define mass communication

An artificial satellite revolving in a circular orbit round the earth in the equatorial plane, in the same sense as that of the rotation of the earth and with the same period of revolution as the period of rotation of the earth (i.e. 24 hours or 86400 seconds), is called a communication satellite (Fig. 2.6). Such a satellite always appears stationary from the surface of the earth and hence it is also called a geostationary satellite or a geosynchronous satellite.In order to launch a communication satellite in its orbit, it is first raised to a certain height above the equator and then projected with a certain velocity in the same direction as that of the sense of rotation of the earth. The height and the velocity of the satellite are determined as follows.(1) If r is the radius of the orbit of the satellite, the period (T) of the satellite is given byT = 2n J-; \GMT2 GM' r3 = —...(2.37)AnNow, M = mass of the earth = 5.98 x 1024 kg and G = constant of gravitation = 6.67 x 10"11 Nm2/kg2. For the communication satellite, 7=24 hours = 86400 s. Substituting these values in the above equation, we get(86400J2 x6.67xl0~n x5.98 x 1024^ = 4 x (3.14 J2= 7.55 x 1022r = (7.55 x 1022)1/3 = 4.227 x 107 m = 42.27 x 106 mIf h is the height of the satellite above the surface of the earth and R is the radius of the earth,r = R + hh = r-RNow R = 6400 km = 6.4 x 106 mh =r-R = 42.27 x 106 - 6.4xl06 = 35.87 x 106 m= 35870 km(2) The velocity of projection ( vc) of the satellite is given byIGM lGM~ 16.67 xlO"11 x 5.98 x 1024~ vc= ]lR + h=i= V 4.227 xlO7= 3.072 x 103 m/s = 3.072 km/s The above consideration shows that the height of the communication satellite above the surface of the earth is about 36000 km and its speed is about 3.1 km/s.