Sense-and-Avoid

Employing the latest research and testing tools that include networked live, virtual and constructive simulation, NASA is providing support to the FAA and the RTCA (formerly Radio Technical Commission for Aeronautics) in the ongoing effort to develop solutions leading to the safe and successful integration of unmanned aerial systems into the US National Airspace System. Chuck Weirauch reports.

As a part of the federal agency's Aeronautics Research Mission Directorate, all four of NASA's Aeronautical Research Centers are teamed together to contribute research and test data to the overall NASA UAS Integration in the  National Airspace System (NAS) Project, which is being led by the Armstrong Flight Research Center at Edwards, CA.

According to Laurie Grindle, the NASA UAS Integration Project Manager, the five-year Project currently is in its three-year Second Phase and will be concluded in fiscal year 2016. While the Langley Research Center in Hampton, VA and the Ames Research Center in Ames, IA are focusing on the technological challenges of UAS Sense-and-Avoid issues, the John Glenn Research Center at Cleveland, OH is responsible for Command, Control and Communications research. The Neil H. Armstrong Flight Research Center at Palmdale, CA (formerly Dryden Research Center) has overall Project management responsibility, sharing Integrated Test and Evaluation duties with Ames, conducting system integrated tests for the other three Technical Challenges groups. That latter Center is also looking into UAS Human Systems UAS Technical Challenges.

“Our actual Project Goal is about developing research findings towards reducing technological barriers associated toward the integration of UAS into the NAS,” Grindle reported. “And we do that by utilizing integrated system-level tests in a relevant environment.”

SC-228 Support

In the Project Phase Two work begun this year, NASA started to work with the RTCA Special Committee 228 (SC-228) formed in May 2013.This Committee's responsibility is to develop “Minimum Operational Performance Standards for Unmanned Aircraft Systems.” The RTCA works in response to requests from the FAA to develop comprehensive, industry-supported and endorsed recommendations for the government on issues ranging from technical performance standards to operational concepts for air transportation.

Such standards are vital to the development of UAS technologies such as sense-and-avoid that will allow UAS to operate in the NAS, Grindle explained. Much sense-and-avoid technology will be developed and provided by the aviation and UAS industry, but for industry to build such technology, its members need to know the constraints and the boundaries that they have to work under to create it, she pointed out. And creating such requirements for the establishment of minimum standards is the role of the SC-228 Committee, she added.

“NASA is supporting the SC-228 initiative by helping come up with the requirements for sense-and-avoid and in the other areas,” Grindle stated. “We have come up beside them to provide research findings that will help them define those requirements. Once the RTCA creates those requirements, industry will be able to take that information and build the systems that they need.”

Simulated NAS Research

One major research and testing tool that NASA is employing for the UAS Integration Project is the Live Virtual Constructive-Distributed Environment (LVC-DE). According to NASA, the LVC-DE is essentially a simulation and flight test environment designed to simulate the NAS. The LVC-DE effort was developed and is managed by Armstrong Center personnel. Simulation centers at NASA Centers are networked together to create the virtual distributed NAS, with the central computer simulation node at Ames, which generates the virtual air traffic data.

The LVC-DE system generates simulated air traffic, representing radar and ADS-B-derived surveillance tracks, to test advanced airspace integration concepts, technologies and procedures. The system incorporates flight performance data from real aircraft, like NASA's own UAS, and other manned and unmanned aircraft, to provide realism and demonstrate actual system capabilities. The LVC-DE system also keeps humans in the loop, specifically air traffic controllers and pilots, for a fully integrated virtual and real-world simulation experience. NASA hires retired ATCs to help conduct these simulations.

Implemented for initial testing in late 2013, one of the first live elements to fly in the LVC-DE was a modified, ADS-B-equipped NASA MQ-9 B Predator UAS. Plans are to link in the FAA's William J. Hughes Technical Center in Atlantic City, NJ so that research personnel there will also be able to participate in the networked simulations and flight tests. The LVC-DE can function with the Airspace Concept Evaluation System (ACES), which is a newly implemented simulation and modeling system that is designed to provide gate-to-gate behavioral representation of all the major components of the NAS, including aircraft and air traffic control systems.

Sense-and-Avoid

According to Project Chief Systems Engineer Debra Randall, the LVC-DE was developed so that all of the elements of the NAS systems could be integrated together. With the LVC environment spread out over several NASA centers, it can leverage the capabilities and assets located at each center for integrated human-in-the-loop simulations. For example, a Boeing 747 simulator at Ames sent positional data to a simulation that was ongoing at Langley, she reported. That information allowed air traffic controllers to access the simulator's display in that particular simulation. At the same time, the ATCs at Ames could see the display from a UAS ground controller station for the UAS pilot at Ames who operates a NASA Predator B UAS.

“We did this so that we could we could assess ATC acceptability of the maneuvers that the UAS pilot was making, while also assessing the pilot's interpretation of whether those maneuvers were safe, or where he should be, based on elements on the UAS pilot's display screen that both he and we could see,” Randall explained. “You have to have the sense-and-avoid boundary somehow show up for the pilot so that he can interpret where it is at and what kinds of maneuvers that he needs to make.”

As a part of the sense-and-avoid research being conducted at Ames and Langley, the two centers are working together to support the SC-228 Committee and are studying ways and means to meet “well clear” requirements. Under FAA regulations, UAS will be required to be equipped with sense-and-avoid systems to fulfill the requirement to remain well clear of other aircraft.

“The goal is to provide a mathematical boundary line that would help a UAS pilot on the ground determine where that bubble around his aircraft is that allows him to sense other aircraft and avoid them,” Randall explained. “We are looking at all of the different aspects of sense-and-avoid that are integrated into the UAS system.”

UAS Simulations Critical

NASAhas this year employed the LVC-DE system for flight evaluations ofan ADS-B aircraft tracking system adapted for UAS by flying its ADS-B equipped Predator live, with the its ground station controller linked into the simulated NAS environment. Since ASD-B is a critical element of the FAA's NextGen satellite-based air traffic control system, such work is expected to be continued beyond the conclusion of the UAS Integration in the NAS Project. That effort will end in September 2016.

“There will be more to do once this project is completed,” Grindle said. “The Aeronautics Research Mission Directorate is looking at what the next steps will be in the UAS arena. The LVC-DE capability is a tool will remain for such future work.”

Simulation technologies and applications will continue to play a critical role in the research, tests and evaluations that need to be conducted to validate the safety of UAS operations in the NAS before they ever become reality, Grindle added. One reason is that such simulations are simply far cheaper than conducting real flight tests, she pointed out.

“And from a historical perspective, I think that UAS will probably leverage simulation more than most systems do,” Grindle summarized. “So from that perspective, the simulation capabilities that we are building up at both Ames and Langley and the integrated flight tests that we do to validate those simulations help make them more robust. We can look at specific items much quicker now (with simulations rather than actual flight tests). There will be things that we will need answers to in a relatively short period of time. We have staged our team to provide those answers to the SC-228 Committee and the FAA so that they are constantly aware of them. And being in a simulation, those folks can be specific in their work and quickly find very specific answers to their questions.”

Near-Future Research

In September, NASA announced that that a series of potentially multiple Requests for Information (RFI) are planned to be released as a part of the NASA UAS integration in the NAS Project that involve small UAS (sUAS). Earlier project work has been focused on larger UAS like the Predator. According to the agency, these RFIs will place a special emphasis on the evaluation of key sUAS autonomy technologies that can be used to for future sUAS missions in the NAS.