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''Galileo'' was an American robotic
space probe A space probe, or simply probe, is a robotic spacecraft that doesn't Earth orbit, orbit the Earth (planet), Earth, but instead explores farther into outer space. A space probe may approach the Moon; travel through interplanetary space; planeta ...
that studied the
planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and ...

planet
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

Jupiter
and its moons, as well as the asteroids
Gaspra Gaspra ( uk, Гаспра, officially transliterated Transliteration is a type of conversion of a text from one script Script may refer to: Writing systems * Script, a distinctive writing system, based on a repertoire of specific eleme ...

Gaspra
and
Ida
Ida
. Named after the Italian astronomer
Galileo Galilei Galileo di Vincenzo Bonaiuti de' Galilei ( , ; 15 February 1564 – 8 January 1642), commonly referred to as Galileo, was an astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific q ...

Galileo Galilei
, it consisted of an orbiter and an entry probe. It was delivered into
Earth orbit A geocentric orbit or Earth orbit involves any object orbit In celestial mechanics, an orbit is the curved trajectory of an physical body, object such as the trajectory of a planet around a star, or of a natural satellite around a planet, ...
on October 18, 1989 by . ''Galileo'' arrived at Jupiter on December 7, 1995, after
gravitational assist In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement (e.g. orbit around the Sun) and gravity of a planet or other astronomical object to alter the C ...
flybys of
Venus Venus is the second planet from the Sun. It is named after the Venus (mythology), Roman goddess of love and beauty. As List of brightest natural objects in the sky, the brightest natural object in Earth's night sky after the Moon, Venus can ...

Venus
and
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
, and became the first spacecraft to orbit an outer planet. The
Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a federally funded research and development center Federally funded research and development centers (FFRDCs) are public-private partnerships which conduct research and development Research is " c ...
built the ''Galileo'' spacecraft and managed the ''Galileo'' program for
NASA The National Aeronautics and Space Administration (NASA; ) is an independent agency A regulatory agency or regulatory authority, is a Public benefit corporation Public-benefit corporation is a term that has different meanings in differen ...

NASA
.
West Germany West Germany is the common English name for the Federal Republic of Germany (FRG; german: Bundesrepublik Deutschland , BRD) between its formation on 23 May 1949 and the German reunification German reunification (german: Deutsche Wieder ...
Messerschmitt-Bölkow-Blohm Messerschmitt-Bölkow-Blohm (MBB) was a West German ) , capital = Bonn The Federal city of Bonn ( lat, Bonna) is a city on the banks of the Rhine in the German state of North Rhine-Westphalia, with a population of over 300 ...
supplied the propulsion module. NASA's
Ames Research Center The Ames Research Center (ARC), also known as NASA Ames, is a major NASA The National Aeronautics and Space Administration (NASA; ) is an independent agencies of the United States government, independent agency of the Federal government ...
managed the atmospheric probe, which was built by
Hughes Aircraft Company The Hughes Aircraft Company was a major American aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applicati ...
. At launch, the orbiter and probe together had a mass of and stood tall. Spacecraft are normally stabilized either by spinning around a fixed axis or by maintaining a fixed orientation with reference to the Sun and a star. ''Galileo'' did both. One section of the spacecraft rotated at 3
revolutions per minute Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is the number of turns in one minute The minute is a unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the ...
, keeping ''Galileo'' stable and holding six instruments that gathered data from many different directions, including the fields and particles instruments. The mission operations team used software containing 650,000 lines of code in the orbit sequence design process; 1,615,000 lines in the telemetry interpretation; and 550,000 lines of code in navigation.


Development

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

Jupiter
is the largest planet in the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

Solar System
, with more than twice the mass of all the other planets combined. Consideration of sending a probe to Jupiter began as early as 1959. NASA's Scientific Advisory Group (SAG) for Outer Solar System Missions considered the requirements for Jupiter orbiters and atmospheric probes. It noted that the technology to build a
heat shield An heat shield is designed to protect an object from overheating by dissipating, reflecting, absorbing heat, or simply gradually burn and fall away from the aircraft, pulling the excess heat with it. The term is most often used in reference to exh ...
for an atmospheric probe did not yet exist, and facilities to test one under the conditions found on Jupiter would not be available until 1980. NASA management designated the
Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a federally funded research and development center Federally funded research and development centers (FFRDCs) are public-private partnerships which conduct research and development Research is " c ...
(JPL) as the lead center for the Jupiter Orbiter Probe (JOP) project. The JOP would be the fifth spacecraft to visit Jupiter, but the first to orbit it, and the probe would be the first to enter its atmosphere. An important decision made at this time was to use a
Mariner program The Mariner program was conducted by the American space agency NASA to explore other planets. Between 1962 and late 1973, NASA’s Jet Propulsion Laboratory (JPL) designed and built 10 Robotic spacecraft, robotic Space probe, interplanetary prob ...
spacecraft like that used for Voyager for the Jupiter orbiter, rather than a Pioneer. Pioneer was stabilized by spinning the spacecraft at 60
rpm Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is the number of turns in one minute The minute is a unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the ...
, which gave a 360-degree view of the surroundings, and did not require an attitude control system. By contrast, Mariner had an attitude control system with three
gyroscopes A gyroscope (from Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek ...

gyroscopes
and two sets of six
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
jet thrusters. Attitude was determined with reference to the Sun and
Canopus Canopus () is the brightest star in the southern constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived outline or pattern, typically representing an animal, mythologic ...

Canopus
, which were monitored with two primary and four secondary sensors. There was also an
inertial reference unit An inertial reference unit (IRU) is a type of inertial sensor which uses gyroscopes A gyroscope (from Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , ...
and an
accelerometer An accelerometer is a tool that measures proper acceleration In relativity theory, proper acceleration is the physical acceleration (i.e., measurable acceleration as by an accelerometer) experienced by an object. It is thus acceleration relative ...

accelerometer
. This allowed it to take high-resolution images, but the functionality came at a cost of increased weight. A Mariner weighed compared to just for a Pioneer.
John R. Casani
John R. Casani
, who had headed the Mariner and Voyager projects, became the first project manager. He solicited suggestions for a more inspirational name for the project, and the most votes went to "Galileo" after
Galileo Galilei Galileo di Vincenzo Bonaiuti de' Galilei ( , ; 15 February 1564 – 8 January 1642), commonly referred to as Galileo, was an astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific q ...

Galileo Galilei
, the first person to view Jupiter through a telescope. His 1610 discovery of what is now known as the
Galilean moons The Galilean moons (or Galilean satellites) are the four largest moons of Jupiter—Io (moon), Io, Europa (moon), Europa, Ganymede (moon), Ganymede, and Callisto (moon), Callisto. They were first seen by Galileo Galilei in December 1609 or Janua ...
orbiting Jupiter was important evidence of the
Copernican model Copernican heliocentrism is the name given to the astronomical scientific modeling, model developed by Nicolaus Copernicus and published in 1543. This model positioned the Sun at the center of the Universe, motionless, with Earth and the other pla ...
of the solar system. It was also noted that the name was that of a
spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite alt=, A full-size model of the Earth observation satellite ERS 2 ">ERS_2.html" ;"title="Earth observation satellite ERS 2">Earth obse ...
in the ''
Star Trek ''Star Trek'' is an American science fiction media franchise created by Gene Roddenberry, which began with the Star Trek: The Original Series, eponymous 1960s series and quickly became a worldwide Popular culture, pop-culture Cultural influ ...
'' television show. The new name was adopted in February 1978. The
Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a federally funded research and development center Federally funded research and development centers (FFRDCs) are public-private partnerships which conduct research and development Research is " c ...
built the ''Galileo'' spacecraft and managed the ''Galileo'' mission for NASA.
West Germany West Germany is the common English name for the Federal Republic of Germany (FRG; german: Bundesrepublik Deutschland , BRD) between its formation on 23 May 1949 and the German reunification German reunification (german: Deutsche Wieder ...
Messerschmitt-Bölkow-Blohm Messerschmitt-Bölkow-Blohm (MBB) was a West German ) , capital = Bonn The Federal city of Bonn ( lat, Bonna) is a city on the banks of the Rhine in the German state of North Rhine-Westphalia, with a population of over 300 ...
supplied the propulsion module. NASA's
Ames Research Center The Ames Research Center (ARC), also known as NASA Ames, is a major NASA The National Aeronautics and Space Administration (NASA; ) is an independent agencies of the United States government, independent agency of the Federal government ...
managed the atmospheric probe, which was built by
Hughes Aircraft Company The Hughes Aircraft Company was a major American aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applicati ...
. At launch, the orbiter and probe together had a mass of and stood tall. Spacecraft are normally stabilized either by spinning around a fixed axis or by maintaining a fixed orientation with reference the Sun and a star; ''Galileo'' did both. One section of the spacecraft rotated at 3
revolutions per minute Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is the number of turns in one minute The minute is a unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the ...
, keeping ''Galileo'' stable and holding six instruments that gathered data from many different directions, including the fields and particles instruments. Back on the ground, the mission operations team used software containing 650,000 lines of code in the orbit sequence design process; 1,615,000 lines in the telemetry interpretation; and 550,000 lines of code in navigation. All of the spacecraft components and spare parts received a minimum of 2,000 hours of testing. The spacecraft was expected to last for at least five years—long enough to reach Jupiter and perform its mission. On December 19, 1985, it departed the JPL in
Pasadena, California Pasadena ( ; ) is a city in Los Angeles County, California Los Angeles County, officially the County of Los Angeles, and sometimes abbreviated as L.A. County, is the List of the most populous counties in the United States, most populous co ...
, on the first leg of its journey, a road trip to the
Kennedy Space Center The John F. Kennedy Space Center (KSC, originally known as the NASA Launch Operations Center), located on Merritt Island, Florida, is one of the NASA, National Aeronautics and Space Administration's (NASA) ten NASA facilities#List of field ...

Kennedy Space Center
in
Florida Florida is a U.S. state, state located in the Southeastern United States, Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia (U.S. state), Geor ...

Florida
. Due to the Space Shuttle ''Challenger'' disaster, the May launch date could not be met. The mission was re-scheduled October 12, 1989. The ''Galileo'' spacecraft would be launched by the
STS-34 STS-34 was a NASA Space Shuttle program, Space Shuttle mission using Space Shuttle Atlantis, ''Atlantis''. It was the 31st shuttle mission overall, and the fifth flight for ''Atlantis''. STS-34 launched from Kennedy Space Center, Florida, on 18 ...
mission in the . As the launch date of ''Galileo'' neared, anti-nuclear groups, concerned over what they perceived as an unacceptable risk to the public's safety from the
plutonium Plutonium is a radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material co ...

plutonium
in the ''Galileo''
radioisotope thermoelectric generator A radioisotope thermoelectric generator (RTG, RITEG) is a type of nuclear battery An atomic battery, nuclear battery, radioisotope battery or radioisotope generator is a device which uses energy from the decay of a radioactive isotope A r ...
s (RTGs) and General Purpose Heat Source (GPHS) modules, sought a court injunction prohibiting ''Galileo'' launch. RTGs were necessary for deep space probes because they had to fly distances from the Sun that made the use of solar energy impractical. The launch was delayed twice more: by a faulty main engine controller that forced a postponement to October 17, and then by inclement weather, which necessitated a postponement to the following day, but this was not a concern since the launch window extended until November 21. ''Atlantis'' finally lifted off at 16:53:40 UTC on October 18, and went into a orbit. ''Galileo'' was successfully deployed at 00:15 UTC on October 19. Following the IUS burn, the ''Galileo'' spacecraft adopted its configuration for solo flight, and separated from the IUS at 01:06:53 UTC on October 19. The launch was perfect, and ''Galileo'' was soon headed towards Venus at over . ''Atlantis'' returned to Earth safely on October 23.


Command and Data Handling (CDH)

The CDH subsystem was actively redundant, with two parallel data system buses running at all times. Each data system bus (a.k.a. string) was composed of the same functional elements, consisting of multiplexers (MUX), high-level modules (HLM), low-level modules (LLM), power converters (PC), bulk memory (BUM), data management subsystem bulk memory (DBUM), timing chains (TC), (PLL), Golay coders (GC), hardware command decoders (HCD) and critical controllers (CRC). The CDH subsystem was responsible for maintaining the following functions: #decoding of uplink commands #execution of commands and sequences #execution of system-level fault-protection responses #collection, processing, and formatting of telemetry data for downlink transmission #movement of data between subsystems via a data system bus. The spacecraft was controlled by six
RCA 1802 The COSMAC is an 8-bit In computer architecture In computer engineering, computer architecture is a set of rules and methods that describe the functionality, organization, and implementation of computer systems. Some definitions of archi ...
COSMAC
microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip ...

microprocessor
CPUs A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controllin ...

CPUs
: four on the spun side and two on the despun side. Each CPU was clocked at about 1.6 MHz, and fabricated on
sapphire Sapphire is a precious gemstone A gemstone (also called a fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical c ...

sapphire
(
silicon on sapphire Silicon on sapphire (SOS) is a hetero-epitaxial process for metal-oxide-semiconductor (MOS) integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electr ...
), which is a radiation-and static-hardened material ideal for spacecraft operation. This microprocessor was the first low-power
CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "see-moss"), also known as complementary-symmetry metal–oxide–semiconductor (COS-MOS), is a type of metal–oxide–semiconductor field-effect transistor The metal–oxide–se ...
processor chip, quite on a par with the 8-bit
6502 The MOS Technology 6502 (typically pronounced "sixty-five-oh-two" or "six-five-oh-two") William Mensch and the moderator both pronounce the 6502 microprocessor as ''"sixty-five-oh-two"''. is an 8-bit In computer architecture In computer ...
that was being built into the
Apple II The Apple II (stylized as apple ] '') is an 8-bit home computer">8-bit.html" ;"title="'') is an 8-bit">'') is an 8-bit home computer and one of the world's first highly successful mass-produced microcomputer products. It was designed primari ...

Apple II
desktop computer A desktop computer is a personal computer A personal computer (PC) is a multi-purpose computer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, ...
at that time. The Galileo Attitude and Articulation Control System (AACSE) was controlled by two Itek Advanced Technology Airborne Computers (ATAC), built using radiation-hardened 2901s. The AACSE could be reprogrammed in flight by sending the new program through the Command and Data Subsystem. ''Galileo'' attitude control system software was written in the
HAL/S HAL/S (''High-order Assembly Language/Shuttle'') is a real-time computing, real-time aerospace programming language compiler and cross-compiler for avionics applications used by NASA and associated agencies (JPL, etc.). It has been used in many U. ...
programming language, also used in the
Space Shuttle program The Space Shuttle program was the fourth human spaceflight Human spaceflight (also referred to as manned spaceflight or crewed spaceflight) is spaceflight Spaceflight (or space flight) is an application of astronautics to fly spacecr ...
. Memory capacity provided by each BUM was 16K of
RAM Random-access memory (RAM; ) is a form of computer memory In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic proces ...

RAM
, while the DBUMs each provided 8K of RAM. There were two BUMs and two DBUMs in the CDH subsystem and they all resided on the spun side of the spacecraft. The BUMs and DBUMs provided storage for sequences and contain various buffers for telemetry data and interbus communication. Every HLM and LLM was built up around a single 1802 microprocessor and 32K of RAM (for HLMs) or 16K of RAM (for LLMs). Two HLMs and two LLMs resided on the spun side while two LLMs were on the despun side. Thus, total memory capacity available to the CDH subsystem was 176K of RAM: 144K allocated to the spun side and 32K to the despun side. Each HLM was responsible for the following functions: #uplink command processing #maintenance of the spacecraft clock #movement of data over the data system bus #execution of stored sequences (time-event tables) #telemetry control #error recovery including system fault-protection monitoring and response. Each LLM was responsible for the following functions: #collect and format engineering data from the subsystems #provide the capability to issue coded and discrete commands to spacecraft users #recognize out-of-tolerance conditions on status inputs #perform some system fault-protection functions.


Propulsion

The propulsion subsystem consisted of a 400  N main engine and twelve 10 N thrusters, together with propellant, storage and pressurizing tanks and associated plumbing. The 10 N thrusters were mounted in groups of six on two 2-meter booms. The fuel for the system was of
monomethylhydrazine Monomethylhydrazine (mono-methyl hydrazine, MMH) is a highly toxic, volatile hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like ...

monomethylhydrazine
and
nitrogen tetroxide Dinitrogen tetroxide, commonly referred to as nitrogen tetroxide (NTO), and occasionally (usually among ex-USSR/Russia rocket engineers) as amyl, is the chemical compound A chemical compound is a chemical substance composed of many identical ...

nitrogen tetroxide
. Two separate tanks held another of
helium Helium (from el, ἥλιος, helios Helios; Homeric Greek: ), Latinized as Helius; Hyperion and Phaethon are also the names of his father and son respectively. often given the epithets Hyperion ("the one above") and Phaethon ("the shining" ...

helium
pressurant. The propulsion subsystem was developed and built by
Messerschmitt-Bölkow-Blohm Messerschmitt-Bölkow-Blohm (MBB) was a West German ) , capital = Bonn The Federal city of Bonn ( lat, Bonna) is a city on the banks of the Rhine in the German state of North Rhine-Westphalia, with a population of over 300 ...
and provided by West Germany, the major international partner in Project ''Galileo''.


Electrical power

At the time,
solar panel A solar cell panel, solar electric panel, photo-voltaic (PV) module or just solar panel is an assembly of photo-voltaic cells mounted in a framework for installation. Solar panels use sunlight Sunlight is a portion of the given off by ...

solar panel
s were not practical at Jupiter's distance from the Sun; the spacecraft would have needed a minimum of of panels. Chemical batteries would likewise be prohibitively large due to technological limitations. The solution was two
radioisotope thermoelectric generator A radioisotope thermoelectric generator (RTG, RITEG) is a type of nuclear battery An atomic battery, nuclear battery, radioisotope battery or radioisotope generator is a device which uses energy from the decay of a radioactive isotope A r ...
s (RTGs) which powered the spacecraft through the radioactive decay of
plutonium-238 Plutonium-238 (238Pu) is a radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nucleus is the ...

plutonium-238
. The heat emitted by this decay was converted into electricity through the solid-state
Seebeck effect The thermoelectric effect is the direct conversion of temperature Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of ...
. This provided a reliable and long-lasting source of electricity unaffected by the cold environment and high-radiation fields in the Jovian system. Each
GPHS-RTG GPHS-RTG or general-purpose heat source The general-purpose heat source is a United States Department of Energy, U.S. DOE-designed radioactive heat source for radioisotope thermoelectric generators (RTG) or Stirling radioisotope generators (SRG) ...

GPHS-RTG
, mounted on a boom, carried of . Each RTG contained 18 separate heat source modules, and each module encased four pellets of
plutonium(IV) oxide Plutonium(IV) oxide or (plutonia) is the chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, elem ...
, a
ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant Corrosion is a Erosion, natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, carbonate or sulfide. ...

ceramic
material resistant to fracturing. The plutonium was enriched to about 83.5 percent plutonium-238. The modules were designed to survive a range of potential accidents: launch vehicle explosion or fire, re-entry into the atmosphere followed by land or water impact, and post-impact situations. An outer covering of
graphite Graphite (), archaically referred to as plumbago, is a Crystallinity, crystalline form of the element carbon with its atoms arranged in a Hexagonal crystal system, hexagonal structure. It occurs naturally in this form and is the most stable for ...

graphite
provided protection against the structural, thermal, and eroding environments of a potential re-entry into Earth's atmosphere. Additional graphite components provided impact protection, while
iridium Iridium is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, beh ...

iridium
cladding of the fuel cells provided post-impact containment. The RTGs produced about 570 watts at launch. The power output initially decreased at the rate of 0.6 watts per month and was 493 watts when ''Galileo'' arrived at Jupiter.


Telecommunications

The spacecraft had a big high-gain antenna which failed to deploy while in space, so the low-gain antenna was used instead, although at slower data transfer speeds.


Instruments

Scientific instruments to measure fields and particles were mounted on the spinning section of the spacecraft, together with the main
antenna Antenna (pl. antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two col ...
, power supply, the propulsion module and most of ''Galileo'' computers and control electronics. The sixteen instruments, weighing altogether, included
magnetometer A magnetometer is a device that measures magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each point in a subset of space. For instance, a vector field in ...
sensors mounted on an boom to minimize interference from the spacecraft; a
plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral) or heliotrope, a mineral aggregate * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood plasma ...
instrument for detecting low-energy charged particles and a plasma-wave detector to study waves generated by the particles; a high-energy particle detector; and a detector of cosmic and Jovian
dust Dust is made of s of solid . On Earth, it generally consists of particles in the that come from various sources such as lifted by wind (an ), , and . Dust in homes is composed of about 20–50% dead . The rest, and in offices, and other ...
. It also carried the Heavy Ion Counter, an engineering experiment to assess the potentially hazardous charged particle environments the spacecraft flew through, and an
extreme ultraviolet Extreme ultraviolet radiation (EUV or XUV) or high-energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which re ...
detector associated with the UV spectrometer on the scan platform. The despun section's instruments included the camera system; the
near infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natur ...
mapping spectrometer to make multi-spectral images for atmospheric and moon surface chemical analysis; the ultraviolet spectrometer to study gases; and the photopolarimeter-radiometer to measure radiant and reflected energy. The camera system was designed to obtain images of Jupiter's satellites at resolutions 20 to 1,000 times better than ''Voyager'' best, because ''Galileo'' flew closer to the planet and its inner moons, and because the more modern CCD sensor in ''Galileo'' camera was more sensitive and had a broader color detection band than the
vidicon Video camera tubes were devices based on the cathode ray tube A cathode-ray tube (CRT) is a vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current An elec ...

vidicon
s of ''Voyager''.


Despun section


Solid State Imager (SSI)

The SSI was an 800-by-800-pixel
charge-coupled device A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a ...
(CCD) camera. The optical portion of the camera was a modified flight spare of the ''
Voyager Voyager may refer to: Science and Astronomy * Voyager 1 – a space probe launched by NASA September 5, 1977 as part of the Voyager program. * Voyager 2 – a space probe launched by NASA on August 20, 1977. Computing and communications * L ...
'' narrow-angle camera; a . The CCD had radiation shielding a thick layer of
tantalum Tantalum is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that ...

tantalum
surrounding the CCD except where the light enters the system. An eight-position filter wheel was used to obtain images at specific wavelengths. The images were then combined electronically on Earth to produce color images. The spectral response of the SSI ranged from about 400 to 1100 nm. The SSI weighed and consumed, on average, 15 watts of power.


Near-Infrared Mapping Spectrometer (NIMS)

The NIMS instrument was sensitive to 0.7-to-5.2-
micrometer Micrometer can mean: * Micrometer (device) A micrometer, sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw widely used for Accuracy and precision, accurate measurement of components in mechanical enginee ...
wavelength
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior ...

infrared
light, overlapping the wavelength range of the SSI. NIMS used a aperture reflecting telescope. The
spectrometer A spectrometer () is a scientific instrument used to separate and measure Spectrum, spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon ...

spectrometer
used a grating to disperse the light collected by the telescope. The dispersed spectrum of light was focused on detectors of
indium Indium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical element ...

indium
,
antimonide Antimonides (sometimes called stibnides) are compounds Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), ...
and
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

silicon
. NIMS weighed and used 12 watts of power on average.


Ultraviolet Spectrometer / Extreme Ultraviolet Spectrometer (UVS/EUV)

The of the UVS had a aperture. Both the UVS and EUV instruments used a ruled
grating A grating is any regularly spaced collection of essentially identical, parallel Parallel may refer to: Computing * Parallel algorithm In computer science Computer science deals with the theoretical foundations of information, algorithms ...

grating
to disperse light for spectral analysis. Light then passed through an exit slit into
photomultiplier A photomultiplier is a device that converts incident photons into an electrical signal In signal processing, a signal is a function that conveys information about a phenomenon. In electronics and telecommunications, it refers to any time vary ...

photomultiplier
tubes that produced pulses of electrons, which were counted and the results sent to Earth. The UVS was mounted on ''Galileo'' scan platform. The EUV was mounted on the spun section. As ''Galileo'' rotated, EUV observed a narrow ribbon of space perpendicular to the spin axis. The two instruments combined weighed about and used 5.9 watts of power.


Photopolarimeter-Radiometer (PPR)

The PPR had seven radiometry bands. One of these used no filters and observed all incoming radiation, both solar and thermal. Another band allowed only solar radiation through. The difference between the solar-plus-thermal and the solar-only channels gave the total thermal radiation emitted. The PPR also measured in five broadband channels that spanned the spectral range from 17 to 110 micrometers. The radiometer provided data on the temperatures of Jupiter's atmosphere and satellites. The design of the instrument was based on that of an instrument flown on the ''
Pioneer Venus The Pioneer Venus project was part of the Pioneer program The Pioneer programs were two series of United States lunar and planetary space probes exploration. The first program, which ran from 1958 to 1960, unsuccessfully attempted to send ...
'' spacecraft. A aperture reflecting telescope collected light and directed it to a series of filters, and, from there, measurements were performed by the detectors of the PPR. The PPR weighed and consumed about 5 watts of power.


Spun section


Dust Detector Subsystem (DDS)

The Dust Detector Subsystem (DDS) was used to measure the mass, electric charge, and velocity of incoming particles. The masses of dust particles that the DDS could detect go from to grams. The speed of these small particles could be measured over the range of . The instrument could measure impact rates from 1 particle per 115 days (10 megaseconds) to 100 particles per second. Such data was used to help determine dust origin and dynamics within the
magnetosphere In astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies astronomical object, celestial objects and celestial event, phenomena. It uses m ...

magnetosphere
. The DDS weighed and used an average of 5.4 watts of power.


Energetic Particles Detector (EPD)

The Energetic Particles Detector (EPD) was designed to measure the numbers and energies of ions and electrons whose energies exceeded about . The EPD could also measure the direction of travel of such particles and, in the case of ions, could determine their composition (whether the ion is
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
or
sulfur Sulfur (in nontechnical British English: sulphur) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

sulfur
, for example). The EPD used silicon solid-state detectors and a
time-of-flight Time of flight (ToF) is the measurement of the time taken by an object, particle or wave (be it acoustic, electromagnetic, etc.) to travel a distance through a medium. This information can then be used to measure velocity or path length, or as a wa ...
detector system to measure changes in the energetic particle population at Jupiter as a function of position and time. These measurements helped determine how the particles got their energy and how they were transported through Jupiter's magnetosphere. The EPD weighed and used 10.1 watts of power on average.


Heavy Ion Counter (HIC)

The HIC was, in effect, a repackaged and updated version of some parts of the flight spare of the ''Voyager'' Cosmic Ray System. The HIC detected heavy
ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
s using stacks of single crystal silicon wafers. The HIC could measure heavy ions with energies as low as and as high as per nucleon. This range included all atomic substances between
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
and
nickel Nickel is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

nickel
. The HIC and the EUV shared a communications link and, therefore, had to share observing time. The HIC weighed and used an average of 2.8 watts of power.


Magnetometer (MAG)

The
magnetometer A magnetometer is a device that measures magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each point in a subset of space. For instance, a vector field in ...
(MAG) used two sets of three sensors. The three sensors allowed the three orthogonal components of the
magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each point in a subset of space. For instance, a vector field in the plane can be visualised as a collection of arrows with ...

magnetic field
section to be measured. One set was located at the end of the magnetometer boom and, in that position, was about from the spin axis of the spacecraft. The second set, designed to detect stronger fields, was from the spin axis. The boom was used to remove the MAG from the immediate vicinity of ''Galileo'' to minimize magnetic effects from the spacecraft. However, not all these effects could be eliminated by distancing the instrument. The rotation of the spacecraft was used to separate natural magnetic fields from engineering-induced fields. Another source of potential error in measurement came from the bending and twisting of the long magnetometer boom. To account for these motions, a calibration coil was mounted rigidly on the spacecraft to generate a reference magnetic field during calibrations. The magnetic field at the surface of the Earth has a strength of about 50,000  nT. At Jupiter, the outboard (11 m) set of sensors could measure magnetic field strengths in the range from ±32 to ±512 nT, while the inboard (6.7 m) set was active in the range from ±512 to ±16,384 nT. The MAG experiment weighed and used 3.9 watts of power.


Plasma Subsystem (PLS)

The PLS used seven fields of view to collect
charged particle In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. " ...
s for energy and mass analysis. These fields of view covered most angles from 0 to 180 degrees, fanning out from the spin axis. The rotation of the spacecraft carried each field of view through a full circle. The PLS measured particles in the energy range from . The PLS weighed and used an average of 10.7 watts of power.


Plasma Wave Subsystem (PWS)

An electric
dipole antenna In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of antenna (radio), antenna. The dipole is any one of a class of antennas producing a radiation pattern approximating that of an elementary el ...

dipole antenna
was used to study the electric fields of plasmas, while two search coil magnetic antennas studied the magnetic fields. The electric dipole antenna was mounted at the tip of the magnetometer boom. The search coil magnetic antennas were mounted on the high-gain antenna feed. Nearly simultaneous measurements of the electric and magnetic field spectrum allowed electrostatic waves to be distinguished from
electromagnetic wave In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular s ...

electromagnetic wave
s. The PWS weighed and used an average of 9.8 watts.


''Galileo'' entry probe

The atmospheric probe was built by
Hughes Aircraft Company The Hughes Aircraft Company was a major American aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applicati ...
at its
El Segundo, California El Segundo (; ; Spanish language, Spanish for "The Second") is a city in Los Angeles County, California, United States. Located on Santa Monica Bay, it was incorporated on January 18, 1917, and is part of the South Bay (Los Angeles County), South ...
plant. It weighed and was high. Inside the probe's
heat shield An heat shield is designed to protect an object from overheating by dissipating, reflecting, absorbing heat, or simply gradually burn and fall away from the aircraft, pulling the excess heat with it. The term is most often used in reference to exh ...
, the scientific instruments were protected from extreme heat and pressure during its high-speed journey into the Jovian atmosphere, entering at . Temperatures reached around 16,000°C (28,832°F). NASA built a special laboratory, the Giant Planet Facility, to simulate the heat load, which was similar to the convective and radiative heating experienced by an
ICBM An intercontinental ballistic missile (ICBM) is a missile In military terminology, a missile is a guided airborne ranged weapon . English longbowmen figure prominently in the foreground at right where they drive away the French crossbow ...
warhead reentering the atmosphere.


Batteries

The probe's electronics were powered by 13 manufactured by
Honeywell Honeywell International Inc. is an American public company, publicly traded, multinational corporation, multinational conglomerate (company), conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four are ...

Honeywell
's Power Sources Center in
Horsham, Pennsylvania Horsham is a census-designated place (CDP) in Montgomery County, Pennsylvania, Montgomery County, Pennsylvania, United States. The population was 14,842 at the 2010 United States Census, 2010 census. Horsham is located entirely within Horsham Towns ...
. Each cell was the size of a
D battery A D battery (D cell or IECIEC may refer to: Businesses and organisations * International Electrotechnical Commission The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an int ...
so existing manufacturing tools could be used. They provided a nominal power output of about 7.2-ampere hours capacity at a minimal voltage of 28.05 volts.


Scientific instruments

The probe included seven instruments for taking data on its plunge into Jupiter: In addition, the probe's heat shield contained instrumentation to measure
ablation Ablation is removal or destruction of material from an object by vaporization, chipping, or other erosion, erosive processes. Examples of ablative materials are described below, and include spacecraft material for ascent and atmospheric reentry, ...
during descent.


Names

The Galileo Probe had
COSPAR The Committee on Space Research (COSPAR) was established in 1958 by the International Council for Scientific Unions (ICSU). Among COSPAR's objectives are the promotion of scientific research in space Space is the boundless three-dimensio ...
ID 1989-084E while the orbiter had id 1989-084B. Names for the spacecraft include ''Galileo Probe'' or ''Jupiter Entry Probe'' abbreviated JEP. The related COSPAR IDs of the Galileo mission were: *1989-084A STS 34 *1989-084B ''Galileo'' *1989-084C
IUS __NOTOC__ ''Ius'' or ''Jus'' (Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the pow ...
(Orbus 21) *1989-084D IUS (Orbus 6E) *1989-084E ''Galileo'' Probe


Notes


References

* * * * * * * * * * * * * *


See also

*
List of spacecraft powered by non-rechargeable batteries This is a list of spacecraft powered by non-rechargeable batteries. While most spacecraft are powered by longer-lasting power sources such as Solar cell, solar cells or Radioisotope thermoelectric generator, radioisotope thermoelectric generators, ...


External links


''Galileo'' mission site
by NASA's Solar System Exploration
''Galileo'' legacy site
by NASA's Solar System Exploration
''Galileo'' Satellite Image Mosaics
by Arizona State University
Galileo image album
by Kevin M. Gill
Early probe results report

''Galileo'' Probe
NASA Space Science Data Coordinated Archive {{DEFAULTSORT:Galileo (Spacecraft) spacecraft Spacecraft launched by the Space Shuttle Spacecraft launched in 1989 Destroyed space probes Galileo Galilei Nuclear-powered robots Extraterrestrial atmosphere entry Attached spacecraft