An Adaptive Six-Layer Safety Bubble for Non-Cooperative UAV Self-Separation

The integration of unmanned aerial vehicles (UAVs) into shared airspace requires on-board safety mechanisms for self-separation without cooperation between platforms or centralised air-traffic services. This paper proposes the UAV Safety Bubble (USB), which is a six-layer geometric model that defines an adaptive safety envelope around the UAV. Each layer corresponds to a distinct physical contribution: platform dimensions, positioning uncertainty, communication performance, wind disturbance, detection-processing latency, and avoidance manoeuvrability. The model was evaluated through 5300 closed-loop Monte Carlo simulation instances across six conflict scenarios: static-obstacle avoidance; head-to-head encounters; 90∘, 30∘, and 60∘ approaches between two dynamic UAVs; and a non-reacting-intruder case. Platform, sensing, communication, and environmental parameters were sampled from uniform distributions across operational ranges. Under these simulation assumptions, no instance produced an intrusion into the fifth layer (USB5), which was the model’s operational separation boundary. The smallest clearance between the USB5 outer edge and the obstacle’s centre of mass was 35.36 m, recorded in the 90∘ approach scenario, and the one-sided 95% upper bound on the composite intrusion probability over the 1000 independent parameter sets was 0.299%. The adaptive envelope achieved this at per-scenario median route-length overheads of 15–46% relative to nominal straight-line routes. The USB complements downstream planners by providing an adaptive no-go region. The avoidance manoeuvres evaluated are restricted to the horizontal plane; full 3D avoidance is left for future work.