This data set includes all processed electron, proton, and alpha particle data from the S3-3 Magnetic Electron Spectrometer (MES). The electron data were sampled at 1/16 second intervals and include differential counts for twelve channels at the following mean energies, determined from calibrations for flat spectra: 12, 33, 70, 120, 170, 235, 433, 654, 880, 1110, 1350, and 1600 keV. The counts for 433 to 654 keV electrons are provided with and without corrections for saturation effects. Proton data consists of integral counts per channel for incident energies above 80, 150, 350, 770, and 1550 keV. Counts for 4 - 12 MeV alphas were sampled in one channel at 1/4 second intervals. Pitch angle information was provided for computation of directional fluxes at intervals of 1/16 second for electrons and 1/4 second for protons. At a spacecraft spin rate of 18 degrees per second this gave 1.1-degree sampling intervals for electrons and four-degree intervals for protons. Pitch-angle values may be in error by as much as one degree at times due to the fact that the raw magnetometer data was fitted to a field model and the calculations of pitch-angle were then performed using that field model. The aperature half-angle was two degrees for the five lowest electron channels (12 - 170 keV) and five degrees for the ion and higher energy electron channels. The full MES data files are reformatted in this data set from the data provider's 'VAX tape format' into Intel-PC 32-bit words with 164 words per one-second data 'frame' and 200 frames per data set record. All of the 32-bit words include two INTEGER2 parameters, except that Universal Time and L are stored in INTERGER4 words. Each data frame also includes time tags along with ephemeris, and geomagnetic coordinate data. The ephemeris and geomagnetic data include values pertaining to the intersection points of the local field line on which the satellite is situated and conjugate mirror points at 100-km altitude in the northern and southern hemispheres. Detailed information on the MES sensors and the data file formats are provided in ascii text format. The data set includes FORTRAN source codes, and some Intel-PC executables, used to process the proton and electron data and for calculation of geometric factors.\n