A triaxial-accelerometer system will be included in each of the Atmosphere Explorer (AE) payloads. The instrument consists of three uniaxial miniature-electrostatic-accelerometer units mounted mutually at right angles. This paper provides a description of the accelerometer system being designed for AE. It includes the principles of the instrument operation, the measurement capabilities, and the relation between the measured data and the scientific and engineering results. The functions of the instrument are to determine the density of the neutral atmosphere, monitor the thrust of the orbit-adjust propulsion system, determine the satellite minimum altitude, measure spacecraft roll, and provide some attitude-sensing information. Measurements will be made four times per second or approximately once every 2 km of flight path. Density variations will be determined with an accuracy ranging from approximately 1% below 200 km to 10% at 350 km, not including any error in ephemeris or drag coefficient.