It is bound to happen: a while ago I wrote about the extremely accurate navigation possibilities that the Galileo satellite system will be able to offer. Now it appears that a number of the atomic clocks on board of a few of the satellites have given up the ghost – and that while extremely accurate timing and absolute requirement is for any navigation system.

At this moment, 18 Galileo satellites (of the 24 required) orbit the earth. Each satellite has four atomic clocks on board: two traditional rubidium clocks and two, more accurate, hydrogen-maser clocks. The latter would have ensured that the Galileo system has (much) better performance than the American GPS system. To give an idea: the hydrogen-maser clocks have an accuracy of one second in three million years – good enough for position measurement on the surface of the Earth of 1 meter or less, significantly better than the freely available (non-encrypted) American GPS system.

It now appears that nine clocks are not working any more: three rubidium and six hydrogen models. The system remains operational for the time being, but one satellite has only two functional clocks on board.

It appears that the problem with the rubidium clocks has been caused by a test procedure before launch. And for the hydrogen clocks, the suspicion is that after a long period of no use they are reluctant to start up again.