A. Famili, C. Tomlinson and A. Otto
A2 Labs, LLC, Virginia, United States
Keywords: Passive Radar; Spaceborne Illumination; Stealth Detection; Early Threat Warning; Space Domain Awareness; AI/ML Signal Processing; Real-Time 3D Tracking
We develop TRIPWIRE (Tracking and Reconnaissance via Spaceborne Illumination for Passive Wide-area Intrusion-Responsive Enforcement), a novel passive radar architecture that leverages spaceborne illuminators and forward-scatter techniques to deliver cost-effective, stealthy, and scalable detection across the entire air and near-space domain. Unlike traditional active radar, TRIPWIRE requires no transmissions, making the system undetectable to adversaries while consuming minimal power. By exploiting commercial satellite constellations (e.g., Starlink) as illuminators of opportunity, our approach enables detection of any object between low Earth orbit (LEO) at ~550 km altitude and the ground, covering drones, fighter aircraft, ballistic and hypersonic missiles, and other stealth or anti-radar platforms that evade backscatter-based radars. Our proof-of-concept system integrates a programmable Kymeta phased-array antenna with a USRP X310 software-defined radio to lock onto satellite beacons and measure signal perturbations caused by airborne objects. We have experimentally demonstrated real-time detection of small commercial drones through amplitude dips and Doppler shifts, while theoretical analysis confirms even greater sensitivity for high-altitude and high-velocity threats. Ongoing developments include AI/ML-powered decision algorithms, fuzzy detection to minimize false alarms, and multi-receiver trilateration for 3D localization. Future extensions deploy receivers in LEO, using MEO satellites as illuminators, enabling coverage above LEO for space domain awareness.