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Gazette Premium Content Intricate satellite maneuvers improve GPS accuracy for troops

TOM ROEDER Updated: January 28, 2011 at 12:00 am

Airmen at Schriever Air Force Base this spring will finish a project to make the navigation system that guides everything from rent-a-cars to one-ton bombs more accurate.

The fix itself seems simple: Move navigation satellites a little farther apart to cover more of the globe.

In practice, it’s months of work and millions of math problems to initiate dozens of small moves in space.

“One of the concerns with GPS is when you’re moving those satellites around, you can create gaps in coverage,” explained Micah Walter-Range, a research analyst with the Colorado Springs-based Space Foundation.

The average Global Positioning System user won’t notice a change. The system of 31 satellites has always been accurate enough to tell you when you’ve missed a freeway exit or passed grandma’s driveway.

But in some places — tightly-packed urban areas and the canyon-cluttered landscape of Afghanistan — it could make a big difference.

GPS is arguably the most popular thing the Air Force has ever done. Invented as a top-secret navigation system for the military using signals from space to triangulate position, it’s now available on most smart phones.

“We have more than one billion customers,” said Col. Wayne Monteith, commander of Schriever’s 50th Space Wing, which oversees the GPS constellation.

The first GPS satellite rocketed into orbit in 1978. The machines are clocks that send timing signals 12,600 miles to earth with radio waves.

The timing signal lets users on the ground know how far they are from the satellite. Knowing the distance to three or more of the satellites allows users to triangulate their location on Earth using fairly simple geometry.

Over time, a wide range of industries found other uses for the signals. Accurate to the millionth of a second, GPS allowed the creation of automated teller machines and electronic stock trades. The GPS signal is also used to time the millions of pieces of data flying through wires on computer networks.

But GPS has always had an Achilles heel: It loses accuracy and can even fail in canyons like the ones in Afghanistan or in the urban canyons of big cities where skyscrapers take the place of mountains.

The best way to tackle the canyon problem is to make sure there are plenty of navigation satellites overhead at any one time.

Allowing users to “see” more satellites with their receivers is the goal of the latest GPS initiative started Jan. 13, 2010, when airmen at the 50th’s 2nd Space Operations Squadron began maneuvers to reposition three of the navigation satellites. One of the satellites took 351 days to reach its new orbit and the moves weren’t finished until earlier this month.

In August, the Air Force began moving another three GPS satellites, moves that will be finished in June.

“When complete, the constellation will attain the most optimal geometry in its 42-year-history, maximizing GPS coverage for all users,” Air Force Space Command wrote in a news release.

Per K. Enge, a Stanford University engineering professor who studies GPS accuracy, said the big change will mostly go unnoticed on the ground. But when compiled with other initiatives in recent years to improve GPS, including the launch of a new generation of satellites, all the small changes add up.

“It helps a lot,” said Enge.

It could help most in Afghanistan, where troops need the accuracy to target Taliban fighters with high-tech weapons in a tortured landscape Montieth called “terrain challenged.”

“All that terrain does a great job of blocking the GPS signal,” explained Walter-Range.

When the space maneuvering is complete, though, the military will have more satellites directly overhead, beating the canyon challenge, he said.

While the accomplishment will be felt worldwide, the folks at the 50th are nonchalant about what they’ve done.

“It’s what we do every day,” Monteith said.


Call the writer: 636-0240

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