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After recognizing an issue with satellite momentum wheels, Globalstar exchanged one of the six satellites set to launch in December with a spare satellite to make sure there would not be a repeat of Globalstar’s recently launched satellites.
Globalstar and Thales Alenia Space, the satellite manufacturer, decided to exchange the satellite after tests show it might have an issue with its momentum wheels. The momentum wheels maintain the orientation of the satellite in space.
The current launch is scheduled for December 25 from the Baikonur Cosmodrome in Kazakhstan using a Soyuz rocket.
Globalstar is in the middle of a four launch campaign to establish a new second generation constellation of 24 satellites. One of the satellites launched in October is currently out of service due to issues with two of its momentum wheels.
The six satellites launched in July are showing signs of problems with their momentum wheels.
"We have two wheels from the first batch which are in degraded operations," said Tony Navarra, president of global operations for Globalstar Inc. "They continue to operate, but they have increased friction torque. Then we have two in batch two, which were launched in July, that have increased friction torque."
After the July launch six more satellites where planned to be launched in October, but the failure of a Soyuz rocket in August caused the launch to be moved to early December.
The launch was moved again to late December as Globalstar and Thales decided to replace one of the satellites with a spare satellite which was already at the launch site.
"The delay that took from July to the late December date was to make certain that all the momentum wheels were flight-worthy," Navarra said Thursday. "We did have to swap out one satellite which is in Baikonur with another satellite which was already there for the fourth launch."
Two of the six satellites for the fourth launch are already at the Baikonur Cosmodrome. The other four will be shipped later this month. The fourth launch is planned to take place in the first few months of 2012.
Globalstar and Thales officials are developing software to save the satellites having the momentum wheel issue that are already in orbit.
According to Nararra the software fix should allow the effected satellites to return to full service. The service life of the Globalstar satellites is expected to be 15 years.
The software testing has shown that the fix would allow the satellites to function with reduced momentum wheel usage. The tests have shown they would be able to fly the satellite with only two functioning momentum wheels.
Globalstar’s existing satellites have problems with degrading S-band antennas; this has limited voice and duplex communication since 2007. The simplex data relay has not been affected.
Globalstar plans to purchase 24 more satellites from Thales in the future as cash flow allows.