What happened to GALILEO - GNSS programmer version

Since the speculation has already begun that Spectrum-WP has attacked GALILEO , I would like to state my version of events.


Spectrum-WG was launched on July 13, 2019 at 15:31 Moscow time. The problems with GALILEO became known on July 11, 2019 14:45 UTC (17:45 Moscow time):

UNTIL FURTHER NOTICE, USERS MAY EXPERIENCE SERVICE DEGRADATION ON ALL GALILEO SATELLITES. THIS MEANS THAT THE SIGNALS MAY NOT BE AVAILABLE NOR MEET THE MINIMUM PERFORMANCE LEVELS DEFINED IN THE SERVICE DEFINITION DOCUMENTS AND SHOULD BE EMPLOYED AT USERS' OWN RISK. THE NOMINAL SERVICE WILL BE RESUMED AS SOON AS POSSIBLE.

July 12 - cessation of work. The last valid ephemeris taken was from around 20:00 UTC on July 11th.
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July 13, 2019 at 20:15 UTC (23:15 Moscow time) repeated message:

UNTIL FURTHER NOTICE, USERS EXPERIENCE A SERVICE OUTAGE. THE SIGNALS ARE NOT TO BE USED.


Now what happened. The point in the bookmark ephemeris, which produces the command segment. Normal work looks like this. The command segment measures the orbits of the satellites and regularly updates the orbits to the satellite. In between the tabs, the satellites recalculate the ephemeris data themselves.

GPS is a military system, it is designed to destroy the command segment and work up to six months without a link with the command segment. If anyone is interested, this is described in Section 6.3.2 of the ICD . Moreover, in this case, the new satellites provide an independent definition of ephemeris by inter-satellite measurements (this is 6.3.5 in the ICD). As a result, there is information in the transmitted data in case of a long work without updating the ephemeris, and GNSS receivers can (or rather should be able to) work in this situation.

GALILEO - the system, alas, civil. If we look at ICD GALILEO, nothing is provided there for working without a command segment. But - this is a high-precision system. For example, to increase accuracy, satellites recalculate the F / NAV ephemeris every 10 minutes, rather than every 2 hours, as in GPS.

So, the sequence of events from my bell tower.

• Around July 10 - failure hours on the command (ground) segment. Bookmark ephemeris on satellites stopped.
• July 11, 14:45 UTC - it becomes clear that they will not be able to recover quickly, issues a warning about degradation.
• July 11 evening - the satellites see that when recalculating the ephemeris, the accuracy decreases and the state of Working without guarantee set in the DVS field (ICD table 7.1), which indicates the incorrectness or inaccuracy of the ephemeris. Unfortunately, most receivers are designed to display this flag in 1-2 satellites. That is, the reaction of the receiver - to exclude such a satellite from the calculation.
• July 12 night - disconnecting GALILEO for residential consumers. Those who have their own code for the navigation solution can read further, simply by ignoring DVS in the code.
• July 13, 20:15 UTC - repeated NAGU about complete system shutdown
• July 17 morning - the laying of the ephemeris began. Apparently, in honor of this, an official message was issued that everyone is working tirelessly (24/7) on restoration.
• July 17 evening - on those satellites that I see - ephemeris laid. Apparently in the morning an official notice of the restoration of workability is expected. But, perhaps, he will be detained to achieve the desired accuracy. The fact is that the process is iterative - measurements are made using ordinary ephemeris, the measurement of high-precision orbits is done using the measurement residual, and the motion prediction is calculated using the measurement residual, which is included in the ephemeris.

The current official status of GALILEO is here .

PS If anyone is interested in doing conspiracy - I recommend reading this news until it is lost.

PPS GALILEO performance restored. Here is the NAGU , and here is the message . From the important: although some fluctuations may be experienced until further notice . This means that the full accuracy of the ephemeris data has not yet been reached. Approximately about 2 weeks accuracy will improve.

PPPS Add a link to the previous article on the same topic.

PPPPS Link to inside GNSS with information about the failure of the clock. It is alleged that two systems failed at the same time, as for me - this is doubtful. Most likely the systems diverged so that it was not clear which of them is correct. Or, in the process of synchronization, they confused which of them is correct and who is faulty. But here I am not a specialist at all.