On Monday, December 14, the EU’s Galileo program posted an official notice advising users that Galileo service was degraded on all satellites until further notice. Nominal service was then resumed about six hours later.
A subsequent communication posted on the European GNSS Service Centre said Galileo service had been affected, “by an anomaly in the time determination function of the ground segment of the system.”
The communication went on: “This resulted in signals flagged as MARGINAL (SISA=NAPA) for all satellites. During this period, pseudorange errors in excess of nominal performance were experienced by user receivers.
“The system was reconfigured and restored to a nominal situation as of Dec 14, 06:00 UTC. A NAGU [NOTICE ADVISORY TO GALILEO USERS] will be published shortly with the exact chronology of the event. Further communication will be published as the investigation on the root cause for the event and its effect on the service progresses.”
Many users will recall the events of July 2019, when Galileo service went down for several days without explanation. That event was eventually attributed to a problem of the PTF (Precise Timing Facility) in Italy. The PTF is a ground station that generates the Galileo System Time, or GST. The GST is uploaded to the Galileo satellites to make the user localization possible, and it is also disseminated to every user as an accurate time reference. The Precise Timing Facility hosts several Cesium clocks and a Hydrogen Maser clock.
The technical incident itself was exacerbated by what many observers considered to be an inadequate response in terms of communication by the Galileo program towards its users. In the aftermath, the Galileo program undertook a series of measures aimed at preventing such events in the future. Today, users will be eagerly awaiting an official explanation of what happened on 14 December 2020.
NOTICE ADVISORY TO GALILEO USERS (NAGU) 2020021
DATE GENERATED (UTC): 2020-12-14 14:00
NAGU TYPE: GENERAL (NOTICE)
NAGU NUMBER: 2020021
NAGU SUBJECT: SERVICE DEGRADATION
NAGU REFERENCED TO: N/A
START DATE EVENT (UTC): 2020-12-14 00:00
END DATE EVENT (UTC): 2020-12-14 06:12
SATELLITE AFFECTED: ALL
EVENT DESCRIPTION: USERS HAVE EXPERIENCED A SERVICE DEGRADATION ON ALL GALILEO SATELLITES. SIGNALS DID NOT MEET THE MINIMUM PERFORMANCE LEVELS DEFINED IN THE GALILEO OPEN SERVICE DEFINITION DOCUMENT STARTING 2020.12.14 AT 00:00 UTC ENDING 2020.12.14 AT 06:12 UTC. ALL SATELLITES PROVIDING NOMINAL SIGNALS AS OF 2020.12.14 AT 06:55 UTC. NOMINAL SERVICE HAS BEEN RESUMED.