What is Rocket Propulsion?
Rocket propulsion is defined as
The force that is used by the rocket to take off from the ground and into the atmosphere.
The principle on which rocket propulsion works is based on Newton’s third law of motion. Here, the fuel is forcibly ejected from the exit such that an equal and opposite reaction occurs.
Table of Contents
- Diagram of Rocket Propulsion
- Rocket Propulsion Types
- Acceleration of Rocket
- Factors Affecting Rocket’s Acceleration
- Example on Rocket Propulsion
- Frequently Asked Questions-FAQs
Rocket Propulsion Diagram
In the below diagram, there is a simplified diagram of liquid-fuel rockets and solid-fuel rockets.
In a liquid-fuel rocket, the following things are found:
- A liquid rocket fuel such as liquid oxygen, liquid nitrogen
- An oxidizer
- Pumps to carry the fuel and the oxidizer
- A combustion chamber where the two liquids mix and burn
- A hot exhaust choke
- Exit from where the exhaust is removed
In a solid-fuel rocket, the following things are found:
- A solid fuel-oxidizer mixture with a cylindrical hole in the middle (ammonium nitrate, ammonium dinitramide)
- An igniter to combust the propellant surface
- The hole in the middle of the propellant act as a combustion chamber
- The hot exhaust is choked at the throat
- Exit from where the exhaust is removed
Similar reads:
Types of Rocket Propulsion
The following are the different types of rocket propulsion:
- Liquid-fuel chemical propulsion
- Solid fuel chemical propulsion
- Cold-gas chemical propulsion
- Ion
Acceleration of Rocket
The acceleration of the rocket is given as:
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\(\begin{array}{l}a=\frac{v_{e}}{m}\frac{\Delta m}{\Delta t}-g\end{array} \)
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Where,
- a is the acceleration of the rocket
- ve is the exhaust velocity
- m is the mass of the rocket
- Δm is the mass of the ejected gas
- Δt is the time taken to eject the gas
- g is the acceleration due to gravity
Factors Affecting Rocket’s Acceleration
- The acceleration will be greater when the exhaust velocity ve of the gases is greater with respect to the rocket.
- The acceleration is greater when the fuel in the rocket is burned faster.
- As the mass of the rocket decreases, greater will the acceleration.
Understand the principle of rocket propulsion through an experiment.
Example on Rocket Propulsion
Example:
2.80×106 kg is the mass at liftoff of Saturn. The fuel is burnt at the rate of 1.40×104 kg/s and the exhaust velocity is 2.40×103 m/s. What is the initial acceleration?
Solution:
Given:
Exhaust velocity, ve = 2.40×103 m/s
Mass of the rocket, m = 2.80×106 kg
Mass of fuel burnt, Δm = 1.40×104 kg/s
Acceleration due to gravity, g = 9.80 m/s2
Substituting the above, in the formula, we get
a=2.20 m/s2
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Summary: |
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Also, the below video is an application of Newton’s third law of motion:
Frequently Asked Questions – FAQs
How much thrust does a rocket need to take off?
For a rocket to take off from its launch pad, the thrust must be greater than 98 N. This is because the force of gravity pulling the rocket downward is 10×9.8=98 N. Therefore, it must be greater than 98 N.
What is the world’s most powerful rocket engine?
The F-1 engine is the most powerful single-nozzle liquid-fuelled rocket engine.
Is acceleration of a rocket constant?
No, a rocket does not have a constant acceleration. The force on the rocket is constant, but the acceleration keeps increasing.
What kind of fuel do rockets use?
The fuel used in a rocket is highly refined kerosene called RP-1. Usually, petroleum fuels are used along with liquid oxygen as an oxidizer.
Do rockets pollute the air?
Most rockets are propelled by liquid hydrogen fuel, producing clean water vapour exhaust. However, this also results in emission of carbon. Also, in the upper atmosphere, the traces of gases cause the depletion of the ozone layer. There are also particles of soot that are found. Therefore, it can be said that, yes, rockets do pollute the air.
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