THEMIS mission launches to study geomagnetic substorms

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 01:07 UTC, 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."

Image Credit: NASA
High resolution image

The Delta II rocket with NASA's THEMIS spacecraft aboard lifts off Pad 17-B.




Image Credit: NASA

This is an artist's concept of the THEMIS spacecraft as it might appear in orbit.




Image Credit: ESA

THE five THEMIS scientific satellites join the spacefleet of Sun-Earth connection explorers - four from the ESA Cluster mission and two from the CNSA/ESA Double Star mission.

For the first time, about half of the magnetosphere and its environment will be monitored simultaneously by state-of the-art scientific instrumentation, thanks to these three missions.

Six plus five equals eleven

ESA's Cluster is the first space mission composed of four satellites flying in formation to study the Sun-Earth connection. Launched in 2000, this mission, originally planned for two years, has been extended to the end of 2009. It was joined in 2003 by the first Double Star spacecraft named TC-1 and in 2004 by TC-2, both partially equipped with spare instruments of the Cluster satellites. Double Star is the first Chinese scientific space mission in the Earth's magnetosphere.

The THEMIS satellites will be highly complementary to the Cluster and Double Star ones since they will monitor opposite regions of the magnetosphere with respect to Earth. For example, during winter season 2007/2008, while THEMIS will be in the magnetotail (nightside) studying the source region of the substorms, the Cluster mission will spend a significant part of its orbit around Earth in the solar wind (dayside) and cross the auroral region at mid-altitude. The apogee of TC-1 is located approximately in between. For the first time, about half of the magnetosphere and its environment will be monitored simultaneously by state-of the-art scientific instrumentation, thanks to these three missions.

European involvement

The development of two of these instruments was done in close collaboration between American and European institutes from Austria, France and Germany. Part of the electronics of these instruments has been manufactured in Europe. Several European research institutes will take an active part in the scientific exploitation of these future measurements. Such a deep scientific collaboration is not a first. It is built on years of fruitful collaboration such as that on Cluster where discoveries have been made thanks to active collaboration between researchers from both sides of the Atlantic.

"This is the first time in history of Space Physics that such a high number of scientific satellites are in operation simultaneously. It represents an unprecedented opportunity to study the global solar-magnetospheric environment and the physical processes involved.", says ESA's Philippe Escoubet, Double Star and Cluster project scientist.