Institutional Escalation: ICAO and ITU Act

The most significant development for the GNSS community may be regulatory rather than technical. In October 2025, the International Civil Aviation Organization passed a resolution condemning GNSS interference originating from both Russia and North Korea as violations of the 1944 Convention on International Civil Aviation. The following month, the ITU’s Radio Regulations Board, at its 100th meeting, again urged Russia to “immediately cease any source of harmful interference” to safety services in the Radio Navigation Satellite Service — specifically interference affecting receivers in Estonia, Finland, Latvia, and Lithuania originating from Russian territory.

The Baltic situation had intensified steadily through the year. Lithuania coordinated a letter signed by 17 EU transport and digital ministers in June 2025 calling for a coordinated European Commission response. The European Council’s own data showed aircraft GNSS interference cases in Poland rising from 1,908 in October 2024 to 2,732 by January 2025. Estonia announced in July 2025 that Russia had moved jamming equipment to a site at Kingissepp, 20 kilometers from its border, and reported that GPS jamming had caused over €500,000 in damage in the preceding three months alone. Sweden’s Department of Transport stated that interference over the Baltic was occurring “almost daily” and had spread “both geographically and in scope.”

Active Conflict: Iran, India-Pakistan, Israel

The SWF report also documents the operational deployment of GNSS interference in three distinct conflict contexts in 2025.

During Iran’s 12-day war with Israel in June 2025, Iran jammed GPS over multiple metropolitan areas to counter drone and missile threats. Iran’s Deputy Communications Minister publicly acknowledged the disruptions were “for military and security purposes.” The Maritime Information Cooperation and Awareness Center estimated that 970 ships per day experienced GPS jamming in the Strait of Hormuz during this period, causing traffic through the Strait to drop by 20 percent as vessels limited transits to daylight hours. The report adds a technically notable January 2026 data point: during protests in Iran, Starlink ground terminals were found to have had their GPS units spoofed, causing packet losses of 30 to 80 percent. Users who switched to Starlink’s internal position estimates restored connectivity; SpaceX subsequently pushed a software update to mitigate the interference.

In South Asia, during India’s Operation Sindoor against Pakistan in May 2025, Indian electronic warfare forces were deployed specifically to interfere with GNSS signals to hamper Pakistani military aircraft navigation. The report notes that GPS spoofing has since migrated from the border zone into civilian airspace: more than 10 percent of flights in the Delhi region have reported spoofing incidents, and in November 2025 interference around Indira Gandhi International Airport was severe enough to divert flights to alternate airports.

Israel, for its part, entered into a formal commitment at the ITU in late 2025 to limit RNSS-interfering transmissions to situations involving imminent threats to life or critical infrastructure, capped at 15 minutes per incident — following a July 2025 meeting with Jordan and Egypt convened under ITU auspices.

The LEO Dimension

Perhaps the most technically striking finding for GNSS engineers: the report cites Aerospace Corporation research from July 2025 indicating that GPS jamming over Ukraine has created what researchers described as “a giant hole” in GPS coverage for small LEO satellites carrying onboard GPS receivers for position, navigation, and timing. The jamming environment over a conflict zone is now affecting space-segment PNT — not just ground users.

The Secure World Foundation’s Global Counterspace Capabilities 2026 is available here.

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The satellite had reached its 10-year design life on March 10. ISRO indicated the spacecraft will remain operational for limited services, including one-way messaging, but it will no longer support standard navigation functions that depend on precise onboard timing.

Timing loss directly impacts PNT performance

Atomic clocks are the foundational element of any GNSS or regional PNT system. Navigation signals rely on nanosecond-level synchronization between satellites and user receivers; without a stable onboard clock, a satellite cannot provide accurate ranging. In practical terms, the loss of IRNSS-1F as a timing node reduces usable signal geometry and degrades overall system robustness rather than simply removing a satellite from inventory.

IRNSS-1F was launched in March 2016 as part of the original IRNSS constellation, now branded as NavIC. Its loss for navigation further compresses a system already operating with limited redundancy. Public disclosures and recent reporting indicate that only a subset of NavIC satellites are currently fully usable for positioning services, leaving less margin for fault tolerance across the regional coverage area.

Persistent clock reliability challenges

The latest failure reinforces a long-standing issue within the NavIC program: the reliability of space-qualified rubidium atomic clocks. Earlier IRNSS satellites experienced similar failures, forcing ISRO to operate the constellation conservatively and accelerate plans for replacement spacecraft. Across GNSS architectures, clock reliability is a critical determinant of system availability—satellites can remain on orbit yet become functionally irrelevant for navigation if timing degrades.

ISRO has been pursuing second-generation NavIC satellites to restore and expand capability, but progress has been uneven. The NVS-02 satellite, part of this next-generation effort, encountered issues following launch despite successful orbital insertion. At the same time, ISRO continues to invest in the broader timing infrastructure supporting NavIC, including international metrology collaborations aimed at strengthening reference time systems.

Strategic implications for sovereign PNT

The immediate effect is not a loss of NavIC service, but a reduction in resilience at a time when sovereign PNT capability is increasingly treated as critical infrastructure. NavIC was designed to reduce India’s reliance on foreign GNSS for both civilian and government applications. As jamming, spoofing and geopolitical risk reshape the PNT landscape, constellation health—particularly onboard timing integrity—becomes a primary measure of operational capability.

Timing integrity remains the system’s linchpin

The IRNSS-1F failure underscores a fundamental point: end-to-end resilience begins with stable space-segment timing. Advances in signal structure, augmentation and receiver design cannot compensate for degraded clocks in orbit. Restoring NavIC’s full capability will depend not only on replenishment launches, but on achieving durable, next-generation clock performance across the constellation.

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Over the last several days, maritime analytics providers have documented interference events affecting more than 1,000 ships in the Middle East Gulf, alongside a growing pattern of AIS anomalies and “dark” operations. At the same time, tanker and container traffic has slowed or stopped near the Strait of Hormuz, and leading war-risk insurers are withdrawing cover for the region. 

The episode illustrates in practical terms what a contested RF environment means for ships that still rely heavily on satellite-derived position for navigation, tracking and compliance.

Interference profile: GPS jamming and AIS spoofing on a regional scale

Maritime intelligence firm Windward reports that more than 1,100 vessels experienced GPS and AIS interference across the Middle East Gulf within a single 24-hour period following the outbreak of hostilities between Iran, the United States and Israel. Ships’ reported positions were displaced onto airports, inland locations in Iran and the Gulf states, and even over a nuclear power plant, producing track histories that are clearly inconsistent with physical reality. 

A parallel assessment reported by Wired, based on analysis of satellite navigation attacks since the start of the air campaign against Iran, arrives at a similar figure of roughly 1,100 ships affected, underscoring that interference is not limited to a small subset of vessels or a single narrow area. 

Dryad Global notes “heightened risk of GPS jamming and AIS spoofing” in the Gulf of Oman and Strait of Hormuz, explicitly linking recent anomalies to Iranian naval exercises and electronic warfare activity. 

Taken together, the data suggests:

• GNSS-derived position can become systematically biased over wide areas, not only momentarily lost.
• AIS tracks based on those positions may show vessels apparently transiting over land, clustered around inland targets, or moving in circular or jagged patterns that reflect repeated loss and reacquisition of signal.
• Some operators respond by switching AIS off altogether, which protects them from misinterpretation of spoofed positions but reduces visibility for collision-avoidance and traffic management.

From a PNT standpoint, this is a textbook case of how GNSS jamming and spoofing propagate through downstream systems that treat satellite position as authoritative.

Shipping, insurance and security advisories

The interference is occurring against the backdrop of a broader shipping disruption centered on the Strait of Hormuz.

Reuters reports that around 150 ships, including oil and LNG tankers, are currently stranded near the Strait of Hormuz, with at least five tankers damaged and crew casualties following drone and missile attacks. In the wake of US and Israeli strikes, Iran has announced that it is closing the strait, and many market participants now characterize conditions as a “de facto” closure of a route that normally carries about one-fifth of global oil exports and substantial volumes of gas.

In response to the increased risk:

• Major war-risk underwriters, including Gard, Skuld, NorthStandard, the American Club and others, are cancelling war-risk cover for ships operating in Gulf and Iranian waters from early March, with premiums for any residual cover rising sharply. 
• Container carriers such as Maersk and CMA CGM have begun rerouting or suspending services that would normally pass through Hormuz, adding to the reduction in commercial traffic through the area. 

On the governmental side, a recent advisory from the US Maritime Administration designates the Strait of Hormuz, Persian Gulf, Gulf of Oman and parts of the Arabian Sea as an area of active military operations and potential retaliatory strikes by Iranian forces. The advisory highlights the risk of hailing, boarding or detention of commercial vessels and directs operators to closely monitor updates and guidance from US Naval Forces Central Command. 

Although these notices are primarily focused on kinetic threats, several security circulars from P&I clubs and risk advisers now explicitly call out the likelihood of GPS interference and AIS anomalies in the region and recommend that ships treat GNSS-based position with caution when operating there. 

Implications for PNT resilience

The current pattern of events around Hormuz reinforces several points that have been discussed in standards bodies and industry forums for some time:

• GNSS reliability is not uniform. In certain strategic waterways, including parts of the Gulf and Strait of Hormuz, interference can reach a level where satellite-based positioning should be treated as advisory rather than authoritative. 
• Spoofed or displaced positions can have regulatory and commercial consequences, not just navigational ones, when automated compliance systems interpret false AIS tracks as evidence of port calls or territorial incursions. 
• “Going dark” on AIS reduces exposure to mis-located tracks but increases dependence on radar and visual watchkeeping, especially in confined waters.

For PNT system designers and policy-makers, the current situation underscores the value of alternative and complementary positioning sources, whether that means terrestrial systems, inertial aids, or hardened multi-constellation receivers, and the need to assume that in some regions, GNSS degradation will not be an exception but a recurring operating condition.

In that sense, the developments around Hormuz are less an isolated crisis than another data point in an evolving pattern: satellite navigation has become a routine instrument in regional competition, and maritime navigation practices are having to adjust accordingly.

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According to Divirod’s announcement, the deployment targeted mountainous terrain exposed to extreme rainfall and seismic activity and collected “continuous, all-weather” measurements across three areas of interest during the monitoring period. Divirod said its algorithms analyzed daily GNSS-R measurements to detect subtle changes in the ground surface, then classified observed changes into three categories: slope failure events, creep/slow-moving landslides, and temporary terrain changes often linked to rainfall or ground-moisture variations. Divirod reported detecting “hundreds” of terrain changes and correlating them with rainfall measurements and earthquake events, producing risk mapping and identification of active zones. 

A highlighted event in the release was a landslide at Hakikoga in the city of Asakura. Divirod said imagery taken on Aug. 10 and 11 showed visible slope changes during daylight, while its GNSS-R terrain change maps indicated the slope movement occurred overnight when on-site cameras could not observe the event due to darkness; Divirod reported its sensors registered a spike in ground movement associated with the terrain shift. 

GNSS-R, sometimes described as “bistatic radar of opportunity,” is a passive remote-sensing technique that uses reflected GNSS signals to infer properties of the reflecting surface. In spaceborne applications it has been used for ocean and land remote sensing (including soil moisture and other geophysical parameters), with the “passive” characteristic often cited as a differentiator versus active radar systems. Divirod positions its approach as GNSS-R sensing plus algorithms for environmental intelligence and deformation/anomaly detection in support of risk monitoring and early warning. 

Divirod CEO Javier Marti said the work demonstrates how “advanced GNSS-R solutions” can enhance early detection and situational awareness for geohazards in Japan and that the company aims to expand deployments in Japan and globally. OKI CTO and head of technology division Yoichi Kato said the joint demonstration contributes to early response to natural disasters and strengthening regional resilience, and that OKI expects to continue the partnership to enhance disaster-prevention capabilities. 

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SES, a space solutions company, and the European Union Agency for the Space Programme (EUSPA) today announced an extension of the European Geostationary Navigation Overlay Service (EGNOS) GEO-1 satellite service agreement through 2030, with an option to extend until 2032, helping maintain high-precision navigation services for aviation and other critical users across Europe.

By improving the accuracy and integrity of satellite positioning signals, EGNOS supports aircraft in landing in low-visibility conditions, as well as planning more efficient routes, reducing fuel burn and CO₂ emissions. At the core of the EGNOS service is Europe’s regional Satellite-Based Augmentation System (SBAS) that improves the accuracy and reliability of Global Navigation Satellite System (GNSS) signals, such as GPS. Beyond aviation, EGNOS supports maritime navigation and precision-driven agriculture, contributing to efficient operations and sustainability by reducing fuel consumption and emissions.

Under the extended GEO-1 contract, SES will continue operating an EGNOS hosted payload on its SES-5 satellite, as well as the ground segment from its facilities in Europe.

“This extension ensures a robust EGNOS space segment, ready for the transition towards its next version and the development of new services, while safeguarding high-precision navigation for aviation and other critical users across Europe,” said Rodrigo da Costa, EUSPA Executive Director.

“EGNOS is a cornerstone of Europe’s aviation and broader navigation applications. The agreement underscores SES’ and EUSPA’s joint commitment to advancing satellite-based services that enable secure, reliable, and sustainable navigation solutions,” said Philippe Glaesener, Senior Vice President, Global Government at SES. “Thanks to the service, millions of users and operators will benefit from efficient and more reliable air transportation services across all of Europe. This commitment reflects our broader mission of delivering resilient satellite solutions for critical infrastructures.”

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As SBAS services continue to evolve and new satellite platforms emerge, payload designers must integrate augmentation functionality within ever tighter constraints on mass, volume, power and interface compatibility.

Kongsberg Space Electronics has developed a compact, versatile SBAS onboard down converter with support from the European Space Agency (ESA). “An SBAS onboard down converter receives correction and integrity signals uplinked from ground stations to the satellite in C-band, converts them to the navigation L-band, amplifies the signal, and broadcasts it to users over a wide service area.”

Although this function is well proven, many existing designs offer limited adaptability when confronted with new frequency plans, platform interfaces or multi-channel requirements. The Kongsberg project focused on the design, and development of an engineering qualification model (EQM) suitable for SBAS payloads on geostationary satellites, with potential applicability to future medium Earth orbit (MEO) platforms.

Addressing a real need

The project results were presented at a recent ESA-hosted event by Kongsberg Product Responsible and Radio Frequency Design Lead Angelica Viola Marini, and R&D Project Manager Grunde Joheim. Their new solution employs a highly integrated yet modular architecture that enables efficient SBAS down-conversion while maintaining design flexibility. It supports both single-channel (L1) and dual-channel (L5 and E5b) SBAS configurations, with adaptable uplink and downlink frequency plans.

Modular building blocks, including C-to-L band converter hybrids, SAW filter modules, flexible frequency generation, and configurable DC/DC power conversion, allow the design to be tailored to different satellite buses without extensive redesign.

Technical performance was demonstrated through a comprehensive qualification campaign, including vibration, shock, thermal-vacuum, EMC and electrical testing. Results showed stable gain and output power over temperature, low noise figure, strong spurious suppression and good return loss, confirming suitability for operational SBAS payloads.

Importantly, the compact unit achieves this performance with a mass below 1.6 kg and a reduced envelope, directly supporting more efficient payload integration. For end users of SBAS, ranging from aviation to maritime and emerging autonomous applications, this work delivers space segment robustness, which directly translates into service availability and integrity on the ground.

The project ‘Compact versatile SBAS down converter’, was funded under ESA’s NAVISP program, aimed at strengthening the competitiveness of the European positioning, navigation and timing (PNT) industry.

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Established under a bilateral partnership between Australia’s Geoscience Australia (GA) and New Zealand’s Toitū Te Whenua Land Information NZ (LINZ), SouthPAN is the first satellite-based augmentation system (SBAS) in the Southern Hemisphere, designed to deliver next-generation PNT services across Australasia and its maritime zones.

From the outset, SouthPAN has embraced a dual-frequency multi-constellation (DFMC) SBAS architecture, explicitly augmenting both GPS and European Galileo signals (E1/E5a). This DFMC capability, when operational, along with precise point positioning via SouthPAN (PVS), will place SouthPAN in the vanguard of regional SBAS programs, offering sub-meter and potentially decimeter-level precision across land and sea without reliance on terrestrial networks.

2025 benchmarks

Late 2025 has seen the successful completion of SouthPAN’s critical design review, a pivotal systems engineering milestone validating the technical maturity of mission design and subsystem integration ahead of full scale deployment. The review was led by Lockheed Martin Australia with strategic contributions from European partner GMV, signaling SouthPAN is on track for integration and testing phases towards safety-of-life SBAS certification by 2028.

On the occasion of the completion of the review, Myra Sefton, Head of the SouthPAN Branch at Geoscience Australia, stated, “This milestone underlines our commitment to providing navigation solutions that significantly enhance safety, efficiency, and innovation across Australia, New Zealand, and beyond. SouthPAN exemplifies effective international collaboration, setting a global standard in satellite navigation infrastructure.”

Also in 2025, Australia and New Zealand expanded SouthPAN’s space segment through a A$252 million contract with Viasat. The agreement extends earlier arrangements originally signed with Inmarsat, which has since been acquired by Viasat, and ensures long-term access to geostationary satellite payloads needed to broadcast SouthPAN correction signals.

DFMC born and bred

SouthPAN’s DFMC service augments both GPS and Galileo, closely aligning with emerging dual-frequency, multi-GNSS standards promoted in Europe and through ICAO.

While it has remained largely in the background of global GNSS discourse, SouthPAN stands apart because it was designed from the outset as a DFMC system, not an upgrade of a single-frequency, single constellation, legacy architecture. By natively integrating both constellations for Southern Hemisphere conditions and supporting SBAS and PPP services, it serves as an early testbed for next-generation augmentation.

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Although the second iteration of the EU-Latin America and Caribbean Aviation Partnership Project (EU-LAC APP II) formally concluded in September 2025, participating governments and regional organizations have expressed a clear intention to continue cooperation under a prospective EU-LAC APP III, identifying SBAS as a priority area for sustained technical and institutional engagement.

Ongoing progress has built on momentum generated by an EASA-supported regional workshop held in Lima in April 2025, where participants established a permanent SBAS working group tasked with coordinating planning, technical alignment, and implementation efforts across participating states and air navigation service providers.

Activities under EU-LAC APP are organized into defined work streams, structured around six practical pillars: governance and institutional arrangements; ionospheric monitoring and modeling; demonstrator and validation testbeds; cost-benefit and financing analysis; capacity building and training; and an implementation roadmap.

EASA has highlighted the initiative’s broader impact on regulatory and operational practices, including close coordination with the International Civil Aviation Organization (ICAO). At an EU-LAC APP forum, ICAO Secretary General Juan Carlos Salazar said “The cooperation established by the project with ICAO regional offices has been unique in the world,” underscoring the depth of institutional involvement supporting continuing SBAS activities.

As of late 2025, participating stakeholders have outlined next steps focused on phased demonstrator concepts and validation testbeds, including testing of SBAS corrections and localizer performance with vertical guidance (LPV) procedures.

Why it matters

A South American SBAS would materially improve vertical guidance and precision-approach availability across regional airports, especially in terrain-challenged or remote locations. EU-LAC APP also creates a mechanism for European technical support, including sharing of expertise, standards and training, while keeping governance and ownership regional.

Industry contributors, including Spanish technology and consulting company Indra, regional air navigation service providers and European SBAS experts. A provisional timetable has demonstrator design and initial field trials ramping up by mid-2026.

Participants have also examined the potential for future regional data-sharing hubs and identified candidate pilot airports capable of supporting SBAS demonstrators, including Lima, Bogota, and Brasilia. In parallel, discussions are underway on targeted training cohorts to upskill air navigation service provider engineers and regulators.

A follow-up working group meeting is expected in early 2026 to confirm demonstrator sites, timelines, and financing approaches, and to initiate coordinated lab-to-field test campaigns at the national level.

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The ROK’s Loran-C system was installed by U.S. Forces in 1979. The ROK took over the Loran-C system from U.S. Forces in 1989 and has continually maintained the transmitters, recently upgrading them to the eLoran system. Initial Operational Capability (IOC) for eLoran was achieved in 2023.

The U.K. and France cooperated with other nations in a Loran-C network until the end of 2015. The system was dis-established in deference to the developing Galileo GNSS, which would become operational at the end of 2016. While other nations decommissioned their stations, the U.K. maintained its single transmitter for use as a timing source. The U.K. is in the process of establishing its own sovereign eLoran network of six transmitters and has allocated a first funding tranche of $93 million. French President Emmanuel Macron announced In July that his nation would join with the U.K. in providing eLoran.

As the first nation allied with the West to establish an eLoran network, the ROK has taken the initiative to begin international discussions to ensure sovereign eLoran systems are standardized to support global transportation and trade. We reached out to the ROK’s Ministry of Oceans and Fisheries, the department responsible for the nation’s eLoran system, to learn more about the country’s motivations and plans.

Q: The ROK has operated Loran for decades. What was the motivation behind the recent upgrade from Loran-C to eLoran?

A: Since 2010, ROK has intermittently experienced GPS jamming in the West Sea. In such cases, vessels become unable to receive GPS position information through their navigation equipment. Therefore, to provide resilient and robust positioning, navigation and timing (PNT) services even under GPS jamming conditions, we developed the eLoran system and built the necessary infrastructure. A pilot service is currently being conducted in the West Sea.

Q: Is the eLoran standards meeting with the U.K. and France the first of its kind?

A: Yes. We held the meeting to share each country’s policy direction and technology development status related to eLoran, and to discuss future mutual development plans.

Q: Do the ROK, U.K. and France have a shared vision for the future of eLoran?

A: In order to respond to GPS jamming incidents occurring worldwide, we shared information on eLoran technologies and policies, and discussed potential future cooperation. Through this process, we believe a consensus was built on the importance of mutual collaboration.

Q: The ROK is on the opposite side of the globe from the U.K. and France and the countries’ eLoran systems won’t interact. Why is it important to establish shared standards?

A: Due to the recent increase in radio jamming incidents, IMO, ICAO and ITU issued a joint statement in March recommending measures to strengthen resilient and robust PNT systems for the safety of vessels, aircraft and timing systems.

With the goal of advancing eLoran as a resilient and robust alternative navigation system, we discussed technical standards such as signal specifications, data formats and receiver performance.

Even if the three countries’ systems are not directly interconnected at the moment, we believe that if more countries adopt eLoran standards in the future, gradual interconnection across regions such as Europe and Asia will become possible.

Q: Will the three countries be building on the existing eLoran standards set by SAE, or proposing something new?

A: We are reviewing areas where existing technical standards developed by international organizations—such as SAE, IMO, IALA, RTCM and ITU—may need to be supplemented or expanded. Through this process, we plan to continue discussions on standardization to promote the activation of eLoran services and to facilitate a smooth user environment.

Q: Does the Far East Radio Navigation Service organization still exist and meet? Will there be eLoran standards meetings that include China and Russia?

A: ROK, China and Russia operate the Far East Radio Navigation Service [FERNS] to promote cooperation and the development of maritime safety and radio navigation aids, and this cooperation continues.

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KEIDAI IIYAMA, SAM PULLEN AND GRACE GAO, STANFORD UNIVERSITY

Interest in establishing a sustainable human presence on the Moon has grown significantly in the last 20 years, with more than 200 missions planned over the next decade. To support these activities, robust positioning, navigation and timing (PNT) services are essential both on the lunar surface and in orbit. NASA and its international partners are developing a “network of networks” known as LunaNet designed to provide communications, PNT, detection and science services across the lunar environment [1].

This article reviews current proposals for LunaNet and its international partners: Moonlight (ESA) and LNSS (JAXA). It examines the technical challenges faced by lunar PNT and highlights emerging solutions from Stanford’s Navigation and Autonomous Vehicles (NAV) Lab, including orbit determination and time synchronization (ODTS) algorithms, spreading code design, differential carrier-phase techniques, rover navigation, and autonomous fault monitoring.

LunaNet PNT Services

LunaNet envisions two classes of PNT services:

• Point-to-Point (P2P) Navigation, which delivers PNT through direct communication links between a provider and user. 

• Lunar Augmented Navigation Service (LANS), which broadcasts navigation signals—augmented forward signals (AFS)—to lunar users. LANS is the lunar counterpart to terrestrial GNSS.

To provide these services, a lunar system must overcome fundamental challenges in constellation design, ODTS, and navigation message definition. 

Key Challenges in Lunar PNT

Lunar PNT systems must address several unique challenges compared with terrestrial GNSS:

Orbital Dynamics and Satellite Geometry

Terrestrial GNSS relies on circular orbits that provide stable, global coverage. Around the Moon, however, strong third-body perturbations from Earth destabilize most circular orbits, requiring frequent station-keeping. Early deployments will also prioritize coverage of the lunar South Pole. Elliptical Lunar Frozen Orbits (ELFOs), which offer long-term stability under three-body perturbations and continuous South Pole visibility, are strong candidates for navigation satellites.

Satellite Orbit Determination and Time Synchronization (ODTS)

Accurate ODTS is essential for LANS, as errors directly propagate into user equivalent range error (UERE). Current requirements specify 40 m (95%) for position and 10 mm/s (95%) for velocity. Terrestrial GNSS achieves ODTS using ground monitoring stations distributed worldwide, but establishing an equivalent network on the Moon is prohibitively expensive in the early stages of LunaNet. Alternative frameworks must therefore rely on Earth-based ground stations or onboard ODTS approaches (e.g., exploiting GNSS sidelobe signals).

Ephemeris Message Definition

Navigation satellites broadcast orbital parameters (ephemerides) that allow users to compute satellite positions at any desired epochs. Terrestrial GNSS ephemerides are based on Keplerian elements with harmonic corrections. For lunar orbits, however, more appropriate parameterizations are required to accurately capture elliptical, perturbed trajectories while minimizing ephemeris message size. 

Reference Frames and Time Scales

Terrestrial GNSS is referenced to Earth’s geoid and GPS time. Lunar PNT requires definitions of both a geodetic reference frame and a standard time scale. Two frames are currently in use—the Mean Earth (ME) frame and the Principal Axis (PA) frame—but a single standard must be adopted or a new one established. For time reference, LunaNet proposes to define LunaNet Reference Time (LRT), aligned with the AFS signals, which will link to Coordinated Lunar Time (LTC) referenced to the lunar geoid.

Operation and Integrity Monitoring

Navigation services for safety-critical applications, such as lunar landings and human surface operations, require robust integrity monitoring. As with terrestrial GNSS, signal quality can degrade due to satellite clock drift, unflagged maneuvers, payload failures, or code–carrier incoherence. These anomalies may be detected at surface monitoring stations, onboard satellites, or by receivers using Receiver Autonomous Integrity Monitoring (RAIM). However, in the near term, lunar systems will face limited surface stations and sparse satellite visibility, complicating the application of existing integrity monitoring methods.

Receiver-Side Algorithms

Receivers must also adapt to lunar constraints. With only one or two satellites visible during early deployments, rovers cannot rely on standard snapshot solutions requiring four or more signals. Instead, receiver algorithms must integrate navigation signals with onboard sensors (e.g., IMUs, cameras) to achieve reliable localization.

Satellite Navigation Systems under Development: LCRNS (NASA), LCNS (ESA) and LNSS (JAXA)

Lunar navigation capability is being advanced in parallel by NASA, ESA and JAXA. Each agency is preparing to deploy satellites broadcasting Augmented Forward Signals (AFS) in support of the LANS. NASA’s Lunar Communication Relay and Navigation System (LCRNS), ESA’s Lunar Communications and Navigation System (LCNS) under the Moonlight program, and JAXA’s Lunar Navigation Satellite System (LNSS) will serve as the first AFS providers under the LunaNet framework.

To ensure interoperability, the agencies are coordinating through the LunaNet Interoperability Specification (LNIS), which defines common standards for service interfaces, navigation messages, and time references. The most recent update, LNIS Version 5, establishes the baseline requirements for interoperable lunar PNT services [2].

Satellite Orbits: Initial Focus on Lunar South Pole

The first operational service volume targets latitudes south of 70° up to an altitude of 200 km, reflecting the high-priority needs of lunar South Pole missions. To minimize satellite numbers while maintaining coverage and long-term orbital stability, LCRNS and LNSS plan to deploy spacecraft in elliptical lunar frozen orbits (ELFOs). ESA’s first Moonlight satellite, Lunar Pathfinder, will also be positioned in ELFO to provide early relay and navigation services.

Assets for Operation

Each agency is developing supporting infrastructure for orbit determination (OD), time synchronization (TS), and system operation:

NASA (LCRNS): 

LCRNS satellites will carry the LCRNS PNT Instrument (LPI), consisting of a GPS receiver, stable clock, and an onboard ODTS filter that estimates position, velocity and clock offset. In May, the LuGRE mission successfully demonstrated the tracking of GPS and Galileo signals in lunar orbit and on the lunar surface. NASA also plans to establish three Lunar Earth Ground Stations (LEGS) at White Sands Missile Range (WSMR) in the U.S., South Africa and Western Australia, enabling direct-to-Earth communication. With pseudorandom noise ranging and 1-/2-way X-band Doppler tracking, LEGS will support both user services and ODTS of lunar satellites.

ESA (LCNS): 

ESA has proposed ATLAS (Advanced Tracking and Location Architecture for the Moon), a dedicated tracking and timing network that integrates ground and potential lunar assets. ATLAS aims to deliver orbit and clock accuracy at the tens-of-meters and nanosecond levels, respectively. ESA also plans NOVAMOON, a differential reference station near the lunar South Pole, designed to provide decimeter-level accuracy across the region. Equipped with a Mini-RAFS clock and laser retroreflector, NOVAMOON will also serve as a lunar time and geodetic reference.

JAXA (LNSS):

JAXA plans to leverage GNSS sidelobe signals for orbit determination and synchronization, reducing ground dependency and enabling autonomous navigation in cislunar space.

Signal Design

According to the LunaNet Signal-in-Space Standard (LSIS) [3], the AFS will be broadcast at 2,492.028 MHz (2,436 times the GPS L1 C/A-code signal chipping rate), harmonized with legacy GNSS frequencies. The AFS comprises two channels:

In-phase (I) channel: A 1.023 Mcps Gold-coded BPSK sequence of length 2046, carrying data for low-complexity access. Compared with GPS C/A code, it offers an acquisition gain of ~3 dB and a tracking gain of ~1 dB.

Quadrature (Q) channel: A 5.115 Mcps BPSK pilot (no data) using a Weil sequence of length 10,230, optimized for high-precision tracking and applications such as lunar landing and surface navigation.

The navigation message uses a 250-bps data rate (5 × GPS C/A) with 1,200-bit blocks (4 × GPS C/A), providing greater flexibility for future integrity and safety-of-life services and supporting diverse lunar ephemeris representations.

Research Efforts at the Stanford NAV Lab

Lunar PNT is an active research area across many groups in academia, government and industry. Here, we focus on our ongoing research at the Stanford NAV Lab led by Prof. Grace Gao.

ODTS

NAV Lab has investigated time transfer and orbit determination algorithms for lunar navigation satellites using GNSS sidelobe signals. These signals offer a way to reduce reliance on terrestrial ground stations, but their performance is limited by (1) poor geometry (signals arriving from nearly the same direction), (2) unmodeled biases from Earth’s ionosphere and plasmasphere, and (3) large thermal noise on pseudorange measurements. To overcome these challenges, NAV Lab has pursued the following research directions:

• Feasibility study of using GNSS signals: Bhamidipati et al. first showed it is feasible to use GNSS signals for lunar satellite time transfer by developing a timing filter to correct clock estimates via intermittently available terrestrial-GPS signals [4]. She then performed case studies to analyze trade-offs among various grades of clocks and lunar orbits [5]. This enabled her to conceptualize the design of a SmallSat-based Lunar Navigation and Communication Satellite System (LNCSS) with GPS time-transfer that provides navigation and communication services near the lunar South Pole [6]. 

• Time-differential carrier phase (TDCP): TDCP measurements can cancel most slowly varying delays and provide millimeter-level range-rate accuracy. Iiyama et al. demonstrated that, by jointly processing pseudorange and TDCP with adaptive state noise compensation and a cycle slip detector, significant performance improvements were achieved [7].

• Sensor fusion with complementary measurements: Vila et al. investigated fusing GNSS sidelobe signals with inter-satellite ranging and optical navigation (horizon detection from onboard cameras). This diversifies measurement geometry and reduces dilution of precision [8].

• Modeling ionospheric and plasmaspheric delays: Iiyama et al. analyzed GNSS signal delays in lunar orbit using the Global Core Plasma Model (GCPM). Results show that main-lobe signals grazing Earth’s ionosphere (tangential altitudes below ~1,000 km) can experience delays up to 100 to 200 m, highlighting the importance of bias mitigation [9].

Ephemeris Design

Ephemeris parameterization for lunar navigation satellites must strike a balance between high-accuracy orbital representation and compact message size. The latest LSIS requirements specify 40 m (95%) position accuracy and 10 mm/s (95%) velocity accuracy, with about 900 bits available for ephemeris data in each navigation frame.

We presented one of the earliest studies on ephemeris parameterization for lunar orbits (ELFO and LLO), proposing Chebyshev polynomial representations [10]. By tuning the polynomial degree, the trade-off between fitting accuracy and message size can be optimized. The study showed feasible representations covering more than half an ELFO orbital period exist, particularly near apoapsis, making Chebyshev polynomials a strong candidate for operational ephemeris encoding.

Spreading Code Design

We developed efficient methods for designing families of binary spreading codes [11]. We cast code design as minimizing a convex function of the codes’ auto- and cross-correlation values, subject to constraints. We propose a bit-flip descent algorithm capable of quickly finding codes with good correlation properties. We also show the problem of optimizing over subsets of code entries while keeping others fixed can be formulated as a mixed-integer program. This approach enables block coordinate descent methods that can, in each iteration, simultaneously optimize over tens of code entries more quickly than brute force search. 

We also extended this approach to account for Doppler effects by optimizing an expected objective over a continuous frequency distribution. We evaluated our methods on examples that include Lunar ELFO constellations. Our methods matched or exceeded more sophisticated baselines, including natural evolution strategies, genetic algorithms, and classical Gold/Weil codes. 

Single-Satellite Doppler-Based Positioning (Endurance Mission)

For missions preceding full deployment of LANS AFS, alternative navigation strategies are required. One case is NASA’s Endurance rover, which will traverse ~2,000 km across the lunar far side. Coimbra et al. investigated rover localization by opportunistically exploiting Doppler shifts from the Lunar Pathfinder’s communication downlink, despite the spacecraft lacking a dedicated navigation payload [12]. Results showed that with Doppler-only navigation, the Endurance rover can achieve sub-10 m average positioning accuracy (when stationary) within two orbital periods of Lunar Pathfinder, providing a promising solution for early surface missions.

Clock Fault Detection Using Rigid Graphs

Integrity monitoring is critical for lunar navigation systems, which must detect and exclude faulty satellites. In [13], NAV Lab designed a clock fault detection algorithm using inter-satellite ranging, independent of prior ephemeris or lunar surface monitoring (both of which may be unavailable in early deployments). The method models the constellation as a graph, where satellites are vertices and inter-satellite links are edges. A malfunctioning onboard clock’s phase jump introduces range biases that make the graph unrealizable in 3D space. By searching for redundantly rigid subgraphs (rigid even after removing any vertex) and evaluating the singular values of Euclidean distance matrices from measured ranges, faulted satellites can be isolated and excluded.

Mapping and Path Planning for Lunar Rovers

Lunar rovers face hazardous, unstructured terrain and extreme lighting conditions that degrade perception. To advance autonomous navigation, NAV Lab participated in the NASA Lunar Autonomy Challenge managed by APL under the Lunar Surface Innovation Initiative (LSII). The challenge used a high-fidelity simulator (Unreal Engine + CARLA) with realistic rover dynamics and photorealistic lunar terrain. NAV Lab developed a full-stack autonomous agent integrating semantic perception, stereo visual odometry, pose-graph SLAM with loop closures, and hierarchical path planning [14]. The system achieved robust mapping and localization across diverse simulated conditions, culminating in a first-place finish in the final competition evaluation.

Open-Source Simulator Development (LuPNT)

To support the growing lunar PNT research community, NAV Lab has developed LuPNT, a comprehensive open-source simulation framework [15]. Implemented primarily in C++ for efficiency and with Python bindings for usability, LuPNT integrates astrodynamics, communication, and PNT modules in a unified platform. Key capabilities include ODTS of lunar satellites using GNSS signals, lunar constellation and contact-plan design, inter-satellite link analysis, and surface navigation simulation via Unreal Engine. LuPNT provides a flexible, extensible toolset to accelerate algorithm development and mission design for LunaNet and future lunar PNT systems.

Summary

A reliable lunar PNT system is rapidly becoming a necessity as space agencies and industry plan hundreds of missions to the Moon. NASA, ESA and JAXA are leading with early deployments of interoperable LANS providers under the LunaNet framework, standardized through the LunaNet Interoperability Specification (LNIS). These initial constellations—leveraging elliptical frozen orbits, ground stations, GNSS receivers, and new signal designs—represent the first steps toward a sustainable lunar navigation architecture.

At the Stanford NAV Lab, research is addressing the core technical challenges of this emerging system: orbit determination and time synchronization, ephemeris representation, autonomous fault detection, and rover navigation. Open-source simulation efforts such as LuPNT further support algorithm development and mission design. Together, these deployments and academic innovations are laying the foundation for a robust lunar PNT infrastructure to enable sustained human presence on the Moon. A future column will provide more details on several of these research efforts. 

References 

[1] D. J. Israel, et al., “LunaNet: a Flexible and Extensible Lunar Exploration Communications and Navigation Infrastructure,” 2020 IEEE Aerospace Conference, Big Sky, MT, USA, 2020, pp. 1-14, doi: 10.1109/AERO47225.2020.9172509.

[2] LunaNet Interoperability Specification, Version 5, February 2025. https://www.nasa.gov/directorates/somd/space-communications-navigation-program/lunanet-interoperability-specification/

[3] LunaNet Signal-in-Space Recommended Standard, February 2025.  https://www.nasa.gov/wp-content/uploads/2025/02/lunanet-signal-in-space-recommended-standard-augmented-forward-signal-vol-a.pdf?emrc=0f6993

[4] Sriramya Bhamidipati, Tara Mina and Grace Gao, Time Transfer from GPS for Designing a SmallSat-Based Lunar Navigation Satellite System, Navigation: Journal of the Institute of Navigation. September 2022, 69 (3); DOI: 10.33012/navi.535. 

[5] Sriramya Bhamidipati, Tara Mina and Grace Gao, A Case Study Analysis for Designing a Lunar Navigation Satellite System with Time-Transfer from Earth-GPS, Navigation: Journal of the Institute of Navigation. December 2023, 70 (4); DOI: 10.33012/navi.599.

[6] Sriramya Bhamidipati, Tara Mina, Alana Sanchez, and Grace Gao, Satellite Constellation Design for a Lunar Navigation and Communication System, Navigation: Journal of the Institute of Navigation. December 2023, 70 (4); DOI: 10.33012/navi.613.

[7] K. Iiyama, S. Bhamidipati, and G. Gao, Precise Positioning and Timekeeping in Lunar Orbit via Terrestrial GPS Time-Differenced Carrier-Phase Measurements, Navigation: Journal of the Institute of Navigation. March 2024, 71(1); DOI: 10.33012/navi.635.

[8] G. C. Vila and G. Gao, Sensor Fusion for Autonomous Orbit Determination and Time Synchronization in Lunar Orbit, IEEE Aerospace Conference, Big Sky, MT, March 2025

[9] K. Iiyama and G. Gao, Plasmaspheric Delay Characterization and Comparison of Mitigation Methodologies for Lunar Terrestrial GNSS Receivers, Proceedings of the Institute of Navigation GNSS+ conference (ION GNSS+ 2025).

[10] M. Cortinovis, K. Iiyama, and G. Gao, Satellite Ephemeris Parameterization Methods to Support Lunar Positioning, Navigation, and Timing Services, Navigation: Journal of the Institute of Navigation. December 2024, 71 (4) ; DOI: 10.33012/navi.664. 

[11] A. Yang, T. Mina, and G. Gao, Spreading Code Sequence Design via Mixed-Integer Convex Optimization, Navigation: Journal of the Institute of Navigation. September 2025, 72 (3); DOI: 10.33012/navi.706.

[12] K.  M. Y. Coimbra, M. Cortinovis, T. Mina, and G. Gao, Single-Satellite Lunar Navigation via Doppler Shift Observables for the NASA Endurance Mission, Navigation: Journal of the Institute of Navigation. September 2025, 72 (3); DOI: 10.33012/navi.710.

[13] K. Iiyama, Daniel Neamati, and Grace Gao, Autonomous Constellation Fault Monitoring with Inter-satellite Links: A Rigidity-Based Approach, Proceedings of the Institute of Navigation GNSS+ conference (ION GNSS+ 2024), Baltimore, MD, Sep 2024.

[14]  A. Dai, A. Wu, K. Iiyama, G. C. Vila, K. M. Y. Coimbra, A. Carlhammar, B. Wu, and G. Gao, Full Stack Navigation, Mapping, and Planning for the Lunar Autonomy Challenge, Proceedings of the Institute of Navigation GNSS+ conference (ION GNSS+ 2025), Baltimore, MD, Sep 2025.

[15] G. C. Vila*, K. Iiyama*, and G. Gao, LuPNT: An Open-Source Simulator for Lunar Communications, Positioning, Navigation, and Timing, IEEE Aerospace Conference, Big Sky, MT, March 2025.

Authors

Keidai Iiyama is a Ph.D. candidate in the Department of Aeronautics and Astronautics at Stanford University advised by Prof. Grace Gao. He received his M.E. degree in Aerospace Engineering in 2021 from the University of Tokyo, where he also received his B.E. in 2019. His research is on positioning, navigation and timing of lunar space- craft and rovers, and system designs for lunar navigation systems. 

Grace Gao is an associate professor in the Department of Aeronautics and Astronautics at Stanford University, leading the Navigation and Autonomous Vehicles Laboratory (NAV Lab). Her research is on robust and secure positioning, navigation and timing with applications to manned and unmanned aerial vehicles, autonomous driving cars, as well as space robotics.

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