Harris Corp. has received a two-year, $500,000 grant from the North Dakota Centers of Excellence Commission to enable and test beyond-visual-line-of-sight-operations (BVLOS) for unmanned aircraft systems using an augmented ADS-B network for traffic separation of UASs with other aircraft in the Northern Plains state. The Melbourne, Florida aerospace company is partnering with the University of North Dakota and the Northern Plains UAS Test Site to develop a network infrastructure scalable to the state of North Dakota and eventually to the entire U.S. that would allow UASs to be safely integrated into the National Airspace System (NAS).

According to Harris Electronic Systems vice president and general manager of commercial UAS solutions George Kirov, this infrastructure will leverage the existing FAA ADS-B ground station network, which the company manages, and use strategically located, Harris-built ADS-B Xtend units to fill in coverage gaps below 400 feet. With six ADS-B Xtend units already in place, “the majority” of North Dakota now has full coverage, he said. Both the 1090-MHz and universal access transceiver (UAT) ADS-B frequencies will be used in the trials.

BNSF Railway is already using Harris X-Tend units placed along its lines and ADS-B-equipped UASs to inspect its tracks, so Harris is confident that this technology can be used on a broader scale. "This is a scalable system," Kirov said. And compared with heavier and higher-cost “see and avoid” systems that can be used only on larger UAS platforms, Harris believes that the availability of low-cost, small and lightweight ADS-B units makes this technology more suitable and economical to safely separate unmanned aircraft—regardless of size—from other traffic throughout the NAS. 

Meanwhile, the company is now working to finalize its command-and-control system that it will use for the tests in North Dakota. Harris had explored using the 4G/LTE network to transmit commands to UASs flyng beyond visual line of sight, but it has decided to use a more secure, aviation-protected spectrum outlined in RTCA SC-228, "Minimum Operational Performance Standards for Unmanned Aircraft Systems," which outlines L-Band and C-Band solutions. It expects to have its command-and-control system in place by year-end.

In case of loss or interruption in either control or ADS-B signals, Harris engineers are integrating onboard "last ditch" functions. If the ADS-B network signal is lost, the onboard command-and-control computer can still receive ADS-B broadcasts from nearby aircraft and automatically maintain a one-mile separation. And if the control signal is lost, the UAS will land automatically. For normal air traffic separation, UAS operators in the North Dakota trials will communicate by voice to air traffic controllers.

Harris and its partners plan to begin testing of UAS BVLOS flights using ADS-B for traffic separation and its command-and-control system in North Dakota early next year. A wide variety of UAS vehicles will be used during the trials, some of which could possibly fly into the flight levels, said Kirov.