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''Giotto'' was a
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
an
robotic spacecraft A robotic spacecraft is an uncrewed spacecraft, usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather ...
mission from the
European Space Agency , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (120 ...
. The spacecraft flew by and studied
Halley's Comet Halley's Comet or Comet Halley, officially designated 1P/Halley, is a short-period comet visible from Earth every 75–79 years. Halley is the only known short-period comet that is regularly visible to the naked eye from Earth, and thus the on ...
and in doing so became the first spacecraft to make close up observations of a comet. On 13 March 1986, the spacecraft succeeded in approaching Halley's nucleus at a distance of 596 kilometers. It was named after the Early
Italian Renaissance The Italian Renaissance ( it, Rinascimento ) was a period in Italian history covering the 15th and 16th centuries. The period is known for the initial development of the broader Renaissance culture that spread across Europe and marked the trans ...
painter Painting is the practice of applying paint, pigment, color or other medium to a solid surface (called the "matrix" or "support"). The medium is commonly applied to the base with a brush, but other implements, such as knives, sponges, and ...
Giotto di Bondone. He had observed Halley's Comet in 1301 and was inspired to depict it as the
star of Bethlehem The Star of Bethlehem, or Christmas Star, appears in the nativity story of the Gospel of Matthew chapter 2 where "wise men from the East" (Magi) are inspired by the star to travel to Jerusalem. There, they meet King Herod of Judea, and ask hi ...
in his painting ''Adoration of the Magi'' in the Scrovegni Chapel.


Mission

Originally a United States partner probe was planned that would accompany ''Giotto'', but this fell through due to budget cuts at
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
. There were plans to have observation equipment on board a
Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program n ...
in low-Earth orbit around the time of ''Giotto''s fly-by, but they in turn fell through with the ''Challenger'' disaster. The plan then became a cooperative armada of five space probes including ''Giotto'', two from the
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...
's
Vega program The Vega program (Cyrillic: ВеГа) was a series of Venus missions that also took advantage of the appearance of comet 1P/Halley in 1986. ''Vega 1'' and '' Vega 2'' were uncrewed spacecraft launched in a cooperative effort among the Soviet ...
and two from Japan: the ''
Sakigake , known before launch as MS-T5, was Japan's first interplanetary spacecraft, and the first deep space probe to be launched by any country other than the USA or the Soviet Union. It aimed to demonstrate the performance of the new launch vehi ...
'' and ''Suisei'' probes. The idea was for Japanese probes and the pre-existing American probe
International Cometary Explorer The International Cometary Explorer (ICE) spacecraft (designed and launched as the International Sun-Earth Explorer-3 (ISEE-3) satellite), was launched 12 August 1978, into a heliocentric orbit. It was one of three spacecraft, along with the mo ...
to make long distance measurements, followed by the Russian Vegas which would locate the nucleus, and the resulting information sent back would allow ''Giotto'' to precisely target very close to the nucleus. Because Giotto would pass so very close to the nucleus ESA was mostly convinced it would not survive the encounter due to the spacecraft colliding at very high speed with the many dust particles from the comet. The coordinated group of probes became known as the
Halley Armada The Halley Armada is the name of a series of space probes, five of which were successful, sent to examine Halley's Comet during its 1986 sojourn through the inner Solar System, connected with apparition "1P/1982 U1". The armada included one prob ...
.


Design

The cylindrical spacecraft was 1.85 m in diameter and had three internal platforms. It was derived from the GEOS research satellite built by British Aerospace in Filton, Bristol, and modified with the addition of a dust shield (
Whipple shield The Whipple shield or Whipple bumper, invented by Fred Whipple, is a type of hypervelocity impact shield used to protect crewed and uncrewed spacecraft from collisions with micrometeoroids and orbital debris whose velocities generally range be ...
) as proposed by
Fred Whipple Fred Lawrence Whipple (November 5, 1906 – August 30, 2004) was an American astronomer, who worked at the Harvard College Observatory for more than 70 years. Amongst his achievements were asteroid and comet discoveries, the " dirty snowball" h ...
. The shield comprised a thin (1 mm)
aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...
sheet separated by a space and a thicker (12 mm)
Kevlar Kevlar (para-aramid) is a strong, heat-resistant synthetic fiber, related to other aramids such as Nomex and Technora. Developed by Stephanie Kwolek at DuPont in 1965, the high-strength material was first used commercially in the early 1970s a ...
sheet. The later ''Stardust'' spacecraft would use a similar Whipple shield. Giotto also had a 1.51 m diameter antenna that it used to communicate with
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...
. A mock-up of the spacecraft resides at the Bristol Aero Collection hangar, at
Filton Filton is a town and civil parish in South Gloucestershire, England, north of Bristol. Along with nearby Patchway and Bradley Stoke, Filton forms part of the Bristol urban area and has become an overflow settlement for the city. Filton Church ...
,
Bristol Bristol () is a City status in the United Kingdom, city, Ceremonial counties of England, ceremonial county and unitary authority in England. Situated on the River Avon, Bristol, River Avon, it is bordered by the ceremonial counties of Glouces ...
,
England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...
,
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...
,
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
.


Science Instruments

Giotto had 10 science instruments. * MAG: a magnetometer * HMC (Halley Multicolour Camera): a 16-cm telescope and camera * DID (Dust Impactor Detector System): measured the mass of dust particles that hit the instrument * RPA (Rème Plasma Analyser): studied solar wind and charged particles * JPA (Johnstone Plasma Analyser): also measured solar wind and charged particles * PIA (Particulate Impact Analyser): studied the size and chemistry of particles * OPE (Optical Probe Experiment): examined the emissivity of gas and dust behind the spacecraft * EPA (Energetic Particle Analyser): analyzed alpha-particles, electrons, and neutrons * NMS (Neutral Mass Spectrometer): measured the composition of the particles around the comet * IMS (Ion Mass Spectrometer): measured the amount of ions from the sun and the comet * GRE (Giotto Radio Experiment): used Giotto's radio signals to study Halley's comet


Timeline


Launch

The mission was given the go-ahead by ESA in 1980, and launched on an Ariane 1 rocket (flight V14) on 2 July 1985 from Kourou, French Guiana. The craft was controlled from the European Space Agency ESOC facilities in
Darmstadt Darmstadt () is a city in the state of Hesse in Germany, located in the southern part of the Rhine-Main-Area (Frankfurt Metropolitan Region). Darmstadt has around 160,000 inhabitants, making it the fourth largest city in the state of Hesse ...
(then West Germany) initially in
Geostationary Transfer Orbit A geosynchronous transfer orbit or geostationary transfer orbit (GTO) is a type of geocentric orbit. Satellites that are destined for geosynchronous (GSO) or geostationary orbit (GEO) are (almost) always put into a GTO as an intermediate step ...
(GTO) then in the Near Earth Phase (NEP) before the longer Cruise Phase through to the encounter. While in GTO a number of slew and spin-up manoeuvres (to 90 RPM) were carried out in preparation for the firing of the Apogee Boost Motor (ABM), although unlike orbit circularisations for
geostationary orbit A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular geosynchronous orbit in altitu ...
, the ABM for Giotto was fired at
perigee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any el ...
. Attitude determination and control used sun pulse and IR Earth sensor data in the telemetry to determine the spacecraft orientation.


Halley encounter

The
Soviet The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...
Vega 1 Vega 1 (along with its twin Vega 2) was a Soviet space probe, part of the Vega program. The spacecraft was a development of the earlier '' Venera'' craft. They were designed by Babakin Space Centre and constructed as 5VK by Lavochkin at Khim ...
started returning images of Halley on 4 March 1986, and the first ever of its nucleus, and made its flyby on 6 March, followed by Vega 2 making its flyby on 9 March. Vega 1's closest approach to Halley was 8 889 km. ''Giotto'' passed Halley successfully on 14 March 1986 at 596 km distance, and surprisingly survived despite being hit by some small particles. One impact sent it spinning off its stabilized spin axis so that its antenna no longer always pointed at the Earth, and its dust shield no longer protected its instruments. After 32 minutes ''Giotto'' re-stabilized itself and continued gathering science data. Another impact destroyed the Halley Multicolor Camera, but not before it took photographs of the nucleus at closest approach.


First Earth flyby

''Giotto''s trajectory was adjusted for an Earth flyby and its science instruments were turned off on 15 March 1986 at 02:00 UTC.


Grigg-Skjellerup encounter

''Giotto'' was commanded to wake up on 2 July 1990 when it flew by Earth in order to sling shot to its next cometary encounter. The probe then flew by the Comet Grigg-Skjellerup on 10 July 1992 which it approached to a distance of about 200 km. Afterwards, Giotto was again switched off on 23 July 1992.


Second Earth flyby

In 1999 ''Giotto'' made another Earth flyby but was not reactivated.


Scientific results

Images showed Halley's nucleus to be a dark peanut-shaped body, 15 km long, 7 km to 10 km wide. Only 10% of the surface was active, with at least three outgassing jets seen on the sunlit side. Analysis showed the comet formed 4.5 billion years ago from volatiles (mainly ice) that had condensed onto interstellar dust particles. It had remained practically unaltered since its formation. Measured volume of material ejected by Halley: * 80%
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
, * 10%
carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...
* 2.5% a mix of
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
and
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
. * other
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s,
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
, and
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
were detected in trace amounts. ''Giotto'' found Halley's nucleus was dark, which suggested a thick covering of dust. The nucleus's surface was rough and of a porous quality, with the density of the whole nucleus as low as 0.3 g/cm3. Sagdeev's team estimated a density of 0.6 g/cm3, but S. J. Peale warned that all estimates had error bars too large to be informative. The quantity of material ejected was found to be three tonnes per second for seven jets, and these caused the comet to wobble over long time periods. The dust ejected was mostly only the size of cigarette smoke particles, with masses ranging from 10 ag to 0.4 g. (See
Orders of magnitude (mass) To help compare different orders of magnitude, the following lists describe various mass levels between 10−59  kg and 1052 kg. The least massive thing listed here is a graviton, and the most massive thing is the observable universe. ...
.) The mass of the particle that impacted ''Giotto'' and sent it spinning was not measured, but from its effects—it also probably broke off a piece of ''Giotto''—the mass has been estimated to lie between 0.1 g and 1 g. Two kinds of dust were seen: one with carbon, hydrogen, nitrogen and oxygen; the other with calcium, iron, magnesium, silicon and sodium. The ratio of abundances of the comet's light elements excluding nitrogen (i.e. hydrogen, carbon, oxygen) were the same as the Sun's. The implication is that the constituents of Halley are among the most primitive in the Solar System. The plasma and ion mass spectrometer instruments showed Halley has a carbon-rich surface.


Spacecraft achievements

* ''Giotto'' made the closest approach to Halley's Comet and provided the best data for this comet. * ''Giotto'' was the first spacecraft to provide detailed pictures of a cometary nucleus. * ''Giotto'' was the first spacecraft to make a close flyby of two comets. Young and active comet Halley could be compared to old comet
26P/Grigg–Skjellerup Comet Grigg–Skjellerup (formally designated 26P/Grigg–Skjellerup) is a periodic comet. It was visited by the Giotto probe in July 1992. The spacecraft came as close as 200 km, but could not take pictures because some instruments were da ...
. * ''Giotto'' was the first spacecraft to return from interplanetary space and perform an Earth swing-by. * ''Giotto'' was the first spacecraft to be re-activated from hibernation mode. * ''Giotto'' was the first spacecraft to use Earth for a gravity assist.


See also

*
Timeline of Solar System exploration This is a timeline of Solar System exploration ordered by date of spacecraft launch. It includes: *All spacecraft that have left Earth orbit for the purposes of Solar System exploration (or were launched with that intention but failed), includ ...


Notes


External links


Mission website

Interview with the mission's Deputy Project Scientist
b
NASA's Solar System Exploration



Giotto di Bondone's ''Adoration of the Magi'' painting that includes his rendition of Halley's Comet

Image of Halley in 1986 by ''Giotto'' spacecraft

''Giotto Mission Archive''
at the NASA Planetary Data System, Small Bodies Node
''Giotto Extended Mission Archive''
at the NASA Planetary Data System, Small Bodies Node {{Authority control Giotto di Bondone European Space Agency space probes Missions to comets Satellites orbiting the Sun 1985 in spaceflight Derelict space probes Missions to Halley's Comet Spacecraft launched in 1985