About the STEREO Mission

Mission Design | The basics:

• Two Sun-pointed observatories with identical instrument complements.
• Each in a heliocentric orbit drifting away from the Earth, one leading and one lagging.

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The most efficient and cost-effective method to place the twin observatories, launched aboard a single rocket, into their respective orbits was to use what is known as "lunar swingbys." This was the first time this technique has been used to manipulate orbits of more than one spacecraft at the same time. Mission designers use the Moon's gravity to redirect the observatories to their appropriate orbits - something the launch vehicle alone is not able to do.

For the first three months after launch, the two observatories flew in highly elliptical orbits extending from very close to Earth to just beyond the Moon's orbit. STEREO Mission Operations personnel at the Johns Hopkins University's Applied Physics Laboratory (APL) in Laurel, Maryland, synchronized spacecraft orbits so that about two months after launch they encountered the Moon, at which time one of them was close enough to use the Moon's gravity to redirect it to a position "behind" Earth. Approximately one month later, the second observatory encountered the Moon again and was redirected to its orbit "ahead" of Earth.

Thus, the two STEREO spacecraft provide a stereoscopic view of the Sun and its atmosphere, similar to the way our two eyes allow us to see the three-dimensional world around us. When combined with data from observatories on the ground and in low-Earth orbit, STEREO's data allows scientists to track the buildup and lift-off of magnetic energy from the Sun and the trajectory of Earth-bound CMEs in 3-D.

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• STEREO orbit simulations