Pioneer 8

Description

Pioneer 8 was the third in a series of solar-orbiting, spin-stabilized, solar-cell and battery-powered satellites designed to obtain measurements of interplanetary phenomena from widely separated points in space on a continuing basis. The spacecraft carried experiments to study the positive ions and electrons in the solar wind, the interplanetary electron density (radio propagation experiment), solar and galactic cosmic rays, the interplanetary magnetic field, cosmic dust, and electric fields. Its main antenna was a high-gain directional antenna. The spacecraft was spin-stabilized at about 60 rpm, and the spin axis was perpendicular to the ecliptic plane and pointed toward the south ecliptic pole. By ground command, one of five bit rates, one of four data formats, and one of four operating modes could be selected. The five bit rates were 512, 256, 64, 16, and 8 bps. Three of the four data formats were used primarily for scientific data and consisted of 32 seven-bit words per frame. One scientific data format was used at the two highest bit rates. Another was used at the three lowest bit rates. The third was used for data from only the radio propagation experiment. The fourth data format was used mainly for engineering data. The four operating modes were (1) real time, (2) telemetry store, (3) duty cycle store, and (4) memory readout. In the real-time mode, data were sampled and transmitted directly (without storage) as specified by the data format and bit rate selected. In the telemetry store mode, data were stored and transmitted simultaneously in the format and at the bit rate selected. In the duty cycle store mode, a single frame of scientific data was collected and stored at a rate of 512 bps. The time interval between the collection and storage of successive frames could be varied by ground command between 2 and 17 min to provide partial data coverage for periods up to 19 h, as limited by the bit storage capacity. In the memory readout mode, data were read out at whatever bit rate was appropriate to the satellite distance from the Earth.

Pioneer 8 was launched on 13 December 1967 into a heliocentric orbit with a mean radius of 1.1 AU. The spacecraft was last tracked successfully on 22 August 1996, after being commanded to the backup transmitter tube (TWT). There are no further plans to track or attempt communications with Pioneer 8.