July 9, 2010

Zombie Satellite Still Drifting In Earth’s Orbit

The zombie satellite that controllers lost contact with in April is still drifting around in space, with engineers keeping a close eye as the Galaxy 15 satellite approaches two other spacecraft.

According to its operator Intelsat, the satellite is currently heading toward a stable and predictable path.  The main focus now is to keep the Galaxy 15 from interfering with other satellites that are close-by.

"The overall goal is to minimize disruption," Steve Good, Intelsat's global director of customer solutions engineering, told SPACE.com. "It's in all of our best interests to minimize any disruption."

The company is preparing several techniques to help mitigate potential signal interference as the zombie satellite is expected to fly by two other Intelsat satellites this month:  Galaxy 13 and Galaxy 14.

The 4,171-pound zombie satellite went rogue on April 5 after it stopped responding to controllers on the ground.

However, while the satellite veered from its assigned orbital slot of 133 west longitude, the satellite maintained an active payload, with its C-band telecommunications still functioning.

Intelsat officials have said that interference from the Galaxy 15's C-band signal is the main concern, since the chances of it crashing into other satellites are so slim.

"Galaxy 15 has a very large inclination, and if it stayed there, that would be great," Good said, referring to the tilt of the satellite's orbit with respect to Earth's equator. "But, twice a day it crosses the zero longitude line. At that point in time, that's when the physical distance between the two satellites is going to be minimized."

The Galaxy 13 and Galaxy 14 satellites both provide video media services, and the satellite operator has been in regular contact with customers.

"We're looking at each customer specifically," Good said. "We're working with them and we've offered them options. We've been in talks almost daily."

Galaxy 15 is expected to be in Galaxy 14's orbit on July 26.  It will make its closest pass on July 30.

Intelsat engineers have planned a variety of techniques in order to try and address interference concerns.  They have also arranged for customers who uplink to Galaxy 13 or Galaxy 14 to shift their antennas, depending on the location of the rogue satellite.

"If you have a large antenna, for example, you can miss-point to the east, and as soon as Galaxy 15 passes, you then miss-point to the west," Good explained. "It's like you're intentionally avoiding the Galaxy 15 satellite."

Several attempts have been made to try and shut down Galaxy 15, but those attempts were unsuccessful.

"Normally when an anomaly occurs, the satellite just stops working and we don't have to worry about it," Good said. "Galaxy 15 is still operational, so in this case, the satellite is still "functioning" in a deterministic state. But, we know exactly where it is, we know what it's doing, and we know the settings of the satellite."

The Galaxy 15 satellite launched on October 13, 2005 aboard an Ariane rocket. Orbital Sciences Corp., the manufacturer of the satellite, said that an intense solar storm in early April might have caused the breakdown in communication.

"This is definitely a unique situation," Good said. "There are people who have worked here for over 40 years who have not seen such a thing."

Galaxy 15 is expected to eventually lose its Earth-pointing capability.  Once this lock on Earth is lost and its solar panels are no longer pointed at the sun, the satellite's battery power will eventually die.

"When the battery power decreases past a certain threshold, the payload will shut off," Good explained. "It will no longer receive and transmit, and its batteries will continue to deplete."

Good said that the satellite could reach a threshold that causes its onboard computers to reset.  However, he added that the possibility of that taking place is still unknown.

"There is a possibility that the onboard computer could reset, but we don't know what that probability is," he said. "Still, there is a chance. It would almost be like a "control-alt-delete" on your computer. It would begin sending telemetry again. It would wake up and realize 'What am I doing here?'"


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