PARIS – Ten atomic clocks have failed onboard the European Union’s Galileo navigation satellites, casting doubt on when the unfinished constellation’s next batch of spacecraft will be orbited.
European Space Agency Director-General Jan Woerner told reporters Jan. 18 that the agency has not decided whether to go ahead as planned with an Ariane 5 launch in August of the next batch of four Galileo spacecraft. The launch is one of two scheduled over the next two years to complete the constellation of 26 needed to give Europe’s GPS alternative global coverage.
“We have to find some systematic root cause, or go on [launching] and say, ‘OK, there might be some failures’,” Woerner, said during the agency’s annual briefing at its headquarters here. “Should we not launch until [we have] solved the problem? We are right now in this discussion as to what to do.”
In a statement released after the briefing, ESA said that it was committed to launching the next four satellites before the end of the year. Galileo’s launch service provider, Arianespace of Evry, France, has said it expects to conduct eight Ariane 5 campaigns this year — one more than it squeezed into 2016.
Galileo’s rash of atomic clock failures have involved both types of clocks aboard the 18 Galileo satellites launched to date. Three of the clocks that failed were rubidium atomic frequency clocks and seven were newer, more-precise passive hydrogen maser clocks, one of which has since restarted. Swiss firm Spectratime produces both clocks, but the company declined to comment.
ESA said in its statement that while investigations continue, the 22-nation space agency and its industrial partners have agreed “that some refurbishment is required on the remaining [rubidium] clocks still to be launched on the eight Galileo satellites currently being constructed or tested.
“A plan to refurbish the remaining [hydrogen maser] clocks still to be launched is currently being finalised,” the statement said.
So far, the clock failures have yet to sideline any of the in-orbit Galileo satellites, which are equipped with two of each kind of clock for redundancy.
ESA’s post-briefing statement said that, “in recent months a total of three [rubidium] clocks have undergone unexpected failure on Galileo satellites — all on Full Operational Capability (FOC) satellites, the latest Galileo model.” The agency thinks short circuits caused the failures. One FOC satellite suffered a hydrogen maser clock failure. The 14 operational FOC satellites launched since August 2014 were built by OHB System AG of Bremen, Germany, which referred all questions about the failures to ESA.