Named for the turbulent atmospheric eddies it was designed to study, the Eddy instrument was launched from the El Tortuguero Launch Facility, Puerto Rico, in February 1998.

Designed, built, and calibrated by SDL, Eddy studied invisible turbulence using variety of sensors that measured densities of electrons, atoms and oxygen molecules, and energetic hydroxyl, an ion that emits faint red "airglow" 53 miles above Earth.

Eddy was part of the Coqui Dos series of 11 small rocket launches funded by NASA's Atmospheric Study Program to improve radio and satellite communications by learning more about how such systems are disrupted by "space weather." Space weather results from the interactions of the Sun's and Earth's magnetic fields, a "plasma" of electrically charged particles spewed from the Sun, and gases and dust in Earth's upper atmosphere.