Galileo’s failed clocks latest hurdle to overcome

Nine high precision clocks on board Europe’s Galileo satellites – vital for the necessary synchronisation of critical satellite navigation technology – have failed, according to a space agency chief.

Watch the ESA briefing (watch 12:40s and 56:20s)

ESA director general Jan Woerner, speaking to journalists in Paris, said the failure of the clocks on board five of the 18 navigation satellites it has already launched for the Galileo global navigation satellite system was ‘a sensitive issue’.

Three of the failed clocks are the more technically mature rubidium type – six are hydrogen maser instruments – that were designed to give Galileo superior performance to the American GPS network, enabling more resilient time synchronisation of industrial networks.

“Unfortunately we have right now the situation that we have failed rubidium clocks as well as failed hydrogen maser clocks – nine in total,” Woerner said. “We don’t know whether we can revitalise them, it’s much too early for that.”

The first four Galileo satellites launched in the current fleet were designed as In-Orbit Validation, or IOV, testbeds and delivered to orbit on two Soyuz rocket flights from French Guiana in 2011 and 2012. They were subsequently transitioned into the active constellation.
Fourteen more Full Operational Capability, or FOC, satellites have been added to the fleet by Soyuz and Ariane 5 rockets since 2014. The FOC spacecraft were built by OHB in Bremen, Germany, with navigation payloads provided by Surrey Satellite Technology of the United Kingdom. Three of the rubidium clocks have failed, all on the more recent FOC model satellites, according to the European Space Agency, which acts as a technical contractor and procurement agent for the Galileo programme on behalf of the European Commission. Six passive hydrogen maser clocks have also failed in the last two years, five of which were on the earlier-generation IOV test satellites now incorporated into the operational Galileo fleet.

While all 18 satellites launched to date are working Woerner said two faulty clocks were on one single satellite although its operational ability had not been affected, adding that each satellite within the eventual constellation of 30 satellites needs only one working clock for the system to function.

“However, we are not blind … If this failure has some systematic reason we have to be careful not to place more flawed clocks in space,” he said.

“Everybody is raising this question: should we postpone the next launch until we find the root cause, or should we launch?” Woerner said. “We have to look into… whether we find finally some systematic root cause and to change it, or whether we have to just go on and rely on the backup clocks.”

“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.”

The next four satellites are due to launch in the second half of this year. The full constellation foresees another 12 satellites being launched between now and 2020, when Galileo will become fully operational.

“These failures are better understood, linked to two apparent causes,” ESA said in a subsequent January 19 statement. “One is a low margin on a particular parameter that leads, on some units, to a failure. The second is related to the fact that when some healthy PHM clocks are turned off for long periods, they do not restart because of a change in clock characteristics in orbit.”


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