February 15, 2007
Friday Launch for NASA Satellite Mission
CAPE CANAVERAL, Fla. -- So many satellites. Just one rocket.
Five NASA satellites stacked like a wedding cake are set to launch on a single rocket Friday, part of a mission to figure out the source of powerful geomagnetic substorms in the Earth's atmosphere.These storms 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.
"It affects satellites in space. It affects humans. It has radiation," said Vassilis Angelopoulos of the University of California, Berkeley, principal investigator for the Themis mission. "We want to know more about it to protect our assets in space."
Just what unleashes these powerful energy bursts, blown by solar winds, is a mystery, one to be unraveled by Themis.
"I call it the Holy Grail of space physics, the oldest unanswered question in space physics today," Angelopoulos said.
Themis, both an acryonym and the name of the Greek goddess of order and justice, will cost $200 million.
For NASA, it's the most probes ever launched on a single rocket; scientists needed at least four to study the substorms. However, last year a joint venture of Taiwan and the U.S. National Science Foundation launched six weather microsatellites on one rocket.
The Themis probes had to be free of magnetic charge, invincible to radiation, able to survive wild temperture swings, and extremely lightweight. Each satellite weighs 282 pounds.
"This was a very difficult mission to implement," said project manager Peter Harvey of the University of California, Berkeley. "Every time you added a gram to a satellite, you added 5 grams to the vehicle's launch to orbit."
Engineers also had to devise a way to separate the satellites from the Delta 2 rocket more than an hour after launch without crashing into each other. A single satellite will first break free of the rocket, followed three seconds later by the other four probes.
Each satellite will magnetically map North America every four days for about 15 to 20 hours in tandem with 20 ground stations. The satellites won't be in proper position until the fall and won't be collecting their primary data until next winter.
Based on information provided by the five satellites, scientists and engineers hope to create models for the substorms that could be used to forecast their disruptions, much like meteorologists predict when and where hurricanes strike.
At stake, also, are the bragging rights of scientists over two competing theories.
The first camp holds that the substorms are triggered about 50,000 miles above Earth's equator, about a sixth of the way to the moon, when electromagnetic turbulence disrupts the flow of intense space currents.
The other theory is that the substorms start about 100,000 miles above the equator with the spontaneous conversion of magnetic energy into heat. Particle acceleration then triggers the substorm energy.
To test each theory, two satellites will be lined up a sixth of the way to the moon, and two others will placed respectively about a third and halfway to the moon. The fifth satellite will be on hand "to replace a brother or sister if they get into trouble," said Angelopoulos.
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