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Rocket Science & Engineering with Vithu— Part 01: Rockets, Rocket Propulsion & Orbits

Hello there!

If you are someone who is considering Rocket Science as one of the most complex things to understand. This article will probably change your current perspective. I have been always keen to learn Rocket Science. And I think this is one of the topics you will get inspired by learning more and more. But, I am nowhere close to this domain as of now. The industry I am currently in, opportunities around my environment, and my academics are not very relatable to Rocket Science or spacecraft engineering. So, I just thought of taking the challenge of doing self-learning to grab at least the fundamentals. Then I can co-relate my Computer Science, Engineering & problem-solving background with this area. Also, I thought it would be a great idea to document what I am learning which would also be helpful to many people who are willing to follow the same path. So, this is going to be a series of articles/documentation starting from here.

To start, I chose the topic of Rockets & Orbits. Anyhow, this will be kind of an introduction material touching all the basics at a high level, and I will be getting into the details of all the individual elements in the upcoming sequence of articles.

Before everything, let’s see a few of the key differences between our earth’s atmosphere and the area above Low-Earth Orbit (Known as LEO).

01. Lack of gravity in space: This is a well-known differentiator. It directly impacts the motion of any object.

02. No air pressure: This will have an impact on most of the valid laws which are being used on the earth. For example, fluid mechanics. You can simply imagine taking notes using a pen where you won’t be able to do the same in space.

03. Temperature & Radiation: This is one of the things which makes the space travel way complex. Because most of the objects will be either cold or hot for a long amount of time. The reason why this is happening in the laws of thermodynamics doesn’t directly apply there in space. Because there are no atmospheres. Therefore it has very little thermal conductivity and that’s by the radiation. There is another major impact on the computers because of the radiation. This is because the way the circuit boards works will be impacted by interaction with different particles. Currently, this has been handled in the spacecraft by doing parallel computing while validating the process between each other.

Likewise, there are so many differences which we need to consider while architecting a spacecraft. This is probably the reason why space exploration requires a considerable amount of dedication to achieve success.

Now let’s understand what is the definition of spacecraft first. Well, whatever you can put on the space is a spacecraft. It could be a satellite, space rover, space capsules, space shuttles, even the International Space Station itself is a spacecraft. But all of these have one thing in common. That is the engineering behind rocket propulsion which means the propulsion it takes to bring the spacecraft to orbit. That’s where the rocket comes into the picture.

A Rocket works as per the following fundamental laws.

Newton’s second law of motion: when a quantitative description of the changes that a force can produce on the motion of a body. It states that the time rate of change of the momentum of a body is equal in both magnitude and direction to the force imposed on it. The momentum of a body is equal to the product of its mass and its velocity.

known as, F=MA

Newton’s universal law of gravitation: every particle attracts every other particle in the universe with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

Known as, F=G(m1*m2)/r²

In simple words, the momentum has to be there gains the gravitational force which is pulling towards the canter of the earth to escape the earth’s atmosphere. So, the thrust to create the momentum is being produced from the Rocket engine which is one of the core components of the Rocket. There will be multiple Rocket engines for a Rocket. Before we talk about these in detail let’s understand the orbital motions.

Orbits are nothing but just a line of parabolic motion right from the earth’s surface towards the absence of atmosphere known as Low-Earth Orbit (LEO). But when I say parabolic, it becomes arguable. because our earth is not a flat object. Therefore, it can’t be a true parabolic motion. But it’s very similar.

So when a Rocket is being launched the velocity it takes to reach the circle of Low-Earth Orbit (LEO) from the parabolic motion will be precisely calculated which is known as the escape velocity from the surface of the planet. When it comes to earth the atmosphere surrounding is somewhere around 50km from the surface. So from that point when the spacecraft will keep functioning at the same velocity without any additional engine burns as there is no gravitational pull towards the center of the earth in theory. Anyhow the LEO is not a perfect circle. So, there will be few burns here and there to keep the object in the LEO. Otherwise, it will fall towards the center of the earth. these burns are possibly required at least once per year at International Space Station.

And, there is a confusion that the people always ask why the launch can not be perpendicular motion rather than parabolic motion. The answer is efficiency. less amount of exhaust velocity is needed to reach the low earth orbit by a parabolic motion. But this highly depends on the purpose of the launch. for example, the launch to mars or the moon would be way different from a launch to International Space Station in the low earth orbit. I will be going into details of the formula representations in the upcoming sequence of this series.

Now back to the Rocket engines. there are so many types of engines that produce the thrust. A few of the popular ones are as follows

01. Chemical Combustion Engine: This is the kind of engine, that has a combustion chamber that allows the fuels such as liquid hydrogen and liquid oxygen to react to cause the explosion required to push the exhaust velocity via nozzles.

02. Electrostatic Engine: This doesn’t facilitate any reactions. Rather it uses the coulomb’s law to produce required force.

F=k(q1*q2)/r²

03. Electro-Thermal Engine: This is also an electric engine that uses superconducting magnetic coils to produce the force.

Likewise, there are so many types of engineering on Rocket engines. even the same type of engine won’t be the same as another Rocket. for example, there are so many differences in chemical combustion engines in two different Rockets.

Now let’s talk about the most interesting part. There is a mathematical representation for everything. Likewise, the formula for a Rocket motion is known as the Rocket equation.

ΔV = Ve * ln(m0/m1)
Where ΔV is the change in velocity
and Ve is the exhaust velocity, means the velocity of explosion at the nozzle
and m0 is the final mass after all burns
and m1 is the initial mass

Let’s consider the following example based on the above equation,

How much of a Rocket fuel is needed to carry a person who is 50Kg when the exhaust velocity is 4.5km/s and escape velocity is 11.5km/s.

Here, we need to take one assumption.
The fuel mass will be approximatly equalent to the entire payload of the Rocket includeing fuel.

Also, let’s say mass of the fuel is x.
m0 = x + 50 Kg
m1 = 50 Kg
x=526Kg

So, the fuel it takes is nearly 526Kg which is approximately 10 times the actual payload. In real-time, this ratio would be worse than this. That’s why there are so many engineering designs being implemented to increase efficiency such as multiple-stage separation. Which would possibly reduce the probability of carrying unwanted parts after the fuel burn. I will be explaining all of these mechanisms in detail in the upcoming topics.

I guess that covers the bare minimum introduction to Rocket Science and Spacecraft Engineering. So I will conclude this part of the series here. Thanks for sticking around up until here. If you find this article useful, please share it with your network.

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