Threat from Wayward Intelsat Satellite Diminishes

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PONTE VEDRA, Fla. — Intelsat’s runaway Galaxy 15 telecommunications satellite, which stopped responding to commands in April and since has been in an uncontrolled drift around the Earth along the principal orbital highway, has lost enough power that 95 percent of its electrical payload has shut down, a senior Intelsat official said Dec. 22.

The shutdown, which Luxembourg-based Intelsat originally had hoped would occur in August, finally arrived Dec. 17, all but ending an eight-month drama in which Intelsat had to warn owners of satellites in Galaxy 15’s path to perform occasionally elaborate maneuvers to prevent frequency interference for their customers.

Starting Dec. 17, Galaxy 15 lost its lock on Earth long enough for its batteries to drain sufficient power to force a shutdown of the satellite’s 24-transponder C-band payload, said Tobias Nassif, Intelsat vice president for satellite operations and engineering.

But in an example of the resilience that Intelsat in this case would like to have been spared, Galaxy 15 regained Earth-pointing mode after about 12 hours. Despite the on-again, off-again Earth lock, the payload since Dec. 17 has remained switched off except for its basic telemetry-sending capacity, which allows Intelsat ground teams to assess its health.

In an interview, Nassif said the telemetry function equivalent in power to about one 36-megahertz transponder still poses a risk to nearby satellites as Galaxy 15 continues its drift along the geostationary arc some 36,000 kilometers over the equator. But the risk is far less than it has been since the satellite malfunctioned in April with its full payload still on.

“The most painful part is over,” Nassif said. “The satellite is going from being 12 hours off, and then 12 hours on Earth pointing, with the off-pointing mode increasing by about 10 minutes per day. We are developing models to determine when it will shut down completely. Is it 13 hours?, 14 hours? We think it will be a matter of weeks.”

Launched in October 2005 on a planned 15-year mission, Galaxy 15 has enough on-board fuel remaining that Intelsat and the satellite’s manufacturer, Orbital Sciences Corp. of Dulles, Va., will try to recover its full functions once the batteries have drained completely and the satellite has shut down.

Nassif said that, in Intelsat’s judgment, the risk of a repeat of the April problem is remote. Intelsat and Orbital have tested the reset maneuver on the ground since April and have concluded that switching on the satellite will not trigger a repeat of the uncontrolled-drift scenario.

The satellite’s payload shuts down when the batteries have only 20 percent of their power remaining. To force a reset of the electronics, the batteries must fully discharge following a prolonged period of not pointing to the Earth.

There are more than 100 retired or defective satellites performing a slow seesaw drift in geostationary orbit. While they are nuisances, operators of active satellites know where these dead satellites are and how to avoid them when they enter the orbital neighborhood of an active spacecraft.

What made Galaxy 15 exceptional was the fact that its electrical payload remained stuck in the “on” position, looking for signals to rebound back to Earth as the satellite drifted from one satellite orbital slot to another. It passed through the orbital slots of about 15 satellites owned by operators including SES of Luxembourg, Telesat of Canada and Mexico’s Satmex