The STEREO mission: an overview

In February 2006, NASA will launch the twin STEREO spacecraft from Kennedy Space Center aboard a Delta 7925 launch vehicle. After a series of highly eccentric Earth orbits with apogees beyond the moon, each spacecraft will use close flybys of the moon to escape into heliocentric orbits at 1 AU, with one spacecraft trailing Earth and the other leading Earth. As viewed from the Sun, the two spacecraft will separate at approximately 45° per year. The purposes of the STEREO Mission are to understand the causes and mechanisms of coronal mass ejection initiation and to follow the propagation of CMEs through the heliosphere. Additionally, STEREO will study the mechanisms and sites of energetic particle acceleration and develop 3D time-dependent models of the magnetic topology, temperature, density and velocity of the solar wind between the Sun and Earth. To accomplish these goals, each STEREO spacecraft will be equipped with a set of optical, radio and in situ particles and fields instruments. The SECCHI suite of instruments includes two white light coronagraphs covering the range from 1.4 to 15 solar radii, an extreme ultra violet imager covering the chromosphere and inner corona, and two heliospheric white light imagers covering the outer corona from 12 solar radii to 1 AU. The IMPACT suite of instruments will measure in situ solar wind electrons in the energy range from essentially 0 to 100 keV, energetic electrons to 6 MeV, and protons and heavier ions to 100 MeV/nucleon. IMPACT also contains a magnetometer to measure the in situ magnetic field strength and direction. The PLASTIC instrument will measure the composition of heavy ions as well as protons and alpha particles. The SWAVES instrument will use radio waves to track the location of CME-driven shocks and the 3D topology of open field lines along which energetic particles flow. Additionally, SWAVES will measure in situ plasma waves to provide an independent estimate of the local plasma density and temperature. Each of the four instruments will produce a small real-time stream of selected data for purposes of predicting space weather events at Earth, primarily for NOAA forecasters. In addition to the four instrument teams, there will be substantial participation by modeling and theory oriented teams. All STEREO data will be freely available through individual Web sites at the four Principal Investigator institutions as well as at the STEREO Science Center located at NASA Goddard Space Flight Center.