Pioneer 7

Purpose

Pioneer 7 was built to make detailed measurements of the solar wind, solar magnetic field, and cosmic rays, studying large-scale magnetic phenomena and particles in interplanetary space. Its data helped understand stellar processes and solar wind structure. It also served as part of the first space-based solar weather network, providing practical data on solar storms. Experiments examined positive ions and electrons in the solar wind, interplanetary electron density, solar and galactic cosmic rays, and the interplanetary magnetic field.

Communications

By ground command, one of five bit rates (512, 256, 64, 16, or 8 bit/s), one of four data formats, and one of four operating modes could be selected. Three scientific data formats each contained 32 seven-bit words per frame: one for the two highest bit rates, one for the three lowest, and one for the radio propagation experiment only.

The fourth format held engineering data. The four operating modes were real-time, telemetry store, duty-cycle store, and memory readout. In duty-cycle store mode, a single frame was collected at 512 bit/s, with intervals between frames adjustable from 2 to 17 minutes, providing partial coverage for up to 19 hours.

Timeline and current status

Pioneer 7 was launched on August 17, 1966, from Cape Canaveral into a solar orbit with a mean distance of 1.1 AU. On March 20, 1986, it flew within 12.3 million kilometers of Halley's Comet, monitoring the interaction between the cometary hydrogen tail and the solar wind, and discovered He+ plasma produced by charge exchange of solar wind He++ with neutral cometary material.

It was tracked successfully on March 31, 1995, with the spacecraft and one science instrument still functioning. The program has been described as one of the least expensive NASA spacecraft programs in terms of scientific results per dollar spent. Although the four spacecraft have not been regularly tracked for science data return in recent years, it is believed that contact is still possible with Pioneer 7 and 8; only Pioneer 9 is definitely not working.

Did You Know?

• The spacecraft was spin-stabilized at about 60 RPM, with its spin axis perpendicular to the ecliptic plane and pointed toward the south ecliptic pole.
• Pioneer 7 was commanded to switch to its backup traveling-wave tube on August 22, 1996, after which the downlink signal was re-acquired and one science instrument again functioned.