Previous Year Question
Satellites used for telecommunication relay are kept in a geostationary orbit. A satellite is said to be in such an orbit when
the orbit is geosynchronous.
the orbit is circular.
the orbit lies in the plane of the Earth’s equator.
the orbit is at an altitude of 22,236 km.
Select the correct answer using the codes given below.
1, 2 and 3
1, 3 and 4
2 and 4
1, 2, 3 and 4
Correct Answer: A
Detailed Solution
Statement 1 is correct.
A satellite in a geostationary orbit is geosynchronous.
Its orbital period is equal to Earth’s sidereal rotation period, approximately 23 hours, 56 minutes and 4 seconds.
Therefore, the satellite revolves with the same angular velocity as the Earth rotates.
Statement 2 is correct.
The orbit of a geostationary satellite must be circular or almost perfectly circular.
If the orbit is elliptical, the satellite’s position would appear to change in the east-west direction when viewed from the Earth, and it would not appear truly stationary.
Statement 3 is correct.
The orbit must lie in the plane of the Earth’s equator; that is, its inclination must be approximately 0°.
The satellite must orbit in the direction of Earth’s rotation, from west to east.
If the inclination is not zero, the satellite would appear to move in the north-south direction when viewed from the Earth.
Statement 4 is not correct.
A geostationary orbit is approximately 35,786 km above the Earth’s surface, not 22,236 km.
Its orbital radius from the centre of the Earth is approximately 42,164 km.
22,236 is approximately the altitude of a geostationary orbit in miles, not kilometres. An altitude of 22,236 miles is approximately equal to 35,786 km.
Difference between Geosynchronous and Geostationary
Every geostationary satellite is geosynchronous because its orbital period equals Earth’s rotation period.
However, every geosynchronous satellite is not geostationary.
To become geostationary, an orbit must be geosynchronous as well as circular, equatorial and in the direction of Earth’s rotation.
A satellite in an inclined or elliptical geosynchronous orbit does not appear stationary from the Earth.
Why is a geostationary orbit useful for telecommunications?
The satellite appears stationary above a fixed longitude on the Earth.
A ground antenna does not need to continuously track the satellite; it can remain pointed in a fixed direction.
A single geostationary satellite can provide signal coverage over a very large part of the Earth’s surface.
It is used for television broadcasting, telephone connectivity, weather communication, satellite news gathering and disaster communication.
Because of its high altitude, signals must travel a long distance, giving GEO communication higher latency than LEO systems.
Geostationary satellites provide weak coverage in polar regions because they are positioned above the equator.