Five spacecraft launched to probe explosive space storms
BY JUSTIN RAY
Posted: February 19, 2007
Aiming to uncover the physics that power the auroras that crown Earth's poles, five tiny probes have been launched into space for a synchronized orbital dance to locate where the trigger is pulled to create the eerily magnificent displays.
The 73-minute flight of the three-stage launcher culminated off the northeastern coast of Australia, when the five probes were flung off their spinning carrier.
Each of the 282-pound spacecraft is equipped with identical suites of instruments to examine the origin of space explosions known as substorms. The events start with the soup of ionized particles from the sun, called the solar wind, buffeting the Earth at a million miles per hour. Some of that energy gets trapped in the magnetic field, causing the field lines to stretch back in the direction opposite the sun like rubberbands. But when stretched too far the lines snap, releasing the energy that generates shimmering auroral displays.
"For over 30 years, the source location of these explosive energy releases has been sought after with great fervor. It is a question almost as old as space physics itself," said THEMIS principal investigator Vassilis Angelopoulos. "A substorm starts from a single point in space and progresses past the moon's orbit within minutes, so a single satellite cannot identify the substorm origin. The five-satellite constellation of THEMIS will finally identify the trigger location and the physics involved in substorms."
"Substorms are what make the aurorae interesting," said John Bonnell, a plasma physicist and aurora specialist with THEMIS. "Without them, the greenish white sheets are static, like a cloud. Substorms make the sheets ripple and create different colors, such as red borders and colorful edge effects."
"THEMIS is so important because the same fundamental physical process is seen around all planets, it happens on the sun in solar flares, and in astrophysical systems such as black holes," Angelopoulos said. "It's amazing that being so close to us, here at Earth, it is not understood yet."
"They say good things come in small packages. I'd have to say these probes are great by that measure," said Peter Harvey, the THEMIS project manager from the University of California at Berkeley.
"They are powerful. It is amazing to think that these things will accelerate themselves over half-way to the moon. Each one has 40 percent of its weight as fuel. So it's able to change its orbit and go quite a distance.
"The probes are tough. They can take flying through the radiation belts and keep on going. They can take three-hour shadows of the Earth and keep every component inside warm while the outside is freezing cold.
"The probes are smart. Every one of them travels a vast distance from the Earth and can't do that in contact with the Earth. So it can't constantly telemeter. So each probe has to then detect the substorm, capture that data, compress it and then wait until it gets closer to Earth to transmit that data to the ground.
"The probes are really efficiently packed. Things are so jam-packed inside each probe that you can't fit your hand in between any two items."
The probes were built by Swales Aerospace, and their measurements will be combined with a network of observatories across the northern U.S. and Canadian.
"I cannot explain all my excitement. This has been a truly exciting project -- building five spacecraft and 20 ground-based observatories, flying spacecraft in synchronized orbits. You couldn't ask for more," Harvey said.
Saturday's launch marked the 72nd consecutive successful flight by a Delta 2 rocket since 1997 and the 125th success overall in the 127-flight history of the workhorse booster dating back to 1989.
"The United Launch Alliance team is proud to support the science and robotic mission of NASA's space exploration program by successfully completing our first east coast launch," said Mike Gass, president and chief executive officer of ULA.
The newly-formed United Launch Alliance now manages all Delta and Atlas rocket missions. ULA is the joint venture between Boeing and Lockheed Martin that has combined the Delta and Atlas rocket fleets.
"This is the first of a total of 21 launches we have manifested in 2007 consisting of a dozen Delta 2s, six Atlas 5s and three Delta 4s from the east and west coasts," said Dan Collins, ULA chief operating officer. "As our team proved today, they are up to the task. By focusing on safe practices, customer needs and mission success, I believe 2007 will be a banner inaugural year for ULA."
Next up is the Atlas 5 launch of six experimental satellites for the U.S. military. That liftoff from Cape Canaveral had been planned for February 22, but officials ordered a two-week delay while the Sea Launch failure investigation continues. The Atlas 5's RD-180 first stage main engine is derived from the Russian powerplant used on the Sea Launch Zenit boosters.
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