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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It will distribute highly accurate time signals from atomic clocks over terrestrial networks as a complement and backup to space-based systems. 

Terrestrial timing to complement GNSS

Announced by the Department for Science, Innovation and Technology, the investment will support the next phase of the NTC programme, led by the National Physical Laboratory (NPL). Two dedicated sites equipped with advanced atomic clocks will generate an independent national time scale and distribute it via fibre and satellite links, providing a terrestrial timing source alongside GPS, Galileo and other GNSS constellations. 

The government’s statement frames the goal clearly: reduce the UK’s reliance on satellite-delivered timing that can be “targeted and disrupted,” and ensure that critical services – including telecom networks, online banking, transport systems and emergency services – continue to function even during GNSS outages. 

Free timing over air, internet and fibre

A key feature of the NTC build-out is wide distribution. The timing signal will be provided free over the air, via the internet and through fibre networks, giving operators multiple ways to access resilient time. 

When existing timing sources fail or are degraded, the NTC infrastructure is intended to act as a safety net for “vital digital infrastructure,” from mobile base stations and financial trading platforms to energy networks and data centres. 

According to NPL, the programme is also designed to support emerging high-precision, low-latency applications such as 5G/6G networks, smart cities and connected autonomous vehicles, all of which require tightly synchronised time across distributed nodes. 

GNSS vulnerability and economic stakes

The timing expansion is explicitly framed as a resilience measure against GNSS disruption, an issue that has moved steadily up the risk agenda for PNT professionals. The UK government notes that satellite signals can be deliberately jammed or spoofed, and that an extended outage affecting timing-dependent services could cost the UK economy on the order of £1.4 billion in just 24 hours. 

Those concerns echo a wider international debate. Recent analysis has highlighted both accidental incidents – such as the 2016 GPS timing anomaly – and deliberate interference, including Russian jamming of GNSS signals in and around the Ukraine conflict, as evidence that “single-string” reliance on space-based timing is no longer acceptable for critical infrastructure. 

In that context, the NTC’s terrestrial time distribution looks less like a niche scientific project and more like a national security and economic continuity measure, similar in intent to work on eLoran, portable atomic clocks and distributed time networks in other countries. 

Atomic clocks, supply chain and skills

Beyond the network itself, a portion of the £180 million will go into the UK timing ecosystem: supporting domestic supply chains for critical timing components and expanding the skills base in precision timekeeping. 

The NTC programme will fund training for graduates, apprentices and PhD-level specialists, reflecting the fact that resilient timing is becoming a cross-cutting requirement for telecoms, finance, energy, transport and quantum technologies. 

That emphasis on both hardware and human capital is notable. GNSS timing remains central, but as more infrastructure operators move to “multi-source” architectures – combining GNSS with disciplined local oscillators, terrestrial time feeds and holdover strategies – the availability of in-country expertise and trusted components becomes a competitive and security factor in its own right.

What it means for the PNT community

For the global PNT community, the UK’s move is another concrete example of a GNSS-heavy economy investing in terrestrial timing as a first-class utility rather than a backup of last resort.

Key implications:

• Critical infrastructure operators in the UK can plan around a nationally supported, standards-based terrestrial time source instead of building bespoke solutions in isolation.
• The programme reinforces the shift toward layered PNT resilience, where GNSS is complemented by terrestrial timing, local atomic clocks and, potentially, other alternative PNT (A-PNT) technologies.
• By putting significant funding behind NPL and the NTC, the UK is signalling that precision timing is not just a scientific capability but a strategic asset, on par with national compute resources and secure telecoms. 

The development is a reminder that timing, not just positioning, is now driving major infrastructure decisions. As more countries pursue similar investments, the interplay between satellite time transfer and terrestrial time distribution is likely to become a central theme in PNT architecture and policy debates over the rest of the decade.

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DARPA has outlined new details of its Robust Optical Clock Network (ROCkN) program, describing how high-precision optical clocks could allow U.S. forces to retain GPS-grade positioning, navigation and timing (PNT) in contested environments while also enabling timing precision well beyond what space-based GNSS currently provides. The agency’s latest update, released March 2, emphasizes GPS-free operations for platforms and networks operating under jamming, spoofing or prolonged signal outages. 

Modern missiles, sensors, aircraft and artillery all depend on the nanosecond-accurate timing disseminated by GPS satellites. A timing error of just a few billionths of a second translates into position errors on the order of a meter or more, which can quickly degrade weapon accuracy and sensor coherence. Despite hardening measures, the space-to-ground link remains vulnerable to electronic attack and interference, making assured timing one of the central challenges for GNSS-dependent forces. 

ROCkN Pushes Optical Clocks From Physics Labs Into Tactical Form Factors

ROCkN’s answer is to push optical-domain timing out of the lab and into tactical-grade hardware. The program is developing two classes of clocks: a compact, shoebox-sized unit with power consumption comparable to a household lightbulb, designed to hold GPS-level timing (sub-nanosecond precision) for up to two weeks without any satellite updates; and a larger, “washing-machine”-sized master clock intended to provide a regional time reference with GPS-level precision for more than six months without resynchronization. Both clocks are being engineered under strict size, weight and power constraints for deployment on mobile or forward-based platforms. 

At the network level, ROCkN is also demonstrating over-the-air optical time-transfer techniques that push beyond GPS’ few-nanosecond accuracy. According to DARPA, recent field tests have achieved femtosecond-level synchronization over hundreds of kilometers and have operated multi-node clock networks in challenging weather, from tropical humidity to heat waves and blizzards. Moving from nanosecond to picosecond-and-better timing is expected to unlock new capabilities in distributed sensing, coherent radar and electronic warfare, as well as wideband, high-capacity communications.

Femtosecond-Level Synchronization Targets Next-Gen Sensing, EW and Comms 

The most immediate impact is in timing resilience. Optical clocks with weeks- to months-long holdover effectively create local and regional “mini-time scales” that can maintain GPS-equivalent performance through prolonged outages or deliberate interference. In practice, that means platforms and sensor networks could retain precise time tags and navigation solutions even when denied access to GPS, and could re-align with space-based systems once signals become available again. DARPA also highlights the potential for coherent synthesis of data from multiple compact, mobile sensors at frequencies beyond X-band, improving emitter geolocation and target characterization in contested spectrum. 

DARPA reports that ROCkN hardware has already been flown on fixed-wing aircraft, integrated on ground vehicles and deployed at sea for a three-week demonstration aboard a naval vessel operating in the Pacific. Over the coming year, the agency plans a series of field exercises showcasing ROCkN-enabled capabilities across next-generation PNT, electronic warfare and ISR mission sets, alongside a pilot-line manufacturing effort aimed at supplying Department of Defense transition partners. 

Taken together, ROCkN positions optical-clock-based timing as a key pillar in the broader push toward alternative and complementary PNT. For GNSS users and system designers, it underscores a strategic shift: from relying solely on space-borne signals for timing, to a hybrid model in which resilient, GPS-independent local time sources and optical time-transfer networks backstop – and ultimately extend – the performance envelope of satellite navigation.

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JUDAH LEVINE, UNIVERSITY OF COLORADO, PASCALE DEFRAIGNE, ROYAL OBSERVATORY OF BELGIUM, ILARIA SESIA, ITALIAN METROLOGY INSTITUTE, GIULIO TAGLIAFERRO, INTERNATIONAL BUREAU OF WEIGHTS AND MEASURES, MICHAEL WOUTERS, NATIONAL MEASUREMENT INSTITUTE

Coordinated Universal Time (UTC) has been recommended as the unique time scale for international reference time stamps and is the basis for civil time in most countries [1]. Time zones, which are established by local administrations, are defined by an offset from UTC. Some applications are required to use time stamps based on UTC either by regulation or by statute [2-4]. There are advantages to the use of time stamps based on UTC, even when it is not required to do so, because this facilitates combining data from multiple sources or when international coordination is important.

Time signals from global navigation satellite systems (GNSS) are widely used as the reference time in many applications, and it is important to understand the requirements that ensure GNSS time stamps are traceable to UTC from both a technical and a regulatory perspective [5]. This article describes how UTC is defined and realized and how a prediction of UTC is included in GNSS data transmissions.

The Definition and Realization of UTC 

The UTC time scale is a paper time scale that has no physical realization. It is computed monthly by the International Bureau of Weights and Measures (BIPM) based on data from several hundred atomic clocks located at National Metrology Institutes (NMIs) and other time centers in various countries. Many laboratories operate local ensembles of atomic clocks and use the data from these ensembles to compute and disseminate a local UTC estimate. This local estimate is identified as UTC(k), where k is the acronym for the laboratory. The estimate of UTC computed by the U.S. Naval Observatory (USNO) is UTC(USNO) and the estimate computed by the National Institute of Standards and Technology (NIST) is UTC(NIST). 

The computation of UTC for any month is published in BIPM Circular T by the tenth day of the following month [6]. This circular tabulates UTC-UTC(k) every five days for every participating laboratory. A rapid version of UTC, called UTCr [7], is also published by the BIPM every Wednesday. It lists daily values of UTCr-UTC(lab) through the previous Sunday. These data are published on the BIPM website and are distributed by email (Figures 1 and 2). 

GNSS Time Signals

The system time of a GNSS constellation, GNSS_T, is generated by the ground segment from an ensemble of clocks located on the ground at the control center and tracking stations. It also can include the clocks in the satellites [8-11]. Each satellite in a constellation transmits a prediction of the offset between the time of the clock on the satellite and the system time of the constellation, which is uploaded to the satellites periodically. GNSS constellations also broadcast bUTC_GNSS, a prediction of the difference between GNSS_T and UTC (including a 3-hour offset for the GLONASS system) that is derived from the UTC prediction of timing laboratories. This prediction is transmitted in two parameters: an integer giving number of whole seconds difference between UTC and the GNSS system time, and a fractional part, which specifies the difference modulo 1 s. The first parameter changes only when a leap second is inserted into UTC and not at other times. (The GLONASS constellation uses UTC as the system time so only the fraction is transmitted in the navigation message.)

For the GPS constellation, this prediction is derived from UTC(USNO) maintained at the U.S. Naval Observatory. The GLONASS constellation broadcasts a prediction based on UTC(SU), which is realized at the Russian Metrology Institute of Technical Physics and Radio Engineering (FSUE, VNIFTRI). The Galileo constellation uses a prediction derived from a collaboration of five European National Metrology Institutes. The BeiDou system uses UTC(NTSC) realized at the National Time Service center of China and UTC(NIM) realized at the China National Institute of Metrology. Regional systems also broadcast similar messages. The formats of the respective messages are GNSS-specific and are documented in the respective Interface Control Documents.

The Role of the BIPM

In addition to computing UTC and publishing the differences of UTC-UTC(k), the BIPM evaluates the difference between UTC and the predictions of UTC broadcast by the various GNSS constellations, bUTC_GNSS. These differences are published in Section 4 of BIPM circular T [6]. This section lists the difference in ns between UTC computed by the BIPM and the prediction of UTC transmitted by the GPS, GLONASS, Galileo and BeiDou satellites for every day in the monthly reporting period for that issue of Circular T. Table 1 shows the values from the August 2025 editor of Circular T interpolated from the five-day reporting interval in Circular T to a daily value at 0 UTC [12]. 

Linking User Equipment to UTC

There are two common configurations that support a link between the user’s time reference and UTC(k) or UTC. In the first configuration, the user has a clock (or an ensemble of clocks) that provides the reference signal for a GNSS timing receiver. The receiver does not discipline the free-running local clock (or ensemble) in the short term, but measures its time with respect to the signal broadcast by the satellites of some constellation. These data are combined with the data in the navigation message to (1) correct for the transit time between the satellite and the receiver, (2) include the offset between the satellite clock and the GNSS system time, and (3) add the prediction of the offset between the system time and UTC. 

Most receivers can be configured to implement these calculations in firmware, and the output data gives the difference between the local reference and the broadcast prediction of UTC. The signal from this clock (or clock ensemble) can be used in the user’s application or the application’s clock can be compared to it. The system connected to the GNSS receiver may be completely free-running and not disciplined by the GNSS data; its offset is recorded and used to adjust the downstream data. In some configurations, the time or frequency of the local reference clock is adjusted from time to time so the measured time difference is kept within some administratively defined tolerance. The interval between adjustments depends on this tolerance and on the frequency stability of the local reference, and it can range from minutes for a rubidium-based reference to hours or days for a cesium-based device. 

The second configuration, which is much more common, combines a GNSS receiver and an oscillator in a single device. There are many commercial systems that realize this configuration and often provide several outputs (5 MHz, 10 MHz and 1 pps) that are disciplined by the data received from the GNSS constellation. The simpler systems use the code data transmitted on the L1 frequency, but dual-frequency receivers and more sophisticated carrier-phase analyses are possible. The first GNSS disciplined oscillators usually used signals from the GPS constellation, but newer systems can track satellites from more than one constellation simultaneously. The output signal might be based on only the satellites from one constellation at any time or on a combination of the data received from multiple constellations. Either solution can produce significant steps in the output signals, especially in the PPS data, when the reference constellation changes. The details of the disciplining algorithm are often proprietary; the output could be disciplined to GNSS system time or to the prediction of UTC, and traceability to UTC would require the additional adjustment that incorporated the data published in BIPM Circular T. This additional adjustment, based on data from Circular T, may be small enough to ignore in some applications. 

The first configuration is more flexible; the measurement process can accept data from multiple sources, including common-view data, and implement more sophisticated post-processing methods. The adjustment process for the local reference clock can be adjusted to meet the requirements of the user’s application. The second configuration, on the other hand, may provide adequate performance in many applications. It is much simpler to operate, and this simplicity may be the deciding factor for many users.

Combining Data from Multiple Constellations

Combining GNSS signals from multiple constellations can significantly improve the timing performance of a user’s receiver, especially in locations with limited visibility of the sky. This approach requires a knowledge of the offsets between different GNSS time scales, which are at the level of a few ns and vary in time. It is possible for a user to solve for the inter-system bias between constellations [13] if enough satellites from both constellations are visible at the same time, but this is not always the case, and the broadcast values must be used [14]. The broadcast of the predicted time difference between each GNSS system time and UTC greatly simplifies the job of combining signals from multiple constellations when only broadcast data are available. The use of UTC as the common reference time scale eliminates the need for maintaining multiple inter-system bias values.

Metrological Traceability

The International Vocabulary of Metrology (VIM) defines traceability as the “property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty” [15]. The International Telecommunications Union (ITU) [16] and the International Laboratory Accreditation Conference adopted the same definition and refer to the International Organization for Standardization (ISO/IEC) standard 17025 [17].

The signals transmitted by the GNSS constellations can be traceable to UTC. The broadcast signals are linked to UTC through the UTC(k) data of a timing laboratory, and the transmissions are monitored by the BIPM with results published in Circular T. A user can also establish a common-view relationship with a timing laboratory, which can provide a near-real-time estimate of the offset of the user’s timing system with respect to the UTC(k) of that laboratory. In either case, these data are processed by the receiving system at the user’s site, and the calibration and statistical characteristics of this system directly affect the accuracy and stability of the timing data that control the user’s application. 

Timing Receiver Calibration

The calibration of the user’s equipment that is required to complete the demonstration of traceability should be performed by a method validated by a National Metrology Institute or a Designated Institute that participates in the Mutual Recognition Agreements (MRA) and have their Calibration and Measurement Capabilities (CMC) published in the Key Comparison Database maintained by the BIPM [18]. The Key Comparison Database maintains the equivalency between different organizations and guarantees the international acceptance of calibrations performed by different agencies that participate in the MRA.

The manufacturer’s published specifications can be the basis for specifying the performance of a stand-alone GNSS receiver or a GNSS receiver and disciplined oscillator combination. These specifications should be based on a calibration of one example of a particular model with some allowance for the variation among devices of the same type. For applications that require only modest accuracy (not greater than about 1 µs) a statement by the manufacturer that the device has been type-approved to that level is sufficient. The transmission delay even through a very long antenna cable is unlikely to invalidate this assumption.

The use of “type approval” may not be adequate for applications that require sub-microsecond accuracy. One method of calibrating a receiving system is to compare the output of the system to a source of UTC(k) by using a time-interval counter to monitor the difference. This method depends on an independent source of UTC(k), which might be provided by a traveling calibrated receiver, by transporting a running clock from the UTC(k) source to the location of the receiver, or by operating the device to be calibrated at a laboratory where a source of UTC(k) is available. 

Using a traveling receiver is the best choice because it tests the receiving hardware with the antenna and cables in the environment where it will be used. The BIPM uses this option to calibrate the time-transfer equipment at timing laboratories. Although the traveling receiver is calibrated, it is operated at a location where its position may not be known accurately, and where it may be influenced by multipath effects that are not the same as the effects on the device under test. These considerations are usually not important unless the required accuracy must be better than about 50 ns.

A calibration based on carrying a running clock from the source of UTC(k) to the location of the user’s equipment is feasible if the distance is not too great and the required calibration accuracy is not too high. For example, the GPS receivers at the NIST radio station in Fort Collins, Colorado, are calibrated by carrying a rubidium oscillator from the source of UTC(NIST) in Boulder to Fort Collins, a distance of about 100 km by road. The calibration is repeated by carrying a calibrated GPS receiver between the two locations. The accuracy of either method is estimated to be about 15 ns, and the two methods agree within this uncertainty.

Transporting the device under test to a location where an independent source of UTC(k) is available is usually the most difficult solution. It may be impractical to disconnect the antenna cable at the site, so a different cable must be used for the calibration. The delay through the actual cable can be estimated with a time domain reflectometer, but this method tests the cable with signals that are not the same as signals from real satellites. The impedances at the end-points are also different. 

If the system to be calibrated provides the contribution of each satellite in view to the composite output, then the common-view method can be used to calibrate the receiver. (Unfortunately, many disciplined oscillators do not provide these data.) The system to be calibrated measures the difference between the local clock (or clock ensemble) and the system time of the constellation by using the data from each satellite in view. These data are compared, satellite by satellite, with the same measurements made at a location where UTC(k) is available. The common-view difference cancels or attenuates the contributions of the satellite clock and the orbital parameters, which are common to both data sets and cancel in the differences in first order. If the distance between the locations of the user and the UTC(k) laboratory is not too great, the contribution of the ionosphere may also be common to both measurements and cancel in the difference. A multiple-frequency measurement, which can correct for the contribution of the ionosphere, may not offer a significant improvement over a simple L1 comparison in this configuration, because the contribution of the ionosphere will be cancelled or attenuated in the common-view subtraction. The common-view method can operate continuously, and can also monitor the stability of the remote system.

Frequency Calibration

The techniques described for timing calibration can also calibrate the output frequency of the user’s system. A frequency calibration can be easier to realize than a time calibration because the absolute values of the delays in the equipment are not important, only the stability of these delays is. The stability of the output frequency of a quartz oscillator may be degraded by fluctuations in the ambient temperature, and the frequency estimated with a reference based on a rubidium or cesium device may be degraded by changes in the multipath contribution.

Specific Recommendations

The documentation from the manufacturer is the best source of information about a particular device. The following specifications provide general guidance on the methods to establish traceability [19].

1. If the application can accept a fractional frequency uncertainty of 10^-8 or greater with an averaging time of one day, or a time uncertainty of 1 µs or greater, then a certificate by the manufacturer that at least one unit of the model satisfies the requirement is adequate to establish traceability at this level. (A receiver used only as the reference for a server that supports NTP, the Network Time Protocol, may not require calibration, because the accuracy and stability of the NTP service is usually limited to not better than about 1 ms by the characteristics of the network connection between the server and the client systems.) 

2. If the application requires a fractional frequency uncertainty between 10^-8 and 10^-10 with an averaging time of one day or a time uncertainty between 100 ns and 1 µs, then the manufacturer should provide a certificate with every unit that satisfies the requirement. The manufacturer could validate the performance of each unit by comparing its output with a calibrated reference unit maintained at the manufacturer’s facility. 

3. If the application requires a fractional frequency uncertain of less than 10^-10 with an averaging time of one day or a time uncertainty of less than 100 ns, then the calibration can be challenging and should be performed at the user’s facility, if possible. 

4. If the application requires a fractional frequency stability of less than 10^-12 or a time uncertainty of less than 50 ns, then the calibration should be repeated periodically or the performance of the system should be monitored by common-view or an equivalent technique, which will require a dedicated GNSS timing receiver at the user’s site. The contributions of multipath reflections and the sensitivity of the equipment to fluctuations in the ambient temperature may be important. The impact of multipath reflections can be minimized by locating the antenna so it has an unobstructed view of the sky, and by using a directional “choke ring” antenna, which attenuates signals coming from low elevations. The sensitivity to fluctuations in the ambient temperature may be a problem if the local reference device is a simple quartz oscillator or if a long antenna cable is exposed to direct sunlight. 

It is important to maintain documentation that validates the traceability of any system. Configurations that support this capability are particularly useful.

Summary and Conclusion

Applications that use the timing data from GNSS systems often require legal and technical traceability to UTC. Even when traceability is not legally required, maintaining traceability to UTC simplifies combining the data from multiple constellations. The signals transmitted by GNSS systems are monitored by the BIPM and can be made traceable to UTC by the methods discussed. Ensuring the traceability of the timing data in a user application also depends on a calibration of the receiving equipment. The methods for realizing this calibration were presented and specific recommendations provided. Maintaining adequate documentation is important, and configurations that support real-time monitoring and log files are particularly useful. 

References 

(1) Conference generale des poids et mesures (CGPM) 2018 Resolution 2 of the 26th CGPM (2018), on the definition of time scales (https://bipm.org/en/committees/cg/cgpm/26-2018)

(2) MiFiR RTS 25: https://ec.europa.eu/finance/securities/docs/isd/mifid/rts/160607-rts-25_en.pdf

(3) Finra Rule 6820: https://www.finra.org/rules-guidance/rulebooks/finra-rules/6820

(4) IEEE Standard for Synchrophasor Measurement for Power Systems, IEEE C37.118.1-2011. https://standards.ieee.org/ieee/C37.118.1/4902.

(5) Dimetrios Matsakis, Judah Levine, and Michael Lombardi, Metrological and Legal Traceability of Time Signals, Inside GNSS, March/April 2019, pp. 48-58.

(6) https://www.bipm.org/en/time-ftp/circular-t

(7) https://www.bipm.org/en/time-ftp/utcr

(8) GPS system time: https://www.gps.gov/applications/timing

(9) Galileo system time: https://www.gsc-europa.eu/GST

(10) GLONASS system time: https://www.unoosa.org/documents/pdf/icg/2020/GLONASS_Time_2017_E.pdf

(11) BeiDou system time: http://en.beidou.gov.cn/SYSTEMS/Officialdocument/202001/P020231201549662978039.pdf

(12) https://webtai.bipm.org/ftp/pub/tai/other-products/notes/explanatory_supplement_v0.8.pdf

(13) G. Huang, Q. Zhang, W. Fu and G. Guo, GPS/GLONASS time offset monitoring based on combined precise point positioning approach, Advances in Space Research, Vol. 55, number 12, 15 June 2015, pp. 2950-2960. DOI: https://doi.org/10.1016/j.asr.2015.03.003. See also references in that text.

(14) GPS-Galileo Time Offset (GGTO): https://www.unoosa.org/documents/pdf/icg/2017/wgd/wgd4-2-2.pdf

(15) https://www.bipm.org/documents/20126/54295284/VIM4_CD_210111c.pdf

(16) ITU-R, TF-686-3, Glossary and Definitions of Time and Frequency Terms p 16. https://www.itu.int/dms_pubrec/itu-r/rec/tf/r-rec-tf.686-3-201312-i!!pdf-e.pdf

(17) SO 17025:2017, General requirements for the competence of testing and calibration laboratories, https://www.iso.org/ISO-IEC-17025-testing-and-calibration-laboratories.html

(18) https://www.bipm.org/en/cipm-mra

(19) P. Defraigne, J. Achkar, M. J. Coleman, M. Gertsvolv, R. Ichikawa, J. Levine, P. Uhrich, P. Whibberley, M. Wouters and A. Bauch, Achieving traceability to UTC through GNSS measurements, Metrologia, vol. 59, Number 6, October 2022. Metrologia, 59, 064001. DOI: 10.1088/1681-7575/ac98cb.

Authors

Judah Levine is on the faculty of the Department of Physics at the University of Colorado at Boulder. He recently retired from the Time and Frequency Division of NIST, where he worked on time scales and methods of distributing time and frequency information. He is continuing those projects at the University and is also a member of committees of the International Bureau 
of Weights studying the future of Coordinated Universal Time and possible time scales for the Moon.

Pascale Defraigne obtained her Ph.D. in Geophysics in 1995 at the Université Catholique de Louvain. Since 1997, she has managed the time and frequency activities at the Royal Observatory of Belgium, where the Belgian reference UTC (ORB) is maintained. Her research activities mainly concern the use of satellite navigation systems for time and frequency transfer. Pascale presently chairs the CCTF working group on GNSS time transfer, and contributes to the validation of Galileo timing signals.

Ilaria Sesia is a Senior Researcher and Head of the Time and Frequency Department at INRiM, where she works on time transfer, atomic clocks and time scales for satellite applications. Since 2004, she has been deeply involved in the design and development of the timing aspects of the Galileo System.

Giulio Tagliaferro received his Ph.D. in 2021 from Politecnico di Milano on precise GNSS measurement adjustment. He is currently a physicist at BIPM, where he works on GNSS time-transfer activities and receiver calibration supporting the realization of UTC.

Michael Wouters leads the time and frequency group at the National Measurement Institute in Sydney, Australia. His research focuses on using low-cost GNSS receivers for time-transfer. He chairs the Consultative Committee on Time and Frequency’s task group working on the traceability of GNSS timing signals to UTC.

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Storytelling is the most powerful communication tool we have. Stories can inform and inspire. Stories can also mislead.

The biggest challenges to advancing PNT policy in the U.S. are false and misleading stories around the need for resilient PNT. These myths have frozen the nation in place for decades while our adversaries and allies have made tremendous advances. Here are some of the most pernicious and why they need to be eliminated from our discussions.

1. “GPS/GNSS is enough.” 

Of all the PNT policy myths, at least this one seems to be on the way to being dispelled.

It was certainly solidly in place in 2009. That’s when the National Space-based PNT Executive Committee’s decision to transform Loran-C to eLoran to meet a presidential mandate for a backup was overturned.

Bureaucrats, lobbyists and budgeteers refused to accept that the tens of billions of dollars invested in GPS, admittedly the most important, empowering and beneficial technology in the previous 40 years, hadn’t solved America’s utility-level PNT needs forever.

Today, most officials across the federal government familiar with the problem, including those in Congress, seem to have admitted the problem. Now, the challenges seem to be a lack of clarity about who is responsible for ensuring America has the resilient PNT it needs and how to get there.

This has likely been exacerbated by the abundance of non-GNSS PNT technologies developed in the last two decades. For some, more options seem to have made decisions more difficult.

2. “We have to (or ‘they want to’) replace GPS.”

Only someone deliberately trying to confuse things or who is entirely unfamiliar with the issues would propose “replacing GPS.”

GPS is an amazing system that will be the centerpiece of America’s PNT architecture for decades. There are an estimated 10 to 15 billion user devices across the world, far more than one for every person on the planet. GPS signals are an essential component of innumerable systems and applications. Not maintaining GPS for the foreseeable future is almost unimaginable, and certainly not practical.

Our efforts must be to complement and backup GPS/GNSS with other PNT. One or more widely adopted alternative sources will make GPS and other GNSS safer and more reliable in two ways.

First, it will “get the bullseye off GPS” by making satellites and signals much less desirable targets. If users are not impacted by interference, or impacts are greatly lessened, bad actors will have little reason to interfere. Over time, jamming and spoofing equipment will become less popular, less available and more expensive. A virtuous cycle will begin to nearly eliminate deliberate interference.

Second, users and their applications will be protected in the event of any interference with GPS/GNSS, malicious or not.

Ongoing non-malicious threats to GPS/GNSS also pose significant risk for users. 

Accidental interference, while often low level and benign, is commonplace. Europe’s STRIKE3 project detected more than 450,000 signals that could interfere with GNSS reception. Only about 10% were judged to be deliberate.

And while the probabilities of events like severe solar activity and Kessler syndrome debris damage are low, those probabilities are greater than zero.

Our efforts must be to complement and backup GPS/GNSS, not replace it.

3. “More study is needed.”

During World War II, America’s Office of Strategic Services published its “Simple Sabotage Manual” for agents embedded in adversary governments. It advised “Whenever possible refer all matters to committees for further study and consideration.”

While having more information is almost always good, looking for more when you already have enough is a classic way to avoid making decisions and taking action.

America’s growing over-dependence on GPS was formally recognized in a 1998 Presidential Decision Directive by President Bill Clinton. This resulted in the Department of Transportation’s Volpe Center producing a report in 2001 that validated a variety of concerns. It also predicted jamming and spoofing would be growing problems and recommended maintenance of terrestrial PNT capabilities.

Unfortunately, the report published only a few days before 9/11. So, it wasn’t until 2004 that President George W. Bush issued a mandate for a GPS backup. This, of course, generated another study. 

But rather than be guided by the results of that study and others and fulfilling the mandate, subsequent administrations have continued to admire the problem.

There have been more than enough studies of GPS’s vulnerabilities and technologies that can provide complementary and backup services. Major efforts have included DOT’s 2001 Volpe report, a paper by the Institute for Defense Analysis in 2009, an extensive DOD/DHS/DOT analysis in 2014 (never made public), and another report by DOT in 2021.

And yet government PNT studies and analyses continue.

Again, continually increasing our store of knowledge is good, if that is what’s happening. But merely understanding the problem better will not solve it.

Two and a half decades of studies with similar findings are enough to inform action. 

Leadership’s next steps must be establishing performance requirements for America’s resilient core PNT architecture and empowering an executive agent to ensure that architecture is put in place.

4. “It’s all about infrastructure protection.”

“Infrastructure protection” has been a buzz phrase for decades. Infrastructure is important and we must protect it with resilient PNT. That won’t do the whole job, however, because what we really want is a secure and prosperous nation.

National security means domestic resilient PNT to underpin non-
infrastructure applications like Golden Dome, UAS operations, Counter-UAS operations, the many applications used by the defense industrial base, first responders, and the list goes on. 

Likewise, there are far more contributors to the nation’s economy and prosperity beyond just infrastructure. Everything from the corner coffee shop and Uber drivers to complex factory SCADA systems need PNT.

Every American contributes to the economy in some way, and everyone needs PNT. If their PNT is not resilient, the economy and our prosperity are on a knife’s edge. 

Protecting infrastructure is necessary, but not sufficient.

5. “We just need to educate users.”

In 1964, the Surgeon General formally warned Americans about the dangers of smoking. At that time, 42% of Americans were smokers. In 1972, after eight years of warnings and education, 43% of Americans were smokers.

There is a big gap between knowing something and acting on that knowledge.

President Bush formally identified America’s lack of PNT resilience as a problem in December 2004 (and mandated a solution). President Trump issued Executive Order 13905 in February 2020 warning GPS users to get their own backup systems. Yet, in 2026 the nation’s PNT does not seem to be much more resilient.

Changing Americans’ PNT habits will require effort and expense, but most importantly leadership. Members of the National Space-based PNT Advisory Board, attendees of the September 2025 PNT Leadership Summit, and others have all concluded that leadership is the missing piece to addressing resilient PNT in the U.S.

6. “The government needs to build a GPS backup system.”

Nope. The government should not build anything. It should lead and, leveraging competition and America’s commercial sector to its best advantage, ensure something is built.

The government’s responsibility is to ensure Americans have easy access to a backup system and that it is widely adopted. There are several ways to do that including regulation, legislation, allowing public use of a system built to support government missions (ala GPS), and sponsoring a system in part or in whole.

If the latter method is selected, the process must include fair and open competition. 

There are numerous mature and commercially available PNT systems that can be had as services. Once the government establishes performance requirements, it will be a relatively simple matter to let a multi-year service contract. Competition against clear requirements will eliminate the need for endless studies and provide the best value for the public dollar. 

A long, expensive, and painful government major system acquisition must be avoided at all costs.

7. “The market will provide the GPS backup America needs. Government doesn’t need to do anything.”

This is probably the most insidious of all the myths because it speaks to traditional American values of limited government and market economics. Yet, it shows a fundamental misunderstanding of the nature of GPS and PNT.

Some misunderstanding might be due to the existing and thriving market in specialized PNT services for high demand users. When there is a business case, commercial users do regularly pay for resilient PNT. Farmers subscribe for precision agriculture. Day traders pay for resilient nano and picoseconds. Shipping terminals contract for systems that place containers within millimeters.

But GPS, while it began as a military weapons system, quickly became a public utility. One that is integrated with and benefits every aspect of the economy. Government-provided utilities are not easily subject to market forces.

Where is the business case? Why would a potential PNT provider build a national system and try to get consumers to purchase what the government is already giving them for free? 

And what would be the national benefit?

Even if such a company was to somehow survive, would enough Americans subscribe to really protect the economy from a long-term GPS outage? Would having a system that only a fraction of Americans accessed be enough to deter our adversaries from interfering or threatening to interfere with GPS and gain advantage over America?

The United States government has provided utility-level navigation since the formation of the Lighthouse Service in 1789. It has provided timing since the Naval Observatory began dropping a noon time-ball in 1845. Leaders understood that PNT is a fundamental economic driver. That’s why the Department of Commerce’s shield still features a lighthouse and why the department hosts the nation’s civil time scale at the National Institute of Standards and Technology. 

GPS is merely the most recent way the government has provided America with utility-level PNT, and it has been spectacularly successful at boosting the economy.

Claiming the government has no role or responsibility for providing a utility-level backup capability for GPS might be an honest misunderstanding.

It might also be a way some commercial interests are trying to advance their own fortunes. 

It might be how some government officials are trying to shirk what they see as difficult responsibilities.

Regardless, such claims are false and misleading. They continue to harm the nation and increase the risk to America’s security and prosperity.

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The agreement positions LEO PNT not as a standalone alternative, but as an additional signal layer that can complement or, in some cases, substitute for legacy GNSS in environments where interference, jamming and spoofing are now assumed risks rather than edge cases. Furuno explicitly links the move to the U.S. policy push on PNT resilience, including the 2020 Executive Order 13905 on responsible use of PNT services. 

LEO PNT as an engineered signal layer

Furuno describes the target architecture as a “dedicated” LEO PNT constellation in the 500–2,000 km band, on the order of a few hundred satellites, separate from non-terrestrial network (NTN) communications constellations. 

Pulsar fits that template: Xona is building a roughly 258-satellite constellation delivering dual L-band navigation signals designed to be spectrally compatible with existing GNSS services. The lower orbital altitude translates to substantially higher received power—Furuno cites signals on the order of 100× stronger than traditional MEO GNSS, a key lever for resilience and urban performance. 

For receiver OEMs, one of the selling points is that Pulsar’s signal structure is intentionally GNSS-like, so that support can, in principle, be added via firmware to existing multi-band designs rather than requiring a wholesale RF/baseband redesign. Recent technical work has focused on coexistence and Doppler management rather than basic feasibility. 

Timing first, then broader PNT

Although the MoU is framed broadly as “exploring opportunities” for LEO PNT solutions, Furuno’s release is most concrete on timing. The company says integrating Pulsar into its timing products should allow holdover and resynchronization when GNSS is degraded or untrusted, effectively treating LEO PNT as an independent control signal in the timing chain rather than just another GNSS augmentation. 

That emphasis aligns with how many operators are approaching LEO PNT: timing for critical infrastructure and networks is often the first operational use case, with full position/velocity integration following as receiver designs and operational concepts mature.

The MoU also builds on prior technical collaboration between the two companies, including a joint paper on tight GNSS/LEO/INS integration in dense urban environments presented by Furuno at an ION GNSS+ session. 

Part of a broader LEO PNT build-out

Xona has been demonstrating Pulsar capabilities with its Pulsar-0 satellite, including authenticated ranging and live-sky jamming tests, and has raised significant private capital to scale the constellation into the hundreds of spacecraft. 

The MoU does not specify product timelines, but it clearly marks a shift from analysis and experimentation toward integration and packaging for end users who increasingly view GNSS resilience as a procurement requirement rather than an optional feature.

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One effort that has shaped this space originated at Seven Solutions, which developed GNSS-independent timing and synchronization technologies based on signals of opportunity and terrestrial radio-frequency environments.

Founded in Spain in 2019, Seven Solutions is not entirely new to European PNT circles, having participated in the European Commission Joint Research Centre’s 2021-2022 alternative-PNT evaluation initiative. Seven Solutions and its timing technology are now integrated into Orolia’s resilient PNT portfolio within Safran Electronics and Defense, following the 2023 acquisition.

The Seven Solutions team continues to engage with European stakeholders through technical workshops, pilot activities, and participation in collaborative research. Much of this activity has taken place within EU-supported programs focused on synchronization, network resilience, and critical-infrastructure protection, emphasizing validation in operational environments rather than laboratory demonstrations alone.

The work begun at Seven Solutions has focused on maintaining trusted time when GNSS signals are degraded, denied, or spoofed. Instead of requiring new infrastructure, the approach exploits existing RF signals, including broadcast transmissions, cellular networks, and other ambient emissions, to transfer, verify, and keep time. This software-defined capability is intended to complement, not replace, GNSS, adding resilience at the timing layer of the broader PNT stack.

Standing for independence

Accurate and resilient timing underpins a growing range of applications, where even brief disruptions can cascade into significant operational impacts, making continued dependence on a single timing source no longer acceptable.

Seven Solutions technology aligns closely with Europe’s strategic interest in PNT sovereignty. By using only home grown software and leveraging signals already present within national borders, the approach reduces dependence on external systems and new spectrum allocations. It also offers a potentially scalable path to resilience without the cost, regulatory complexity, or long deployment timelines associated with new transmitters or constellations.

The technical challenge lies in extracting stable, traceable timing from signals never designed for that purpose. Variability, interference, and signal diversity demand sophisticated processing and continuous calibration. Advances in digital processing and data-driven techniques are now making this feasible for operational timing applications.

As unease over GNSS vulnerability continues to grow, the timing approach developed at Seven Solutions is strengthening an often overlooked strand of Europe’s alternative-PNT efforts. With pilot results maturing, that approach should draw closer and well-deserved attention from those shaping future European PNT architectures.

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When the Institute of Navigation (ION) brought GNSS+ back to the U.S. East Coast in September, Baltimore was the backdrop for a conference concerned with spectrum conflict and the next generation of navigation infrastructure. With two packed days on the exhibit floor, ION GNSS+ 2025 mixed technical research tracks, commercial updates and policy conversations in a way that underscored how central resilient PNT has become to everything from aviation and space to smartphones and autonomous vehicles.

At the center of the week was a historically minded plenary, “Galileo—A Journey of 30 Years,” delivered by two people who have progressed alongside Europe’s GNSS: Marco Falcone of the European Space Agency (ESA) and Jérémie Godet of the European Commission (EC). Rather than simply a programmatic update, the session walked the audience through three decades of political debates, technical challenges and engineering breakthroughs that turned a fragile concept into a fully global system delivering meter-level open-service accuracy, 20 cm high-accuracy service and near real-time Medium-altitude Earth Orbit Search and Rescue (MEOSAR) performance.

Their framing—“climbing a mountain” with a summit that always reveals a higher peak—fit neatly with the rest of the conference, where almost every track grappled with how to move GNSS beyond “good signals in clear sky” toward assured PNT in contested and cluttered environments.

Galileo as Case Study in Engineering and Governance

Falcone and Godet started in the 1990s, when GPS was declaring Initial Operational Capability (IOC) and GLONASS was operational—and Europe, as they reminded the room, had no navigation system at all. Early ESA and national studies converged on a two-step GNSS1/GNSS2 concept, but nothing could really move without three ingredients: a name, a clear ambition and political backing. The name “Galileo” and the civilian-focused, GPS-interoperable vision appeared in a 1999 European Commission communication, paired with an insistence on European strategic autonomy even as the system was designed to mesh tightly with GPS.

Getting from PowerPoint to space required political heavy lifting. Godet paid tribute to Loyola de Palacio, the Spanish Transport Commissioner he called the “real mother” of Galileo, who pushed the program through an initially hostile Transport Council asking why Europe needed its own GNSS when GPS was “free of charge.” Her approach of systematically addressing each member state’s objections on cost, NATO security and duplication set a tone the program would repeat for decades.

The governance upheaval around 2007 to 2010 will have sounded familiar to many in the room: An over-ambitious PPP model collapsed when private concessionaires balked at taking real risk, forcing a mid-course pivot to full public funding and a more classical ESA–EU division of labor. From there, the talk traced the first “Galileo-only” position fix, the Soyuz launch anomaly that stranded two satellites in eccentric orbits, and the 2016–2017 clock failures traced back to a 50-cent feed-through component. Each episode was treated as evidence that large, safety-critical systems live or die on the ability to change operations quickly without breaking legacy services.

The most sobering moment came with the 2019 ground-segment incident that corrupted the navigation message and forced a week-long service interruption.The independent inquiry and subsequent redesign—shorter restart times, a “navigation extending mode” that allows graceful degradation for up to a week and a full pre-operational chain shadowing major software release—mapped directly onto themes running through multiple ION tracks on continuity and graceful degradation.

More recently, the war in Ukraine and the loss of Soyuz access to Kourou triggered another round of improvisation: Ten built satellites went into long-term storage while Brussels and Washington negotiated the security framework that ultimately allowed launches 12 and 13 on SpaceX Falcon 9 from Cape Canaveral. That experience, Falcone stressed, compressed their launch campaign tempo and forced leaner processes, lessons now being taken back into Europe as Galileo returns to Ariane 6 for launch 14.

In its forward-looking portion, the plenary jumped from Galileo Second Generation—reprogrammable, fully flexible payloads with electric propulsion and inter-satellite links—to low-Earth-orbit (LEO) PNT “pathfinders” as a future third GNSS layer, and then out to Moonlight and Mars comm/nav architectures being co-defined with NASA and the Japan Aerospace Exploration Agency (JAXA). Taken together, these plans cast Galileo not as a finished system, but as the medium Earth orbit (MEO) backbone of a multi-layer, multi-orbit PNT ecosystem. Their closing “recipe” for success—political will, technical excellence, user-driven evolution, industrial strength and international cooperation—could just as easily have served as the conference’s motto.

Themes from the Program

Resilience, AI and multi-layer PNT were strongly reflected in the conference’s technical program and tutorials. Short courses on GNSS jamming and spoofing with LEO constellations as a fallback, signals of opportunity (SoO), ionospheric effects and space applications all picked up on aspects of the resilience story: interference is now assumed, and LEO, SoO and environmental monitoring are no longer niche topics but central planks. 

On the research side, tracks opened with sessions on navigation security and authentication, AI-driven positioning and robust navigation using GNSS, setting the tone for a week that treated jamming and spoofing as operational realities. Papers covered space-based RFI detection, spoofing detection assisted by specific force inputs, RAIM-like anti-spoofing methods and multi-modal signal classification for challenging environments. 

Artificial intelligence and modern estimation methods were everywhere: factor-graph optimization in tightly coupled GNSS/INS, hybrid physics-informed neural networks and deep learning for interference suppression, ionospheric scintillation prediction and context-aware positioning for low-cost receivers in urban canyons. Sessions on smartphones and wearables, autonomous land and sea-based applications and indoor positioning underlined how far GNSS+ has moved beyond its aviation-first focus into mass-market, edge-compute and robotics domains.

Alternative and complementary PNT got full track treatment: atmospheric effects on GNSS and LEO PNT, non-optical and optical approaches for GNSS-denied navigation, geomagnetic and tunnel positioning, and advanced processing of terrestrial and non-terrestrial SoO all pointed to a consensus that “GNSS alone” is no longer a serious design assumption for critical applications. At the same time, classic augmentation work remains vigorous, with papers on global Satellite-Based Augmentation System (SBAS) architectures, Dual-Frequency Multi-Constellation (DFMC) integrity, ionospheric monitoring for GBAS and the modernization of network RTK services to ride out the looming solar maximum.

LEO PNT, referenced in the Galileo plenary as “GNSS3,” was one of the week’s hot topics, with dedicated sessions on LEO satellites for PNT, integrating LEO for enhanced positioning and atmospheric impacts on LEO-based systems. The technical content there dovetailed with Godet and Falcone’s vision of a future where MEO GNSS provides the timing backbone while LEO constellations add power, bandwidth and geometry for robustness and fast convergence.

On the Show Floor: A Dynamic Ecosystem

Those themes carried over into the exhibit hall, where the evening reception “30 Years of Galileo” gave the anniversary a more informal stage amid booths from ESA, DLR, receiver and simulator vendors, timing specialists and the Resilient Navigation and Timing Foundation. Hardware testbeds for spoofing and jamming, compact multi-band GNSS antennas, MEMS inertial units, timing oscillators and real-time PPP-RTK correction services sat alongside new-space LEO PNT players such as Xona.

GNSS is no longer a fragile, single-system asset but a set of global constellations, terrestrial backups and emerging LEO and lunar layers that must be engineered, governed and funded as a whole. The story Falcone and Godet told of difficult political choices, technical challenges turned into features and decades-long continuity of expertise, is now being replayed at new altitudes and in new orbits. For a community gathered in Baltimore to talk about the next 30 years of PNT, that combination of learning from the past and ambition for the future was exactly the signal they came to hear. 

The post ION GNSS+ 2025: Galileo at 30 and the Future of Resilient PNT appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

By Richard Thomas, Abe Peck, Vicki Speed

For more than four decades, satellite-based global navigation systems have served as the invisible infrastructure of the modern world. GPS and its international counterparts underpin navigation, telecommunications, finance and defense—technologies that together define 21st century life. Yet, as the dependence deepens, so do the vulnerabilities. Jamming and spoofing have become easy and commonplace, from conflict zones to commercial ports. In the world’s most sophisticated mines, in dense urban corridors, and under roofs where signals fade, GPS alone cannot sustain the accuracy modern applications demand.

This gap—the inability of space-based signals to penetrate, persist or resist interference—has created an urgent demand for Complementary Positioning, Navigation and Timing (C-PNT). In that space, a small Australian company has quietly built a terrestrial counterpart that operates without satellites, atomic clocks or external corrections. That company is Locata.

Reinventing Synchronization

Locata’s founders, David Small and Nunzio Gambale, began not as engineers but as musicians. In the mid-1990s, they were experimenting with a GPS-based tourism app that would trigger audio and video as a tour bus passed local landmarks. It worked—until they went inside a museum and the satellite signals…vanished. The experience revealed a simple truth: GPS, for all its global reach, had local blind spots.

“What we saw was a system full of holes,” Gambale later recalled. “Malls, mines, ports, warehouses, urban canyons—all the places where productivity was moving—were exactly the places GPS couldn’t reach.”

The pair decided closing those holes meant building a ground-based positioning system that could emulate GPS performance anywhere, even indoors. That ambition presented them with a fundamental obstacle: synchronizing multiple transmitters to billionths of a second without having access to the atomic clocks that fundamentally underpin satellite positioning systems.

Solving that problem has defined the innovation Locata created for the science of PNT.

TimeLoc: The Clockless Breakthrough

TimeLoc has become the core of Locata’s terrestrial architecture. Instead of relying on satellite-borne atomic clocks, TimeLoc synchronizes a network of small ground transmitters—called LocataLites—through a self-referencing feedback loop. Each unit continuously measures and corrects its timing relative to neighboring transmitters. Through this closed-loop process, the entire network converges on a common timescale, achieving sub-nanosecond synchronization without any external clock reference.

The result is a terrestrial grid capable of transmitting GPS-like ranging signals with atomic-clock-level precision. Locata receivers, or “Rovers,” compute position and time using those signals just as a GNSS receiver would, but without dependence on satellites.

Independent testing confirmed that a properly configured LocataNet can maintain timing stability better than one billionth of a second for months or even years. “As long as we have power to the LocataLites, they autonomously remain synchronized…essentially forever,” Small has said.

From this breakthrough grew a vision: a terrestrial complement to GNSS that could provide local, sovereign control of high-precision PNT—indoors, in jammed environments and across critical infrastructure.

Proof Point One: White Sands Missile Range

Locata’s first large-scale validation came not from industry but from defense. In 2011, the U.S. Air Force (USAF) selected the company to provide an alternative truth reference system for aircraft testing at White Sands Missile Range (WSMS) in New Mexico. The question was whether a LocataNet could scale across thousands of square kilometers and deliver centimeter-level accuracy at aircraft speeds while GPS was deliberately jammed.

It could—and still does today. The White Sands installation covers about 2,500 square miles of airspace, its LocataLites synchronized entirely by TimeLoc. Independent USAF reports have verified centimeter-level aircraft positioning and nanosecond timing, even under full-spectrum GNSS denial. Aircraft acquire signals more than 65 kilometers from the nearest transmitter.

For the Air Force, the demonstration established a terrestrial truth reference system unmatched by any other technology. For Locata, it proved the concept’s scalability and reliability in one of the most demanding test environments on Earth.

Proof Point Two: Boddington Gold Mine

A year later, one of the world’s largest open-pit gold mines presented a different challenge. The Boddington Gold Mine, operated by Newmont in Western Australia and supported by Leica Geosystems (later acquired by Hexagon), required continuous centimeter-level positioning for fleet automation deep within the pit. Satellite signals frequently vanished along the pit walls and at the mine base, forcing costly machine downtime.

Leica engineers worked with Locata to integrate a LocataNet with their Jigsaw Positioning System, effectively merging GPS and Locata into a hybrid PNT environment. When satellite visibility dropped, Locata seamlessly maintained centimeter-level position data for the mine’s haul trucks and shovels. The mine reported that the system paid for itself within 90 days through reduced interruptions—a milestone that demonstrates Locata’s compatibility with existing GNSS workflows, rather than competition with them.

Proof Point Three: NASA Langley

In 2015, NASA’s Langley Research Center adopted Locata as a core positioning technology for safety-critical unmanned aircraft systems testing in conjunction with the FAA. Langley’s goal was to validate non-GPS navigation for UAVs operating over urban areas, and near buildings and structures.

NASA engineers confirmed Locata’s phase and pseudo-range methods paralleled GNSS mathematics closely enough for existing navigation algorithms to ingest the data with minimal modification. The tests validated centimeter-level positioning and sub-nanosecond timing across mixed indoor/outdoor environments—precisely the conditions that defeat satellite-based navigation.

Proof Point Four: The European Commission’s JRC Evaluation

Locata’s most rigorous independent trials came from Europe. In 2023, the European Commission’s Joint Research Centre (JRC) completed an eight-month evaluation of alternative PNT systems for potential deployment within the EU. Thirty-two companies applied; seven were selected for final testing. Locata was awarded two of the seven contracts—one for positioning and one for timing.

For the timing test, the company deployed a TimeLoc chain spanning 105 kilometers, cascaded through eight LocataLites. The JRC’s independently measured time deviation across that span was less than 400 picoseconds—a fractional error so small it’s difficult for non-engineers to fathom—one picosecond is to a second as one second is to 31,700 years.

The JRC’s published report concluded that Locata was the only system tested to deliver consistent, centimeter-level positioning and picosecond-level timing in every environment, including indoor, outdoor and transition zones. The findings validated Locata’s claim of clock-free synchronization and established it as a fully mature terrestrial complement to GNSS. 

The Physics of Precision

At the core of TimeLoc’s precision is a method for removing the drift that accumulates when independent oscillators age or fluctuate with temperature. Locata’s algorithmic “Time Lock Loop” continually compares the phase of signals between transmitters, and through what engineers call common-mode differencing aligns each unit’s oscillator accordingly. Because every node actively participates in TimeLoc, the distributed network as a whole behaves as one, sub-billionth-of-a second, synchronized timebase. To a novice, TimeLoc can literally make it look like “time is standing still.”

Locata’s nodes “mesh,” yielding a unified timebase without any atomic reference. The principle may seem simple, but implementing it requires millions of lines of code and years of iteration in the field.

This time synchronization capability gives Locata a strategic advantage: Networks can be scaled, relocated or duplicated without recalibration. In effect, TimeLoc today enables better than GPS-grade synchronization without GPS or atomic clocks—a property increasingly valuable for national infrastructures seeking autonomy in timing.

Solving Multipath: Correlator Beam Forming

Accurate positioning in enclosed or cluttered environments requires more than synchronization. Multipath—signals bouncing from walls or machinery—can overwhelm receivers with incorrect timing and positioning measurements.

To address this, Small invented Correlator Beam Forming, a signal-processing method that creates a time-multiplexed phased array using a single radio front-end. Traditional phased-array antennas require complex, expensive hardware with myriad radio front-end receivers. Locata’s approach performs the equivalent operation in software, forming millions of tight beams that track direct signal paths and suppress reflections.

The first embodiment was the VRay Orb, a basketball-sized, 60-element antenna producing 2.5 million beams per second. The beamforming adapts dynamically as a platform moves, maintaining direct-path lock even in dense multipath environments such as indoor warehouses or cluttered steel environments like container ports.

The company is now testing its new miniature Orb 120 —about the size of a coffee cup—aimed at drones, forklifts and other compact platforms. Prototype designs have already demonstrated feasibility for integration into consumer-scale hardware, from forklifts to industrial robots to smartphones.

Built for Resilience

From the outset, Locata’s engineers designed their system to survive in the noisy 2.4 GHz band—the same unlicensed spectrum used by Wi-Fi. That choice, forced by regulatory constraints, had an unintended benefit: It hardened the technology against interference.

“GPS signals are extraordinarily weak,” Small noted in an early briefing. “A simple jammer can disrupt them. Locata signals are billions of times stronger at the receiver.”

Because Locata networks operate under local control, transmit power can be adjusted to suit the environment. Jamming attempts are easily detected and located. In effect, the network’s own geometry and signal strength becomes a defense mechanism, giving it inherent resilience in contested or congested spectrum.

Lessons From the Red Zones

When Gambale addressed the PNT Leadership Summit in September, his slides carried a blunt message: “Don’t deploy your grandfather’s GPS backup.” The presentation, titled “Report from the Red Zones,” illustrated how civilian systems dependent on GNSS are failing badly in areas of electronic warfare—from Poland’s Baltic ports to Ukrainian agriculture to Middle Eastern construction companies.

In these “red jamming zones,” precision agriculture systems report coordinate shifts of hundreds of meters. Polish offshore wind-farm construction halts under sustained GPS jamming from nearby Kaliningrad. Even commercial container ports see autonomous gantry cranes stop mid-operation when satellite signals disappear. 

One large Baltic port Locata is working with, Gambale said, “has €500 million worth of GNSS-dependent autonomous machines, which are fundamentally ‘turned into bricks’ when GNSS jamming is taking place. This is a serious, existential threat for Poland’s Critical National Infrastructure. We don’t know of any other technology that can deliver the centimeter-level radiopositioning the machines need 24/7/365, across the entire port area, so they can function without GNSS.”

The takeaway is clear: Next-generation C-PNT must meet aviation-grade thresholds of Accuracy, Integrity and Resilience (A-I-R), Gambale said. Laboratory simulations and marketing blurb are not enough; systems must prove performance in real-world environments.

Locata’s long record of field validation—from mines to missile ranges—has now positioned it as one of the few technologies meeting those proven standards today.

Complement, Not Competitor

Locata’s founders have never claimed to replace GPS. The system’s strength lies in complimentary integration—extending GNSS into environments and applications where satellites cannot operate. In a hybrid configuration, GPS can provide a global reference while Locata delivers local precision and continuity.

In the Boddington Gold Mine example, the two systems work in concert: GNSS established absolute coordinates outside the mine pit; Locata maintained accuracy when sky visibility is inadequate in many places. The same model applies to ports, airports, indoors and urban infrastructure.

In practice, GPS + Locata creates a resilient architecture where one layer fortifies the other. It embodies the multi-layered strategy that experts like Dr. Brad Parkinson, the “father of GPS,” have long advocated under the Protect–Toughen–Augment (PTA) framework.

Sovereignty and Spectrum

As nations recognize the strategic vulnerability of space-based PNT, terrestrial solutions are becoming instruments of sovereignty. The U.S. Department of Transportation and its Volpe Center have launched recent programs to evaluate mature, deployable C-PNT technologies—systems with a Technology Readiness Level (TRL) of 8 or higher that can operate within six months of award.

Locata already meets that standard. Its installations in defense, mining, ports and indoor contexts demonstrate operational and commercial success, and its new software-defined radio architecture promises rapid future deployment across licensed or shared spectrum bands.

Gambale has argued publicly that allocating a protected frequency for terrestrial PNT—analogous to GPS’s own protected bands—would multiply system range and penetration. “Give us 30 watts instead of a tenth,” he has said, “and our signal will go through buildings like butter.”

The argument is less about competition for bandwidth than about recognizing that ground-based precision timing deserves the same national protection as space-based navigation.

Building Ubiquitous Terrestrial PNT

Over the past two decades, the two founders surrounded themselves with an extremely tight and dedicated team of engineers that have helped solidify Small’s inventions into rock solid TRL9 commercial systems. The team’s mission has remained crystal clear throughout: non-GNSS-based PNT that Locata users can bet their lives upon. 

To date, this collective mission has gained Locata more than 170 patents and licensing arrangements with major industrial and defense partners, most still under nondisclosure agreements(NDAs). The company’s immediate focus is cost reduction and miniaturization—moving from bespoke hardware toward chipset integration, the same trajectory GPS followed in its early decades.

The vision is straightforward: compact LocataLites mounted in ceilings, poles or towers could provide centimeter-accurate, authenticated positioning across entire industrial zones, critical infrastructure or even cities. Warehouses, ports, logistics centers, airports, data centers and more could maintain assured time and position, even if satellites go dark.

For national infrastructures, this model provides a blueprint for sovereign resilience—a self-contained layer that can be deployed to continue operating through jamming, spoofing or orbital disruption.

The Long Road to Credibility

Locata’s journey has not been easy. For years, the idea of clockless synchronization was dismissed as impossible. When Gambale first presented Locata’s initial results at an Institute of Navigation (ION) conference, one extremely well-known GPS expert literally pounded the table demanding, “Where are your clocks?” The textbooks he’d studied taught him it couldn’t be done.

Since that outburst, Locata has unequivocally proven the textbooks he read now have to be re-written. Renowned, independent agencies on three continents have definitively proven that Locata is both real and transformational. Locata’s TimeLoc synchronization has been verified by NASA, Leica, Maersk, the U.S. Air Force, the EC’s JRC, and many more under NDA. Each validation reinforced the same finding: The system delivers high-precision GPS-class accuracy and timing without requiring atomic clocks or satellites.

The Next Beat

As global policy shifts from awareness to implementation of resilient PNT, Locata’s technology occupies a pivotal niche. It is not a rival to GPS but an enabler of the Protect–Toughen–Augment model—ground truth to complement and buttress space truth.

In a world where positioning and time have become as fundamental as power or communications, Locata demonstrates that those services need not depend solely on orbiting assets. They also can be anchored to Earth itself, and owned by nations and entities that do not (and can never) possess constellations. 

From two musicians working to produce a tour-bus app in the early days of GPS to a revolutionary innovation validated by the world’s foremost navigation authorities, Locata’s evolution underscores a broader principle: The next era of assured positioning will belong not to satellites alone, but to the synergy between sky and ground.

The post Locata: Synchronizing the World Without Satellites appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

Septentrio, part of Hexagon, a leader in high-precision GNSS positioning and timing solutions, announces the launch of a new timing module, the mosaic-G5 T. Measuring only 23 mm by 16 mm and weighing as little as 2.2 grams, this receiver unlocks new opportunities for system designers operating under strict size, weight and power (SWaP)  constraints. Nano-second time precision is complemented by AIM+ Premium anti-jamming and anti-spoofing technology ensuring reliable service uptime and continuity. With built-in cyber-security features this timing receiver is ideal for critical infrastructure that requires a resilient, high-quality timing source such as data centers, telecom, satcom, financial institutions and more.  

“For over 25 years, we have been producing world-recognized timing receivers, serving critical applications and major industry players. With our next-generation technology, we are now bringing precise and resilient time in an ultra-compact form factor to high-volume applications,” explained Yasmine Hunter, Product Manager at Septentrio.  

The mosaic-G5 T module receives signals on multiple frequencies from all available GNSS satellite constellations, achieving high precision even in challenging environments, such as in areas with radio interference. It enables precise, high-resolution timing through two independent and reliable pulse-per-second (PPS)  pulses and has clock and frequency input support for seamless synchronization. The mosaic-G5 T is ready to support Galileo High Accuracy Service (HAS)  and is built to stay agnostic towards other correction services that enhance timing accuracy.

See the mosaic-G5 T ultra-compact GNSS time module for yourself at the International Timing and Sync Forum (ITSF)  in Prague, Czechia, at stand 21 on October 27 – 31. 

For more information about the mosaic-G5 T or other Septentrio products please contact the Septentrio team.

The post Septentrio Launches Mosaic-G5 T Timing Module appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.