Satellites used for telecommunication relay are kept in a geostationary orbit. A satellite is said to be in such as orbit when:

1. The orbit is geosynchronous.
2. The orbit is circular.
3. The orbit lies in the plane of the earth’s equator.
4. The orbit is at an altitude of 22,236 km.

Select the correct answer using the codes given below:

[UPSC Civil Services Exam – 2011 Prelims]

(a) 1, 2 and 3 only

(b) 1, 3 and 4 only

(c) 2 and 4 only

(d) 1, 2, 3 and 4

Answer: (a)        

Explanation:

Geostationary orbit (GEO):

• Satellites in geostationary orbit (GEO) circle Earth above the equator from west to east following Earth’s rotation – taking 23 hours 56 minutes and 4 seconds – by traveling at exactly the same rate as Earth. Hence, statements 1, 2 and 3 are correct.
• This makes satellites in GEO appear to be ‘stationary’ over a fixed position.
• In order to perfectly match Earth’s rotation, the speed of GEO satellites should be about 3 km per second at an altitude of 35 786 km. Hence, statement 4 is not correct.