Unmanned Air Vehicle Airspace Access

Unmanned Aerial Vehicle The Department of Homeland Security Predator that flies within civil airspace for border patrol missions. The Predator is roughly the size of a small corporate jet.

The integration of Unmanned Aerial Vehicles (UAVs) into civil airspace requires new methods of ensuring collision avoidance. Concerns over command and control latency, vehicle performance, reliability of autonomous functions, and interoperability of sense-and-avoid systems with the Traffic Alert and Collision Avoidance System (TCAS) and Air Traffic Control must be resolved.

Under funding from the Air Force and the Department of Homeland Security (DHS), Lincoln Laboratory has been developing the modeling and simulation capabilities (Figure 1) needed to robustly evaluate proposed collision avoidance systems for UAVs.

This includes:

  • Updating airspace encounter models to reflect current airspace usage and also to include aircraft that do not carry transponders. Bayesian statistical techniques are used to estimate the distribution over possible encounters based on radar data collected throughout the United States. Sampling from this distribution produces representative encounters to use as a basis for manned and unmanned aircraft safety analysis.
  • Fast-time simulation capabilities using Lincoln’s parallel computing facility, LLGrid. The simulation tools include the ability to model TCAS surveillance and algorithms, human visual acquisition, and proposed sense-and-avoid systems for UAVs. Analysis is currently focusing on airborne radar and electro-optical sensor systems for Global Hawk.
  • Modeling and evaluation to assess the potential use of existing ground radars to provide a comprehensive traffic situation picture to UAV operators. This includes consideration of aircraft radar cross section, terrain masking, and signal refraction, in addition to multiangulation techniques for aircraft altitude estimation. Analysis of the Beale AFB, CA region has been performed for Global Hawk, and future work may include studying the airspace in the vicinity of Ft. Huachuca, AZ for Army and DHS operations, and Patuxent River, MD for Navy operations of the Global Hawk Maritime Demonstrator.
  • Developing advanced collision avoidance algorithms based on Partially Observable Markov Decision Processes (POMDPs) through collaboration with CSAIL at MIT.

Major accomplishments

Lincoln assessed the impact of command and control latency on TCAS performance on Global Hawk. This involved assessing millions of simulated encounters using several different airspace models. Latency budgets were defined for varying types of intruders and airspace altitudes. The analysis also considered the impact of flight performance characteristics of the UAV.Radar capabilities have been evaluated in the Beale AFB region near Sacramento, CA. Analysis at Lincoln determined the degree to which multiple sensors may detect and track small aircraft without transponders and provide traffic awareness to UAV operators.

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