Is Time Up For Europe’s GPS Satellites?

Atomic clocks are failing at an alarming rate in a network of global positioning satellites over Europe.

Accurate time is crucial to a GPS system because a receiver sets location by measuring the delay between signals from at least four satellites.

To maintain the integrity of the system, each satellite in the European Galileo network has four clocks – two hydrogen maser clocks accurate to a billionth of a second and two rubidium clocks.

But with 18 satellites in orbit with a total of 72 clocks, nine are not working. Six are hydrogen maser clocks and the rest are rubidium.

The European Space Agency confirms all the satellites are in working order, even though one is down to two working clocks.

Why the clocks don’t work

Not only are scientists worried about why the clocks are not working, but another issue is the short time they have been in space.

Galileo is only a part-network and is waiting for six more satellites to launch to complete the configuration and the current satellites were only judged good to go in December 2016.

Worryingly, Galileo has the same clocks as the Indian GPS network, which is yet to report any problems.

The ESA says the rubidium clock failures “seem to have a consistent signature, linked to probable short circuits, and possibly a particular test procedure performed on the ground”.

The team also hinted the hydrogen clocks did not restart properly after a prolonged time switched off.

Launch dilemma

The ESA comments and Indian experience would seem to point at issues with the way Galileo is managed may be the cause of the problems.

To avoid repeating the problems, the ESA is altering operating procedures and redesigning clocks destined for future launches.

ESA director general Professor Jan Woerner said: “Everyone is asking if we should postpone the next launch until we find the root cause, or should we launch?

“You can give both answers at the same time. You can say we wait until we find the solution but that means if more clocks fail we will reduce the capability of Galileo. But if we launch we will at least maintain if not increase the capability, but we may then take the risk that a systematic problem is not considered. We are right now in this discussion about what to do.”

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