Giotto: ESA's mission to Halley's Comet

Illustration of Giotto at Halley's Comet. Credit: ESA

Launch Date: July 10, 1985

Launch Site: European Spaceport at Kourou, French Guiana

Launch Vehicle: Ariane 1 V14

Mission Type: Flyby

Targets: Halley's Comet & Grigg-Skjellerup

Dimensions: 1.85 Meters across and 1.1 Meters tall (Not including antenna)

Mass: 960 Kilograms

You can build you own Giotto spacecraft out of LEGO here.

Giotto was a mission by ESA to explore Halley's Comet, the most famous comet in the solar system. Halley comes by Earth every 76 years, and this makes it the only long period comet that can be seen twice in a human lifetime if your born at the right time. 

The Mission

Giotto launched on July 10, 1985 into a geostationary transfer orbit. After three orbits, Giotto ignited its thrusters to send it on its way to Halley's Comet. On March 12, 1986, Giotto started detecting ionized hydrogen from the cometary nucleus. The tracking camera was activated, and Giotto started to image Halley's nucleus as it approached.

Nucleus of Halley's Comet. Credit: Halley Multicolor Camera Team, Giotto Project, ESA

Giotto wasn't studying Halley alone. The Soviet Union repurposed two of its Venus studing Vega spacecraft to track down Halley's nucleus, and Japan sent a mission to analyze the comet from a distance. As it approached Halley, Giotto started to suffer impacts from comet ice particles. 12,000 impacts were recorded 122 minutes before closest approach. 7.6 seconds before closest approach, Giotto was hit by a massive impact. Giotto started spinning uncontrollably, and the team at mission control saw their monitors go black.

Over the next 32 minutes, Giotto was able to use its thrusters to stabilize itself, and it continued to transmit bsome information to mission control. On March 15, all the science was transmitted, and Giotto's instruments were shut down.

Giotto seemed to be doing fine, despite the holes caused by ice particles, and still had 60 kilograms of propellant left. Giotto made a number of maneuvers that would return it to Earth a few years later. The team hoped to wake up Giotto once it flew by Earth. In February of 1990, the Giotto team sent the signal to wake up the battered space probe. Giotto responded weakly at first, but full control was regained over the next week.

Giotto had many science instruments that were still fully operational, but some, including the camera, were kaput. As Giotto flew by Earth on June 2, 1990, its orbital trajectory was altered so it could fly by the comet Grigg-Skjellerup. On July 10, 1992, Giotto made its flyby of the comet. It approached Grigg-Skjellerup at a distance of only 200 kilometres, which makes the fact that the camera was unoperational especially unfortunate.

The Targets

Giotto image of Halley's Comet. Credit: Halley Multicolor Camera Team, Giotto Project, ESA

• Date Discovered: December 25, 1758 (was seen for hundreds of years before, but wasn't recognized as the same comet)
• Designation: 1P/Halley
• Class: Halley-Type Comet [NEO]
• Radius: 5.5 Kilometres
• Rotational Period: 2.2 Days
• Orbital Period: 27726.15 Days (75.91 Years)

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Giotto's camera was unoperational on its Grigg-Skjellerup flyby, so no image of the comet was obtained.

• Date Discovered: July 23, 1902
• Designation: 26P/Grigg-Skjellerup
• Class: Jupiter-Family Comet [NEO]
• Radius: 1.3 Kilometres
• Rotational Period: Unknown
• Orbital Period: 1934.26 Days (5.3 Years)