During the European Space Agency (ESA) audio press conference held Wednesday morning in advance of Thursday’s launch of two Galileo satellites, there was extended discussion on the problem with the fourth in-orbit validation or IOV satellite (FM4 or GSAT0104 with PRN code E20). The satellite suffered a power anomaly on May 27 as previously reported by GPS World.
The root cause of the problem has still not been identified despite looking at more than 40 possible failure scenarios so far. ESA has conducted extensive analyses of telemetry from the satellite as well as reviews of pre-launch tests. It has been determined, however, that the E5 and E6 frequencies have had a permanent loss of power. E1 appears to be OK and can be switched back into normal operation at any time. Currently, the satellite is transmitting on E1 but using a non-standard test code.
It was also revealed that FM2, the second IOV satellite, suffered a power drop of 2 dB about a year ago, and FM1, the first IOV satellite, has also seen a power drop. In the case of FM1, the problem is in the primary solid-state power amplifier, and there is a plan to switch shortly to the back-up unit. However, there doesn’t appear to be a common-mode of failure relating the power losses on the various satellites.
While the FM4 anomaly investigations are ongoing, the power on all of the IOV satellites has been backed off 1.5 dB.
Concerning the two full operational capability or FOC satellites to be launched tomorrow, ESA is not yet revealing into which orbit plane and slots the satellites will be placed. Nor are they saying yet which pseudorandom noise codes will be used by the satellites. Once the satellites are launched into their preliminary orbits, it will take about two weeks for them to drift to their assigned locations. At that time, we should be able to deduce their locations using, for example, United States Strategic Command (USSTRATCOM) tracking data. And once they begin transmitting standard PRN codes, all-in-view receivers, such as those participating in the International GNSS Service Multi-GNSS Experiment, will be able to identify their codes.
The satellites will undergo testing for 73 days, after which they will be declared operational. ESA intends to use the passive hydrogen maser clocks on the satellites as the primary clocks, with the rubidium clocks used as back-ups.