STEREO (Solar Terestrial Relations Observatory): Capturing the Sun in 3-D
HomeMissionObservatoriesSciencePressGalleryEducation
   

Mission Design

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 had to be placed in a rather challenging orbit where they were offset from one another. One observatory was 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 allowed the STEREO observatories to obtain 3-D images of the sun.
Lunar Swingbys

APL mission designers determined that the most efficient and cost-effective method to place the twin observatories, launched aboard a single rocket, into their respective orbits was to use lunar swingbys. This was the first time this technique was used to manipulate orbits of more than one spacecraft. Mission designers used the moon's gravity to redirect the observatories to their appropriate orbits — something the launch vehicle alone couldn't do.

Artist's depiction of a STEREO observatory's lunar swingby maneuver.

For the first three months after launch, the observatories flew 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, Md., 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 "ahead" of Earth. Approximately one month later, the second observatory encountered the moon again and was redirected to its orbit "behind" Earth. When combined with data from observatories on the ground or in low-Earth orbit, STEREO's data is allowing scientists to track the buildup and lift-off of magnetic energy from the sun and the trajectory of Earth-bound CMEs in 3-D.

NASA Goddard Space Flight Center's Solar Terrestrial Probes Program Office in Greenbelt, Md., manages the STEREO mission, instruments and its science center. The Johns Hopkins University Applied Physics Laboratory, in Laurel, Md., designed and built the spacecraft and will operate the twin observatories for NASA during the two-year mission.

The graphic above shows orbits of the "Ahead" (red) and "Behind" (blue) observatories relative to the Earth's orbit (green).
Click on the image to view larger version.

The graphic above shows orbits of the "Ahead" (red) and "Behind" (blue) observatories relative to the Earth's orbit (green). "Ahead's" elliptical orbit fits inside Earth's orbit and transits around the sun faster than Earth; "Behind's" is larger than Earth's orbit and transits around the sun more slowly. Right graphic shows drifting of the observatories (at a rate of 22 degrees per year) away from Earth relative to an Earth-sun reference line (yellow). The "scalloped" lines are caused by the spacecraft's elliptical orbits.

STEREO "A" observes the sun in an orbit ahead of Earth while the "B" spacecraft follows behind the Earth.
Click on the image to view animation.

STEREO "A" observes the sun in an orbit ahead of Earth while the "B" spacecraft follows behind the Earth. The distance between the two observatories changes over the mission timeframe. Click on image to view animation. Credit: NASA.
 
NASA - National Aeronautics and Space Administration                The Johns Hopkins University Applied Physics Laboratory                  STEREO Web Site      
Editor: JHU/APL Webmaster
JHU/APL Official: Kerri Beisser

+ Contact JHU/APL
Back to STEREO Main Page