In 1980, a group of 19 scientists suggested to ESA that the return of comet Halley in 1986 offered a unique opportunity to investigation a comet from very close range. The mission was studied in the first half of 1980 and was approved in July 1980. The mission was named Giotto after the Italian painter, Giotto di Bondone, who depicted comet Halley as the 'Star of Bethlehem' in one of his frescoes in the Scrovegni chapel in Padua in 1304.
The mission to comet Halley had one major disadvantage. The retrograde orbit of the comet combined with the direct heliocentric orbit of a spacecraft resulted in a high fly-by velocity of nearly 70 km/s. This made the available observation time in the vicinity of the nucleus very short and the near-nucleus dust made a close approach hazardous.
By the end of January 1981, 11 experiments were selected to perform measurements of a close (596 km) fly-by in March 1986. The experiments were
|Halley Multicolour Camera (HMC) - MPS, Lindau|
|Neutral Mass Spectrometer (NMS) - MPIK, Heidelberg|
|Ion Mass Spectrometer (IMS) - (University of Bern)|
|Dust Mass Spectrometer (PIA) - MPIK, Heidelberg|
|Dust Impact Detection System (DIDSY) - University of Kent, Canterbury|
|Johnstone Plasma Analyser (JPA) - MSSL, London|
|Reme Plasma Analyser (RPA) - CESR, Toulouse|
|Energetic Particle Analyser (EPA) - St. Patrick's College, Maynooth|
|Magnetometer (MAG) - University of Cologne|
|Optical Probe Experiment (OPE) - CNRS, Verrieres-le-Buisson|
|Radio Science Experiment (GRE) - University of Bonn|
The Max-Planck-Institut fuer Sonnensystemforschung (MPS) contributed to 5 separate experiments.
The spacecraft was spin-stabilised, rotating at a rate of 15 rpm, with the rotation axis designed to be aligned with the relative velocity of the spacecraft with respect to the comet. The dust shield (at the bottom), which was needed to protect the main elements of the spacecraft from the impacts of dust particles hitting the spacecraft at 70 km/s, was then pointed roughly towards the comet with the detectors of the instruments peeking out from behind this protective shield.
The fly-by was completed on March 14, 1986 at 00:03 UT. All instruments operated well throughout the mission until a few seconds before closest approach when dust particle impacts caused some major disturbances in the power supply. During these moments, several instruments were damaged, including HMC and NMS. However, the spacecraft was in sufficiently good condition that a second fly-by was performed on July 10, 1992 of the comparatively weak comet, comet Grigg-Skjellerup. This was probably the closest encounter of a spacecraft with a comet to date although the precise distance was unknown because the camera (the only remote sensing instrument in the payload) was not functional.
|© 2006, Max Planck Institute for
Solar System Research, Lindau