Mission Objectives
Vanguard 2 was an earth-orbiting satellite designed to measure cloud-cover distribution over the daylight portion of its orbit. The spacecraft was a magnesium sphere 50.8 cm in diameter. It contained two optical telescopes with two photocells. The sphere was internally gold-plated and externally covered with an aluminum deposit coated with silicon oxide of sufficient thickness to provide thermal control for the instrumentation. Radio communication was provided by a 1 W, 108.03 MHz telemetry transmitter and a 10 mW, 108 MHz beacon transmitter that sent a continuous signal for tracking purposes. A command receiver was used to activate a tape recorder that relayed telescope experiment data to the telemetry transmitter. Both transmitters functioned normally for 19 days. The satellite was spin stabilized at 50 rpm, but telemetry data were poor because of an unsatisfactory orientation of the spin axis. The power supply for the instrumentation was provided by mercury batteries.
Mission Results
Satellite Drag Atmospheric Density
Because of its symmetrical shape, Vanguard 2 was selected by the experimenters for use in determining upper atmospheric densities as a function of altitude, latitude, season, and solar activity. This experiment was not planned prior to launch. Density values near perigee were deduced from sequential observations of the spacecraft position, using optical (Baker-Nunn camera network) and radio and/or radar tracking techniques. This experiment obtained reasonable density values. Vanguard 2 has an expected orbital lifetime of 300 yr.
Optical Scanner
The optical scanner experiment was designed to obtain cloud-cover data between the equator and 35 to 45 deg N latitude. As the satellite circled the earth, two photocells located at the focus of two optical telescopes aimed in diametrically opposite directions, measured the intensity of sunlight reflected from clouds (about 80%), from land masses (15 to 20%), and from sea areas (5%). The satellite motion and rotation caused the photocells to scan the earth in successive "lines." Separate solar batteries turned on a recorder only when the earth beneath the satellite was in sunlight and about 50 min of data per orbit were obtained. The measured reflection intensities were stored on tape. Ground stations interrogated the satellite by signaling its command receiver, which caused the entire tape to be played back in 60 s. The tape was then erased and rewound. Experiment equipment functioned normally, but data were poor because of an unsatisfactory satellite spin axis orientation.
See also
Last updated: 05-21-2005 04:58:14
