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Session C5: Military PNT User Equipment Test Results

Flight Test Results for Embedded GPS Inertial Modernization (EGI-M)
Jonathan Lincoln, Northrop Grumman; Kamal Joshi, Northrop Grumman; Michael Hathaway, Northrop Grumman; Patrick Young, Northrop Grumman; Joe Franiak, Northrop Grumman; Joseph B. Lorkowski, Maj. USAF
Location: Ballroom C
Date/Time: Wednesday, Jun. 14, 9:15 a.m.

The EGI-M program is a DoD-funded multi-services program, executed via USAF AFLCMC contract at Robins AFB, to modernize the current EGI to address today’s challenges and prepare for future threats. The five pillars for EGI-M include: (1) the incorporation of an M-Code GPS receiver meeting National Security needs, (2) address Safety and Airspace Access Mandates, (3) reduce the total configuration count through software modularization and common component hardware, (4) address obsolescence in legacy design, and (5) resiliency to enable agile implementation of future Position, Navigation, and Timing (PNT) capabilities. Two system configurations are being developed for the EGI-M program, an LN-351 system to replace the currently fielded LN-251, with E-2D as the lead platform; and an LN-300 system to replace the LN-100, with F-22 as the lead platform. The new EGI-M systems are a form, fit, and function replacement for the lead platforms in order to mitigate the need for expensive modification to be made to the aircraft. The EGI-M has an open model-based, partitioned software architecture meeting DO-178C requirements, and DO-254 firmware certifiability. The system enables rapid response to emerging threats via a Common Application Space (CAS) that uses a Future Airborne Capabilities Environment (FACE) interface as a host for 3rd Party Applications (3PA).
The EGI-M system is a self-contained, worldwide, all-attitude strapdown inertial navigation system with a new M-Code Global Positioning System (GPS) receiver. Three independent, simultaneous navigation solutions are provided - INS-Only, GPS-Only, and Blended (GPS/INS); while providing both stationary and moving base alignment capabilities. The EGI-M system provides information to other vehicle systems to support position, navigation, and timing distribution for mission critical system functions. External communication interfaces include two dual-redundant MIL-STD-1553 data busses, two Gigabit Ethernet Data Busses, configurable RS-422/RS-485 data ports, and up to six ARINC-429 channels.
The purpose of the EGI-M system flight test was to verify the performance of all three navigation solutions of the prototype LN-351 EGI-M system under real aircraft flight dynamics. Flight tests occurred during the first quarter of CY2023 on a Cessna Citation V, flying out of Van Nuys Airport (VNY) located in Southern California. The aircraft is powered by two Pratt & Whitney Canada JT15D-5A turbofans with a cruising speed of 430 knots (kn), max climb rate of approximately 4,230 feet per minute (fpm), and a ceiling of 45,000 ft. The aircraft was modified to mount the provided GPS antenna on the exterior of the aircraft, and proper routing of RF cable into the cab, to a 1-4 splitter that led to the three EGI’s (two LN-251s and one LN-351 with the LN-351 EGI-M as the Unit Under Test (UUT) and the two LN-251 Product Line EGI’s used as reference systems), as well as the Novatel DGPS receiver. Additionally, mounting structures were fabricated in the interior of the aircraft to secure the NG provided test equipment. The aircraft provided Alternating Current (AC) power as well as an RS-422 pressure altitude signal to the test equipment. Each EGI was programmed with an orientation code to align the body axes with the axes of the test aircraft. The test aircraft supplied a Pressure Altitude input via RS-422 which was converted using the Comprehensive Alternative Test Software (CATS) test equipment and output via 1553 to each EGI. CATS was also used to monitor and collect High-Speed Serial Interface (HSSI) data from all three EGIs for post-processing. The navigation pallet consisted of two 13U server racks containing the necessary test equipment and a separate mounting plate for the three EGI systems. The test equipment consisted of four rack-mount PCs running CATS, a data recording PC, a Novatel ProPak v3 DGPS receiver, an AltaDT eNET2-1553 device, three LN-251 breakout boxes (BoB), two 28V power supplies, and a data recording laptop.
GPS time synchronized HSSI data was collected from all three EGI systems for post-processing. The EGI-M navigation performance was assessed by comparing high-accuracy Novatel Differential GPS (DGPS) position and velocity truth data collected during the flight to the time-stamped navigation data outputs. Attitude outputs were verified through comparison of the three system’s attitudes. EGI-M system hybrid Kalman filter performance was compared to the two LN-251 system’s Kalman filter performance, to confirm LN-351 performance. The EGI-M flight test provided a breakthrough in the demonstration of an M-code GPS receiver integrated into an EGI system, tested under real aircraft dynamics.

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