Beware the zombiesat

Beware the ZombieSat

Presented by Science at NASA

On April 5th 2010 something eerie happened to the Galaxy 15 telecommunications satellite, it turned into a zombie.

The day began as usual, with Galaxy 15 relaying TV signals to millions of viewers in North America, when suddenly the geosynchronous satellite stopped taking commands from Earth. It was brain dead. Like any good zombie, however, its body continued to function.

Within days, Galaxy 15 began to meander among other satellites in geosynchronous orbit, transmitting its own signal on top of theirs. Satellite operators scrambled to deal with the interference, all the while wondering what happened?

In horror movies, zombies are usually produced by viruses. “In this case, the culprit was probably the sun,” says Bill Denig of the National Geophysical Data Center in Boulder, Colorado. He and colleague Janet Green of NOAA’s Space Weather Prediction Center recently led a study of the Galaxy 15 anomaly and they believe they’ve figured out what happened.

A couple of days earlier, a relatively minor solar flare launched a cloud of plasma toward Earth. Galaxy 15 had experienced many such events before, but this time there was a difference. “Galaxy 15 was just emerging from the shadow of Earth when the cloud arrived,” explains Denig. Suddenly, the spacecraft was exposed to hot sunlight and a growing storm of charged particles, a truly shocking experience. Electrons swirling around Galaxy 15 stuck to and penetrated the spacecraft’s surface. As more and more charged particles accumulated, voltages began to rise, and zap! A zombie was born.

NASA has a mission in the works to monitor charged particles around Earth. Due to launch in 2012, “the Radiation Belt Storm Probes are equipped to measure not only the so-called ‘killer electrons,’ which penetrate deep inside a spacecraft, but also lower energy particles, such as the ones that stuck to the surface of Galaxy 15,” explains mission team member Harlan Spence of the University of New Hampshire.

Data from the probes could help forecasters issue alerts when dangerous electrons appear. This would allow satellite operators to take protective action, for example putting their birds in “safe mode” and keep the zombie population at bay.

Meanwhile, Galaxy 15 is a zombie no more. In late December 2010, after 9 months of troublemaking, the comsat lost lock with the sun, re-booted, and began responding to commands from Earth. All’s well that ends well? True zombie fighters know better than to relax. Says Spence, “the Storm Probes will have a lot of work to do.”

For more information about the Radiation Belt Storm Probes and other shocking stories, please visit Science. nasa. gov

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Beware the zombiesat