Modern military, aviation, and maritime operations are critically dependent on precise Positioning, Navigation, and Timing (PNT) data. For decades, the Global Positioning System (GPS) and other Global Navigation Satellite Systems (GNSS) have served as the backbone of these capabilities, enabling everything from aircraft navigation and drone guidance to vessel tracking and synchronized global communications. However, as GPS denial and deception events become more frequent and geographically widespread, the need for resilient, assured PNT (A-PNT) solutions has become urgent. Ensuring operational continuity requires a clear understanding of the causes of GNSS disruption, who is most affected, how navigation can be sustained without it, and how technologies such as A-PNT can provide protection and redundancy.

The following GPS/GNSS-denial questions outline the key dimensions of this challenge: the sources of GPS disruption, the sectors and regions most exposed, operational fallback procedures, and the A-PNT technologies and strategies designed to safeguard navigation and timing in an increasingly contested GPS environment.

Q1. What Causes GPS Disruption?

Disruption can arise from unintentional interference, deliberate hostile actions, or natural environmental factors; all of which can degrade, deny, or corrupt the signal in ways that directly impact mission assurance and operational safety.

Unintentional interference remains a common source of disruption, particularly in congested environments, like major shipping ports, airspace hubs, and coastal regions. Overpowered or poorly shielded radio frequency transmitters, such as cellular base stations, radar systems, or satellite uplinks, can unintentionally saturate or desensitize GNSS receivers. Faulty amplifiers, including “personal privacy devices” (PPDs) used illegally in vehicles to block tracking, also generate wideband noise that can overwhelm nearby receivers.

Intentional interference, including jamming and spoofing, poses a more severe and rapidly escalating threat. In the military domain, jamming may occur during electronic warfare or combat operations. Criminal organizations also exploit GPS and GNSS vulnerabilities for illicit purposes such as cargo theft, illegal fishing, or sanctions evasion using low cost jammers and spoofers to conceal location or manipulate tracking data. In aviation and maritime operations, such interference can mislead autopilot systems, distort route data, and undermine collision avoidance and surveillance systems like ADS-B and AIS, potentially leading to incidents that pose a threat to life.

Environmental and natural factors further complicate GPS reliability. Solar flares and ionospheric disturbances can alter signal transmission, particularly at high latitudes or during periods of intense space weather, resulting in signal delays or complete loss of lock.  Multipath reflections from large metallic structures, such as port cranes, vessel superstructures, or urban skyscrapers, can also distort signals and create false positional data. These effects are particularly acute in confined environments like harbors or dense airspace corridors, where reflected signals can be mistaken for valid GPS information.

Detection and characterization of GPS/GNSS disruption requires a combination of technical and procedural measures. RF power monitoring and direction finding equipment can help locate the source of interference, while incident mapping and space weather alerts support broader situational awareness. Crowdsourced interference reporting and data sharing between civil and military authorities enhance detection coverage and enable trend analysis across regions.

Q3. How do Pilots, Mariners, and Military Personnel Navigate Without GPS?

In aviation, when GPS is unavailable, aircraft revert to more traditional navigation systems and navigation aids that must be maintained as essential backups. The backbone is the Inertial Reference System (IRS)  and Inertial Navigation System (INS), which uses accelerometers and gyroscopes to continuously estimate position, velocity, and attitude. However, inertial systems suffer from drift – small sensor errors accumulate over time. To constrain that drift, pilots use periodic corrections from ground-based radio aids such as DME (Distance Measuring Equipment), VOR (VHF Omnidirectional Range), or radar updates from Air Traffic Control. When GPS integrity is lost, pilots may revert to conventional airways and non-GNSS instrument procedures, fly under visual flight rules if weather allows, or rely on approaches guided by the Instrument Landing System (ILS), NDB (Non-Directional Beacon), or local ground-based navigation aids. The FAA explicitly retains a VOR MON (Minimum Operational Network) concept to ensure aircraft can navigate via conventional VOR paths during GPS outages.

In maritime and offshore operations, GNSS denial is a severe vulnerability, particularly for dynamic positioning vessels and precise stationkeeping tasks, so ships rely on a suite of fallback systems. A gyrocompass, Doppler log, and radar-bearing fixes provide coarse navigation and heading references in coastal waters. Electronic Chart Display and Information Systems (ECDIS) allow manual plotting of fixes, and in more extended open ocean transits, celestial navigation or celestial fixes remain usable (albeit with skill). Some operators are evaluating the revival of terrestrial radio systems like eLORAN, which transmit low frequency signals over land that are much harder to jam and can serve as a GNSS backup in restricted regions.

For military operations in contested or GPS-denied environments, reliance on GNSS is particularly fragile, so hybrid navigation is essential. The U.S. Army has actively pursued pseudolite networks (ground-based “pseudo-satellites”) to preserve position information when GPS is denied. Pseudolites broadcast local ranging signals that, when integrated with an INS, give troops a reliable local positioning layer with far higher received power than spaceborne signals and therefore much better resistance to jamming at the tactical scale.

These alternative methods, however, are not without vulnerabilities or trade-offs. Inertial systems drift and must be regularly corrected; radio aids can be jammed, degraded, or decommissioned, vision-based systems fail in low visibility or featureless terrain, and acoustic or pseudolite systems have limited coverage or require infrastructure. This is why cross-training crews in traditional navigation techniques, sensor fusion architectures, and frequent calibration of INS and navigation sensors remains essential. Maintaining up to date navigation charts, ground aids, and fallback databases all help to ensure operational continuity when GNSS is degraded or denied.

Q5. How Is Iridium PNT Improving Navigational Resilience for GPS-denied Territories?

For military and security users, this shift offers critical operational advantages. LEO-PNT services delivered via the Iridium constellation provide encrypted and regionally tailored positioning, navigation, and timing data that can penetrate indoors, under canopy, or through moderate jamming. Iridium’s PNT service leverages Iridium’s 66-satellite global mesh operating in the L-band, distinct from GPS frequencies, making it far harder to disrupt with conventional jamming equipment. Because the Iridium system is already operational and uses cross-linked satellites for global coverage, it provides real time assured timing and location integrity even in contested or denied regions such as the Arctic, the Indo-Pacific, or urban RF-dense zones.

Satellite proximity to the Earth and signal strength alone, however, are not enough to secure PNT. Thus, the Iridium PNT service also incorporates cryptographic authentication to protect against spoofing and tampering. Every navigation and timing message is digitally signed, and receiving devices verify the integrity of those signatures before using the data. Unauthorized or falsified signals are rejected, ensuring that systems operate only on trusted information, delivering a far more robust and resilient service than GPS.

For commercial shipping and aviation, these LEO-based services introduce an accessible layer of resilience. In hybrid navigation, Iridium PNT works alongside GNSS and INS, enabling devices to seamlessly shift or blend inputs as signal conditions change. In maritime environments, where GPS spoofing has been documented in the Black Sea and Eastern Mediterranean, Iridium-based A-PNT can sustain dynamic positioning operations. Similarly, aviation operators can use A-PNT to maintain flight management system synchronization and prevent false positional data from compromising navigation displays.

In practice, A-PNT serves as a critical additional layer of navigation for military, maritime, and aviation operations, allowing personnel, aircraft, ships, and unmanned systems to maintain mission continuity when GNSS is compromised. The resilient and secure design of A-PNT provides operational assurance, mitigating the single point vulnerabilities of space-based GNSS and GPS navigation, and is increasingly becoming recognized for resilient navigational planning in both defense and commercial sectors.

Q7. What are the Early Warning Signs of GNSS Interference?

Early warning signs of GNSS interference are critical for maintaining operational safety across military, aviation, and maritime platforms. Onboard receivers may show a sudden loss of satellite lock, unexpected position or time jumps, or RAIM/integrity alerts in aircraft, all of which indicate potential jamming or spoofing. Unusually high or low signal-to-noise ratios, discrepancies between redundant receivers, or inconsistencies with INS, radar, Doppler logs, or visual bearings, or an Iridium PNT feed, are additional red flags.

In hybrid GNSS + INS + Iridium PNT architectures, the system can continuously compare GNSS against Iridium PNT’s independent time/location. Divergence beyond thresholds, for example, GNSS position drifting while STL-referenced dead reckoning and ship sensors remain coherent, provides early, positive indication of spoofing or severe degradation, enabling alarms, de-weighting of GNSS, or automatic failover/blending to maintain navigation continuity.

At the system level, automated controls may generate alerts: aircraft autopilots or ship dynamic positioning systems may show deviations from expected performance without an apparent environmental cause. Slowly drifting positions or erratic movements that do not match the platform’s true course may suggest spoofing rather than outright jamming. Environmental indicators, such as unusual RF activity in GNSS frequency bands or corroborating reports from nearby vessels or aircraft, can confirm the presence of interference.

In Summary

The vulnerabilities of GPS and GNSS represent a critical operational risk across military, aviation, and maritime domains. Their inherently weak signals are easily disrupted by intentional jamming, spoofing, or even natural phenomena such as solar flares and ionospheric disturbances. Real world incidents from the Black Sea to the Eastern Mediterranean and Arctic corridors have repeatedly demonstrated that overreliance on GNSS can jeopardize mission integrity, navigational safety, and the continuity of operations. To mitigate these threats, both defense forces and commercial operators should invest in A-PNT to further strengthen resilience by providing high-power, encrypted, and timing and positioning data.

The strategic imperative is clear: GNSS dependence must evolve toward a multi-layered ecosystem, integrating terrestrial and PNT technologies, procedural training, and robust reporting chains. For decision makers in defense, aviation, and commercial shipping, building resilience into PNT infrastructure has become an operational necessity for maintaining control, safety, and strategic advantage in an increasingly contested environment.

Every time your phone pings “You have arrived”, it’s easy to forget that satellites, atomic clocks and radio beams are doing the heavy lifting. For decades, GPS has been the quiet backbone of modern life, powering navigation, synchronizing telecom networks, and enabling aviation, shipping and defense operations to function effectively. But GPS dependence is starting to look fragile.

Over the last few years, the world has seen an alarming rise in deliberate GPS jamming and spoofing. In 2024, over 1,000 commercial flights a day were affected by GPS spoofing, and this is not an isolated trend. There’s growing awareness that single-source dependence on GNSS/GPS is a strategic vulnerability. The increase of jamming and spoofing incidents has sparked growing concern that GPS manipulation could be exploited for strategic or economic gain, prompting the United Nations to call for stronger safeguards against GPS satellite interference. Aviation, shipping and defense organizations need a practical, deployable alternative now – and a plan for a layered approach in the future – because the real question isn’t if GPS will fail, but what we’ll do when it does.

The Threat of Jamming and Spoofing

Put in simple terms, “jamming” means drowning satellite signals with noise so receivers can’t hear the real thing, and “spoofing” feeds false satellite signals to trick receivers into believing they’re somewhere they’re not.

Deliberate jamming and spoofing incidents are rising in aviation, commercial shipping and defense, and the consequences are no longer hypothetical. In the Baltic Sea and Gulf of Finland, reports of jamming and spoofing incidents rose from 1,225 affected shipping vessels in Q1 of 2025, to more than 5,800 affected vessels in Q2 – a 127% increase. Six years ago, in 2019, commercial vessels operating in Chinese ports around Shanghai, reported widespread GPS anomalies. Ships experienced sudden changes in reported positions, with some appearing to move erratically or vanish from tracking systems. Investigations revealed that these anomalies were due to GPS spoofing attacks which affected hundreds of vessels and disrupted port operations.

Fast forward to this year, and the Nordic and Baltic nations, including Finland, Latvia, Lithuania and Estonia, repeatedly warned about greater electronic interference from Russia disrupting communications with planes, ships and drones. In September of this year, a plane carrying European Union chief Ursula von der Leyen was forced to land in Bulgaria using paper maps after its GPS navigation systems were jammed.

These incidents alone underscore the growing vulnerability of global navigation systems and highlight the need for stronger safeguards against electronic interference in critical transportation and defense sectors.

When GPS fails in Aviation, Maritime and Defense

The Hybrid Navigation Future

With reliance on GPS across aviation, commercial shipping, and defense sectors, concerns about vulnerability to jamming, spoofing, and system outages have driven efforts to explore more resilient navigation technologies. A range of emerging solutions is shaping the future of Assured Positioning, Navigation, and Timing (A-PNT). Each alternative offers strengths and limitations, highlighting the likelihood that the future of navigation will depend on a hybrid mix rather than a single replacement for GPS.

1. Multi-constellation GNSS

Utilizing signals from multiple satellite systems increases redundancy and complicates blanket jamming – but it doesn’t solve targeted spoofing.

2. Inertial navigation systems (INS) and sensor fusion

High-grade inertial measurement units (IMUs) combined with map-matching can bridge gaps for short to medium durations. Classical INS drifts over time however, unless tightly integrated with GNSS to bound drift, and high-performance INS can be expensive.

3. eLORAN (terrestrial low-frequency radio)

eLORAN is a modernized terrestrial radio navigation system that can provide wide area PNT and is much harder to jam at scale. The UK’s Ministry of Defence is focusing its alternative positioning, navigation and timing (Alt PNT) initiative on developing “a proposal for a resilient, terrestrial, and sovereign Enhanced Long-Range Navigation (eLORAN) system to provide backup position and navigation.” In the proposal stage only, the reintroduction and deployment of eLORAN is not currently an active system for GPS resilience.

4. Quantum and advanced sensing

Quantum sensors – notably atom interferometers, quantum magnetometers and other quantum-enabled instruments – can measure motion, gravity or magnetic anomalies with extremely high precision, potentially enabling navigation without satellite signals for hours. Last year, Boeing completed the first recorded flight using quantum navigation systems to navigate across the central United States for four hours without GPS. These technologies are not available outside of testing yet, but could be an option for navigation independent of GPS in the future.

5. Assured Positioning, Navigation and Timing (A-PNT)

Unlike GNSS satellites in Medium Earth Orbit (MEO), Iridium satellites transmit PNT signals from Low Earth Orbit (LEO) that are approximately 1,000 times stronger than GPS signals, allowing them to penetrate buildings and other hard-to-reach areas. The Iridium PNT service also incorporates cryptographic authentication to protect against spoofing and tampering. Thus, unauthorized or falsified signals are rejected, ensuring that systems operate only on trusted information. To harness Iridium PNT, organizations will need compatible receivers, firmware updates and integration with existing PNT stacks. However, that effort is still easier and faster today than building a whole eLORAN network or replacing INS suites.

A Layered Approach for Future GPS Resiliency

GPS reshaped modern life and will remain vital to everyday navigation and positioning, so the right answer isn’t to replace GPS, but complement it with A-PNT. Jamming and spoofing incidents are real, growing, and in some regions, weaponized. The future of resilient navigation is a hybrid one – multiple GNSS constellations, A-PNT, and in the years to come, hardened terrestrial systems like eLORAN and robust inertial/quantum sensors.

From commercial aviation to maritime shipping, military operations to critical infrastructure, reliance on a single GNNS/GPS source exposes organizations to jamming, spoofing, and unexpected interference. The examples of disrupted flights, misreported vessel locations, and spoofed navigation systems highlight its vulnerabilities.

A layered approach to PNT is essential. Among these, Iridium PNT stands out as an immediate, resilient solution. APNT provides critical timing and location integrity that organizations can rely on while building a more comprehensive layered system. Together, those layers can make sure “You have arrived” stays true, even when someone tries to move you off course.