Onboard Autonomous Sense and Avoid of Non-Conforming Unmanned Aerial Systems

NASA's UAS Traffic Management (UTM) concept proposes a federated, service-based traffic management system for small UAS operating at altitudes below 400 feet. Under this concept, private entities operate UTM Service Suppliers (USS) and are responsible for approval, coordination, and deconfliction of flight plans submitted by mission operators. Due to unforeseen factors, any number of off-nominal conditions could force a participating vehicle to stray from the approved flight plan and become non-conforming. NASA Langley Research Center (LaRC) conducted a series of flight tests referred to as Pathfinder 1 to demonstrate the use of onboard autonomy-enabling technologies in scenarios where a non-conforming UAS flies through the assigned airspace of another vehicle while trying to reach an emergency landing site. Two test vehicles were equipped with an onboard autonomy software developed at NASA LaRC referred to as ICAROUS (Independent Configurable Architecture for Reliable Operation of Unmanned Systems). ICAROUS's autonomous sense and avoid (SAA) and geofence conformance capabilities were tested and demonstrated in the Pathfinder 1 flight tests. In these flight tests, the two aircraft initially follow flight plans that have been previously approved by a USS and determined to be conflict-free. During the flight, a scripted emergency scenario is triggered, requiring one vehicle to make an emergency landing using an onboard application named Safe2Ditch to select the best landing site. A straight-line path to the landing site would cause the UAS to become non-conforming and cross directly through the airspace of the other UAS, creating an elevated risk of collision. Two methods of autonomous onboard conflict resolution were tested to resolve this scenario and prevent collision. In the first method, the nonconforming vehicle flew directly to the landing site, passing through the airspace of the conforming vehicle. The conforming vehicle used ICAROUS's SAA capability to autonomously deviate from its flight plan to maintain a well-clear distance of 500 feet then returned to the flight plan once the conflict had passed. In the second resolution method, a keep-out geofence was placed 500 feet around the flight plan of the conforming vehicle. The non-conforming vehicle used ICAROUS to plan a route to the landing site that respected the geofence and thus maintained a safe separation from the airspace of the conforming vehicle. This paper also reports on the use of FLARM (Flight Alarm), a vehicle-to-vehicle position communication technology that transmits on 915 MHz, to provide traffic vehicle position data for onboard SAA.