Second Satellite in Galileo Constellation Reaches Orbit
FUCINO, Italy – The second of two technology-demonstration satellites for Europe’s future Galileo satellite navigation constellation was successfully launched April 27 and was reported to be healthy despite an initial problem with its momentum wheels and a later anomaly involving the power system.
Program managers expect that a permanent software modification will be sent to the satellite and tested by early in the work week that begins May 5. They anticipate an initial satellite navigation signal transmission “at the earliest opportunity” once the payload instruments have been activated, Javier Benedicto, Galileo project manager at the European Space Agency (ESA), said May 2.
The 500-kilogram Giove-B satellite, which is more than two years behind schedule and substantially over its initial budget of 72.3 million euros ($113 million), will join the Giove-A satellite in medium Earth orbit. Giove-A was launched in December 2005 and continues to operate.
Scheduled to operate for two years, Giove-B carries a payload designed to closely resemble the 30 Galileo satellites that will form the full Galileo constellation. In particular, it features a hydrogen maser atomic clock, which have never before flown in orbit and are designed to be more accurate than the rubidium atomic clocks flown on Giove-A.
Giove-B also carries two rubidium clocks. The future U.S. GPS 3 satellites, to be operational starting around 2014, also will use an advanced rubidium design. European industry officials say it is not straightforward to compare the accuracy of the GPS clocks and those intended for Galileo. “You could say they are equivalent,” said an industry official here at the Fucino Space Center, which is the control center for the Giove-B satellite.
Giove-B managers used the delay in the satellite’s development and launch to upgrade its signal generator to include a new navigation signal to be used by both Galileo and the U.S. GPS-3 satellites following a U.S. agreement with the European Union on navigation interoperability.
The upgrade signal generator for Giove-B was developed by Saab Space of Gothenburg, Sweden, its Austrian Aerospace subsidiary and Astrium Satellites GmbH of Germany.
“We got a software modification order in late 2006 and a hardware modification order in June 2007. We were thus given six months from the last modification order to delivery and we made it in time. The unit has better performance than expected,” Saab Space spokesman Lars Nordfeldt said.
A Russian Soyuz-Fregat rocket, commercialized by the French-Russian Starsem S.A. joint venture, placed Giove-B into a medium-Earth orbit with a high accuracy, according to officials with ESA.
But once it was released from the Fregat upper stage, Giove-B ran into a problem with its four reaction wheels, which are used to provide precise pointing for the satellite.
Benedicto said the reaction wheels were slow to respond to initial commands to turn Giove-B toward the sun to charge its batteries. With no time to lose given that the batteries had not been charged since before the launch, ground teams here bypassed the reaction wheels and instead used the satellite’s on
board thruster motors to turn Giove-B around to face the sun and charge its batteries.
Benedicto said officials initially thought the problem was due to the prolonged exposure to low temperatures. But he said a software patch sent to Giove-B later April 27 resolved the problem, indicating that the cause lay elsewhere.
Benedicto said Giove-B managers determined that the reaction wheel anomaly was due to a mistaken calibration of them. A software upgrade was sent to the satellite, and “they are now working very well,” he said.
Launching Giove-B and putting it into service is perhaps the most spectacular but not the most complicated task facing ESA and the European Commission this year with respect to Galileo.
The European Commission hopes to have a legally binding regulation approving Galileo’s 3.4 billion euros in financing by early June, said Paul Verhoef, head of the Galileo unit at the 27-nation European Commission, which is financing Galileo’s development.
Once that is completed, ESA and the commission must sign an agreement under which the commission will hire ESA to oversee the industrial work to build the full Galileo network.
Four Galileo demonstration satellites, similar to Giove-B but heavier and designed for longer in-orbit lives, are under construction and scheduled for launch in 2010 and 2011.
Once it signs its Galileo agreement with the European Commission, ESA will conduct a contract competition for the different Galileo system elements, including construction of the 26 remaining satellites, their launches and the ground system control elements. These contracts are scheduled to be signed by December or January.
ESA and European Commission officials are sticking with their forecast that the full Galileo system could be in orbit by 2013.