The AFRL requires sub-nanosecond synchronization of drone swarms via atomic clocks to operate without GPS.
The U.S. Air Force Research Laboratory (AFRL) is issuing a request for information (RFI) to design a position, navigation, timing (PNT) system that will enable swarms of small UAS/drones to operate in environments where GPS is jammed, spoofed, or unavailable. The project, called Joint Multi-INT Precision Reference (JMPR), incorporates Next Generation Atomic Clock (NGAC) technology to provide extremely accurate synchronization: stability in the order of a few picoseconds and sub-nanosecond precision. The device must meet strict size, weight, and power (SWaP) constraints, be decentralized, capable of cold-starting without an external reference, and scalable for swarm operations.
Background and challenges of the Atomic Clock for Drone Swarms project
The AFRL has published RFI number FA2377-26-R-B002. This document explains that the Navigation and Communication Branch (AFRL/RYWN) is seeking industry proposals for a testbed called Joint Multi-INT Precision Reference (JMPR). This testbed must integrate Next Generation Atomic Clock (NGAC) technology. The objective is clear: to maintain extreme time synchronization between drones when GPS can no longer be relied upon.
Detailed requirements include picosecond-level stability between platforms and sub-nanosecond accuracy. These figures reflect a very specific requirement. The system must also be resistant to electronic attacks (jamming, spoofing) and operate within SWaP constraints: reduced size, weight, and power, which is crucial for small drones.
The RFI also requires that proposals cover cold-start scenarios, i.e., the swarm starts without any external position or time reference, then refines its spatial and temporal references as it operates.
Technical data, existing capabilities, and challenges
Atomic clock and alternative capabilities
- Current atomic clocks, such as chip-scale atomic clocks (CSAC), consume a few hundred milliwatts and weigh a few dozen grams. Examples: a recent SA65-LN model operates at 295 milliwatts, is small in size (approximately 1.27 cm or half an inch in height) and operates from −40°C to +80°C.
- Optical clocks, used in metrology laboratories, achieve instabilities of around 10⁻¹⁸ after several hours of measurement. This allows for accuracies as high as a few picoseconds for certain uses.
Specific requirements of the JMPR project
- Sub-nanosecond precision: this means synchronization errors of less than 1 nanosecond between drones.
- Picosecond stability: very low temporal oscillations, to prevent temporal drifts between platforms from compromising coordination.
- Decentralized and open architecture (open PNT): no single dependency on an external signal, but inter-platform measurements, data sharing, and on-board sensors.
- Mobility, reduced SWaP: each unit must be lightweight, consume little power, and withstand harsh physical conditions.
Technical challenges to overcome
- Miniaturization: integrating a sufficiently accurate atomic clock into a drone with strict mass and energy limitations.
- Resistance to disturbances: vibrations, temperature changes, electromagnetic interference, turbulent flight conditions.
- Correction of synchronization errors due to relative movement between drones, communication delays, and latency.
- Relative navigation algorithms: in cold-start conditions, without GPS, drones must estimate their position relative to each other, create a local reference frame, while maintaining demanding temporal consistency.
Market data and trends
- The global market for alternative PNT systems is growing rapidly. The governments of the United States, the European Union, and China are investing in redundant systems to ensure the continuity of critical services. For example, the NTIA (United States) report lists numerous space-based, ground-based, or independent solutions capable of supporting or replacing GNSS services in compromised scenarios.
- The market for miniaturized atomic clocks, such as CSACs, is expected to grow at a high compound annual growth rate (CAGR) during the period 2023-2030, driven by demand from the military, communications, data centers, and the space sector.
- Innovation in metrology: optical clocks are advancing, with laboratories achieving uncertainties of 10⁻¹⁸ or better, paving the way for redefining official time in certain uses.
Expected consequences of successful implementation
On military operations
- Swarms of drones capable of operating in GPS-denied or GPS-jammed areas, rendering the jamming and spoofing tactics employed by adversaries less effective.
- Greater consistency between drones for complex tactical missions: coordinated targeting, sensor sharing, adaptive trajectories depending on the environment.
- Reduced dependence on satellite infrastructure or external aids, increasing the resilience of armed forces.
On national and strategic security
- States with such technology would have an advantage in electronic conflicts.
- Adversaries could seek to develop or intensify countermeasures (anti-clocks, widespread jamming, quantum interference), causing a technological escalation.
- Implications for deterrence and counter-espionage doctrines: preventing one’s own swarms from being deceived or rendered ineffective.
Civil or dual uses
- Applications in civil security, critical surveillance, and emergency response where GPS signals may be interrupted (natural disasters, isolated areas).
- Autonomous transport, delivery drones, precision agriculture: even in the civilian sector, the reliability of PNT systems is an issue, particularly in sensitive sectors.
Risks and limitations
- High development costs: prototyping, real-world testing, technical guarantees.
- Regulatory complexity: export of sensitive technologies, component control, regulations on military/dual uses.
- Potential for overconfidence: believing that a swarm can function perfectly without GPS could lead to errors if the solution does not compensate for all forms of interference or hazards.
Extrapolations: what this initiative portends for the future
- It can be predicted that within 5 to 10 years, this type of GPS-free PNT will become standard in the military equipment of technologically advanced countries.
- The convergence of metrology, defense, and quantum technology: advanced optical or atomic clocks could be integrated not only into drones, but also into other platforms: land vehicles, ships, critical infrastructure.
- International standards for synchronization, interference tolerance, and certification of atomic devices. There will be a need for testing, calibration, and certification bodies.
- Innovation in distributed synchronization protocols (algorithms, cryptography, data exchange between drones) to ensure that even in situations where some members of the swarm are lost, consistency is maintained.
Critical analysis
This AFRL project is consistent with real threats: states already using GPS jamming or spoofing. The precision targeted is to be commended: demanding picosecond performance is very ambitious. But is there room for oversizing or for poorly anticipated technological compromises?
- There is a risk that many industrial proposals will not be able to meet these specifications without exorbitant costs, or that they will be fragile in wartime conditions (storms, falls, interference).
- SWaP constraints are real: the energy available on a small drone is limited, and vibrations, extreme temperatures, and hostile environments may damage sensitive atomic components.
- Cold start is a challenge: estimating posture, relative position, and orientation without external reference requires precise inertial sensors (IMU), lidar, or vision, which adds weight and complexity.
If these challenges are overcome, the defense sector could see a significant strategic shift: more systems resistant to electronic warfare, less vulnerable to the loss of GNSS signals, and more onboard autonomy.
War Wings Daily is an independant magazine.