Zombie Satellite Forces More Evasive Maneuvers for Other Craft

PARIS ? Satellite fleet operator Intelsat has successfully negotiated the passage of its out-of-control Galaxy 15 satellite across the path of its Galaxy 13 spacecraft with no signal interruption for Galaxy 13 customers in the second of what likely will be at least four such maneuvers before the so-called "zombie satellite" shuts down on its own in August, Intelsat said.

Galaxy 15, which earned the nickname "zombie satellite" after it stopped responding to commands in April, has since been drifting eastward along the geostationary arc 36,000 kilometers above the equator. Industry officials say it is the first time an uncontrolled satellite has remained electronically active, with its transponders still looking for signals to rebroadcast even as it strays far from its assigned orbital position.

Galaxy 15 traveled through the orbital slot of Luxembourg-based SES's AMC-11 satellite in mid-May. That event caused no service disruptions as Intelsat and SES took measures that included routing some AMC-11 traffic through a 19-meter-diameter antenna at Intelsat's Clarksburg, Md., teleport.

Unable to shut the satellite down, Intelsat officials then prepared for the Galaxy 13 fly-by July 12 and 13, using some of the same interference-avoidance techniques developed for the AMC-11 encounter.

The procedure was completed "without incident," Intelsat Chief Technical Officer Thierry Guillemin said in a July 15 statement. "We will now be implementing the interference-mitigation plan for the fly-by of Galaxy 14, expected to occur at the end of July."

Luxembourg- and Washington-based Intelsat said that at one point during the Galaxy 15 transit through the Galaxy 13 orbital slot, the two satellites were within 0.05 degrees of separation. Some customers continued to use the Galaxy 13 and were able to do so because the satellite's signal reception had been reset as low as possible to permit signals to be sent without attracting Galaxy 15's interest.

Unlike AMC-11, Galaxy 13 also carries Ku-band transponders in addition to its C-band payload, meaning Intelsat was limited in its ability to move the satellite to the extreme eastern edge of its orbital slot to avoid Galaxy 15 before performing a "leapfrog" maneuver back westward as Galaxy 15 continued its eastward move.

Galaxy 15 is on course to enter the Galaxy 14 orbital neighborhood in late July, with a peak interference threat expected July 30, according to Intelsat. In mid-August, it will be Galaxy 18's turn to avoid Galaxy 15.

Intelsat officials are hopeful that sometime in mid-August, Galaxy 15, whose attitude control is slowly degrading, will lose its lock on the sun. Its power will then drain and the satellite will shut down on its own.

Intelsat is already preparing customers using Galaxy 23 for a similar avoidance procedure in late August in the event Galaxy 15 is still active by then. The company has also begun coordinating with satellite fleet operator Telesat of Canada, whose Anik F3 satellite will have to contend with Galaxy 15 in mid-September.

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