The Giotto dust impact detection system

The dust impact detection system (DIDSY) comprises six independent subsystems with the primary aim of registering the impacts of all particulates of significant mass incident on the Giotto probe during the post-perihelion encounter with comet Halley in 1986. Mounted on Giotto's front dust shield, the detectors determine the mass distribution of the dust with a dynamic range of some 16 decades of mass and an ultimate spatial resolution of some 70 km. An additional detector located on the rear shield monitors the dust particles that are able to penetrate the front dust shield. Sensing techniques comprise diaphragm-mounted piezoelectric elements for large and intermediate masses, film capacitance discharge sensors for intermediate masses and impact charge sensors for the smallest masses. They are controlled and the data processed by a microprocessor-based system that allows the wide range of anticipated flux rates to be handled. Measurement principles and sensor characteristics are described.