
Commander Lovell using the sextant, Apollo 8
Sailors have navigated by the stars since the dawn of time. Now, fifty years after Neil Armstrong first set foot on the Moon in the Apollo 11 mission, we shouldn’t forget that even the Apollo astronauts relied on sextants to navigate to the Moon and back. Not only did a sextant help to get to the moon, but Astronaut Jim Lovell’s use of a sextant would be instrumental in saving the crippled Apollo 13 in 1970.
The Apollo sextant was a modern update of device that sailors have used for centuries. It played a key role in the three-part navigation system in the Apollo program. Much of the navigation was performed using ground-based radar. When that was not available, an inertial guidance system was used. The inertial guidance system tended to drift however and needed to be corrected periodically. To do so, the astronauts used a scanning telescope and a sextant to take star sights. These sights were used to correct the inertial guidance system and to confirm the accuracy of the ground-based navigation system. The sextant was also considered to be a backup against the possibility that the Russians would attempt to jam radio transmissions between Mission Control and the Apollo spacecraft.