STEREO (Solar TErrestrial RElations Observatory), launched in 2006, employed two nearly identical space-based observatories - one ahead of Earth, the other trailing behind – that provided the first-ever stereoscopic measurements to study the Sun and the nature of its coronal mass ejections, or CMEs. STEREO currently consists of a single spacecraft, STEREO-A, orbiting the Sun just inside of 1 AU, slowly catching up with Earth. This viewpoint away from the Earth-Sun line allows scientists to see the structure and evolution of solar storms as they blast from the Sun and move out through space.