STEREO (Solar TErrestrial RElations Observatory)
Twin NASA spacecraft designed to explore coronal
mass ejections (CMEs), the "space weather" to which they give rise,
and the potentially serious effects for life on Earth. The $520m STEREO
mission was successfully launched on October 26, 2006 by a Delta II rocket.
It is expected to provide new insight into what causes CMEs, and allow scientists
to track their progress through space. Other solar-observing spacecraft,
such as SOHO, have been unable to tell whether
a CME is heading for Earth or away from it. STEREO should give a couple
of days' notice that a CME is heading our way.
- SECCHI: The Sun-Earth Connection Coronal and Heliospheric Investigation
is a suite of instruments that includes the UK Heliospheric Imager.
Secchi will picture and study coronal mass ejections from their
origin on the Sun to their impact at Earth
- IMPACT: In-situ Measurements of PArticles and CME Transients
is another instrument suite which will measure energetic ions
and electrons accelerated in coronal mass ejections and solar
- PLASTIC: The PLAsma and SupraThermal Ion Composition instrument
will also study CME particles - protons, alpha particles and heavy
- S/Waves: The Stereo/Waves instrument monitors radio disturbances
travelling from Sun to Earth
The STEREO spacecraft carry 16 instruments and are nearly identical. Minor
differences include adjustments allowing one unit to fly upside down, to
point its antenna at Earth. Timing systems will ensure images are taken
by the spacecraft within one second of each other, allowing them to be blended
into 3D pictures.
One STEREO observatory will run slightly ahead of the Earth in its orbit,
taking some 345 days to go around the Sun. Its partner will lag the Earth
slightly, taking 385 days to go around the Sun. The satellites will also
drift further apart each year, widening the angle between themselves and
the Earth as viewed from the Sun. The mission is expected to last at least
AND SPACE PROBES