with chemical
systems. As we found out in the rocket performance section, specific impulse and mass ratio
limit our chemical
systems performance. A rocket has to provide enough energy, essentially 25,000 ft/sec (17,500
mph), to orbit the Earth as a satellite and 36,700 ft/sec (25,000 mph) to escape the Earth’s
gravitational field and become a planetoid circling the Sun.

Page 26 of 41
A body must attain a velocity of nearly 35,000 ft/sec to hit the Moon. No practical rocket
of one stage can reach the critical velocities for satellites or space probes. A solution to this
problem is to mount one or more rockets on top of one another and to fire them in succession at
the moment the previous stage burns out. For example, if each stage provides about 9,000 ft/sec
in velocity when fired as above, it would take three stages to put a satellite in orbit, or four
stages to reach the moon or go beyond it into space as a deep space probe orbiting the sun.
Staging reduces the launch size and weight of the vehicle required for a specific mission
and aids in achieving the high velocities necessary for specific missions. Multistage rockets
allow improved payload capability for vehicles with a high v requirement, such as launch
vehicles or interplanetary spacecraft.
8. What is the need of multi-staging a rocket?
Ans. Multistage rockets allow improved payload capability for vehicles with a high v
requirement, such as launch vehicles or interplanetary spacecraft.
9. What are the cooling techniques used for cooling the chamber and nozzle walls?
Ans. Radiation Cooling, Ceramic Linings, Ablation Cooling, Film Cooling,
Transpirational Cooling and Regenerative Cooling.
10. What is radiation cooling?
Ans. This is probably the simplest method of cooling a rocket engine or motor. The method is
usually used for monopropellant thrusters, gas generators, and lower nozzle sections. The
interior of the combustion chamber is covered with a refractory material (graphite, pyrographite,
tungsten, tantalum or
molybdenum) or is simply made thick enough to absorb a lot of heat. Cooling occurs by heat
loss through radiation into the exhaust plume. Radiation cooling can set an upper limit on the
temperature
attained by the walls of the thrust chamber. The rate of heat loss varies with the fourth power of
the absolute temperature and becomes more significant as the temperature rises.
11. Define ablation cooling.
Ans. In the ablation cooling method, the interior of the thrust chamber is lined with an ablative
material, usually some form of fabric reinforced plastic. This material chars, melts and vaporizes
in the intense heat of the nozzle. In this type of “heat sink cooling,” the heat absorbed in the
melting and burning (the energy alters the chemical form instead of raising its temperature) of
the ablative material prevents the temperature from becoming excessively high. The charred
material also serves as an insulator and protects the rocket case from overheating. The gas
produced by burning the ablative material provides an area of “cooler” gas next to the nozzle
walls. The synthetic organic plastic binder material is reinforced with glass fiber or a synthetic
substance. Solid rocket motors use ablative cooling
almost exclusively, as there are no other fluids to use to cool the nozzle throat.
12. What do you mean by film cooling?
Ans. With this method of cooling, liquid propellant is forced through small holes at the
periphery of the injector forming a film of liquid on the interior surface of the combustion
chamber. The film has a low thermal (or heat) conductivity since it readily vaporizes and
protects the wall material from the hot combustion gases. Cooling results from the vaporization
of the liquid which absorbs considerable heat. Film cooling is especially useful in regions where
the walls become exceptionally hot, e.g., the nozzle throat area.

Page 27 of 41
13. What do you mean by regenerative cooling?
Ans. This is the most common method of cooling for cryogenic propellant rockets. It involves
circulating one of the super cooled propellants through a cooling jacket around the combustion
chamber and nozzle before it enters the injector. The propellant removes heat from the walls,
keeping temperatures at acceptable levels. At the same time, the temperature of the propellant
rises, causing it to vaporize faster upon injection. This cooling method is often used with gas
generator systems as a way to drive turbo pumps.
14. How the cooling is achieved in solid rocket motor?
Ans. In solid propellant motors, the nozzle serves the same purpose as in the liquid engine.
Because there is no super-cooled propellant available to provide cooling, we use other methods
for thermal protection. If not properly constructed, the walls of the combustion chamber will
become excessively hot. This could cause case failure under the high operating pressures
existing in the interior. To prevent this, the inner wall of the motor case is coated with a liner or
inhibitor. This liner provides a bond between the propellant grain and the case preventing
combustion from spreading along the walls, and acts as a thermal insulator, protecting the case
from heat in areas where there is no propellant. The unburned propellant provides additional
thermal protection as it must be vaporized before it will burn.
15. What are the types of propellants?
Ans. Liquid Propellant and Solid Propellant.
16. What do you mean by cryogenic propellants?
Ans. A cryogenic propellant is one that has a very low boiling point and must be kept very
cold. For example, liquid oxygen boils at -2970
F, liquid fluorine at -3060
F and liquid hydrogen
at -4230
F.
17. What is the advantage of multistage in a rocket?
Ans. Multistage rockets allow improved payload capability for vehicles with a high v
requirement, such as launch vehicles or interplanetary spacecraft.
18. What are the disadvantages of single stage in a rocket?
Ans. single stage rocket cannot be used for long range missions and it will be much heavier
than multistage rocket.
19. Define payload fraction.
Ans. The payload mass for any stage consists of the mass of all subsequent stages plus the
ultimate payload itself. A multistage vehicle with identical specific impulse, payload fraction
and structure fraction for each stage is said to have similar stages. For such a vehicle, the
payload fraction is maximized by having each stage provide the same velocity increment. For a
multistage vehicle with dissimilar stages, the overall vehicle payload fraction depends on how
the v requirement is partitioned among stages. Payload fractions will be reduced if the v is
partitioned sub-optimally.
20. What do you mean by mission velocity?
Ans. Mission velocity is the sum of all the flight velocity increments needed to attain the
mission objective. The required mission velocity is the sum of the absolute values of all
translation velocity increments that have forces going through the center of gravity of the vehicle
(including turning maneuvers) during the flight of the mission.
21. What are the usages of tactical missiles?
Ans. For each of the tactical missile applications, there is an optimum rocket propulsion
system and almost all of them use solid propellant rocket motors. For each application there is
an optimum total impulse, an optimum thrust time profile, an optimum nozzle configuration

Page 28 of 41
(single or multiple nozzles, with or without thrust vector control, optimum area ratio), optimum
chamber pressure, and a favored solid propellant grain configuration. Short-range, uncontrolled,
unguided, single-stage rocket vehicles, such as military rocket projectiles (ground and air
launched) and rescue rockets, are usually quite simple in design.
22. What is flight stability?
Ans. Stability of a vehicle is achieved when the vehicle does not rotate or oscillate in flight.
Unstable flights are undesirable, because pitch or yaw oscillations increase drag (flying at an
angle of attack most of the time) and cause problems with instruments and sensors (target
seekers, horizon scanners, sun sensors, or radar). Instability often leads to tumbling
(uncontrolled turning) of vehicles, which causes missing of orbit insertion, missing targets, or
sloshing of liquid propellant in tanks.
23. What is the mass ratio mp/mo for a vehicle that has one-fifth its original take-off mass at
the time of the completion of rocket operation?
Ans. (X – 1/5 X )/ X = (4/5 X ) / X = 0.80
24. What type of nozzle is best for a bullet –shaped toy rocket?
Ans. Converging nozzle.
25. Define ullage.
Ans. The extra volume of gas above the propellant in sealed tanks is called ullage.
PART ‘B’
1. Derive an expression for the velocity of a rocket vehicle at the end of the coasting flight.
Ans. We assume a perfectly vertical launch. If the launch is inclined at some angle, we can
resolve the initial velocity into a vertical and horizontal component. The horizontal motion is
uniform because there is no external force in the horizontal direction. Weight is the only force
acting on the object and weight is always vertical. Because the weight of the object is a constant,
we can use the simple form of Newton's second law to solve for the vertical motion:
-W = F = m a = m dV/dt
where W is the weight, m is the mass, V is the velocity, t is the time, a is the
acceleration, and F is the net external force. The positive direction is upwards, so the weight is
preceded by a negative sign. Solving the equation:
dV/dt = - W/m = -g
V = Vo - g t
where g is the gravitational acceleration which is equal to 32.2 ft/sec^2 or 9.8 m/sec^2 on
the surface of the Earth. The value of the gravitational acceleration is different on the Moon and
Mars. Vo is the initial velocity leaving the launcher. The location at any time is found by
integrating the velocity equation:
dy/dt = V = Vo - g t
y = Vo t - .5 g t^2
where y is the vertical coordinate. With this general description of the motion of a
ballistic object, we can derive some interesting conclusions.
Notice that the flight equation includes no information about the object's size, shape, or
mass. All objects fly the same in purely ballistic flight. This is similar to Galileo's principle that
all objects fall at the same rate in a vacuum. If drag can be ignored, the flight of the object
depends only on the initial velocity and the gravitational acceleration.
At the highest point in the flight, the vertical velocity is zero. From the velocity equation
we can determine the time at which this happens:

Page 29 of 41
V = 0
t = Vo / g
The time to maximum altitude varies linearly with the launch velocity. Plugging this
time into the altitude equation we obtain:
y = Vo (Vo / g) - .5 g (Vo / g)^2
y = .5 * Vo ^2 / g
The maximum altitude changes as the square of the launch velocity. Doubling the launch
velocity produces four times the maximum altitude.
Now consider the impact with the ground at the end of the flight. At impact the altitude
is zero. Using the altitude equation:
y = 0
Vo t = .5 g t^2
t = 2 Vo / g
The total flight time varies linearly with the launch velocity. The total flight time is twice
the time to reach maximum altitude. So a ballistic shell takes as long coming down as it does
going up. If we substitute this time into the velocity equation:
V = Vo - g (2 Vo / g)
V = - Vo
The velocity at impact has the same magnitude but opposite direction as the velocity at
launch.
2. Describe briefly the design part of liquid propellant tanks.
Ans. In liquid bipropellant rocket engine systems propellants are stored in one or more
oxidizer tanks and one or more fuel tanks; monopropellant rocket engine systems have, of
course, only one set of propellant tanks. There are also one or more high-pressure gas tanks, the
gas being used to pressurize the propellant tanks. Tanks can be arranged in a variety of ways,
and the tank design can be used to exercise some control over the change in the location of the
vehicle's center of gravity. Because the propellant tank has to fly, its mass is at a premium and
the tank material is therefore highly stressed. Common tank materials are aluminum, stainless
steel, titanium, alloy steel, and fiber-reinforced plastics with an impervious thin inner liner of
metal to prevent leakage through the pores of the fiber reinforced walls.
3. What are the extra points to be observed while designing the system for cryogenic
propellants?
Ans. Cryogenic propellants cool the tank wall temperature far below the ambient air
temperature. This causes condensation of moisture on the outside of the tank and usually also
formation of ice during the period prior to launch. The ice is undesirable, because it increases the
vehicle inert mass and can cause valves to malfunction. Also, as pieces of ice are shaken off or
break off during the initial flight, these pieces can damage the vehicle; for example, the ice from
the Shuttle's cryogenic tank can hit the orbiter vehicle.
For an extended storage period, cryogenic tanks are usually thermally insulated; porous
external insulation layers have to be sealed to prevent moisture from being condensed inside the
insulation layer. With liquid hydrogen it is possible to liquify or solidify the ambient air on the
outside of the fuel tank. Even with heavy insulation and low-conductivity structural tank
supports, it is not possible to prevent the continuous evaporation of the cryogenic fluid. Even
with good thermal insulation, all cryogenic propellants evaporate slowly during storage and
therefore cannot be kept in a vehicle for more than perhaps a week without refilling of the tanks.

Page 30 of 41
For vehicles that need to be stored or to operate for longer periods, a storable propellant
combination must be used. Prior to loading very cold cryogenic propellant into a flight tank, it is
necessary to remove or evacuate the air to avoid forming solid air particles or condensing any
moisture as ice. These frozen particles would plug up injection holes, cause valves to freeze
shut, or prevent valves from being fully closed. Tanks, piping, and valves need to be chilled or
cooled down before they can contain cryogenic liquid without excessive bubbling. This is
usually done by letting the initial amount of cryogenic liquid absorb the heat from the relatively
warm hardware. This initial propellant is vaporized and vented through appropriate vent valves.
4. Write short notes on:
(a) Piston Expulsion Device
Ans. A piston expulsion device permits the center of gravity (CG) to be accurately controlled
and its location to be known. This is important in rockets with high side accelerations such as
antiaircraft missiles or space defense missiles, where the thrust vector needs to go through the
CG; if the CG is not well known, unpredictable turning moments may be imposed on the
vehicle. A piston also prevents sloshing or vortexing.
(b) Surface Tension Device
Ans. Surface tension devices use capillary attraction for supplying liquid propellant to the tank
outlet pipe. These devices are often made of very fine (300 mesh) stainless steel wire woven into
a screen and formed into tunnels or other shapes. These screens are located near the tank outlet
and, in some tanks, the tubular galleries are designed to connect various parts of the tank volume
to the outlet pipe sump. These devices work best in a relatively low-acceleration environment,
when surface tension forces can overcome the inertia forces.
5. What air tank volume is required to pressurize the propellant tanks of a 9000 N thrust
rocket thrust chamber using 90% hydrogen peroxide as a monopropellant at a chamber
pressure of 2.00 MPa for 30 Sec in conjunction with a solid catalyst? The air tank
pressure is 14 Mpa and the propellant tank pressure is 3.0 MPa. Allow for 1.20 %
residual propellant.
6. Explain briefly the water hammer effect in valves and pipelines.

Page 31 of 41
Ans. Sudden closing of valves can cause water hammer in the pipelines, leading to unexpected
pressure rises which can be destructive to propellant system components. An analysis of this
water hammer phenomenon will allow determination of the approximate maximum pressure.
The friction of the pipe and the branching of pipelines reduce this maximum pressure.
Water hammer can also occur when admitting the initial flow of high-pressure propellant
into evacuated pipes. The pipes are under vacuum to remove air and prevent the forming of gas
bubbles in the propellant flow, which can cause combustion problems.
7. Enumerate and explain the merits and disadvantages of pressurized and turbo pump feed
systems.
Ans. The propellant feed system of a liquid rocket engine determines how the propellants are
delivered from the tanks to the thrust chamber. They are generally classified as either pressure
fed or pump fed.
The pressure-fed system is simple and relies on tank pressures to feed the propellants
into the thrust chamber. This type of system is typically used for space propulsion applications
and auxiliary propulsion applications requiring low system pressures and small quantities of
propellants. The pressure-fed system relies on tank pressures for pressurizing the propellants.
The pressured-fed systems are classified according to the pressurant source, which detennines
how the propellant is expelled from the tank. It can be as simple as a cold gas thruster, which has
a pressurized tank connected to a propellant tank.
The pressure-fed system has general characteristics of being a simple, low-cost design,
which provides low to moderate engine performance. The system can be reliable with few parts,
but are typically heavy because of the pressurized tanks. These systems are primarily used for
orbit maneuver, orbit insertion, attitude control, reaction control, and small upper stage
propulsion.
The pump-fed system uses a turbopump to pressurize and feed the propellants into the
thrust chamber at relatively high pressures. The turbopump typically consists of one or more
pumping elements driven by a turbine. The pump-fed system is used for high pressure, high
performance applications. The use of turbopumps enables an engine operating at high chamber
pressures (i.e. high thrusts) without increasing the vehicle tank weight. The weight savings come
about as a result of a reduction in pressure requirements on the supply tanks and their feed lines.
The tank pressure becomes practically independent of the chamber pressure using the
turbopump. The turbopump requirements are established by the engine power cycle being
considered.
The turbopump operates over a wide pressure range while pumping a fluid from a low
pressure at the inlet to a very high pressure at the discharge. The inlet pressures to the pumps are
relatively low due to low tank pressures. Thus, the potential for pump cavitation must be taken
into account in the design. The cavitation is a phenomenon that occurs when the static pressure
at any point in a fluid flow passage becomes less than the fluid's vapor pressure.
The turbopump being a highly integrated system requires multidisciplinary engineering
and coordination as well as a comprehensive set of design tools. Such complex mechanical
designs require an extensive amount of engineering effort across various technical disciplines
including hydrodynamics, aerodynamics, mechanical, structures, structural dynamics,
rotordynamics, thermal, materials, manufacturing, testing, and instrumentation.
8. Write short notes on:
(a) Space shuttle Orbital maneuver system (OMS)

Page 32 of 41
Ans. The Space Shuttle Orbital Maneuvering System (OMS), is a system of hypergolic
liquid-propellant rocket engines used on the Space Shuttle. Designed and manufactured in the
United States by Aerojet,
the system was used during launch to produce supplementary thrust
and on-orbit to provide orbital injection, orbital correction and the spacecraft's deorbit burn. The
OMS consists of two pods mounted on the Orbiter's aft fuselage, on either side of the vertical
stabilizer. Each pod contains a single AJ10-190 engine, based on the Apollo Service Module's
Service Propulsion System engine which produces 3.87 kilonewtons (870 lbf) of thrust with a
specific impulse (Isp) of 313 seconds. Each engine could be reused for 100 missions and was
capable of a total of 1,000 starts and 15 hours of burn time. These pods also contained the
Orbiter's aft set of reaction control system (RCS) engines, and so were referred to as OMS/RCS
pods. The OM engine and RCS systems both burned monomethylhydrazine (MMH) as fuel,
which was oxidized with dinitrogen tetroxide (N2O4), with the propellants being stored in tanks
within the OMS/RCS pod, alongside other fuel and engine management systems. When full, the
pods together carried around 8,174 kilograms (18,020 lb) of MMH and 13,486 kilograms
(29,730 lb) of N2O4, allowing the OMS to produce a total of around 1,000 feet per second
(300 m/s) of delta-v.
(b) Reaction Control System (RCS)
Ans. A reaction control system (RCS), often called an auxiliary rocket propulsion system, is
needed to provide for trajectory corrections (small au additions), as well as correcting the
rotational or attitude position of almost all spacecraft and all major launch vehicles. If only
rotational maneuvers are made, it has been called an attitude control system. An RCS can be
incorporated into the payload stage and each of the stages of a multiple stage vehicle. In some
missions and designs the RCS is built into only the uppermost stage; it operates throughout the
flight and provides the control torques and forces for all the stages. Liquid propellant rocket
engines with multiple thrusters have been used for almost all launch vehicles and the majority of
all spacecraft. Cold gas systems were used with early spacecraft design. In the last decade an
increasing number of electrical propulsion systems have been used, primarily on spacecraft. The
life of an RCS may be short (when used on an individual vehicle stage), or it may see use
throughout the mission duration (perhaps 10 years) when part of an orbiting spacecraft.
9. What is the need of separation of pressurization gas from the liquid propellant?
Ans. The pressurizing gas must not condense, or be soluble in the liquid propellant, for this
can greatly increase the mass of required pressurant and the inert mass of its pressurization
system hardware. For example, nitrogen pressurizing gas will dissolve in nitrogen tetroxide or in
liquid oxygen and reduce the concentration and density of the oxidizer. In general, about 21
times as much nitrogen mass is needed for pressurizing liquid oxygen if compared to the
nitrogen needed for displacing an equivalent volume of water at the same pressure. Oxygen and
nitrogen tetroxide are therefore usually pressurized with helium gas, which dissolves only
slightly. The pressurizing gas must not react chemically with the liquid propellant. Also, the gas
must be dry, since moisture can react with some propellants or dilute them.
10. Explain briefly tank pressurization in rocket engine.
Ans. Subsystems for pressurizing tanks are needed for both of the two types of feed systems,
namely pressure feed systems and pump feed systems. The tank pressures for the first type are
usually between 200 and 1800 psi and for the second between 10 and 50 psig. Inert gases such
as helium or nitrogen are the most common method of pressurization. In pump feed systems a
small positive pressure in the tank is needed to suppress pump cavitation. For cryogenic
propellants this has been accomplished by heating and vaporizing a small portion of the

Page 33 of 41
propellant taken from the high-pressure discharge of the pump and feeding it into the propellant
tank. This is a type of low-pressure gas feed system.

Page 34 of 41
UNIT – V
PART ‘A’
1. What do you mean by motor case?
Ans. Motor case is the main body of the solid propellant rocket.
2. What are the types of materials used for construction of metal case?
Ans. Three classes of materials have been used: high-strength metals (such as steel,
aluminum, or titanium alloys), wound-filament reinforced plastics, and a combination of these in
which a metal case has externally wound filaments for extra strength. High-strength alloy steels
have been the most common case metals, but others, like aluminum, titanium, and nickel alloys,
are also used for manufacturing case of rockets.
3. What is the need of using ceramic materials in missiles?
Ans. In relatively small (low temperature) rockets, the interior walls of the combustion
chamber and nozzle may be lined with a heat-resistant (refractory) ceramic material. The
ceramic gets hot, but because it is a poor conductor of heat, it prevents the metal walls of the
motor/engine from becoming overheated during the short operating period.
4. How the structural properties of aerospace materials are affected at low and high
temperatures?
Ans. The very high temperatures generated in the combustion chamber transfer a great deal of
heat energy to the combustion chamber and nozzle walls. This heat, if not dissipated, will cause
most materials to lose strength. Without cooling the chamber and nozzle walls, the combustion
chamber pressures will cause structural failure. There are many methods of cooling, all with the
objective of removing heat from the highly stressed combustion chamber and nozzle.
5. Define two dimensional rocket motion.
Ans. The motion of a rocket is particularly complex because the rotations and translations are
coupled together; a rotation affects the magnitude and direction of the forces which affect
translations. To understand and describe the motion of a rocket, we usually try to break down
the complex problem into a series of easier problems. We can, for instance, assume that the
rocket translates from one point to another as if all the mass of the rocket were collected into a
single point called the center of gravity. The calculations are made in X-Y coordinate axes and
hence called two dimensional rocket motion.
6. How many degrees of freedom does a rocket have in two dimensional rocket motion?
Ans. Six degrees of freedom
7. What is Newton’s law of gravitation?
Ans. Newton's law of universal gravitation states that every point mass in the universe
attracts every other point mass with a force that is directly proportional to the product of their
masses and inversely proportional to the square of the distance between them.
8. State the Newton’s law of gravitation formula and explain the terms.
Ans. The gravitational force, F , between two particles equals a universal constant, G, times
the product of the mass of the particles, m1 and m2 ,divided by the square of the distance, d ,
between the particles.
9. What do you mean by mechanics of fluids?
Ans. Fluid mechanics is the study of fluids and the forces on them. (Fluids include liquids,
gases, and plasmas.) Fluid mechanics can be divided into fluid statics, the study of fluids at rest;

Page 35 of 41
fluid kinematics, the study of fluids in motion; and fluid dynamics, the study of the effect of
forces on fluid motion.
10. What are the important external forces acting on a rocket in free flight?
Ans. The general study of the forces on a rocket or other spacecraft is part of ballistics and is
called astrodynamics.
Flying rockets are primarily affected by the following:
• Thrust from the engine(s)
• Gravity from celestial bodies
• Drag if moving in atmosphere
• Lift; usually relatively small effect except for rocket-powered aircraft
In addition, the inertia and centrifugal pseudo-force can be significant due to the path of
the rocket around the center of a celestial body; when high enough speeds in the right direction
and altitude are achieved a stable orbit or escape velocity is obtained. These forces, with a
stabilizing tail (the empennage) present will, unless deliberate control efforts are made, naturally
cause the vehicle to follow a roughly parabolic trajectory termed a gravity turn, and this
trajectory is often used at least during the initial part of a launch. (This is true even if the rocket
engine is mounted at the nose.) Vehicles can thus maintain low or even zero angle of attack
which minimizes transverse stress on the launch vehicle; permitting a weaker and hence lighter,
launch vehicle.
11. Write two assumptions of a ideal rocket motor.
Ans. An ideal rocket motor assumes the following:
• The propellant combustion is complete and does not vary from that assumed by the
combustion equation.
• The combustion products obey the perfect gas law.
• There is no friction impeding the flow of exhaust products.
• The combustion and flow in the motor and nozzle is adiabatic, that is, no heat loss
occurs to the surroundings.
• Unless noted otherwise, steady-state conditions exist during operation of the motor. This
means that the conditions or processes that occur do not change with time (for a given
geometric conditions) during burning.
• Expansion of the working fluid (exhaust products) occurs in a uniform manner without
shock or discontinuites.
• Flow through the nozzle is one-dimensional and non-rotational.
• The flow velocity, pressure, and density is uniform across any cross-section normal to
the nozzle axis.
• Chemical equilibrium is established in the combustion chamber and does not shift during
flow through the nozzle. This is known as "frozen equilibrium" conditions.
• Burning of the propellant grain always progresses normal (perpendicular) to the burning
surface, and occurs in a uniform manner over the entire surface area exposed to
combustion.
12. What is a De-Laval nozzle?
Ans. Supercritical conditions (high chamber pressure exhausting to low external pressure)
gases should be ducted through a nozzle that converges to a throat (section of smallest area) and
then diverges to transform as much of the gases’ thermal energy into kinetic energy. This nozzle
is called De-Laval nozzle.
13. What is thrust magnitude control (TMC)?

Page 36 of 41
Ans. In another term, TMC is also called TVC (Thrust vector Control) in which magnitude
and direction of thrust is changed in order to obtain different directional motions of rocket.
14. Name the two possible systems which allows for TMC.
Ans. Gimballed Engine, Vernier Rockets, Secondary Fluid Injection etc.
15. State Tsiolkovsky rocket equation and explain the terms.
Ans.
∆u = Change in flight speed
Ueq = Effective jet velocity
Mo = Initial Mass
Mf = Final mass
16. What do you mean by Oberth effect?
Ans. In astronautics, the Oberth effect states that the use of a rocket engine traveling at high
speed generates much more useful energy than one at low speed. Oberth effect occurs because
the propellant has more usable energy (due to its kinetic energy on top of its chemical potential
energy) and it turns out that the vehicle is able to employ this kinetic energy to generate more
mechanical power. It is named after Hermann Oberth, the Austro-Hungarian-born, German
physicist and a founder of modern rocketry, who apparently first described the effect.
Oberth effect is used in a powered flyby or Oberth maneuver where the application of an
impulse, typically from the use of a rocket engine, close to a gravitational body (where the
gravity potential is low, and the speed is high) can give much more change in kinetic energy and
final speed (i.e. higher specific energy) than the same impulse applied further from the body for
the same initial orbit. For the Oberth effect to be most effective, the vehicle must be able to
generate as much impulse as possible at the lowest possible altitude; thus the Oberth effect is
often far less useful for low-thrust reaction engines such as ion drives, which have a low
propellant flow rate.
17. Divide cost of rockets under various heads.
Ans. Direct Costs in Manufacturing, Propellant and Other hardwares. Indirect Costs of
storage, periodic maintenance, transportation costs etc.
18. What do you mean by radiation energy?
Ans. Radiant energy is the energy of electromagnetic waves. The quantity of radiant energy
may be calculated by integrating radiant flux (or power) with respect to time and, like all forms
of energy, its SI unit is the joule. The term is used particularly when radiation is emitted by a
source into the surrounding environment. Radiant energy may be visible or invisible to the
human eye.
19. Define nuclear energy and its types.
Ans. Nuclear energy usually means the part of the energy of an atomic nucleus. It can be
released by fusion or fission or radioactive decay.
20. Show graphically the acceleration and velocity change in a staged rocket flight.
Ans.








=∆
f
o
eq
M
M
uu ln

Page 37 of 41
21. Classify nozzles used in rockets.
Ans. Conical , Contour or Bell Shaped, Plug, Expansion – Deflection nozzle
22. What do you mean by expansion – deflection type nozzle?
Ans. The plug and expansion-deflection type nozzles are much shorter than a conventional
conical nozzle with the same expansion ratio. These nozzles have a center body and an annular
chamber. The plug changes the direction of the gas flow from the throat during expansion from
radial to an axial direction. The expansion of exhaust gas is determined by ambient pressure.
23. Name types of ballistics.
Ans. Internal, Transition , External, Terminal and Forensic.
24. What do you mean by terminal ballistics?
Ans. The study of the interaction of a projectile with its target, whether that be flesh (for a
hunting bullet), steel (for an anti-tank round), or even furnace slag (for an industrial slag
disruptor).
25. What do you mean by internal ballistics?
Ans. The study of the processes originally accelerating the projectile, for example the passage
of a bullet through the barrel of a rifle.
PART ‘B’
1. What are the considerations for selection of materials to be used for construction of
thrust chambers of liquid rocket engine?
Ans. The choice of the material for the inner chamber wall in the chamber and the throat
region, which are the critical locations, is influenced by the hot gases resulting from the
propellant combination, the maximum wall temperature, the heat transfer, and the duty cycle.
For high-performance, high heat transfer, regeneratively cooled thrust chambers a material with
high thermal conductivity and a thin wall design will reduce the thermal stresses. Copper is an
excellent conductor and it will not really oxidize in fuel-rich non-corrosive gas mixtures, such as
are produced by oxygen and hydrogen below a mixture ratio of 6.0. The inner walls are therefore
usually made of a copper alloy (with small additions of zirconium, silver, or silicon), which has
a conductivity not quite as good as pure (oxygen-free) copper but has improved high
temperature strength.
2. Explain the ablation cooling method of reentry bodies.
Ans. In the ablation cooling method, the interior of the thrust chamber is lined with an ablative
material, usually some form of fabric reinforced plastic. This material chars, melts and vaporizes
in the intense heat of the nozzle. In this type of “heat sink cooling,” the heat absorbed in the

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Rockets and missiles solved question bank - academic purpose only