Satellite Orbits for Communications Satellites

Abstract

One of the key elements of a communications satellite service is the ability to launch satellites into precisely defined orbits and to maintain them in the desired orbit throughout the lifetime of the satellite. The system control and oversight of satellite orbits both require not only the technical ability to launch and maintain the orbit, but the ability to attain the proper legal authority, at the national and international level, to transmit and/or receive radio signals from these orbits. This regulatory process means a number of specific steps associated with registering for the allocated frequencies from the International Telecommunication Union (ITU)through a national governmental administration, obtaining assignments of those frequencies in the required orbits in accord with national licensing procedures, and coordination of the use of the specific frequencies through intersystem coordination procedures.

There are a wide range of different orbits that are currently used in communication satellite services although the most common are geosynchronous Earth orbits (GEO), medium Earth orbits (MEO), and low Earth orbits (LEO). This chapter explains the various orbits that can be used and the advantages and disadvantages of each of the orbits most often employed for satellite communications. This analysis indicates some of the primary “trade-offs” that are used by satellite system engineers in seeking to optimize a satellite systems performance both in its design and subsequently over its operational lifetime. The activities involved in selecting an orbit; designing and achieving an operational satellite network; and optimizing its technical, operational, and financial performance over the systems lifetime involve a wide range of issues. These start with selecting a desired orbital framework, obtaining authorization for orbital access (including the registering and precoordination of the satellite and its orbit with other systems), launch, deployment and test, systems operation, and end-of-life disposal of a satellite from its orbit.