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Giove-B's first successful signal

Latest update : 2008-05-07

The second test satellite of European navigation system Galileo successfully sent its first signal to Earth with an accuracy never reached before. The first four operational satellites will be sent in 2010.

A second test satellite for Galileo, Europe's rival to the US Global Positioning System, is "in good health" despite a hiccup that emerged after it was placed in orbit last Sunday, the European Space Agency said on Wednesday.
The experimental Giove-B satellite, launched by a Russian Soyuz Rocket from the Baikonur cosmodrome in Kazakhstan, developed a problem with four gyroscope-like wheels designed to turn the spacecraft towards the Sun so that its solar arrays can power its battery.
As the so-called reaction wheels failed to respond fast enough, mission controllers used Giove-B's thrusters to turn the satellite around so that the arrays faced the Sun.
"The initial underperformance of the reaction wheels was found to have occurred due to a mismatch between the onboard avionics software and the reaction wheel calibration data," the agency (ESA) said in a press release.
"This has now been corrected by the uploading of a software patch to the spacecraft, resulting in nominal [normal] performance."
The satellite, a 500-kilogram (1,100-pound) cube constructed by Astrium and Thales Alenia Space, is to take over from the first test satellite Giove-A, launched in December 2005.
Giove-B is carrying a next-generation atomic clock that is accurate to within less than a nanosecond a day.
This accuracy is particularly important as the navigational fix is derived by triangulation, through a constellation of satellites which all send regular signals at the same time.
The difference in the time it takes for these signals to arrive at the receiver's location gives the calculation for latitude and longitude.
Galileo is meant to challenge the dominance of the US-built Global Positioning System (GPS), used in navigation devices in planes, vehicles and ships.
The two experimental satellites are to be followed by some 30 satellites placed in permanent orbit at an altitude of 20,000 kilometres (12,400 miles).
Last week, the much delayed 3.4-billion euro (5.4-billion dollar) scheme cleared a final legal hurdle when it was approved by the European Parliament.

Date created : 2008-05-07