Integrated and distributed Position Navigation and Timing (PNT) data in shipboard environments

The information and communication requirements of 21st Century Navies present dynamic and demanding challenges in the critical area of distributed and synchronized navigation and timing. Information must be integrated from diverse sources and be widely and easily distributed to user systems and platforms while maintaining integrity and security. The Navigation Sensor System Interface (NAVSSI) is a system that continues to expand to meet such ever increasing and demanding ship navigation and war fighting information requirements of today and tomorrow\´s United States and Foreign Military Sales (FMS) navies. NAVSSI is the pre-eminent source of precise, real-time, integrated Position, Navigation, and Timing (PNT) data for the United States and Spanish navies with Japan and South Korea scheduled to receive systems in the near future. NAVSSI is designed to integrate the inputs from various navigation sensors and distribute the integrated navigation solution to shipboard weapon and combat support systems. Since NAVSSI gathers inputs from different shipboard sensors and then distributes the resulting navigation data, it has many "user interface" systems that receive the data. These users have stringent requirements for navigation and timing accuracy. In order to provide a highly accurate and robust navigation solution, NAVSSI has implemented the Navigation Source Integration (NSI) algorithm. This algorithm is based on the integration of the best sources of navigation data (generally GPS and INS). In addition, NAVSSI outputs four different time forms with accuracies between one hundred nanoseconds and ten milliseconds depending on user interface system needs. As a result of higher levels of integration and interoperability requirements, Network Centric Warfare (NCW) has introduced new technological challenges, where once stand-alone systems are now networked together and therefore pose new security issues such as cross-domain connectivity. NAVSSI as a single common source of distributing PNT data on board Navy surface ships, faces the Information Security (IS) challenge of connecting to both classified and unclassified security domains. The strict timing requirements of PNT data, further constrain the scope of available IS products that can be deployed while maintain- ing these security boundaries. While the US Navy has specified that unclassified PNT data can cross from Black unclassified domain to Red classified domain, NAVSSI has the responsibility to ensure that it cannot be used to transfer other than PNT data, or provide connectivity for other types of networking and data communication services. This paper will discuss how the NAVSSI implementation satisfies the requirements for computing timely, integrated and accurate PNT data, its distribution, and means for maintaining security.