Two triaxial systems of 127-deg cylindrical
electrostatic analyzers were used to make three-dimensional
measurements of the electron distribution function. There were
three modes of operation, with the following nominal energy ranges:
solar wind, 7 to 500 eV; magnetosheath, 10 eV to 2 keV;
and magnetotail and solar, 105 eV to 7.05 keV. The energy
resolution (delta E/E) was 0.07. The entire set of six simultaneous
spectrometer measurements was taken while the satellite rotated
through 60 deg. Each spectrometer consisted of a curved-plate
analyzer and two channeltron detectors.