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NSSDCA ID: 1962-012A-04

Mission Name: Ranger 4
Principal Investigator:Dr. Frank Press


A suspended magnetic seismometer was designed to determine the presence or absence of lunar seismicity and of a lunar crust, lava layers, or dust layers. The instrument was intended to collect data on the mechanical properties of lunar materials and to obtain preliminary information on the nature of the lunar core and on the depth and focus of moonquakes. The 3.36-kg instrument comprised a coil, a spring-suspended magnet, and an internal calibration device. The 1.70-kg seismic mass consisted of a permanent magnet suspended from the body of the instrument. It was suspended so as to maintain concentration of the seismic mass within the instrument body and to allow the seismometer to operate at any inclination of its longitudinal axis from 1 to 90 deg. To damp the rapid movement of the seismic mass upon lunar impact, the instrument was vacuum-filled with a protective fluid. Upon impact, the survival package was intended to float into an upright position. The seismic caging fluid would then escape, and a pressure switch would initiate the experiment. A measurement lifetime of 30 days was planned. Preflight instrument calibration was performed in the laboratory, and inflight calibration was to be continued throughout the flight. Because of a spacecraft communications failure, the experiment returned no data.

Alternate Names

  • Ranger4/Seismometer


  • Planetary Science: Geology and Geophysics

Additional Information

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



NameRoleOriginal AffiliationE-mail
Dr. Frank PressPrincipal InvestigatorMassachusetts Institute of Technology
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