Abstract

Global Navigation Satellite System/Position, Navigation and Timing (GNSS/PNT) provides essential services in both positioning and time synchronisation, extending its application well beyond traditional navigation. Synchronised timing is now integral to distributed networks across various sectors, many of which rely on GNSS/PNT in indirect and not fully recognised ways (Government Office for Science, 2018, pp. 4-5). This growing dependence has outpaced user awareness, resulting in a “system of systems” vulnerability in which GNSS/PNT constitutes a single point of failure for multiple interconnected services (Government Office for Science, 2018, p. 5).

The fundamental technical vulnerability is that GNSS/PNT signals, upon reaching Earth's surface, have power levels significantly below ambient noise. This makes receivers susceptible to relatively minor interference, which can result not only in complete outages but also in inaccurate position or time data (Government Office for Science, 2018, p. 7). Within maritime operations, this challenge has evolved from an exceptional circumstance to a routine operational concern, as highlighted by the Royal Institute of Navigation working group: 75% of surveyed participants report interference as persistent or worsening, with noted repercussions across bridge systems, including critical safety equipment, where incorrect location data may be transmitted during emergencies (Royal Institute of Navigation, 2026, pp. 34-35). Accordingly, policy must focus on engineering resilience through diversification, robust monitoring, and reliable contingency capabilities, rather than simply increasing the number of GNSS/PNT sources, since signal weakness remains consistent across all constellations (Government Office for Science, 2018, p. 18; International Telecommunication Union, International Civil Aviation Organization and International Maritime Organization , 2025).

Introduction

GNSS/PNT has emerged as the default engineering solution for position and timing, and its widespread integration underscores the growing importance of system dependencies; it is now embedded within infrastructures that were not originally designed for simultaneous failure (Government Office for Science, 2018, p. 5). This analysis does not suggest that “GPS is broken”; rather, the vulnerability is structural and not merely theoretical. Given that GNSS/PNT signals are received below ambient noise levels, they can be readily compromised by stronger transmissions. The consequences of interference and spoofing include reduced accuracy and abrupt shifts in time or position, which can occur without generating clear alarms for end users (Government Office for Science, 2018, p. 7). Such failure modes are particularly problematic because delivering incorrect information (“wrong”) can be more operationally detrimental than providing no data at all (“absent”), especially when downstream systems rely on PNT data as authoritative (Government Office for Science, 2018, p. 7). In maritime operations, this risk is heightened as GNSS/PNT is integral not only to routine navigation, but also to distress and safety initiatives, including critical GMDSS systems. As a result, normalised or under-reported interference presents significant challenges for the sector ( International Telecommunication Union, International Civil Aviation Organization and International Maritime Organization , 2025). Survey findings from the RIN maritime report indicate that these risks are already manifesting as safety concerns, notably the possibility that SOLAS equipment could broadcast inaccurate location data if an emergency occurs amid a spoofing incident (Royal Institute of Navigation, 2026, p. 35).

An alternative perspective posits that multi-constellation receivers and modernisation efforts inherently resolve these vulnerabilities. While such advancements have improved signal availability, the inherent limitations remain: satellites provide limited power and their signals are inherently weak, meaning the associated vulnerabilities persist across platforms (Government Office for Science, 2018, p. 18). Consequently, the essential question for this newsletter is: What constitutes credible PNT resilience at the user level prior to the next disruptive event that could precipitate an unplanned test of skills? ( International Telecommunication Union, International Civil Aviation Organization and International Maritime Organization , 2025; Government Office for Science, 2018, p. 5).

GNSS/PNT Dependency, and the Quiet Risk of Relying on US GPS

Positioning, Navigation and Timing (PNT) systems are integral to contemporary society, often in ways that are not immediately apparent. These technologies underpin not only spatial awareness, “where am I?” but also the precise synchronisation of time across networks requiring accuracy. When PNT infrastructure relies primarily on space-based sources and a single system, such as GPS, predominates across numerous receivers and standards, this reliance manifests as convenience until it reveals vulnerabilities at a systemic scale (Government Office for Science, 2018, pp. 3-5; Royal Academy of Engineering, 2011, p. 12).

This does not imply that GPS is inherently fragile or that Global Navigation Satellite Systems (GNSS/PNT) are likely to fail imminently. Rather, the primary risks pertain to common-mode failures, limited resilience, and governance assumptions regarded as unchangeable (Government Office for Science, 2018, p. 5; Royal Academy of Engineering, 2011, pp. 26-27).

What GNSS/PNT Actually Is

The Global Navigation Satellite System (GNSS/PNT) determines time delay by measuring signals transmitted from satellites to receivers. When at least four satellites are accessible, the receiver calculates distances based on transmission and receipt delays, enabling it to derive accurate timing and positional information; each satellite is equipped with highly precise atomic clocks (Government Office for Science, 2018, p. 4). The resulting Positioning, Navigation, and Timing (PNT) capability delivers location, movement, and precise timing—essential for telecommunications, financial operations, transport safety systems, and industrial automation, as synchronised time is as critical to distributed infrastructure as accurate positioning (Government Office for Science, 2018, pp. 4, 16).

Consequently, GNSS/PNT serves not only as a navigation tool but also as an underlying timing utility integrated into systems that seldom highlight its role. Accordingly, disruptions and interference can manifest unpredictably; system failures frequently pertain to discrepancies in time synchronisation rather than simply loss of navigational data (Government Office for Science, 2018, pp. 5-6, 16).

The GNSS/PNT Constellations, and Who Runs Them

The principal global constellations currently in operation include GPS (United States), Galileo (European Union), GLONASS (Russian Federation), and BeiDou (China). In addition to these, there are regional systems such as QZSS (Japan) and IRNSS/NavIC (India), along with several augmentation services designed to enhance accuracy and integrity for applications, including aviation (Czaplewski & Goward, 2016, pp. 1-2). Operational ownership is significant, as it aligns policy objectives, military doctrine, and commitments with the operator's continuity. GPS, for example, is offered as a civil service free of direct user fees for global civil, commercial, and scientific use; however, it also serves as a national asset managed to meet both civil and national security requirements (Department of Defense, 2020, pp. 9, 11). Although this dual function is typical among major systems, it forms the foundation for further considerations regarding governance.

What Infrastructure Relies on GNSS/PNT/PNT

The scope of dependency extends beyond mere transport applications. The UK Government Office for Science review (2018, pp. 5, 10) highlights that numerous industries rely heavily on GNSS/PNT inputs, with mobile networks and emerging technologies such as 5G identified as sectors where timing dependency is particularly important.

Finance operates in a comparable manner, though its failure modes are less immediately apparent. Trading platforms and payment systems rely on highly accurate timestamps, comprehensive audit trails, event sequencing, and thorough reconciliation processes. The UK review details the reliance of financial services on GNSS/PNT and emphasises the crucial role that precise timing plays in maintaining transactional integrity (Government Office for Science, 2018, pp. 37-38).

Energy systems integrate elements of positioning, telecommunications, and time. The transmission and distribution of electricity rely on time synchronisation for effective monitoring and control. According to the UK review, GNSS/PNT timing plays a critical role in grid management, notably through the deployment of phasor measurement units that require synchronised timing (Government Office for Science, 2018, pp. 40-42).

Emergency services exhibit multiple layers of dependency, including dispatch and routing functions, as well as the underlying timing and communication infrastructure. The UK review specifically highlights the reliance of emergency services on satellite-derived time and positional data (Government Office for Science, 2018, p. 4).

The economic assessment is direct and data-driven. According to a UK government report, updated from previous analyses, the estimated annual benefits of GNSS/PNT to the UK economy are £13,622 million. In contrast, a disruption of GNSS/PNT is projected to result in losses of £1,424 million within the first 24 hours and £7,644 million over a seven-day period. Notably, emergency services, maritime, and road sectors collectively represent 87.6% of the seven-day impact (London Economics, 2023, pp. 5-7).

This instance does not reflect "panic economics." Rather, it represents a systematic effort to assess a dependency that has gradually developed into an established practice.

What Can Affect GNSS/PNT/PNT

GNSS/PNT signals are intrinsically weak upon arrival at the Earth's surface. The UK Government Office for Science review indicates that these signals are detected at power levels substantially below ambient noise, rendering them susceptible to even low-level interference (Government Office for Science, 2018, p. 7).

Space weather is frequently underestimated as a risk because of its abstract nature until a significant event occurs. The UK review notes that severe space weather—such as events comparable to a Carrington-level occurrence—can disable satellites for prolonged periods. Additionally, engineering literature identifies ionospheric storms as a direct threat to GNSS/PNT system performance (Government Office for Science, 2018, p. 7; Royal Academy of Engineering, 2011, p. 11).

Deliberate interference presents further significant challenges. Jamming methods, though basic, remain effective, while spoofing utilises more sophisticated techniques, requiring only a sufficiently convincing signal to mislead receiver solutions. The UK review recognises both spoofing and meaconing as major threats, while the RIN maritime report underscores how robust local transmissions can easily overpower the inherently weak GNSS/PNT signals (Government Office for Science, 2018, pp. 7, 28; Royal Institute of Navigation, 2026, p. 17).

A critical safety and environmental concern arise from the impact on essential safety systems, including GMDSS and SOLAS-mandated equipment reliant on GNSS/PNT-derived position and time. According to UN agencies, ships and ports primarily depend on GNSS/PNT for systems integral to GMDSS. The Royal Institute of Navigation's maritime report also stresses the vulnerability of SOLAS systems such as EPIRB, AIS-SART, and MOB alerting, noting that erroneous location information may be transmitted during emergencies resulting from spoofing ( International Telecommunication Union, International Civil Aviation Organization and International Maritime Organization , 2025; Royal Institute of Navigation, 2026, pp. 10, 35, 58).

Some sectors have implemented rigorous mitigation measures, including holdover oscillators, disciplined clocks, inertial sensors, and integrity monitoring. Conversely, others have not adopted these strategies, often because GNSS/PNT is integrated into timing components to minimise costs associated with holdover oscillators. Consequently, users may lack a clear understanding of their actual resilience (Government Office for Science, 2018, pp. 9, 70-71). This practice reflects a tendency towards reactive rather than proactive investment in reliability.

The Specific Worry: Could the US Tamper With GPS?

It is important to distinguish capability from intent and further delineate intent from factors subject to change.

Regarding stated intent, the GPS Standard Positioning Service (SPS) performance standard defines SPS as space-based PNT signals provided globally without direct user fees for peaceful civil, commercial, and scientific purposes. The document also clarifies that GPS is owned by the United States Government and operated by the United States Space Force (Department of Defense, 2020, pp. v, 1). The same performance standard affirms the U.S. Government’s commitment to meeting and surpassing the minimum service levels established in the SPS Performance Standard; this represents the official “continuity story” as documented, rather than inferred sentiment (Department of Defense, 2020, p. v). Historically, Selective Availability (SA) exemplifies the use of deliberate signal degradation as a policy instrument. The SPS performance standard indicates that SA has been discontinued. Furthermore, a 2007 U.S. Department of Defense news release states the intention to cease procurement of GPS satellites with the capacity to intentionally degrade civil signal accuracy, and confirms that SA was set to zero as of May 2000 (Department of Defense, 2020, p. 1; Office of the Assistant Secretary of Defense (Public Affairs), 2007).

The most substantial evidence-based argument against the possibility that "the US will degrade GPS for everyone" is the clear, publicly stated commitment to civil accessibility and minimum service levels. This is further supported by the documented elimination of Selective Availability as an intentional degradation feature in future satellites (Department of Defense, 2020, p. v; Office of the Assistant Secretary of Defense (Public Affairs), 2007, p. 1). However, the opposing argument is grounded in considerations of conditionality and regionality rather than conjecture. Although policy risk remains, it is now more reasonably viewed as conditional and region-specific. The Standard Positioning Service performance standard permits optimisation of performance to support high-priority missions within certain operational areas, while specifying that such optimisations must not reduce GPS SPS signal-in-space performance below the defined standards (Department of Defense, 2020, p. 2).

In clear terms, the credible risk is that as conflict-driven denial and interference become increasingly prevalent at the regional level, their effects may extend across borders through signal congestion and receiver vulnerabilities, potentially revealing an over-dependence among civilian users on the assumption that systems will function as they always have (Government Office for Science, 2018, p. 7; ICAO, IMO and ITU, 2024, p. 3).

The recent Gulf escalation involving Iran-associated actors illustrates how "GPS errors" manifest under heightened geopolitical tension. The UK Maritime Trade Operations (UKMTO) issued warnings regarding substantial military activity in the Arabian Gulf region and advised mariners to remain vigilant due to the increased likelihood of electronic interference, including disruptions to AIS and other navigational or communication systems (UK Maritime Trade Operations, 2026).

Subsequently, the Joint Maritime Information Center (JMIC) (2026) documented significant GNSS interference affecting approaches to the Strait of Hormuz, with reported consequences including positional inaccuracies, AIS irregularities, and intermittent signal loss. JMIC specifically identified diminished positional integrity as a factor elevating the risk of navigational incidents or miscalculations.

A recent technical alert from the flag administration highlights a significant issue: ongoing GNSS interference and jamming linked to Gulf tensions continue to pose a notable operational risk to reliance on satellite navigation. In response, resilience strategies are increasingly emphasising multi-sensor PNT systems supported by radar and traditional navigation methods—such as ranges and bearings—for integrity verification, rather than exclusive dependence on satellite technologies (Bahamas Maritime Authority, 2026, pp. 1-2).

Regarding the question of potential changes in governance due to domestic US politics, it is evident that governance arrangements may evolve, given the United States Government’s ownership and the United States Space Force’s operation of GPS (Department of Defense, 2020, p. 1). The primary operational concern is readiness for situations where GNSS produces inaccurate data, as such errors often present greater risks than total service loss (Government Office for Science, 2018, p. 7; Royal Institute of Navigation, 2026, p. 47).

How Resilience Is Being Built Globally

Resilience activities are commonly categorised into three main areas, with the emphasis placed on diversity rather than strict classification.

The first area involves multi-constellation and augmentation approaches. Modern receivers frequently utilise GPS, Galileo, GLONASS, BeiDou, and SBAS, where available, to improve service availability and potentially enhance accuracy and integrity. While these strategies contribute significantly to overall resilience, they remain susceptible to common-mode threats, such as shared-frequency-band jamming, spoofing targeting receiver logic, or ionospheric disturbances affecting multiple constellations simultaneously (Royal Academy of Engineering, 2011, pp. 26–27; Government Office for Science, 2018, pp. 18, 67).

The second category pertains to detection and monitoring initiatives. Both governmental bodies and industry stakeholders are investing in interference monitoring, reporting, and situational awareness, based on the principle that effective management requires visibility. The UK review considers detection and early warning integral to mitigation efforts, while the RIN maritime report highlights that interference monitoring supports route planning and risk management—though it may not directly counteract jamming or spoofing (Government Office for Science, 2018, p. 69; Royal Institute of Navigation, 2026, p. 25).

The third focus is alternatives and holdover solutions. For timing applications, local stability is achieved through disciplined clocks, holdover oscillators, network timing distribution, and robust architectures to prevent telecom and financial sectors from relying solely on GNSS/PNT systems. The UK review cites cases where timing holdover mechanisms avoided disruption during GNSS/PNT anomalies, and economic analysis notes that users may not perceive short outages if holdover capabilities are present (Government Office for Science, 2018, p. 31; London Economics, 2023, p. 7).

Terrestrial radio navigation, such as eLoran, is increasingly recognised for its role in resilience frameworks due to its distinct physical characteristics. Utilising signals from radio masts for position, navigation, and UTC-traceable timing, eLoran’s high-power, low-frequency transmissions are less vulnerable than low-powered microwave GNSS/PNT signals (Government Office for Science, 2018, p. 67). The RIN maritime report also describes eLoran as a long-range terrestrial PNT system independent of GNSS/PNT, with stronger transmitted signals; its value lies in diversification rather than any singular advantage (Royal Institute of Navigation, 2026, p. 86; Westbrook, 2023, p. 87).

US policy language further underscores the need for complementary PNT systems, incorporating governance, adoption, standards, testing, and monitoring measures to enhance resilience among GPS-dependent critical infrastructure (US Department of Transportation, 2023, pp. 3-4).

Ultimately, resilience requires more than simply increasing the number of satellites; it demands a range of technologies, distinct dependencies, and a variety of failure modes.

The Harder Conclusion: Over-Reliance, and the Human Skill Trade

It is common to conclude that additional support is required. This often leads to further recommendations, such as implementing backups for existing backup systems. However, this strategy may not represent the most effective solution.

The UK Government Office for Science review highlights a broader consideration: numerous systems depend indirectly on GNSS/PNT, with many users unaware of this reliance. As a result, technology can become an unseen single point of failure—an outcome of supply chain defaults rather than deliberate intent (Government Office for Science, 2018, pp. 5–6).

GNSS/PNT and automation have significantly enhanced navigation, synchronisation, logistics, and safety systems across various operational contexts. The GPS SPS performance standard confirms that GPS capabilities have consistently met or exceeded established benchmarks since initial operational capability was declared in 1993 (Department of Defense, 2020, p. 9). Nevertheless, when technology is employed to compensate for human error, operational safety improves while manual proficiency diminishes. Research in bridge operations shows that operators tend to reduce monitoring and rely more heavily on automated warning systems rather than manual checks, particularly when automation has performed reliably. Furthermore, ECDIS survey research links excessive dependence on automation to diminished situational awareness and an increased risk of human error (Lützhöft & Dekker, 2002, pp. 2, 9; Kristić, et al., 2021, pp. 1-2; Hasanspahić, et al., 2025, pp. 1-2). Should GNSS/PNT functionality be compromised—whether degraded, jammed, or subtly inaccurate—the consequence extends beyond signal loss, revealing that organisations may have lost critical skills (Royal Institute of Navigation, 2026, pp. 9, 47).

Therefore, over-reliance is a genuine concern. The issue does not stem from GPS being inherently unreliable, but from its widespread and unquestioned trust, which makes it the default response to challenges that have been addressed through multiple independent approaches. This constitutes the fundamental risk that must be managed (Government Office for Science, 2018, pp. 5–6).

References

International Telecommunication Union, International Civil Aviation Organization and International Maritime Organization , 2025. Joint Statement regarding Protection of the Radio Navigation Satellite Service from Harmful Interference. [Online] 
Available at: https://www.itu.int/en/mediacentre/Documents/2025/ICAO-IMO-ITU-Joint-Statement.pdf
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Bahamas Maritime Authority, 2026. Technical Alert 26-03 Straits of Hormuz, Persian Gulf, Gulf of Oman and Arabian Sea Military Operations, Nassau: Bahamas Maritime Authority.

Czaplewski, K. & Goward, D., 2016. Global Navigation Satellite System - Perspectives on Development and Threats to System Operation. The International Journal on Marine Navigation and Safety of the Sea Transportation, 10(2), pp. 183-192.

Department of Defense, 2020. Global Positioning System (GPS) Standard Positioning Service (SPS) Performance Standard, Washington DC: Department of Defense - Chief Information Officer.

Government Office for Science, 2018. Satellite-derived Time and Position: A Study of Critical Dependencies, London: Government Office for Science.

Hasanspahić, N., Brčić, D., Car, D. & Žuškin, S., 2025. From Paper to Digital: The Impact and Hidden Challenges of Mandatory ECDIS on Maritime Safety and Seafarer Practice. The International Journal on Marine Navigation and Safety of Sea Transportation, 19(1), pp. 1-7.

Joint Maritime Information Center, 2026. JMIC Advisory Note 01-06 March 2026, London: Joint Maritime Information Center.

Kristić, M., Žuškin, S., Brčić, D. & Car, M., 2021. Overreliance on ECDIS Technology: A Challenge for Safe Navigation. The International Journal on Marine Navigation and Safety of Sea Transportation, 15(2), pp. 277-287.

London Economics, 2023. The economic impact on the UK of a disruption to GNSS, London: UK Space Agency / Department for Science, Innovation and Technology.

Lützhöft, M. & Dekker, S., 2002. On Your Watch: Automation on the Bridge. The Journal of Navigation, 55(1), pp. 83-96.

Office of the Assistant Secretary of Defense (Public Affairs), 2007. DoD permanently discontinues procurement of Global Positioning System satellites with selective availability, Washington, DC: The White House (George W Bush).

Royal Academy of Engineering, 2011. Global Navigation Space Systems: Reliance and Vulnerabilities. 1st ed. London: Royal Academy of Engineering.

Royal Institute of Navigation, 2026. Impacts of GNSS Interference on Maritime Safety: A special report by the RIN Maritime GNSS Interference Working Group, London: Royal Institute of Navigation.

UK Maritime Trade Operations, 2026. UKMTO is aware of significant military activity, London: UK Maritime Trade Operations (UKMTO).

US Department of Transportation, 2023. Complementary PNT Action Plan: DOT actions to drive CPNT adoption, Washington, DC: US Department of Transportation.

Westbrook, T., 2023. Radiofrequency Interference Strategies Targeting Marine Navigation Systems: Political Motives and Consequences. Journal on Baltic Security, 9(1), pp. 69-97.