Pioneer 6, 7, 8 and 9 were all part of the Pioneer program, and together formed a series of solar-orbiting, spin-stabilized, solar-cell and battery-powered satellites designed to obtain measurements on a continuing basis of interplanetary phenomena from widely separated points in space. They were also known as Pioneer A, B, C and D. A fifth (Pioneer E) lost in a launch accident. Each craft was identical, with an on-orbit dry mass of 146 kg. They were spin-stabilized 0.94 m diameter × 0.81 m tall cylinders with a 1.8 m long magnetometer boom and solar panels mounted around its body.

Launch and Onboard Systems

Pioneer 6 was launched on December 16, 1965 at 07:31:00 UTC, Pioneer 7 on July 17, 1966, Pioneer 8 on December 13, 1967 at 14:08:00 UTC, Pioneer 9 on November 8, 1968 at 09:46:00 UTC, and Pioneer E on July 27, 1969 at 21:59:00 UTC.

Its experiments studied the positive ions and electrons in the solar wind, the interplanetary electron density (radio propagation experiment), solar and galactic cosmic rays, and the interplanetary magnetic field. Its main antenna was a high-gain directional antenna. The spacecraft was spin-stabilized at about 1 Hz, and the spin axis was perpendicular to the ecliptic plane and pointed toward the south ecliptic pole. Pioneers 6, 7, 8, and 9 were created to make the first detailed, comprehensive measurements of the solar wind, solar magnetic field and cosmic rays. Designed to measure large scale magnetic phenomena and particles and fields in interplanetary space, data from the vehicles has been used to better understand stellar processes as well as the structure and flow of the solar wind. The vehicles also acted as the world's first space-based solar weather network, providing practical data on solar storms which impact communications and power on Earth.

Communications

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 bit/s. Three of the four data formats contained primarily scientific data and consisted of 32 seven-bit words per frame. One scientific data format was for use at the two highest bit rates. Another was for use at the three lowest bit rates. The third contained data from only the radio propagation experiment. The fourth data format contained mainly engineering data. The four operating modes were real time, telemetry store, duty cycle store, and 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 bit/s. 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 Earth.

Current Status

The Pioneer 6-9 program has been touted as one of the least expensive of all NASA spacecraft programs in terms of scientific results per dollar spent. Although the spacecraft have not been regularly tracked for science data return in recent years, a successful telemetry contact with Pioneer 6 was made on December 8, 2000 to celebrate 35 years of continuous operation since launch. Its original design life expectancy was only 6 months.