There is a limit to the number of communications satellites that can operate independently in the geostationary 24-hour equatorial orbit. The limitation arises from the fact that global communications systems can best be based on a limited number of synchronous satellites which remain stationary over a predetermined point on the earth's surface due to the properties of the orbit. The orbital altitude required is 36,000 kilometres, for which the time of revolution is 24 hours, thus maintaining the satellite over one position. The minimum angular spacing (estimated at 2-6 degrees, namely 180 to 60 satellites) between satellites in such an orbit without mutual interference depends upon the sophistication of the ground aerials and the frequency used. If satellites operating in the same frequency or covering a similar area are placed within 2.5 degrees (18,750 kilometres) of each other in the parking band, they cause mutual interference.
It is expected that overcrowding may indeed occur very quickly in some specially favoured parts of the orbit. (The range of longitude for a satellite linking London and Tokyo, for example, is such that satellites more than one degree off either way will lose one of the cities). Disputes about usage may lead to political and military action, particularly in view of the difficulty of creating an international mechanism to manage this resource.
In the past 10 years, countries have put more than 120 communications satellites into orbit 36,000 kilometres above the equator, the geosynchronous spot where a satellite appears to hover as it flies around the Earth at the same speed the Earth rotates and where it can serve one country or one region 24 hours a day. Many of those satellites have gone dark, but more than 90 are still at work. No fewer than 19 carry telephone, television and business traffic across the USA, more than 20 serve the former Soviet Union, and the worldwide consortium known as Intelsat now has 34 communications satellites scattered around the globe in geosynchronous orbit. So many communications satellites are working at similar radio frequencies in the same equatorial belt in space that they have begun to interfere with each other.
In 1993, the International Frequency Registration Board reported there has been a competitive rush to place satellites over Asia and the Pacific region, seen as the world's fastest growing areas for telecommunications and television. (In Asia, even small percentages of the population translate into large audiences by Western standards, and as a result the Asian audience is becoming the fastest-growing untapped consumer market on the globe.) With about 35 satellites already positioned above the Equator in the Asia-Pacific region, and more than 15 launchings planned for the next two years alone, rivalry for a diminishing number of available slots in the orbital arc threatens to disrupt communication services and has given rise to concerns over "claim-jumping".
