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Cosmic Ray

NSSDCA ID: 1958-003A-01

Mission Name: Explorer 3
Principal Investigator:Prof. James A. Van Allen


A halogen-quenched anton-type Geiger-Mueller counter that measured the total omnidirectional cosmic-ray intensity was used to study the arrival of primary cosmic radiation on a comprehensive geographical and temporal basis. In addition to real-time data transmission, a tape recorder memory system was used to store a 6-sec averaged counting rate of data acquired. On radio command, the unit transmitted averaged data for an entire orbit. Data were used to aid in outlining the belt of high-intensity radiation at altitudes about 700 km discovered by Explorer 1. This unforeseen high-intensity band saturated the Geiger-Mueller counter. The instrumentation performed well for 44 days. Continuous data were provided until May 10, 1958 and data were transmitted on command until May 14, 1958.

The instrument consisted of a single Geiger-Mueller tube, a scaling circuit to reduce the number of pulses, and a telemetry system to transmit the data to ground receiving stations. The Geiger-Mueller tube was a type 314 Anton halogen quenched counter with stainless steel (approximately 75% iron, 25% chromium) wall of approximately 0.12 cm thickness. The instrument was mounted within the spacecraft hull, which had 0.023 inch thick stainless steel walls. The counter was 10.2 cm long by 2.0 cm diameter and the internal wire was 10 cm in length. The tube had a very small variation in counting efficiency over the range -55 to +175 Celsius. It had approximately 85% counting efficiency for cosmic rays, and about 0.3% counting efficiency for photons of energy 660 keV. The "dead time" (time to reset to record the next count) of the counters was about 100 microseconds.

The counter was connected to a current amplifier, which directly fed a scaler stage, a bistable transistor multivibrator that could operate over a wide range of voltages and a temperature range of -15 to +85 Celsius, limited primarily by the supply batteries. The scaler resolving time was 250 microseconds. For pulse counts higher than 4000 per second, the scaler indicated a count of 4000. Results were sent to a tape recorder data storage device, which would store data for one orbit and then transmit it to a receiving station on ground command.

Alternate Names

  • Explorer3/CosmicRay


  • 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
Dr. George H. LudwigOther InvestigatorNOAA National Environmental Satellite, Data and Information Service
Prof. Louis A. FrankOther InvestigatorUniversity of
Prof. James A. Van AllenPrincipal InvestigatorUniversity of Iowa
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