Know how to read a map? Industry prepares for April’s GPS Rollover event

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WASHINGTON—The Global Positioning System (GPS) is a global public service provided by the U.S. government. On April 6, 2019, there will be an event affecting the electric transmission and distribution system that has industry concerned about the potential for a major disruption.  During the Week Number rollover of the Global Positioning System (GPS), the week number that uses the 10-bit binary system will reach its limit of 1,024 weeks and will be forced to roll over and be reset to week 0.

US Air Force Space Systems Operations photoU.S. Air Force photo

DHS Memo
The U.S. Department of Homeland Security (DHS) has released a memorandum about this year’s GPS rollover event.The memorandum, 
U.S. Owners and Operators Using GPS to Obtain Time, is intended to provide an understanding of the possible effects of the April 6, 2019, GPS Week Number Rollover on Coordinated Universal Time (UTC) derived from GPS devices. DHS recommends critical infrastructure (CI), other owners, and operators prepare for the rollover.

Owners, operators, and technical teams should:

  • investigate and understand all possible dependencies on GPS for obtaining UTC
  • contact original equipment manufacturers (OEMs) and GPS manufacturers of devices currently in inventory (or backorder) used to obtain UTC
  • understand each manufacturers’ preparedness for this rollover
  • for continuity of operations, understand all actions required by CI, other owners, and operators to ensure proper operations through any rollover or possible service disruptions
  • ensure ALL firmware of such devices are patched correctly, tested, and up to date.

Marine Administrative Message
Marine Corps CIO, Brigadier General Lorna Mahlock (center)In January, the United States Marine Corps issued MARADMIN 059/19 advising Marine Corps Global Positioning System (GPS) users about the GPS week number rollover event that may affect GPS receiver operation. The Corps’ MARADMIN directed all Marine Corps GPS users to verify that all of their receivers are running software that will correctly increment the date through the week rollover, contact Marine Corps Tactical Systems Support Activity (MCTSSA) if necessary, or directly contact original equipment manufacturers (OEMs) when applicable. MARADMIN 059/19’s release was authorized by Brigadier General Lorna M. Mahlock (above, center), the Marine Corps’ CIO and Director, Command, Control, Communications, and Computers (C4).

The Power Grid
It may seem odd that the stationary electric grid relies so heavily on GPS, but in fact, GPS supports a wide variety of critical grid functions that allow separate components on the electric system to work in unison.  This is made possible because the GPS signal contains a running timestamp that identifies the current week and current second within that week, which is converted by the signal receiver to the proper date and time which we recognize as day, month, year, and time of day.

For our Coders, Geeks, and Nerds
The initial week 0 started on January 6, 1980, and the first week rollover occurred a few months before “Y2K” on August 21, 1999.  However, a lot has changed on the electric grid since the last rollover such as the addition of Phasor Measurement Units (PMUs) and the North American Electric Reliability Corporation’s (NERC) requirements of synchronizing sequence of event, fault, and dynamic disturbance recording. Synchrophasors, which use systems of phasor measurement units (PMUs) to measure data and time-synchronize it using GPS satellites, provide system operators with a near real-time snapshot of the grid’s operating status.  These changes to grid technology and functions have brought tremendous new insights to manage and assess the bulk power system, but they also open the door to a concern in the industry that the GPS week rollover could impact an operator’s ability to accurately assess grid reliability conditions in real-time.

Updating GPS firmware and patching GPS software
Similar to the MARADMIN cited above, the good news across industry is many signal receiver manufacturers understand the rollover very well and already have prepared for it.  As a result, most of our equipment should operate without any issues on April 6, 2019.  However, now is the time to make sure that all equipment in the field or vehicles in the fleet have received the proper firmware updates.  Operators also must be taking extra care to address core components where any prolonged GPS outages would significantly have negative impacts on systems.

Original article written by Michael Pesin, DOE’s Office of Electricity
— Sources:, and
Images: U.S Air Force, Ford, NASA, and US. Marine Corps


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