3 ms·

You clearly haven't read the rest of the article. It's not even especially far down that it's mentioned that the accumulated error for the orbital calculations

You clearly haven't read the rest of the article. It's not even especially far down that it's mentioned that the accumulated error for the orbital calculations has resulted in errors for satellite positions into hundreds or thousands of meters after a few days. They made the time fields short because the information would have no value on timescales larger than that.

Animats 7y ago
The problem is that the time field apparently wraps in a week. Can receivers then tell the data is totally wrong?
- MrBuddyCasino 7y ago
  Thats what the status bits are for. That they didn't set them to 1 on the full constellation suggests there may have been some trouble they didn't publicize.
  - makomk 7y ago
    The status bit that was set is supposed to mean "working without guarantee" - that is, the satellite may not meet the normal minimum performance level but is still in service. This specific combination of status bits corresponds to a status of "marginal", between full health and actually out of service. In order to actually mark the satellites as fully out of service they'd need to either replace the navigation data with dummy values or upload new navigation data with some additional status bits set. The whole thing seems a little odd. Even the original 80s GPS satellites could automatically update their ephemeris data with stored predictions for 14 to 60 days after the last contact from the ground segment (with a gradual decrease in the signalled accuracy over time), after which time I believe they would switch to invalid dummy data. The current generation can compute their own ephemeris updates at almost full accuracy for months if the ground segment fails. I have to wonder how Galileo ended up transmitting such stale data that ground-based recievers ended up mistaking it for next week's data and still marked it as basically valid. That seems like quite an oversight.

Animats 7y ago

The problem is that the time field apparently wraps in a week. Can receivers then tell the data is totally wrong?

MrBuddyCasino 7y ago
Thats what the status bits are for. That they didn't set them to 1 on the full constellation suggests there may have been some trouble they didn't publicize.
- makomk 7y ago
  The status bit that was set is supposed to mean "working without guarantee" - that is, the satellite may not meet the normal minimum performance level but is still in service. This specific combination of status bits corresponds to a status of "marginal", between full health and actually out of service. In order to actually mark the satellites as fully out of service they'd need to either replace the navigation data with dummy values or upload new navigation data with some additional status bits set. The whole thing seems a little odd. Even the original 80s GPS satellites could automatically update their ephemeris data with stored predictions for 14 to 60 days after the last contact from the ground segment (with a gradual decrease in the signalled accuracy over time), after which time I believe they would switch to invalid dummy data. The current generation can compute their own ephemeris updates at almost full accuracy for months if the ground segment fails. I have to wonder how Galileo ended up transmitting such stale data that ground-based recievers ended up mistaking it for next week's data and still marked it as basically valid. That seems like quite an oversight.