The Equator-S mission

In spite of its short operational life of only five months, the major goals of the Equator-S mission were fulfilled, except that its contribution to t he ISTP science is restricted to the morning sector of the outer magnetosph ere. A set of twelve papers following this introduction is a first document ation of the achievements. They span from the successful testing and operat ion of the most advanced and complex way of measuring electric fields in a hot plasma environment by means of electron beams, to various investigation s at or near the equatorial magnetopause and in the plasma sheet.