Released on December 16, 2008
In the early part of the mission, the five THEMIS satellites follow the same orbit single-file. The apogee of the orbit takes the spacecraft just beyond the bow shock of Earth's magnetosphere. This enables the closely spaced satellites to measure the thickness of the different regions that they encounter.
We move in a little closer to better observe the satellites as their orbits carry them in and out of the magnetosphere. This enables them to sample particles and fields in the solar wind outside the magnetsphere and their effects on the magnetosphere as well.