JPL's Wireless Communication Reference Website

Chapter: Network Concepts and Standards
Section: Satellite Systems, non-geostationary

IRIDIUM Satellite Telephony

The initial plans for IRIDIUM have been proposed by Motorola. This cellular satellite system is called Iridium, after element 77 on the periodic table, because its original design called for 77 satellites. Now the design assumes 66 satellites plus 6 spare ones. Iridium's 66 satellites will be located in eleven nearly polar orbits, which are tilted 86 degrees, some 670 km above the earth. Cells will have a radius of about 300 km. Orbit period is about 100 minutes.

Exercise

assuming circular cells of 300 km radius, and an orbit time of 100 minutes, compute the average time one satellite can maintain a link.

The Iridium satellites will not only set up radio links to handheld terminals and ground stations, but also to each other. Calls can be handed-over to other satellites. Because of these satellite-to-satellite crosslinks, the Iridium system will be able to handle calls to between subscribers without connecting to any ground stations at all, except for signalling messages, such as call set-up, user authentication, billing etc.

Iridium Facts

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