The energetic particle and plasma spectrometer instrument on the MESSENGER spacecraft

The Energetic Particle and Plasma Spectrometer (EPPS) package on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission to Mercury is composed of two sensors, the Energetic Particle Spectrometer (EPS) and the Fast Imaging Plasma Spectrometer (FIPS). EPS measures the energy, angular, and compositional distributions of the high-energy components of the in situ electrons (> 20 keV) and ions (> 5 keV/nucleon), while FIPS measures the energy, angular, and compositional distributions of the low-energy components of the ion distributions (< 50 eV/charge to 20 keV/charge). Both EPS and FIPS have very small footprints, and their combined mass (similar to 3 kg) is significantly lower than that of comparable instruments.