Power Loss Created Trouble Aboard Galileo GNSS Satellite

As reported by GPSWorld: 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.

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 E2, as currently using a rubidium atomic frequency standard.

European Space Agency (ESA) officials further 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 on-board 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-off date.