Editing Apollo 11 (section)

=== Site selection ===

{{Location mark+
| image = Lunar_site_selection_globe.jpg
| caption = Map of Moon showing prospective sites for Apollo 11. Site 2 was chosen.
| width = 220
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| float = right
| marks =
{{Location mark~
  | mark = 1_white,_blue_rounded_rectangle.svg
  | mark_link = Mare Tranquillitatis
  | width = 220
  | x = 760 | y = 365 }} <!-- x y positions relative to the image at 1000px width -->
{{Location mark~
  | mark = 2_white,_blue_rounded_rectangle.svg
  | mark_link = Mare Tranquillitatis
  | width = 220
  | x = 685 | y = 384 }}
{{Location mark~
  | mark = 3_white,_blue_rounded_rectangle.svg
  | mark_link = Sinus Medii
  | width = 220
  | x = 498 | y = 385 }}
{{Location mark~
  | mark = 4_white,_blue_rounded_rectangle.svg
  | mark_link = Oceanus Procellarum
  | width = 220
  | x = 235 | y = 421 }}
{{Location mark~
  | mark = 5_white,_blue_rounded_rectangle.svg
  | mark_link = Oceanus Procellarum
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  | x = 196 | y = 388 }}
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NASA's Apollo Site Selection Board announced five potential landing sites on February 8, 1968. These were the result of two years' worth of studies based on high-resolution photography of the lunar surface by the five uncrewed probes of the [[Lunar Orbiter program]] and information about surface conditions provided by the [[Surveyor program]].<ref name="Site Selection">{{cite web |url=https://www.nasa.gov/feature/50-years-ago-lunar-landing-sites-selected |title=50 Years Ago: Lunar Landing Sites Selected |newspaper=NASA |access-date=September 22, 2018 |date=February 8, 2018 |last1=Garcia |first1=Mark |archive-date=September 27, 2021 |archive-url=https://web.archive.org/web/20210927033702/https://www.nasa.gov/feature/50-years-ago-lunar-landing-sites-selected/ |url-status=live }}</ref> The best Earth-bound telescopes could not resolve features with the resolution Project Apollo required.{{sfn|Cortright|1975|p=79}} The landing site had to be close to the lunar equator to minimize the amount of propellant required, clear of obstacles to minimize maneuvering, and flat to simplify the task of the landing radar. Scientific value was not a consideration.{{sfn|Harland|1999|p=19}}

Areas that appeared promising on photographs taken on Earth were often found to be totally unacceptable. The original requirement that the site be free of craters had to be relaxed, as no such site was found.{{sfn|Cortright|1975|pp=98–99}} Five sites were considered: Sites&nbsp;1 and&nbsp;2 were in the Sea of Tranquility (''[[Mare Tranquillitatis]]''); Site&nbsp;3 was in the Central Bay ({{itco|''[[Sinus Medii]]''}}); and Sites&nbsp;4 and&nbsp;5 were in the Ocean of Storms (''[[Oceanus Procellarum]]'').<ref name="Site Selection" />
The final site selection was based on seven criteria:
* The site needed to be smooth, with relatively few craters;
* with approach paths free of large hills, tall cliffs or deep craters that might confuse the landing radar and cause it to issue incorrect readings;
* reachable with a minimum amount of propellant;
* allowing for delays in the launch countdown;
* providing the Apollo spacecraft with a free-return trajectory, one that would allow it to coast around the Moon and safely return to Earth without requiring any engine firings should a problem arise on the way to the Moon;
* with good visibility during the landing approach, meaning the Sun would be between 7&nbsp;and 20 degrees behind the LM; and
* a general slope of less than two degrees in the landing area.<ref name="Site Selection" />

The requirement for the Sun angle was particularly restrictive, limiting the launch date to one day per month.<ref name="Site Selection" /> A landing just after dawn was chosen to limit the temperature extremes the astronauts would experience.{{sfn|Collins|1994|p=7}} The Apollo Site Selection Board selected Site&nbsp;2, with Sites 3&nbsp;and&nbsp;5 as backups in the event of the launch being delayed. In May 1969, Apollo 10's lunar module flew to within {{convert|15|km|sp=us}} of Site&nbsp;2, and reported it was acceptable.{{sfn|Cappellari|1972|p=976}}<ref>{{cite web|url=https://airandspace.si.edu/explore-and-learn/topics/apollo/apollo-program/orbital-missions/apollo10-facts.cfm|title=Apollo 10|website=Smithsonian Air and Space Museum|access-date=December 26, 2018|archive-date=February 6, 2021|archive-url=https://web.archive.org/web/20210206101450/https://airandspace.si.edu/explore-and-learn/topics/apollo/apollo-program/orbital-missions/apollo10-facts.cfm|url-status=live}}</ref>