ESA Discusses Galileo Satellite Power Loss, Upcoming Launch
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.
About the Author: Richard B. Langley
Richard B. Langley is a professor in the Department of Geodesy and Geomatics Engineering at the University of New Brunswick (UNB) in Fredericton, Canada, where he has been teaching and conducting research since 1981. He has a B.Sc. in applied physics from the University of Waterloo and a Ph.D. in experimental space science from York University, Toronto. He spent two years at MIT as a postdoctoral fellow, researching geodetic applications of lunar laser ranging and VLBI. For work in VLBI, he shared two NASA Group Achievement Awards. Professor Langley has worked extensively with the Global Positioning System. He has been active in the development of GPS error models since the early 1980s and is a co-author of the venerable “Guide to GPS Positioning” and a columnist and contributing editor of GPS World magazine. His research team is currently working on a number of GPS-related projects, including the study of atmospheric effects on wide-area augmentation systems, the adaptation of techniques for spaceborne GPS, and the development of GPS-based systems for machine control and deformation monitoring. Professor Langley is a collaborator in UNB’s Canadian High Arctic Ionospheric Network project and is the principal investigator for the GPS instrument on the Canadian CASSIOPE research satellite now in orbit. Professor Langley is a fellow of The Institute of Navigation (ION), the Royal Institute of Navigation, and the International Association of Geodesy. He shared the ION 2003 Burka Award with Don Kim and received the ION’s Johannes Kepler Award in 2007.
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