Giotto (spacecraft)

Giotto was a European robotic spacecraft mission from the European Space Agency. It flew by and studied Halley's Comet, becoming the first spacecraft to make close-up observations of a comet. On 13 March 1986, Giotto successfully approached Halley's nucleus at a distance of 596 kilometers. The spacecraft was named after the Early Italian Renaissance painter Giotto di Bondone. He had observed Halley's Comet in 1301 and was inspired to depict it as the star of Bethlehem in his painting Adoration of the Magi in the Scrovegni Chapel.

Mission

Development

Members of the European Space Agency’s Solar System Working Group began planning a mission to study Halley’s Comet in 1977. After some changes, the European Space Agency decided to work with NASA on a joint mission called the International Comet Mission. This mission would have included a NASA probe and a smaller European probe. However, the NASA part of the mission was cancelled in 1979.

Later, a new plan was made to launch the mission using an Ariane 1 rocket. Different ideas were suggested, and finally, a mission named Giotto was chosen. The mission was approved in July 1980 with a budget of 80 million accounting units.

In 1981, British Aerospace offered a design for the spacecraft, but it was rejected because of problems with power and temperature control. The design was also outdated, so a new, slightly larger spacecraft was created, with British Aerospace still leading the project.

Originally, Giotto was supposed to launch with another satellite on an Ariane 2 rocket, but this changed. It was then planned to launch on an Ariane 3, but because no customer wanted to launch during the needed time, Giotto was assigned to fly alone on an Ariane 1 rocket.

There were also plans to use equipment on a Space Shuttle in orbit during Giotto’s fly-by, but these plans fell through after the Challenger disaster.

The final plan was for a group of five space probes to study Halley’s Comet together. This group, called the Halley Armada, included Giotto, two probes from the Soviet Union’s Vega program, and two from Japan: the Sakigake and Suisei probes. The American probe International Cometary Explorer would also help. The Soviet probes would find the comet’s nucleus, and Giotto would then fly very close to it. Because Giotto would pass so close, there was a chance it might not survive due to dust particles from the comet.

Design

The Giotto spacecraft was shaped like a cylinder, measuring 1.87 meters wide and 2.85 meters long. It was built by British Aerospace in Filton, Bristol, and included a special shield to protect it from dust, designed by scientist Fred Whipple. This shield had two layers: a thin aluminium sheet and a thicker Kevlar sheet. Giotto also had a large antenna, about 1.51 meters across, to send messages back to Earth.

The spacecraft carried ten different tools to study the comet, including a camera, instruments to measure dust and particles, and devices to analyze the gases around the comet. A model of Giotto can be seen at the Bristol Aero Collection hangar in Filton, Bristol, England.

Timeline

The European Space Agency got the Giotto spacecraft ready in April 1985. It was flown to French Guiana, and the camera followed soon after. The launch happened on July 2, 1985, on an Ariane 1 rocket from Kourou, French Guiana.

Giotto’s journey included testing its camera by taking pictures of the star Vega and Earth. In March 1986, it successfully flew by Halley's Comet, getting as close as 596 kilometers to the comet's nucleus. During this close approach, Giotto faced some challenges but managed to send back important images and data.

After its encounter with Halley, Giotto continued its journey, flying by Earth and later another comet named Grigg–Skjellerup in 1992. The mission cost $6.3 million for its extension.

Scientific results

Images from the spacecraft showed Halley's nucleus to be a dark, peanut-shaped body, about 15 kilometers long and 7 to 10 kilometers wide. Only about 10% of its surface was active, with at least three jets seen on the side facing the Sun. Scientists learned that the comet formed about 4.5 billion years ago from icy materials that stuck to dust particles in space. It has stayed almost the same since then.

The spacecraft measured what the comet threw off, mostly water, with smaller amounts of carbon monoxide, methane, ammonia, and other materials. Halley's nucleus was found to be dark, suggesting it was covered in dust. The surface was rough and porous, with a very low density. The comet threw off about three tonnes of material every second, causing it to wobble over time. Most of the dust particles were very small, similar to cigarette smoke.

Spacecraft achievements

Giotto made the closest ever flyby of Halley's Comet and gave us the best data about this comet. It was the first spacecraft to give us detailed pictures of a comet's nucleus. It also was the first to fly close to two different comets, allowing scientists to compare a young, active comet like Halley to an older comet. Giotto used Earth's gravity to change its path and was brought back to life after resting in space.

Giotto II proposals

Scientists suggested using extra parts to create a backup spacecraft. Another idea was to use a Giotto-like probe to collect a sample from a comet's atmosphere and bring it back to Earth in a special capsule instead of using the Mage motor.