Mumbai University > EXTC > Sem 8 > Satellite Communication and Networks

Marks: 10M

Kepler’s Second Law states that: ‘For equal time intervals, the satellite sweeps out equal areas in the orbital plane.’

The shaded area A1 shows the area swept out in the orbital plane by the orbiting satellite in a one hour time period at a location near the earth. Kepler’s second law states that the area swept out by any other one hour time period in the orbit will also sweep out an area equal to A1.

For example, the area swept out by the satellite in a one hour period around the point farthest from the earth (the orbit’s apogee), labeled A2 on the figure, will be equal to A1, i.e.: A1 =A2. This result also shows that the satellite orbital velocity is not constant; the satellite is moving much faster at locations near the earth, and slows down as it approaches apogee.

The velocity of the satellite at apogee (Point A) is least while that at perigee (Point B) is highest. Hence as satellite approaches towards apogee the velocity of the satellite goes on decreasing.

Hence as shown in diagram the satellite in the highly inclined elliptical orbit spend its most of the orbital period.

Advantages of high inclined orbit:

• There are an infinite number of orbits available.

• These satellites can cover high latitude regions.

Disadvantages of high inclined orbit:

• They require earth stations to continuously track the satellite. This often an acquisition operation, and sometimes involves handover from an orbiting satellite leaving the area to a new satellite entering the area

• Large number of satellites is required to be spaced along the orbit in order to provide continuous coverage to a particular earth station.

• Propagation delay can be higher than GEO system.

• Doppler effect quite significant.

• Satellites tend to pass Van Allen radiation belts regularly to the detriment of electronic component