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Giotto - Mission to comet Halley
The
Giotto
spacecraft was the first interplanetary mission of the
European Space Agency (ESA).
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
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Halley Multicolour Camera (HMC) - MPS, Lindau |
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Neutral Mass Spectrometer (NMS) - MPIK, Heidelberg |
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Ion Mass Spectrometer (IMS) - (University of Bern) |
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Dust Mass Spectrometer (PIA) - MPIK, Heidelberg |
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Dust Impact Detection System (DIDSY) - University of Kent, Canterbury |
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Johnstone Plasma Analyser (JPA) - MSSL, London |
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Reme Plasma Analyser (RPA) - CESR, Toulouse |
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Energetic Particle Analyser (EPA) - St. Patrick's College, Maynooth |
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Magnetometer (MAG) - University of Cologne |
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Optical Probe Experiment (OPE) - CNRS, Verrieres-le-Buisson |
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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.
Where to get the data
All useful data from the encounter have been released on CD-ROM by the
International Halley Watch. The CDs are available from the
NSSDC,
Washington.
MPS Publications
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