 on the Earth was first proposed by Arthur C. Clarke in 1945. Such a space station can receive signal from a point on the Earth, strengthen the signal and then transmit it to another point. The distance between these two points can be tens of thousands of kilometres, as such a satellite can have a line-of-sight to nearly half of the surface of the Earth. How a satellite maintains an orbit around the Earth can be explained by a centrifugal force it feels as it rotates around the Earth which balances the Earth's gravitational pull as illustrated in Figure 11.1. The satellite's orbital velocity determines the centrifugal force: the faster the speed, the more the centrifugal force. On the other hand, the gravitational pull is calculated from the dis- tance of the satellite from the centre of the Earth. The further a satellite is from the Earth, the lower the gravity pull. Therefore a particular application may choose a satellite orbit with a Broadband Telecommunications Technologies and Management Centrifugal force Satellite orbital velocity Gravitational force Figure 11.1 Balancing of centrifugal and gravitational forces particular altitude and an associated orbital velocity and therefore orbital period. The lower the orbit, the higher the orbital velocity and the shorter the orbital period, and the higher the orbit, the lower the orbital velocity and the longer the orbital period. The orbital period, T, is calculated from the following classic physics formula: T Jane 4r2r where T is orbiting time in seconds, r is the radius from the centre of the Earth in kilometres and constant = 398 600 km³/s². Satellite Telecommunications System Structure As noted above, the first international telecommunications satellite system, Intelsat Early Bird, was launched in 1964. This system was designed to provide international telephony service and TV broadcasting to consortium member nations. A number of systems nodes had to be developed for the satellite network to operate: a block diagram of the system's equip- ment is shown in Fi