The Three Dimensional Plasma and Energetic Particle experiment (3DP) consists of two pairs of electrostatic analyzers, the electron ones (EESA-Low and EESA-High) and the ion ones (PESA-Low and PESA-High).
These electrostatic analyzers have been designed for full three-dimensional measurements with widely different geometric factors, in order to cover particle fluxes from ~3 eV to 30 keV.

The analyzer design is a symmetrical spherical section electrostatic analyzer with 360 or 180 degrees disk-shaped field of view. In order to minimize spacecraft potential effects on low energy particles, and to provide unimpeded fields of view, EESAs are mounted at the end of a 0.5 meters boomlet, while PESAs are mounted on an opposing 0.5 meters boomlet.

The scientific objectives of this experiment are:

The first detailed exploration of the interplanetary particle population in the suprathermal energy range. The study of particle acceleration at the Sun, in the interplanetary medium, and upstream from the Earth. The study of the transport of suprathermal particles in the interplanetary medium. The study of basic plasma processes occurring in the interplanetary medium, such as wave-particle interactions, the production of radio emission by beam-plasma processes (Type III bursts), shock waves, nonlinear processes such as soliton collapse, and solar wind heat flux. The measurement of the particle and plasma input to and output from the Earth's magnetosphere.