Artificial satellite & Satellite Launch Vehicles

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Artificial satellite:

   The artificial object, which is made by human, revolves around the earth or any other planet in a fixed orbit it is called an artificial satellite. The satellites work on solar energy and hence solar photovoltaic panels are attached on both sides of these satellites, which look like wings. Satellites are installed with various transmitters and other equipment to receive and transmit signals between the earth and satellite.

The first artificial satellite ‘Sputnik’ was sent to space by Soviet Union in 1957. The “aryabhata” named after the famous Indian astronomer, was India’s first satellite; it was completely designed and assemble in India and launched by a soviet union, in 19 April 1975.

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Orbits of Artificial Satellites :

All artificial satellites do not revolve in similar orbits around the earth. The functions of the satellite decide the height of the satellite’s orbit from the earth’s surface, the nature of the orbit (circular/elliptical) and whether the orbit shall be parallel to equator or making some angle with it.

High Earth Orbit Satellite:

A satellite orbiting at a height equal to or greater than 35780 km above the earth surface is called High Earth Orbit Satellite.

This satellite will take around 24 hours to complete one revolution. Earth also takes almost 24 hours for one revolution. If the satellite is revolving in an orbit parallel to the equatorial plane of the earth. The time of revolution for the earth around itself and that for the satellite to revolve around the earth being the same, the satellite will appear to be stationary with respect to the earth. These satellites are, therefore, called geosynchronous satellites. Therefore they can observe a specific portion of the earth, continuously. Also, they are used in applications like meteorology and for carrying signals for telephone, television, radio etc.

Medium Earth Orbit Satellite:

A satellite orbiting at height above the earth’s surface is in between 2000 km and 35780 km, the orbits are called Medium Earth Orbits. The orbital path of such satellite is normally elliptical and passes through the North and South polar region.

These satellites complete one revolution in 2 to 24 hours. Some of these satellites revolve in circular orbits at a height of around 20,200 km above the earth’s surface. These satellites are useful in navigation.

Low Earth Orbits Satellite:

A satellite orbiting at a height above the earth’s surface is in between 180 km and 2000 km, are called Low Earth Orbits Satellite. Generally, they complete one revolution in around 90 minutes The satellites used for scientific experiments and atmospheric studies revolve in low earth orbits. International Space Station and Hubble telescope also revolve in Low earth Orbits.

Orbits of artificial satellites

Satellite Launch Vehicles

Satellite launch vehicle is typically a rocket. It is  designed for used, to place the satellites in their specific orbits. The launch vehicle uses specific type of fuel. The gas produced due to combustion of the fuel expands due to its high temperature and is expelled forcefully through the nozzles at rear side of the launch vehicle. As a reaction of this, a thrust acts on the vehicle, which drives the vehicle high in to the space.

The structure of the launch vehicle is decided by the weight of the satellite and the type of satellite orbit. The fuel of the vehicle also depends on these factors. The fuel forms a major portion of the total weight of the launch vehicle. Thus, the vehicle has to carry a large weight of the fuel with it. To overcome this problem, launch vehicles with more than one stage are used. Due to this, the weight of the vehicle can be reduced step by step, after its launching.

For example, consider a launch vehicle having two stages. For launching the vehicle, the fuel and engine in the first stage are used. This imparts a specific velocity to the vehicle and takes it to a certain height. Once the fuel in this first stage is exhausted, the empty fuel tank and the engine are detached from the main body of the vehicle and fall either into a sea or on an unpopulated land. As the fuel in the first stage is exhausted, the fuel in the second stage is ignited. However, the vehicle now contains only one (i.e. the second) stage. The weight now being reduced, the vehicle can move with higher speed. Almost all vehicles are made of either two or more stages.

The structure of a Polar Satellite Launch Vehicle (PSLV) developed by ISRO of India is follows:

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