In an update to our July 2 story (recapped below), correspondent Peter de Selding wrote in Space News on July 3 that the trouble aboard the fourth in-orbit (IOV) Galileo satellite arose from a sudden, unexpected loss of power. The power outage flashed on May 27, shutting down the satellite’s E1 signal. The signal “re-established itself almost immediately. But as soon as it was back in service, the two other channels’ power dropped and did not recover. The full satellite then was shut down by ground teams,” reported de Selding.
European Space Agency (ESA) officials stated on July 3 that they would power-on the satellite again sometime this week (July 7–11) to continue investigating the problem. That investigation has been ongoing since the shutdown but has not identified a cause; officials state they have established that it is not related to the onboard atomic clocks.
The four IOV satellites currently aloft differ in both technology and manufacturer from the next phase of Galileo satellites to be launched. Two of these newer generation are at the Guyana spaceport awaiting a possible late August lift date.
July 2 GPS World story:
Galileo GSAT0104, the fourth in-orbit validation (IOV) satellite, has been set “unavailable until further notice” according to the European GNSS Service Centre. International observers (not associated with the European Space Agency, ESA) including those of the International GNSS Service tracking the satellite have not detected a signal from GSAT0104 since May 27. A constellation update appeared June 26 at www.gsc-europa.eu/system-status/Constellation-Information, and is reproduced here.
Speculation by unofficial sources is mounting that something is wrong with the satellite, in particular with its passive hydrogen maser, used for timing the signal for synchronous transmission with other Galileo satellites. The hydrogen maser has “a known problem” according to one source. This is why the web site shows GSAT0104, also known as FM04 and E20, as currently using a rubidium atomic frequency standard.
No statement has been made by the ESA.
According to reports, the root cause of the outage is under investigation. Some unofficial sources have gone so far as to speculate that GSAT0104’s useful transmission life may be over.
The setting of unavailability may be due to in-orbit validation testing, as the website implies may be the case, but no further official statement has appeared. On May 27, an active user notifications (NAGU) appeared at www.gsc-europa.eu/system-status/user-notifications regarding GSAT0104 stating ” Unavailable from 2014-05-27 until further notice.” On June 26, another NAGU appeared for “All” satellites and stating “potential performance degradation.” A footnote states “The Galileo system is undergoing its in-orbit validation campaign. During this campaign of tests, users may experience periods of signal degradation.”
According to the ESA website, “The Galileo satellites carry two types of clocks: rubidium atomic frequency standards and passive hydrogen masers. The stability of the rubidium clock is so good that it would lose only three seconds in one million years, while the passive hydrogen maser is even more stable and it would lose only one second in three million years. However this kind of stability is really needed, since an error of only a few nanoseconds (billionths of a second) on the Galileo measurements would produce a positioning error of metres which would not be acceptable.”
Tim Reynolds is director of Inta Communication Ltd. and a long-term Brussels observer writing on many aspects of European government policy and implementation for a range of clients and publications. He is the contributing editor for GPS World’s new quarterly e-newsletter, EAGER: the European GNSS and Earth Observation Report. Subscribe free at www.gpsworld.com/subscribe.