The cause for their concern, Johnson said, was an unexpected solar radio burst on Dec. 6 that affected virtually every GPS receiver on the lighted half of Earth. Some receivers had a reduction in accuracy while others completely lost the ability to determine position, he said.
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And protecting the system is no simple task, added Paul M. Kintner Jr., a professor of electrical engineering at Cornell University, who monitored the December event. There are two possible ways to shield the system, he said, both very expensive. Either alter all GPS antennas to screen out solar signals or replace all of the GPS satellites with ones that broadcast a stronger signal.

That’s why it’s essential to learn more about the sun’s behavior quickly in an effort to find ways to predict such events, the researchers said. In addition to the GPS system, the December solar flare affected satellites and induced unexpected currents in the electrical grid, Johnson said.
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Dale E. Gary, chairman of the physics department of the New Jersey Institute of Technology, said the burst produced 10 times more radio noise than any burst previously recorded.