The Galaxy 15 satellite is seen before its 2005 launch to geostationary orbit nearly 36,000 kilometers over the Earth's equator.
Credit: Orbital Sciences.
NEW YORK ? The Intelsat satellite that has remained in switched-on mode while in an uncontrolled drift along an orbital highway, posing broadcast interference threats to other satellites, is now expected to continue to emit signals at least through late November and perhaps until late December, Intelsat officials said.
The Galaxy 15 C-band telecommunications satellite, which went out of control in April and has since been drifting eastward along the geostationary arc 36,000 kilometers over the equator, is proving more durable than predicted. When it first failed, Intelsat and the satellite?s builder, Orbital Sciences Corp. of Dulles, Va., had estimated that it would lose momentum control in August.
When that happened, the satellite would lose its ability to point its solar arrays to the sun. Its power would drain and the spacecraft would shut down. At that point, Orbital and Intelsat hoped to use a brief window of opportunity to push the equivalent of a reset button on the assumption that that alone would cause the 7-year-old satellite to return to normal functioning.
If the satellite could not be returned to service, at least it would be in the "off" position, meaning it would join the more than 100 satellites that have failed or been left for junk on the geostationary belt, much like shipwrecks along a heavily used maritime route.
Instead, the satellite has taken advantage of eclipse periods, when it is in Earth?s shadow, to slow down the draining of its momentum system, extending its electronically active life and continuing to pose headaches for Intelsat and the owners of every satellite whose orbital neighborhood Galaxy 15 enters.
"We have been surprised by this," said Tobias Nassif, Intelsat?s vice president for satellite operations and engineering. "This is really a robust satellite. But to our knowledge this has been an unprecedented situation, and we are learning as we go."
Luxembourg- and Washington-based Intelsat invested considerable resources to design a maneuver that would permit satellites threatened by Galaxy 15 to avoid the uncontrolled spacecraft as it traversed other satellites? orbital positions, which are often referred to as "boxes."
SES of Luxembourg was the first Intelsat competitor with a satellite in harm?s way. SES and Intelsat devoted considerable resources in May to avoiding interference with SES?s AMC-11 satellite, and that model has been used since to avoid interference on other companies? spacecraft. The work paid off, and SES reported that none of its AMC-11 customers lost its broadcast signal.
Intelsat has repeated that maneuver, with minor variations, for a half-dozen other satellites since June and now faces continuing the drill for seven more spacecraft between now and late December. These include a satellite owned by Satmex of Mexico, two Anik spacecraft owned by Telesat of Canada, three more SES-owned satellites and, on Dec. 25, an Intelsat satellite.
Most of these collision- and signal-avoidance operations will be simpler than the first operation in early June because Galaxy 15?s orbit has degraded from full geostationary, meaning it wanders above and below the arc, sometimes only barely touching the orbital slots of other satellites along its path.
In an interview here Oct. 13 during the Satcon conference, Nassif said Orbital Sciences has been able to reproduce the low-level electrical short circuit on the ground and then confirm that, once shut down, a satellite in this situation would return to normal status.
Nassif said he remains unconvinced that a solar storm in early April caused the problem, saying that if that were the case the loss of control would have taken more time to occur. He said there are several theories of what caused the problem. Orbital Sciences has since modified its spacecraft so that the same kind of outage does not permit the satellite to wander off in switched-on mode.
Intelsat has not written off the entire value of the Galaxy 15, and the company hopes it will be able to recover its full use. But that will require Intelsat and Orbital to act quickly once the satellite loses sun-pointing ability.
What Intelsat is hoping, he said, is that as Galaxy 15?s batteries drain from lack of solar power, the satellite will be spinning on its axis slowly enough to force a complete shutdown from power deprivation, but fast enough to prevent its propellant tanks and other gear from freezing.
Intelsat and Orbital then would restart the satellite during the period when its solar arrays are pointed to the sun. Both companies have said that, in theory, the reset should result in a fully operational satellite that can be returned to service for another seven years or more.
Galaxy 15 was launched in 2003 and was designed to operate for 15 years.
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