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Schriever Sentinel

Air Force upgrades GPS constellation

The Global Positioning System IIF satellite, developed and built by Boeing, is the next generation of GPS space vehicle. (U.S. Air Force graphic)

The Global Positioning System IIF satellite, developed and built by Boeing, is the next generation of GPS space vehicle. (U.S. Air Force graphic)

By Scott Prater

Schriever Sentinel

The 2nd and 19th Space Operations Squadron will soon take control of the Air Force’s newest GPS satellite following its tentative launch into orbit May 27 from Cape Canaveral Air Force Station, Fla.

The GPS IIF SV-1 satellite represents a substantial upgrade for the GPS constellation. Thanks to improvements with the cesium-based atomic clocks used for timing, the IIF is expected to provide more accurate navigation signals than those of its predecessors.

The new IIF satellite will also broadcast two new signals: a jam resistant military code signal and a third civil signal known as the L5.

This latest addition is part of an ongoing modernization effort for the GPS constellation by the Air Force.

“We’re continuously replacing satellites in the constellation to ensure GPS remains the world’s gold standard for position, timing, and navigation,” said Lt. Col. Mike Manor, 2nd SOPS’ director of operations. “The GPS constellation is made up of 24 slots in space surrounding the earth where we place our satellites. This slot scheme and satellite placement ensures GPS users receive the most accurate navigation data at any time, at any place around the entire globe.”

With the addition of the IIF SV-1, the GPS constellation consists of 31 operational satellites. The idea is to keep newer satellites covering the primary slots. As the older satellites age, the Air Force will move them out of the constellation and replace those primary slots with new vehicles.

“In a way it’s a constant transition as we continue to field newer and more capable vehicles,” Colonel Manor said.

That constant transition into newer, more technologically advanced satellites has allowed the GPS wing, 2nd SOPS and 19th SOPS to exceed the required accuracy performance for GPS.

“We are exceeding the required sub-6 meters at 98 percent accuracy standard,” Colonel Manor said. “We advertise that we are sub-3 meters on average, which is the most accurate GPS signal in the history of the program… so we’re crushing the sub-6 meter requirement for our global users.”

It’s important to note the system’s improving performance because military and civilian users world-wide have come to rely heavily on GPS.

Not since the invention of the radio has a free utility affected so many people on such a wide and varied scale. Although GPS service was initially designed and used for a military purpose, its civilian uses and popularity have brought the Air Force into an increasingly public arena.

GPS satellites provide combat capability for military applications, as well as ground vehicle and aircraft navigation aids. Civilians also use GPS as timing and navigation aids, plus they rely on GPS for power-grid management, banking, stock market transactions and cell-phone service.

The drawback comes when entities experience problems with GPS.

With so many people and organizations relying on the service these satellites provide, the Air Force and GPS organizations become prime targets when problems arise with GPS.

This past January, news reports surfaced concerning a problem with a new military-use GPS receiver manufactured by a private contractor.

“There is a tendency to immediately identify the satellite or the broadcasted navigational signal as being at fault,” Colonel Manor said. “But, we monitor our satellites and their signals 24 hours a day, seven days a week. We have a crew position specifically identified, our payload system operator, to monitor the performance of the signal globally to ensure it’s of highest quality. If there is an issue with a satellite or the broadcast signal, we take immediate actions to rectify the problem.”

The GPS Operations Center receives 75 to 100 requests each week for various levels of support. Its primary mission is to support military users, providing them with information to take full advantage of the modernized utility of the GPS signal.

“Any time a civil user of GPS reports a loss of GPS signal, we provide a current status of the GPS constellation and provide additional information to help them determine the cause of their outage,” said 1st Lt. Caitlyn Diffley, 2nd SOPS payload systems operator. “The vast majority of the time, I’d say 99 percent, the outage is related to some issue with the receiver unit, such as software glitches or installation issues.”

Colonel Manor said in this most recent case, the issue involved a decryption problem with a specific vendor, which affected a specific military-use receiver.

He described the issue as something similar to the way a computer experiences slower processing speed when a user opens too many applications at one time.

“If you have a lot of applications open and you try to open a high-megabit power-point document for example, your computer may get bogged down — and that’s what happened with this contractor’s receiver. Its ability to process or decrypt the new signal causes it to bog down, and by the time it is able to decrypt, it loses its link with the broadcasted signal,” he said.

This specific problem was fixed within six weeks.

Through a partnership, the GPS wing, 2nd SOPS, 19th SOPS, the 50th Space Wing and the Air Force developed a solution through what is known as an iKey. Basically, the receiver is instructed to recognize the new signal as an old one.

Military and warfighter operations were not affected during the receiver’s down time, and redundant systems and work arounds allowed the military to operate with GPS at all times.

The most recent launch of the new IIF satellite represents the first of 12 IIFs scheduled for launch in the next few years.

After a three to four month checkout of the new satellite, the vehicle will enter the operational constellation and begin broadcasting its navigation signal to users. The next IIF launch is anticipated for November of this year.

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