Image: THEMIS satellites
NASA's five THEMIS satellites are shown just after deployment in this artist's interpretation.
updated 2/17/2007 7:35:00 PM ET 2007-02-18T00:35:00

Five science satellites blasted off on a single rocket into a golden sunset Saturday on a mission to figure out the source of powerful geomagnetic substorms in the Earth's atmosphere.

The launch at 6:01 p.m. from the Cape Canaveral Air Force Station came a day after it was scrubbed Friday after strong upper winds forced officials to wait 24 hours, said Rani Gran, NASA spokeswoman.

Scientists hope the $200 million Themis mission unravels the mystery behind the storms that can damage communications satellites, disable power grids and shoot high levels of radiation down on spacewalking astronauts and airplane passengers flying over northern latitudes.

Scientists believe they also periodically intensify the spectacular light shows seen in the northern lights, or aurora borealis.

"For 30 years, people have tried to understand what causes the onset of these substorms," said Vassilis Angelopoulos of the University of California, Berkeley, principal investigator for the Themis mission. "Finding out the origin ... has been so elusive."

It is the most probes NASA has ever launched on a single rocket. However, last year a joint venture of Taiwan and the U.S. National Science Foundation launched six weather microsatellites on one rocket.

The five Themis probes are expected to separate from the Delta II rocket more than an hour after launch. After separation, scientists at a University of California at Berkeley ground station will then begin initiating signals with each probe.

Scientists plan to begin receiving data from the probes in about two months and continue receiving information for many years, officials said.

The mission, if successful, will end the debate scientists hold as to when the substorms are triggered.

One theory holds that the substorms start about 50,000 miles above the Earth's equator, about a sixth of the way to the moon, when the electromagnetic turbulence disrupts the flow of intense space currents.

The other theory is that the substorms are triggered about 100,000 miles above the equator with the spontaneous conversion of magnetic energy into heat. Particle acceleration then triggers the substorm energy.

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