Fundamental of Rockets

1. ROCKET
PROPELLANTS
Subtitle

2. • Unlikely the jet engines the
rockets cannot draw oxygen into
their engines from the
surrounding air and they must
carry oxygen with them into
space where there is no air.

3. SPECIFIC IMPULSE
• Specific Impulse is basically the
efficiency of the rocket propellant
and is measured in seconds. It
indicates how many pounds (kg) of
thrust is obtained by consuming 1 kg
(1 pound) of propellant in one
second.

4. • The specific impulse of a rocket
propellant is a rough measure of how
fast the propellant is ejected out from
the back of the rocket. A rocket with
higher specific impulse does not
need as much fuel as a rocket with
low specific impulse.
Higher the specific impulse, higher will be
the push to move rocket forward

5. FUEL MEASURING
• Fuel measuring i.e the amount of
fuel that goes into space is important
to get the required amount of thrust
that a rocket should have.
• As each drop of fuel and oxidizer
that goes into space adds up to the
mass and weight of the spacecraft,
so the scientists will carry the exact
amount of fuel and nothing extra.

6. • Scientists also know about the chemical
reactions that will result when the fuel
and the oxidizer combines and so they
know what would be the proportion of
the two.
• In order to get the right proportions they
use the molecular formula of rocket
fuels to calculate the no. of moles
needed and once they know it they can
calculate the right amount of fuels.

7. Some Basics
• Rocket Motion
is very much
like the motion
of a air filled
balloon which
is set free.

8. ROCKET Principle
• Rockets generate large
amounts of high-
pressure combustion
gas in their engines, and
this gas is ejected
rearwards at high speed
providing the force that
drives the rocket
forward.
• To burn fuel in space
where no air exists, an
oxidizer is necessary.

10. • Thrust indicates how much
cargo a rocket can lift .
• A rocket flies faster than a rifle
bullet
• A rocket must travel at a speed
of 7.9 km per second to put a
satellite into orbit.
• To leave the earth's gravity for a
trip to the moon or a planet
requires a speed of 11.2 km per
second.
• The relationship between the
speed of ejected combustion
gas and what is called "mass
ratio" is a vital factor in achieving
such high speeds.
ROCKET THRUST

11. SOLID PROPELLANTS
• Solid fueled rockets started with
fireworks but then with time possess
more advanced fuels, designs and
functions. Solid fueled rockets are
used in space shuttle dual booster
engines and the Delta series booster
engines.
• The basic idea of solid fueled rockets
is to create something that burns very
quickly bit does not explode.

12. FUNCTION
• Solid fueled rockets are the
simplest rockets. They have two
main parts.
i. The body or the Casing where
propellant is stored
ii. Combustion Chamber having the
nozzle

14. • The gun powder has the composition
as:
75% nitrate 15% carbon 10% sulphur
• The casing is made up of steel
containing fuel and the oxidizer which
burns at a rapid rate expelling hot gases
from the nozzle to produce thrust.
• The casing that contains the propellant
opens to a combustion chamber at one
end.

15. • Most rocket casings are cylindrical but some are
spherical as well.
• The solid mass of the propellant is called
“charge or grain”.
• The propellant grain is an important factor in
determining a rocket’s performance and the
variables that are important to judge the rocket’s
performance are surface area and specific
impulse.

16. • By changing the
shape and size of
the perforation we
can control the rate
and duration of
burning and thus
control the thrust .

18. • To increase the thrust a hole is
made when the propellant is
cast. It is called as perforation.
• More the thrust required, larger
will be the perforation but the
fuel will burn for a smaller time.

19. • Lesser the thrust required,
smaller will be the perforation
but the fuel will burn for a very
long time.
• The burning period and the
thrust depends upon the type of
perforation in the fuel.

21. SURFACE AREA
• Surface area is the amount of
propellant that is exposed to the
combustion chamber for burning and
is directly related to thrust.
• An increase in surface area will
increase thrust but will reduce burn-
time since the propellant is being
consumed at an accelerated rate.

22. SPECIFIC IMPULSE
• The gauge for rating the efficiency of
rocket propellants is called specific
impulse and it is measured in seconds.
• Specific impulse indicates how many
pounds (or kg) of thrust are produced
by consuming one pound (or 1 kg) of
propellant in one second.

23. • If a propellant with high specific impulse is
used as the fuel for a rocket whose grain
design has a high surface area ratio, high
amounts of thrust will be produced.
• If the engine grain casing cannot bear the
extreme pressure and temperature it will just
explode. So a great care should be taken
while making the grain ratio of both the
variables i.e specific impulse and surface
area.

24. Double Based Propellants
• Initial solid fueled rockets include
gun powder and mixtures containing
nitroglycerine and nitrocellulose
which were also called double based
propellants
• Double based propellants are the
combination of two propellants.

25. Synthetic Rubber &
Additives
• These oxidizers are often mixed, in
making composite propellants, with
synthetic rubbers such as
polystyrenes & polysulfides.
• Additives are also added to
composite propellants.
• Additives have binders that hold the
fuel together and increases its specific
impulse.

26. • More is the specific impulse the
faster the rocket burns and more is
the thrust that pushes it upward and
so a great care is needed in solid
fueled rockets as once the
propellant is ignited it cant be
stopped (very difficult to stop)

27. Boosters & Sustainers
• Booster rockets (huge rockets) need a
large amount of thrust in a short time
and they use chemicals to increase the
burning rate.
• Also there are other rockets that need to
produce less thrust over a longer period
of time and they use chemicals to
decrease the burning rate. Such longer
burning rockets are called “sustainers”

28. FAMILIES
• There are two families of solid
fueled propellants.
• Homogeneous propellants
•Composite propellants

29. Homogeneous Propellants
• Simple based or double based (uses a
single or double propellant).
• Simple homogeneous propellants consist
of a single compound (nitrocellulose)
and double based propellant consist of
two compounds (nitrocellulose and
nitroglycerine with a plasticizer added
to it).

30. • Specific impulse is not greater
than 210 seconds in normal
conditions.
• They are mainly used in tactical
weapons.

31. Composite Propellants
• Modern composite propellants are
heterogeneous mixtures.
• The oxidizer normally uses is called
ammonium perchlorate and the fuel
used is aluminium.
• Additional compounds e.g catalyst
is added to increase the burning
rate.

32. IGNITIORS
i. The ignition of solid propellants use
different types of ignitors:
ii. Initially fire arrows were used as ignitors
but they were not considered to be safe
as they exploded.
iii. Now the safe method used is the
electric current which heats up a
specific wire inside the rocket. It results
in increasing the temperature of the
propellant inside the combustion
chamber.

33. iv. Some ignitors use a chemical that
ignites itself first and then ignites the
propellant.
v. For large rockets the ignitors are the
rocket engines themselves. The engines
inside the rocket blasts a stream of
flames and hot gases rush down from
the top of the rockets igniting the entire
surface of propellants within a fraction of
second.

34. ADVANTAGES
i. Simple in design.
ii. Require little pre-flight checkup.
iii. Use that propellant that do not
leak/spill.
iv. Indefinite storage (5-30) years and
used at high level in the military.
v. Instant ignition without fuelling
operations.

35. DISADVANTAGES
i. Exhaust gases are usually toxic.
ii. Once ignited cannot be shut
down easily so they are designed
for a specific mission.
iii. Re-start requires a separate
ignition system.
iv. Once ignited cannot change their
thrust.

36. v. Manufacturing of solid propelled
rockets may get expensive due to
separate ignition system(id re-start
needed)
vi. Cracks may develop in the solid
propellant that increases the
exposed surface area and the
propellant burns faster than the
planned rate.

37. In case of too many cracks
pressure inside the combustion
chamber rises and the rocket may
explode.

40. LIQUID PROPELLANTS
• The first liquid fuel rocket was produced
by Robert Goddard in 1926 (How Rocket
Engines Work). In a liquid propellant
rocket the fuel and the oxidizer are stored
in separate tanks i.e one for the fuel and
the other for the oxidizer.
• The liquid propellants carry their own fuel
and the oxidizer in liquid form. The fuel
and the oxidizer are taken to the
combustion chamber through pipes,
valves and turbo pumps where they are
combined and burned to produce thrust.

42. • Liquid fueled rockets provide greater specific
impulses than solid fueled rockets.
• Engineers can control combustion in liquid
fueled rockets by changing the rate at which
the pumps move the liquid propellant to the
combustion chamber vai valves.
• Combustion can be stopped and re-started
by stopping the fuel pumps completely. This
stopping and re-starting combustion is very
useful in space missions as in space the
course correction (trajectory) may needs to
be changed that require short bursts from the
rocket.

43. • Liquid fueled rockets are more complex
to handle than solid fueled rockets as in
liquid propellants the fuel and the
oxidizer are stored in different tanks.
• Simplest liquid fueled rockets use
nitrogen gas (high pressurized and non-
reactive gas) which forces the propellant
into the combustion chamber.

44. Robert Goddard

45. • Liquid fueled rockets use different types of
fuels and oxidizers like:
i. Fuels (alcohols, kerosene)
ii. Oxidizer (liquid oxygen)
A good liquid fueled rocket is the one that
ejects high speed gases at a brisk rate
which gives high combustion temperature.

46. FAMILIES
• Liquid propellants are classified into
three families:
i. Petroleum
ii. Crogenics
iii. Hypergolics

47. PETROLEUM
i. They are the fuels refined from
crude oil and are the mixtures of
hydro carbons.
ii. Petroleum fuel used as rocket fuel is
kerosene.
iii. Used in combustion with liquid
oxygen (oxidizer).

48. CRYOGENICS
i. Crogenic is a greek word which means
cold.
ii. Use liquid hydrogen as fuel and liquid
oxygen as oxidizer.
iii. Liquid H2 remains liquid at -253 C and
liquid O2 remains liquid at -183C.
iv. Liquid H2 and liquid O2 are used as
propellants in main engines of the space
shuttle.

49. v. Liquid H2 and liquid O2 also power the
upper stages of Saturn V and Saturn 1B
rockets and also the second stage of Atlas
launch vehicle .
vi. Due to these low temperatures of liquid
crogenic propellants cannot be stored for
longer periods of time and due to this
reason they are less desirable to be used
in military rockets which might require
the rocket to be ready at launch for
months.

50. HYPERGOLICS
i. They are the fuels and the oxidizers which
came to in contact with each other and ignite
at once without any ignition source.
ii. They have the easy start and re-start
capability.
iii. Remain liquid at ordinary temperature and
so no storage problem.
• Typical Oxidizers= Nitrogen Tetra Oxide
(N2O4) or Nitric acid (HNO3)
• .

51. ADVANTAGES
i. Higher specific impulse
ii. Can be stopped and re-started
iii. Accurately controllable thrust
iv. Can be stored for longer periods
v. Can be reused after service and
checking

52. DIS-ADVANTAGES
i. Complex in design
ii. Crogenic propellants cannot be
stored for longer periods of time
iii. Propellant spills could be toxic and
dangerous
iv. Combustion instability is difficult to
control
v. Non-hypergolic fuels need an
ignition system

53. TYPES
• There are two types of liquid
propelled systems:
i. Gas Pressure Feed System.
ii. Turbo Pump Feed System.

54. Gas Pressure Feed
System
• In this type of propellant a high
pressure gas under a pressure
regulator displaces the propellant in
the combustion chamber.
• It is used to produce low thrust and
short duration.

55. F u e l T a n k
P r o p e lle n t V a lu e
R o c k e t T h r u s t C h a m b e r
P r o p e lle n t V a lu e
O x id iz e r T a n k
P r e s s u r e R e g u la t o r
H ig h P r e s s u r e G a s S u p p ly t a n k
S c h e m a t ic D ia g r a m o f G a s - P r e s s u r e F e e d S y s t e m

56. Turbo Pump Feed System
• In this type the propellant is pressurized
by pumps driven by gas turbine and
finally displaced into the combustion
chamber.
• Combination of pumps and turbine is
called turbo pump.

57. O x id iz e r T a n k
F u e l P u m p
O x id iz e r P u m p
T h r u s t C h a m b e r
S h a f t
F u e l T a n k
H o t G a s T u r b in e
S c h e m a t ic D ia g r a m o f T u r b o - P u m p F e e d S y s t e m