U.S. Defense Program Advances GPS-Free Timekeeping for Contested Battlefields

A U.S. defense research program is developing optical clock technology designed to maintain precise time synchronization in GPS-denied and contested environments, reducing reliance on satellite-based timing for military operations.

According to Defense Advanced Research Projects Agency (DARPA), the Robust Optical Clock Network (ROCkN) program focuses on strengthening position, navigation, and timing (PNT) capabilities by creating tactical-grade optical clocks that can sustain GPS-level precision without access to satellite signals. Modern missiles, aircraft, ships, artillery, and sensors depend on atomic clocks aboard GPS satellites for nanosecond-level synchronization. Even a timing error of a few billionths of a second can result in positioning errors of a meter or more.

Despite upgrades to improve resilience, GPS signals remain vulnerable to jamming and spoofing. ROCkN aims to provide an alternative by enabling extended operations without GPS-based timing.

The program is developing two types of clocks. A compact, shoebox-sized unit, using power comparable to a lightbulb, can maintain sub-nanosecond precision for up to two weeks without intervention. A larger “local master clock,” roughly the size of a washing machine, is designed to support a regional network for more than six months without synchronization to GPS.

In recent demonstrations, ROCkN achieved optical synchronization at the femtosecond level over distances of hundreds of kilometers. Multi-node clock networks were tested in varied weather conditions, including humidity, heat waves, and blizzards.

Program data indicates that moving from nanosecond to picosecond-or-better precision could support improved communications, distributed sensor networks, and battlefield awareness. Demonstrations suggest the enhanced timing could allow more precise coordination of mobile sensors operating beyond the X-band frequency range, supporting geolocation, targeting, electronic warfare functions, and resilient high-speed communications.

ROCkN systems have been tested on fixed-wing aircraft, ground vehicles, and aboard a naval ship operating for three weeks in the Pacific Ocean tropics.

Over the next year, field exercises are planned to demonstrate capabilities in next-generation PNT, electronic warfare, and intelligence, surveillance, and reconnaissance missions. The program also plans to begin pilot-line manufacturing of clock units to support Department of War transition partners and potential broader deployment.