In-situ dust mass distribution measurements from Giotto encounter with comet P/Halley.

On the night of the 13/14th of March 1986 the European Space Agency's Giotto spacecraft passed within 600km of the nucleus of comet P/Halley. On board the spacecraft was an impressive array of experiments designed to study all aspects of the cometary coma and provide high resolution images of the nucleus. The principle experiment designed to measure the coma dust mass distribution was called the Dust Impact Detection System (DIDSY). The design operation and performance of this experiment are considered and details are provided of post-mission recalibration, including the development of a software simulation to aid in the interpretation of the returned data. The faulty operation of one of the DIDSY sensors resulted in the use of ) the front end channels of the Particulate Impact Analyser Experiment (PIA) to provide information on particles of mass 10*19kg < m < 10-15kg. The techniques used to extract the required information and calibrate the sensor using encounter data and the inter-relationship between different operating modes is described. The analysis of impacts which caused multiple detection by two or more of the DIDSY sensors is described and the results from these multi-sensor events used to extend the measured mass range up to 10_5kg. A mass distribution representative of the coma passed through by Giotto was constructed and this is combined with a simple model to obtain the dust production rate and dust to gas ratio.