Air Force

Smartphone sextant

Alternative to GPS which works with a smartphone and can operate without a visible horizon

Communications

Air Force electronics engineer Eric Vinande has developed a smartphone sextant for navigation in GPS-degraded environments. The patented technology is available via license agreement to companies that would make, use, or sell it commercially.

Illustration from U.S. Patent 10,323,939, which was issued to the Air Force Research Laboratory on June 18, 2019.

Global Positioning System (GPS) navigation is based on radio signals and transmission can be degraded or immobilized via other radio emissions, intentional or accidental jamming, and naturally occurring weather interference.

As an alternative, traditional celestial navigation requires measuring the elevation angle of a celestial object such as a star, planet, sun, or moon above the horizon. An accurate time estimate to within a few seconds is required along with a rough estimate of position and tabulated positions of celestial objects. When the horizon is not visible, an artificial horizon or electronic sextant can be used to estimate a navigator’s position.

While smartphone cameras have much of the capability to serve as a navigation system, one challenge is that their onboard cameras are wide-angle, which means they can’t focus on faint stars, making them unsuitable for sextant aiming. However, these smartphones do contain a magnetic compass and gyroscope. The Air Force invention takes advantage of this and works by attaching a small telescope thereby addressing the focus issue.

The collapsible apparatus includes a holder to clamp a visual spotting scope along an optical axis and a second holder to attach to an electronic navigation device – a smartphone or tablet – comprising a tilt sensor, a clock, and a geomagnetic compass. The tilt sensor includes a tilt axis, and the first holder is connected to the second holder to dispose the tilt axis at an adjustable angle with respect to the optical axis.

Without needing to view the horizon, position updates are possible as long as a celestial object is detectable visually. Once the altitudes of several stars, or the moon, and sun are determined, the smartphone navigation app can map the user’s position.

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