ROCKET PROPULSION – I

The radiant blue sky enveloping us has always been a subject of interests since ages. The countries, as we see today, were bordered by religion, faith, and belief. A numerous curious brains went on exploring distant lands and civilizations including the well-known Columbus, Vasco-da-Gama, Magellan, Dias and many more.

earth gif
This led to the discovery of diverse land masses and oceans hence mapping the boundaries. Gradually with evolution in science and inquisitiveness in humans, it was discovered that earth is a spherical mass of rocks and soil accommodating air and water, exclusively to sustain life and participates in this solar system along with its sibling planets. Earlier, cosmos was studied with the help of telescopes; some of the renowned space observers Galileo and Copernicus who laid down the foundations of the current known solar system and the celestial bodies engaged in it. Further, Kepler a German mathematician, astronomer, and astrologer laid down the laws of planetary motion. Till then, it was too much of observations from the earth, so man decided to crack the shell and have a look, from outside the planet. This article brags about the rockets used to propel spaceships, satellites, and probes to our planet’s orbit. Any rocket that is used to carry a payload to some distant location is sometimes referred to as a booster.

flat earth 2
Flat Earth Theory

Since the beginning, the configuration of the earth, satellites, planets, and the universe were a debatable subject. A mighty class began supporting a new belief that our planet is not a spheroid but a flat two-dimensional surface, with sun and other cosmological bodies circling around periodically. In 1956, Samuel Shenton created the International Flat Earth Research Society for the members who believed earth to be a flat web of land, water, and air. In contrary, it was the first time in 1957 when the first rocket was propelled to space by the Soviet Union carrying the Sputnik-1 satellite. It has been more than sixty years, we have been visiting space but there are still debates on the flat earth theory. So now just for the sake of our senses and let’s continue by assuming earth an ‘oblate spheroid’ (the exact shape of the earth as described by Space Organizations).

close up on the rocket engine and exhaust pipes of Saturn 5 rocket
Rocket Engine Nozzles

Some important considerations when we talk about space travel are: How do we reach the outer space? How much energy does it require? How to beat Earth’s gravity to propel a heavy load out of Earth’s proximity? Where does this energy come from? And how exactly is a launch sequence executed? The answer is, physics assorted with mathematics and chemistry, garnished with a sense of keen knowledge and curiosity.

Being the writer of this article, I need to be careful with my word selection, to make it more interesting and engaging for all my readers. Should you feel any difficulty in understanding a term, feel free to click on the links highlighted to learn more of it. Remember,

“Research is creating new knowledge”

Neil Armstrong

NEIL-ARMSTRONG

Outer space is reached by exploiting Sir Newton’s 3rd law which states that every action (force) has a reaction of equal magnitude, in the opposite direction. Fuel is burnt to produce energy and is allowed to rush out in a controlled and confined manner so as to produce thrust on the payload it grips, carrying the spaceship/satellite/probes/extra-terrestrial vehicles to outer earth orbits.

Trajectory Planning of a Rocket:

Rocket-from-ground
Trajectory of a Rocket

You might have noticed that rockets are pushed vertical from the launch pad, but as it progresses it starts to tilt, to follow a parabolic path. This is an intentional act of pushing the rocket out, to the earth’s orbit with minimal fuel consumption. In a planet’s orbit, its gravitational tug is high enough to keep the rocket from drifting off away from the planet. Also, the rocket doesn’t have to burn much fuel to counter the gravity of the earth when it is in the orbit; the centrifugal force and the gravity are acting in opposite directions to keep the rocket in the orbit. To exit from the orbit of a planet and go out further in space the payload must be propelled to the escape velocity of that particular planet (11.2 km-per-sec for earth; at escape velocity body becomes free form the influence of the gravitational pull of a massive body like earth). This is the journey of a rocket from the surface to the orbit.

lanch ground

Now how is it carried out? The governing system is employed in a rocket to make it follow the desired trajectory. Governing System comprises of Navigation System, Guiding System, and Flight Control System.

Capture 1
The navigation system continuously monitors its latitude and longitude, altitude, its speed and direction at every point of time using some sensing instruments like a gyroscope, altimeter, compass etc, and gives output to the guiding system and the ground station. A guiding system which receives inputs from the navigation system do calculations to determine the trajectory of the rocket. The trajectory has to be monitored and maintained continuously throughout the flight. This information is given to the flight control system which is the main unit that drives the rocket on the path planned by guiding system using the control surfaces like ailerons, flaps, rudder etc.; but usually the control surfaces (as you may have seen on commercial aircraft) are not that effective at super-sonic and hyper-sonic speeds, so method known as thrust vectoring is employed.
Control-Surfaces
Now, what is Thrust Vectoring? In rockets, thrust force has a line of action which passes through its centre of mass, thus the net moment acting on the rocket will be zero. Now suppose, if we somehow manage to displace the thrust force vector by some angle, the result would be net moment acting on the rocket which will allow the rocket to pitch (rotate about a horizontal axis) or yaw (rotate about a vertical axis).

interplanetry launch
Inter-planetary Space Jump

The displacement of thrust vector is achieved with the help of gimbaled engine or gimbaled nozzle from where the burnt gasses and hot air are blown out (to obtain thrust). The movement of the gimbals is controlled with the help of highly sophisticated servo-mechanisms. This aids in altering the trajectory of the rocket with respect to the aero-system.

This was all about how the trajectory of a rocket is planned and followed strategically. Next part will tend to answer that, how exactly a the launch sequence is accomplished and where does the rocket get the enormous burst of energy.

…to be continued

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