Cassini-Huygens
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Instrument Overview
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The Cosmic Dust Analyser instrument (CDA) on the Cassini orbiter is the successor of the dust detectors flown on the Ulysses and the Galileo spacecraft. The instrument accomplishes the detection of dust impacts by two different means: (1) a high rate detector (HRD) using two separate polyvinylidene fluoride (PVDF) sensors, and (2) a Dust Analyser (DA) based upon impact ionization. The DA measures the electric charges carried by the dust particle, the impact direction, the impact speed, mass, and the chemical composition, whereas the HRD is only capable to determine the mass for particles with a known speed. The DA detector consists of three components: the charge detection unit, the impact ionizationdetector itself, and the time-of-flight (TOF) mass spectrometer.
Note that the charge detection unit subsystem generates signals (so-called 'QP signals') with a higher sampling rate than the signals generated by the impact ionization detector (QI, QT, QC, MP signals.) Furthermore, as the charge detection unit subsystem is sensitive to big particles only (> 5 microns), it was triggered only 6 times during the cruise phase. Therefore, in order to keep the telemetry data volume low, the QP signals were not always transmitted to Earth. This explains why the QI, QT, QC and MP signals directories in thePDS volumes may contain more signals than the QP directory.
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