Editing Viking 1 (section)

=== 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.