Automated Marine Navigation

Abstract

A navigation system based upon the Navy's low-drift, high-precision, Electrically Suspended Gyros has been demonstrated to have surprisingly low error over long periods of time. By taking full advantage of this experience and other recent advances in the electronics art, a new, all-weather, non-radiating, automatic system is now possible. The system will operate at all latitudes and is independent of shore stations. Infrequent manual, celestial resets will serve to update or confirm the self-contained system's position, velocity and heading information. The equipment is being planned to meet the anticipated needs for extremely high precision position finding in future naval and commercial marine operations. Basically, local gravity vertical (from accelerometers in a Schuler loop) is referred continuously to the celestial coordinate system. Coordinates are represented between celestial sightings by a pair of electrically suspended gyros. All data inputs are digital and are recorded at high sampling rates by a general purpose computer which smoothes data to reduce random errors. Similar smoothing is applied to the occasional celestial tracking inputs. Semi-automated manual “sextants” are remotely read out by the computer to obtain hundreds of simultaneous, two-body fixes per second; this permits, in effect, the averaging of thousands of sightings within a few minutes of “tracking” for position, velocity and heading resets to the computer. The computer not only yields position, but calculates vector velocity (ground speed and course), present true heading, steering order to maintain great circle course to destination, distance to go and expected arrival time at present speed. Observation of drifts is possible by comparing average, past heading to distance made good over a period of minutes or hours. Steering orders can be modified to compensate for drift.