TABLE OF CONTENTS The idea that three geostationary satellites could provide communications coverage for the whole of the earth, apart from relatively small regions at the north and south poles, is generally credited to Clarke (1945). The basic idea was sound, but of course the practicalities led to the development of a much more complex undertaking than perhaps was envisioned originally. Technological solutions were found to the many problems that were encountered, and as a result, satellite services expanded into many new areas. Geostationary satellites are still the most numerous and well in excess of three! If an average of 2 spacing is assumed, the geostationary orbit would provide 180 orbital positions, and in practice satellites are often employed in clusters, with more than one satellite at an assigned orbital position. The 180 orbital positions are not occupied in a uniform distribution as in practice satellites are concentrated to serve regions where services are most in demand. In addition to geostationary satellites, much more use is being made of nongeostationary orbits, especially low earth orbits (LEOs) and medium earth orbits (MEOs). As described in Chap. 15, a service may utilize a combination of geostationary and nongeostationary satellites.
Although the developments in satellites generally have led to a need for larger satellites, a great deal has been happening with small satellites, often referred to as microsats (see Sweeting, 1992, and Williamson, 1994). In this chapter, brief descriptions are given of some of these services to illustrate the range of...
