Low-Earth Orbit Satellites

These satellites lie very close to earth and moving with greater speeds. Due to their rapid motion, large number of satellites is required for achieving a particular task. The advantage here is that the ground station power requirement is very low. In 1990, Motorola launched 77 low-orbit satellites as part of its IRIDIUM project. Later they withdrawn 11 satellites and the project proved excellent and economical. IRIDIUM satellites are providing worldwide telecommunication services using hand-held devices. Services provided by IRIDIUM satellites were effectively used by maritime, aviation and oil exploration industries. An altitude of 750 km was chosen for positioning IRIDIUM satellites. They were positioned in circular orbits in a north-south necklace arrangement; with one satellite every 32 degrees of latitude. Globalstar, a system with 48 LEO satellites was launched as an alternative to IRIDIUM. Globalstar uses a traditional bent-pipe design. Teledesic, a system with 30 larger footprints satellite was launched to facilitate internet service. Here system is packet switched, and all satellites are capable of routing packets to its neighboring satellites.