Inertial navigation unit protocol converter

Device translates the ARINC-429 protocol output of an inertial navigation system to the National Marine Electronics Association 0183 protocol

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A P-3C Orion. Navy photo.

The Department of Homeland Security utilizes airborne surveillance operations to monitor illegal activities which have an impact on national security. These activities include drug trafficking, illegal immigration, and terrorist activities.

Many ride-along sensor units often deployed with a surveillance P-3 aircraft require the implementation of the National Marine Electronics Association 0183 (NMEA-0183) serial navigation data format. Other components for geospatial video recording and reproduction also require the ability to utilize this format. There is currently an immediate need to provide aircraft navigation data in real time to produce a coherent video data stream for situational awareness during the transport of sensor video to the ground for analysis. The NMEA-0183 protocol provides a low-bandwidth, commonly utilized format that end users can easily make use of for situational awareness.

ARINC-429 is a data transfer standard for avionics and in order for this to work with a broad range of sensors, a protocol converter is needed. ARINC-429 to NMEA-0183 protocol converters are commercially available but none are specifically designed to utilize the wide variety of parameters available from the Litton LTN-92 Inertial Navigation System (INS), used on the P-3 aircraft. These protocol converters extract only the most commonly used parameters from the ARINC-429 protocol (such as time, position, ground speed, and heading) and output only a small fixed set of NMEA-0183 sentences (short ASCII serial communications). None of the NMEA-0183 sentences provided by these protocol converters are capable of providing pointing information that is used to indicate the location of an object relative to the P-3 aircraft.

Navy scientists have filled the above void with a  protocol converter that generates a custom sentence which includes pointing information that is used to indicate the location of an object relative to the P-3 aircraft. The Inertial Navigation Unit (INU) Protocol Converter translates the ARINC-429 protocol output of a Litton LTN-92 INS to the NMEA-0813 protocol. The converter comprises one commercially available ARINC-429 interface board with cable and software operating in a computer running a Windows operating system. The protocol conversion software comprises two files (INU_Convert.exe, and INU_Convert.ini). INU_Convert.exe is the executable program that performs the protocol conversion while INU_Convert.ini is an initialization file used by the executable at startup to initialize its configuration.

The protocol conversion program is installed to start upon computer startup and appears as a small P-3 aircraft icon in the operating system’s system tray. The user can expand this icon to view the status of the ARINC-429 and serial communications interfaces as well as change the configuration of the protocol conversion program.

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