A new project at the University of Bath is exploring how high-altitude aircraft can harness atmospheric gravity waves, increase flight endurance and enable year-round operations.
Researchers at the university’s Centre for Climate Adaptation and Environment Research have been awarded £1.9 million from the Advanced Research + Invention Agency (ARIA) for the project, which will see the development of a ‘stratospheric sat-nav’ to help high-altitude unmanned aircraft ride atmospheric waves.
Project STRAT-NAV forms part of ARIA’s Enduring Atmospheric Platforms Programme, which is developing platforms that can remain aloft in the stratosphere for extended periods. The aim is to use these platforms to provide the high-performance communications infrastructure needed to deliver truly global connectivity, support the next generation of AI and digital services, and reduce dependence on satellites.
High-Altitude Pseudo-Satellites (HAPS) operate between 10-25km above the earth to provide remote-sensing observations or communications services. Most HAPS are solar-powered ultralight gliders with limited battery capacity onboard, and face acute power challenges.
Invisible energy highways
Atmospheric gravity waves are ripples in the atmosphere created when air is forced upwards by mountains or from deep convection. Like eagles riding thermals, STRAT-NAV will guide HAPS platforms to soar on these waves, delivering energy savings similar to carrying a 20-40% larger battery at no additional cost.
“This project is an exciting opportunity to translate our knowledge of the atmosphere into a practical tool to transform high-altitude aviation and unlock the stratosphere as an operating environment,” said Dr Neil Hindley, project lead and research fellow at the Centre for Climate Adaptation and Environment Research.
“Atmospheric gravity waves have been studied by scientists for decades, but until recently we’ve lacked the sub-km scale forecasting capability needed to predict them accurately enough to use operationally. If we can help HAPS aircraft navigate and exploit these naturally occurring energy sources, it could fundamentally change what’s possible for long-endurance HAPS flights over the UK and beyond.”
The UK’s unique position beneath the undulating jet stream, combined with the rugged mountain terrain of Wales and the Pennines and the stratospheric polar vortex that forms each winter, makes it a global hotspot for gravity wave activity.
“Exploiting stratospheric gravity waves for HAPS is a uniquely advantageous strategy for the UK due to our geography,” Hindley added. “While the available solar energy falls to a minimum during winter, this is when gravity wave activity maximises over the UK – exactly when it is needed.”
This could allow HAPS to operate year-round to provide services that so far have only been possible from satellite.
AI-based real-time forecasting
However, atmospheric gravity waves are difficult to forecast and exploit. HAPS aircraft need reliable, high-accuracy forecasts and intelligent routing systems to find and use these rising currents safely and efficiently.
STRAT-NAV will use AI-enhanced, ultra-high-resolution, real-time atmospheric modelling, validated by observations, to forecast the gravity wave field around HAPS up to 72 hours in advance. It will then use platform-specific intelligent routing algorithms to maximise gravity wave energy for soaring, while maintaining communications coverage.
The project will move from model development to field testing through observational campaigns in late 2026 and 2027, validating gravity-wave forecasts ahead of flight trials with HAPS industry partners later in the programme.
The ‘gravity wave assist’ capability is designed for use with any HAPS platform, whether they are lightweight fixed-wing aircraft or even rotary platforms, with no modifications or expensive ground infrastructure.
The STRAT-NAV project begins in September 2026.
