View source for Viking program

{{short description|Pair of NASA landers and orbiters sent to Mars in 1976}}
{{about|the NASA Mars probes|the Swedish spacecraft|Viking (satellite)}}
{{redirect|Viking Mars|the cruise ship|Viking Cruises}}
{{Use American English|date=January 2014}}
{{Use mdy dates|date=September 2012}}
{{Infobox spacecraft class
| image        = Viking Orbiter releasing the lander.jpg
| caption      = Artist impression of a Viking orbiter releasing a lander descent capsule

| name         = Viking
| manufacturer = [[Jet Propulsion Laboratory]] /  [[Martin Marietta]] 
| country      = [[United States]]
| applications = Mars orbiter/lander
| orbits       = [[Areocentric orbit|Areocentric]]
| operator     = [[NASA]] / [[JPL]]
| lifetime     = Orbiters: 4&nbsp;years at Mars<br/>Landers: 4–6&nbsp;years at Mars

| status       = Retired
| built        = 2
| launched     = 2
| first        = ''[[Viking 1]]''<br/>August 20, 1975<ref name="NASA-20061218" /><ref name="NASA-Viking1">{{Cite web |last=Nelson |first=Jon |title=Viking 1 |url=https://www.jpl.nasa.gov/missions/viking-1 |url-status=live |archive-url=https://web.archive.org/web/20231024145216/https://www.jpl.nasa.gov/missions/viking-1 |archive-date=October 24, 2023 |access-date=February 2, 2014 |publisher=[[JPL]] }}</ref> 
| last         = ''[[Viking 2]]''<br/>September 9, 1975<ref name="NASA-20061218" /><ref name="NASA-Viking2">{{Cite web |last=Nelson |first=Jon |title=Viking 2 |url=https://www.jpl.nasa.gov/missions/viking-2 |url-status=live |archive-url=https://web.archive.org/web/20231008204431/https://www.jpl.nasa.gov/missions/viking-2 |archive-date=October 8, 2023 |access-date=February 2, 2014 |publisher=[[JPL]] }}</ref>
| retired      = ''[[Viking 1]]'' orbiter<br/>August 17, 1980<ref name="NASA-20061218" /><br/>''[[Viking 1]]'' lander<br/>July 20, 1976<ref name="NASA-20061218" /> (landing) to November 13, 1982<ref name="NASA-20061218" /><br/><br />''[[Viking 2]]'' orbiter<br/>July 25, 1978<ref name="NASA-20061218" /><br/>''[[Viking 2]]'' lander<br/>September 3, 1976<ref name="NASA-20061218" /> (landing) to April 11, 1980<ref name="NASA-20061218" />

|autoconvert = off
| mass         = {{convert|3527|kg|lb}}
| power        = Orbiters: 620&nbsp;watts ([[solar array]])<br/>Lander: 70&nbsp;watts (two [[radioisotope thermoelectric generator|RTG]] units)
| batteries    = 
| equipment    =

| dimensions   = 
| x_axis       = 
| y_axis       = 
| z_axis       = 
}}

The '''''Viking'' program''' consisted of a pair of identical American [[space probe]]s, ''[[Viking 1]]'' and ''[[Viking 2]]'' both launched in 1975, and landed on [[Mars]] in 1976.<ref name="NASA-20061218">{{Cite web |last=Williams |first=David R. Dr. |date=December 18, 2006 |title=Viking Mission to Mars |url=https://nssdc.gsfc.nasa.gov/planetary/viking.html |url-status=live |archive-url=https://web.archive.org/web/20231206095644/https://nssdc.gsfc.nasa.gov/planetary/viking.html |archive-date=December 6, 2023 |access-date=February 2, 2014 |publisher=[[NASA]] }}</ref> The mission effort began in 1968 and was managed by the NASA Langley Research Center.<ref name= "SoffenViking1978">Soffen, G. A. (July–August 1978). "Mars and the Remarkable Viking Results." ''Journal of Spacecraft and Rockets''. '''15''' (4): 193-200.</ref> Each [[spacecraft]] was composed of two main parts: an [[orbiter]] spacecraft which photographed the surface of Mars from [[orbit]], and a [[Lander (spacecraft)|lander]] which studied the planet from the surface. The orbiters also served as communication relays for the landers once they touched down.

The Viking program grew from [[NASA]]'s earlier, even more ambitious, [[Voyager program (Mars)|Voyager Mars]] program, which was not related to the successful [[Voyager program|Voyager deep space probes]] of the late 1970s. ''Viking 1'' was launched on August 20, 1975, and the second craft, ''Viking 2'', was launched on September 9, 1975, both riding atop [[Titan IIIE]] rockets with [[Centaur (rocket stage)|Centaur]] upper stages. ''Viking 1'' entered Mars orbit on June 19, 1976, with ''Viking 2'' following on August 7.

After orbiting Mars for more than a month and returning images used for landing site selection, the orbiters and landers detached; the landers then entered the Martian [[atmosphere]] and [[Soft landing (rocketry)|soft-landed]] at the sites that had been chosen. The ''Viking 1'' lander touched down on the surface of Mars on July 20, 1976, more than two weeks before ''Viking 2''{{'}}s arrival in orbit. ''Viking 2'' then successfully soft-landed on September 3. The orbiters continued imaging and performing other scientific operations from orbit while the landers deployed [[Measuring instrument|instrument]]s on the surface. The program terminated in 1982.

The project cost was roughly US$1&nbsp;billion at the time of launch,<ref name="nssdc-viking1orbiter" /><ref name="space.com">{{Cite news |last=Howell |first=Elizabeth |date=October 26, 2012  |title=Viking 1: First U.S. Lander on Mars |url=https://www.space.com/18234-viking-1.html |url-status=live |access-date=December 13, 2016 |archive-url=https://web.archive.org/web/20230906024226/https://www.space.com/18234-viking-1.html |archive-date=September 6, 2023 |newspaper=[[Space.com]] }}</ref> equivalent to about ${{Inflation|US-GDP|1|1970|r=0}}&nbsp;billion in {{Inflation-year|US-GDP}} dollars.{{Inflation-fn|US-GDP}} The mission was considered successful and formed most of the body of knowledge about Mars through the late 1990s and early 2000s.<ref name="cps-viking">{{Cite web |title=The Viking Program |url=https://planetary-science.org/mars-research/mars-landings/the-viking-program/ |url-status=live |archive-url=https://web.archive.org/web/20231120170823/http://planetary-science.org/mars-research/mars-landings/the-viking-program/ |archive-date=November 20, 2023 |access-date=April 13, 2018 |publisher=The Center for Planetary Science }}</ref><ref name="csc-viking-lander">{{Cite web |date=July 3, 2014 |title=Viking Lander |url=https://californiasciencecenter.org/exhibits/air-space/mission-planets/viking-lander |url-status=live |archive-url=https://web.archive.org/web/20230527121521/https://californiasciencecenter.org/exhibits/air-space/mission-planets/viking-lander |archive-date=May 27, 2023 |access-date=April 13, 2018 |publisher=[[California Science Center]] }}</ref>

==Science objectives==
*Obtain high-resolution images of the Martian surface
*Characterize the structure and composition of the atmosphere and surface
*Search for evidence of [[life on Mars (planet)|life on Mars]]

==Viking orbiters==
The primary objectives of the two Viking orbiters were to transport the landers to Mars, perform reconnaissance to locate and certify landing sites, act as communications relays for the landers, and to perform their own scientific investigations. Each orbiter, based on the earlier [[Mariner 9]] spacecraft, was an [[octagon]] approximately {{cvt|2.5|m|ft}} across. The fully fueled orbiter-lander pair had a [[mass]] of {{cvt|3527|kg|lb}}. After separation and landing, the lander had a mass of about {{cvt|600|kg|lb}} and the orbiter {{cvt|900|kg|lb}}. The total launch mass was {{cvt|2328|kg|lb}}, of which {{cvt|1445|kg|lb}} were propellant and [[Spacecraft attitude control|attitude control]] gas. The eight faces of the ring-like structure were {{cvt|0.457|m|in|0}} high and were alternately {{cvt|1.397|and|0.508|m|in|0}} wide. The overall height was {{cvt|3.29|m|ft}} from the lander attachment points on the bottom to the launch vehicle attachment points on top. There were 16 modular compartments, 3 on each of the 4 long faces and one on each short face. Four solar panel wings extended from the [[Coordinate axis|axis]] of the orbiter, the distance from tip to tip of two oppositely extended solar panels was {{cvt|9.75|m|ft|0}}.

===Propulsion===
The main [[Spacecraft propulsion|propulsion]] unit was mounted above the [[satellite bus|orbiter bus]]. Propulsion was furnished by a [[bipropellant]] ([[monomethylhydrazine]] and [[nitrogen tetroxide]]) liquid-fueled [[rocket engine]] which could be [[gimbal]]led up to 9&nbsp;[[degree (angle)|degree]]s. The engine was capable of {{convert|1323|N|lbf|abbr=on|lk=on}} thrust, providing a [[delta-V|change in velocity]] of {{cvt|1480|m/s|mph}}. [[Spacecraft attitude control|Attitude control]] was achieved by 12 small compressed-nitrogen jets.

===Navigation and communication===
An acquisition [[Sun sensor]], a cruise Sun sensor, a [[Canopus]] [[star tracker]] and an inertial reference unit consisting of six [[gyroscope]]s allowed three-axis stabilization. Two [[accelerometers]] were also on board.

Communications were accomplished through a {{Nowrap|20 W}} [[S-band]] (2.3 [[gigahertz|GHz]]) [[transmitter]] and two {{Nowrap|20 W}} [[TWTA]]s. An [[X-band|X band]] {{Nowrap|(8.4&nbsp;GHz)}} [[downlink]] was also added specifically for [[Doppler effect|radio science]] and to conduct communications experiments. [[Uplink]] was via S band {{Nowrap|(2.1&nbsp;GHz).}} A two-axis steerable [[Directional antenna|parabolic dish antenna]] with a diameter of approximately 1.5 m was attached at one edge of the orbiter base, and a fixed low-gain antenna extended from the top of the bus. Two tape recorders were each capable of storing 1280 [[megabit]]s. A 381-[[MHz]] relay radio was also available.{{citation needed|date=December 2023}}

===Power===
The power to the two orbiter craft was provided by eight {{cvt|1.57|×|1.23|m|in}} [[solar panels]], two on each wing. The solar panels comprised a total of 34,800 solar cells and produced 620&nbsp;W of power at Mars. Power was also stored in two [[nickel-cadmium]] 30-[[ampere hour|A·h]] [[battery (electricity)|batteries]].

The combined area of the four panels was {{convert|15|m2|ft2|abbr=off|sp=us}}, and they provided both regulated and unregulated direct current power; unregulated power was provided to the radio transmitter and the lander.

Two 30-amp·hour, nickel-cadmium, rechargeable batteries provided power when the spacecraft was not facing the Sun, during launch, while performing correction maneuvers and also during Mars occultation.<ref name="jpl-factsheet-viking">{{Cite web |title=Viking Fact Sheet |url=https://www.jpl.nasa.gov/news/fact_sheets/viking.pdf |url-status=dead |archive-url=https://web.archive.org/web/20120310184911/https://www.jpl.nasa.gov/news/fact_sheets/viking.pdf |archive-date=March 10, 2012 |access-date=March 27, 2012 |publisher=[[Jet Propulsion Laboratory]] }}</ref>

===Main findings===
[[File:Mars Valles Marineris.jpeg|thumb|Mars image mosaic from the ''Viking 1'' orbiter]]
By discovering many geological forms that are typically formed from large amounts of water, the images from the orbiters caused a revolution in our ideas about [[water on Mars]]. Huge river valleys were found in many areas. They showed that floods of water broke through dams, carved deep valleys, eroded grooves into bedrock, and travelled thousands of kilometers. Large areas in the southern hemisphere contained branched stream networks, suggesting that rain once fell. The flanks of some volcanoes are believed to have been exposed to rainfall because they resemble those caused on Hawaiian volcanoes. Many craters look as if the impactor fell into mud. When they were formed, ice in the soil may have melted, turned the ground into mud, then flowed across the surface. Normally, material from an impact goes up, then down. It does not flow across the surface, going around obstacles, as it does on some Martian craters.<ref name="Kieffer1992">{{Cite book |url=https://archive.org/details/marsspacescience00unse |title=Mars |publisher=[[University of Arizona Press]] |year=1992 |isbn=978-0-8165-1257-7 |editor-last=Kieffer |editor-first=Hugh H. |lccn=92010951 |access-date=March 7, 2011 |editor-last2=Jakosky |editor-first2=Bruce M. |editor-last3=Snyder |editor-first3=Conway W. |editor-last4=Matthews |editor-first4=Mildred S. }}</ref><ref name="raeburn-1998">{{Cite book |last=Raeburn |first=Paul |url=https://archive.org/details/marsuncoveringse00raeb |title=Mars: Uncovering the Secrets of the Red Planet |publisher=[[National Geographic Society]] |year=1998 |isbn=0-7922-7373-7 |editor-last=Mulroy |editor-first=Kevin |lccn=98013991 }}</ref><ref name="moore-1990">{{Cite book |last1=Moore |first1=Patrick |last2=Hunt |first2=Garry |last3=Nicolson |first3=Iain |last4=Cattermole |first4=Peter |url=https://archive.org/details/atlasofsolarsyst0000unse_o5j4 |title=The Atlas of the Solar System |publisher=[[Mitchell Beazley]] |year=1990 |isbn=0-86134-125-2 |editor-last=Garlick |editor-first=Judy }}</ref> Regions, called "[[Martian chaos terrain|Chaotic Terrain]]," seemed to have quickly lost great volumes of water, causing large channels to be formed. The amount of water involved was estimated to ten thousand times the flow of the [[Mississippi River]].<ref name="morton-2002">{{Cite book |last=Morton |first=Oliver |url=https://archive.org/details/mappingmarsscien00mort_0 |title=Mapping Mars: Science, Imagination, and the Birth of a World |publisher=[[Picador (imprint)|Picador]] |year=2002 |isbn=0-312-24551-3 }}</ref> Underground volcanism may have melted frozen ice; the water then flowed away and the ground collapsed to leave chaotic terrain.

{{Clear}}
{{Gallery
|align=center
|title = '''Viking mosaics'''
|width=160
|File:Streamlined_Islands_in_Maja_Valles.jpg|alt1=Streamlined islands show that large floods occurred on Mars. (location: Lunae Palus quadrangle). |<small>Streamlined islands show that large floods occurred on Mars. <br />(''[[Lunae Palus quadrangle]]'')</small>
|File:Chryse Planitia Scour Patterns.jpg|alt2=Scour patterns were produced by flowing water. [[Dromore (crater)|Dromore]] crater is at bottom. <br />(''[[Lunae Palus quadrangle]]'') |<small>Scour patterns were produced by flowing water. [[Dromore (crater)|Dromore]] crater is at bottom. <br />(''[[Lunae Palus quadrangle]]'')</small>
|File:Detail of Maja Valles Flow.jpg|alt3=Large floods of water likely eroded the channels around the crater. (''[[Lunae Palus quadrangle]]'') |<small>Large floods of water likely eroded the channels around [[Dromore (crater)|Dromore]] crater. <br />(''[[Lunae Palus quadrangle]]'')</small>
|File:Viking Teardrop Islands.jpg|alt4=Tear-drop shaped islands carved by flood waters from [[Ares Vallis]]. (''[[Oxia Palus quadrangle]]'') |<small>Tear-drop shaped islands carved by flood waters from [[Ares Vallis]]. <br />(''[[Oxia Palus quadrangle]]'')</small>
|File:Vedra,_Maumee,_and_Maja_valles.jpg|alt5=Image of three valleys: [[Vedra Valles]], [[Maumee Valles]], and [[Maja Valles]]. (''[[Lunae Palus quadrangle]]'') |<small>Image of three valleys: [[Vedra Valles]], [[Maumee Valles]], and [[Maja Valles]]. <br />(''[[Lunae Palus quadrangle]]'')</small>
|File:Flow from Arandas Crater.jpg|alt6=[[Arandas (crater)|Arandas]] crater may be on top of large quantities of water ice, which melted when the impact occurred leaving a mud-like [[ejecta]]. (''[[Mare Acidalium quadrangle]]'') |<small>[[Arandas (crater)|Arandas]] crater may be on top of large quantities of water ice, which melted when the impact occurred, producing a mud-like ejecta. <br />(''[[Mare Acidalium quadrangle]]'')</small>
|File:Alba Patera Channels.jpg|alt7=Channels running through [[Alba Mons]]. (''[[Arcadia quadrangle]]'') |<small>Channels running through [[Alba Mons]]. <br />(''[[Arcadia quadrangle]]'')</small>
|File:Branched Channels from Viking.jpg|alt8=Branched channels in [[Thaumasia quadrangle]], possible evidence of past rain on Mars. |{{small|Branched channels in [[Thaumasia quadrangle]] provide possible evidence of past rain on Mars.}}
|File:Dissected Channels, as seen by Viking.jpg|alt9=These branched channels provide possible evidence of past rain on Mars. (''[[Margaritifer Sinus quadrangle]]'') |{{small|These branched channels provide possible evidence of past rain on Mars. (''[[Margaritifer Sinus quadrangle]]'')}}
|File:Ravi Vallis.jpg|alt10=[[Ravi Vallis]] was possibly formed from extreme flooding. <br />(''[[Margaritifer Sinus quadrangle]]'') |<small>[[Ravi Vallis]] was possibly formed from extreme flooding. <br />(''[[Margaritifer Sinus quadrangle]]'')</small>
}}

==Viking landers==
[[File:NASM-A19790215000-NASM2016-02690.jpg|thumb|Proof test article of the Viking lander]]
[[File:Sagan large.jpg|thumb|Astronomer [[Carl Sagan]] stands next to a model of a ''Viking'' lander to provide scale]]
Each lander comprised a six-sided aluminium base with alternate {{convert|1.09|and|0.56|m|in|abbr=on}} long sides, supported on three extended legs attached to the shorter sides. The leg footpads formed the vertices of an equilateral triangle with {{convert|2.21|m|ft|abbr=on}} sides when viewed from above, with the long sides of the base forming a straight line with the two adjoining footpads. Instrumentation was attached inside and on top of the base, elevated above the surface by the extended legs.<ref>{{cite magazine|magazine=Popular Mechanics|author=Hearst Magazines|title=Amazing Search for Life On Mars|url=https://books.google.com/books?id=aOIDAAAAMBAJ&pg=PA66|date=June 1976|publisher=Hearst Magazines|pages=61–63}}</ref>

Each lander was enclosed in an [[aeroshell]] heat shield designed to slow the lander down during the entry phase. To prevent contamination of Mars by Earth organisms, each lander, upon assembly and enclosure within the aeroshell, was enclosed in a pressurized "bioshield" and then [[Sterilization (microbiology)|sterilized]] at a temperature of {{convert|111|°C|sp=us}} for 40 hours. For thermal reasons, the cap of the bioshield was jettisoned after the Centaur upper stage powered the Viking orbiter/lander combination out of Earth orbit.<ref name="science-19760827">{{Cite journal |last1=Soffen |first1=G. A. |last2=Snyder |first2=C. W. |date=August 27, 1976 |title=The First Viking Mission to Mars |url=https://www.science.org/doi/10.1126/science.193.4255.759 |url-status=live |journal=[[Science (journal)|Science]] |volume=193 |issue=4255 |pages=759–766 |doi=10.1126/science.193.4255.759 |pmid=17747776 |bibcode=1976Sci...193..759S |archive-url=https://web.archive.org/web/20230211150701/https://www.science.org/doi/10.1126/science.193.4255.759 |archive-date=February 11, 2023 |access-date=December 21, 2023 |url-access=subscription }}</ref>

Astronomer [[Carl Sagan]] helped to choose landing sites for both ''Viking'' probes.<ref name="britannica-carl-sagan">{{Cite encyclopedia |last=Kragh |first=Helge |title=Carl Sagan |encyclopedia=[[Encyclopædia Britannica]] |url=https://www.britannica.com/biography/Carl-Sagan |access-date=August 9, 2022 |archive-url=https://web.archive.org/web/20231108075739/https://www.britannica.com/biography/Carl-Sagan |archive-date=November 8, 2023 |url-status=live }}</ref>

===Entry, Descent and Landing (EDL)===
Each lander arrived at Mars attached to the orbiter. The assembly orbited Mars many times before the lander was released and separated from the orbiter for descent to the surface. Descent comprised four distinct phases, starting with a [[Deorbit#Deorbit and re-entry|deorbit burn]]. The lander then experienced [[atmospheric entry]] with peak heating occurring a few seconds after the start of frictional heating with the Martian atmosphere. At an altitude of about {{convert|6|km|mi|abbr=off|sp=us}} and traveling at a velocity of 900 kilometers per hour (600&nbsp;mph), the parachute deployed, the aeroshell released and the lander's legs unfolded. At an altitude of about 1.5 kilometers (5,000 feet), the lander activated its three retro-engines and was released from the parachute. The lander then immediately used [[retrorockets]] to slow and control its descent, with a [[soft landing (rocketry)|soft landing]] on the surface of Mars.<ref name="astro.if.ufrgs.br-viking">{{Cite web |title=Viking |url=http://astro.if.ufrgs.br/solar/viking.htm |url-status=live |archive-url=https://web.archive.org/web/20230813090441/http://astro.if.ufrgs.br/solar/viking.htm |archive-date=August 13, 2023 |website=astro.if.ufrgs.br }}</ref>
{{Wide image|Mars_Viking_12a001.png|800px|First "clear" image ever transmitted from the surface of Mars – shows [[List of rocks on Mars#Viking|rocks]] near the ''[[Viking 1]]'' lander (July 20, 1976).}} At landing (after using rocket propellant) the landers had a mass of about 600&nbsp;kg.

===Propulsion===

Propulsion for deorbit was provided by the [[monopropellant]] [[hydrazine]] (N<sub>2</sub>H<sub>4</sub>), through a rocket with 12 [[Rocket engine nozzles|nozzle]]s arranged in four clusters of three that provided {{convert|32|N|lk=in|sp=us}} thrust, translating to a [[delta-V|change in velocity]] of {{convert|180|m/s|abbr=on}}. These nozzles also acted as the control [[Spacecraft propulsion|thrusters]] for [[translation (geometry)|translation]] and [[rotation]] of the lander.

Terminal [[descent (aircraft)|descent]] (after use of a [[parachute]]) and [[landing]] used three (one affixed on each long side of the base, separated by 120&nbsp;degrees) monopropellant hydrazine engines. The engines had 18 [https://artsandculture.google.com/asset/_/fgFN2s2GG-OfQA nozzles] to disperse the exhaust and minimize effects on the ground, and were [[throttle]]able from {{convert|276|to|2667|N|lk=in|sp=us}}. The hydrazine was purified in order to prevent contamination of the Martian surface with Earth [[microbes]]. The lander carried {{convert|85|kg|abbr=on}} of propellant at launch, contained in two spherical [[titanium]] tanks mounted on opposite sides of the lander beneath the RTG windscreens, giving a total launch mass of {{convert|657|kg|abbr=on}}. Control was achieved through the use of an [[inertial reference unit]], four [[gyroscope|gyros]], a [[radar altimeter]], a terminal descent and landing [[radar]], and the control thrusters.

===Power===
Power was provided by two [[radioisotope thermoelectric generator]] (RTG) units containing [[plutonium-238]] affixed to opposite sides of the lander base and covered by wind screens. Each Viking RTG<ref>{{cite web |title=SNAP-19 Radioisotope Thermoelectric Generator Fact Sheet by Energy Research & Development Administration (ERDA) Diagram 2 - The Energy Research and Development Administration |url=https://artsandculture.google.com/asset/_/twFyqw9QR3uOoQ |website=Google Arts & Culture |access-date=9 August 2022 |language=en}}</ref> was {{convert|28|cm|abbr=on}} tall, {{convert|58|cm|abbr=on}} in diameter, had a mass of {{convert|13.6|kg|abbr=on}} and provided 30&nbsp;watts of continuous power at 4.4&nbsp;volts. Four [[wet cell]] sealed nickel-cadmium 8 [[ampere hours|Ah]] (28,800&nbsp;[[coulomb]]s), 28&nbsp;volt [[rechargeable battery|rechargeable batteries]] were also on board to handle peak power loads.

===Payload===
[[File:Viking2lander1.jpg|thumb|right|Image from Mars taken by the ''Viking 2'' lander]]

==== Communications ====
Communications were accomplished through a 20-watt S-band transmitter using two [[traveling-wave tube]]s. A two-axis steerable high-gain parabolic antenna was mounted on a boom near one edge of the lander base. An [[omnidirectional antenna|omnidirectional]] low-gain S-band antenna also extended from the base. Both these antennae allowed for communication directly with the Earth, permitting Viking 1 to continue to work long after both orbiters had failed. A [[UHF]] {{Nowrap|(381 MHz)}} antenna provided a one-way relay to the orbiter using a 30&nbsp;watt relay radio. Data storage was on a 40-Mbit tape recorder, and the lander computer had a 6000-[[Word (data type)|word]] memory for command instructions.

==== Instruments ====
The lander carried instruments to achieve the primary scientific objectives of the lander mission: to study the [[biology]], chemical composition ([[organic compound|organic]] and [[inorganic]]), [[meteorology]], [[seismology]], [[magnetism|magnetic]] properties, appearance, and physical properties of the Martian surface and atmosphere. Two 360-degree cylindrical scan cameras were mounted near one long side of the base. From the center of this side extended the sampler arm, with a collector head, [[Sensor#Thermal|temperature sensor]], and [[magnet]] on the end. A [[Climate of Mars|meteorology]] boom, holding temperature, wind direction, and wind velocity sensors extended out and up from the top of one of the lander legs. A [[seismometer]], magnet and camera [[test target]]s, and magnifying [[mirror]] are mounted opposite the cameras, near the high-gain antenna. An interior environmentally controlled compartment held the [[biology]] experiment and the [[gas chromatography|gas chromatograph]] mass spectrometer. The [[X-ray]] [[fluorescence]] spectrometer was also mounted within the structure. A [[pressure]] sensor was attached under the lander body. The scientific [[Payload (air and space craft)|payload]] had a total mass of approximately {{convert|91|kg|abbr=on}}.

===Biological experiments===
{{Main|Viking biological experiments}}
The Viking landers conducted [[Viking biological experiments|biological experiments]] designed to detect [[life on Mars (planet)|life in the Martian soil]] (if it existed) with experiments designed by three separate teams, under the direction of chief scientist [[Gerald Soffen]] of NASA. One experiment turned positive for the detection of [[metabolism]] (current life), but based on the results of the other two experiments that failed to reveal any [[Organic matter|organic molecules]] in the soil, most scientists became convinced that the positive results were likely caused by non-biological chemical reactions from highly oxidizing soil conditions.<ref name=Beegle >{{Cite journal|title=A Concept for NASA's Mars 2016 Astrobiology Field Laboratory|journal=Astrobiology|date=August 2007|first=LUTHER W.|last=BEEGLE|display-authors=etal |volume=7 | issue = 4|pmid=17723090 |pages=545–577|doi=10.1089/ast.2007.0153|bibcode=2007AsBio...7..545B}}</ref>

{{Multiple image
|direction=vertical
|align=right
|image1=Mars Viking 11a097.png
|image2=Mars Viking 11d128.png
|width=220
|caption1=Dust dunes and a large boulder taken by the ''Viking 1'' lander.
|caption2=Trenches dug by the soil sampler of the  ''Viking 1'' lander.
}}

Although there was a pronouncement by NASA during the mission saying that the Viking lander results did not demonstrate conclusive [[biosignature]]s in soils at the two landing sites, the test results and their limitations are still under assessment. The validity of the positive 'Labeled Release' (LR) results hinged entirely on the absence of an oxidative agent in the Martian soil, but one was later discovered by the [[Phoenix lander|''Phoenix'' lander]] in the form of [[perchlorate]] salts.<ref name="latimes-20080806">{{Cite web |last=Johnson |first=John |date=August 6, 2008 |title=Perchlorate found in Martian soil |url=https://www.latimes.com/la-sci-phoenix6-2008aug06-story.html |url-status=live |archive-url=https://web.archive.org/web/20230419020853/https://www.latimes.com/la-sci-phoenix6-2008aug06-story.html |archive-date=April 19, 2023 |work=[[Los Angeles Times]] }}</ref><ref name="sciencedaily-20080806">{{Cite news |date=August 6, 2008 |title=Martian Life Or Not? NASA's Phoenix Team Analyzes Results |work=Science Daily |url=https://www.sciencedaily.com/releases/2008/08/080805192122.htm |url-status=live |archive-url=https://web.archive.org/web/20231118165426/http://www.sciencedaily.com/releases/2008/08/080805192122.htm |archive-date=November 18, 2023 }}</ref> It has been proposed that organic compounds could have been present in the soil analyzed by both ''Viking 1'' and ''Viking 2'', but remained unnoticed due to the presence of perchlorate, as detected by Phoenix in 2008.<ref>{{Cite news |url=http://www.agu.org/pubs/crossref/2010/2010JE003599.shtml |title=Reanalysis of the Viking results suggests perchlorate and organics at midlatitudes on Mars |journal=Journal of Geophysical Research: Planets |volume=115 |issue=E12010 |date=December 15, 2010 |access-date=January 7, 2011 |first=Rafael |last=Navarro–Gonzáles |author2=Edgar Vargas |author3=José de la Rosa |author4=Alejandro C. Raga |author5=Christopher P. McKay |archive-date=January 9, 2011 |archive-url=https://web.archive.org/web/20110109102058/http://www.agu.org/pubs/crossref/2010/2010JE003599.shtml |url-status=dead }}</ref>  Researchers found that perchlorate will destroy organics when heated and will produce [[chloromethane]] and [[dichloromethane]], the identical chlorine compounds discovered by both Viking landers when they performed the same tests on Mars.<ref>{{cite magazine| url=https://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/| archive-url=https://web.archive.org/web/20120415072431/http://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/| url-status=dead| archive-date=April 15, 2012| magazine=National Geographic| title=Life on Mars Found by NASA's Viking Mission| first=Ker| last=Than| date=April 15, 2012| access-date=April 13, 2018}}</ref>

The question of microbial life on Mars remains unresolved. Nonetheless, on April 12, 2012, an international team of scientists reported studies, based on mathematical speculation through [[complexity analysis]] of the [[Viking biological experiments#Labeled release|Labeled Release experiments]] of the 1976 Viking Mission, that may suggest the detection of "extant microbial life on Mars."<ref name="Bianciardi-2012">{{cite journal |last1=Bianciardi |first1=Giorgio |last2=Miller |first2=Joseph D. |last3=Straat |first3=Patricia Ann |last4=Levin |first4=Gilbert V. |title=Complexity Analysis of the Viking Labeled Release Experiments |journal=IJASS |date=March 2012 |volume=13 |issue=1 |pages=14–26 |doi=10.5139/IJASS.2012.13.1.14 |bibcode=2012IJASS..13...14B |df=mdy-all |doi-access=free |hdl=11365/27718 |hdl-access=free }}</ref><ref name="Discovery-20120412">{{cite web |last=Klotz |first=Irene |title=Mars Viking Robots 'Found Life' |url=http://news.discovery.com/space/mars-life-viking-landers-discovery-120412.html |date=April 12, 2012 |publisher=[[Discovery Channel|DiscoveryNews]] |access-date=April 16, 2012 |archive-date=April 14, 2012 |archive-url=https://web.archive.org/web/20120414163121/http://news.discovery.com/space/mars-life-viking-landers-discovery-120412.html |url-status=dead }}</ref> In addition, new findings from re-examination of the Gas Chromatograph Mass Spectrometer (GCMS) results were published in 2018.<ref>{{Cite journal|last1=Guzman|first1=Melissa|last2=McKay|first2=Christopher P.|last3=Quinn|first3=Richard C.|last4=Szopa|first4=Cyril|last5=Davila|first5=Alfonso F.|last6=Navarro-González|first6=Rafael|last7=Freissinet|first7=Caroline|date=2018|title=Identification of Chlorobenzene in the Viking Gas Chromatograph-Mass Spectrometer Data Sets: Reanalysis of Viking Mission Data Consistent With Aromatic Organic Compounds on Mars|journal=Journal of Geophysical Research: Planets|language=en|volume=123|issue=7|pages=1674–1683|doi=10.1029/2018JE005544|bibcode=2018JGRE..123.1674G|s2cid=133854625 |issn=2169-9100|url=https://hal-insu.archives-ouvertes.fr/insu-01820363/file/2018JE005544.pdf |archive-url=https://web.archive.org/web/20201103090059/https://hal-insu.archives-ouvertes.fr/insu-01820363/file/2018JE005544.pdf |archive-date=2020-11-03 |url-status=live}}</ref>

===Camera/imaging system===
[[File:Viking mission - Viking Lander Camera.png|thumb|Viking Lander Camera]]
The leader of the imaging team was [[Thomas A. Mutch]], a geologist at [[Brown University]] in [[Providence, Rhode Island]]. The camera uses a movable mirror to illuminate 12 [[photodiode]]s. Each of the 12 silicon diodes are designed to be sensitive to different frequencies of light.

Several broad band diodes (designated BB1, BB2, BB3, and BB4) are placed to focus accurately at distances between six and 43 feet away from the lander.<ref name=":1">{{Cite web |title=PDS: Instrument Information |url=https://pds.nasa.gov/ds-view/pds/viewInstrumentProfile.jsp?INSTRUMENT_ID=CAM1&INSTRUMENT_HOST_ID=VL1 |access-date=2023-03-28 |website=pds.nasa.gov}}</ref> A low resolution broad band diode was named SURVEY.<ref name=":1" />  There are also three narrow band low resolution diodes (named BLUE, GREEN and RED) for obtaining [[RGB color model|color images]], and another three (IR1, IR2, and IR3)  for [[infrared]] imagery.<ref name=":1" />

The cameras scanned at a rate of five vertical scan lines per second, each composed of 512 pixels. The 300 degree panorama images were composed of 9150 lines. The cameras' scan was slow enough that in a crew shot taken during development of the imaging system several members show up several times in the shot as they moved themselves as the camera scanned.<ref>{{cite book|chapter-url=https://history.nasa.gov/SP-425/ch8.htm|title=The Martian Landscape|author=The Viking Lander Imaging Team|publisher=NASA|date=1978|chapter=Chapter 8: Cameras Without Pictures|page=22}}</ref><ref name="nytimes-19760721">{{Cite news |last=McElheny |first=Victor K. |date=July 21, 1976 |title=Viking Cameras Light in Weight, Use Little Power, Work Slowly |url=https://www.nytimes.com/1976/07/21/archives/viking-cameras-light-in-weight-use-little-power-work-slowly.html |url-status=live |access-date=September 28, 2013 |archive-url=https://web.archive.org/web/20210222145516/https://www.nytimes.com/1976/07/21/archives/viking-cameras-light-in-weight-use-little-power-work-slowly.html |archive-date=February 22, 2021 |newspaper=[[The New York Times]] }}</ref>

=== Mass Breakdown of Viking Landers === 


{| class="wikitable"
|-
! Item !! Mass,kg (lb)<ref name=MarsLanderRetroprop>{{Cite web |title=Mars Lander Retro Propulsion (IAF-99-S.2.02) |url=https://www.researchgate.net/publication/232617757 |access-date=2024-05-14 |website= |language=en |archive-date=|archive-url= |url-status= }}</ref> 
|-
| Structures and Mechanisms 
|| {{cvt|132|kg|lb}}
|-
| Propulsion 
|| {{cvt|56|kg|lb}}
|-
| Pyro and Cabling
|| {{cvt|43|kg|lb}}
|-
| Thermal Control 
|| {{cvt|36|kg|lb}}
|-
| Guidance and Control 
|| {{cvt|79|kg|lb}}
|-

| Power 
|| {{cvt|103|kg|lb}}
|-
| Communications / Telemetry 
|| {{cvt|57|kg|lb}}
|-
| Science Instruments 
|| {{cvt|91|kg|lb}}
|-

| ='''Total Dry Mass'''  || {{cvt|595|kg|lb}} 
|-
| +Landing Propellant (incl. ~{{cvt|15|kg|lb}} residuals)
|| {{cvt|84|kg|lb}}
|-
| +Decelerator (incl.lander deorbit propellant)
|| {{cvt|118|kg|lb}}
|-
| +Aeroshell
|| {{cvt|269|kg|lb}}
|-
| +Bioshield
|| {{cvt|74|kg|lb}}
|-
| +Cap
|| {{cvt|54|kg|lb}}
|-
| ='''Total Launch Mass''' (Lander+Flight Capsule)  || {{cvt|1194|kg|lb}} 
|-

|-

|}



[[File:Viking control room.jpg|thumb|Viking control room at the [[Jet Propulsion Laboratory]], days before the landing of Viking 1.]]

==Control systems==
The Viking landers used a Guidance, Control and Sequencing Computer (GCSC) consisting of two [[Honeywell]] HDC 402 24-bit computers with 18K of [[Plated wire memory|plated-wire memory]], while the Viking orbiters used a Command Computer Subsystem (CCS) using two custom-designed 18-bit serial processors.<ref name="nasa-computers">{{Cite tech report |last=Tomayko |first=James |url=https://history.nasa.gov/computers/Ch5-6.html |title=Computers in Spaceflight: The NASA Experience |date=March 1988 |publisher=[[NASA]] |id=CR-182505 |access-date=February 6, 2010 |archive-url=https://web.archive.org/web/20230506223908/https://history.nasa.gov/computers/Ch5-6.html |archive-date=May 6, 2023 |url-status=live }}</ref><ref>{{Cite web|last=Holmberg|first=Neil A.|author2=Robert P. Faust |author3=H. Milton Holt |url=https://ntrs.nasa.gov/api/citations/19810001592/downloads/19810001592.pdf| access-date=February 6, 2010|title=NASA Reference Publication 1027: Viking '75 spacecraft design and test summary. Volume 1 – Lander design|publisher=NASA|date=November 1980}}</ref><ref>{{Cite web|last=Holmberg|first=Neil A.|author2=Robert P. Faust |author3=H. Milton Holt |url=https://ntrs.nasa.gov/api/citations/19810001593/downloads/19810001593.pdf|access-date=February 6, 2010|title=NASA Reference Publication 1027: Viking '75 spacecraft design and test summary. Volume 2 – Orbiter design|publisher=NASA|date=November 1980}}</ref>

==Financial cost of the Viking program==
The two orbiters cost US$217&nbsp;million at the time, which is about ${{Inflation|r=0|US-GDP|.217|1970}}&nbsp;billion in {{Inflation-year|US-GDP}} dollars.<ref name="marsmoney">{{Cite book|url=https://books.google.com/books?id=5Dy6z6DQDNoC&pg=PA68|title=Faster, Better, Cheaper: Low-Cost Innovation in the U.S. Space Program|last=McCurdy|first=Howard E.|date=2001|publisher=JHU Press|isbn=978-0-8018-6720-0|page=68}}</ref><ref name=":0" /> The most expensive single part of the program was the lander's life-detection unit, which cost about $60 million then or ${{Inflation|r=-2|US-GDP|60|1970}}&nbsp;million in {{Inflation-year|US-GDP}} dollars.<ref name=marsmoney/><ref name=":0" /> Development of the Viking lander design cost $357&nbsp;million.<ref name=marsmoney/> This was decades before NASA's [["Faster, better, cheaper" approach|"faster, better, cheaper" approach]], and Viking needed to pioneer unprecedented technologies under national pressure brought on by the [[Cold War]] and the aftermath of the [[Space Race]], all under the prospect of possibly discovering extraterrestrial life for the first time.<ref name=marsmoney/> The experiments had to adhere to a special 1971 directive that mandated that no single failure shall stop the return of more than one experiment{{mdash}}a difficult and expensive task for a device with over 40,000 parts.<ref name=marsmoney/>

The Viking camera system cost $27.3&nbsp;million to develop, or about ${{Inflation|r=-2|US-GDP|27.3|1970}}&nbsp;million in {{Inflation-year|US-GDP}} dollars.<ref name=marsmoney/><ref name=":0" /> When the Imaging system design was completed, it was difficult to find anyone who could manufacture its advanced design.<ref name=marsmoney/> The program managers were later praised for fending off pressure to go with a simpler, less advanced imaging system, especially when the views rolled in.<ref name=marsmoney/> The program did however save some money by cutting out a third lander and reducing the number of experiments on the lander.<ref name=marsmoney/>

Overall NASA says that $1&nbsp;billion in 1970s dollars was spent on the program,<ref name="nssdc-viking1orbiter" /><ref name="space.com"/> which when inflation-adjusted to {{Inflation-year|US-GDP}} dollars is about ${{Inflation|r=0|US-GDP|1|1970}}&nbsp;billion.<ref name=":0">As the Viking program was a government expense, the inflation index of the United States [[Nominal GDP|Nominal Gross Domestic Product]] per capita is used for the inflation-adjusting calculation.</ref>

==Mission end==
{| class="wikitable"
|+The craft all eventually failed, one by one, as follows:<ref name="NASA-20061218" />
! Craft || Arrival date || Shut-off date || Operational lifetime || Cause of failure
|-
| ''Viking 2'' orbiter || August 7, 1976 || July 25, 1978 || 1 year, 11 months, 18 days || Shut down after fuel leak in propulsion system.
|-
| ''Viking 2'' lander || September 3, 1976 || April 11, 1980 || 3 years, 7 months, 8 days || Shut down after battery failure.
|-
| ''Viking 1'' orbiter || June 19, 1976 || August 17, 1980 || 4 years, 1-month, 19 days || Shut down after depletion of [[Spacecraft attitude control|attitude control]] fuel.
|-
| ''Viking 1'' lander || July 20, 1976 || November 13, 1982 || 6 years, 3 months, 22 days || Shut down after human error during software update caused the lander's antenna to go down, terminating power and communication.
|}
The Viking program ended on May 21, 1983. To prevent an imminent impact with Mars the orbit of ''Viking 1'' orbiter was raised on August 7, 1980, before it was shut down 10 days later. Impact and potential contamination on the planet's surface is possible from 2019 onwards.<ref name="nssdc-viking1orbiter">{{Cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1975-075A |title=Viking 1 Orbiter spacecraft details |access-date=July 10, 2019 |date=March 20, 2019 |work=[[NASA Space Science Data Coordinated Archive]] |publisher=NASA }}</ref>

The ''Viking 1'' lander was found to be about 6 kilometers from its planned landing site by the [[Mars Reconnaissance Orbiter]] in December 2006.<ref>{{cite magazine| url=https://www.newscientist.com/article/dn10727-probes-powerful-camera-spots-vikings-on-mars.html#.UlIB7FDrwbN| title=Probe's powerful camera spots Vikings on Mars| last=Chandler| first=David| magazine=New Scientist| date=December 5, 2006| access-date=October 8, 2013}}</ref>

== Message artifact ==
{{See also|List of extraterrestrial memorials}}

Each ''Viking'' lander carried a tiny dot of microfilm containing the names of several thousand people who had worked on the mission.<ref>{{Cite web|url=https://www.planetary.org/outreach/visions-of-mars-then-and-now|title=Visions of Mars: Then and Now|website=The Planetary Society}}</ref> Several earlier and later space probes had carried message artifacts, such as the [[Pioneer plaque]] and the [[Voyager Golden Record]]. Later probes also carried memorials or lists of names, such as the [[Perseverance (rover)|''Perseverance'']] rover which recognizes the almost 11 million people who [[Perseverance (rover)#Commemorative artifacts|signed up to include their names]] on the mission.

==See also==
* {{annotated link|Exploration of Mars}}
* {{annotated link|Life on Mars}}
* {{annotated link|List of missions to Mars}}
* {{annotated link|Mars Science Laboratory}}
* {{annotated link|Mars Pathfinder}}
* {{annotated link|Norman L. Crabill}}

==References==
{{Reflist|30em}}

==Further reading==
* [http://www.hq.nasa.gov/office/pao/History/SP-4212/on-mars.html On Mars: Exploration of the Red Planet] {{Webarchive|url=https://web.archive.org/web/20070205092559/http://www.hq.nasa.gov/office/pao/History/SP-4212/on-mars.html |date=February 5, 2007 }}
* [https://history.nasa.gov/SP-441/cover.htm Viking Orbiter Views of Mars]
* [https://history.nasa.gov/SP-425/cover.htm The Martian Landscape SP-425]
* [http://pubs.acs.org/subscribe/journals/ancham/79/i19/pdf/1007feature_viking.pdf ''Analytical Chemistry'' feature article about the Viking spacecraft's scientific mission]
* [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810001592_1981001592.pdf Viking '75 spacecraft design and test summary. Volume 1 Lander design – NASA Report] {{Webarchive|url=https://web.archive.org/web/20201027065224/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810001592_1981001592.pdf |date=October 27, 2020 }}
* [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810001593_1981001593.pdf Viking '75 spacecraft design and test summary. Volume 2 Orbiter design – NASA Report] {{Webarchive|url=https://web.archive.org/web/20201027062855/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810001593_1981001593.pdf |date=October 27, 2020 }}
* [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810002594_1981002594.pdf Viking '75 spacecraft design and test summary. Volume 3 Engineering test summary – NASA Report] {{Webarchive|url=https://web.archive.org/web/20201028054352/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810002594_1981002594.pdf |date=October 28, 2020 }}

==External links==
{{Commons category|Viking mission}}
* [http://www.nasa.gov/mission_pages/viking/ NASA Mars Viking Mission] {{Webarchive|url=https://web.archive.org/web/20070223062630/http://www.nasa.gov/mission_pages/viking/ |date=February 23, 2007 }}
* [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19740026174_1974026174.pdf Viking Mission to Mars (NASA SP-334)] {{Webarchive|url=https://web.archive.org/web/20130807125926/http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19740026174_1974026174.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19740026174_1974026174.pdf |archive-date=2022-10-09 |url-status=live |date=August 7, 2013 }}
* [http://www.solarviews.com/span/vikingfs.htm Solar Views Project Viking Fact Sheet]
* [http://www.maniacworld.com/Viking-Mission-to-Mars.htm Viking Mission to Mars] {{Webarchive|url=https://web.archive.org/web/20110716215016/http://www.maniacworld.com/Viking-Mission-to-Mars.htm |date=July 16, 2011 }} Video
* [http://www.flightglobal.com/airspace/photos/missilespacesystemscutaways/nasa-viking-cutaway-10304.aspx A diagram of the Viking and its flight profile]
* [https://web.archive.org/web/20150117191711/http://airandspace.si.edu/exhibitions/exploring-the-planets/online/mars/viking_lab.html Article at Smithsonian Air and Space Website]
*[https://vikingpreservationproject.org/ The Viking Mars Missions Education & Preservation Project (VMMEPP)] 
*[https://artsandculture.google.com/exhibit/the-viking-mars-mission-the-viking-mars-missions-education-and-preservation-project/RQKiJsUJbOktIw?hl=en VMMEPP Online exhibit]
* [https://www.nasa.gov/feature/45-years-ago-viking-1-touches-down-on-mars 45 years ago: ''Viking'' 1 Touches Down on Mars]

{{Viking program}}
{{Jet Propulsion Laboratory}}
{{NASA navbox|state=collapsed}}
{{NASA planetary exploration programs}}
{{Mars spacecraft}} 
{{Authority control}}
{{Portal bar|Astronomy|Biology|Solar System}}

{{DEFAULTSORT:Viking Program}}
[[Category:Viking program| ]]
[[Category:Spacecraft launched in 1975]]
[[Category:Missions to Mars]]
[[Category:NASA programs]]
[[Category:Astrobiology]]
[[Category:Derelict landers (spacecraft)]]
[[Category:1976 on Mars]]
[[Category:1975 in Florida]]