Invariant Corporation announced the successful integration of the FireFLY passive acoustic sensor and its artificial intelligence-driven EO/IR architecture with the Surface to Air Kinetic Engagement (STAKE) counter-unmanned aircraft system, establishing a completely passive sensor-to-effector kill chain for the detection and defeat of unmanned aerial systems.
FireFLY is a passive acoustic sensor developed jointly by Invariant Corporation and Hyperion Technology Group located in Tupelo, Mississippi.
“Small UAS have created an urgent need for distributed sensing and affordable defeat capabilities that can operate with maneuver forces in contested environments,”
said Danny Levis, Invariant President.
“FireFLY adds passive acoustic coverage where radar and RF are challenged. By integrating that passive acoustic detection directly with a proven kinetic effector, we’ve completed a sensor-to-effector kill chain that detects and defeats unmanned aerial systems without ever emitting a signal. It gets us from detection to defeat faster, with less equipment and a smaller electromagnetic footprint. Invariant identified where the battlefield is heading and built for it.”
The integrated capability uses acoustic signatures generated by UAS to detect, classify, and determine the location and altitude of an approaching aircraft without transmitting radar or radio-frequency energy. Track-quality detection data is passed directly to the kinetic system’s command-and-control architecture, providing operators with an actionable track.
The acoustic detection system automatically cues Invariant’s passive EO/IR sensor toward the area of interest. An onboard AI stack, named Drone Vision, then searches the live video, locates the UAS within the image, fuses the data, and maintains target lock as the aircraft moves through the environment, without any operator input required. The resulting track data is passed to the kinetic system’s fire control to develop a refined firing solution, supporting rapid engagement of the confirmed threat.
This layered approach combines the broad-area awareness of passive acoustic sensing with image-based EO/IR AI-enabled identification and tracking performance. Detection, classification, sensor cueing, visual target acquisition, and precision tracking can occur at the edge without an active sensor transmission, reducing the electromagnetic signature of the force.
Unlike traditional radar-dependent architectures, the Invariant solution can maintain continuous awareness without creating an electromagnetic signature that may reveal the location of friendly forces. The system is designed to complement, not replace, radar, electro-optical/infrared, and radio-frequency sensors, allowing commanders to construct a layered architecture appropriate to the mission, terrain, threat, and available resources.
In addition to supporting fully passive engagements, FireFLY can serve as a complementary sensor layer inside broader counter-UAS architectures. When active systems are constrained by radar masking, low-altitude flights, terrain, clutter, or RF-silent/wire-guided control methods, passive acoustic detection can provide an independent alert and cue other sensors or effectors toward the threat.
The integration directly addresses emerging Department of War (DoW) priorities. Recent DoW experimentation efforts have emphasized combinations of passive and active sensors, portable shooters, AI-enabled command and control, and live data networks. DoW leaders have also highlighted the operational value of passive systems that allow forces to detect threats without revealing their positions in the electromagnetic environment.
Government demand for acoustic detection is also accelerating. Recent Army market research has specifically sought acoustic capabilities for detecting small UAS, while Army operational analysis has identified persistent, low-signature passive sensing synchronized with direct-fire defeat systems as an important element of future counter-UAS formations.
The Invariant architecture reflects this evolving operational model through:
- Passive detection and classification without radar or RF transmission.
- Automated sensor-to-effector data exchange that reduces operator workload and engagement timelines.
- Modular integration with additional sensors, command-and-control systems, and kinetic or non-kinetic effectors.
- Distributed employment supporting fixed-site, mobile, and expeditionary missions.
- Improved detection opportunity against low-altitude, terrain-masked, radar-masked, or wire-guided UAS approaches
- Human-in-the-loop engagement authority consistent with applicable rules of engagement and weapons-release requirements
- Complementary integration with active radar, EO/IR, and RF sensor systems
The Department of War requested approximately $3.1 billion for counter-UAS capabilities in fiscal year 2026, reflecting the urgency of protecting maneuver forces, installations, critical infrastructure, and strategic assets from rapidly proliferating unmanned threats.
Invariant plans to continue system testing and interoperability demonstrations with U.S. government and industry partners. Future activities will focus on expanding acoustic detection coverage, integrating additional identification and tracking sensors, and connecting the architecture with government command-and-control networks.
STAKE is an integrated C-UxS system capable of kinetic defeat of Group 1-4 UAS at range. Utilizing the Advanced Precision Kill Weapon System (APKWS), coupled with a proximity fuse and fragmenting warhead, STAKE provides a cost-effective, available, and capable mechanism of defeat. At a rough cost of $30,000 per shot, STAKE dramatically improves the economics of Air Defence around the globe.
FireFLY is an acoustic sensor deployed globally that provides acoustic detection of gunshots, rocket and mortar fire, and aircraft, including unmanned aircraft. A completely passive system, FireFLY comes in multiple form factors and supports a variety of missions, from integrated base defence at military installations to aiding in crime gun investigations with local police departments.
FireFLY can serve as a fixed-site capability, while on the move or at the halt, in mounted or dismounted configurations. Utilizing a Sensor Open Systems Architecture (SOSA), FireFLY is capable of being integrated into any C2 or integrated system.
Source: Invariant Corporation