A rocket blasted off from Cape Canaveral, Florida, Friday carrying a replacement satellite to help improve the accuracy of the space-based U.S. navigation network, the Global Positioning System. The government hopes to enhance the system by linking it to a similar Russian satellite network and one being developed for Europe.

The new satellite is heading for its place in orbit to take over for one of the 24 primary Global Positioning System satellites that circle about 18,000 kilometers above Earth.

Together with several backup satellites, the constellation of orbiters enables anyone with a special receiver to get signals from them to know his location anywhere on the planet within four to six meters.

The latest satellite is the third with improved features that will transmit additional signals for military and civilian users, promising greater accuracy and more resistance to interference. "We're now in the mode of putting new satellites up to replace some of the older ones," he said.

Michael Shaw, who directs the office that coordinates U.S. government interagency policy and activities for the Global Positioning System, or GPS, said "those replacement satellites will have new capabilities that will make the performance of this global navigation, positioning, and timing service better for the worldwide community."

When the advancements are spread among more of the new GPS satellites, the U.S. military will have a signal more resistant to jamming, one that will enable better targeting of GPS-guided weapons during war. The new civilian signal removes navigational errors caused by Earth's ionosphere, a layer of the atmosphere that influences the propagation of radio signals.

The system was originally designed for the armed forces, but the U.S. government dropped its ban on civilian use in 2000 and deactivated technology that degraded its accuracy to anyone without special military style receivers.

Shaw sees the GPS system as a new utility for the public good, as electricity and telephones became in previous centuries. "As we continue to improve this exact position information for the global community both in the developed and developing worlds, there is almost a limitless number of applications that can be made to improve the economic situation, the transportation situation" and more, he said.

The Global Positioning System is helping geologists track ground movements that could become earthquakes. Its ability to sense rising water levels can help officials warn citizens to flee impending floods. By monitoring signals from vehicles with GPS receivers, urban planners can improve traffic flows. GPS officials say even agriculture can benefit by using the system for such things as field mapping and tractor guidance.

The U.S. State Department's director for space and advanced technology, Ralph Braibanti, says Washington is promoting the network's use throughout the world. His office has held bilateral talks with governments and workshops in several regions to pass the word about employing GPS for sustainable development.

"We want this to be truly a global utility. It should be because the signals are available throughout the world, the signals are free throughout the world, and so we hope that people will make maximum use of what is there," he said.

GPS enhancement is not limited to just improving the technology of the satellites. The United States seeks to expand the network by linking it to a Russian satellite navigation system already in operation and one being planned for Europe. Shaw says that if technical barriers are overcome to make the different systems compatible, the world could someday have twice as many navigation satellites for greater positioning accuracy. "If all these satellites are interoperable, there is much more likelihood that we're going to have multiple satellites in view and deliver that performance down into the couple meter accuracy level and maybe the sub-meter accuracy level," he said.