NASA Satellites Will Improve Understanding the Sun (STEREO)

Aug. 17, 2006

Erica Hupp/Dwayne Brown
Headquarters, Washington
202-358-1237/1726

Rachel Weintraub
Goddard Space Flight Center, Greenbelt, Md.
301-286-0918

RELEASE: 06-294

NASA SATELLITES WILL IMPROVE UNDERSTANDING OF THE SUN

NASA's Solar Terrestrial Relations Observatory mission will
dramatically improve understanding of the powerful solar eruptions
that can send more than a billion tons of the sun's outer atmosphere
hurtling into space.

The STEREO mission comprises two nearly identical spacecraft the size
of golf carts, which are scheduled to launch on Aug. 31 aboard a
Delta II rocket from Cape Canaveral Air Force Station, Fla. Their
observations will enable scientists to construct the first-ever
three-dimensional views of the sun. These images will show the sun's
stormy environment and its effect on the inner solar system. The data
are vital for understanding how the sun creates space weather.

During the two-year mission, the two spacecraft will explore the
origin, evolution and interplanetary consequences of coronal mass
ejections, some of the most violent explosions in our solar system.
When directed at Earth, these billion-ton eruptions can produce
spectacular aurora and disrupt satellites, radio communications and
power systems. Energetic particles associated with these solar
eruptions permeate the entire solar system and may be hazardous to
spacecraft and astronauts.

"In terms of space-weather forecasting, we're where weather
forecasters were in the 1950s," said Michael Kaiser, STEREO project
scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.
"They didn't see hurricanes until the rain clouds were right above
them. In our case, we can see storms leaving the sun, but we have to
make guesses and use models to figure out if and when they will
impact Earth."

To obtain their unique stereo view of the sun, the two observatories
must be placed in different orbits, where they are offset from each
other and Earth. Spacecraft "A" will be in an orbit moving ahead of
Earth, and "B" will lag behind, as the planet orbits the sun.

Just as the slight offset between eyes provides depth perception, this
placement will allow the STEREO observatories to obtain 3-D images of
the sun. The arrangement also allows the spacecraft to take local
particle and magnetic field measurements of the solar wind as it
flows by the spacecraft.

STEREO is the first NASA mission to use separate lunar swingbys to
place two observatories into vastly different orbits around the sun.
The observatories will fly in an orbit from a point close to Earth to
one that extends just beyond the moon.

Approximately two months after launch, mission operations personnel at
the Johns Hopkins University Applied Physics Laboratory, Laurel, Md.,
will use a close flyby of the moon to modify the orbits. The moon's
gravity will be used to direct one observatory to its position
trailing Earth. Approximately one month later, the second observatory
will be redirected after another lunar swingby to its position ahead
of Earth. These maneuvers will enable the spacecraft to take
permanent orbits around the sun.

Each STEREO observatory has 16 instruments. The observatories have
imaging telescopes and equipment to measure solar wind particles and
to perform radio astronomy.

"STEREO is charting new territory for science research and the
building of spacecraft. The simultaneous assembly, integration and
launch of nearly identical observatories have been an extraordinary
challenge," said Nick Chrissotimos, STEREO project manager at
Goddard.

The STEREO mission is managed by Goddard. The Applied Physics
Laboratory designed and built the spacecraft. The laboratory will
maintain command and control of the observatories throughout the
mission, while NASA tracks and receives the data, determines the
orbit of the satellites, and coordinates the science results.

For more information about STEREO, visit:

http://www.nasa.gov/stereo

For more information about NASA and agency programs, visit:

http://www.nasa.gov/home


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