The Cassini spacecraft is designed to operate with a "balanced" voltage source to create a tolerance to short circuits. On May 1, a voltage shift occurred, most likely explained by a short circuit happening somewhere in the system. On June 11, a voltage shift in the opposite direction occurred, indicating an additional short circuit. In both cases, all instruments and engineering subsystems continued to operate properly.
Analysis of telemetry data from the spacecraft by the engineering team pointed to the Cassini plasma spectrometer instrument as the cause of the voltage shifts. The instrument has additional capacitors in the power lines for noise reduction. The concern was that one or more of these capacitors may have short-circuited, which would cause the voltage to shift and explain the observed changes. Although the instrument was operating properly, engineers decided to turn it off as a precaution until the events could be better understood.
The suspension of the plasma spectrometer operations is not expected to affect other science data gathering or navigation. The plan is to resume normal plasma spectrometer operations after further analysis is completed to understand the cause of the issue better.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington.
For more information visit http://www.nasa.gov/mission_pages/cassini/whycassini/cassini20110615.html
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