the equator of the sphere at 90° intervals. A small solar cell and cadmium sulfide cell were also mounted on the sphere wall near the equator. The magnetometer sensor head was mounted at the end of the conical boom. The sphere was spin-stabilized and had passive thermal control. It had no engines for thrust or attitude control. Launch Vanguard 3 was launched at 05:20:07 GMT (12:20:07 a.m. EST) on 18 September 1959 from the Eastern Test Range of the Atlantic Missile Range at Cape Canaveral into a geocentric orbit. The satellite was then injected at 05:29:49 GMT into a 33.35° inclination Earth orbit with a perigee altitude of , apogee of , and an orbital period of 130.0 minutes. The third stage was purposely left attached to the satellite, in order to produce a long tumble period, to avoid corrections to the magnetometer that would be necessary with a rapidly rotating satellite. Perigee remained on the night side of Earth throughout the mission. All experiments functioned normally and the batteries lasted for 84 days, until 11 December 1959, at which time all communication with the spacecraft ceased. It was still tracked optically (telescopes) for the atmospheric drag experiment. The objectives of the flight were to measure the Earth's magnetic field, the solar X-ray radiation and its effects on the Earth's atmosphere, the near-Earth micrometeoroid environment, and the drag effects and density of the upper atmosphere. Instrumentation included a proton magnetometer, X-ray ionization chambers, radio transmitters, and various micrometeoroid detectors. The data obtained provided a comprehensive survey of the Earth's magnetic field over the area covered, defined the lower edge of the Van Allen radiation belt, and provided a count of micrometeoroid impacts. Vanguard 3 has an expected orbital lifetime of roughly 300 years from launch. Mission objectives The objectives of the flight were to measure the Earth's magnetic field, the solar X-ray radiation and its effects on the atmosphere of Earth, and the near-Earth micrometeoroid environment. Instrumentation included a proton magnetometer, X-ray ionization chambers, and various micrometeoroid detectors. The spacecraft was a of diameter magnesium sphere. The magnetometer was housed in a fiberglass/phenolic resin conical tube attached to the sphere. Data transmission stopped on 11 December 1959, after 84 days of operation. The data obtained provided a comprehensive survey of the Earth's magnetic field over the area covered, defined the lower edge of the Van Allen radiation belt, and provided