For Inertial Labs, the Virginia-based inertial navigation specialist acquired by VIAVI Solutions in 2025, that challenge has become the central driver of product development.

Speaking to Inside GNSS in Paris, Inertial Labs Sales Engineer Jackson Williams said his company has spent more than two decades refining inertial technologies while steadily expanding into sensor fusion and assured navigation. “We’re kind of a 25-year overnight success,” he quipped. The company started in 2001, based in Northern Virginia. “We also have manufacturing in Rapid City, South Dakota, and another R&D office in Kiev, Ukraine,” Williams said.

Over the past two decades, the company has evolved from a sensor manufacturer into a provider of complete navigation solutions. At the heart of that portfolio are gyroscopes and accelerometers, the foundational sensors that measure rotational and linear motion. Those are integrated into inertial measurement units (IMUs), which then form the basis of increasingly sophisticated inertial navigation systems.

Core competence

Williams summarized the company’s mission simply: “We do GPS&I, that is GPS plus inertial navigation, for autonomous vehicles. Starting with the base level sensors, we build our IMUs, and then create more complex inertial navigation systems out of those.” That focus has naturally led the company toward sensor fusion, using further data sources to constrain drift and improve overall navigation performance.

“Our main selling point and our kind of specialty is sensor fusion,” Williams said. “So we bring in aiding forms of data, such as air data computers, magnetometers for heading, fiber optic and man-time use, and low Earth constellation satellites for assured position and navigation and timing.”

Multiple aiding sources help constrain inertial drift and improve solution integrity. By fusing diverse, independent measurements, Inertial Labs seeks to maintain navigation performance in degraded environments, a sensor-diversity approach that Williams described as central to the company’s strategy.

“We bring in things like radio as well, line of sight, time of flight, time of arrival data,” he said. “We fuse these all together, curate them to our customers’ requirements, specifications, and support them when they’re on. We like to be very hands-on with our projects.”

Where it matters

Electronic warfare systems deployed particularly in Ukraine have demonstrated how vulnerable GNSS signals can be to interference. Modern assured-PNT architectures increasingly depend on multiple complementary sensors working together.

One example of a key aiding source is Inertial Labs’ miniature Air Data Computer (ADC). Designed for low size, weight and power consumption, the ADC provides airspeed, altitude and atmospheric measurements that can be fused with inertial data. For unmanned aircraft operating in dynamic flight conditions, those measurements provide an additional reference that helps maintain navigation accuracy during GNSS degradation or loss.

The war in Ukraine has also had a direct influence on product development. Inertial Labs’ Kiev office, originally established in 2006 as a conventional R&D center, now plays an important role in testing and validation. The value of that operational feedback has been significant. “All of our products are battlefield tested and qualified, vetted through our people in Ukraine,” he said. “And with everything that’s going on there, we’re getting a lot of feedback. That’s been a large factor in driving our innovation and our improvements in our devices.”

For many of the companies we met at Eurosatory, the war in Ukraine has become an unprecedented laboratory for navigation technologies. GNSS denial, electronic attack and contested electromagnetic environments have shifted inertial navigation from a backup capability to a central component of military positioning architectures.

Partnering in space

The emphasis on multiple, complementary navigation sources is also reflected in Inertial Labs’ work with the Iridium company. Iridium operates a global low-Earth-orbit (LEO) satellite constellation whose signals are increasingly being explored for resilient PNT applications. LEO-PNT satellites operating in low Earth orbit transmit significantly stronger signals than traditional medium-Earth-orbit GNSS constellations. Inertial Labs’ partnership with Iridium emerged publicly in 2026 with the introduction of IRINS, a system that combines Inertial Labs’ tactical-grade inertial sensors with Iridium’s LEO satellite capabilities.

Despite defense dominating current demand, Williams emphasized that commercial applications remain important. “Right now our main market obviously is the defense space and things of that nature,” he said. “But our IMUs are industrial grade up to tactical grade, so there is a portfolio, or a space in the portfolio for your commercial base use cases.”

He pointed specifically to the company’s LiDAR payload business. “That payload is called RESEPI and is used primarily in the commercial space, meaning farming, construction, things of that nature,” Williams said. Whatever the application, whether it’s about supporting battlefield autonomy, or infrastructure mapping and precision agriculture, the underlying requirement remains the same: reliable motion sensing and navigation in challenging environments.

Eurosatory 2026 showed clearly what our readers already knew – assured PNT is now a necessity rather than a specialized capability. Listening to Williams, a consistent case emerged: the future of navigation will not depend on a single sensor, signal or satellite constellation, but will require the ability to combine and interweave the widest available selection of them.

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According to a Telegram post by Ukrainian Defense Ministry advisor Serhii “Flash” Beskrestnov on June 16, Guarantor was developed by the company Rossiysky Kupol LLC based in Simferopol, Crimea and first appeared in 2024 near Kharkiv—where at least one system was destroyed.

But recently in 2026, Russia began multiplying Guarantor deployment along the southern highway “land bridge” between Russian soil and Crimea to counter Ukraine’s destructive medium-range strike drones that have ravaged fuel truck logistics, causing a stark fuel shortage in Crimea.

In response, Ukraine’s military has released videos showing two strikes on individual trailers of Guarantor systems by the 422nd “Luftwaffe” Unmanned Systems Regiment—attached to the 17th Corps operating in central-southern Ukraine.

Beskrestnov describes an approach intended to interfere with a Starlink satellite’s reception of terminal uplinks by transmitting interference in the relevant Ku-band uplink channels:

“Technically, a Starlink satellite receives signals from terminals in the 14–14.5 GHz range. This range is divided into 8 channels, each 62.5 MHz wide. The Russians basically took 8 satellite dishes, pointed them at the satellite, and each dish transmits interference on its own channel.” Beskrestnov claims this can effectively “deafen” the satellite to terminals in the affected area.

He further details that each Guarantor system encompasses six trailers, each with capacity for two of the system’s eight rotating dish antennas, each of which is covered by egg-shaped domes. Implicitly, then, some trailers carry just one antenna. The antennas can be optionally dismounted, and the power-hungry system can either be sustained by trailer-mounted generators or from external sources.

Beskrestnov concludes each system can effectively deny Starlink access across “roughly 20 square kilometers.” Calculating backwards, this implies a circular radius of just over 2.52 kilometers, or 1.57 miles.

That suggests point defense of a local area, but the radius remains small enough that a Starlink-controlled drone with automatic target tracking could still acquire an optical lock from outside this defensive bubble on targets within the protected area, including Guarantor systems themselves. Indeed, optical lock-on seems possibly present in at least one of the videos released by the 422nd Regiment.

Russian Telegram drone blogger “Unmanned Brotherhood” claims Guarantor is causing Ukrainian forces to complain of “significant problems” but concedes the system has downsides: “the EW system is currently quite large and conspicuous, though this issue is expected to be rectified in the future.” Another Russian technical specialist, Sergei Trukhachev, told Russia’s TASS news agency that the system demonstrated “high effectiveness during local tactical operations.”

Beskrestnov claims the systems are being sold at the “absolutely magical” price of $1.5 million apiece. While that does not seem prohibitive by American standards, in consideration of the limited area protected, that price point may prevent deployment from being scaled to extend coverage over large areas like the hundreds of miles of highway in southern Ukraine under assault by Starlink-enabled drones.

That Ukraine itself is striking Guarantor systems suggests they are effective enough to be worth attacking, but nonetheless apparently vulnerable to strikes. Besides being targetable at distance with electro-optical guidance, the system’s high-power emissions could also make it vulnerable to emitter-location tactics, including electronic support measures, loitering munitions cued by RF detection, or purpose-built home-on-jam weapons.

Jamming a cloud of gnats

Starlink is notoriously difficult to jam compared to traditional geostationary satellites, for the same reason it is harder to swat a cloud of gnats than an individual fly: it consists of a network of over 10,000 low-Earth orbit satellites that are constantly moving at high speed. Although each satellite remains overhead for roughly five to seven minutes, Starlink’s network timing and beam/satellite management operate on short, synchronized intervals, and user terminals can transition among satellites as geometry changes, complicating attempts to focus jamming on a single moving spacecraft.

This means that a huge number of emitters would be needed to continuously jam Starlink over a wide area; for example, a study by China’s Zhejiang University and Beijing Institute of Technology estimated China would require at least 935 high-powered, or 2,000 low-powered, aerial jamming platforms to deny Starlink across an area the size of Taiwan, or 13,900 square miles.

With its focus on just one satellite at a time, it is not clear how well Russia’s Guarantor overcomes the Starlink “cloud of gnats” challenge. Is an external system continuously re-cueing the Guarantor jammers to target the next most relevant satellite as their orbital positions shift? And if Guarantor only jams one satellite at a time, does that really suffice to ensure another Starlink satellite is not also able to cover that area simultaneously?

It is also worth bearing in mind that Starlink’s jamming resistance extends beyond distributed targeting to other design characteristics, including the ability to adaptively null interference returns from areas generating jamming signals.

Intel on Rossiysky Kupol LLC

A Russian article in March 2025 provides additional details on a C-UAS “super EW” system developed by approximately 150 scientists at Rossiysky Kupol LLC, funded in part by local authorities in Crimea, and allegedly effective against UAS targets at a 20-kilometer radius, or 12.4 miles. Without otherwise mentioning satellite jamming, the article alleges this system “unintentionally suppressed” GPS signals in a neighboring European country, presumably Romania, and allegedly “prevented” an attack by 25 drones targeting a plant near Rostov.

The rise of satellite mega-constellations

It is instructive to observe Russia’s efforts to defend against a distributed satellite mega-constellation, because this technology is not destined to remain uniquely in American hands.

Russia itself is spending approximately $5.3 billion attempting to build a constellation of 292 satellites by 2030 called Rassvet, or “Dawn,” with plans to further scale to 900 satellites. Progress to date has been slow, with 16 operational satellites launched from Plesetsk, one of which has since failed.

Meanwhile, China is advancing three mega-constellations: the commercially oriented Qianfan, or “Thousand Sails,” aiming for 15,000 satellites; the state-owned GuoWang, or “National Network,” a dual-use constellation with 13,000 satellites; and the telecom-oriented Honghu-3, aiming for 10,000 satellites.

Implications for LEO constellation resilience

Guarantor is clearly no panacea. It cannot broadly overcome the distributed redundancy of the Starlink mega-constellation—a single system covering 20 square kilometers against a network of more than 10,000 satellites performing rapid handoffs is, at best, a pinhole defense. Yet the ability to shield a limited, high-value area can still be meaningfully preferable to having no defense at all, and Russian commanders appear to have drawn that same conclusion.

The more consequential lesson is strategic. Russia, China, and the United States all possess broader, not fully disclosed counterspace capabilities, but those tools are rarely available to tactical field commanders. What Guarantor represents is an attempt to bring satellite denial to the unit level—trading coverage breadth for deployability. As LEO mega-constellations multiply and become the backbone of battlefield communications for multiple powers, the tactical demand for localized counter-constellation tools will only grow. The U.S. and its allies, potentially facing adversary LEO networks of comparable scale within a decade, would be prudent to treat Guarantor not as a curiosity but as an early indicator of a new category of tactical electronic warfare.

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SkyBarrier is designed to jam all four major global navigation satellite systems simultaneously: GPS, GLONASS, Galileo, and BeiDou. HENSOLDT states the jamming effect covers both civilian and military signal variants, including encrypted signals, across the full range of currently relevant frequency and coding variants.

The system is built around rapid deployment: HENSOLDT says two operators can complete setup — including mast assembly and cabling — within minutes, with activation via a mechanical front-panel switch requiring no software configuration. The complete system consists of a single portable electronics unit, an extendable telescopic mast, and associated accessories.

HENSOLDT designed SkyBarrier for incremental upgradability, stating that new signal types can be added by replacing individual components rather than the full system. The company also notes a minimal physical interface profile — three hardware interfaces with no external data communication pathways — as a deliberate cybersecurity measure.

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PANOSETI — Pulsed All-sky Near-infrared Optical SETI — is a multi-institutional program led by researchers at the University of California, Berkeley. The system requires extremely precise time coordination across widely separated telescope nodes to detect fast-transient optical and near-infrared signals. Traditionally that level of synchronization has depended on fiber-based infrastructure such as White Rabbit, which is costly and impractical to deploy at remote observatory sites.

Using the u-blox ZED-F9T, the PANOSETI team demonstrated approximately 0.7 nanosecond standard deviation between 1PPS signals over a 1-kilometer baseline, with performance improving to around 200 picoseconds using filtering techniques — meeting or exceeding the requirements for next-generation distributed sensing systems.

“Achieving this level of synchronization without fiber is a significant step forward for distributed instrumentation,” said Dan Werthimer, Chief Scientist of the PANOSETI project at UC Berkeley. “It allows us to achieve the timing precision we need for our telescope array in locations where traditional fiber-based systems are not feasible.”

The u-blox announcement frames the result as extending beyond scientific research, pointing to applications in distributed sensor networks, remote timing systems, and resilience of critical infrastructure.

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The milestone centers on Qualinx’s QLX3xx — a reconfigurable GNSS SoC and Analog Front End targeting secure positioning, navigation, and timing applications, including resilient timing and synchronization networks and ultra-low-power GNSS receivers for connected edge deployments. The chip was designed, taped out, and manufactured entirely at GF’s Dresden fab using its FDX process technology. No design data or physical materials left the European Union at any stage of production.

“Our partnership with Qualinx marks the first operational milestone,” said Dr. Manfred Horstmann, SVP and General Manager at GF. “It shows that complex, security-relevant ASIC designs for aerospace, defense, and critical infrastructure can already be industrialized today using a fully European, trusted manufacturing path.”

Qualinx CEO Tom Trill characterized the flow as proof that full European manufacturing control is no longer theoretical. “This first secure product demonstrates that a fully European manufacturing path — from mask services to wafer production — is already a reality today,” he said, adding that the effort gives Qualinx complete control over IP, data, and supply chain within Europe.

The Dresden fab’s sovereign manufacturing capability is co-funded under the European Chips Act. GF says it aims to have a fully automated trusted European flow in place by end of 2026, with regular foundry engagements available to aerospace and defense customers starting in 2027. That roadmap will incorporate European IP partners, mask houses, and OSAT service providers.

GF is also working with Deutsche Telekom on a parallel effort to ensure that production data — from design and tape-out through manufacturing and quality — can be processed, transported, and stored entirely on European networks, cloud infrastructure, and data centers. The practices developed there are intended to feed directly into the scaling of the sovereign manufacturing model.

Qualinx, headquartered in Delft, Netherlands, was founded in 2015. The company’s proprietary Digital Radio Frequency technology implements traditional analog receive-chain functions in digital hardware, targeting GNSS, PNT, and PVT chipsets and modules for applications ranging from automotive and fleet to wearables and asset tracking.

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It’s late at night, January 29, 2026. Most of Southern California is asleep. Ships approaching Long Beach harbor from the West key their mics on VHF channel 14 and report GNSS outages to LA/Long Beach Vessel Traffic Service (VTIS). Aircraft over the Channel Islands squawk the same via ADS-B. NOAA Continuously Operating Reference Station (CORS) sites record anomalies in L1 and L2 signal-to-noise ratios. All of this within an hour.  

While spoofing and jamming of GNSS have been recurring issues in conflict zones, incidents like this show no one is immune. 

Maritime Impacts

Automatic Identification System (AIS) reports from at least 7 vessels indicate position jumps indicative of spoofing. At least one vessel’s AIS system ceased transmitting altogether for nearly an hour, likely due to an invalid GNSS solution. Data indicates this event covered greater than a 100-mile area, including the critical LA/Long Beach Traffic Separation Scheme. 

All of the documented GNSS anomalies occurred within one hour, but the most dramatic position jumps shown by AIS messages lasted only several minutes. The short duration of the event is the only factor that prevented greater impact on PNT and limited public awareness of the event.

All of the reported interference occurred between 11 p.m. and midnight local time, with good visibility and no inclement weather, and all the vessels involved entered port without incident.  But, it should be noted that several of the vessels were navigating in close proximity to one another in the vessel traffic separation scheme, and loss of valid GNSS solution could impact situational awareness and create distraction at a critical point in their voyages.

Figure 2 shows the AIS track of a large container ship showing position jumps resulting in invalid, erratic course and speed over ground:

A tanker experienced similar position jumps:

In addition to AIS vessel reports, which typically are transmitted at about 10 second intervals while underway, three local NOAA CORS sites recorded Signal-to-Noise Ratio (SNR) anomalies in the same hour:

Figure 4 

Aviation Affected

Additionally, the GPSjam.org website showed aircraft evidence (ADS-B messages) of GNSS anomalies much further to the southwest of the reporting commercial ships, indicating the interference may have covered a far larger area than AIS data indicates. 

Figure 5 

The Source

On February 4, six days after the event, the minutes of the L.A./Long Beach Harbor Safety Committee meeting recorded:

“GPS Outages: On the evening of January 29, VTS LA-LB received multiple reports of GPS outages from vessels in the LA-LB AOR. Sector personnel, with support from our port partners and the Coast Guard Navigation Center, were able to identify a GPS testing event as the likely cause. While there were no incidents or negative impacts due to the outages, the Coast Guard continues to investigate the outages and will take action to prevent recurrence.”

While GPS testing is a regular occurrence, interference like that of Jan 29, 2026, is quite rare.  

The available data does not provide certainty, but the most likely source of these anomalies was a GPS test dubbed PMSRCA 26-02, that is, Point Mugu Sea Range California 26-02.  

An FAA Notices to Airmen (NOTAMs) released on January 22, 2026. states: 

“GPS testing is scheduled as follows and may result in unreliable or unavailable GPS signal.”

A. Centered at 332451N1183430W or the SXC VOR 272-degree radial at 8 NM. 

                                        (near Catalina Island)

B. Dates and times (Dates and times are based on GMT (Z).): 

27 – 31 JAN 26 DLY 0700Z – 1400Z  (event occurred 30 Jan 0700Z – 0800Z)

D. NOTAM INFO: NAV GPS (PMSRCA GPS 26-02) (INCLUDING WAAS, GBAS, AND ADS-B) MAY NOT BE AVBL WI A 452NM RADIUS CENTERED AT 332451N1183430W (SXC272008) FL400-UNL, 

                   …and included this graphic (Figure 6):

While NOTAMs alert aviation, the U.S. Coast Guard Navigation Center (NAVCEN) website publishes monthly schedules of GPS testing for mariners. However, PMSRCA 26-02 was not listed on the January schedule, but did appear on the February GPS testing schedule released on February 13, 2026, about two weeks after the January 29 jamming and spoofing instances.

Even though the NAVCEN website may not have published notification of that particular GPS test in a timely manner, GPS anomalies are so infrequent in the Americas that few mariners would likely have been alerted. The unfortunate reality is the United States, unlike China, Russia, South Korea, the United Kingdom, Saudi Arabia and India, has not established a viable alternate PNT system.  

When GPS/GNSS is unreliable or unavailable, AIS goes down with it, or, even worse, will transmit and receive spoofed position, courses and speeds. Until an alternative PNT system to backup GNSS is a reality, the only option is to defend GNSS against jamming and spoofing. There are technologies with such capabilities, but they have yet to be embraced by the shipping industry.  That risk-reward calculation may change if GNSS reliability continues to erode not only in conflict zones, but other parts of the globe as well. We may be entering new frontiers in electronic warfare as recent reports of space-based interference could raise the stakes for PNT users across the globe.

Authors 

Captain James Haley is a senior consultant for UHU Technologies. He served for 32 years as a harbor pilot and navigation technology expert in Long Beach, Calif.

Captain Dana A. Goward is President of the Resilient Navigation and Timing Foundation. He retired from the Senior Executive Service and served as the maritime navigation authority for the U.S.

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Cold War shortwave numbers stations broadcast strings of digits to anonymous listeners, content that’s meaningless to anyone without a matching one-time pad. They still operate today.

As it turns out, GPS broadcasts in much the same way.

Buried in every L1 C/A navigation message is Subframe 4, Page 17—a 176-bit field that IS-GPS-200 reserves for “special messages with the specific contents at the discretion of the Operating Command.” Every satellite broadcasts it. Every receiver decodes the subframe that contains it. And for nearly two decades, no one has publicly explained what it contains.

We analyzed 12.16 million observations in this field from 2007 through early 2026. The content is not text. It is encrypted material consistent with the military’s Over-the-Air Distribution (OTAD) global rekeying network. For 19 years, every operational GPS satellite has been a numbers station—broadcasting ciphertext on a public channel, to billions of receivers, in plain sight.

If you build receivers, write firmware, run signal monitoring, or care about the gap between civil and military signal transparency, this is your field too. You just have not been reading it.

What follows is the story of how a forgotten 176-bit slot in the world’s most successful navigation signal turned out to be its quietest and most consequential broadcast—and how a few weeks of analysis on a laptop, applied to 19 years of public archive data, was enough to read its operational history off the bytes.

176 Bits, Eight Words, One Forgotten Page

The L1 C/A signal carries 50 bits per second. Every bit must earn its place. The Legacy Navigation message organizes those bits into 1,500-bit frames, each frame into five 300-bit subframes, each subframe into ten 30-bit words. Subframes 1 to 3 carry the heavy work—clock corrections, ephemeris, the data your receiver needs every few seconds. Subframes 4 and 5 multiplex 25 rotating pages. A receiver sees Page 17 of Subframe 4 every 12.5 minutes.

Across 32 satellites, that is roughly 3,700 special-message payloads per day, fleet-wide. Multiplied across 19 years and the global ground-station archive, the figure climbs to 12.16 million observations.

176 bits is barely enough for a few floating-point numbers, but in a 50 bps signal, it is roughly 12% of every Subframe 4 broadcast. For the control segment to use that bandwidth consistently for two decades implies the content matters—even if no civilian receiver has ever rendered it.

Figure 1 shows how the bits are arranged. The 176-bit payload is fragmented across Words 3 to 10 of Subframe 4, Page 17: 16 data bits in Word 3 (after eight bits of Data ID and SV ID = 55, the marker that identifies Page 17), 24 data bits in each of Words 4 to 9, and 16 data bits in Word 10. The final six bits of every word carry the parity bits. After parity stripping and reassembly, the 22 bytes of payload are decoded under a subset of Code Page 437.

Mining 19 Years of Navbits

The corpus comes from the GFZ Potsdam open archive GNSS recordings collected from a wide network of ground stations, dating back to 2007. After extraction, the numbers settle: 12.16 million observations of Subframe 4, Page 17, drawn from every operational PRN, spanning 19 years, yielding 3,994 unique 176-bit messages.

Initial Python implementations needed hours to process a single year. To make iterative analysis practical, we wrote a Julia pipeline: NetCDF source files are converted to Apache Arrow, then thread-parallel bit extraction is performed into a DuckDB database. The full 19-year corpus extracts in seconds on a laptop. SQL across the lot returns in milliseconds.

With 12.16 million payloads in a queryable database, the question becomes: What does this field actually contain?

It Is Not Text. It Never Was.

The first thing a researcher tries in an unknown field is the obvious one: maybe it is text in a different encoding. We computed the frequency of each of the 45 alphabet symbols defined by IS-GPS-200 across all 12.16 million observations. In English, frequencies have a fingerprint—E and T are common, J and Z are rare, spaces and full stops are more common than digits. In a uniform random stream, each of the 45 symbols should appear with probability one in 45—about 2.22%.

The observed frequencies tracked the uniform baseline with remarkable precision. A chi-squared test against uniform yielded a z-score of 1.84, well inside the range where we cannot reject the null hypothesis of randomness. Across 12.16 million observations, the distribution is statistically indistinguishable from random data.

A stronger test asks the same question from a compression angle: How much information does each unique message contribute, given the others? An order-8 PPM-D compression model trained on the full corpus measures the marginal entropy of each payload—the additional cost, in bits, of encoding that message given everything else the model has seen. Real text would compress: Any recurring phrase, formatting block, or repeated formula would become almost free to code. Random data would not. Figure 2 plots the resulting distribution alongside a synthetic random baseline of 3,994 messages drawn uniformly from the 45-symbol alphabet and scored against the same model. The two distributions overlap almost perfectly, with means within half a bit of each other. By every available statistical lens, the GPS messages are almost indistinguishable from random, but there are intriguing outliers. At the lower end, messages are much more predictable than you would expect from random data; at the higher end, sentinels stand out from the rest. 

In Figure 2, blue indicates the marginal coding cost of each of the 3,994 unique 22-byte payloads under an order-8 PPM-D model trained on the corpus (μ≈131.5 bits per message≈6.0 bits per byte, σ≈7.6). Red indicates the same model scored against a synthetic baseline of 3,994 messages drawn uniformly from the 45-symbol GPS alphabet (μ≈132.0 bits, σ≈3.8). The two distributions overlap almost perfectly—the GPS messages are indistinguishable from random under the model. 

The next issue is that high-entropy output can come from encryption, compression or genuine randomness, and entropy alone cannot tell us which. This is correct. It is also the entry point to the rest of the article. If the field is encrypted, the protocol shape may still leave traces—placeholders where no payload is loaded, regime changes where policy shifts. In these structural metadata, the cipher does not reach. Encryption doesn’t hide “traffic data” of when and how often messages are sent and from which satellites. Each of those is a crack in the randomness, and the rest of this story walks through them in order.

What the entropy result does close off is the comfortable interpretation. Between 2007 and late 2023, no readable English appears anywhere in the dataset. No call signs, no acknowledgments, no test patterns of “the quick brown fox” variety. The field has not carried text in any conventional sense for the entire archived history of the GPS constellation.

For an engineer, that absence is itself information. The interface specification says this field is for text from the control segment. The bytes flatly disagree, and they have done so consistently, across every satellite, for 19 years.

High entropy on its own tells us only what the field is not. To learn what it is, we had to look for the cracks in the randomness.

A Single Byte, Repeated 22 Times, for 10 Years

The first crack in the randomness is also the most visible. Three messages, out of 3,994, have Shannon entropy of exactly zero. They are sentinels: 22 consecutive identical bytes broadcast as a single repeating pattern across the full payload.

• All-spaces—22 of byte 0x20.

• All-NUL—22 of byte 0x00.

• All-¬—22 of byte 0xAA, the CP437 negation glyph.

The all-¬ pattern is the longest-lived artifact in the dataset. It first appears on PRN 25 in February 2010, and quickly becomes the dominant default for the constellation, persisting intermittently across all 32 satellites for more than a decade.

The choice of byte 0xAA is not accidental. In binary, it is the perfectly alternating bit pattern 10101010—the canonical test sequence for bit synchronization, parity verification, and frame-alignment checks in receiver hardware. A satellite broadcasting all-¬ is broadcasting the protocol equivalent of a tone: present, parseable and intentionally empty. It is also outside of the characters permitted in the special message field, causing receivers to flag up data validation errors.

That intentionality matters. Encryption alone does not produce a constant. A genuinely random stream visits all-0xAA with negligible probability. The sentinels are placeholders by design—slots in the protocol marked as “no operational payload loaded.”

Their behavior fits that reading. Cross-referencing with GPS status reports (Notice Advisory to Navstar Users—NANU) shows satellites often enter sentinel states during commissioning and decommissioning. PRN 25 itself is the textbook case. The Block IIA satellite using that slot was decommissioned in December 2009. By February 2010, the slot was broadcasting all-¬. Its replacement, the first Block IIF, launched in May 2010, began pre-commissioning tests in August and also broadcast the all-¬ sentinel for several days before being declared fully operational on August 27. The pattern is unambiguous: When no operational payload is loaded, the field broadcasts the sentinel.

In a corpus where messages are replaced and never repeated, the sentinels are the only payloads that recur. Every other unique 176-bit message in the dataset appears in fewer than two calendar months for any given PRN. The sentinels persist for years. So, messages are replaced, never repeated—except the sentinels.

Why a system would broadcast a no payload loaded placeholder at all, and to what kind of receiver, needs the operational context that the rest of this article rests on.

Why GPS Carries Encrypted Signals—and What That Costs to Run

GPS broadcasts more than the open civilian C/A code. Since the activation of Anti-Spoofing on January 31, 1994, the constellation has carried encrypted military signals on the same frequencies: the Y-Code (the encrypted form of the precision P-Code on L1 and L2) and, on modernized satellites, the newer M-Code introduced with the GPS IIR-M block from 2005 onwards. These signals provide authorized receivers with jamming and spoofing resistance that civilian users do not have. The separation between open and encrypted signals also allows the operator to degrade the accuracy of civilian receivers while maintaining the precision of authorized ones. 

Encrypted signals need keys. Authorized receivers built since the late 1990s integrate a tamper-resistant cryptographic module called the Selective Availability Anti-Spoofing Module (SAASM)—the cryptographic basis of in-service infantry units such as the Defense Advanced GPS Receiver (DAGR). The SAASM holds a cryptographic key that lets the receiver lock onto the encrypted signal; without a current key, the receiver falls back to the unencrypted C/A code that anyone can track.

Keys do not sit still. To limit the damage from any single compromise, operational keys rotate on a schedule that, depending on the key class, can be as short as a single day. Every receiver in service—and the U.S. military operates them in the hundreds of thousands, across every theatre, vehicle platform, weapon system, and aircraft—needs each new key before its current one expires.

For most of GPS’s history, that meant physical key-fill: specialized loader devices had to be carried to each receiver, plugged in, and used to push the new key into the SAASM module. The keys themselves were distributed through NSA secure-courier channels. The logistics were demanding even in peacetime; in deployment, units that missed a key-fill window lost access to the encrypted signal until they could be reached again.

Over-the-Air Distribution (OTAD) and the closely related Over-the-Air Rekeying (OTAR) were the answer to that logistics problem. The principle is straightforward. A receiver that is powered on and already holds a valid current key can have its next key delivered via the GPS navigation message itself—encrypted under the current key and decoded within the SAASM module—without physical contact, a courier chain, or missed-window failures. The OTAD payload, the “next black key” in military parlance (where “black” denotes encrypted-at-rest), is what the GPS control segment must deliver to every authorized receiver on a schedule, via a public broadcast channel.

That delivery mechanism is what we believe Subframe 4, Page 17 has been carrying since at least 2007. If so, the constellation should reveal somewhere in its 19-year broadcast history the moment the delivery system went operational. And it does.

May 26, 2011: The Day the Constellation Spoke in Unison

May 26, 2011. Above the Earth, 31 active GPS satellites in 12-hour MEO orbits, each in its own slot, each broadcasting its own special message. By the end of the day, every one of them was broadcasting the same one.

Within a window of a few hours, all 31 operational satellites switched to the all-¬ sentinel. Every active PRN. Same payload. Same byte. Same coordinated event.

Figure 3 shows the 48-hour per-PRN timeline of the transition. It reads as a vertical bar slicing across the constellation: a step change so sharp and so simultaneous that no observational artifact can explain it. The data come from multiple receivers, ruling out a station-side glitch. Every PRN is involved, ruling out a single-satellite anomaly. No NANU was issued announcing a fleet-wide event of this kind.

In Figure 3, the Per-PRN broadcast state across a 48-hour window is centered on the transition. Each row corresponds to one of the 31 active GPS satellites; time runs from left to right in UTC. Within a few hours, every PRN switches to the all-¬ sentinel (red), holds it for between three and 24 hours, and exits to a new operational message at the end of the day. No publicly recorded NANU announces a fleet-wide event of this kind in the surrounding window. The transition coincides with the operational activation of the U.S. Over-the-Air Distribution rekeying network.

What remains is a coordinated, control-segment-driven blanking of the field across the entire operational constellation—the kind of thing that happens once, when an underlying system goes operational.

Declassified documentation places such a milestone in this exact period. A 2015 briefing by Maj Scott Tyley of the Space and Missile Systems Center describes the operational rollout of the U.S. OTAD system and its companion OTAR. The briefing identifies March 2011 as the start of continuous operational U.S. OTAD on all space vehicles.

Temporal alignment is not enough on its own to prove the connection; operational systems achieve operational status every year, and most of them do not announce themselves on L1 C/A. What raises the alignment from coincidence to causation is what happened next.

In the pre-OTAD era of 2007 to 2010, the constellation rotated unique payloads on average every 3.4 days; the 2007 to 2008 sub-period averaged about 2.3 days. In the operational era of 2012 to 2021, that rate jumped to once every 0.9 days, with a median message duration of 23 hours—almost exactly once a day. The H1 2011 period itself shows a cascade of four coordinated change points (January, February, May, June) culminating in the May 26 fleet flash, consistent with a phased activation rather than a single instantaneous transition. The result is consistent with the field being switched from a pre-operational test mode to an automated daily key-distribution cadence—exactly the operational tempo OTAD requires to deliver “next black keys” to SAASM-equipped receivers in the field.

Within a single 24-hour window, every operational GPS satellite switched to the same value.

From One Message a Week to One a Day, and Back Again

The 2011 flash drew a line through the dataset. Looking across the full 19 years, the field exhibits three behavioral regimes, each separated by a coordinated change point detected by Cumulative Sum (CUSUM) analysis applied to per-PRN message rotation rates.

The Pre-Operational Era, 2007 to 2011: A new payload per satellite roughly every 3.7 days on average. The rotation is irregular, the diversity is low, and the sentinel fractions are high. The pattern is consistent with field testing, including the 2010 coalition key transition exercises described in Tyley’s briefing. The system existed but was not yet running at operational tempo, or perhaps a predecessor system was in operation.

The Operational Era, 2011 to 2022: A new payload per satellite roughly every 1.8 days, fleet-wide, with median per-message duration of 23 hours. Daily cadence is the lifetime of a tactical cryptographic key; daily replacement of the field’s content is the operational signature of automated key distribution. The sentinels recede into the background; unique payloads dominate, with 162 to 381 distinct messages per year. For 11 years, the GPS constellation has operated the most widely used automated rekeying network on Earth.

The Modern Era, 2022 to Present: In May 2022, there is a sharp coordinated change point. The rotation rate drops to one payload every 4.3 days at the regime boundary, then keeps slowing. By 2025, it is approximately one payload per 6 days, and by early 2026 it is closer to one per 6.8. The shift is fleet-wide, simultaneous across 17 to 32 satellites, depending on which metric is examined, and again unaccompanied by a publicly recorded NANU.

Three rates: 3.7, 1.8, 4.3+ days per payload (the third era’s rate is not stable and has continued to slow). Three regimes: pre-operational, operational, post-2022. Figure 4 shows them as three plateaus separated by sharp coordinated transitions.

The fleet-mean per-message duration in days is plotted across the full 19 years of the corpus in Figure 4. The pre-OTAD era (2007 to 2010) cycles roughly every 3.7 days. From May 2011 the rotation accelerates to one payload every 1.8 days, sustained for 11 years and consistent with daily tactical key distribution. In May 2022, a coordinated change point detected by CUSUM analysis reverses the trend on roughly 30 satellites simultaneously; rotation slows to 4.3 days per payload at the boundary and continues to slow within the era — to 6.8 days by early 2026. Vertical lines mark coordinated change points (≥ 8 PRNs within ± 3 days).

The 2022 reversion is the most interesting open question in the dataset. Several readings are consistent with the data, and none are conclusive.

It could mark the migration of OTAD traffic from L1 C/A to a different signal, most plausibly M-Code on L1/L2, where modernized military receivers have been operating since the GPS III deployments began.

It could reflect a change in cryptographic policy: longer key lifetimes, fewer rotations, more reliance on session-key derivation at the receiver.

It could be the first visible footprint of the recently terminated Next Generation Operational Control System (OCX) ground segment, whose deliberate, staged rollout was a public program for years.

What the data say definitively is that whatever the explanation, it was a single decision applied across the entire fleet at once, and the public record contains no notification of the kind we would expect.

A field that announces operational changes by the cadence of its own ciphertext is a field worth watching.

When Encrypted Messages Share Their Spelling

If the messages were genuinely random—random or properly encrypted with independent keys, padding, and initialization vectors—then no two unique payloads should share any meaningful structure. Each 176-bit message would be statistically independent of every other.

They are not.

A Prediction by Partial Matching (PPM-D) order-8 compression model, trained over the full 3,994-message corpus, identifies pairs and small groups of unique messages that share long, identical substrings at the same byte positions. Examples from the catalog:

• Two messages broadcast on October 8, 2014, share 10 identical characters in identical positions.

• A message from June 2021 and a message from September 2020 share a 9-character substring at the same offset.

• A pair of late-2019 messages, broadcast three weeks apart, share eight characters at identical byte positions.

• The substring LY47IRP16—9 bytes—appears in messages broadcast nine months apart.

• S°6L.D°—7 bytes—recurs three months apart.

The probability that any given pair of 22-character messages drawn independently from a 45-symbol alphabet would share a nine-character substring at the same offset by chance is negligible. Across the full corpus, the matches are not coincidental; they are structured. 

In Figure 5, five message pairs are identified by an order-8 PPM-D compression model as sharing long substrings at identical byte positions, despite being broadcast days, weeks or months apart. Each pair is shown one above the other, with shaded cells highlighting the matching bytes. The remainder of each message is the high-entropy ciphertext that fills almost the entire corpus.

The most likely explanation is protocol metadata leaking through. Every cryptographic transport protocol wraps its payload in headers—key identifiers, sequence numbers, etc. However, this alone is not a sufficient explanation because these values are encrypted and should therefore differ for every message. In addition to fixed metadata, there would need to be re-use of a key, whether due to operational error or exceptional circumstances. In such a scenario, we would expect to see partial matches between two different messages.

There is a practical consequence. If the substring matches are protocol metadata, they offer an external observer something the cryptography was meant to deny: a way to fingerprint and track individual key-distribution events from public signal data. A monitoring receiver, watching a small set of fixed byte positions across the entire constellation, could, in principle, detect when a particular key identifier or routing header is reused, retired or correlated with a NANU-announced operation. Cryptographically, the keys remain secure. Operationally, the metadata is loud.

In a stream that should be indistinguishable from noise, the protocol left a fingerprint.

The First Readable Bytes in 19 Years

In the corpus that runs from 2007 to mid-2023, no payload anywhere contains a recognizable word from any language that’s intended for direct human consumption. Then, on December 13, 2023, PRN 8 broadcasts a message that begins with the literal four-byte string TEXT.

After 16 years of pure ciphertext, the field has begun to use the format the standard always described. 

The migration is both staged and deliberate, reading like a deployment plan rather than just a casual flip of a switch.

• December 13, 2023—first appearance, on PRN 8 alone.

• March 18, 2024—the same TEXT-prefixed message broadcast on 10 PRNs simultaneously: a one-day fleet-wide distribution event.

• July 31, 2024—a second TEXT message, on PRN 3 alone.

• October 10, 2024—a four-PRN distribution.

• December 29, 2024—January 13, 2025—daily TEXT messages on PRN 1, with a different payload each day.

• March, June 2025—the daily-broadcast PRN moves to PRN 21.

• July–August 2025—the daily-broadcast PRN moves to PRN 20.

Each TEXT-prefixed message rotates daily and carries an 18-byte payload following the prefix. The payload itself remains high-entropy—by every statistical measure indistinguishable from the ciphertext that preceded it. The format has changed. The content shape has not.

The most plausible reading is a generational upgrade. OCX is rolling out. GPS III satellites are operational and growing as a fraction of the constellation. A new variant of OTAD, or a new auxiliary use of the field bolted alongside it, is being commissioned by PRN.

For receiver firmware, the migration matters in a way the previous 19 years did not. A field containing static-looking ciphertext is one that most parsers ignore. A field that apparently carries a structured type identifier followed by a payload must be parsed correctly.

The September 2020 SVN 74 anomaly is a cautionary tale, even though it concerns a different field: an ICD-defined alarm pattern transmitted as prescribed, with a minority of commercial receivers failing to handle it correctly and pushing bad positions to ADS-B users. The TEXT-prefix migration is an analogous situation—content that finally matches the special-message field’s standard format, arriving on receivers that may have spent two decades treating this field as static or ignored. Either direction of mismatch, content the standard did not describe, or content that suddenly does, can produce the same kind of outcome.

For the receiver and firmware teams, the practical action is short. Audit any code path that touches Subframe 4, Page 17. If the field is currently being skipped, logged as static, or assumed to be text, that assumption now has an expiration date. The TEXT prefix suggests the message is intended for human consumption; the trailing 18 bytes are the payload, which the standard has always permitted. Code that handles both is forward-compatible. Code that handles only one is the next September 2020 waiting to happen.

The migration is happening now. As of early 2026, only a handful of satellites have broadcast TEXT-prefixed messages, and the rest of the fleet continues to use the unstructured format. Which PRN converts next, and what its first TEXT-formatted message says, is the most accessible real-time measurement of GPS ground-segment evolution available to anyone with a receiver and patience.

Figure 6 plots every TEXT-prefix broadcast event in the corpus, satellite by satellite.

It shows 26 unique messages, 38 (PRN, day) combinations and 2,398 total observations. Marker size scales with daily observation count. Five distinct phases are visible. The first TEXT message appears on PRN 8 on December 13, 2023 (red). Three multi-PRN distribution events follow in 2024 (teal): a 10-PRN event on March 18, 2024, a single-PRN appearance on July 31, and a four-PRN distribution on October 10. From December 29, 2024, the protocol stabilizes into bursts of consecutive daily broadcasts that migrate between satellites: first PRN 1 (dark grey, December 2024 to January 2025), then PRN 21 (purple, March and June 2025), then PRN 20 (amber, July to August 2025). The migration looks far more like a staged deployment than an organic spread.

The Bottom of the Rabbit Hole, Or the Top of It

For nearly two decades, every operational GPS satellite has broadcast an encrypted stream consistent with the backbone of the U.S. military’s global cryptographic key distribution system.

The 2011 fleet flash was the constellation-wide synchronization that brought the system to operational capability. The 0xAA sentinel is the protocol’s no payload loaded marker. The shared substrings are the structural fingerprints of an OTAD frame leaking through the cipher. The 2022 reversion is the system in transition. The TEXT prefix is the system in renewal.

This matters in three ways:

• For signal authentication. OTAD is the proven, decades-long predecessor to civilian schemes like Galileo OSNMA and GPS CHIMERA. Its operational history, until now invisible, is data that the authentication community can study.

• For operational transparency. Both the 2011 flash and the 2022 reversion happened without the kind of public NANU record one might expect for a fleet-wide operational change. The methodology in this article, open archives, off-the-shelf tooling, 18k lines of Julia, gives the GNSS community the means to monitor the constellation’s internal states for itself.

• For pure engineering curiosity. Every receiver in the world decodes Subframe 4, Page 17. Almost none of them have ever looked at it. The lesson generalizes: There is more to learn from the bytes already arriving at our antennas than from the bytes we wish were specified differently.

The data are publicly available. The signal is overhead, twice a day, every day. We invite the GNSS engineering community to join the audit for L1 C/A and the newer signals that will inherit its role.

Every GPS satellite is a numbers station. The receivers were always listening. We just had not been. 

Acknowledgements 

This article is based on a project developed by Ahmed Kamruddin during his MSc studies at University College London. Thanks also to Ramsey Faragher and Markus Kuhn for valuable comments on this work. The initial stages of the work were performed within the Trusted Innovative GNSS receivER (TIGER) project, co-funded by the European GNSS Agency (GSA) under grant agreement 228443. Source code supporting this project can be found at https://doi.org/10.5281/zenodo.20073222.

Author

Steven J. Murdoch is Professor of Security Engineering, head of the Information Security Research Group and lead for the Foundational Computer Science section in University College London. His research encompasses payment system security, privacy enhancing technologies, online safety, and the intersection of computer science and law. He teaches on the UCL MSc in Information Security. He has worked with the OpenNet Initiative, investigating Internet censorship, and for the Tor Project, on improving the security and usability of the Tor anonymity system. His current research focuses on how computer systems can generate evidence to facilitate fair and efficient dispute resolution. He is a member of REPHRAIN, the National Research Centre on Privacy, Harm Reduction and Adversarial Influence Online and co-leads the CRANE NetworkPlus on Cybersecurity. He is a director of the Open Rights Group, a UK-based digital campaigning organization that works to protect rights to privacy and free speech online. He is also a Fellow of the IET and BCS.

The post The Empty Field that Wasn’t: GPS, OTAD and Two Decades of Encrypted Broadcasts appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

Murata had previously invested in Xona through WONDERSTONE Ventures, its corporate venture capital arm. The MOU moves the relationship downstream toward hardware, pairing Murata’s capabilities in high-frequency communications, sensors, timing devices and module design with Xona’s LEO-based PNT infrastructure.

Xona’s Pulsar service is built on a dedicated LEO constellation designed to deliver significantly stronger signals than conventional GNSS, with centimeter-level positioning accuracy, faster convergence times, reduced multipath error and improved performance in urban and indoor environments. Pulsar is designed for GNSS compatibility, enabling integration with existing user equipment as a complement rather than a replacement.

The two companies identified data centers and financial institutions requiring precise timing synchronization for 5G and 6G communications infrastructure, and off-road construction and agricultural machinery operating in environments where GNSS availability is limited, as near-term application targets.

Murata described the space domain as a new growth area, framing the partnership as part of a broader commitment to advancing positioning and timing synchronization as foundational technology across communications infrastructure, industrial equipment, mobility and consumer IoT. The company’s scale — it is among the world’s largest manufacturers of passive electronic components — gives the partnership potential reach across global industrial supply chains that few LEO PNT agreements to date have carried.

The announcement follows Xona’s appearance in GPS Innovation Alliance testimony before the House Energy and Commerce Subcommittee on Communications and Technology last week, where GPSIA executive director Lisa Dyer cited six Xona satellite launches planned for this fall and called on Congress to urge FCC approval of the company’s pending radionavigation-satellite service license application.

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“Chasing Lightning: Detecting, Characterizing, and Identifying a Powerful Space-Based GNSS Interference Source” is the title of a new paper Zachary Clements, Argyris Kriezis, and Prof Todd Humphreys. It details how, after almost two years of effort, they were able to identify a constellation of Russian early warning satellites in Molniya (“lightning”) orbits as the source of a series of difficult-to-detect disruptions to GPS signals. 

The paper identified 75 events over a seven-year period in which terrestrial reference stations operated by the International GNSS Service in Europe, Greenland and Canada recorded simultaneous and significant drops in carrier to noise ratio (CNR). 

The story of this jammer hunt in space began in September 2024. During a presentation to the Civil GPS Service Interface Committee  in Baltimore, Humphreys opined “There is every reason to believe China’s BeiDou global navigation satellite system has the ability to imitate American GPS signals and those of Europe’s Galileo,” His remarks were reported in SpaceNews along with speculation about Russia’s capabilities.

The SpaceNews article prompted a call to the Resilient Navigation and Timing Foundation from a researcher in the United Kingdom. The researcher reported that deliberate disruption from space was not just speculation – he had observed it. While the researcher did not want to be publicly identified, he was happy to provide the data and allow others to confirm his findings.

With the researcher’s permission, the Foundation connected him with several GNSS experts who could confirm his findings and met with U.S. government officials to convey the extensive data package.

Clements and Humphreys reported on their initial findings in the paper “Transient Space-Based GNSS Interference: Observations and Analysis” at the Institute of Navigation Conference in September 2025. At that point they had not yet identified the source of the interference.

In the new paper the researchers outline how they accessed data from 165 reference stations. Seventy-five simultaneous drops in CNR across multiple stations, with at least one station recording a drop of 5 dB or more, were identified. 

Humphreys is confident that the interference is purposeful, not hardware malfunctions or accidental emissions. 

“The pattern is far too consistent for this to be accidental. In fact, our data shows it has to be intentional.” 

The interference:

• Has almost always been on a weekday – usually Tuesday through Thursday,
• Events are not regularly spaced out and are transient (less than 10 seconds) rather than periodic or continuous as would be expected from an equipment malfunction,
• Events are quite powerful. CNR drops of up to 10 dB have been observed in some cases, and 
• Impacts are to the most commonly used GPS frequency, L1, but don’t affect other GPS bands like L5.

Also, the signals interfering with GPS are not exactly astride the L1 frequency but are slightly offset. They are centered at 1577.5 MHz, about 2 MHz above the GPS L1 center frequency. This may be an effort to test the capability while avoiding detection.

Perhaps most damning, Humphreys’ team has found that the same Russian constellation has been impacting signals from China’s Bei Dou satellite navigation system in an almost identical way since June 2020.

It is clear that one of this constellation’s primary capabilities is disruption and denial of America’s GPS and China’s Bei Dou navigation systems, should the Kremlin decide to do so. A slight change in frequency and an increase in transmitted power is all that is needed to prevent reception across continental size areas.

The new paper provides six insights for GNSS experts and observers. It:

• Provides measurement models and a detection framework for transient wide area interference,
• Details the spatial, temporal, and spectral properties of multiple wide-area GNSS outage events from the space-based interference source and distinguishes these from a naturally occurring solar radio burst,
• Presents a basic satellite identification strategy to narrow the candidate satellites and estimate the minimum satellite altitude at apogee,
• Presents an advanced satellite associate framework using the generalized likelihood ratio test (GRLT) and applies the framework to a test scenario, 
• Details a framework for instantaneously identifying an interference satellite based on a brief time history of TDOA measurements, and gives an error sensitivity analysis, and 
• Combines IGS CNR data and raw wideband samples from two additional receivers in Europe to confidently identify the source, which is revealed to be a small constellation of Russian satellites in Molniya (“lightning”) orbit.

The paper reveals a significant threat to GPS and other GNSS that has heretofore been unknown to the general public. Findings have already been reported by the New York Times and a video about the discovery has been posted on YouTube by the science education channel Veritasium. 

Many in the community expect that it will increase already high levels of concern about the vulnerability of GPS and other GNSS and how it is used as a tool in great power competition. 

Russia has been particularly open about its use interference from terrestrial sources to punish its neighbors in the Baltic and eastern Europe for growing closer to the West. 

In November 2021 as it prepared to invade Ukraine, Russia shot down one of its defunct satellite with a ground-based missile. The following day state-sponsored media threatened that if NATO got in its way in Ukraine, Russia would shoot down all 32 GPS satellites.

While Russia many not have had the capability to destroy all GPS satellites, it is now clear they had the ability to prevent reception of signals across very wide areas of the globe. 

It is unknown how Russia’s threat influenced the West’s actions in Ukraine. Or how Russia’s ability to turn off reception of GPS and other GNSS with the flip of the switch will impact international relations and actions in the future.

What we do know is that Russia and China have terrestrial PNT systems to complement and backup their systems in space. 

Unlike the United Kingdom and France which are building such systems, and South Korea and Saudi Arabia which have them already in place, the United States has yet to act.

GPS is an amazing and priceless asset. Yet without the protection of a robust and resilient complementary and backup system it remains, as a member of the National Security Council once said, “a single point of failure” for America.

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What emerged was a detailed picture of a system that remains the world’s gold standard for civil and military PNT—operationally reliable, economically indispensable—but one whose modernization has fallen behind the pace of threat, and whose complement architecture is now the subject of a spectrum dispute with consequences well beyond the PNT community.

This account is based on the written statements submitted to the subcommittee by the five witnesses.

The five witnesses were Lisa Dyer, executive director of the GPS Innovation Alliance (GPSIA); Sam Matheny, chief executive of the newly launched Merkhet Solutions; Mariam Sorond, CEO and board chair of NextNav; Harold Feld, senior vice president of Public Knowledge; and J. David Grossman, vice president for policy at the Consumer Technology Association.

The constellation: strong record, narrowing margins

Dyer’s written statement provided the most technically grounded account of GPS’s current status.

The constellation has not experienced a system-wide outage since achieving full operational capability in 1995. The FAA reports GPS system availability at 99.9999 percent. Thirty-two satellites are on orbit, eight above the 24-satellite minimum required for global coverage. The Wide Area Augmentation System extends accuracy and monitors signal integrity across the National Airspace System.

Against that record, Dyer placed a more pressing set of facts. Eight of the 32 satellites are operating on a single string—one subsystem failure each from becoming non-operational. More consequentially, on April 17, 2026, the Space Force terminated the GPS Next Generation Operational Control System program, the long-delayed ground-segment effort that had run more than a decade behind schedule and triggered a Nunn-McCurdy cost breach. Dyer framed the cancellation as an overdue clearing of the path for rapid modernization, and for what she described as a more deliberate integration of commercial satellite PNT data into military operations.

She also documented a capability asymmetry that the subcommittee has not previously examined at this level of specificity. GPS III satellites deliver eight times the anti-jamming protection for military users over their predecessors. GPS IIIF satellites, when fielded, will deliver 63 times. Neither generation extends those protections to civil, commercial or scientific signals. Dyer argued the civil-signal gap carries national security implications precisely because aviation, maritime and surface transportation operators—sectors that depend on civil GPS signals—provide mission-critical logistical support to the Defense Department.

GPSIA submitted formal recommendations on GPS modernization to the defense subcommittees of both Appropriations Committees and both Armed Services Committees the week of the hearing. In September 2025, the Alliance sent a letter to Secretaries Hegseth and Duffy outlining a range of whole-of-government options for addressing jamming and spoofing.

Interference: from conflict zone to domestic runway

Witnesses presented interference as a problem that has moved decisively from theoretical to operational. Sorond cited two 2022 incidents on U.S. soil: a jamming event of unknown origin that shut down a runway at Dallas–Fort Worth International Airport and disrupted roughly 40 miles of airspace for nearly two days, and a separate unauthorized transmitter that interfered with GPS operations at Denver International Airport, affecting both aircraft and air traffic control. Feld’s written statement pointed to a more recent example: Russia’s jamming of the GPS systems aboard the RAF aircraft carrying UK Defense Minister John Healey as he returned from a visit to Estonia. Dyer referenced third-party data aggregating more than 55,000 reported GPS interference events in commercial aviation in 2025—a 24 percent increase over 2024—noting that while the majority occurred overseas and near active conflict zones, a portion occurred within U.S. airspace or on approaches to U.S. destinations.

Dyer was pointed on enforcement. The legal framework is not the problem—federal law already prohibits the manufacture, sale and operation of jamming equipment that interferes with authorized radio communications. In her written statement, she argued that the FCC and the Department of Transportation lack the budget and personnel to enforce those laws, coordinate a whole-of-government response, or adequately address the growing volume of incidents. She called on Congress to provide both agencies with the resources to meet their existing mandates.

The complement landscape: consensus on need, but not on method

Where the panel converged on the modernization and interference questions, it divided sharply on the path to a resilient complementary architecture.

Matheny testified on behalf of Merkhet Solutions, an independent company launched June 2 to commercialize the Broadcast Positioning System (BPS), a terrestrial PNT technology developed at the National Association of Broadcasters starting in 2021. BPS embeds timing and tower-location data within ATSC 3.0 transmission signals. A single tower provides traceable time; multiple towers enable positioning by the same multilateration geometry as GPS. The system requires no internet, satellite or cellular connectivity, operates on existing licensed broadcast spectrum, and supports passive, unlimited simultaneous reception.

Matheny cited a 2025 peer-reviewed NIST finding—produced under a 2024 cooperative research and development agreement—that BPS time-transfer performance is “comparable to or better than GNSS” and constitutes a “viable complementary PNT solution.” A Department of Transportation field trial with Dominion Energy, contracted in August 2025, is underway at a major East Coast substation, assessing BPS performance for grid timing applications. Merkhet currently has deployments in Washington, D.C., Baltimore and Denver. ATSC 3.0 is live in 80 markets reaching more than 75 percent of the U.S. population.

NextNav’s position was presented by Sorond. The company’s Pinnacle vertical-location service is operational in more than 4,400 cities, serves more than 90 percent of U.S. commercial buildings taller than three stories, and provides commercial Z-axis with deployments on all three national wireless carriers and FirstNet. NextNav holds more than 150 patents and describes itself as the largest license holder in the only band the FCC has designated for ground-based positioning.

The company has a petition pending before the FCC that it characterizes as a modernization of its existing licenses in the 902–928 MHz band, to support what it describes as a 5G-based horizontal PNT complement and backup to GPS, deployable on existing wireless infrastructure at no direct cost to taxpayers. The band supports a wide range of licensed and unlicensed operations — among them electronic toll collection systems such as E-ZPass, utility smart meters, home security alarms, agricultural sensors, RFID inventory systems and medical alert devices — that collectively represent decades of investment built on the FCC’s existing coexistence framework.

On the question of modernization, Feld argued that the petition does not update existing rules but asks the FCC to eliminate them—specifically, the protective conditions the Commission attached to the M-LMS licenses when it created them in 1995. That order explicitly acknowledged that Part 15 unlicensed devices had “developed and proliferated in this band and are providing services that are valuable and in the public interest,” and conditioned the new licenses on field testing to demonstrate no unacceptable interference. Feld wrote that NextNav has since “consistently requested that the FCC eliminate the rules protecting unlicensed operations in the band” rather than pursue the cooperative coexistence the 1995 order envisioned.

On the cost question, Feld wrote that the proposed transaction would exchange roughly 14 MHz of shared, low-power spectrum with a partial national footprint for 15 MHz of full-power, flexible-use national spectrum—rights that would be worth billions of dollars if acquired at auction. Feld wrote that, based on the company’s filings, PNT would occupy a small fraction of the resulting network capacity, with the remainder available for mobile carrier use. On the question of deployability, Feld wrote that the proposal would require development of new chips and new 5G standards before any commercial deployment—a process that would take years and depends on wireless carrier adoption that has not been secured.

Grossman characterized the proposal as a structural reconfiguration of the band’s operating environment, not a marginal technical adjustment, and argued that the record of innovation built on existing rules must be weighed against claims of future benefit.

The LEO tier: commercial systems advancing without Washington

Running through the hearing but never its explicit focus was the accumulating progress in commercial low Earth orbit PNT—the tier that may ultimately prove most consequential for complementary architecture.

Dyer described three U.S. companies in various stages of deployment. Iridium operates the first commercial LEO PNT system in the United States, with more than 70 partners across 25 states. TrustPoint is developing a C-band constellation designed for orbital, signal and frequency diversity relative to L-band GPS; three satellites are on orbit, four more in development, with commercial service targeted for 2027. Xona is broadcasting a new signal designed for compatibility with existing GPS receiver infrastructure, scaling manufacturing in California with six launches planned this fall. GPSIA formally recommended that Congress urge FCC approval of Xona’s pending radionavigation-satellite service license application (ICFS File No. SAT-LOA-2023-0711-00165).

Feld anchored the panel’s broader policy argument in the GPS-as-public-good framing, warning against any architecture evolution that would introduce tiered access, impose new costs on agricultural and rural users who rely on free GPS today, or allow the existing system to degrade in favor of proprietary alternatives. He called for privacy-by-design principles to be incorporated into next-generation PNT at the system level rather than addressed through post-hoc regulation.

The record as it stands

The hearing did not resolve the FCC proceedings it illuminated. Its contribution was to put the state of the U.S. PNT posture on the legislative record at a moment when three distinct tracks—GPS modernization, interference enforcement and complement architecture—are simultaneously in motion, each with its own pending proceedings and its own constituency of stakeholders whose written positions now form part of the official record.

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