Satellites to Study Geomagnetic Substorms

Satellites to Study Geomagnetic Substorms



Feb 2007 - For the 
first time on Saturday, NASA launched five satellites aboard a 
single rocket from Cape Canaveral. 
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. 
It is known as the THEMIS mission for the Time History of 
Events and Macroscale Interactions during Substorms. 
During the next two years, THEMIS' satellite constellation 
will line up along the Sun-Earth line, collect coordinated 
measurements, and observe substorms. 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," said 
Angelopoulos. 
The bow shock is the boundary at which the solar wind abruptly 
drops as a result of its approach to the Earth's magnetic 
envelope. 
The Earth's bow shock is about 100 to 1,000 kilometers (60 to 
600 miles) thick and located about 90,000 km (56,000 miles) 
from the Earth. 
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.

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