Clinton lifts GPS blinders

A White House decision last week to take the Pentagon-imposed blinders off

the Global Positioning System will lead to faster, better and cheaper government

services, according to federal officials.

President Clinton on May 1 delivered on a 4-year-old promise to improve

the accuracy of the satellite navigation system for civilian users by deactivating

a feature that intentionally skewed GPS positioning and timing data sent

to civilian receivers.

The feature, known as selective availability, was intended to prevent

hostile forces from using GPS positioning information in strikes against

the United States. But the Pentagon has concluded such a feature is no longer


Selective availability was set to zero at midnight May 1, with GPS satellite

operators commanding the satellites to stop distorting the signal transmitted

to civilian users, said Neal Lane, the president's science adviser, during

a press briefing earlier in the day.

"It's rare that you can press a button and make something you already

own instantly more valuable," Lane said.

At the Commerce Department's National Oceanic and Atmospheric Administration,

James Baker foresees speedy delivery of weather predictions and evaluations

from less expensive future weather satellites.

The improved accuracy of GPS will require less data processing of positioning

and timing information received by NOAA weather satellites. Because weather

satellites will no longer have to be equipped with all the instruments needed

to correct GPS data, the cost of a satellite launch, which is calculated

per pound, will be lower, said Baker, undersecretary of commerce for oceans

and atmosphere and NOAA's administrator.

"This is only the tip of the iceberg for improvements to the GPS system,"

Baker said. The Defense Department plans to provide civilian GPS users with

a second satellite signal as part of satellites scheduled for launch beginning

in 2003, and with a third signal starting in 2005.

The additional satellite signals will provide much-needed redundancy,

like the second engine on an airplane. People using GPS for life-and-death

applications cannot afford to have the signal suddenly disappear. The additional

signals will allow GPS to overcome the natural interference that occurs

when the satellite signal passes through the ionosphere.

GPS is a system of at least 24 orbiting satellites — there are now 27 — operated by DOD that provides accurate positioning and timing information

to users on the ground, in the air or in space. GPS is used to guide missiles,

navigate civilian aircraft and synchronize cellular and digital telecommunications


In a presidential directive in 1996, Clinton promised to annually revisit

the issue of intentionally degrading the civilian GPS signal beginning in


The White House decided to deactivate selective availability now because

DOD has sufficiently proved its ability to deny the GPS signal to adversaries

in a specific region while maintaining availability to users elsewhere,

said Arthur Money, assistant secretary of defense for command, control,

communications and intelligence.

DOD would not agree to shut off selective availability until it had

developed and tested technology that protects the advantage of the warfighter

in a conflict area, Money said.

Although the modification significantly improves the accuracy of the

GPS signal, the Transportation Department is still committed to developing

systems that augment GPS capability, said Eugene Conti, assistant secretary

of transportation for transportation policy.

Those systems, such as the Federal Aviation Administration's Wide-Area

and Local-Area augmentation systems and the Coast Guard's National Differential

GPS, verify that the GPS signal is reliable and improve accuracy even more.

U.S. officials will continue discussions with their counterparts in

Europe about the European Union's plans to develop another satellite navigation

system called Galileo that could be interoperable with GPS, said Jeffrey

Bialos, head of the U.S. delegation for discussions with the EU. "This decision

means we have a more robust and precise GPS than before," he said. How that

will affect the European strategy remains to be seen, he said.


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