Key Dates:
- 07.02.85 Launch (11:23:16 UT)
- 03.14.86 Comet Halley Flyby (00:03:02 UT)
- 07.02.90 Earth Gravity Assist
- 07.10.92 Comet Grigg-Skjellerup Flyby
- Status: Mission Complete
Scientific Instruments:
- Narrow-angle camera
- Three mass spectrometers for neutrals, ions and dust
- Various dust detectors
- Photopolarimeter
- Set of plasma experiments
Fast Facts:
- Giotto was hammered by an average of 100 dust particles as second as it flew past comet Halley.
- The spacecraft was named in honor of 14th century Italian artist Giotto di Bondone. His Adoration of the Magi is the first time the Star of Bethlehem was represented as a comet.
- Giotto was the first spacecraft to use Earth's gravity to assist it on its journey.
Mission Results:
Designed to study Comet P/Halley, Giotto was the first deep space probe launched by the European Space Agency (ESA). Originally put forward as part of a joint NASA/ESA comet mission, the United States eventually pulled out. There was little leeway for delays if the ESA planned to continue alone. If the opportunity was missed, the next chance at Halley's Comet would be 75 years later.
The major objectives of the mission were to:
- Obtain color photographs of the nucleus
- Determine the elemental and isotopic composition of volatile components in the cometary coma, particularly parent molecules
- Characterize the physical and chemical processes that occur in the cometary atmosphere and ionosphere
- Determine the elemental and isotopic composition of dust particles
- Measure the total gas-production rate and dust flux and size/mass distribution and derive the dust-to-gas ratio
- Investigate the macroscopic systems of plasma flows resulting from the cometary-solar wind interaction.
The Craft:
Because the cylindrical spacecraft was designed to approach closer to comet Halley than any other probe, Giotto was equipped with two dust shields separated by 23 centimeters; the first would bear the shock of impact and spread the impact energy over larger areas of the second, thicker rear sheet. The design of the spacecraft was based on the spin-stabilized magnetospheric Geos satellites launched in 1977 and 1978.
The Mission:
The spacecraft encountered the comet on March 13, 1986, at a distance of 0.89 AU from the sun and 0.98 AU from the Earth. The spacecraft was based as much as possible on the ESA-GEOS spacecraft and was spin stabilized with a rate of 15 rpm. During the encounter with Halley's comet, the spin axis was aligned with the relative velocity vector. The 1.5 m dish antenna, operating in the X-band, was inclined and despun in order to point at the Earth. The goal was to come within 500 km of Halley's comet at closest encounter. The actual closest approach was measured at 596 km.
Results:
Giotto returned 2,000 images of Halley. After the encounter, ESA decided to redirect the vehicle for a flyby of Earth. The spacecraft was officially put in hibernation mode on 2 April 1986. Course corrections on 19 March, 20 March and 21 March 1986, however, set it on a 22,000-kilometer flyby of Earth on 2 July 1990 for a gravity-assist (the first time that Earth had been used for such a purpose) to visit a new target: Giotto successfully flew by comet Grigg-Skjellerup at 15:30 UT on 10 July 1992 ar a range of approximately 200 kilometers. Eight experiments provided extensive data on a wide variety of cometary phenomena during this closest ever (at the time) flyby of a comet.
After the Mission:
After formal termination of the encounter on 23 July 1992, Giotto was put in hibernation. In September 1999, ESA scientists revealed that a second comet or cometary fragment may have been accompanying Grigg-Skjellerup during the encounter in 1992. The spacecraft repeated a flyby of Earth at 02:40 UT on 1 July 1999 at a range of 219,000 kilometers.
According to the ESA, Giotto had a number of very impressive ‘firsts’ and achievements to its credit:
- It was Europe's first deep-space mission.
- It photographed the first close-up images of a comet nucleus (Halley). It discovered the size and shape of Halley's nucleus and discovered that the surface is very dark and that bright jets of gas and dust spring out of its nucleus.
- It was the first deep-space mission to change orbit by returning to Earth for a gravity-assist manoeuvre.
- Giotto made the closest comet fly-by to date by any spacecraft (about 200 kilometres from Comet Grigg-Skjellerup) and studied the interaction between the solar wind, the interplanetary magnetic field, and the comet itself.
- It was the first spacecraft to encounter two comets and in doing so measured the size, composition, and velocity of dust particles and measured the composition of those two comets.
