Implementation Of Geostationary Orbits

A satellite closely revolving near the Earth’s surface will complete a revolution around the Earth in about 107 minutes. Therefore, if a satellite is made to revolve from west to east in a close circular orbit concentric and coplanar with the Earth’s equatorial plane, from Earth, it appears to be moving.

However, suppose the satellite’s revolution period is synchronised to just 24 hours. In that case, the satellite’s revolution is equal to the Earth’s rotational period about its axis. The satellite launched will stay over the same place on Earth, and hence it will appear stationary. 

Geostationary Satellite

At a given place (g=constant), the revolution period of the Earth’s satellite depends solely on its height above the surface. 

Let us calculate the satellite’s height above the Earth’s surface, to conclude that a satellite will have a revolutionary period of 24 hours and appear as a stationary satellite. 

Since earth’s revolutionary period

T= 24 hr = 24 × 3,600s; 

Radius of Earth, R = 6,400 km, and, g= 9.8 ms-2 = 0.0098 km s-2.

Thus, a satellite will appear stationary if it revolves around the Earth from west to east in a coplanar circular orbit on an equatorial plane at approximately 36,000 km above the Earth’s surface. 

Such an orbit is known as synchronous, geostationary, or parking orbit; the satellite revolving in this orbit is called a geostationary satellite or simply a stationary satellite. 

From the equation, v= √ (gR2 / (R+x)), the orbital velocity of the geostationary satellites comes out to be about 3.08 km s-1. 

Such a satellite will always appear to be over the same place relative to an observer on Earth. 

Key point: A geostationary satellite always stays over the same place above the Earth. Such a satellite is never at rest. It appears stationary due to its zero satellite velocity concerning its location above the Earth.

Conditions for a Satellite to Appear Stationary

• It should revolve in orbit concentric and coplanar with the equatorial plane.
• Its sense of revolution should be the same as the Earth’s rotation about its axis. I.e., in an anticlockwise direction (from west to east)
• Its period of revolution around the Earth should be the same as the Earth’s about its axis, i.e., exactly 24 hours. 

For this, a geostationary satellite should revolve at the height of 35,930 km above the surface of the Earth. 

Uses of Geostationary Satellite

• They are used for communication purposes, i.e., to transmit radio and T.V. programmes and send telephone signals across the oceans. As such, a geostationary satellite is called a communication satellite. 
• They are used for weather forecasting. 
• Geostationary satellites are employed to study the atmosphere’s upper region.
• They are used to study solar radiation.
• Furthermore, for studying cosmic rays to carry out research work. 

Space rockets are always launched from west to east and in the Earth’s equatorial plane. When a space rocket is launched from west to east, the linear speed of the Earth, due to its rotational motion, also gets added to the rocket’s launching speed. Further, as the Earth’s radius in the equatorial plane is maximum, its linear speed will also be maximum. 

Allocation of Orbits 

All satellites must fit within a single ring over the equator in a geostationary orbit. As these spacecraft must be spaced apart to avoid damaging radio-frequency interference during operations, only a limited number of orbital slots are available. Hence, only a few satellites may operate in the geostationary orbit. 

Satellite Proposal

A satellite alters its orbit by utilising the radiation of the sun’s applied pressure against a solar sail. It would continue to exist at around 30° over the Earth’s dark region. A satellite stays constant in its place concerning the earth and sun system rather than the Earth’s surface, and it may help relieve crowding in the geostationary orbital ring.

Conclusion

The idea of the geostationary orbit has been in existence since the twentieth century. Arthur C. Clarke is primarily credited with inventing the idea of exploiting this orbit for communications. “Extra-Terrestrial Relays — Can Rocket Stations Give World-Wide Radio Coverage”, an article he wrote and published in the Wireless World, October 1945 publication. Clarke extrapolates from German rocket development from then to date, when a network of three geostationary satellites set at equal intervals around the Earth’s equator may provide global communications.

The advantages are: 

• High coverage area. 
• Five geostationary satellites are enough to cover all of the Earth’s regions. 
• One ground segment is enough for satellite monitoring. 
• No problem with frequency changes.