114 Global Navigation Satellite Systems (GNSS) are spectacularly effective sources of positioning, navigation and timing (PNT) information, but they all rely on low-power, short-wavelength radio signals that are vulnerable to spoofing and jamming, so the military in particular is pushing the development of alternatives. Unsurprisingly, there is no single substitute that will work for all vehicles in all circumstances, leaving a multiplicity of candidates, writes Peter Donaldson. One of the latest to be validated in flight is the Kepler Advance system. It exploits the RF signals between a UAV and its GCS to work out the position of the former. The core technology was developed by Wavenet RF Engineering, while UAV Navigation-Grupo Oesia is responsible for the integration of the information in its estimator software, as well as evaluation of the system in operation in UAVs. Spain’s defence ministry is funding the project. Kepler Advance converts interrogation signals from the vehicle’s GCS into outgoing responses to that GCS, and then processes them at its own ground station to determine the UAV’s distance from it, the UAV’s angle relative to the station and to North, and its height above ground. Kepler Advance uses this information to determine the vehicle’s position in a data format similar to that provided by GNSS and then delivers it to the UAV’s GCS. The developers claim accuracy 40% better than unaided GNSS, resistance to jamming, thanks to its use of low probability of interception (LPI) signals and an operating frequency that is not predetermined. Spoofing is said to be unlikely, while it is unaffected by terrain or weather. Unlike inertial systems, Kepler Advance does not accumulate errors so its accuracy remains constant. Conducted in late 2024, the validation flights involved a Class 1 UAV using Kepler Advance as its sole positioning and navigation system, and they were reported to be successful. The vehicle was equipped with UAV Navigation’s Vector-600 autopilot, while the GCS was running the company’s Visionair software. In real operations, Kepler Advance will not be used in isolation, but combined with other sensors, and its output fused with those of inertial measurement units (IMUs), barometers, magnetometers, optical cameras and Lidars. This is an example of the kind of hybrid solution that industry comes up with to compensate for the effective loss of GNSS. Increasingly, such systems are enhanced by AI and machine learning to interpret sensor data dynamically using algorithms designed to recognise patterns, correct errors and adapt to unpredictable conditions in real time. Many other technologies can provide some or all the information that GNSS does, but not everything everywhere all at once. They are a mixture of improvements to long-established technologies such as INS and ground-based radio navigation systems, rapidly evolving technologies such as optical navigation (which relies on visual recognition of landmarks, celestial objects or terrain features), exploitation of signals of opportunity such as wi-fi, Bluetooth, cellular, TV or non-GNSS satellite signals, and true exotica such as pulsar-based navigation using X-ray or radio pulses from rapidly rotating neutron stars, optical star tracking, hyperfine atomic clocks and even quantum navigation (still in early development). None of these options is a magic bullet, but we can expect to see some fascinating hybrid systems tailored to a variety of operational and environmental circumstances in the years ahead. February/March 2025 | Uncrewed Systems Technology PS | Kepler Advance system Now, here’s a thing Validated in flight is the Kepler Advance system. It exploits the RF signals between a UAV and its GCS to work out the position of the former
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