The device was used repeatedly throughout the Apollo program across many phases of the missions, up to and including re-entry. Although all Apollo astronauts trained to some extent in the use of the sextant, it was perhaps most famously used by Jim Lovell aboard Apollo 8 during its circumlunar flight. The device was integrated into the manned spaceflight program before NASA realized how much the astronauts would depend on help from ground crew and at a time when there were real fears about the Soviet Union trying to “jam” communications between Ground Control and the astronauts to foul a space mission.
(While it may seem silly to think this way now, it’s worth remembering that the Space Race took place at the very height of the Cold War, when such concerns were widespread and taken very seriously.)
The sextant could also be used as a simple telescope when needed. In July 1969, Michael Collins tried — without success — to use the Apollo 11 sextant to find the Lunar Module Eagle in the Sea of Tranquility after landing. His failure probably stemmed from the fact that Neil Armstrong had piloted the craft to a site about four miles (six kilometers) from the intended landing zone. In November 1969, during the Apollo 12 mission, Richard Gordon was able to use the 28x telescope portion of the sextant in the Command Module Yankee Clipper to clearly see the,Lunar Module Intrepid and the nearby Surveyor probe in the Moon’s Ocean of Storms after Pete Conrad and Alan Bean landed.
For those curious to see the sextant in use, a video made by NASA is embedded below and an episode of the 1998 miniseries about the Apollo program, “From the Earth to the Moon,” features a scene of Lovell operating the sextant during Apollo 8.
NASA, Jeff Quitney
While manned missions to the Moon or even Mars are years away, it seems likely that future astronauts traveling to these destinations would be wise to bring along a sextant given the accuracy, ease of use, and value of such a device in addition to whatever other technology they carry with them. Sometimes the old ways really are the best.