Jayshree was on her way back from work after a long shift. As she was walking back home, she looked up at the sky and noticed a jet aircraft speeding upward leaving a long stream of smoke in the process. She went into deep thought and wondered how aircraft and rockets are able to produce enough energy that enables them to soar high into the sky and leave the Earth’s atmosphere. She pulled out her smartphone, opened YouTube, and began watching videos explaining rocket propulsion. However, to her dismay, none of those videos seem to explain the concept clearly. That’s when it struck her, what’s better than to ask her boyfriend, Rupesh, who worked at the ISRO space station at Sriharikota as a senior engineer.
When Jayshree reached home, she took a bath and prepared Dosa and Kadai mutton gravy. She finished dinner and decided to call Rupesh and ask him about the question which has been eating her head for the past few hours. She opened Google Keep on her tab to take notes and called her boyfriend.
“Hi babe, how was your day sweetie? I hope all is going well.”
“Everything is going just fine babe, it has been a rough day at work today, as the Chief of Defence visited the ISRO station. We had to keep everything in check and ensure that they were all in order.”
“Oh I see, I hope you are less stressed out now, cause I really need you to explain to me about the science of rocket propulsion.”
“Wow Jayshree, I thought you were not much into the stuff that I do. Anyways, I am all fine and am ready to explain to you, babe.”
Rupesh was quite excited to see that his girlfriend had gained a sudden interest in his line of work and most importantly, was eager to know about rocket propulsion.
What is Rocket Propulsion?
Rupesh cleared his throat and began the lesson, “Just like how you light up a firework during Diwali, rockets work in a similar mechanism to that but with a lot more changes with regards to fuel, combustion method, and other related principles. Let us delve into these concepts step by step.”
“Newton’s third law of motion plays a pivotal role in understanding the principle of rocket propulsion. This states that force exists in pairs. Let’s say an object A exerts force FA on another object which is B. Then B simultaneously exerts a force FB on A, with two forces being equal and opposite. FA= -FB. There are three key factors which contribute to the rocket’s acceleration which are, the rocket’s mass, the exhaust velocity, and the rate at which the exhaust is ejected.”
“In order for a rocket to escape Earth’s gravity, the exhaust velocity needs to be proportional to the gravity of Earth. In other words, the velocity and force exerted by the exhaust need to be powerful enough to counter the gravity of Earth. The force used by the rocket is driven by the fuel which is combusted and forcefully ejected from the exhaust that an equal and opposite reaction occurs.”
“Hmm, I see so that’s how the theory of rocket propulsion plays in. Now can you please elaborate on the components of a rocket?” Asked Jayshree.
Rocket Propellent and its Types
“Jayashree, there are two main types of rocket propellants used in rockets. One is the liquid propellant and the other is a solid propellant. A rocket that is powered by a liquid propellant contains liquid fuel such as liquid oxygen, liquid nitrogen, and an oxidizer. The liquid oxidizer is present on top, with the fuel tank below it, and the pumps, which are below that. The pumps are responsible to carry the fuel and the oxidizer to the combustion chamber, which is right below the exhaust. Since there is no oxygen in outer space, rockets need a liquid oxidizer to ensure combustion as fire cannot burn without oxygen. Liquid propellant-powered rockets are mainly used on space shuttles and unmanned missiles to place satellites in orbit.”
“You have explained it so clearly Rupesh, can you tell me about solid propellant rockets?”
“Of course, Jayshree, you see, solid propellant rockets mainly comprise of two components, which are the solid oxidizer and the solid fuel. The solid fuel oxidizer is a mixture of ammonium nitrate and ammonium dinitramide, which is present in a cylindrical hole in the middle of the rocket. The igniter is used to combust the propellant surface and the hole in the middle acts as the combustion chamber. These rockets comprise a hot exhaust choke which is also found in automobiles. This hot exhaust is choked and the exhaust is expelled from the exit.”
Rupesh continued, “Now that you have learned about the principle of rocket propulsion and the types of rockets, you need to understand what are the factors which influence the rocket’s acceleration Jayashree. You see, the acceleration of the rocket will be greater with the exhaust velocity of the gases being greater than the rocket. Also, the acceleration is greater if the fuel in the rocket burns faster. As the mass of the rocket decreases, the acceleration will be greater, that’s why rockets tend to go faster as they reach the outer layers of the Earth’s atmosphere. This is because half of the fuel would have got burnt, thereby reducing the mass of the rocket.”
Conclusion
“Thanks, Rupesh, you are such a charmer, no wonder I fell for a rocket enthusiast like you. I am so glad that you took the time to explain this, you made complex rocket science seem like a walk in the park.”
“The pleasure is mine babe, I would love for you to visit Sriharikota sometime, I would give you a full-on tour of the place.”
“That would be awesome babe, now that my newfound interest is about science, I would love to visit ISRO soon. Let our next date be amongst large rockets ready to leave the Earth.”
“Absolutely Jayashree, I would love that. And also, always remember, there is always a lot of research going on in the field of rocket science. Did you know that scientists like us are working towards finding different propulsion systems and nuclear-powered rockets? Fossil fuels are going to go extinct in a couple of decades and we need to find new ways to reach outer space.”
Space Age 