Editing Viking 1 (section)

== Mission ==
Following launch using a [[Titan IIIE|Titan]]/[[Centaur (rocket stage)|Centaur]] launch vehicle on August 20, 1975, and an 11-month cruise to Mars,<ref>{{Cite web|url=http://www.nasa.gov/image-feature/august-20-1975-launch-of-viking-1|title=20 August 1975, Launch of Viking 1|last=Loff|first=Sarah|date=August 20, 2015|website=NASA|access-date=July 18, 2019}}</ref> the orbiter began returning global images of Mars about five days before orbit insertion. The ''Viking 1'' Orbiter was inserted into Mars orbit on June 19, 1976,<ref name=":0">{{Cite book|url=https://books.google.com/books?id=VUWno1sOwnUC&pg=PA641|title=Encyclopedia of Space and Astronomy|last=Angelo|first=Joseph A.|date=May 14, 2014|publisher=Infobase Publishing|isbn=9781438110189|pages=641|language=en}}</ref> and trimmed to a 1,513 x 33,000&nbsp;km, 24.66 h site certification orbit on June 21. Landing on Mars was planned for July 4, 1976, the [[United States Bicentennial]], but imaging of the primary landing site showed it was too rough for a safe landing.<ref name=":1">{{Cite book|url=https://books.google.com/books?id=9YkMOHsVyUYC&pg=PA23|title=Magnificent Mars|last=Croswell|first=Ken|date=October 21, 2003|publisher=Simon and Schuster|isbn=9780743226011|pages=23|language=en}}</ref> The landing was delayed until a safer site was found,<ref name=":1" /> and took place instead on July 20,<ref name=":0" /> the seventh anniversary of the [[Apollo 11]] Moon landing.<ref>{{Cite book|url=https://books.google.com/books?id=Q8P3CwAAQBAJ&pg=PA19-IA43|title=The International Atlas of Mars Exploration: Volume 1, 1953 to 2003: The First Five Decades|last=Stooke|first=Philip J.|date=September 24, 2012|publisher=Cambridge University Press|isbn=9781139560252|language=en}}</ref> The lander separated from the orbiter at 08:51 [[UTC]] and landed at [[Chryse Planitia]] at 11:53:06 UTC.<ref name="NSSDCA">{{NSSDC|id=1975-075A|access-date=July 18, 2019|title=Viking 1 Orbiter}}</ref> It was the first attempt by the United States at landing on Mars.<ref>{{Cite web|url=https://history.nasa.gov/marschro.htm|title=Chronology of Mars Exploration|website=history.nasa.gov|access-date=August 16, 2019}}</ref>

=== Orbiter ===
The instruments of the [[orbiter]] consisted of two [[vidicon]] cameras for imaging, an infrared spectrometer for water vapor mapping, and infrared radiometers for thermal mapping.<ref name="Soffen & Snyder">{{cite journal|author=Soffen, G.A.|author2=Snyder, C.W.|date=August 1976|title=The First Viking Mission to Mars|journal=Science|series=New Series|volume=193|issue=4255|pages=759–766|bibcode=1976Sci...193..759S|doi=10.1126/science.193.4255.759|jstor=1742875|pmid=17747776}}<!--|access-date= 2008-01-17-->
</ref> The orbiter primary mission ended at the beginning of [[solar conjunction]] on November 5, 1976. The extended mission commenced on December 14, 1976, after solar conjunction.<ref>{{cite web|title=Viking 1 Orbiter Mission Profile|url=https://www.tsgc.utexas.edu/spacecraft/viking/profile_vik1orb.html|publisher=University of Texas|access-date=November 10, 2022}}</ref> Operations included close approaches to [[Phobos (moon)|Phobos]] in February 1977.<ref>{{Cite journal|last1=R.E. Diehl|first1=M.J. Adams|last2=Rinderle|first2=E.a.|date=March 1, 1979|title=Phobos Encounter Trajectory and Maneuver Design|journal=Journal of Guidance and Control|volume=2|issue=2|pages=123–129|doi=10.2514/3.55847|issn=0162-3192|bibcode=1979JGCD....2..123.}}</ref> The [[apsis|periapsis]] was reduced to 300&nbsp;km on March 11, 1977.<ref>{{Cite book|url=https://books.google.com/books?id=Fi1mCYJWBwAC&pg=PA251|title=Robotic Exploration of the Solar System: Part I: The Golden Age 1957–1982|last1=Ulivi|first1=Paolo|last2=Harland|first2=David M.|date=December 8, 2007|publisher=Springer Science & Business Media|isbn=9780387739830|pages=251|language=en}}</ref> Minor orbit adjustments were done occasionally over the course of the mission, primarily to change the walk rate — the rate at which the areocentric longitude changed with each orbit, and the periapsis was raised to 357&nbsp;km on July 20, 1979. On August 7, 1980, ''Viking 1'' Orbiter was running low on [[Spacecraft attitude control|attitude control]] gas and its orbit was raised from 357 × 33,943&nbsp;km to 320 × 56,000&nbsp;km to prevent impact with Mars and possible contamination until the year 2019. Operations were terminated on August 17, 1980, after 1,485 orbits. A 2009 analysis concluded that, while the possibility that ''Viking 1'' had impacted Mars could not be ruled out, it was most likely still in orbit.<ref name=Jefferson>{{cite conference |url=http://enu.kz/repository/2009/AIAA-2009-6002.pdf |title=An Investigation of the Orbital Status of Viking-1 |first1=David C |last1=Jefferson |first2=Stuart W|last2=Demcak |first3= Pasquale B|last3= Esposito |first4=Gerhard L |last4=Kruizinga |date=August 10-13, 2009 |conference=AIAA Guidance, Navigation, and Control Conference|archive-url=https://web.archive.org/web/20171107021706/https://www.enu.kz/repository/2009/AIAA-2009-6002.pdf|archive-date=November 7, 2017 }}</ref> More than 57,000 images were sent back to Earth.

===Lander===
[[File:Viking Aeroshell - GPN-2000-001903.jpg|left|thumb|''Viking'' aeroshell]]
The lander and its [[aeroshell]] separated from the orbiter on July 20 at 08:51 UTC. At the time of separation, the lander was orbiting at about {{convert|5|km/s|abbr=off|sp=us}}. The aeroshell's retrorockets fired to begin the lander de-orbit maneuver. After a few hours at about {{convert|300|km|abbr=off|sp=us}} altitude, the lander was reoriented for atmospheric entry. The aeroshell with its ablative [[heat shield]] slowed the craft as it plunged through the [[Atmosphere of Mars|atmosphere]]. During this time, entry science experiments were performed by using a retarding potential analyzer, a [[mass spectrometer]], as well as pressure, temperature, and density sensors.<ref name="Soffen & Snyder" /> At {{convert|6|km|abbr=on}} altitude, traveling at about {{convert|250|m/s|abbr=off|sp=us}}, the 16 m diameter lander parachutes deployed. Seven seconds later the aeroshell was jettisoned, and eight seconds after that the three lander legs were extended. In 45 seconds, the [[parachute]] had slowed the lander to {{convert|60|m/s|abbr=off|sp=us}}. At  {{convert|1.5|km|abbr=on}} altitude, retrorockets on the lander itself were ignited and, 40 seconds later at about {{convert|2.4|m/s|abbr=on}}, the lander arrived on Mars with a relatively light jolt. The legs had honeycomb aluminum shock absorbers to soften the landing.<ref name="Soffen & Snyder"/>
[[File:Documentary clip of Viking 1 landing (JPL-19760720-VIKINGf-0002-AVC2002151).webm|thumb|Documentary clip recounting the ''Viking 1'' landing with animation and video footage of the control centre]]
The landing rockets used an 18-nozzle design to spread the hydrogen and nitrogen exhaust over a large area. NASA calculated that this approach would mean that the surface would not be heated by more than one 1&nbsp;°C (1.8&nbsp;°F), and that it would move no more than {{convert|1|mm|sigfig=1|abbr=off|sp=us}} of surface material.<ref name="NSSDCA" /> Since most of Viking's experiments focused on the surface material a more straightforward design would not have served.<ref name=v1land>{{cite web|title=Viking 1 Lander Mission Profile|url=https://www.tsgc.utexas.edu/spacecraft/viking/profile_vik1lan.html#:~:text=The%20landing%20rockets%20used%20an,material%20would%20be%20stripped%20away.|publisher=University of Texas|access-date=November 10, 2022}}</ref>

The ''Viking 1'' lander touched down in western [[Chryse Planitia]] ("Golden Plain") at {{Coord|22.697|N|312.05|E|globe:Mars}}<ref name="NASA-20061218"/><ref name="NSSDCA" /> at a reference altitude of {{convert|−2.69|km|sp=us}} relative to a reference ellipsoid with an equatorial radius of {{convert|3,397|km|sp=us}} and a flatness of 0.0105 (22.480° N, 47.967° W planetographic) at 11:53:06 UTC (16:13 local Mars time).<ref name=v1land/> Approximately {{convert|22|kg}} of propellants were left at landing.<ref name="NSSDCA" />

Transmission of the first surface image began 25 seconds after landing and took about four minutes (see below). During these minutes the lander activated itself. It erected a high-gain antenna pointed toward Earth for direct communication and deployed a meteorology boom mounted with sensors. In the next seven minutes the second picture of the 300° panoramic scene (displayed below) was taken.<ref>{{cite journal|author=Mutch, T.A.|display-authors=etal|date=August 1976|title=The Surface of Mars: The View from the Viking 1 Lander|journal=Science|series=New Series|volume=193|issue=4255|pages=791–801|bibcode=1976Sci...193..791M|doi=10.1126/science.193.4255.791|jstor=1742881|pmid=17747782|s2cid=42661323}}<!--|access-date= 2008-01-17 --></ref> On the day after the landing the first colour picture of the surface of Mars (displayed below) was taken. The seismometer failed to uncage, and a sampler arm locking pin was stuck and took five days to shake out. Otherwise, all experiments functioned normally.

The lander had two means of returning data to Earth: a relay link up to the orbiter and back, and by using a direct link to Earth. The orbiter could transmit to Earth (S-band) at 2,000 to 16,000 bit/s (depending on distance between Mars and Earth), and the lander could transmit to the orbiter at 16,000 bit/s.<ref name=JPL-facts-VMM>{{Cite web|url=https://faculty.tamuc.edu/cdavis/resources/AESP/InstructionalMaterials/Viking%20Fact%20Sheet.pdf|title=''Viking Mission to Mars'' JPL}}</ref> The data capacity of the relay link was about 10 times higher than the direct link.<ref name="Soffen & Snyder"/>
{{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 (20 July 1976). The haze on the left is possibly dust that had recently been kicked up by the landing rockets. Because of the "slow scan" facsimile nature of the cameras, the dust settled by mid-image.}}
The lander had two facsimile cameras; three analyses for metabolism, growth or photosynthesis; a gas chromatograph-mass spectrometer; an x-ray fluorescence spectrometer; pressure, temperature and wind velocity sensors; a three-axis seismometer; a magnet on a sampler observed by the cameras; and various engineering sensors.<ref name="Soffen & Snyder"/>
[[File:PSP 001521 2025 RED VL-1 lander.png|thumb|Photo of the Viking 1 Mars lander taken by the Mars Reconnaissance Orbiter in 2006]]
The ''Viking 1'' lander was named the '''Thomas Mutch Memorial Station''' in January 1981 in honour of [[Thomas A. Mutch]], the leader of the Viking imaging team.<ref>{{cite web |title=NASA – NSSDCA – Spacecraft – Details |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1975-075C |website=nssdc.gsfc.nasa.gov |access-date=March 5, 2021}}</ref> The lander operated for 2,245 [[Timekeeping on Mars#Sols|sol]]s (about 2,306 Earth days or 6 years) until November 11, 1982 (sol  {{age in sols|1975|07|20|1982|11|11|format=commas}}), when a faulty command sent by ground control resulted in loss of contact. The command was intended to uplink new battery charging software to improve the lander's deteriorating battery capacity, but it inadvertently overwrote data used by the antenna pointing software. Attempts to contact the lander during the next four months, based on the presumed antenna position, were unsuccessful.<ref>{{cite report|author=D. J. Mudgway|publisher=[[NASA]] [[Jet Propulsion Laboratory]]|date=1983|title=Telecommunications and Data Acquisition Systems Support for the Viking 1975 Mission to Mars|url=http://www.atmos.washington.edu/~mars/LFEM/lfemstep/lfemstep_slides/viking_documents/Pdf/JPL_Publication_82-107.pdf|access-date=June 22, 2009}}</ref> In 2006, the ''Viking 1'' lander was imaged on the Martian surface by the ''[[Mars Reconnaissance Orbiter]]''.<ref>{{cite report|publisher=[[NASA]]|date=2006|title=NASA Mars Orbiter Photographs Spirit and Vikings on the Ground|url=http://www.nasa.gov/mission_pages/MRO/news/mro-20061204.html|access-date=July 20, 2011|archive-date=August 5, 2011|archive-url=https://web.archive.org/web/20110805030058/http://www.nasa.gov/mission_pages/MRO/news/mro-20061204.html|url-status=dead}}</ref>