A Return to the Sextant—Maritime Navigation Using Celestial Bodies and the Horizon

Satellite navigation over recent decades has become the default and, in some cases, sole source of positioning for maritime vessels. The classic sextant has been all but forgotten by a significant number of ship navigators. However, recent risks to RF-derived positioning by jamming and spoofing have resurfaced the need to train sailors again in the art. Innovations in space optical navigation have long been perfecting the art of using celestial bodies and horizons to determine a space vessel’s attitude and position. This paper explores their application to the much older ship navigation problem. Models are introduced that utilize the stars and horizon to derive latitude and longitude. When assuming good star visibility conditions on the ocean, the accuracy delivered is at the 100 m level. This can meet requirements for ship navigation in coastal and oceanic voyages.