s may be assigned frequencies and satellite systems in bands which have not been planned for the in bands allocated to the fixed satellite service for up-links. How- satellite service apply in the allotment plan bands also. ever, other frequency bands, not to be used for fixed satellite These two sets of frequency plans for satellite systems are limited systems, have been set aside especially for these feeder links and to geostationary satellites. Most communication satellites operating assignment plans have been drawn up. The plans are in the bands in other bands are also geostationary, but a few use other orbits. given in Table 51.4 (ITU, 1990h). Satellites in non-geostationary equatorial orbits would present a Various other bands have been allocated for satellite broadcasting persistent interference hazard for geostationary satellites. Non- (down-links), in particular around 42GHz and 85GHz, but there is geostationary satellites in orbits inclined to the equator, which pass little sign at present of these allocations being taken into use. through the equatorial plane twice in every orbit, could cause and Finally, frequency bands have been allocated (ITU, 1990a) for suffer intermittent interference. Since it is agreed that the geosta- assignments to inter-satellite links, used for any kind of satellite tionary satellite orbit is the most important, especially for the fixed system. The main bands below 100GHz are:22.55GHz-23.55GHz; satellite service, there is a regulation (RR 2613) that requires sys- 32.0GHz-33.0GHz; 54.25GHz-58.2GHz; 59GHz-64GHz. tems using non-geostationary satellites using fixed satellite alloca- Spacecraft technology 51/5 tions must cease operation whenever this is necessary to prevent 188dB. This loss has particularly serious consequences for satellite interference to a geostationary satellite system (ITU, 1990i). communication with mobile earth stations and in particular for hand There are also agreed procedures, implemented under the super- portable and vehicle mounted stations, which typ