Low Earth Orbit

LEO satellites can be divided into "Big LEOS" and "Little LEOS." "Little LEOS" provide pager, cellular telephone and location services. An examples of a "Little LEO" system is Motorola's Iridium, which declared bankruptcy after putting a 66 satellite constellation into space. "Big LEOs" carry voice and data broadband services. If your discussing internet access, which I am on this site, you have to talk about the "Big LEOS," which hope to be an internet in the sky.

Low earth orbit is approximately 300 to 1,000 miles above the earth. It takes about 20 to 40 milliseconds for a signal to bounce from an earth bound station to a LEO then back to an earth station. This is compared to the ½ second it takes the same signal to bounce off a GEO satellite.

Using a LEO satellite, a consumer can make a phone call or access the internet from anywhere on earth, compared to cellular service which only covers 20% of North America.

But LEO constellations may be costly. Earth coverage requires many more satellites from LEO than from GEO. Some LEO-satellite-system plans call for over 200 satellites, which runs up the cost of the system. And the LEO-satellite technology is not as advanced as GEO technology.

LEOs are expected to be in demand for three markets: rural conventional telephone service, global mobile service, and international broadband service.

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Dec. 7, 1999