The Mission

Despite the importance of coronal mass ejections (CMEs), scientists don't fully understand the origin and evolution of CMEs, nor their structure or extent in interplanetary space. STEREO's unique 3-D images of the structure of CMEs will enable scientists to determine their fundamental nature and origin.

The STEREO mission will provide a totally new perspective on solar eruptions by imaging CMEs and background events from two observatories simultaneously.

To obtain unique views of the Sun, the twin observatories must be placed into a rather challenging orbit where they will be offset from one another. One observatory will be placed "ahead" of the Earth in its orbit and the other, "behind" using a series of lunar swingbys. 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 of the Sun.

For the first three months after launch, the observatories will fly in an orbit from a point close to Earth to one that extends just beyond the moon. STEREO Mission Operations personnel at The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland will synchronize spacecraft orbits so that about two months after launch they encounter the moon. At this point one of them is close enough to use the moon's gravity to redirect it to a position "behind" the Earth. Approximately one month later, the second observatory will encounter the moon again and be redirected to its orbit "ahead" of Earth.

When combined with data from observatories on the ground or in low-Earth orbit, STEREO's data will allow scientists to track the buildup and lift-off of magnetic energy from the Sun and the trajectory of Earth-bound CMEs in 3-D.