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Cosmic Dust Detector

NSSDCA ID: 1961-032A-07

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

Description

The Cosmic Dust Detector was designed to measure the flux of dust particles in cislunar space and to obtain rough values of the particles' energy and momentum distributions. The scientific objectives were to make determinations about dust density and the effects of the Earth's gravitational field on this density, the mass and velocity distributions of the dust particles, and any time variation of these properties that may exist.

The Cosmic Dust detector package was housed in a 8.6 x 15.2 x 15.2 cm (3.375 x 6 x 6 inch) extruded magnesium box, plated with 0.005 cm (0.002 in) of 24 k gold to stabilize the operating temperature at 15.5 C (60 F). The experiment had a mass of 1.60 kg (3.55 lb) and required 2 W power. It was mounted on the top of the main spacecraft structure with the detectors pointed at 90 degrees to the expected probe-Sun line and in the Earth-probe-Sun plane. The detector comprised two types of particle sensors, one to measure energy and one to measure momentum.

The energy impact detector was a light flash detector that measured the light emission during micro-crater formation and operated on the assumption that the intensity of the light emitted is roughly proportional to the kinetic energy of the impacting particle. The detector was a photomultiplier 3.49 cm (1.375 in) in diameter with an 800 angstrom thick aluminum layer deposited onto the outer front surface of the tube to shield the photocathode against extraneous light. Outputs were taken from the anode, the tenth dynode, and the ninth dynode of the photomultiplier, each multiplied separately. The ratio of the pulse sizes were 1000:31.6;1 respectively. The greatest sensitivity anode circuit fed into a 5-bit counter. The tenth and ninth dynode outputs fed 3- and 2-bit counters, respectively The minimum energy detectable was roughly 0.005 erg. The 5-bit counter was modified with an inhibit circuit that prevented recycling during overflow conditions.

The momentum impact detector was a piezo-electric crystal microphone mechanically coupled to the sensitive surface of the photomultiplier tube. The microphone output drives a parallel resonant amplifier with a mid-frequency of 100 kHz and a voltage gain of 80 db. The output drove both a 2-bit counter circuit and another amplifier with a voltage gain of 20 db, which fed into another 2-bit counter. The trigger circuits were arranged so only the initial pulse was seen. Assuming the response of the detector is proportional to the momentum of the impacting particle, the threshold is approximately 0.0001 dyne sec.

The experiment was on a timer, so power was only turned on 78.5 minutes into the flight to avoid high-voltage corona problems. After turn-on, anomalously high counting rates were recorded by the light flash detecor, presumably due to direct or reflected sunlight reaching the photocathode through pin holes in the aluminum protective surface from previous particle impacts. For the first several hours after launch, the microphone output was erratic, probably because of acoustic noise from outgassing.

Alternate Names

  • Ranger2/CosmicDustDetectors

Discipline

  • 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. McMillanOther InvestigatorNASA Jet Propulsion Laboratory
Dr. Wesley M. AlexanderPrincipal InvestigatorBaylor University
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