After The Attacks, New Attention On GPS.


Mar 11, 2001
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After The Attacks, New Attention On GPS.

By Arik Hesseldahl,


It could turn out to be a frightening irony. Is it possible that the terrorists who attacked the U.S. three weeks ago used a Global Positioning System navigational device to help pinpoint the World Trade Center buildings and the Pentagon?

The FBI is investigating whether hijackers bought a GPS navigational device
typically used by noncommercial pilots. The fact that the bad guys may have
used our own navigational technology against us may be scary. But no more
so than if they had used a telephone, a computer or public transportation in
the course of hatching their evil plans. GPS is just entering the public
consciousness, and there's a lot of misunderstanding about what it is and what
it does.

GPS was originally built for military use. Central to the system is a 28-satellite
constellation that circles the Earth, broadcasting signals used as a navigational
tool. These satellites can't track your movements, as some people think, but
instead just bombard the Earth with radio signals that are used to determine a
receiver's precise latitude and longitude.

Chances are that if the hijackers had GPS devices, they wouldn't have been
helpful. Cockpit windows are equipped with layers of material that prevents
the glass from icing up. That same material would probably have prevented
the type of GPS device in question from receiving satellite signals, according
to people familiar with the technology.

Originally conceived in the 1970s, GPS was a military-only technology until
the early 1980s, when President Reagan, following the Soviet shoot-down of
a South Korean airliner that had lost it way, decided the technology could be
adapted for public use. By the early 1990s, civilians could buy GPS equipment
that was accurate to within about 300 feet. But since no one wanted the
technology to be used in a military attack on the U.S., the military deliberately
distorted the signal to keep civilian gear from being more accurate. This was
called "selective availability," or "SA" for short.

On May 1, 2000, President Clinton signed an order ending SA and making
civilian GPS readers a lot more accurate. Now they're accurate to within 40
feet, and often much better than that. Military GPS is even more accurate and
has a margin of error of only a few centimeters. Still, in the world of GPS
technology, the end of selective availability marked a major parting of the

But it also potentially parted the clouds for the bad guys, since there are no
controls on who can build a GPS receiver or buy one. The electronic designs
for making receiver equipment are an open standard freely available to
anyone. The signals from the satellites themselves are freely available all over
the planet. The same signal that lets a GPS receiver tell you you're in
Dubuque, Iowa, can just as accurately tell you you're in Baghdad or
Pyongyang, North Korea. Nor is there any restriction on the sale of GPS
receivers or their export.

News reports have said the FBI is investigating whether the hijackers bought
a $500 GPS-based navigational device intended for use in airplanes and made
by Garmin International , the market leader for consumer GPS devices.
The device would typically be used to tell a pilot location and altitude, and
would help plot a course from one place to another.

The news reports led to some uninformed speculation that some GPS
companies like Garmin, Lowrance Electronics and Thales Navigation, a
Santa Clara, Calif.-based unit of French electronics and aerospace concern
Thales Group, might have to struggle with new restrictions on GPS
technology in the wake of the attacks. One columnist even suggested that the
government could force Garmin to "scale back" the devices it sells. The very
idea is utter hogwash.

When the government sets policy for the GPS system, that policy has to do
with the signals broadcast from the satellites, not the devices themselves. Now
that the technology is open to the public, it's all but impossible to put the
toothpaste back in the tube. If new restrictions are needed, there's basically
two choices: Turn SA back on and go back to the days of less accuracy for
civilians, or leave it off.

Immediately after the attacks, the industry buzzed over the possibility of a
return to SA. That ended on Sept. 17, when the Interagency GPS Executive
Board, which governs the system, posted a statement on its Web site. SA, the
agency said, will never be turned back on.

That's good news, since the market is wider than just gadgets for hikers and
pilots. When combined with technologies that enable tracking of people and
products, GPS can be useful in tracking the progress of shipping goods. It's
also used in construction, excavation, building roads, farming, mapping and
even marketing. The atomic clocks on the GPS satellites also make their
signals perfect for keeping highly accurate time, an essential function in
telecommunications networks.

Estimates vary, but market research firm Meta Group of Stamford, Conn.,
pegs the civilian GPS market as being worth $14 billion this year, with the
potential to grow to $20 billion by 2004. Last year chip company Trimble
Navigation sold more than $100 million worth of GPS chips. The same year,
Garmin reported $345 million in sales of its devices, and Lowrance did $73
million in sales.

Of course GPS is still a critical military technology. Soldiers on the ground use
it to find their way, as do ships and planes. Precision-guided munitions like
Tomahawk cruise missiles use GPS signals to zero in on non-moving targets
like enemy airfields.

It's so important to military missions that the government couldn't turn off
selective availability for civilian gear until the Air Force had developed the
capability for something called "selective deniability." In essence, this
technique distorts or denies GPS signals over a certain area of the world
where U.S. forces are fighting or conducting other sensitive operations,
without interfering with its use elsewhere. But it allows American or other
friendly forces to still use their own GPS gear, says Glen Gibbons, editor of
GPSWorld, a trade magazine based in Eugene, Ore.

That opens up a possibility, Gibbons says, for "navigational warfare" in which
forces play a cat-and-mouse game of trying to jam each other's ability to
receive GPS signals, and also counteract jamming attempts made by others.
Denying an enemy access to GPS, Gibbons says, might make a big difference
in fighting a conventional war against a foe with modern equipment.

But Afghanistan is a poor country, and the ruling Taliban regime, if it turns
out to be an enemy, is poorly equipped. "I would say the Afghans are probably
able to navigate around their own country without any help from GPS,"
Gibbons says. But then, again, no one's sure how well equipped Osama bin
Laden's terrorist camps are.

And presumably, if the military can selectively deny GPS signals over
Afghanistan and Central Asia, it could, in the worst of emergencies, do the
same thing over the U.S. if it had to, though not without severe consequences.
Let's hope it won't come to that.

Link to Interagency GPS Executive Board

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