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Faraday Cup Plasma Probe

NSSDC ID: 1961-010A-02
Mission Name: P 14
Principal Investigator: Prof. Herbert S. Bridge


This experiment consisted of a Faraday cup with four grids and a collector designed to provide data on the density of the solar plasma and the magnitude and direction of its bulk motion. Protons were measured in the following energy ranges: 0 to 5, 0 to 20, 0 to 80, 0 to 250, 0 to 800, and 0 to 2300 eV. The experiment was mounted on the spacecraft so that the symmetry axis of the plasma probe was perpendicular to the spacecraft spin axis. The Faraday cup had its maximum response to particles incident at 0 deg to its symmetr axis. The response fell off rapidly until the instrument had a zero response to particles coming in at 63 deg and greater to its normal. The effective area of collection for normal incidence was 28 sq cm. The instrument had two outputs: a dc component related to photoelectric effects and the plasma flux, and an ac component related only to the plasma flux. The shift in the frequency of the ac output component was encoded to be proportional to the plasma flux. A calibration curve to convert from frequency shift to current input to the amplifier is available in Data User's Note: Explorer 10 (1961 Kappa 1) Plasma Probe Experiment, January. 1967 (NSSDC 67-05). The upper energy limit of the plasma particles generating the ac component was determined by the value of a positive retarding voltage applied to one of the grids. This "modulating voltage" had six possible values, from 5 to 2300 eV, and it could also be set to 0. During each 148-s telemetry sequence, 5 s were used by the plasma probe. These 5-s intervals, subcommutated by an interval program, were used to transmit sequentially a marker signal, the dc output of the instrument, and the ac output of the experiment at one of the six modulating voltages. Thus, a complete plasma probe sequence, consisting of eight telemetering cycles, lasted 19 min and 44 s. No inflight calibration was provided, and no onboard processing was done. Because of the limited lifetime of the spacecraft battery, only 52 h of data were acquired. A more detailed description may be found in A. Bonetti et al., "Explorer 10 plasma measurements," J. Geophys. Res., v. 68, pp. 4017-4064, 1963.


  • Space Physics: Magnetospheric Studies

Additional Information

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



NameRoleOriginal AffiliationE-mail
Dr. Bruno B. RossiOther InvestigatorMassachusetts Institute of Technology 
Prof. Frank ScherbOther InvestigatorUniversity of
Prof. Herbert S. BridgePrincipal InvestigatorMassachusetts Institute of Technology 
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