The Stereo Mission PDF Download

Coronal mass ejections (CMEs) are massive outflows of material from the Sun's corona, traveling into the surrounding heliosphere at speeds up to 1000-2000 kilometers per second. When directed toward the Earth, CMEs can result in damage to satellites, enhanced auroral displays, blackouts of power grids on Earth, and interference with surface radio communications. The first CME detected from space was observed by an NRL coronagraph onboard the Seventh Orbiting Solar Observatory (OSO-7) in December 1971. Much of our recent knowledge of CMEs has been obtained from an NRL visible-light coronagraph (LASCO, the Large Angle Spectroscopic Coronagraph(2)) on the Solar and Heliospheric Observatory (SOHO) spacecraft, launched in 1995. But SOHO observes from only one viewpoint, leaving three-dimensional structure ambiguous for individual CMEs. The next step beyond SOHO is the Solar Terrestrial Relations Observatory (STEREO) mission, consisting of two spacecraft observing the Sun from two different viewpoints, allowing a three-dimensional view of the initiation of CMEs and their propagation outwards. In addition, STEREO will carry a new type of heliospheric coronagraph that is off-pointed from the solar disk, and can observe from the side the Sun-Earth line all the way out to Earth. The STEREO mission is meant to increase our understanding of such topics as solar structures and their properties involved in CME initiation; threedimensional structure and kinematics of CMEs; three-dimensional structure of active regions, coronal loops, and streamers; propagation of CMEs into the corona and interplanetary medium; and the effects of CMEs through the heliosphere to the Earth.