The term "Rocket Propulsion" instills the general perception of complexity among humans. The widespread assumption is that it is beyond our level of comprehension. A glimpse of a rocket launch leaves us with a sense of awe. By the end of this blog, we will realize that the principle of rocket propulsion bestows upon us, a crucial aspect of life.
Basic Principle
A rocket follows the principle of the Conservation of Linear Momentum to power itself out of the gravitational pull of the Earth. Linear momentum is the product of mass and velocity.
When the fuel and oxidizer react together in the combustion chamber of a rocket's propulsion module, the exhaust gas usually accompanies high chamber temperature, low exit to chamber pressure ratio, and has low molecular mass. Consequentially, it emerges out of the rocket nozzle with high jet velocity. This high-velocity exhaust mass provides a substantial momentum for the rocket in the opposite direction by the law of momentum conservation. We should remember that as the exhaust gushes out, the mass of the rocket decreases simultaneously. As a result, it experiences a vast acceleration to make use of the enormous momentum available. In other words, the rocket propels itself to its glory by leaving the exhaust behind.
Multiple stages
We face another problem as the fuel tank gets depleted. A considerable part of the propulsion system becomes empty and contributes to ‘dead weight’ or dry mass. Without the dead weight, the rocket can attain a higher velocity. Thus, we arrive at the concept of multistage rockets where a rocket has multiple stages/parts. The lowest stage mostly contains the propulsion system with the fuel and oxidizer tanks. When the tanks become empty, it detaches itself from the rocket. The subsequent ones may have smaller propulsion systems and other modules according to their functionality.
The smart usage of the concepts of exhaust and staging can do wonders by minimizing the wastage of cost and energy and maximizing efficiency.
Momentum in movies
The following instances that establish the conservation of momentum may relate to the ardent fans of science fiction movies. In Marvel's The Avengers (2012), after Iron man nukes the Chitauri spaceship stationed outside the wormhole, we notice that the back thrusters detach from his armor in a way that pushes him back into the Earth. In Interstellar (2014), Cooper ejects himself with his pod towards Gargantua (black hole) to provide sufficient momentum for Dr. Brand to overcome the deadly gravitational pull of the black hole, allowing her to slingshot towards Edmund’s planet.
Life lesson
We can observe how a rocket designates the sky as the lower limit by leaving the exhaust and initial stages behind. But here we are, wallowing in sorrow and self-pity and complaining about how bitterly unfair our lives are (credits to Severus Snape). Well, life is not fair. We should learn to leave the regrets and mistakes of yesterday in the past and move on - create our destiny - who knows, someday we might shoot for the stars and make history.
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