The objective of this experiment was to study quasi-static and low-frequency electric fields in the plasmasphere, magnetosphere, magnetosheath, and solar wind. Measurements were made of the potential difference between a pair of 8-cm diameter vitreous carbon spheres which were separated by 73.5 m and mounted on the ends of wire booms in the satellite spin plane. To attempt to overcome the spacecraft sheath (a potential problem which plagues all electric field detectors), an electron gun for changing the spacecraft potential was included, and all exposed spacecraft surfaces were made electrically conducting. The instrument was designed to be sensitive to fields from 0.1 to 200 mV/m in the frequency band of 0 to 12 Hz. The experiment also measured the electric field component of waves at frequencies below 1000 Hz.