Graduate student Alessandro Cerruti, left, and Professor Paul Kintner work on the antenna on the roof of Phillips Hall. They have found that the kinds of large solar flares expected in five years or so could produce massive outages of all GPS receivers on the day side of the Earth.

Strong solar flares cause Global Positioning System (GPS) receivers to fail, Cornell researchers have discovered. Because solar flares -- larger-than-normal radiation "burps" by the sun -- are generally unpredictable, such failures could be devastating for "safety-of-life" GPS operations -- such as navigating passenger jets, stabilizing floating oil rigs and locating mobile phone distress calls.

"If you're driving to the beach using your car's navigation system, you'll be OK. If you're on a commercial airplane in zero visibility weather, maybe not," said Paul Kintner Jr., professor of electrical and computer engineering at Cornell and head of Cornell's GPS Laboratory.

Kintner told that solar flares are accompanied by solar radio bursts. Because the bursts occur over the same frequency bands at which GPS satellites transmit, receivers can become confused, leading to a loss of signal.

The Sep 2005 flare consisted of two events about 40 minutes apart: The first lasted 70 seconds and caused a 40 percent signal drop; the second lasted 15 minutes and caused a 50 percent drop. But this flare was moderate and short-lived; in 2011 and 2012, during the next solar maximum, flares are expected to be 10 times as intense and last much longer, causing signal drops of over 90 percent for several hours.

"Soon the FAA will require that every plane have a GPS receiver transmitting its position to air traffic controllers on the ground," warned Cerruti. "But suppose one day you are on an aircraft and a solar radio burst occurs. There's an outage, and the GPS receiver cannot produce a location. ... It's a nightmare situation. But now that we know the burst's severity, we might be able to mitigate the problem."

The only solutions, suggested Kintner, are to equip receivers with weak signal-tracking algorithms or to increase the signal power from the satellites. Unfortunately, the former requires additional compromises to receiver design, and the latter requires a new satellite design that neither exists nor is planned.

"I think the best remedy is to be aware of the problem and operate GPS systems with the knowledge that they may fail during a solar flare," Kintner said.

Graduate student Alessandro Cerruti accidentally made this discovery because the solar flare happened in the day time. Had the solar flare occurred at night in Puerto Rico where he was working or had Cerruti been working at night, he would not have made the discovery.