The design of a satellite system is closely tied to the market it is intended to serve and the type of communications services it is intended to offer. There are four general system designs, which are differentiated by the type of orbit in which the satellites operate: Geostationary Orbit (GEO), Low-earth Orbit, Medium-earth Orbit (MEO), and Highly Elliptical Orbit (HEO). Each of these has various strengths and weaknesses in its ability to provide particular communications services.
Outside of the well-defined GEO universe, the differences between these systems is often not absolute and the acronyms applied to a system can be confusing and sometimes misleading. Several systems, for example, are variously described as LEOs and MEOs. Constantly evolving technology along with newly developing markets and service definitions combine to blur the lines between one satellite system and another.
The definitions below are meant to describe the general characteristics of GEOs, MEOs, LEOs and HEOs. Although examples of commercial systems employing these satellites are given, keep in mind that each system has unique characteristics that may not match precisely the general descriptions. The same caution should be applied to ascribing a particular satellite type's limitations to any one commercial system, since each uses several strategies for minimizing or overcoming the limitations inherent in satellite designs. For example, some systems may employ more than one type of satellite.
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