On August 3, 1981, a Delta rocket launched from Vandenberg Air Force Base successfully placed the two Dynamics Explorer (DE) spacecraft into coplanar polar orbits. The purpose of the mission was to acquire data relevant to processes coupling the magnetosphere, ionosphere, and upper atmosphere. The high-altitude satellite, DE-1, carried an auroral imager and detectors designed primarily for field and particle measurements. One of these was the Retarding Ion Mass Spectrometer (RIMS).
The RIMS experiment onboard the DE-1 satellite was designed to perform energy and mass-per-charge analysis on low-energy ions (less than 50 eV) with mass/charge ranging from 1 to 40 amu/Z. RIMS significantly improved capabilities over previous retarding potential analyzer instruments (RPA) by providing ion mass/charge separation so that RPA and spin curves are obtained separately for each programmed species. These enhanced instrument capabilities, combined with the DE-1 orbit, produced a unique opportunity to investigate the variable dynamics and composition of the low-energy ion population in the near-Earth space environment.
DE-1/RIMS consists of four instrument assemblies interconnected to form one experiment. Three of the assemblies are sensor heads and one is the central electronics assembly. The three heads are labeled according to the mounting axis on the DE-1 spacecraft: Radial, +Z, and -Z. The radial sensor views perpendicular to the spacecraft spin axis, while the ±Z sensors on the ends of the spacecraft view parallel and anti-parallel to the spin axis. The central electronics assembly (CEA) provides the spacecraft interface, all data processing, command decoding, and complete timing control of the entire RIMS experiment.