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Cosmic Dust Detector

NSSDCA ID: 1962-041A-05

Mission Name: Mariner 2
Principal Investigator:Dr. Wesley M. Alexander

Description

Direct measurement of the flux of interplanetary dust as a function of time and as a function of the distance from the Sun, Earth, and Venus was made by means of a two-channel pulse-height analysis of a microphone momentum detector output. The Cosmic Dust (or Micrometeoroid) detector consisted of a crystal-transducer microphone bonded to the center of an approximately 5 x 10 inch magnesium sensor plate (0.035 sq m). It was mounted on the lower part of the spacecraft frame. The microphone was tuned to 100 kHz, with a gain of 100 db. It could differentiate two momentum ranges differing in magnitude by a factor of ten. The system was capable, at both momentum levels, of counting three events and storing them for later telemetry to Earth. After the data were transmitted, a delayed data-reset command signal reset the data binaries and initiated an electrical calibration pulse across the sensor crystal in the input of the microphone amplifier. The detector had a solid viewing angle of pi steradians and a minimum threshold sensitivity of 0.00074 +/- 0.00017 dyne s. Measurable flux was between 1.5 and 2.8 impacts per square meter per second. Particles with masses as low as 0.13 nanograms could be detected.

The performance of the less sensitive channel of the detector became degraded 2 weeks prior to Venus encounter, initially missing calibration, and, after 45 minutes, no longer displaying calibration. At Venus encounter, the more sensitive channel, too, began missing calibration, and, after 45 minutes, it also stopped showing calibration altogether. This degradation was due, apparently, to overheating of the crystal transducer, which caused a change in the impedance. This change in impedance degraded the calibration amplitude but not the electronics. Despite this degradation, the experiment accumulated data throughout the trajectory (129 days), observing, at different times, particles with direct or retrograde heliocentric orbits. The data contained two definite hits along with several others that remain questionable due to the calibration problem.

Alternate Names

  • Mariner2/CosmicDustDetector
  • Micrometeoroid Detector

Facts in Brief

Mass: 0.84 kg
Power (avg): 0.1 W

Disciplines

  • Space Physics: Zodiacal Light/Interplanet Dust
  • Planetary Science: Small Bodies

Additional Information

Questions and comments about this experiment can be directed to: Dr. David R. Williams

 

Personnel

NameRoleOriginal AffiliationE-mail
Mr. Elmer S. McMillanCo-InvestigatorNASA Jet Propulsion Laboratory
Dr. Wesley M. AlexanderPrincipal InvestigatorBaylor University

Selected References

  • Alexander, W. M., The mission of Mariner II: Preliminary observations, cosmic dust, Science, 138, 1098-1099, doi:10.1126/science.138.3545.1098, Dec. 1962.
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