The BBC has an interesting story on the Galileo navigation satellites:

The onboard atomic clocks that drive the satellite-navigation signals on Europe's Galileo network have been failing at an alarming rate.

Across the 18 satellites now in orbit, nine clocks have stopped operating.

Three are traditional rubidium devices; six are the more precise hydrogen maser instruments that were designed to give Galileo superior performance to the American GPS network.

Galileo was declared up and running in December.

For more on the story, see: http://www.bbc.com/news/science-environment-38664225

--- Zach N0ZGO