The Electron Spectrometer Experiment on ISEE-1

A six-axis electron spectrometer for the ISEE-1 spacecraft is described and some typical early results presented. This instrument, designed for three-dimensional plasma distribution function studies in the solar wind, magnetosheath, outer magnetosphere, and near tail regions, has three energy ranges: 7.5-512 eV, 11-2062 eV, and 109-7285 cV, respectively. Two channel electron multipliers are used at the output of each of six cylindrical electrostatic analyzers. The total mass of two sensors and a data processing unit is 4.9 kg and the power comsumption is 3.5 W. Two hundred information bits/s telemetry rate is required.