Knowledge of the fluxes and energy of high-energy protons, alpha particles, and electrons is essential in understanding the dynamic behavior of solar flare, CIR and ESP events. These measurements are made by EPAM, the Electron, Proton, and Alpha Monitor. This instrument provides information that can reflect changes in both coronal and interplanetary magnetic fields, and information on solar flares. EPAM covers the range of energies from 30 keV/nucleon up to 4 MeV/nucleon. It measures the composition of elements up through iron.

EPAM includes five telescopes of three different types. Two Low Energy Foil Spectometers (LEFS) measure the flux and direction of electrons above 30 keV. Two Low Energy Magnetic Spectometers (LEMS) measure the flux and direction of ions greater than 30 keV. And the Composition Aperture (CA) measures the composition of the ions. Solid-state detectors on each telescope analyze the energy of the incoming particles. These telescopes use the spin of the spacecraft to sweep the full sky.

The EPAM instrument was built by JHU/APL with DR. L. J. Lanzerotti of Lucent Technologies as Prinicipal Investigator. It is the flight spare of the HI-SCALE instrument from the Ulysses spacecraft.