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Galaxy 15 'zombiesat' still alive after expected off date

Posted: September 15, 2010

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Intelsat says its out-of-control Galaxy 15 communications satellite did not power down as expected in late August and will continue threatening interference with broadcasting signals from other spacecraft for the foreseeable future.

File photo of Galaxy 15 before launch in 2005. Credit: Orbital Sciences
Galaxy 15 has not responded to commands from the ground since April, but the craft continues blaring powerful communications signals as it drifts through geosynchronous orbit more than 22,000 miles above Earth.

There is no threat of the satellite colliding with another craft.

Engineers at Intelsat and Orbital Sciences Corp., the builder of Galaxy 15, expected the errant satellite's reaction wheels to become saturated with momentum by late August or early September.

The reaction wheels control the satellite's orientation in space, and engineers expected Galaxy 15 would lose its lock on the sun and drain its batteries when the reaction wheels failed.

But Intelsat officials say the "off-point" did not occur, and now Galaxy 15 is in an eclipse season where the Earth blocks sunlight from reaching the solar panels for a few minutes each day.

Intelsat does not expect Galaxy 15 to turn itself off during the eclipse season, based on how momentum builds up on the satellite, according to Dianne VanBeber, the company's vice president of investor relations and communications.

Galaxy 15 will exit the annual fall eclipse season in early October.

"The flight engineers are back at the drawing boards to determine another estimate for the off-point," VanBeber told Spaceflight Now in an email.

Galaxy 15 is moving east along the equator at less than two-tenths of a degree of longitude per day.

Because it continues to be powered, Galaxy 15 will fly near another communications satellite while uncontrollably transmitting powerful C-band signals.

The encounter due for Sept. 21 is with Mexico's Satmex 5 satellite positioned at 116.8 degrees west longitude.

Intelsat has managed six flybys of other C-band satellites since they lost control of Galaxy 15, including four of the company's own broadcasting satellites positioned over North America.

Galaxy 15 has also sailed past AMC 11, an SES World Skies high-definition television broadcasting satellite providing core programming to millions of viewers in North America.

The craft flew by the Canadian Anik F3 communications satellite operated by Telesat on Sept. 9.

If Galaxy 15 is still turned on, it will approach the Satmex 6 and Anik F2 C-band satellites of Mexico and Canada by mid-October. Galaxy 15 does not affect strictly Ku-band communications platforms.

"The fact that you haven't heard about channels lost or interference is the proof that we have been able to avoid issues operationally," said Nick Mitsis, an Intelsat spokesperson. "I don't want to underplay that."

Intelsat has worked closely with other satellite operators to avoid interference that could lead to cable or satellite television interruptions across the United States, Canada and Latin America.

"We have a team of engineers that have become experts at turning traffic and implementing a number of other in-flight tricks to avoid interference," Mitsis said.

According to Mitsis, predicting the off-point of Galaxy 15 is an inexact science because engineers are not receiving data from the spacecraft.

Officials believe the anomaly in April may have been caused by a solar flare that zapped the satellite's electronics.

When Galaxy 15 does power itself down, officials say there is a small chance they could reboot the satellite and recover its functionality.