Troposphere is the layer of atmosphere that spreads till the height of 15 km from the surface of the earth. It is dense with the presence of air molecules and protects us from the UV rays.
Do you know that a commercial aircraft flies at the height of 9km from the surface of the earth? A military aircraft flies at the height of 15km or even more. The layer of atmosphere just above the troposphere is called Stratosphere. Atmosphere become thinner as one goes away from the surface of the air. So in Stratosphere very less air molecules are present. But they are enough to balance an aircraft.
Ionosphere starts from the height of 50km from the surface of the earth. In the lower levels of this layer, molecules, electrons, ions are moving at a high velocity because of the magnetic field of the earth.
If a satellite is launched here, because of its friction with electrons and ions moving with great velocity, it will slowdown, get heated and will get pushed down to the lower layers of atmosphere where it will get burnt like meteorites.
To avoid this problem a satellite should be placed in an orbit at the height of 400-500km from the surface of the earth.
But it is not an easy job.
Temperature of troposphere is more because of the heat reflecting from the earth surface. To avoid adverse effects of heat a rocket (satellite launcher) has to cover the distance of troposphere quickly. The shortest way through troposphere is straight up. Hence rocket flies in straight upward direction.
In a multi-staged rocket, fuel is stored in various shells. As the fuel in a shell is over, the empty shell is dropped down and the fuel in the next shell starts burning. This reduces the weight of rocket helping it to achieve the desirable speed for launching a satellite.
Once the rocket is out of troposphere it starts slanting slowly. This is called ‘pitching’. At time of launching it is almost parallel to the surface of the earth. Now the satellite is projected in a certain direction at a certain velocity with help of system control. At this time the speed of rocket is about 7.5 km per second.
Now our satellite is supposed to orbit around the earth. How this is achieved?
A ball thrown in an upward direction will come down. A flying gas balloon will also come down eventually. An aircraft also has to come down to the earth before it runs out of fuel.
It sounds like a difficult job, doesn’t it?
According to Newton’s law of motion any object will remain to be in its state of rest or of continuous motion unless and until acted upon by external unbalanced force.
In other words a ball thrown in an upward direction will go up and up if it wasn’t pulled down by gravitation force (external force).
Our satellite is also pulled down by gravitation force. But there is another force called centrifugal force which being equal to gravitational force and being in opposite direction nullifies the gravitational force. And satellite is set in an orbit.
The following example will make it clear.
When your car takes a sharp turn at a corner, you must have felt a force pushing your car away from the arc of the turn. This force is nothing but centrifugal force. You try hard to keep your car on the arc by pulling it inside. When the force pushing your car outwards and the force pulling your car inwards become equal they nullify each other and the car travels in an arc.
The logic is simple but lots of calculations and science is required in making the mission successful.
Now a satellite will revolve around the earth, just like the moon rotates around our earth.
Mission is successful. Cheers!