posted 02-17-2007 10:14 PM               

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NASA's THEMIS Mission Launches to Study Geomagnetic Substorms

NASA's THEMIS mission successfully launched Saturday, Feb. 17, at 6:01 p.m. EST from Pad 17-B at Cape Canaveral Air Force Station, Fla.

THEMIS stands for the Time History of Events and Macroscale Interactions during Substorms. It is NASA's first five-satellite mission launched aboard a single rocket. The spacecraft separated from the launch vehicle approximately 73 minutes after liftoff. By 8:07 p.m. EST, mission operators at the University of California, Berkeley, commanded and received signals from all five spacecraft, confirming nominal separation status.

The mission will help resolve the mystery of what triggers geomagnetic substorms. Substorms are atmospheric events visible in the Northern Hemisphere as a sudden brightening of the Northern Lights, or aurora borealis. The findings from the mission may help protect commercial satellites and humans in space from the adverse effects of particle radiation.

THEMIS' satellite constellation will line up along the sun-Earth line, collect coordinated measurements, and observe substorms during the two-year mission. Data collected from the five identical probes will help pinpoint where and when substorms begin, a feat impossible with any previous single-satellite mission.

"The THEMIS mission will make a breakthrough in our understanding of how Earth's magnetosphere stores and releases energy from the sun and also will demonstrate the tremendous potential that constellation missions have for space exploration," said Vassilis Angelopoulos, THEMIS principal investigator at the University of California, Berkeley. "THEMIS' unique alignments also will answer how the sun-Earth interaction is affected by Earth's bow shock, and how 'killer electrons' at Earth's radiation belts are accelerated."

The Mission Operations Center at the University of California, Berkeley, will monitor the health and status of the five satellites. Instrument scientists will turn on and characterize the instruments during the next 30 days. The center will then assign each spacecraft a target orbit within the THEMIS constellation based on its performance. Mission operators will direct the spacecraft to their final orbits in mid-September.

During the mission the five THEMIS satellites will observe an estimated 30 substorms in process. At the same time, 20 ground observatories in Alaska and Canada will time the aurora and space currents. The relative timing between the five spacecraft and ground observations underneath them will help scientists determine the elusive substorm trigger mechanism.

"I am proud to manage the fifth medium class mission of the Explorer Program," said Willis S. Jenkins, the THEMIS program executive. "As we seek the answer to a compelling scientific question in geospace physics, we are keeping up the tradition that began with Explorer I."

NASA's Launch Services Program at the Kennedy Space Center was responsible for the launch of THEMIS aboard a Delta II rocket. The United Launch Alliance, Denver, provided launch service.

The Explorer Program Office at Goddard manages the NASA-funded THEMIS mission. The Space Sciences Laboratory at the University of California, Berkeley, is responsible for project management, space and ground-based instruments, mission integration, mission operations and science. Swales Aerospace, Beltsville, Md., built the THEMIS probes. THEMIS is an international project conducted in partnership with Germany, France, Austria and Canada.

For more information about the THEMIS mission and imagery on the Web, visit: www.nasa.gov/themis

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