Impacts of the Global Positioning System

     The Global Positioning System (GPS), in operation since January 6, 1980, was designed to broadcast date and satellite identification information used to determine the position of the receiver on the ground. The position of the receiver is extrapolated from the timestamp of the received signal from each of satellites that are within view of the receiver. Once the receiver knows its exact distance from at least four satellites, it can use geometry to determine its location on earth in three dimensions. As you can see, the time stamp of the signal from the satellite provides critical information for determining your location.

By United States Government

A GPS Block IIR(M) satellite.

     There is a reason an article about GPS, which many of us use regularly, is necessary at this time. In the original design of the system, a week number was included as part of the time stamp to reduce the size of the information packet from the satellite. This was done to improve the overall performance of the system. The week number was set up as a 10-bit binary number, forcing it to roll over back to zero at the end of 1,024 weeks. This happened the first time on Aug. 21, 1999, and there was minimal impact to the system. This roll-over will happen again on April 6, 2019.

     Most of the GPS receiver manufacturers understand what the roll-over means and have software verification code in place to insure that the date remains correct and the equipment can operate without issues. However, if equipment is not running a proper version of the software when the week rolls over on April 6, unpatched GPS receivers will roll back in time to August 21, 1999. This is not expected to be a problem for newer GPS receivers, but older units may experience very unexpected behavior.

     You might be wondering what the impact of a failed time stamp roll-over would be. There is a slight possibility of major impacts to the electrical grid as a result of the inaccurate time information coming from the satellites. How does GPS affect our stationary electric grid? It may seem odd, but the grid depends heavily on GPS for time synchronization of all the control systems in order to keep all the critical components of the system in sync. Currently these systems rely entirely on the timestamp signals from the GPS system that identifies the current week and second within the week. The signal is then converted to a proper date by the receiver. 

     Essentially what is going to happen on April 6 is a reset that will cause the satellites to send a signal of week 0, which is the week beginning August 21, 1999, instead of Week 1025, April 6, 2019. The receivers are responsible for making the adjustment. The electric grid uses these time signals as part of the Phasor Measurement Units and the North American Electric Reliablity Corporations’ (NERC) requirements use these Syncophasers, along with the GPS systems to get real-time snapshots of grid performance to adjust the power levels at the power plants in real-time to create a more stable electric grid. These changes in technology have greatly increased the chances of the GPS rollover event impacting our electric grid.

     Operators of these mission critical systems have been notified of the forth-coming event and been given guidelines to circumvent any problems. Notifications were sent January 25 to all power companies, airline industries, and other critical use industries.

     If you have an older model GPS receiver, now is the time to call your manufacturer and find out if you need to perform a software update, or you might just travel back in time to 1999 on Saturday.