STEREO mission overview
FROM NASA PRESS KIT
Posted: October 21, 2006
STEREO is also designed to provide unique alerts for Earth-directed CMEs and new information regarding their propagation and associated phenomena throughout the solar system. The mission will provide a new perspective on solar eruptions by imaging CMEs and background events from the two observatories simultaneously. The first spacecraft will lead and the second will fly behind the Earth in its orbit.
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 (JHU/APL), in Laurel, Md., will synchronize spacecraft orbits so that about two months after launch they encounter the moon, at which time 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 and magnetic field geometry of Earth-bound CMEs in 3-D.
NASA Goddard Space Flight Center's Solar Terrestrial Probes (STP) Program Office in Greenbelt, Md., manages the STEREO mission, instruments and its science center. The Johns Hopkins University Applied Physics Laboratory (JHU/APL) designed, built, and will operate the twin observatories for NASA during the two-year mission.
What exactly is space weather?
What are coronal mass ejections (CMEs) and why study them?
Understanding what causes CMEs and how they move through the solar system is one of the chief goals of the STEREO mission. The different telescopes in the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument suite image the CMEs. The actual material in CMEs is measured as they pass the spacecraft using the In situ Measurements of Particles and CME Transients (IMPACT) and PLAsma and Supra Thermal Ion and Composition (PLASTIC) instruments. The STEREO/WAVES (SWAVES) instruments observe radio signals produced by shock waves formed as the CMEs plow through the solar wind.
What are solar flares?
Although most of what is called a solar flare occurs relatively low in the sun's atmosphere, flares do release charged particles that travel along the magnetic field lines of the interplanetary magnetic field (IMF). Electrons emitted this way by flares produce radio waves detected by the SWAVES instruments and allow researchers to map the IMF.
Sometimes these charged particles may be high enough in energy to qualify as solar energetic particles (SEPs). SEPs, along with the X-rays and gamma-rays produced by flares, can be very harmful to astronauts.
What will the 3-D images look like?
How does the solar cycle influence STEREO's mission?
STEREO will track these disturbances from their onset at the sun's surface to beyond Earth's orbit, measure energetic particles generated by CMEs and flares, and sample fields and particles in the disturbances as they pass near Earth. The STEREO scientific program does not depend on the phase of the solar cycle because CMEs and other phenomena to be studied are common to all phases of the cycle. Although the CME rate varies with the solar cycle, assuming a CME rate consistent with the minimum of the solar magnetic activity cycle, STEREO expects to observe at least 60 CMEs in remote sensing instruments and at least 24 interplanetary events in-situ.
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