One nautical mile per month fog-based strapdown inertial navigation system: A dream already within reach?

Abstract

In 2006, we presented at DGON symposium in Stuttgart [2] the design and navigation results of MARINS, the first FOG-based navigation system within the class of 1 nautical mile per day. This navigation system in now in production and has been delivered to numerous navies.

Today we are challenged by even better performance and the question is: have we reached the limits of the technology or can we still improve the performance of our sensors? One nautical mile in a month means a bias stability of 2 × 10⁻⁵ degrees per hour! It may look foolish for a strapdown system with a dynamic range of at least 100 degrees per second. However, based on tests results, we provide evidence showing that FOG is the right technology to build a fully strapdown INS of this class. In particular we present:

• • Noise improvement.

• • Very long term pure inertial navigation (several weeks) of a FOG-based system with temperature controlled environment.

Of course, the present FOG design is not good enough for the required performance, even in a strictly controlled environment. The first way to go about this is obviously to increase the geometry factor (and therefore sensitivity) by increasing both diameter and length of the fiber coils, but this will not be sufficient. It will be necessary to improve detection noise, to control more accurately the light source wavelength, to reduce temperature gradient...Clearly there are difficulties on the way to a FOG-based strapdown system able to navigate with an accuracy of 1 nautical mile over several weeks; however, we show that FOG technology has not reached its ultimate potential yet and that the dream of even higher performance is within reach.