The SARSAT system was developed in a joint effort by the United States, Canada, and France. A similar system, COSPAS, was developed by the Soviet Union. The four nations banded together in 1979 to form COSPAS-SARSAT. In 1982, the first satellite was launched, and by 1984 the system was fully operational.

The combined system now involves 29 nations, 28 ground stations and 15 mission control centers worldwide.

SARSAT's budget is about $5 million a year, funded by NOAA, the Coast Guard, and the Air Force.

SARSAT employs two NOAA satellites, called GOES East and West, that sit in fixed perches above Earth, so-called geosynchronous orbits. These satellites cover the entire globe from 70 degrees North latitude to 70 degrees South.

No corner of the globe is uncovered, Mehta said, though a signal sent from a polar region is sometimes not picked up for hours due to the orbits of the satellites.

Two types of beacons are in use. Older ones operate at a frequency of 121 megahertz. They send a signal with no information, and the satellite determines the position, sometimes only to within a mile or two.

"The newer beacons at 406 megahertz actually send a digital message which contains information about the type of beacon it is, whether it's made to be used on water, on land, or by a person," Mehta said. "It may even contain information about the owner/operator."

Some of these newer beacons also have built in Global Positioning System (GPS) receivers, so they transmit their own positions -- very accurately.

There are about 600,000 beacons worldwide operating at 121 megahertz. Another 250,000 operate at 406 megahertz. Only about 2,000 have built-in GPS.