In an unprecedented total disruption of a fully operational GNSS constellation, all satellites in the Russian GLONASS broadcast corrupt information for 11 hours, from just past midnight until noon Russian time (UTC+4), on April 2 (or 5 p.m. on April 1 to 4 a.m. April 2, U.S. Eastern time). This rendered the system completely unusable to all worldwide GLONASS receivers. Full and correct service has now been restored.
“Bad ephemerides were uploaded to satellites. Those bad ephemerides became active at 1:00 am Moscow time,” reported one knowledgeable source. For every GNSS in orbit, the navigation messages include ephemeris data, used to calculate the position of each satellite in orbit, and information about the time and status of the entire satellite constellation (almanac); this data is processed by user receivers on the ground to compute their precise position.
According to another source, a GLONASS fix could not take effect until each satellite in turn passed back over control stations in the Northern Hemisphere to be reset, thus taking nearly 12 hours.
During the outage, CEO Neil Vancans of Altus Positioning Systems reported “We are currently experiencing calls from customers all over the world who are experiencing GLONASS ‘outages’ and we have advised customers to switch GLONASS tracking off on our receivers. We don’t have any better information on when normal service is likely to resume from GLONASS satellites. If you do, let me know!”
Such a — possibly human, possibly computer-generated — error could conceivably occur with GPS, Galileo, or BeiDou. “Another reason to have backups,” mused Richard Langley of the University of New Brunswick. “And not just other GNSS.”
A recent plot shows all satellites restored to normal service: