Christine Hackman and Ken Senior, Advanced Space PNT Branch, United States Naval Research Laboratory

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Continued US reliance on GPS for time and frequency transfer (TFT) has prompted the development of new TFT techniques that are cooperative with but independent from GPS, an effort referred to as “altPNT.” Before integrating such new technologies with the warfighter, it is prudent to evaluate accuracies and reliability over a variety of environmental conditions and time spans, and with respect to established techniques. The US Naval Research Laboratory (NRL) and the US Naval Observatory (USNO), 11 km apart, are linked by multiple TFT technologies – e.g., GNSS5, TWSTFT6, optical fiber, (hopefully) free-space links - in various states of operational readiness. Some links continuously provide measurements as expected; some did but have ceased working; others await completion. The NRL-USNO Time-Transfer Testbed project aims to support the development of cutting-edge, cost-effective TFT methods by advancing the operational/technical readiness of the NRL-USNO links into a testbed that can serve as a proving ground for additional altPNT technologies. The fully-integrated NRL-USNO testbed will: • expand global timing options by providing testing for active and passive technologies of different form factors across a wide range of wavelengths, precisions, and costs • enable discovery of potential issues with new technologies under test prior to deployment, and • maintain or improve global time synchronization through its links to extant timing networks. This paper describes the testbed concept, further explains the rationale behind the work, updates readers on its current state of readiness, and presents examples of TFT analyses/comparisons that can be performed using the testbed.