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The newspaper of The Johns Hopkins University August 21, 2006 | Vol. 35 No. 42
Set to Launch: APL-Built STEREO Spacecraft on Target for Aug. 31
The two-year mission will provide scientists with first 3-D views of the sun

By Kristi Marren
Applied Physics Laboratory

Two nearly identical spacecraft, destined to capture the first-ever 3-D views of the sun, are scheduled for launch on Aug. 31 aboard a Delta II rocket from Cape Canaveral Air Force Station, Fla., at 3:12 p.m. or 4:20 p.m. The window extends through Sept. 4, with two launch opportunities daily for the spacecraft, which were built and will be operated for NASA by Johns Hopkins' Applied Physics Laboratory.

The two-year STEREO mission--which gets its name from Solar TErrestrial RElations Observatory--will explore the origin, evolution and interplanetary consequences of coronal mass ejections. These powerful solar eruptions are a major source of the magnetic disruptions on Earth and a key component of space weather, which can greatly affect satellite operations, communications, power systems and the lives of astronauts in space.

"Building and testing two spacecraft simultaneously has been a technical and scheduling challenge, but an effort at which we've been successful," says Ed Reynolds, APL STEREO project manager.

To capture the sun in 3-D, the twin observatories will fly as mirror images, with one placed ahead of Earth in its orbit around the sun and the other behind. Just as the slight offset between a person's eyes provides depth perception, this placement will allow the observatories to obtain 3-D images and particle measurements of the sun.

Mission designers determined that the most efficient and cost-effective way to get the observatories into space was to launch them aboard a single rocket and use lunar swingbys to place them into their respective orbits. This is the first time lunar swingbys will be used to manipulate orbits of more than one spacecraft. Mission designers will use the moon's gravity to redirect the observatories to their appropriate orbits.

After launch, the observatories will initially fly in an elliptical orbit that extends from Earth just beyond the moon. Approximately two months later, mission operations personnel at APL will synchronize the orbits and direct one observatory to its position trailing Earth; about one month after that, the second observatory will be redirected to its position ahead of Earth.

Each observatory will carry more than a dozen instruments. When combined with data from observatories on the ground or in space, STEREO's data will allow scientists to track in 3-D the buildup and liftoff of magnetic energy from the sun and the trajectory of Earth-bound coronal mass ejections.

The third mission in NASA's Solar Terrestrial Probes Program, STEREO is sponsored by NASA's Science Mission Directorate. NASA Goddard's Solar Terrestrial Probes Program Office manages the mission, instruments and science center.

For more about STEREO, go to


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