NASA THEMIS mission adds five spacecraft to the Sun-Earth flotilla (Forwarded)

ESA News
http://www.esa.int

16 February 2007

NASA THEMIS mission adds five spacecraft to the Sun-Earth flotilla

Tonight NASA plans to launch its five THEMIS scientific satellites onboard a
Delta-2 rocket from Cape Canaveral, Florida USA, to join the spacefleet of
Sun-Earth connection explorers -- four from the ESA Cluster mission and two
from the CNSA/ESA Double Star mission.

The main scientific objective of THEMIS (Time History of Events and
Macroscale Interactions during Substorms) is to find what triggers magnetic
substorms. This phenomenon corresponds to periods of time during which
violent changes happen within the Earth's magnetic environment or
magnetosphere. It is triggered at distances from one tenth to half the
Earth-Moon distance on the nightside of Earth and hurls energetic particles
towards our planet. These particles are responsible for the very bright and
colourful auroras and are usually harmless. However, when the Sun unleashes
massive clouds of charged particles towards Earth, a series of 10 or more
substorms can occur in rapid succession. Such a series may be responsible
for the failure of power grids and satellites observed during some of these
events.

Six plus five equals eleven

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

THEMIS is the fifth mediumclass mission selected by NASA under its Explorer
Program with Professor Vassilis Angelopoulos (Space Science Laboratory of UC
Berkeley, USA) as Principal Investigator of the mission. Each THEMIS
satellite carries an identical set of five scientific instruments. 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. We wish all the best to our
American colleagues for a successful launch", says ESA's Philippe Escoubet,
Double Star and Cluster project scientist.

For more information on the Sun-Earth explorers, contact:

Philippe Escoubet
ESA Cluster Project Scientist
Email: philippe.escoubet @ esa.int

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