Galileo: A Constellation of One? - GPS World

Galileo: A Constellation of One?

October 29, 2014  - By
Image: GPS World

Matters sit not well with Galileo, the European GNSS. Only one of six currently orbiting satellites can be said to be truly and fully operational. With these troubles augmented by persistent uncertainties regarding the fitness of Soyuz rockets, despite a recent inquiry panel that identified a root cause of the August launch failure, the European Commission has nixed an upcoming December launch. The European Space Agency will have to wait until February 2015 to see if the skies clear by then for the next opportunity to place two new satellites into orbit.

Hard-charging veteran investigative reporter Richard Langley has learned from his eastern listening post in New Brunswick that “E11 and E12 [launched three years ago] exhibit ongoing problems with the onboard clocks. E20 [launched two years ago] has experienced power-supply problems and, following a brief outage, is now broadcasting on E1 only and with a reduced power. The latest two satellites [rose August 22 of this year] are in irregular orbits and will likely not form part of the final constellation. This leaves E19 [born October 12, 2012] as the only fully operational satellite operating within specifications.

“So, strictly speaking, only one of the currently orbiting satellites is fully operational. However, for most (E1/L1-only, single-point) users, four of the six satellites are currently quite useable. Moreover, preliminary studies suggest that, once on line, the latest two satellites will be perfectly usable, despite the irregular orbits. And, as we have heard, there will be attempts to make the orbits somewhat more circular.”

Langley cites “knowledgeable researchers” as his sources.

The initial quartet of in-orbit validation (IOV) satellites — E11, E12, E19, and E20 — constructed by Astrium GmbH and Thales Alenia Space have experienced a range of difficulties outlined above. The decision to cancel the next scheduled launch in December of the newest duo of full operational capability (FOC) satellites, manufactured by a consortium led by OHB AG, comes on the heels of a completed inquiry that blamed a “design ambiguity” of the Soyuz rocket’s Fregat stage for the too-low orbits of Satellites 5 and 6, but left several lingering doubts about other Soyuz issues that were uncovered and must be corrected.

The situation is complicated by further unresolved issues aboard the two FOC satellites themselves.  They each failed to deploy one of their two solar arrays on the first try. After several days of effort and re-orientation of the satellites by ground controllers, the arrays were successfully unfolded, but the cause of the initial failure remains unknown. “There is no conclusion on a root cause,” stated one official. “Was it a consequence of the bad orbit, or is there an issue with the solar array deployment mechanism? We cannot yet say for sure.”

As for their incorrect orbit, getting them into their originally planned paths around the Earth is impossible. They simply do not have enough fuel onboard. ESA does, however, plan to raise the perigees of the satellites to get them out of the Van Allen radiation belt, which could severely damage the satellites. The agency also envisions reducing the maximum Doppler frequency shift from 9.6 kHz to at least 6.8 kHz to allow receivers to easily acquire and track the satellites but leave enough hydrazine for future station-keeping. Spokespersons hold out hope that the satellites may yet be usable somehow, someday, after some adjustment measures are taken: a rephasing, a special almanac, perhaps other adjustments.

Overall, a disheartening picture, with some pessimists concluding that “2013 and 2014 have been lost.” The recent slip of full operational capability declaration from 2018 to 2020 may have to be revised yet again. However, lessons learned, etcetera. Galileo has had its ups and down. Advocates may draw comfort from the wisdom imparted by 19th-century German philosopher Friedrich Wilhelm Nietzsche, “Was mich nicht umbringt, macht mich stärker.” That which does not destroy me, makes me stronger.

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About the Author: Alan Cameron

Alan Cameron is the former editor-at-large of GPS World magazine.