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Giotto
Country European Space Agency
Mission Comet Halley Flyby
Launch Date July 2, 1985
Launch Vehicle Ariane 1
Spacecraft Mass 960 kg
Key Dates Mar 13, 1986 - Comet Halley Flyby
Jul 02, 1990 - Earth Flyby
Jul 10, 1992 - Comet Grigg-Skjellerup Flyby Jul 01, 1999 - Earth Flyby
End of Mission Jul 23, 1992
Comments First closeup images of a comet nucleus
First European deep space mission
First spacecraft to encounter two comets
First spacecraft returning from deep space to use Earth gravity assist

giotto_s.jpg The spacecraft Giotto was named after artist Giotto di Bondone, who had used the appearance of Comet Halley in 1301 as the model for the Star of Bethlehem in his 1304 painting titled "Adoration of the Magi". The purpose of the Giotto mission was to study Comet Halley during the comet's perihelion passage in 1986. Giotto also encountered Comet Grigg-Skjellerup during an extended mission in 1992. The major objectives of the mission were:

Giotto was launched on an Ariane-1 rocket by the European Space Agency (ESA) on July 2 1985. The spacecraft design was based on the GEOS research satellites, and a 600kg shield had to be added to ensure it would survive a close comet encounter. Giotto carried 10 instruments which included a multicolor camera, mass spectrometers, dust impact detector, plasma instruments, energetic particle analyzer, and a magnetometer. The power source was a 5,032 cell solar array that provided 190 watts of power during the first comet encounter, and four silver-cadmium batteries was carried along as well.

gio_halley1_s.jpg On March 13, 1986, Giotto approached Comet Halley for a targeted 500 km flyby. The spacecraft crossed the bow shock of the solar wind, and into the comet's coma. At this point the camera was switched to tracking mode to follow the brightest object (the comet nucleus) in its field of view and was returning images back to Earth. The images revealed the comet nucleus to be a dark peanut-shaped body with two bright jets spewing material out. The dust impacts were lower than expected until a few minutes prior to closest approach when the impact rate rose sharply, as the spacecraft apparently crossed into the path of one of the jets. Just 14 seconds prior to closest approach, the spacecraft was struck by a large dust particle which knocked the spacecraft off Earth point, and it took approximately 30 minutes for the spacecraft to recover and point its antenna back to Earth and reestablish communications.

Passing by the comet at a velocity of 68 km/second, the spacecraft had suffered some damage. Some of the instruments no longer worked or were partially functional. The star mapper's baffle was peppered with holes.

Subsequent analysis of Giotto's data showed a new wealth of data collected. Water accounted for about 80% by volume of all of the material being thrown out by the comet. Seven jets were identifed which threw out 3 tons/sec of material. The largest grain detected was 40mg, though the large particle that hit the spacecraft was estimated to be from 0.1 to 1 gram. The data from the plasma and ion mass spectrometer instruments indicated that the surface of Comet Halley is covered in a layer of organic material. The actual closest approach was measured at 596 km. On April 2, 1986, Giotto was placed into hibernation. gio_halley3_s.jpg

In April 1990, Giotto was reactivated. Three of the instruments proved fully operational, four partially damaged but usable, and the remainder, including the camera, were unusable. On July 2, 1990, Giotto made a close encounter with Earth and was retargeted to a flyby of Comet Grigg-Skjellerup on July 10, 1992. Aimed directly at the comet, Giotto missed the comet by 200 km in the closest ever flyby of a comet. Flying by at 14 km/second (as opposed to 68 km/sec for Halley), and with a dust production rate about 1/200 of Halley's, the Comet Grigg-Skjellerup encounter was expected to have very little dust damage to the spacecraft.

After the 1992 comet encounter, Giotto was placed into an Earth-return orbit using almost all remaining fuel. The satellite was put back into hibernation on July 23, 1992 and the Giotto mission officially terminated. In its present orbit, Giotto will pass silently within 300,000 km of the Earth on July 1, 1999 (best estimate 220,000) : no satellite operations are planned.


Ron Baalke, STARDUST Webmaster, ron@jpl.nasa.gov
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