This paper focuses on a hardware-in-the-loop facility aimed at real-time testing of architectures and algorithms of multisensor sense and avoid systems. It was developed within a research project aimed at flight demonstration of autonomous non-cooperative collision avoidance for Unmanned Aircraft Systems. In this framework, an optionally piloted Very Light Aircraft was used as experimental platform. The flight system is based on multiple-sensor data integration and it includes a Ka-band radar, four electro-optical sensors, and two dedicated processing units. The laboratory test system was developed with the primary aim of prototype validation before multi-sensor tracking and collision avoidance flight tests. System concept, hardware/software components, and operating modes are described in the paper. The facility has been built with a modular approach including both flight hardware and simulated systems and can work on the basis of experimentally tested or synthetically generated scenarios. Indeed, hybrid operating modes are also foreseen which enable performance assessment also in the case of alternative sensing architectures and flight scenarios that are hardly reproducible during flight tests. Real-time multisensor tracking results based on flight data are reported, which demonstrate reliability of the laboratory simulation while also showing the effectiveness of radar/electro-optical fusion in a non-cooperative collision avoidance architecture. 1. Introduction Following the most important guidelines about Unmanned Aircraft Systems (UAS) integration into civil airspace, the onboard avionics of these aircraft has to include a Sense and Avoid (S&A) system that is capable of replacing the human pilot in performing visual collision threat detection and avoidance [1–3]. Therefore, several experiences have been carried out worldwide in order to develop a system that can perform the above-mentioned function. In all these projects, the configuration comprises two subsystems:(1)the Obstacle Detection and Tracking subsystem that permits to reveal flying intruders in a selected Field of Regard and to estimate their motion;(2)the Collision Avoidance subsystem that provides Conflict Detection and Resolution capabilities. Regarding the “Sense” function, several solutions have been proposed depending on available budget and onboard resources, ranging from standalone electro-optical (EO) sensors [4–7] to integrated architectures which comprise airborne radars and collaborative systems based on broadcast information, such as TCAS and ADS-B [8–10]. Within the research
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