The Delta II rocket with the STEREO spacecraft next to the launch gantry ready for liftoff.

The Delta II rocket with the STEREO spacecraft at top stands next to the launch gantry, ready for liftoff. Launch is scheduled in a window between 8:38 and 8:53 p.m. on Oct. 25.STEREO (Solar Terrestrial Relations Observatory) is a two-year mission using two nearly identical observatories, one ahead of Earth in its orbit and the other trailing behind. The duo will provide 3-D measurements of the sun and its flow of energy, enabling scientists to study the nature of coronal mass ejections and why they happen. The ejections are a major source of the magnetic disruptions on Earth and are a key component of space weather. The disruptions can greatly effect satellite operations, communications, power systems, humans in space and global climate. Designed and built by the Johns Hopkins University Applied Physics Laboratory (APL) , the STEREO mission is being managed by NASA Goddard Space Flight Center. APL will maintain command and control of the observatories throughout the mission, while NASA tracks and receives the data, determines the orbit of the satellites, and coordinates the science results. Photo credit: NASA/Kim Shiflett