This experiment was designed to study plasma velocity distributions and their spatial and temporal variations in the solar wind, bow shock, magnetosheath, magnetopause, and magnetotail (within the magnetosphere). One-, two-, and three-dimensional velocity distributions for positive ions and electrons were measured using two 90-deg spherical electrostatic analyzers with channeltron electron multipliers as detectors. In conjunction with similar instrumentation (77-102A-01) provided by S. J. Bame/LANL for the mother spacecraft, protons from 50 eV to 40 keV (and electrons from 5 eV to 20 keV) were measured with 10% energy resolution in two ranges each.