The UK, along with every other country globally, is becoming increasingly vulnerable. Our critical national infrastructure (CNI) is facing an array of escalating threats, including climatic change and the security implications of rising geopolitical tension as identified within the recent Strategic Defence and Security review. A significant concern is the continued over-reliance on global navigation satellite systems (GNSS) that can be compromised by both natural phenomena and bad actors.

From chemicals to defence, emergency services to finance, food to health, transport to water, effective, resilient CNI underpins every aspect of life. These industries are highly dependent on the provision of accurate position and timing information – and often that provision is provided by GNSS. Mitigation strategies are available, including GNSS-hardened systems that reduce the risk of compromise, and complementary technologies including Alternative Navigation (Alt-Nav) sensors and atomic clocks as Prof Aled Catherall discovers…

The Unseen Vulnerability

The chaos wrought by infrastructure failure in today’s interconnected world is highlighted far too frequently. When a simple fire in one substation takes out the UK’s leading airport, Heathrow, for an entire day, or a faulty software update such as CrowdStrike affecting an estimated 8.5 million companies globally, or a cyber-attack which can paralyse airlines, banks, hospitals, shops, and government services, questions are inevitably asked about resilience and redundancy of processes and procedures. Such questions are increasingly being raised about our global (over)reliance on Global Navigation Satellite Systems (GNSS) – including GPS, GLONASS, Galileo, and BeiDou – for the provision of time and position. The degradation of GNSS is simply far too easy to achieve, affecting both positioning accuracy and timing precision. While deliberate jamming of GNSS is illegal in the UK, degradation and denial can result from malicious activity, natural phenomena like solar flares, or even faults within the satellites themselves – a recent example occurred in late May 2025, when a GPS satellite (PRN 37) experienced a data format change, leading to ‘Dual/Complete GPS Failures’ on various aircraft.

In today’s modern world, industries are highly dependent on the provision of accurate position and timing information, often delivered by GNSS. Whilst the public widely recognises GNSS’s role in providing position data, its equally vital function in disseminating precise time often goes unnoticed. Yet, precise timing underpins a vast array of critical modern systems: radio and TV broadcast towers and cellular networks often rely on it for seamless transitions between coverage areas, while power grids need it for synchronised phase measurements, the financial sector for timestamping high-frequency trades, and industrial control systems for operational integrity. Many of these demand sub-microsecond-level accuracy to function efficiently and reliably. Crucially, systems designed with sole dependence on GNSS for timing render them dangerously exposed.

Moreover, GNSS degradation for position and navigation proves equally disruptive, particularly for transport. As the primary source of position information for aircraft, ships, and vehicles, GNSS is vital – its interference, for example, was the primary reason the MSC Antonia container ship ran aground in the Red Sea in May of this year. Even modern precision agriculture is reliant on GNSS for accurate positioning – and its loss would result in lower crop yields such is the entrenchment of GNSS reliance in the modern world.

The vulnerability of the UK’s CNI to GNSS degradation is gaining increasing recognition.  And, the UK government recently estimated that a GNSS outage for 24 hours would cost the UK economy over £1.4 billion.The effect of widespread satellite compromise could be catastrophic. And yet, despite awareness, discussion, and debate, vulnerability still exists. So, what can be done to provide resilience to GNSS degradation?

Building GNSS Resilience 

The first step in bolstering this resilience is to choose GNSS receivers capable of using a mix of constellations (GPS, Galileo, GLONASS, and BeiDou) across as many of their respective frequency bands (e.g., GPS L1, L2, and L5) as possible. While not a guarantee of complete resilience, this provides some redundancy against a fault in one system and significantly complicates the task of deliberate jamming or spoofing by malicious actors. A complementary method is the use of Controlled Reception Pattern Antennas (CRPAs) – these are able to null out and reject signals coming from unwanted sources (such as jammers), further improving robustness.

To achieve the greatest level of resilience, fusing information from one or more non-GNSS sources is essential. Highly stable atomic clocks provide critical timing hold-over for periods when GNSS is lost, while next-generation quantum technologies are also being explored for even more resilient timing and positioning. Similarly, inertial sensors can offer reliable short-term position hold-over. Furthermore, visual navigation systems, leveraging cameras and image processing, can provide accurate position for some applications. Even satellite signals of opportunity – like those from communication satellites (e.g., Inmarsat or Starlink), though not primarily designed for Positioning, Navigation, and Timing (PNT) – have been shown capable of enabling accurate PNT derivation.

A multi-layered approach, combining an appropriate set of diverse PNT sources with multi-constellation, multi-band GNSS receivers and even CRPAs, is essential to ensure the continuity and integrity of critical civilian infrastructure in the face of GNSS disruption. The success of such multi-layered models is dependent upon the way the diverse data sources are brought together.

True GNSS resilience demands a diverse range of sources using different sensing modalities, coupled with an intelligent fusion algorithm capable of identifying when a PNT source is degraded and dynamically prioritising which sources to use and adjusting their respective weighting.

In addition to advanced filter algorithms for data fusion, AI will likely play a key role in the next generation of high-performance data fusion solutions enabling multiple technologies to be deployed in tandem. Working together, these diverse PNT technologies can be used to build resiliency and redundancy into CNI and ensure that any individual technology can experience degradation or failure without affecting the integrity of the timing or position data and, hence, safeguard operations.

Driving Down Cost

For several applications, the technologies are available and the risk is now increasingly recognised. So, what is holding back routine implementation of GNSS resilience? Cost is, of course, a concern. A basic GNSS receiver is very cheap – incredibly so given it provides position to a few metres and time to a few tens of nanoseconds almost anywhere on the planet. Adding resilience costs. A GNSS receiver covering all constellations and bands, equipped with on-board intelligence to detect spoofing and discrepancies, costs more than a simple GNSS receiver. CRPA antennas are significantly more expensive than a basic on-chip antenna package. Similarly, technologies such as atomic clocks and navigation-grade inertial sensors are not cheap, and neither is providing large infrastructure sources such as eLoran transmitters. However, the cost of resilience pales in comparison to the cost of inaction.

It is imperative that governments and industry accelerate their commitment to investing in cost-effective resilience, including standard deployments that support plug-and-play architectures, with standardised interfaces for PNT solutions. The ability to rapidly integrate an array of third-party alternative PNT solutions will transform the cost model and allow both civilian organisations and governments to overcome one of the key barriers to safeguarding CNI today. Furthermore, access to robust simulation environments allows infrastructure owners to assess the viability of the multi-layered approach without requiring a significant up-front investment. De-risking the investment in this way transforms accessibility and removes a further barrier to leveraging multiple PNT solutions to deliver vital redundancy and resilience.

Conclusion

The escalating frequency of disruptions underscores a critical vulnerability in our interconnected world: the pervasive overreliance on GNSS for precise timing and positioning. The immediate and severe cascading consequences for CNI can lead to significant economic losses and jeopardise public safety. The often-unseen dependence on GNSS for timing presents a profound risk. While implementing robust resilience measures carries a cost, the escalating economic and societal costs of inaction, exemplified by an estimated £1.4 billion impact from a 24-hour UK GNSS outage, are far greater.

Therefore, safeguarding CNI demands a fundamental shift towards a multi-layered, diverse approach to PNT. This involves combining multi-constellation, multi-band GNSS with complementary sources like eLoran, atomic clocks, inertial systems, and other alternative navigation and timing technologies supported by intelligent fusion algorithms. Governments and industries alike must collaborate to accelerate investment in cost-effective, plug-and-play resilience solutions with standardised interfaces. By proactively embracing these “system of systems” architectures, we can ensure the continuity and integrity of essential services, mitigating the catastrophic potential of GNSS degradation and securing our future.