View source for Engineering:Galileo (spacecraft)

{{Short description|NASA probe sent to Jupiter (1989–2003)}}
{{Italic title}}
{{Infobox spaceflight
| auto = all
| name = ''Galileo''
| names_list = Jupiter Orbiter Probe
| image = Artwork Galileo-Io-Jupiter.JPG
| image_caption = Artist's concept of ''Galileo'' at Io with Jupiter in the background. In reality, the high-gain foldable antenna failed to deploy in flight.
| image_size =
| mission_type = [[Astronomy:Jupiter|Jupiter]] orbiter
| operator = [[Organization:NASA|NASA]]
| COSPAR_ID = 1989-084B
| SATCAT = 20298
| website = {{url|solarsystem.nasa.gov/galileo/}}
| mission_duration = {{plainlist|
* Planned: {{time interval|18 October 1989|7 December 1997|show=ymd|sep=,}}
* Jupiter orbit: {{time interval|8 December 1995 01:16|21 September 2003 18:57|show=ymd|sep=,}}
* Final: {{time interval|18 October 1989|21 September 2003 18:57|show=ymd|sep=,}}
}}
| distance_travelled = {{convert|4631778000|km|e9mi|sigfig=3|abbr=unit}}<ref name="jpl-20030921">{{cite press release |title=The Final Day on Galileo |url=https://www2.jpl.nasa.gov/galileo//news/thiswk/today030921.html |publisher=[[Organization:Jet Propulsion Laboratory|Jet Propulsion Laboratory]] |archive-url=https://web.archive.org/web/20230930032039/https://www2.jpl.nasa.gov/galileo/news/thiswk/today030921.html |archive-date=30 September 2023 |date=21 September 2003 |url-status=live}}</ref>
| manufacturer = {{plainlist|
* [[Organization:Jet Propulsion Laboratory|Jet Propulsion Laboratory]]<ref name="galileo-arrival">{{cite web |url=http://www.jpl.nasa.gov/news/press_kits/gllarpk.pdf |title=Galileo Jupiter Arrival |type=Press Kit |publisher=NASA{{\}}Jet Propulsion Laboratory |date=December 1995}}</ref>
* Messerschmitt-Bölkow-Blohm<ref name="galileo-arrival" />
* [[Company:General Electric|General Electric]]<ref name="galileo-arrival" />
* [[Company:Hughes Aircraft Company|Hughes Aircraft Company]]<ref name="galileo-arrival" />
}}
| launch_mass = {{plainlist|
* Total: {{convert|2560|kg|lb|abbr=on}}<ref name="galileo-arrival" />
* Orbiter: {{convert|2220|kg|lb|abbr=on}}<ref name="galileo-arrival" />
* Probe: {{convert|340|kg|lb|abbr=on}}<ref name="galileo-arrival" />
}}
| dry_mass = {{plainlist|
* Orbiter: {{convert|1880|kg|lb|abbr=on}}<ref name="galileo-arrival" />
* Probe: {{convert|340|kg|lb|abbr=on}}<ref name="galileo-arrival" />
}}
| payload_mass = {{plainlist|
* Orbiter: {{convert|118|kg|lb|abbr=on}}<ref name="galileo-arrival" />
* Probe: {{convert|30|kg|lb|0|abbr=on}}<ref name="galileo-arrival" />
}}
| power = {{plainlist|
* Orbiter: 570 watts at launch,<ref name="galileo-arrival" /> 493 watts on arrival,{{sfn|Taylor|Cheung|Seo|2002|p=86}} 410 watts at end-of-life
* Probe: 730 watt-hours<ref name="galileo-arrival" />
}}
| launch_date = {{start-date|October 18, 1989, 16:53:40}}&nbsp;[[UTC]]
| launch_rocket = {{OV|104}} <br /> [[Engineering:STS-34|STS-34]]/[[Engineering:Inertial Upper Stage|IUS]]
| launch_site = Kennedy [[Astronomy:Kennedy Space Center Launch Complex 39|LC-39B]]
| launch_contractor =
| entered_service = December 8, 1995, 01:16&nbsp;UTC&nbsp;[[Physics:Spacecraft Event Time|SCET]]
| disposal_type = Controlled entry into Jupiter
| decay_date = {{end-date|September 21, 2003, 18:57:18}} UTC
| instruments_list = {{Infobox spaceflight/Instruments
  | acronym1 = SSI  | name1 = Solid-State Imager
  | acronym2 = NIMS | name2 = Near-Infrared Mapping Spectrometer
  | acronym3 = UVS  | name3 = Ultraviolet Spectrometer
  | acronym4 = PPR  | name4 = Photopolarimeter-Radiometer
  | acronym5 = DDS  | name5 = Dust Detector Subsystem
  | acronym6 = EPD  | name6 = Energetic Particles Detector
  | acronym7 = HIC  | name7 = Heavy Ion Counter
  | acronym8 = MAG  | name8 = Magnetometer
  | acronym9 = PLS  | name9 = Plasma Subsystem
  | acronym10 = PWS | name10 = Plasma Wave Subsystem
 }}
| programme = NASA Flagship Program
| previous_mission = [[Astronomy:Voyager program|''Voyager'' program]]
| next_mission = ''[[Astronomy:Cassini–Huygens|Cassini–Huygens]]''
| insignia = Galileo mission patch.png
| insignia_size = 140px
}}

'''''Galileo''''' was an American robotic [[Engineering:Space probe|space probe]] that studied the planet [[Astronomy:Jupiter|Jupiter]] and [[Astronomy:Moons of Jupiter|its moons]], as well as the asteroids [[Astronomy:951 Gaspra|Gaspra]] and [[Astronomy:243 Ida|Ida]]. Named after the Italian astronomer [[Biography:Galileo Galilei|Galileo Galilei]], it consisted of an orbiter and an entry probe. It was delivered into Earth orbit on October 18, 1989, by {{OV|Atlantis}}, during [[Engineering:STS-34|STS-34]]. ''Galileo'' arrived at Jupiter on December 7, 1995, after [[Astronomy:Gravity assist|gravitational assist]] flybys of Venus and Earth, and became the first spacecraft to orbit an outer planet.<ref>{{Cite web|title=Galileo – Overview|url=https://solarsystem.nasa.gov/missions/galileo/overview|access-date=December 7, 2021|website=NASA Solar System Exploration}}</ref>

The [[Organization:Jet Propulsion Laboratory|Jet Propulsion Laboratory]] built the ''Galileo'' spacecraft and managed the [[Astronomy:Galileo project|''Galileo'' program]] for [[Organization:NASA|NASA]]. West Germany's Messerschmitt-Bölkow-Blohm supplied the propulsion module. NASA's [[Organization:Ames Research Center|Ames Research Center]] managed the atmospheric probe, which was built by [[Company:Hughes Aircraft Company|Hughes Aircraft Company]]. At launch, the orbiter and probe together had a mass of {{convert|2562|kg|lb|abbr=on}} and stood {{convert|6.15|m|ft|abbr=on}} 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, keeping ''Galileo'' stable and holding six instruments that gathered data from many different directions, including the fields and particles instruments. 

''Galileo'' was intentionally destroyed in Jupiter's atmosphere on September 21, 2003. The next orbiter to be sent to Jupiter was [[Engineering:Juno (spacecraft)|''Juno'']], which arrived on July 5, 2016.

==Development==
{{For timeline}}
[[Astronomy:Jupiter|Jupiter]] is the largest planet in the [[Astronomy:Solar System|Solar System]], with more than twice the mass of all the other planets combined.<ref>{{cite web |title=In Depth {{pipe}} Jupiter  |publisher= NASA Solar System Exploration |url=https://solarsystem.nasa.gov/planets/jupiter/in-depth/ |access-date=October 27, 2020}}</ref>  Consideration of sending a probe to Jupiter began as early as 1959.{{sfn|Meltzer|2007|pp=9–10}} 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 [[Astronomy:Heat shield|heat shield]] 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.{{sfn|Meltzer|2007|pp=29–30}} NASA management designated the [[Organization:Jet Propulsion Laboratory|Jet Propulsion Laboratory]] (JPL) as the lead center for the Jupiter Orbiter Probe (JOP) project.{{sfn|Meltzer|2007|pp=32–33}} 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.{{sfn|Dawson|Bowles|2004|pp=190–191}}

[[File:Galileo Preparations - GPN-2000-000672.jpg|thumb|left|In the Vertical Processing Facility (VPF), ''Galileo'' is prepared for mating with the [[Engineering:Inertial Upper Stage|Inertial Upper Stage]] booster.]]
An important decision made at this time was to use a [[Astronomy:Mariner program|Mariner program]] spacecraft like that used for Voyager for the Jupiter orbiter, rather than a Pioneer. Pioneer was stabilized by spinning the spacecraft at 60 rpm, 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 and two sets of six [[Chemistry:Nitrogen|nitrogen]] jet thrusters. Attitude was determined with reference to the Sun and [[Astronomy:Canopus|Canopus]], which were monitored with two primary and four secondary sensors. There was also an [[Engineering:Inertial reference unit|inertial reference unit]] and an [[Physics:Accelerometer|accelerometer]]. This allowed it to take high-resolution images, but the functionality came at a cost of increased weight. A Mariner weighed {{convert|722|kg}} compared to just {{convert|146|kg}} for a Pioneer.{{sfn|Meltzer|2007|pp=30–32}}

John R. Casani, who had headed the Mariner and Voyager projects, became the first project manager.<ref>{{cite web |publisher=NASA |title=NASA's 50 Year Men and Women |url=https://www.nasa.gov/50th/50th_magazine/50yearsEmployees.html |access-date=October 28, 2020 |archive-date=March 19, 2010 |archive-url=https://web.archive.org/web/20100319002842/https://www.nasa.gov/50th/50th_magazine/50yearsEmployees.html |url-status=dead }}</ref> He solicited suggestions for a more inspirational name for the project, and the most votes went to "Galileo" after [[Biography:Galileo Galilei|Galileo Galilei]], the first person to view Jupiter through a telescope. His 1610 discovery of what is now known as the [[Astronomy:Galilean moons|Galilean moons]] orbiting Jupiter was important evidence of the [[Astronomy:Copernican Revolution|Copernican model]] of the solar system. It was also noted that the name was that of a spacecraft in the ''Star Trek'' television show. The new name was adopted in February 1978.{{sfn|Meltzer|2007|p=38}}

The [[Organization:Jet Propulsion Laboratory|Jet Propulsion Laboratory]] built the ''Galileo'' spacecraft and managed the ''Galileo'' mission for NASA. West Germany{{'s}} Messerschmitt-Bölkow-Blohm supplied the propulsion module. NASA's [[Organization:Ames Research Center|Ames Research Center]] managed the atmospheric probe, which was built by [[Company:Hughes Aircraft Company|Hughes Aircraft Company]].<ref name="galileo-arrival" /> At launch, the orbiter and probe together had a mass of {{convert|2562|kg|lb|abbr=on}} and stood {{convert|6.15|m|ft|abbr=on}} tall.<ref name="galileo-arrival" />
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]], keeping ''Galileo'' stable and holding six instruments that gathered data from many different directions, including the fields and particles instruments.<ref name="in depth">{{cite web |title=Galileo In Depth  |publisher=NASA |url=https://solarsystem.nasa.gov/missions/galileo/in-depth/#otp_spacecraft_and_instruments |access-date=December 6, 2020}}</ref> 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.<ref name="galileo-arrival" /> 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.{{sfn|Meltzer|2007|pp=68–69}}

[[File:STS-34 Launch 2.jpg|thumb|Launch of [[Engineering:Space Shuttle Atlantis|Space Shuttle ''Atlantis'']] on STS-34, carrying ''Galileo'' into Earth orbit]]
On December 19, 1985, it departed the JPL in Pasadena, California, on the first leg of its journey, a road trip to the Kennedy Space Center in Florida.{{sfn|Meltzer|2007|pp=68–69}}{{sfn|Beyer|O'Connor|Mudgway|1992|p=}} Due to the [[Engineering:Space Shuttle Challenger disaster|Space Shuttle ''Challenger'' disaster]], the May launch date could not be met.{{sfn|Meltzer|2007|p=78}} The mission was re-scheduled October 12, 1989. The ''Galileo'' spacecraft would be launched by the [[Engineering:STS-34|STS-34]] mission in the {{OV|Atlantis}}.<ref>{{cite press release |first=Jeffrey |last=Carr |id=88-049 |date=November 10, 1988 |title=Four New Shuttle Crews Named (STS-32, STS-33, STS-34, STS-35) |publisher=NASA |url=https://www.nasa.gov/centers/johnson/pdf/83140main_1988.pdf |access-date=November 5, 2020 |archive-date=February 25, 2017 |archive-url=https://web.archive.org/web/20170225161928/https://www.nasa.gov/centers/johnson/pdf/83140main_1988.pdf |url-status=dead }}</ref> 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 [[Chemistry:Plutonium|plutonium]] in the ''Galileo''{{'s}} [[Physics:Radioisotope thermoelectric generator|radioisotope thermoelectric generator]]s (RTGs) and General Purpose Heat Source (GPHS) modules, sought a court injunction prohibiting ''Galileo''{{'s}} launch.<ref name="Groups Protest Use of Plutonium">{{cite news |newspaper=The New York Times |title=Groups Protest Use of Plutonium on Galileo |first=William J. |last=Broad |date=October 10, 1989 |url=https://www.nytimes.com/1989/10/10/science/groups-protest-use-of-plutonium-on-galileo.html |access-date=November 4, 2020}}</ref> RTGs were necessary for deep space probes because they had to fly distances from the Sun that made the use of solar energy impractical.<ref name="Sagan">{{cite web |last=Sagan |first=Carl |author-link=Carl Sagan |title=Galileo: To Launch or not to Launch? |date=October 9, 1989 |url=http://www.dartmouth.edu/~chance/course/Syllabi/97Dartmouth/day-6/sagan.html |access-date=November 4, 2020 |archive-date=January 26, 2021 |archive-url=https://web.archive.org/web/20210126152333/http://www.dartmouth.edu/~chance/course/Syllabi/97Dartmouth/day-6/sagan.html |url-status=dead }}</ref>

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,<ref name="STS-34" /> but this was not a concern since the launch window extended until November 21.<ref name="Galileo Launch Nears">{{cite news |title=Galileo Launch Nears |first=Kathy |last=Sawyer |date=October 17, 1989 |newspaper= The Washington Post |url=https://www.washingtonpost.com/archive/politics/1989/10/17/galileo-launch-nears/d61c4140-7588-4637-b1c1-6b3ce69ac473/ |access-date=November 5, 2020}}</ref> ''Atlantis'' finally lifted off at 16:53:40 [[UTC]] on October 18, and went into a {{convert|213|mi|order=flip|sp=us|adj=on}} orbit.<ref name="STS-34">{{cite web |url=https://www.nasa.gov/mission_pages/shuttle/shuttlemissions/archives/sts-34.html |title=Mission Archives: STS-34 |publisher=NASA |date=February 18, 2010 |access-date=January 7, 2017}}</ref> ''Galileo'' was successfully deployed at 00:15 UTC on October 19.{{sfn|Meltzer|2007|p=78}} 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.<ref name="PDS">{{cite web |title=PDS: Mission Information |publisher=NASA |url=https://pds.nasa.gov/ds-view/pds/viewMissionProfile.jsp?MISSION_NAME=GALILEO |access-date=November 9, 2020}}</ref> The launch was perfect, and ''Galileo'' was soon headed towards Venus at over {{convert|9000|mph|order=flip|abbr=on}}.<ref>{{cite news |title=Galileo Travels 292,500 Miles Toward Venus |newspaper= The Washington Post |url=https://www.washingtonpost.com/archive/politics/1989/10/20/galileo-travels-292500-miles-toward-venus/0ca00a5a-a443-4cc2-85ac-817b9514941b/ |access-date=November 5, 2020}}</ref> ''Atlantis'' returned to Earth safely on October 23.<ref name="STS-34"/>
[[File:Galileo Diagram.jpg|thumb|''Galileo''{{'s}} main components]]

==Command and Data Handling (CDH)==
The CDH subsystem was actively redundant, with two parallel [[Engineering:System bus|data system buses]] running at all times.{{sfn|Siewiorek|Swarz|1998|p=683}} 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), [[Engineering:Phase-locked loop|phase locked loops]] (PLL), [[Binary Golay code|Golay]] coders (GC), hardware command decoders (HCD) and critical controllers (CRC).{{sfn|Tomayko|1988|pp=198–199}}

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.{{sfn|Tomayko|1988|pp=193–198}}

The spacecraft was controlled by six RCA 1802 COSMAC [[Engineering:Microprocessor|microprocessor]] [[Central processing unit|CPUs]]: four on the spun side and two on the despun side. Each CPU was clocked at about 1.6&nbsp;MHz, and fabricated on [[Chemistry:Sapphire|sapphire]] ([[Physics:Silicon on sapphire|silicon on sapphire]]), which is a [[Engineering:Radiation hardening|radiation-and static-hardened]] material ideal for spacecraft operation. This 8-bit microprocessor was the first low-power [[Engineering:CMOS|CMOS]] processor chip, similar to the 6502 that was being built into the Apple II [[Engineering:Desktop computer|desktop computer]] at that time.<ref name="engineering" />

The Galileo Attitude and Articulation Control System (AACSE) was controlled by two Itek [[Engineering:Advanced Technology Airborne Computer|Advanced Technology Airborne Computer]]s (ATAC), built using radiation-hardened 2901s. The AACSE could be reprogrammed in flight by sending the new program through the Command and Data Subsystem.{{sfn|Tomayko|1988|pp=198–201}} The attitude control system software was written in the HAL/S programming language,{{sfn|Tomayko|1988|p=199}} which was also used in the [[Engineering:Space Shuttle program|Space Shuttle program]].{{sfn|Tomayko|1988|p=110}}

Memory capacity provided by each BUM was 16K of 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.{{sfn|Tomayko|1988|pp=190–198}}
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.{{sfn|Tomayko|1988|pp=190–198}}

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.{{sfn|Tomayko|1988|pp=190–198}}
<!-- The HCD received command data from the modulation/demodulation subsystem, decoded these data and transferred them to the HLMs and CRCs. The CRC controlled the configuration of CDH subsystem elements. It also controlled access to the two data system buses by other spacecraft subsystems. In addition, the CRC supplied signals to enable certain critical events (e.g. probe separation). The GCs provided [[Binary Golay code|Golay]] encoding of data via hardware. The TCs and PLLs established timing within the CDH subsystem. -->

==Propulsion==
[[File:Galileo propulsion module.jpg|thumb|Propulsion module]]
The propulsion subsystem consisted of a {{cvt|400|N|lbf|adj=on}} main engine and twelve {{cvt|10|N|lbf|adj=on}} thrusters, together with propellant, storage and pressurizing tanks and associated plumbing. The 10&nbsp;N thrusters were mounted in groups of six on two {{convert|2|m|ft|sp=us|adj=on}} booms. The fuel for the system was {{convert|925|kg|lb|abbr=on}} of [[Chemistry:Monomethylhydrazine|monomethylhydrazine]] and nitrogen tetroxide. Two separate tanks held another {{convert|7|kg|lb|abbr=on}} of [[Chemistry:Helium|helium]] pressurant. The propulsion subsystem was developed and built by Messerschmitt-Bölkow-Blohm and provided by West Germany, the major international partner in Project ''Galileo''.<ref name="engineering">{{cite web |url=http://www.resa.net/nasa/engineer.htm |title=Galileo Engineering |archive-url=https://web.archive.org/web/20080613233904/http://www.resa.net/nasa/engineer.htm |publisher=RESA |archive-date=June 13, 2008 }}</ref>

==Electrical power==
At the time, [[Physics:Solar panel|solar panel]]s were not practical at Jupiter's distance from the Sun; the spacecraft would have needed a minimum of {{convert|65|m2|sqft|sp=us}} of panels. Chemical batteries would likewise be prohibitively large due to technological limitations. The solution was two [[Physics:Radioisotope thermoelectric generator|radioisotope thermoelectric generator]]s (RTGs) which powered the spacecraft through the radioactive decay of [[Physics:Plutonium-238|plutonium-238]]. The heat emitted by this decay was converted into electricity through the solid-state Seebeck effect. This provided a reliable and long-lasting source of electricity unaffected by the cold environment and high-radiation fields in the Jovian system.<ref name="engineering" /><ref name="RTG">{{cite web |title=What's in an RTG? |publisher=NASA |url=http://www2.jpl.nasa.gov/galileo/messenger/oldmess/RTG.html |access-date=May 15, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20100411024748/http://www2.jpl.nasa.gov/galileo/messenger/oldmess/RTG.html |archive-date=April 11, 2010 }}</ref>

Each [[Engineering:GPHS-RTG|GPHS-RTG]], mounted on a {{convert|5|m|ft|adj=mid|long|sp=us}} boom, carried {{convert|7.8|kg|lb}} of {{chem2|^{238}Pu|auto=yes}}. Each RTG contained 18 separate heat source modules, and each module encased four pellets of [[Chemistry:Plutonium(IV) oxide|plutonium(IV) oxide]], a ceramic material resistant to fracturing.<ref name="RTG" /> The plutonium was enriched to about 83.5 percent plutonium-238.{{sfn|Bennett|Hemler|Schock|1994|p=4}} 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 [[Chemistry:Graphite|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 [[Chemistry:Iridium|iridium]] cladding of the RTGs provided post-impact containment.<ref name="RTG" /> The RTGs produced about 570&nbsp;watts at launch. The power output initially decreased at the rate of 0.6&nbsp;watts per month and was 493&nbsp;watts when ''Galileo'' arrived at Jupiter.{{sfn|Taylor|Cheung|Seo|2002|p=86}}

==Telecommunications==
The spacecraft had a large high-gain antenna which failed to deploy while in space, so the low-gain antenna was used instead, although at slower data transfer speeds.<ref>{{cite web |url=http://www2.jpl.nasa.gov/galileo/faqhga.html |title=''Galileo'' FAQ – ''Galileo''{{'s}} Antennas |publisher=.jpl.nasa.gov |access-date=May 15, 2011 |archive-url=https://web.archive.org/web/20100528014039/http://www2.jpl.nasa.gov/galileo/faqhga.html |archive-date=May 28, 2010}}</ref>

==Instruments==
Scientific instruments to measure fields and particles were mounted on the spinning section of the spacecraft, together with the main [[Engineering:Antenna (radio)|antenna]], power supply, the propulsion module and most of ''Galileo''{{'s}} computers and control electronics. The sixteen instruments, weighing {{convert|118|kg|lb|abbr=on}} altogether, included [[Physics:Magnetometer|magnetometer]] sensors mounted on an {{convert|11|m|ft|abbr=on}} boom to minimize interference from the spacecraft; a [[Physics:Plasma|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. It also carried the Heavy Ion Counter, an engineering experiment to assess the potentially hazardous charged particle environments the spacecraft flew through, and an [[Physics:Extreme ultraviolet|extreme ultraviolet]] detector associated with the UV spectrometer on the scan platform.<ref name="galileo-arrival" />

The despun section's instruments included the camera system; the near infrared 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 [[Astronomy:Voyager program|''Voyager'']]{{'s}} best, because ''Galileo'' flew closer to the planet and its inner moons, and because the more modern [[Engineering:Charge-coupled device|CCD]] sensor in ''Galileo''{{'s}} camera was more sensitive and had a broader color detection band than the vidicons of ''Voyager''.<ref name="galileo-arrival" />

===Despun section===

====Solid-state imager (SSI)====
[[Image:Galileo Solid- State Imaging.jpg|thumb|Solid-state imager]]

The SSI was an 800-by-800-pixel [[Engineering:Charge-coupled device|charge-coupled device]] (CCD) camera. The optical portion of the camera was a modified flight spare of the ''[[Astronomy:Voyager program|Voyager]]'' narrow-angle camera; a Cassegrain telescope.<ref>{{cite web |title=Solid-State Imaging (SSI) |publisher=NASA |url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1989-084B-10 |access-date=November 19, 2020}}</ref>  The CCD had radiation shielding a {{convert|10|mm|in|1|abbr=on}} thick layer of [[Chemistry:Tantalum|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&nbsp;nm. The SSI weighed {{convert|29.7|kg|lb|abbr=on}} and consumed, on average, 15 watts of power.<ref>{{cite web |url=http://www2.jpl.nasa.gov/galileo/instruments/ssi.html |title=SSI – Solid State Imaging |publisher=NASA |access-date=May 15, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20100701191402/http://www2.jpl.nasa.gov/galileo/instruments/ssi.html |archive-date=July 1, 2010 }}</ref><ref>{{cite web |url=http://www2.jpl.nasa.gov/galileo/sepo/ |title=SSI Imaging Team |publisher=NASA |url-status=dead |archive-url=https://web.archive.org/web/20090802125619/http://www2.jpl.nasa.gov/galileo/sepo/ |archive-date=August 2, 2009 }}</ref>

====Near-infrared mapping spectrometer (NIMS)====
[[File:Galileo - NIMS photo - nims1.jpg|thumb|left|Near-infrared mapping spectrometer]]

The NIMS instrument was sensitive to 0.7-to-5.2-[[Micrometre|micrometer]] wavelength [[Physics:Infrared|infrared]] light, overlapping the wavelength range of the SSI. NIMS used a {{convert|229|mm|in|0|abbr=on}} aperture reflecting telescope. The [[Physics:Spectrometer|spectrometer]] used a grating to disperse the light collected by the telescope. The dispersed spectrum of light was focused on detectors of [[Chemistry:Indium|indium]], [[Chemistry:Antimonide|antimonide]] and [[Chemistry:Silicon|silicon]]. NIMS weighed {{convert|18|kg|lb|abbr=on}} and used 12 watts of power on average.<ref>{{cite web |url=http://www2.jpl.nasa.gov/galileo/instruments/nims.html |title=NIMS – Near-Infrared Mapping Spectrometer |publisher=NASA  |access-date=May 15, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20100528003812/http://www2.jpl.nasa.gov/galileo/instruments/nims.html |archive-date=May 28, 2010}}</ref><ref>{{cite web |url=http://jumpy.igpp.ucla.edu/~nims/ |publisher=UCLA |title=NIMS Team |archive-url=https://web.archive.org/web/19991010031508/http://jumpy.igpp.ucla.edu/%7Enims/ |archive-date=October 10, 1999 }}</ref>

====Ultraviolet spectrometer / extreme ultraviolet spectrometer (UVS/EUV)====
[[File:Galileo - UVS photo - uvs1.jpg|thumb|Ultraviolet spectrometer]]

The Cassegrain telescope of the UVS had a {{convert|250|mm|in|1|abbr=on}} aperture. Both the UVS and EUV instruments used a ruled [[Engineering:Grating|grating]] to disperse light for spectral analysis. Light then passed through an exit slit into [[Physics:Photomultiplier|photomultiplier]] tubes that produced pulses of electrons, which were counted and the results sent to Earth. The UVS was mounted on ''Galileo''{{'s}} 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 {{convert|9.7|kg|lb|abbr=on}} and used 5.9 watts of power.<ref>{{cite web |url=http://www2.jpl.nasa.gov/galileo/instruments/euv.html |title=EUVS – Extreme Ultraviolet Spectrometer |publisher=NASA  |access-date=May 15, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20100605121337/http://www2.jpl.nasa.gov/galileo/instruments/euv.html |archive-date=June 5, 2010}}</ref><ref>{{cite web |url=http://lasp.colorado.edu/galileo/ |publisher=University of Colorado at Boulder |title=EUV Team |archive-url=https://web.archive.org/web/20100814151709/http://lasp.colorado.edu/galileo/ |archive-date=August 14, 2010}}</ref>

====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'' spacecraft. A {{convert|100|mm|in|0|abbr=on}} 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 {{convert|5.0|kg|lb|abbr=on}} and consumed about 5 watts of power.<ref>{{cite web |url=http://www2.jpl.nasa.gov/galileo/instruments/ppr.html |title=PPR – Photopolarimeter-Radiometer |publisher=NASA |access-date=May 15, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20100614024507/http://www2.jpl.nasa.gov/galileo/instruments/ppr.html |archive-date=June 14, 2010 }}</ref><ref>{{cite web |url=http://www.lowell.edu/users/ppr/ |title=PPR Team |publisher=Lowell Observatory |archive-url=https://web.archive.org/web/20040721081850/http://www.lowell.edu/users/ppr/ |archive-date=July 21, 2004 }}</ref>

===Spun section===

====Dust-detector subsystem (DDS)====
[[File:Galileo - DDS photo - dds1.jpg|thumb|Dust-detector subsystem]]

The [[Astronomy:Galileo and Ulysses Dust Detectors|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 {{10^|-16}} to {{10^|-7}} grams. The speed of these small particles could be measured over the range of {{convert|1|to|70|km/s|1|sp=us}}. 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 [[Astronomy:Magnetosphere|magnetosphere]]. The DDS weighed {{convert|4.2|kg|abbr=on}} and used an average of 5.4 watts of power.<ref>{{cite web |url=http://www2.jpl.nasa.gov/galileo/instruments/dds.html |archive-url=https://web.archive.org/web/20100619000004/http://www2.jpl.nasa.gov/galileo/instruments/dds.html |archive-date=June 19, 2010 |title=DDS – Dust Detector Subsystem |publisher=NASA |url-status=dead |access-date=May 15, 2011}}</ref><ref>{{cite web |url=http://www.mpi-hd.mpg.de/dustgroup/galileo/galileo.html  |title=Cosmic Dust: Messengers from Distant Worlds |publisher=High Energy Stereoscopic System |access-date=December 10, 2012 |quote=DSI via Stuttgart University |archive-url=https://web.archive.org/web/20070210224655/http://www.mpi-hd.mpg.de/dustgroup/galileo/galileo.html |archive-date=February 10, 2007 |url-status=dead }}</ref>

====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 {{convert|20|keV|sigfig=2|abbr=on}}. 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 [[Chemistry:Oxygen|oxygen]] or [[Chemistry:Sulfur|sulfur]], for example). The EPD used silicon solid-state detectors and a time-of-flight 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 {{convert|10.5|kg|lb|abbr=on}} and used 10.1 watts of power on average.<ref>{{cite web |url=http://www2.jpl.nasa.gov/galileo/instruments/epd.html |archive-url=https://web.archive.org/web/20100621064711/http://www2.jpl.nasa.gov/galileo/instruments/epd.html |archive-date=June 21, 2010 |title=EPD – Energetic Particles Detector |publisher=NASA |url-status=dead |access-date=May 15, 2011}}</ref><ref>{{cite web |url=http://sd-www.jhuapl.edu/Galileo_EPD/ |access-date=December 5, 2020 |title=Galileo EPD |publisher=Johns Hopkins University Applied Physics Laboratory }}</ref>

====Heavy-ion counter (HIC)====
[[Image:Galileo Heavy Ion Counter.jpg|thumb|Heavy-ion counter]]

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 [[Physics:Ion|ion]]s using stacks of single crystal silicon wafers. The HIC could measure heavy ions with energies as low as {{convert|6|MeV|sigfig=1|abbr=on}} and as high as {{convert|200|MeV|sigfig=2|abbr=on}} per nucleon. This range included all atomic substances between [[Chemistry:Carbon|carbon]] and [[Chemistry:Nickel|nickel]]. The HIC and the EUV shared a communications link and, therefore, had to share observing time. The HIC weighed {{convert|8.0|kg|lb|abbr=on}} and used an average of 2.8 watts of power.<ref>{{cite web |url=http://www2.jpl.nasa.gov/galileo/instruments/hic.html |title=HIC – Heavy Ion Counter |publisher=NASA |access-date=May 15, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20100702142209/http://www2.jpl.nasa.gov/galileo/instruments/hic.html |archive-date=July 2, 2010 }}</ref><ref>{{cite web |url=http://www.srl.caltech.edu/galileo/galHIC.html |title=HIC Team |publisher=Caltech |access-date=December 5, 2020 |archive-date=December 2, 2005 |archive-url=https://web.archive.org/web/20051202114030/http://www.srl.caltech.edu/galileo/galHIC.html |url-status=dead }}</ref>

====Magnetometer (MAG)====
[[File:Galileo - MAD photo - mag1.jpg|thumb|left|Magnetometer (stowed)]]

The [[Engineering:Spacecraft magnetometer|magnetometer]] (MAG) used two sets of three sensors. The three sensors allowed the three orthogonal components of the [[Physics:Magnetic field|magnetic field]] section to be measured. One set was located at the end of the magnetometer boom and, in that position, was about {{convert|11|m|ft|abbr=on}} from the spin axis of the spacecraft. The second set, designed to detect stronger fields, was {{convert|6.7|m|ft|abbr=on}} 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&nbsp;[[Tesla (unit)|nT]]. At Jupiter, the outboard (11 m) set of sensors could measure magnetic field strengths in the range from ±32 to ±512&nbsp;nT, while the inboard (6.7 m) set was active in the range from ±512 to ±16,384&nbsp;nT. The MAG experiment weighed {{convert|7.0|kg|lb|abbr=on}} and used 3.9 watts of power.<ref>{{cite web |url=http://www2.jpl.nasa.gov/galileo/instruments/mag.html |title=MAG – Magnetometer |publisher=NASA |access-date=May 15, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20100218031649/http://www2.jpl.nasa.gov/galileo/instruments/mag.html |archive-date=February 18, 2010 }}</ref><ref>{{cite web |url=http://www.igpp.ucla.edu/galileo/ |title=MAG Team |publisher=UCLA |archive-url=https://web.archive.org/web/20040721081612/http://www.igpp.ucla.edu/galileo/ |archive-date=July 21, 2004 }}</ref>

====Plasma subsystem (PLS)====
The PLS used seven fields of view to collect [[Physics:Particle radiation|charged particle]]s for energy and mass analysis. These fields of view covered most angles from 0 to 180&nbsp;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 {{convert|0.9|to|52000|eV|sigfig=2|abbr=on|lk=on}}. The PLS weighed {{convert|13.2|kg|lb|abbr=on}} and used an average of 10.7 watts of power.<ref>{{cite web |url=http://www2.jpl.nasa.gov/galileo/instruments/pls.html |archive-url=https://web.archive.org/web/20100621070453/http://www2.jpl.nasa.gov/galileo/instruments/pls.html |archive-date=June 21, 2010 |title=PLS – Plasma Subsystem |publisher=NASA |url-status=dead |access-date=May 15, 2011}}</ref><ref>{{cite web |url=http://www-pi.physics.uiowa.edu/www/pls/ |title=PLS Team |publisher=University of Iowa |archive-url=https://web.archive.org/web/20070210105913/http://www-pi.physics.uiowa.edu/www/pls/ |archive-date=February 10, 2007 }}.</ref>

====Plasma-wave subsystem (PWS)====
[[File:Galileo - PWS photo - pws1.jpg|thumb|Plasma-wave subsystem]]

An electric [[Physics:Dipole antenna|dipole antenna]] was used to study the electric fields of [[Physics:Plasma|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 waves. The PWS weighed {{convert|7.1|kg|lb|abbr=on}} and used an average of 9.8 watts.<ref>{{cite web |url=http://www2.jpl.nasa.gov/galileo/instruments/pws.html |title=PWS – Plasma Wave Subsystem |publisher=NASA |access-date=May 15, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20091213142656/http://www2.jpl.nasa.gov/galileo/instruments/pws.html |archive-date=December 13, 2009}}</ref><ref>{{cite web |url=http://www-pw.physics.uiowa.edu/plasma-wave/galileo/home.html |title=Galileo PWS |publisher=University of Iowa |access-date=December 5, 2020}}</ref>

==''Galileo'' entry probe==
{{Infobox spaceflight
| name = ''Galileo'' entry probe
| names_list = <!--list of previous names if the spacecraft has been renamed.
Include the dates applicable if possible, and separate each name with a linebreak.
Omit if the spacecraft has only ever been known by one name.
Do not include Harvard, COSPAR/NSSDC or SATCAT/NORAD/NASA designations as alternative names-->

<!--image of the spacecraft/mission-->
| image = File:Galileo Probe diagram.jpeg
| image_caption = Diagram of the atmospheric entry probe's instruments and subsystems
| image_alt = <!--image alt text-->
| image_size = <!--include px/em; defaults to 220px-->

<!--Basic details-->
| mission_type = [[Engineering:Lander (spacecraft)|Lander]]{{\}}[[Astronomy:Atmospheric entry|Atmospheric probe]]
| operator = [[Organization:NASA|NASA]]
| Harvard_designation = <!--spacecraft launched 1962 and earlier only (eg. 1957 Alpha 2)-->
| COSPAR_ID = 1989-084E
| SATCAT = <!--satellite catalogue number, omit leading zeroes (e.g. 25544)-->
| website =
| mission_duration = 0 days
| distance_travelled = <!--How far the spacecraft travelled (if known)-->
| orbits_completed = <!--number of times the spacecraft orbited the Earth - see below for spacecraft beyond Earth orbit-->
| suborbital_range = <!--downrange distance reached if spacecraft did not enter orbit-->
| suborbital_apogee = <!--altitude reached if spacecraft did not enter orbit-->

<!--Spacecraft properties-->| spacecraft = <!--Spacecraft name/serial number (eg. Space Shuttle ''Discovery'', Apollo CM-118), etc-->
| spacecraft_type = <!--eg. GPS Block II, Kobalt-M, US-K, etc-->
| spacecraft_bus = <!--eg. A2100M, Star-2, etc-->
| manufacturer = [[Company:Hughes Aircraft Company|Hughes Aircraft Company]]
| launch_mass = <!--fuelled mass at launch, not including rocket or upper stage-->
| BOL_mass = {{Convert|340|kg|abbr=on}}
| landing_mass = <!--Mass after landing (recovered spacecraft only)-->
| dry_mass = <!--spacecraft mass in orbit without fuel-->
| payload_mass = <!--Mass of cargo carried by spacecraft (eg. for Space Shuttle), or total mass of instrumentation/equipment/experiments for mission-->
| dimensions = <!--body dimensions and solar array span-->
| power = <!--end-of-life power, in watts-->

<!--Launch details-->| launch_date = {{start date|1989|10|18}}
| launch_rocket = [[Engineering:STS-34|STS-34]] piggybacking with ''Galileo'' orbiter
| launch_site = Kennedy Space Center, Launch Complex 39B
| launch_contractor = <!--organisation(s) that conducted the launch (eg. United Launch Alliance, Arianespace, etc)-->
| deployment_from = <!--place where deployed from-->
| deployment_date = <!--date deployed-->
| entered_service = <!--date on which the spacecraft entered service, if it did not do so immediately after launch-->
<!-- * - e.g. Proton-M/Briz-M not Proton-M, but Titan IV(401)A not Titan IV(401)A-Centaur-->

<!--end of mission-->| disposal_type = <!--Whether the spacecraft was deorbited, decommissioned, placed in a graveyard orbit, etc-->
| deactivated = <!--when craft was decommissioned-->
| destroyed = <!--when craft was destroyed (if other than by re-entry)-->
| last_contact =
| recovery_by = <!--recovered by-->
| recovery_date = <!--recovery date-->
| decay_date = <!--when craft re-entered the atmosphere, not needed if it landed-->
| landing_date = <!--when the spacecraft made a controlled landing, not needed if it did not return intact-->
| landing_site = <!--where the craft landed; site/runway or coordinates-->
<!--
    The following template should be used for ONE of the three above fields "end_of_mission", "decay" or "landing" if the spacecraft is no longer operational.
    If it landed intact, use it for the landing time, otherwise for the date it ceased operations, or the decay date if it was still operational when it re-entered.
    {{end date|YYYY|MM|DD|hh|mm|ss|TZ=Z}} (for Zulu/UTC) or {{end date|YYYY|MM|DD}} (if time unknown)
-->

<!--orbit parameters-->
<!--as science-related articles, SI units should be the principal units of measurement, however we usually use {{convert}} to display imperial units in parentheses after the initial values-->| orbit_reference = <!--geocentric, selenocentric, etc - please link (e.g. [[Astronomy:Geocentric orbit|Geocentric]])-->
| orbit_regime = <!--high, low, medium, molniya, GSO - please link (e.g. [[Astronomy:Low Earth orbit|Low Earth]] - please don't use acronyms-->
| orbit_longitude = <!--geosynchronous satellites only-->
| orbit_slot = <!--Designation of orbital position or slot, if not longitude (e.g plane and position of a GPS satellite)-->
| orbit_semimajor = <!--semimajor axis-->
| orbit_eccentricity = <!--orbital eccentricity-->
| orbit_periapsis = <!--periapsis altitude-->
| orbit_apoapsis = <!--apoapsis altitude-->
| orbit_inclination = <!--orbital inclination-->
| orbit_period = <!--time taken to complete an orbit-->
| orbit_RAAN = <!--right ascension of the ascending node-->
| orbit_arg_periapsis = <!--argument of perigee/periapsis-->
| orbit_mean_anomaly = <!--mean anomaly at epoch, only use in conjunction with an epoch value-->
| orbit_mean_motion = <!--mean motion of the satellite, usually measured in orbits per day-->
| orbit_repeat = <!--repeat interval/revisit time-->
| orbit_velocity = <!--speed at which the spacecraft was travelling at epoch - only use for spacecraft with low orbital eccentricity-->
| orbit_epoch = <!--the date at which the orbit parameters were correct-->
| orbit_rev_number = <!--revolution number-->
| apsis = <!--planet specific apsis term (eg. gee/helion/selene/etc - defaults to generic "apsis")-->
| interplanetary = <!--Infobox spaceflight/IP can be called multiple times for missions with multiple targets or combined orbiter/lander missions, etc-->

<!--transponder parameters-->| trans_band = <!--Transponder frequency bands-->
| trans_frequency = <!--specific frequencies-->
| trans_bandwidth = <!--bandwidth-->
| trans_capacity = <!--capacity of the transponders-->
| trans_coverage = <!--area covered-->
| trans_TWTA = <!--TWTA output power-->
| trans_EIRP = <!--equivalent isotropic power-->
| trans_HPBW = <!--half-power beam width-->

<!--Only use where a spacecraft/mission is part of a clear programme of sequential missions.
If in doubt, leave it out-->| programme =
| previous_mission =
| next_mission = <!--mission insignia or patch-->
| insignia = <!--omit the "file" prefix-->
| insignia_caption = <!--image caption-->
| insignia_alt = <!--image alt text-->
| insignia_size = <!--include px/em; defaults to 180px-->
}}
[[File:Descent Module.jpeg|thumb|right|Inner Descent Module of the ''Galileo'' Entry Probe]]

The atmospheric probe was built by Hughes Aircraft Company's Space and Communications Group at its El Segundo, California plant.<ref>{{cite web|url=http://www.flightglobal.com/pdfarchive/view/1989/1989%20-%200347.html|access-date=May 15, 2011|publisher=Flightglobal |title=Hughes Science/Scope Press Release and Advertisement |archive-url=https://web.archive.org/web/20120112141851/http://www.flightglobal.com/pdfarchive/view/1989/1989%20-%200347.html |archive-date=January 12, 2012 }}</ref><ref name="Galileo Arrives at Kennedy Space Center">{{cite press release |id=1989-1242  |title=Galileo Arrives at Kennedy Space Center |date=May 17, 1989 |publisher=NASA |url=https://www.jpl.nasa.gov/news/galileo-arrives-at-kennedy-space-center |access-date=March 6, 2021}}</ref> It weighed {{convert|339|kg}} and was {{convert|86|cm|in|sp=us}} high.<ref name="galileo-arrival" /> Inside the probe's [[Astronomy:Heat shield|heat shield]], the scientific instruments were protected from extreme heat and pressure during its high-speed journey into the Jovian atmosphere, entering at {{convert|48|km/s|mph|sp=us|abbr=}}.<ref name="gpr">{{cite web |url=http://www2.jpl.nasa.gov/sl9/gll38.html |title=Galileo Probe Science Results |date=January 22, 1996 |first1=Douglas |last1=Isbell |first2=David |last2=Morse |publisher=JPL |access-date=March 4, 2016}}</ref> Temperatures reached around {{cvt|16000|C|F|sigfig=2}}.<ref>{{Cite web|url=https://solarsystem.nasa.gov/missions/galileo-probe/in-depth|title=In Depth &#124; Galileo Probe|website=NASA Solar System Exploration}}</ref> 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 warhead reentering the atmosphere.{{sfn|Laub|Venkatapathy|2003||pp=1–9}}<ref>{{cite web |url=http://asm.arc.nasa.gov/full_text.html?type=materials&id=1 |title=Development of New Ablative Thermal Protection Systems (TPS) |author=Bernard Laub |publisher=NASA Ames Research Center |date=October 19, 2004 |access-date=December 12, 2006 |url-status=dead |archive-url=https://web.archive.org/web/20061019034219/http://asm.arc.nasa.gov/full_text.html?type=materials&id=1 |archive-date=October 19, 2006 }}</ref>

=== Batteries ===
The probe's electronics were powered by 13 [[Engineering:Lithium–sulfur battery|lithium sulfur dioxide batteries]] manufactured by [[Company:Honeywell|Honeywell]]'s Power
Sources Center in Horsham, Pennsylvania. Each cell was the size of a D battery so existing manufacturing tools could be used.{{sfn|Meltzer|2007|p=118}}{{sfn|Hofland|Stofel|Taenaka|1996|p=9}} They provided a nominal power output of about 7.2-ampere hours capacity at a minimal voltage of 28.05 volts.{{sfn|Blagdon|1980|p=83}}

=== Scientific instruments ===
The probe included seven instruments for taking data on its plunge into Jupiter:{{sfn|Meltzer|2007|p=122}}<ref>{{cite web |title=NASA – NSSDC – Experiment – Query Results |publisher=NASA |url=http://nssdc.gsfc.nasa.gov/nmc/experimentSearch.do?spacecraft=Galileo%20Probe |archive-url=https://web.archive.org/web/20090118032728/http://nssdc.gsfc.nasa.gov/nmc/experimentSearch.do?spacecraft=Galileo%20Probe |archive-date=January 18, 2009 |url-status=dead }}</ref>
{| class="wikitable"
|+ Scientific instruments
! Instrument !! Function !! Mass !! Power consumption !! Principal investigator !! Organizations
|-
| Atmospheric structure instrument || Measuring temperature, pressure and deceleration || {{convert|4.1|kg|abbr=on}} || 6.3 W || Alvin Seiff || [[Organization:Ames Research Center|Ames Research Center]] and [[Organization:San Jose State University|San Jose State University]] Foundation
|-
| [[Physics:Quadrupole mass analyzer|Neutral mass spectrometer]] || Analyze the gas composition of the atmosphere || {{convert|13|kg|abbr=on}} || 29 W || Hasso Niemann || [[Organization:Goddard Space Flight Center|Goddard Space Flight Center]]
|-
| Helium Abundance Detector || An interferometer supporting atmospheric composition studies || {{convert|1.4|kg|abbr=on}} || 1.1 W  || Ulf von Zahn || [[Organization:University of Bonn|University of Bonn]], [[Organization:University of Rostock|University of Rostock]]
|-
| [[Chemistry:Nephelometer|Nephelometer]] || Cloud location and cloud-particle observations || {{convert|4.8|kg|abbr=on}} || 14 W || Boris Ragent || [[Organization:Ames Research Center|Ames Research Center]] and [[Organization:San Jose State University|San Jose State University]] Foundation
|-
| Net-flux [[Physics:Radiometer|radiometer]] || Measuring the difference between upward and downward [[Physics:Radiant flux|radiant flux]] at each altitude || {{convert|3.0|kg|abbr=on}} || 7.0 W || L. Sromovsky || University of Wisconsin
|-
| [[Astronomy:Lightning|Lightning]] and radio emission detector and energetic particles instrument || Measuring light and radio emissions associated with lightning, and fluxes of protons, electrons, alpha particles and heavy ions || {{convert|2.7|kg|abbr=on}} || 2.3 W || Louis Lanzerotti || Bell Laboratories, [[Organization:University of Florida|University of Florida]] and Federal Republic of Germany
|-
| Radio equipment || Measuring wind speeds and atmospheric absorption || || || David Atkinson || University of Idaho
|}

In addition, the probe's heat shield contained instrumentation to measure [[Physics:Ablation|ablation]] during descent.{{sfn|Milos|1997|pp=705–713}}

==Termination==
Lacking the fuel to escape Jupiter's gravity well, at the end of ''Galileo''{{'s}} life, the probe was deliberately crashed into Jupiter on September 21, 2003, to prevent [[Astronomy:Interplanetary contamination|forward contamination]] of possible life of Jupiter's moon Europa.<ref>{{cite web|url=https://www.universetoday.com/8884/galileo-plunges-into-jupiter/|title=Galileo Plunges Into Jupiter|date=September 22, 2003 |accessdate=February 10, 2022}}</ref>

==Names==
The Galileo Probe had COSPAR ID 1989-084E while the orbiter had id 1989-084B.{{sfn|Badescu|Zacny|2018|p=836}} Names for the spacecraft include ''Galileo Probe'' or ''Jupiter Entry Probe'' abbreviated JEP.{{sfn|Ritter|Mazoue|Santovincenzo|Atzei|2006|p=6}} The related COSPAR IDs of the Galileo mission were:<ref>{{Cite web|url=https://www.lib.cas.cz/space.40/1989/084.HTM|title=Space Launch 1989-084 |publisher=Knihovna Akademie věd ČR |access-date=December 3, 2018}}</ref>
*1989-084A  STS 34
*1989-084B  ''Galileo''
*1989-084C [[Engineering:Inertial Upper Stage|IUS]] (Orbus 21)
*1989-084D IUS (Orbus 6E)
*1989-084E  ''Galileo'' Probe
{{clear right}}

==See also==
*[[Astronomy:Exploration of Jupiter|Exploration of Jupiter]]
*[[Astronomy:List of missions to the outer planets|List of missions to the outer planets]]
*[[Engineering:Juno (spacecraft)|Juno (spacecraft)]]
*[[Astronomy:Atmosphere of Jupiter|Atmosphere of Jupiter]]
*[[Physics:List of spacecraft powered by non-rechargeable batteries|List of spacecraft powered by non-rechargeable batteries]]

==Notes==
{{Reflist|30em}}

==References==
{{refbegin|30em}}
* {{cite book |last1=Badescu |first1=Viorel |last2=Zacny |first2=Kris |title=Outer Solar System: Prospective Energy and Material Resources |date=2018 |publisher=Springer |isbn=978-3-319-73845-1 |oclc=1042249198}}
* {{cite conference |last=Blagdon |first=L. |contribution=Galileo Lithium SO<sub>2</sub> |pages=83–95 |location=Goddard Space Flight Center |title=The 1979 Goddard Space Flight Center Battery Workshop |year=1980  |publisher=NASA |url=https://ntrs.nasa.gov/api/citations/19800012343/downloads/19800012343.pdf |access-date=March 7, 2021 }}
* {{cite journal |last1=Beyer |first2=R. C. |last2=O'Connor |first3=D. J. |last3=Mudgway |title=Galileo Early Cruise, Including Venus, First Earth, and Gaspra Encounters |journal=The Telecommunications and Data Acquisition Report |first1=P. E.  |pages=265–281 |date=May 15, 1992 |id=TDA Progress Report 42-109 |url=http://ipnpr.jpl.nasa.gov/progress_report/42-109/109T.PDF |access-date=March 6, 2021}}
* {{cite conference |last1=Bennett |first1=Gary L. |last2=Hemler |first2=Richard J. |last3=Schock |first3=Alfred |title=Development and Use of the Galileo and Ulysses Power Sources |conference= 45th Congress of the International Astronautical Federation |date=October 9–14, 1994 |location=Jerusalem, Israel |url=https://www.osti.gov/servlets/purl/1033366 |access-date=December 7, 2020 }}
* {{cite book |last1=Dawson |first1=Virginia |first2=Mark |last2=Bowles |title=Taming Liquid Hydrogen: The Centaur Upper Stage Rocket |series=The NASA History Series |id=SP-4230 |url=https://history.nasa.gov/SP-4230.pdf |location=Washington, DC |year=2004 |publisher=NASA |access-date=October 1, 2020 }}
* {{cite conference |last1=Hofland |first1=L. M. |first2=E. J. |last2=Stofel |first3=R. K. |last3=Taenaka |contribution=Galileo Probe Lithium-Sulfur Dioxide Cell Life Testing |title=Proceedings of 11th Annual Battery Conference on Applications and Advances |location=Long Beach, California |year=1996 |pages=9–14 |doi=10.1109/BCAA.1996.484963 }}
* {{cite conference |last1=Laub |first1=B. |last2=Venkatapathy |first2=E. |contribution=Thermal Protection System Technology and Facility Needs for Demanding Future Planetary Missions |title=International Workshop on Planetary Probe Atmospheric Entry and Descent Trajectory Analysis and Science |location=Lisbon, Portugal |pages=1–9 |date=October 6–9, 2003 |publisher=University of Idaho |url=http://www.mrc.uidaho.edu/entryws/presentations/Papers/laub_tps.pdf |access-date=December 12, 2006 |url-status=dead|archive-url=https://web.archive.org/web/20070108095028/http://www.mrc.uidaho.edu/entryws/presentations/Papers/laub_tps.pdf |archive-date=January 8, 2007}}
* {{cite book |last=Meltzer |first=Michael |title=Mission to Jupiter: A History of the ''Galileo'' Project |year=2007 |id=SP-4231 |series=The NASA History Series |publisher=NASA |location=Washington, DC  |oclc=124150579 |url=https://history.nasa.gov/sp4231.pdf |access-date=January 19, 2021}}
* {{cite journal |last=Milos |first=Frank S.|journal=Journal of Spacecraft and Rockets |issn=1533-6794 |year=1997 |doi=10.2514/2.3293 |title=Galileo Probe Heat Shield Ablation Experiment |volume=34 |issue=6 |pages=705–713 |bibcode=1997JSpRo..34..705M |url=https://zenodo.org/record/1235941}}
* {{cite journal |last1 = Ritter |first1 = H. |last2 = Mazoue |first2 = F. |last3 = Santovincenzo |first3 = A. |last4 = Atzei |first4 = A.|title = Jupiter Entry Probe Feasibility Study from the ESTEC CDF Team: Heat Flux Evaluation & TPS Definition |journal = Thermal Protection Systems and Hot Structures |volume = 631 |pages = 6 |year = 2006|bibcode = 2006ESASP.631E...6R }}
* {{cite book |last1=Siddiqi|first1=Asif A. |title=Beyond Earth: A Chronicle of Deep Space Exploration, 1958–2016 |lccn=2017059404 |isbn=978-1-62683-042-4 |publisher=NASA History Program Office |edition=second |year=2018 |id=SP-4041 |series=The NASA History Series |location=Washington, DC|url=https://www.nasa.gov/sites/default/files/atoms/files/beyond-earth-tagged.pdf |access-date=October 29, 2020 |ref=none}}
* {{cite book |last1=Siewiorek |first1=Daniel |last2=Swarz |first2=Robert S. |title=Reliable Computer Systems |url=https://archive.org/details/reliablecomputer00siew |date=1998 |publisher=A K Peters |location=Natick, Massachusetts |isbn=1-56881-092-X |oclc=245700546 }}
* {{cite book |last1=Taylor |first1=Jim |last2=Cheung |first2=Kar-Ming |last3=Seo |first3=Dongae |title=Galileo Telecommunications |series=DESCANSO Design and Performance Summary Series |publisher=NASA |location=Washington, DC |date=July 2002  |url=http://descanso.jpl.nasa.gov/DPSummary/Descanso5--Galileo_new.pdf |access-date=November 15, 2020 }}
* {{cite report|last=Tomayko |first=James E. |title=Computers in Spaceflight: The NASA Experience |publisher=NASA History Office |date=March 1988 |url=https://ntrs.nasa.gov/api/citations/19880069935/downloads/19880069935.pdf |access-date=October 29, 2020}}
{{refend}}



==External links==
* [https://web.archive.org/web/20151114055422/http://solarsystem.nasa.gov/missions/Galileo ''Galileo'' mission site] by NASA's Solar System Exploration
* [https://web.archive.org/web/20041103173530/http://solarsystem.nasa.gov/galileo/ ''Galileo'' legacy site] by NASA's Solar System Exploration
* [http://rpif.asu.edu/Galileo/ ''Galileo'' Satellite Image Mosaics] by Arizona State University
* [https://www.flickr.com/photos/kevinmgill/albums/72157651267182078 Galileo image album] by Kevin M. Gill
* [http://nssdc.gsfc.nasa.gov/planetary/text/gal_probe_new_results.txt Early probe results report]
* [https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1989-084E ''Galileo'' Probe] NASA Space Science Data Coordinated Archive

{{Solar System probes}}
{{Jupiter spacecraft}}
{{Venus spacecraft}}
{{Jet Propulsion Laboratory}}

{{DEFAULTSORT:Galileo (Spacecraft)}}
[[Category:Galileo program| spacecraft]]
[[Category:Nuclear-powered robots]]
[[Category:Extraterrestrial atmosphere entry]]
[[Category:Attached spacecraft]]

{{Sourceattribution|Galileo (spacecraft)}}