Rocket Propulsion

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Introduction:-

Rocket Propulsion:-

The propulsion of a rocket is an example of momentum of conservation. In a rocket, gases at high temperature and pressure, are produced by the combustion of fuel. They escape with a large constant velocity through a nozzle.
The large backward momentum of the gases imparts an equal forward momentum to the rocket. But due to the decrease in the mass of the rocket fuel system, the acceleration of the rocket keeps on increasing.

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Rocket Propulsion-Rocket
Rocket

Mathematical expression:-

(i) It is an example of variable mass system.
(ii) It is based on the principle of conservation of linear momentum (if effect of gravity neglected) or Newton’s third law.
(iii) If Ur is the velocity of emerging gases relative to rocket and dm/dt is the rate of fuel consumption.
  • Thrust on rocket [F] = Ur dm/dt
  • Net force on rocket = Ur dm/dt – mg
  • Net acceleration of rocket a = Ur / m . dm / dt – g
Where m = m0 – dm /dt . t,
m0 = Initial velocity
  • Velocity of rocket at any instant  v = ur loge {m0 / m} (When velocity is zero)
Example:- A 800 kg rocket is fired from earth so that exhaust speed is 1200 m/s. Then calculate mass of fuel burning per second, to provide initial thrust to overcome its weight. (g = 10 m/s2).
Solution:-  [F] = Ur dm / dt = mg
                800 X 10 = 1200 X dm / dt
                Dm /dt = 80 / 12 = 40 / 6 = 20 / 3 = 6.67 kg / sec.

Types of Rocket Propulsion

There are various types of rocket propulsion systems, each with its exclusive advantages and challenges. The most common types include:

1. Chemical Propulsion:-

This is the most widely used method, where chemical reactions (normally combustion) produce hot gases that are expelled to generate thrust.

Chemical rockets are divided in following categories:-

(i) Solid-propellant rockets:– Solid-propellant rocket uses a solid mixture of fuel and oxidizer as its propellant, which is packed into the combustion chamber. When ignited, the propellant burns from the inside to out and produces hot gases to expelled through a nozzle to generate thrust. Solid-propellant rockets are simple in quality, reliability, and ability to be stored for long periods without degradation.
(ii) Liquid-propellant rockets:-  Liquid-propellant rocket uses liquid fuel and oxidizer, stored in separate tanks, which are pumped into a combustion chamber where they mix and burn to produce thrust. Liquid-propellant rockets offer greater control and efficiency compared to solid-propellant rockets.
(ii) Hybrid rockets:- Hybrid rocket combines elements of both solid and liquid propulsion systems. It normally uses a solid fuel and a liquid or gaseous oxidizer. The solid fuel is stored in the combustion chamber and oxidizer is stored in a separate tank and fed into the combustion chamber during operation. Hybrid rockets offer a balance between the simplicity of solid-propellant rockets and the controllability of liquid-propellant rockets.
Rocket Propulsion-Rocket Propulsion engine
Rocket Propulsion engine

2. Electric Propulsion:

Electric propulsion, electric fields or electromagnetic fields are used to accelerate ions to create thrust. Although electric propulsion systems generate much less thrust than chemical rockets, They are more efficient and ideal for long-duration missions in space.
Rocket Propulsion-Magnetic ball

3. Nuclear Propulsion:-

Nuclear propulsion uses nuclear reactions to produce heat, which then expels propellant to generate thrust. While still largely experimental, nuclear propulsion offers the potential for very high efficiency and thrust, which could be essential for deep space exploration.

Challenges in Rocket Propulsion

Significant challenges of rocket propulsion:-

(a) Primary challenges is the need for high energy density in fuel. So that, rockets gain heavy amount of energy to prevail over Earth’s gravity,
(b) Managing the high temperatures and pressures within the rocket engine.
 (c) To ensure the structural integrity of the rocket at high speeds and in varying atmospheric conditions, are major engineering challenges.
(d) Another big challenge is the efficiency of fuel usage, which adds extra kilogram of fuel to the mass that require to propelled. Optimising the rocket’s design to minimize fuel consumption and maximize the thrust is a critical aspect of rocket engineering.

Conclusion:-

Rocket propulsion is a complex area that involves fundamental physics principles to solve practical problems of moving objects through space. These principles is essential for advancing space exploration and developing more efficient and powerful rockets for future missions.
Rocket propulsion is the method by which a rocket generates thrust to move. It works by expelling gas at high speed in the opposite direction of the required movement, Its work on Newton’s third law of motion: “For every action, there is an equal and opposite reaction.”
Rocket generates thrust by burning fuel in its engine, which produces hot gases. Gases are expelled at high speed through a nozzle, creating a force that pushes the rocket in the opposite direction. The faster the gases are expelled, the greater the thrust.
Rockets don’t depend on air to generate thrust. They carry both fuel and an oxidizer on board, so they can operate in the vacuum of space. Thrust is produced by expelling gases, not by pushing against air, so that rockets are moving in space just as effectively as in the Earth’s atmosphere.
Solid rocket engines use a solid fuel mixture that burns to produce thrust, but, liquid rocket engines use liquid fuel and oxidizer stored separately, which are mixed and burned in the engine. Liquid engines tender better control and can be shut down, while solid engines are simpler but can’t be turned off once ignited.
Rockets have multiple stages to improve efficiency. Each stage has its own engine and fuel supply, and after the fuel is used up, that stage is discarded to reduce weight. This allows the remaining stages to operate more efficiently, enabling the rocket to reach higher speeds and altitudes.

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