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Build-up of static electricity turned satellite into zombie
BY STEPHEN CLARK
SPACEFLIGHT NOW

Posted: January 14, 2011


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In a remarkable reversal of fortune, Intelsat is on the verge of returning a crippled communications satellite to service over North America, company officials said Thursday.

 
Galaxy 15 under construction before launch in 2005. Credit: Orbital Sciences Corp.
 
The Galaxy 15 satellite stopped responding to commands and sending telemetry after an anomaly last April 5, beginning a slow drift east along the equator from its original position 22,300 miles over the Pacific Ocean. Its powerful C-band communications payload continued broadcasting television signals, threatening to interfere with other spacecraft as Galaxy 15 moved uncontrollably nearby through geosynchronous orbit.

The April 5 malfunction can likely be attributed to electrostatic discharge, or shock from static electricity, a concern for all satellites in space, according to Tobias Nassif, Intelsatís vice president of satellite operations and engineering.

Investigators from Intelsat, Orbital Sciences Corp. and Aerospace Corp. are completing an inquiry into the Galaxy 15 anomaly. The team has settled on two potential causes for the glitch - both encompassing software effects of a static charge - and will release its report in February, Nassif said.

"It was an electrostatic discharge, or a build-up of energy from the space environment," Nassif said. "I don't think it was the spacecraft itself that generated this energy. It was from the external environment. What they are working on and tracing down is where this energy came from and how it got in and where did it build up to that caused this."

Despite preliminary reports, the investigation has ruled out a solar flare as the reason for the problem, officials said.

The mishap set off nearly nine months of nail-biting flybys as Galaxy 15 started sliding toward other satellites. There was never a threat of a physical collision between satellites, but Intelsat and competing operators worked together to minimize interference with television programming across North America.

"It was a lot of work and a lot of anxiety over the course of the last eight months," said Dianne VanBeber, Intelsat's vice president of corporate communications and investor relations. "It's amazing how little collateral damage there's been from this really unprecedented event."

The worry was that Galaxy 15's errant signals would overwhelm normal broadcasts coming from operational satellites.

"Overall, we conducted 15 flybys and had very little, if any, impact on service," Nassif said.

Engineers regained control of Galaxy 15 in late December after the craft's reaction wheels became saturated by momentum, causing the satellite to lose its lock on Earth and sun. Without attitude control, Galaxy 15 stopped generating electricity and drained its batteries, triggering on-board software to automatically shut down the communications payload, according to Nassif.

The Dec. 17 reset ended Galaxy 15's threat to other satellites, but the work wasn't finished. After several days of stabilization activities, Intelsat returned the spacecraft to normal mode Dec. 27.

The recovery proved the source of the satelliteís problems was in its software and not indicative of a hardware issue.

Officials said the satellite appears to be working normally, but controllers have not finished reactivating all of Galaxy 15's transponders and transmitters.

Engineers are now moving the spacecraft to 93 degrees west longitude for several weeks of testing. The checks will mimic the usual post-launch testing every satellite undergoes before beginning service, Nassif said.

Assuming officials verify the satellite is in good shape, the company could place Galaxy 15 back into the Intelsat fleet by March. An announcement on the satellite's next post could come by the end of January, according to VanBeber.

Speaking to reporters Thursday, Intelsat officials said Galaxy 15 could resume its role as a primary C-band broadcasting satellite over North America. The company might also assign the satellite as a spare at 129 degrees or 133 degrees west longitude, Nassif said.

The satellite's design life extends until 2022. It was launched in October 2005.

Intelsat has uplinked software patches to prevent similar occurrences in the future. The updates will ensure the satellite responds to orders in the event of another static discharge event, and the communications payload will turn itself off after 21 days without commands.

The company transmitted the software patches to the rest of its Orbital Sciences Star 2 satellites in October. Nassif said Orbital is also instituting fixes for its spacecraft still under construction.


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