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Solar Plasma Detector

NSSDCA ID: 1968-100A-02

Mission Name: Pioneer 9
Principal Investigator:Dr. John H. Wolfe


A truncated hemispherical electrostatic analyzer (120-deg total parallel-plate curvature) with three contiguous current collectors was used to study the directional intensity of the electrons and positive ions in the solar wind. Ions were detected in 30 logarithmically equispaced energy per unit charge (E/Q) steps from 150 to 15,000 V. There was an electron mode of operation in which electrons were measured in 14 logarithmically equispaced E/Q steps ranging from 12 to 1000 V. There was also a zero E/Q, or background, step. The three collectors measured particles incident from three different contiguous angular intervals relative to the spacecraft equatorial plane (same as the ecliptic plane). Two collectors measured flux from 10 to 85 deg on either side of the spacecraft equatorial plane, and the third measured flux in a 20-deg interval centered on the spacecraft equatorial plane. As the spacecraft was spinning, fluxes were measured in 23 possible 2-13/16-deg-wide azimuthal angular sectors. Seventeen of these sectors were contiguous and bracketed the solar direction. The remaining six sectors were widely spaced. The instrument had three modes of data collection: polar scan, azimuthal scan, and maximum flux. At the two highest bit rates (512 and 256 bps), the polar-scan mode was alternated with the azimuthal scan mode at each E/Q step. In the polar-scan mode, all three collectors were observed, and the peak flux obtained and the azimuthal direction (to 2-13/16 deg) of the observation were reported for each collector. In the azimuthal scan mode, the peak flux observed in the 23 azimuthal sectors was recorded for the central collector at each E/Q step. At the low bit rates (64, 16, and 8 bps), the maximum flux mode was used at each E/Q step followed by either (1) for ions, a polar scan and an azimuthal scan at that E/Q step where the peak flux measurement during the maximum flux mode was obtained, or (2) for electrons, a polar scan and an azimuthal scan at E/Q = 100 V. In the maximum flux mode, only the central collector was observed, the peak flux obtained, and the azimuthal direction (to 2-13/16 deg) of the observation reported. A complete set of measurements consisted of seven sets of ion measurements (at each E/Q step) and one set of electron measurements (at each E/Q step). At the high bit rates (512 and 256 bps) one set of ion measurements took 62 s and one set of electron measurements, 38 s. At the low bit rates (64, 16, and 8 bps), one set of ion measurements took 37 s and one set of electron measurements took 28 s. At 64 bps, a complete set of measurements (seven ions plus one electron) was taken and telemetered every 402.5 s. At 16 bps, it took 1610 s, and, at 8 bps, it took 3220 s.

Alternate Names

  • Pioneer9/SolarPlasmaDetector

Facts in Brief

Mass: 2.6 kg

Funding Agency

  • NASA-Office of Space Science Applications (United States)


  • Space Physics: Heliospheric Studies

Additional Information

Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Mr. Darrell D. McKibbinOther InvestigatorNASA Ames Research Center
Dr. John H. WolfePrincipal InvestigatorNASA Ames Research Center
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