The Navy is using laser gyroscope tech to navigate in GPS-denied environments

Even at sea, GPS signals are increasingly at risk of being disrupted by electronic warfare measures. To combat the problem, the Navy is upgrading its inertial gyrocompass navigation system for surface ships with improvements to AN/WSN-7(V) ring laser gyroscope technology.

Through a recent contract with Northrop Grumman, upgraded items for the AN/WSN-7B navigation system will be installed on Navy surface ships and submarines, according to the Department of Defense.

The AN/WSN-7 is an inertial navigation system (INS), and according to DARPA, INS will be crucial for the future of naval navigation. According to Northrop Grumman, the AN/WSN-7 is entirely self-contained, which means that it is does not rely on external satellite signaling, thereby making it immune to any enemy electronic countermeasures.

According to industry developers, the latest generation of ring laser gyro systems use two counter-propagating laser beams directed at a photo detector. If the platform is rotating, one laser wavelength will become out of phase with the other, creating discrepancies between the peaks and troughs of the two wavelengths. The system software measures the discrepancies and translates them to digital pulses, then calculates the rates of these pulses to determine the rotation angle.

“If you had a linear laser and the light bounced back and forth between two mirrors at either end, and if you increased the spacing between those two mirrors slightly, you would actually stretch one wavelength of light,” said James Koper, manager of ring laser gyro components at Kearfott Navigation and Guidance Systems. This stretching is what creates the phasing discrepancy between wavelengths in rotational motion.

In addition to the ring laser gyroscopes, DARPA publications state that inertial navigation also requires accelerometers for calculating speed and distance based on inertial data from an initial starting point. The result is GPS-less position and timing data from a self-contained navigation system.

Northrop Grumman will receive $11,026,388 for the production of AN/WSN-7V ring laser gyro navigation system components over a one-year period, reports the Department of Defense. The development is expected to be complete by April of 2019 for installation onboard the Navy’s AN/WSN-2 surface ships and AN/WSN-2A submarines.