longitude at high latitudes, found 12-hour elliptical orbits into one phase. A single liquid propellant rocket may combine the inclined at about 63° to the equatorial plane to be preferable for its functions of apogee motor and perigee motor. This, in fact, is the domestic ORBITA network. These satellites are operated for procedure that is most commonly used today; it is illustrated in periods of about eight hours when they are close to their apogee, Figures 51.2 and 51.3. Despite such variants, however, the prin- about 40000km high above Siberia, but three satellites are required ciples of the classic procedure are generally applicable for all to provide continuous coverage. geostationary launchings and may also be used, with appropriate Satellites in geostationary and 12-hour elliptical orbits are at great changes, for launching satellites which are not to be geostationary. distances from the surface of the Earth and the transmission loss is Launching facilities are available from a number of providers, very high; at 1.6GHz, for example, the free space loss is about government and commercial, in USA, USSR, France, Japan and 51/6 Communication satellites and systems View from satellite C Satellite B Satellite C 180W 150W 120W View from satellite A View from satellite B Satellite A Figure 51.1 The concept of a world-wide geostationary satellite system China. The mass which these launch vehicle systems can deliver west longitude. In many parts of the orbit a significant drift in into, for example, the geostationary satellite orbit ranges from location, due to this cause, accumulates within a few weeks if not 350kg to 4000kg, and the more powerful systems can also be used corrected. to deliver several light weight satellites into the same, or similar, The gravitational fields of the Sun and the Moon cause the orbital orbits. A comparison between the payload capabilities of major plane of a geostationary satellite, initially co-incident with the communication satellite launchers is shown in Table 51.5. equatorial pl