The scientific objectives of this USN-APL spacecraft were to accurately map the earth's magnetic field over the regions covered by the satellite orbit, to map the celestial sphere in the ultraviolet region, to study the solar spectrum, and to determine the sublimation rates of selected metals. This magnetically aligned and polar-orbiting spacecraft was powered with solar cells and nickel-cadmium batteries. There were three transmitters--two were used for tracking, and the third was used for the transmission of analog and digital data. The digital data were transmitted at 195 bps. Only real-time data were acquired from the satellite. Because of power limitations, it was necessary to switch the power from experiment to experiment and to the Doppler navigational transmitters with the experiments turned off. The satellite provided good quality data until June 1965.