Number 20: 24/05/2003
A scientific publication by SGF and NEODyS

NEOs' Spacemissions Special

Mission Giotto: ESA's first deep space mission

Giotto Mission fast facts: an introduction

The 3D model of the spacecraft

Click here for a 3d interactive model of the spacecraft and of its scientific instruments.

The Giotto mission was launched by ESA, on an Ariane rocket, on the 2th of July 1985 to study Comet P/Halley, and a second Comet called P/Grigg-Skjellerup during its extended phase. Giotto became famous as the first spacecraft to image the nucleus of a comet on 1986, but it was also the first to encounter two comets and to change orbit by returning to Earth for a gravity assist
Originally, the project was a joint U.S.- European comet mission to Halley, but Giotto soon became ESA's first deep space mission and part of an ambitious international effort to solve the mysteries surrounding Comet Halley. The plan was to send five space probes to meet Halley in 1986, during its closest passage to the Sun (known as perihelion): two Soviet (Vega 1 and 2), two Japanese (Sakigake and Suisei) and finally the European Giotto.While the Japanese spacecraft made long distance measurements, the Soviet Vegas would act as pathfinders, passing close enough to locate the comet's nucleus. The information they sent back would allow Giotto to home in with great accuracy on Halley's solid heart and on Earth. (read "The international Halley Watch" by D.K.Yeomans).

Halley comet as seen from earth
The 13th of march 1986, Giotto met comet Halley, taking the first pictures of the nucleus. The encounter was not an easy task and no-one expected the spacecraft to survive its battering from comet dust during this encounter (read "The night of the comet" by E. Perozzi). During that night, Giotto was damaged, but most of its instruments remained operational: during the flyby, 2112 images were returned before communications were disrupted. A unique series of images sent back by the spacecraft revealed the comet nucleus to be a dark, peanut-shaped body, about 15 km long and 7 to 10 km wide. At least three bright jets could be seen spewing out material from the warmer sunlit side, but only about 10% of the surface was active.

In the evening of 9 July 1992, after a period of hibernation, Giotto arrived at its second target: comet Grigg-Skjellerup, about 215 million km from Earth. It aimed directly at the nucleus, that it missed by a mere 100 to 200 km: the closest ever cometary flyby made at that moment. Flyby conditions were very different from those during the Halley encounter. Due to the slower relative approach speed and a dust production rate of about 1/200 that of Halley, the Comet Grigg-Skjellerup encounter caused very little dust damage to the spacecraft. The eight operational experiments provided a surprising wealth of exciting data revealing an object which was pretty different from comet Halley. Strangest of all was the discovery of unusual magnetic waves, each about 1000 km apart, near the comet. The waves were generated by 'pick-up ions' - charged particles created from the break up of water molecules around the comet - as they moved in the magnetic field created by the solar wind. (read "The Giotto mission and comet Halley" by H.U.Keller to know more)

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