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The newspaper of The Johns Hopkins University November 14, 2005 | Vol. 35 No. 11
Coming Soon: The Sun and Solar Winds in 3-D

Artist's concept of the twin STEREO Observatories studying the sun.

APL-built twin solar probes shipped to Goddard for more pre-launch tests

By Kristi Marren
Applied Physics Laboratory

The first spacecraft designed to capture 3-D "stereo" views of the sun and solar wind were shipped last week from the Applied Physics Laboratory, where they were designed and built, to NASA Goddard Space Flight Center in Greenbelt, Md., for their next round of pre-launch tests.

The two nearly identical observatories, called STEREO for Solar TErrestrial RElations Observatory, were recently tested in APL's vibration lab, where engineers used a large shake table to check their structural integrity. These tests simulate the ride into space the spacecraft will encounter aboard a Delta II launch vehicle from Cape Canaveral Air Force Station, Fla., where they're scheduled for a spring launch.

"Delivery of the twin observatories to NASA is a program milestone," Ed Reynolds, APL STEREO project manager, said. "Building two nearly identical spacecraft simultaneously was a technical and scheduling challenge, but one our team welcomed and tackled with extreme professionalism and dedication. With the design, construction and now delivery of the observatories to NASA Goddard, we're very excited to help NASA get one step closer to launch and capturing the first-ever 3-D images of the sun."

During the next three months at Goddard Space Flight Center, the twin observatories will undergo additional pre-launch checks, including spin tests to check the spacecraft's balance and alignment, thermal vacuum tests to duplicate the extreme temperature and airless conditions of space, and acoustic tests that simulate the noise-induced vibrations of launch. The mission team plans to transport the spacecraft to Florida in March for final launch preparations.

During the two-year STEREO mission, the space-based observatories 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 humans in space.

To obtain "stereo" views of the sun, the observatories must be placed into different orbits where they're offset from each other and the Earth. One observatory will be placed ahead of Earth in its orbit around the sun and the other behind. Just as the slight offset between your eyes provides you with depth perception, this placement will allow the STEREO observatories to obtain 3-D images and particle measurements of the sun.

"This is the first time lunar swingbys will be used to place multiple spacecraft into their respective orbits," APL's Andy Driesman, STEREO system engineer, said. "Mission designers at APL will use the moon's gravity to redirect the observatories to their appropriate orbits around the sun. This innovative mission design allows the use of a single launch vehicle."

After launch, the observatories will fly in an orbit from a point close to Earth to one that extends just beyond the moon. Approximately two months later, mission operations personnel at APL will synchronize spacecraft orbits, directing one observatory to its position trailing Earth in its orbit. Approximately one month later, the second observatory will be redirected to its position ahead of Earth.

STEREO is the third mission in NASA's Solar Terrestrial Probes Program and is sponsored by NASA's Science Mission Directorate, Washington, D.C. NASA GSFC's Solar Terrestrial Probes Program Office manages the mission, instruments and science center. APL designed, built and will operate the twin observatories for NASA during the mission.

For more information about the mission, go to


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