The Globalstar™ constellation consists of 48 LEO (low-Earth-orbiting) satellites, plus an additional four satellites in orbit as spares. Each consists of an antenna, a trapezoidal body, two solar arrays and a magnetometer, and operates at an altitude of 1414km (876 miles). The satellites are placed in eight orbital planes of six satellites each, inclined at 52 degrees to provide service on Earth from 70 degrees North latitude to 70 degrees South. Because of this configuration, the polar regions, including most of Greenland, small parts of Alaska, Canada, Scandinavia, Siberia, and regions in the Southern Hemisphere, including Antarctica and parts of South America are not covered. "Bent-Pipe" Technology Like "bent-pipes", or mirrors in the sky, the Globalstar™ constellation of satellites can pick up signals from over 80% of the Earth's surface. Several satellites pick up a call, and this "path diversity" assures that the call does not get dropped even if a phone moves out of sight of one of the satellites. If buildings or terrain block your phone signal, a "soft-handover" takes place, and the call's transmission is switched to an alternate satellite with no interruption. This satellite now maintains transmission of the original signal to one of several terrestrial Globalstar™ Gateways. Because all the switches and complex hardware are located on the ground in the Gateways, Globalstar™ satellites are relatively simplistic, leading to dramatically increased system reliability. Additional advantages of using low-Earth-orbiting satellites within the Globalstar™ Communications System include lighter, smaller, all-in-one handsets and no perceptible voice delay. LEO satellites also minimize call transmission time delays. Long transmission delays cause noticeable gaps between the time a caller speaks and when the listener hears what is being said. Satellite Footprint The satellite coverage beams for satellite phone communication links and the Gateway communication links are quite large. The picture to the right gives you a sense of scale for the coverage of a typical thirty-six hundred mile diameter beam footprint. Each footprint moves rapidly across the Earth's surface. A satellite that passes directly overhead is visible to that spot for only about 15 minutes. When a user places a Globalstar™ satellite call, the nearest satellite picks up the signal. Globalstar™ satellite phones can operate with a single satellite in view, though typically two to four satellites will be overhead. This simultaneous coverage by multiple satellites is called "path diversity," which enhances the quality of the Globalstar™ satellite call. Path Diversity Path diversity is a method of signal reception that combines multiple signals of varying power strengths into a single coherent signal. Satellite phones communicate with as many as three satellites simultaneously, combining those signals into a single, static-free signal. Globalstar™ satellite phones also alter power levels to compensate for shadowing and interference as needed. As satellites move in and out of view, they will be seamlessly added to and removed from the calls in progress, reducing call interruption. This enables the Globalstar™ system to provide superior service to a wide variety of locations with less potential for signal blockage from buildings, terrain, or other natural features.