Mission Type: Flyby
Launch Vehicle: Ariane 1 rocket (flight V14)
Launch Site: Kourou, French Guiana
Spacecraft Mass: 960 kg
References:
Deep Space Chronicle, pg. 137

Giotto was the first deep space probe launched by the European Space Agency (ESA). Because the cylindrical spacecraft was designed to approach closer to comet Halley than any other probe, it 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.

After course corrections on 26 August 1985, 12 February 1986 and 12 March 1986, Giotto was put on a 500-kilometer flyby to the comet's core. Data on its trajectory was based upon tracking information from the Soviet Vega 1 and 2 probes.

The spacecraft eventually passed by Halley on 14 March 1986. Closest encounter was at a range of 605 kilometers at 00:03:02 UT. At a range of 137.6 million kilometers from Earth, just two seconds before closest approach, telemetry stopped due to impact with a heavy concentration of dust that probably knocked the spacecraft's high-gain antenna out of alignment with Earth. Fortunately, data transmission was restored within 32 minutes. On average, Giotto had been hit 100 times a second by particles up to 0.001 grams. By the end of its encounter with Halley, the spacecraft was covered in at least 26 kilograms of dust.

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 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.