GLOBAL CHALLENGES

When Zombie Satellites Attack

Michael Steinhart | Date: 05-21-10 | Comments

Mission control lost contact with a communications satellite last month. What kind of havoc can it wreak as its orbit degrades?

About a month ago, the Galaxy 15 communications satellite, owned and operated by Intelsat, went "zombie." Something�possibly a solar storm�caused it to stop responding to instructions sent from Earth. Its onboard systems, however, are still operating at full power, which means they can interfere with other satellites. From the Intelsat release:

"Launched in 2005, G-15 is an Orbital Star satellite. Intelsat and Orbital Sciences Corporation, the manufacturer of G-15, are conducting a technical investigation with respect to the anomaly, which has had no impact on the communications services delivered by the spacecraft. Galaxy 15 has 24 C-band transponders and was designed to be operational through 2022."

Communications satellites occupy geostationary orbital slots, and the "zombie" Galaxy 15 spacecraft is drifting slowly into the orbit of an Internet and cable TV-carrying satellite.

Communications satellites carry phone, Internet and TV signals around the globe, and each occupies a geostationary slot, orbiting above the same spot on Earth as it rotates. Galaxy 15�s orbit is decaying, and it will drift into the path of a North American TV and Internet satellite on or around May 23. It will spend about two weeks in that slot, potentially interfering with AMC-11 (run by Luxembourg-based SES World Skies).

Space junk is not a new phenomenon, but the kind that�s still operating at full power apparently is. Space.com reports:

"In what industry officials called an unprecedented event, Intelsat's Galaxy 15 communications satellite has remained fully 'on,' with its C-band telecommunications payload still functioning even as it has left its assigned orbital slot of 133 degrees west longitude 36,000 kilometers over the equator.

"Satellites like Galaxy 15 and AMC-11 are so-called 'bent-pipe' designs that receive signals from the ground, amplify them on board and redistribute them to customers' ground antennas. Emptied of its customers�except one, the U.S. Federal Aviation Administration, which uses an L-band payload on Galaxy 15 to guide aircraft landings�Galaxy 15 is no longer broadcasting. But its electronics payload is ready to capture and rebroadcast signals it receives that are intended for other spacecraft."

AMC-11 is stationed at 131 degrees west, just two degrees away from Galaxy 15's starting position. SES is working to adjust the orbit of AMC-11 to reduce the potential for interference.

For its part, Intelsat has tried to shut down Galaxy 15 remotely by sending high-powered signals aimed at overloading its power systems, but these attempts have not succeeded. Once the zombiesat passes through AMC-11�s slot�presumably in early June�it will spend a few weeks in the 129 degrees west slot, which is unoccupied. Intelsat will resume its remote shutdown attempts then. Throughout July, it will drift through the orbits of several other Intelsat-owned spacecraft.

The media and communications companies that rely on these satellites are planning to reroute their signals via other spacecraft, hoping to avoid any significant impact on service delivery. Experts estimate that Galaxy 15 will lose Earth orientation sometime in late July or early August. When that happens, its solar arrays will lose their lock on the sun. The satellite will switch to battery power and then shut down on its own when the batteries are depleted.

Because this kind of malfunction has never happened before, and because of the vagaries of orbital science, the Galaxy 15 story may yet have a few twists in store. We�ll keep an eye on it here at Smarter Technology and update our readers regularly.