This award, granted through the Space Technology Advanced Research – Fast-tracking Innovative Software and Hardware (STAR-FISH) program, brings Xona’s total signed contracts to over $20 million to date.

Through this contract, Xona will demonstrate key performance aspects of its PULSAR™ high-performance satellite navigation service on multiple commercial user devices and in a variety of scenarios, including where GPS and other Global Navigation Satellite Signals (GNSS) may be challenged or denied. Testing will include demonstrations of jamming and spoofing resilience, multipath effect reduction, and security key distribution. This effort will accelerate the readiness of advanced alt-PNT capabilities in commercial off-the-shelf user equipment to meet DoD user needs with rapid acquisition times.

As part of this contract Xona has partnered with several leading GPS/GNSS user equipment providers with the ability to rapidly manufacture and deploy PULSAR enabled devices. Partners who will be demonstrating performance of their devices with the PULSAR service as part of this contract include QinetiQ, StarNav, and Locus Lock.

“The technology in modern GNSS user equipment is incredibly advanced these days, and capable of very high-performance if you can provide it a high-performance signal,” said Brian Manning, Xona CEO & Co-Founder. “This contract is enabling us to demonstrate not only the advanced capabilities these receivers can achieve with the PULSAR service, but also the utility of combining mass produced hardware with a securely controlled PNT service to support anything from small drones to large DoD systems.”

This multi-year award will feature Xona’s advanced simulation capabilities along with demonstrations using the first PULSAR satellite that is scheduled to launch in June 2025.

The post Xona Secures $4.65M Contract with AFRL to Demonstrate Capabilities of Low-Earth Orbit (LEO) GPS Alternative in Commercial User Equipment appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

A terrible thing happened on the night of January 29th in Washington DC, within view of our Nation’s capital. A U.S. Army Blackhawk helicopter collided with an American Eagle Regional Jet over the Potomac river, killing all 67 people aboard both aircraft.

Any loss of life is a terrible thing, but this specific accident is very disturbing for me because as a licensed commercial pilot and flight instructor with multi-engine and instrument ratings, and being CEO of an aviation technology company, I know that technology is available that could have prevented this accident.

Why wasn’t it being used? Some of it was…but not ALL of it and not EVERYWHERE. It may be shocking to know that our current approach to regulations and policy is that it usually does not change until something like this happens. In parallel, subtle exceptions to rules creep in from a variety of sources over time. We are left with a largely safe system, but one that has various ‘gaps’. While these ‘gaps’ might be small, when they line up, catastrophic events can occur, like this collision.

Below is a map image that illustrates the path of the American Eagle Regional Jet. This path is consistent with a visual approach to runway 33 at Reagan National Airport. This approach is often used for regional jets because they can use the shorter runway (Runway 33), allowing controllers to more efficiently move traffic on Runway 1 (the primary runway) as well as the ramp areas. uAvionix systems are able to track this data using Automatic Dependent Surveillance-Broadcast (ADS-B). Put simply, ADS-B is a way for an aircraft to share its own position (referred to as Ownship) with air traffic control and other aircraft in the area. It shares this information over a radio signal that broadcasts every 1 sec (referred to as 1 Hertz (Hz). In the USA, all commercial and private aircraft are required by regulation to transmit ADS-B position when in specific classes (areas) of the National Airspace (NAS). The DC airspace is one of those areas, so the airliner was compliant and was transmitting ADS-B, as you can see in the image. Notice the helicopter’s path is not illustrated. That is because the Blackhawk helicopter, being a military aircraft, is not required to broadcast ADS-B (nor is it required to receive ADS-B), and as such, is not picked up by ADS-B receivers.

Also required in this class of airspace is a device known as a transponder. A transponder responds to a radio frequency signal (referred to as an interrogation, usually emitted by a ground based radar) and returns data about the aircraft’s type, callsign and altitude as measured by equipment on the aircraft. This allows air traffic controllers to receive higher quality altitude data about each aircraft than the radar itself can provide (most radars only return bearing and range information). In the case of this accident, both aircraft were equipped with transponders and both transponders were sharing position information. The image below shows the transponder tracks for each aircraft.

In addition to ADS-B and transponders, all transport category aircraft operated under Part 121 of the FAA regulations (14 CFR 121) are also required to have a system called Traffic Collision Avoidance System (TCAS) aboard. TCAS uses the transponders on each aircraft to query other aircraft’s transponders to determine if they are on a collision course. If the systems determine they are on a collision course, warnings and commands are issued to the flight crew from the TCAS. These are known as Traffic Advisories (TA) and Resolution Advisories (RA). A TA is for awareness only, but an RA is a command that must be followed by the crew immediately.

So why didn’t the TCAS tell the American Airlines crew to do something? Well, the airport environment is a busy place with aircraft operating very near each other. Further, the final approach segment for a flight crew is a high workload time of flight. Since the TCAS would likely trigger a large number of TA’s and the potential for false RA’s at low altitude, it is suppressed below 1,000 feet above ground level (AGL). Specifically, there are no RA’s issued below 1,000 feet AGL, and all TA’s are muted below 500 feet AGL.  This accident occurred at roughly 300 feet AGL.

The U.S. Army Blackhawk Helicopter is not required to have TCAS aboard, and even if it did, it would have been suppressed just as the American Airlines jet’s was.

This is point #1 – in this type of airspace with this volume and proximity of traffic, why are all aircraft not required to use all available technology to avoid collision?

To address that, we must look at how aircraft are typically separated by pilots and air traffic control.

The last line of defense against mid-air collision is the human eyeball. The regulations (14 CFR 91.113) clearly spell out that it is the pilot’s responsibility to ‘see and avoid’ all other aircraft to avoid a collision.  Most general aviation operations rely on this method to avoid collisions as most of the country is not covered by radar or managed by air traffic control. There are strategic and tactical operations that we use to minimize the chances of a mid-air collision – things like specific traffic patterns, cruising altitudes, right of way rules, radio calls – but at the end of the day, it is a human pilot looking out the window that is the last line of defense.

Air traffic control exists to assist the pilot with that task by deploying a variety of techniques and technologies ranging from calling out the position of other aircraft, to tracking aircraft on radar to issuing heading and altitude commands to pilots to help them navigate away from potential collisions.  Controllers talk to pilots over good ol’ radios.  Simplex radios, to be specific. Simplex means that only one person can broadcast at a time, and if two people key the microphone at the same time, they will cancel each other out (we call this getting ‘stepped on’). To help alleviate that risk, specific frequencies are used in different sectors of airspace, and the community uses a specific syntax, cadence and sequence of communication to minimize ‘two talking at once’. The system works remarkably well.  Additionally, when all the pilots in a specific area are on the same frequency, we can all hear the communications between ATC and the other aircraft, allowing us each to form a mental picture of the aircraft in the airspace (something we call situational awareness, or SA).

So what happened in DC?  Both aircraft WERE in communication with air traffic control, but they were NOT on the same frequency. Military aircraft use Ultra High Frequency (UHF) radios and civilian aircraft use Very High Frequency (VHF) radios. The helicopter and the airliner could not hear each other, nor could they hear what the controller was saying to the other aircraft. That is to say that the respective crew’s ability to build a mental picture of the airspace and aircraft in it was limited.

Additionally, when the weather conditions are clear, it is routine practice for a controller to call out traffic to a crew, something like “American 2135, traffic 12 o’clock and 4 miles is a United Boeing 737, report that traffic in sight”. If the crew responds saying they see the traffic, the controller can then direct the crew to ‘maintain visual separation’ with that traffic, effectively handing off the accountability for separation to the flight crew. It seems this happened properly on the night of the collision, with the controller calling out the airliner’s position to the helicopter crew and the helicopter crew acknowledging they had the traffic in sight. But there is a wrinkle in this…did the helicopter crew have the SAME aircraft in sight that the controller was calling out? If you look at the geometry of the aircraft just prior to the collision, there were likely TWO airliners within the field of view of the Blackhawk crew – the one they eventually collided with and a different airliner that was on final approach to a different runway at DCA much farther away. IF the Blackhawk crew looked up when the traffic was called and happened to see the more distant aircraft first, they MIGHT have acknowledged the controller that they had the aircraft in sight, but it was the wrong aircraft. This situation is demonstrated in the image below and a 3D model describes the view in this Washington Post article, (Washington Post – 3D Model of DC Plane Crash):

Put simply, if both aircraft were transmitting and receiving ADS-B, they would have likely both been aware of each other’s position in plenty of time to avert a collision. In our opinion, the only reason ADS-B equipage is not mandatory for ALL aircraft is that there have been too many opposing voices in our country, citing reasons like privacy, government overwatch, frequency and system saturation, etc. Those voices have been successful in ‘carving out’ specific exceptions to the rule the FAA enacted in 2020, mandating the use of ADS-B Out in specific classes of airspace for just about all types of aircraft, except military, law enforcement and some other special cases. Outside of those classes of airspace, ADS-B Out (or In) is not required.

In partnership with a Boeing subsidiary called ForeFlight, uAvionix manufactures and sells a device called a Sentry. It is a portable device that contains sensors and receivers that provide a pilot with their position, attitude and receipt of ADS-B data, which contains both weather information and traffic information. It connects wirelessly to Apple and Android devices allowing for traffic and weather data to be shown on a moving map in the cockpit. In the case of the DC mid-air, this device, if it were used on the Blackhawk helicopter, would have alerted the crew to the presence of the airliner (since the airliner was transmitting ADS-B), and potentially could have mitigated this disaster.

So there are a bunch of ‘Yes, IF’s…’ here:

• IF the Blackhawk helicopter had a Sentry and an iPad running ForeFlight, they would have been alerted to the airliner.
• IF the Blackhawk helicopter was broadcasting ADS-B, the airliner would have been alerted.
• IF both aircraft were talking to tower on the same frequency, they would have been more aware of each other’s position.
• IF we did not rely on human eyesight for the safe separation of aircraft…
• IF instead of a set of exceptions to rules, we had mandatory equipage of position reporting technology for ALL aircraft…

I resonate deeply with our company’s ‘why’ of radically innovating to make the skies open and safe for all. We have done the innovation part, and we continue to do so, aligned with this mission. It is sad and frustrating when I know we have the means to avoid these types of tragedies, but special cases and exceptions preclude those technologies from getting deployed. Nevertheless, this event strengthens our resolve to get our capabilities into the field to prevent this type of accident in the future. I firmly believe we not only have the technology to address these challenges, but that we can also assuage the concerns of those who have objections to the technologies in a positive way so that no one ever has to lose a loved one to a mid-air collision ever again.

The post Mitigating Mid-Air Collisions: The Reagan Mid-Air appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

LuGRE was developed in Italy by Qascom on behalf of the Italian Space Agency, in collaboration with NASA and scientific support from the Politecnico di Torino. The receiver is integrated into the commercial lander Blue Ghost 1, which Firefly Aerospace built in the United States as part of NASA’s Commercial Lunar Payload Services (CLPS) program.

The signal acquisition occurred in the L1/E1 and L5/E5 bands throughout the Blue Ghost 1 lander’s journey to the Moon. The most distant GNSS satellite signal received was from the Galileo constellation, at a distance of 67.79 Earth radii, about 432,384 kilometers from the LuGRE receiver.

This recent operation demonstrated that the receiver could use GNSS signals even near the Moon, where the lander orbited in low lunar orbit at a speed of approximately 1.66 kilometers per second.

Despite the significant distance and high speed, the position was calculated with very high accuracy, with an error margin of about 1.5 kilometers for position and about 2 meters per second for velocity. Signals were successfully acquired from four GPS satellites on the L1 and L5 frequencies and from one Galileo satellite on the E1-E5 frequency bands during a one-hour time window.

It also demonstrates the power of using multiple GNSS constellations together, such as GPS and Galileo, to perform navigation. After lunar landing, LuGRE will operate for 14 days and attempt to break another record – first reception of GNSS signals on the lunar surface.

The post LuGRE Successfully Tracks GNSS Signals in Lunar Orbit appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

This is the first step toward a potential in-orbit demonstrator for optical time synchronisation and ranging (OpSTAR) that will be proposed at the ESA Council at Ministerial Level in November 2025, to validate intersatellite optical links before future use in operational satellite navigation systems.

Optical links, which transmit data using laser beams instead of radio signals, are already well established in the field of satellite communications. To be used in navigation, they still require technological advancements and in-orbit validation of the end-to-end system concept.

ESA aims to develop and test optical technology for time synchronisation and ranging. To that end, the agency has signed a contract with a consortium led by German OHB System as prime industry to conduct a concept definition study (Phase A/B1 study) and technology predevelopments. The European consortium involves 33 companies from across ESA Member states.

After this study, the next step would be to develop and test the technology in-orbit in order to validate novel system concepts and explore new architectures. The results will assess the readiness of optical technology and provide essential inputs for decision-makers with regards to incorporating it into future operational systems.

Javier Benedicto, ESA Director of Navigation: “We are thrilled to kick off this project now, as we gear up to the ESA Council at Ministerial Level in November, a crucial milestone in demonstrating the benefits of new technologies and shaping the future of navigation in Europe.”

José Ángel Ávila Rodríguez, Head of Future Programmes at ESA Navigation: “In addition to laying the foundation for a future in-orbit demonstration, OpSTAR will contribute to define an international interoperability standard for optical timing and ranging in PNT. By involving the main industry players at this early stage, we empower European industry to keep leading global PNT and benefit from potential implementation in future operational systems that use this technology.”

The use of laser beams has the potential to provide additional resilience and robustness at system level, reducing reliance on space atomic clocks and ground segment. Optical links are also immune to jamming and spoofing by nature.

Thanks to the high data transfer rates, intersatellite optical links also have the potential to enable new, more robust architectures, supporting a multi-layer system of systems approach to navigation, in line with the vision of the ESA’s LEO-PNT programme.

In addition, the superior precision offered by optical systems is expected to improve the performance of current navigation systems by an order of magnitude—reaching millimetre-level spatial accuracy and picosecond-level timing, ultimately enabling better services to benefit billions of users around the world.

The post ESA Developing Optical Technology for Navigation appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

As part of the program, Zephr.xyz’s dual-use “networked GNSS” technology – which turns ordinary mobile phones into a high-fidelity GNSS receiver network – will undergo rigorous field testing in Ukraine and multiple U.S. military exercises before integration with the Department of Defense’s Tactical Assault Kit (TAK) and the Department of Homeland Security’s Team Awareness Kit (TAK).

“We are excited to work with AFRL to equip warfighters and civilian agencies with real-time signal detection capabilities for jamming and spoofing while also determining the locations of these emitters so that countermeasures can be taken,” said Sean Gorman, PhD, CEO of Zephr.xyz. “With GNSS interference becoming a persistent threat in modern conflicts, having a scalable, mobile-based solution that delivers rapid, high-fidelity detection and geolocation is a game-changer. This technology will enable frontline forces to maintain situational awareness in contested environments and provide a critical tool for defending both military and civilian infrastructure against electronic warfare threats.”

A Critical Challenge in an Increasingly Contested World

As geopolitical conflicts intensify, GNSS interference poses a severe risk to battlefield situational awareness, force protection and national security. It also threatens civilian infrastructure, with the potential to disrupt commercial aviation, maritime navigation, medevac operations and financial systems.

Current methods for detecting jamming, spoofing and the sources of these attacks are often ineffective. Zephr.xyz’s field research in active conflict zones in Ukraine and Israel has demonstrated that many GNSS interference detection and localization techniques – while widely cited in the literature – fail in real-world battlefield conditions. For instance, Russia’s high-powered wideband jammers in Ukraine have made time-difference-of-arrival (TDoA) techniques difficult to implement. By jamming all frequency bands, they not only disrupt timing information for TDoA but can also saturate nearby receivers. Even outside combat zones, lower-grade adversary tactics can overwhelm conventional monitoring systems due to insufficient sensor coverage and technical limitations. These shortcomings lead to low-fidelity results and significant gaps in the “areas of effect.”

Delivering a Battlefield-Ready Solution

Zephr.xyz is addressing these challenges with a customized solution for real-time detection, classification and localization of signals of interest (SoI) and signals of opportunity (SoOPs). Since early 2024, the company has conducted extensive field testing and research in Ukraine and Israel to analyze evolving GNSS interference tactics.

Its advanced software suite leverages widely distributed mobile devices to create a decentralized sensor network. By collecting raw GNSS measurements – such as carrier-to-noise ratio – Zephr.xyz can identify key indicators of electronic attacks. These insights are processed in a mobile client-server environment, enabling real-time detection and classification, a capability that is critical for military operations. Additionally, Zephr.xyz’s technology can geolocate the source of an attack using sophisticated signal processing techniques.

Beyond detection, Zephr.xyz has the ability to enhance positioning accuracy on TAK devices, providing critical support for various operational scenarios. By deploying a cooperative positioning system that integrates GNSS measurements from multiple devices with Position, Velocity, Attitude and Timing (PVAT) data, Zephr.xyz strengthens both resilience and accuracy in contested environments.

Zephr.xyz’s detection and classification capabilities will be available as an SDK, allowing mobile applications like TAK to alert users and enhance positioning accuracy in electronic warfare scenarios.

The post Zephr.xyz Awarded $1.7M Air Force Research Laboratory Contract for GNSS Jamming Detection Technology appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

Working with partners Luminous Cyber Corporation and Eritek Inc., the team recently completed Preliminary Design Review (PDR).

The Air Force Research Laboratory (AFRL) and SpaceWERX, the innovation arm of the U.S. Space Force and a unique division within AFWERX, have partnered to streamline the Small Business Innovation Research (SBIR) and Small Business Technology Transfer (STTR) process by accelerating the small business experience through faster proposal-to-award timelines, changing the pool of potential applicants by expanding opportunities to small business and eliminating bureaucratic overhead by continually implementing process improvement changes in contract execution.

The DAF started the Open Topic SBIR/STTR program in 2018 to expand the range of innovations that it funds. Under this program, Xairos is creating groundbreaking capabilities that strengthen the national defense of the United States of America.

“Xairos is thrilled to have this opportunity to address a critical need for secure PNT and communications in a GPS-denied environment for the Alt-PNT Challenge,” said David Mitlyng, Xairos CEO. “This program gives us an opportunity to integrate Quantum Time Transfer (QTT) with Luminous Cyber’s novel clock ensemble and Eritek’s compact optical communications terminal to demonstrate a field deployable terminal that is a major step towards the commercialization of a resilient and accurate global timing network.”

The post Xairos is Awarded Direct-to-Phase II SBIR by SpaceWERX to Develop a Fusion PNT of Quantum and Optical Synchronization of Clock Ensembles appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

The LN-251M features M-code – an encrypted, military-specific signal with stronger jam resistance to shield against adversarial threats.

• This is the first M-code navigation system for naval aircraft.
• M-code technology provides enhanced robustness to counter GPS signal degradation, enabling pilots greater ability to effectively operate in air spaces where GPS has been shut down or spoofed.
• LN-251s equipped with Selective Availability Anti-Spoofing Modules GPS may easily upgrade to M-code configuration.

Ryan Arrington, vice president, navigation and cockpit systems, Northrop Grumman: “The LN-251M is Northrop Grumman’s newest innovation in elevating airborne navigation to the next level. This important enhancement is a critical milestone for delivering advanced positioning, navigation and timing capabilities because it enables pilots to safely operate with a jam-resilient navigation system for naval aircraft.”

LN-251s are designed to seamlessly integrate with current aircraft navigation systems and perform cohesively with future software and GPS modernization upgrades. Northrop Grumman began producing the LN-251 INS/GPS in 2003.To date, the company has delivered nearly 5,000 LN-251s and similar LN-270 INS/GPS units.

The post Northrop Grumman Advances Airborne Navigation Capabilities for the US Navy appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

THIERRY AUTHIÉ, GUILLAUME COMELLI, SÉBASTIEN TRILLES, THALES ALENIA SPACE, TOULOUSE, FRANCE BYUNGSEOK LEE, MINHYUK SON, KOREA AEROSPACE RESEARCH INSTITUTE, REPUBLIC OF KOREA CHEON SIG SIN, ELECTRONICS AND TELECOMMUNICATION RESEARCH INSTITUTE, REPUBLIC OF KOREA

The Korean Augmentation Satellite System (KASS) is a satellite-based augmentation system (SBAS) developed by the Republic of Korea (South Korea) to augment the functionality of the Global Positioning System (GPS) in the Korean Peninsula and the surrounding regions. KASS was designed to enhance the accuracy and reliability of GPS signals within the country. In aviation, it enables more precise and reliable navigation for aircraft, supporting instrument approach procedures and improving operational efficiency.

A SBAS is a Global Navigation Satellite System (GNSS) augmentation system standardized in the International Convention on Civil Aviation SARPS Annex 10 [1], Volume 1, published and maintained by the International Civil Aviation Organization (ICAO). KASS provides safety-critical services for civil aviation, up to Approach with Vertical Guidance 1 (APV I ) service level, as well as an open service usable by other forms of transportation and possibly other position, navigation and timing (PNT) applications.

The KASS system provides improved GNSS navigation services for suitably equipped users in the agreed service areas of the Republic of Korea by broadcasting an augmentation signal of the GPS Standard Positioning Service (SPS).

To ensure the smooth operation of the system, KASS includes a network of ground receiver stations dedicated to collecting GPS measurements, a set of ground processing stations responsible for monitoring and controlling the satellites, and a set of ground uplink stations managing the transmitted signals toward two Geostationary Earth Orbiting (GEO) satellites. These ground control stations accurately calculate the orbit and clock information of the satellites, as well as the mono frequency L1 ionosphere delay, and continuously update the transmitted signals accordingly.

One of the system’s key features is its ability to enhance the integrity and reliability of positioning information. KASS incorporates integrity monitoring functions to detect and alert users of any potential errors or anomalies in the GPS signals. This is crucial for safety-critical applications that require precise positioning data, such as aviation and maritime navigation.

The augmentation signal provides corrections of GPS satellites orbits and clocks and integrity bounds of orbit/clock residual errors, as well as corrections and integrity bounds for ionosphere delays. The KASS satellites transmit signals that are compatible with GPS, allowing KASS-capable receivers to seamlessly switch between GPS and KASS signals and to compute a navigation solution with greater accuracy.

The KASS system qualification was achieved by December 15, 2023, and safety of life aeronautical services have been fully operational since December 28, 2023. 

The current network of KASS Reference Stations (KRS) is composed of seven KRS sites all deployed on the Republic of South Korea land masses. Each KRS includes two independent channels based on NovAtel WAAS GIII receivers that provide GPS signal tracking and measurements. This concentrated network allows users to reach APV I service level but not more stringent service levels like the Category 1 (CAT 1) approach.

This article presents an analysis of a system upgrade to reach the CAT I service level based on representative synthetic data scenario. This analysis involves an extension of the KRS network and minor changes in the navigation algorithms.

KASS Services and Architecture

KASS is designed to provide performance-based navigation (PBN) aeronautical procedures, such as RNAV or RNP approaches, enable aircraft to fly along precise paths during departure, enroute and approach phases. PBN is a modern concept in aviation that uses satellite-based navigation technology and proposes a set of procedures that enhance operating efficiency, reduce flight distances, improve airspace capacity and enhance safety.

The KASS system is designed to ensure four safety critical service levels:

• Enroute continental over the Incheon FIR area. Flight segments after arrival at initial cruise altitude until the start of descent to the destination.

• Enroute terminal over the Incheon FIR area for descent from cruise to Initial Approach Fix. 

• NPA over the Incheon FIR area. For non-precision approaches in aviation, this instrument approach and landing uses lateral guidance but not vertical guidance.

• APV I over South Korea landmasses (including Jeju Island) for precision approaches with vertical guidance.

KASS will provide open service over Incheon FIR area. 

Figure 1 shows the KASS service areas.

The KASS system is designed to be a system-of-systems ensuring the following main functions [2-3]:

• Collect GPS data at various locations in the Republic of Korea (and possibly other states in the future) through Korea Receiver Stations (KRS).

• Compute corrections and associated integrity bounds from ranging measurements of GPS satellites in view of KASS, and format messages compliant with the SBAS user interface standardized in ICAO SARPS Annex 10 [1] and the RTCA MOPS 229-D Change 1 [4]. This function is ensured by the Korean Processing Stations (KPS).

• Uplink a signal carrying these messages to navigation payloads on the KASS GEOs with Korean Uplink Stations (KUS).

• Broadcast the signal to users after frequency-conversion to the L1 band.

The KPS is the core component of the KASS system responsible for computing orbit, clock, ionosphere corrections, and alert information below the Navigation Overlay Frame (NOF). It uses data from a set of reference stations, the KRS, to perform these calculations. The KPS consists of two independent elements known as the processing set (PS) and the check set (CS).

The PS is responsible for computing the complete navigation context for the GNSS constellation, including orbits, clocks and the ionosphere model. It then prepares and sends the NOF, which is broadcasted to users. The CS acts as a supervisory entity by applying the NOF to GPS messages, ensuring consistency with an independent set of measurements to maintain integrity and control.

The KPS-PS component plays a critical role in achieving high-performance levels, specifically for the APV I service level. APV I is a type of PBN approach that provides lateral and vertical guidance to aircraft during the approach and landing phase. APV I approaches typically use satellite-based augmentation systems like the Wide Area Augmentation System (WAAS), the European Geostationary Navigation Overlay Service (EGNOS) and now the Korean Augmentation Satellite System (KASS). These approaches provide accurate lateral and vertical guidance, allowing pilots to perform precision approaches with reduced reliance on ground-based navigational aids.

From APV I to CAT I Aviation Service for KASS

CAT I (localizer performance with vertical guidance 200) is another type of PBN approach that offers even higher precision and accuracy than APV I. CAT I approaches also use satellite-based augmentation systems like WAAS or EGNOS. With CAT I, the lateral and vertical guidance is provided by the aircraft’s flight management system, enabling pilots to fly approach paths that closely resemble traditional instrument landing system (ILS) approaches. CAT I approaches can provide the same level of guidance and minimums as Category I ILS approaches, with decision heights as low as 200 feet above the runway.

Both APV I and CAT I approaches provide increased flexibility, safety and efficiency compared to traditional ground-based navigation systems. They allow for greater access to airports in various weather conditions, reduce reliance on infrastructure, and enable more precise and efficient aircraft operations. These approaches have become increasingly popular and are being implemented worldwide to enhance flight safety and optimize airspace use.

Performance of a satellite navigation system can be expressed through Five Criteria: accuracy, integrity, continuity, availability and time-to-alert (TTA). The overall detailed performance specifications are depicted in Table 1.

Accuracy is the difference between the computed value and the actual value of the user position and time. Usually, accuracy is defined as the 95th percentile of the positioning error distribution.

The system TTA is defined as the time starting when an alarm condition occurs to the time the alarm is displayed in the cockpit. Time to detect the alarm condition is included as a component of integrity.

The alert limits are the maximum allowable error in the user position solution before an alarm is to be raised within the specific time to alert. This alert limit is dependent on the flight phase, and each user is responsible for determining its own integrity in regard to this limit for a given operation phase following the information provided by the SBAS SIS.

The integrity risk is the probability during the period of operation that an error, whatever the source, might result in a computed position error exceeding a maximum allowed value, called alert limit, and the user not be informed within the specific time to alert.

To display the integrity of the satellite corrections for each GPS satellite, the UDRE Safety Index is used to assess the integrity margin. The UDRE Safety Index is defined as the ratio . The Satellite Residual Error for the worst user location (SREW) was computed as the pseudorange error projection due to the remaining satellite ephemeris and clock errors, after KASS corrections were applied for the worst user location of the relevant service area. The relevant service area corresponds to the intersection of the service area and of the monitored satellite footprint.

Also, to display the integrity of the ionosphere corrections for each IGP, the notion of Grid Ionosphere Vertical Error (GIVE) Safety Index is used. The GIVE Safety Index is defined as the ratio , with the GIVE Error defined as the vertical pseudorange error at the considered IGP location due to the remaining ionospheric delay after applying the GIVE corrections.

Continuity defines the ability of a system to perform its function without interruption during the operation planned by the user (for example landing phase of an aircraft). It is evaluated as the probability that from the moment when the criteria of precision and integrity are completed at the beginning of an operation, they remain so for the duration of the operation.

Availability is the percentage of time when, over a certain geographical area, the criteria of accuracy, integrity and continuity are met.

Finally, the service area is the geographic zone where the SBAS shall provide service availability.

As depicted in Table 1, the major difference between CAT I and APV I is more demanding requirements in terms of vertical alarm limit and TTA, resulting in a reduction from 50m to 35m for the vertical protection level and from 10s to 6s for TTA.

The KASS system is designed according to the same architectural principles as the European EGNOS system, which complies with the CAT I service requirements concerning TTA. Therefore, all the elements justifying the TTA performance developed for the EGNOS system apply to the KASS system without any restrictions. This aspect is thus not considered a difficulty.

The main challenge in achieving the CAT I service level concerns the domain of vertical protection volume. Currently, KASS is compliant to APV I precision approach procedure but is limited for the achievement of CAT I service level due to the impact of ionosphere error estimation. With the low number of available measurements from only seven collocated stations, it results in very high integrity bounds (GIVE), which directly affects protection volumes in the vertical direction.

To overcome the limitation of the available measurement volume using only the contributions from the GNSS system, two steps are being considered.

The first step is to include new observables by incorporating measurements from the Galileo constellation into the ionosphere estimation algorithms. It should be noted that Galileo measurements are not incorporated into other navigation algorithms, meaning the system does not monitor the Galileo constellation or calculate any orbit or clock corrections for it.

The second step is to add stations outside of Korea, which would provide better observability in both the dynamics of ionosphere activity and orbit estimation. This addition of external stations would enhance the overall measurement coverage and improve the accuracy of the estimation process.

For all these assessments, fault-free synthetic data are used (analyzed September 3-5, 2002), allowing a first level of performance the KASS system may reach for the provision of CAT I approach service. The results are produced with the same set of KPS navigation algorithms.

CAT I Performances Reached with Introduction of Galileo 

The first extended configuration considers the introduction of Galileo measurements and the current KASS reference station network.

The simulations is realized with:

• Seven reference stations (Yangju, Gwangju, Jeju AP, Jeju TS, Yeongdo, Dodong and Yangyang).

• 27 GPS: for satellites and ionosphere monitoring.

• 24 Galileo: for ionosphere monitoring only.

The different cases presented indicate the availability of CAT I by monitoring the satellites from a minimum elevation angle of 5° with at least one station in the network, then at 10° and 15°.

This experimentation shows CAT I service level can be reached by introducing more observables for the ionosphere monitoring. Indeed, the availability at 99% is reached with the constraint of satellites monitored from 5° elevation by one station. 

First, these new measurements enrich the internal ionosphere model and then contribute to reduce the ionosphere correction errors.

However, because of the direct impact of the integrity bounds on the calculation of protection volumes, the most visible impact of these new measurements on achieving availability is their contribution to reducing GIVE at each Ionosphere Grid Point. 

Second, we observe a clear and direct dependence between the availability of CAT I service level and the minimum angle of satellite monitoring. This phenomenon is the result of waveform deformation (EWF for Evil Wave Form) processing in navigation algorithms, which requires at least one multi-correlator station to lock onto a satellite.

In all maps the integrity target is held with a good margin:

• The maximum satellite Safety Index is 0.77.

• The maximum Ionospheric Grid Point Safety Index is 0.76.

• Integrity is ensured as long as the Safety Index is below 5.33.

Focusing on the Incheon Airport location [127° E;37° N], Figure 3 shows performance in terms of position error and protection levels achieved for Sept. 4, 2022.

The VPL evolves mainly between 15m and 30m, except for a few minutes where it goes above the alarm limit of 35m. The HPL always remain below 30m. 

CAT I Performances Reached with Reference Station Extension (Large Network)

The second extended configuration considers the introduction of Galileo measurements and additional reference stations located outside South Korea landmass to build a large station network.

The added KASS reference stations are depicted in Figure 4.
Five new references stations are considered: Ulaanbaatar (Mongolia), New Delhi (India), Perth (Australia), Wellington (New Zealand) and Hawaii.

The simulation is performed with:

• 12 reference stations.

• 27 GPS: for satellites and ionosphere monitoring.

• 24 Galileo: for ionosphere monitoring only.

Figure 5 shows the availability performance results with satellite monitoring performed using measurements at a minimum of 15° elevation. 

• Again, in all maps, the integrity target is held with a good margin.

• The maximum satellite Safety Index is 0.92.

• The maximum Ionospheric Grid Point Safety Index is 1.33.

In this case, CAT I availability performance is improved with 12 stations. The effect is not on the reduction of integrity value (GIVE) regarding the ionosphere, as the additional five stations are too far away to have an impact. However, having remote stations allows for much better satellite monitoring. This is clearly visible in Figure 6. 

Because satellites are monitored much earlier with 12 stations, the effect of EWF monitoring becomes negligible by removing satellites if they are not seen by at least one station at more than 10° or 15°. As soon as a satellite becomes visible in the service area, there is always a remote station that can see the satellite with a good elevation.

However, EWF monitoring has a noticeable effect in the case with seven KRS, where the availability decreases as the minimum angle increases.

Focusing on Incheon Airport location [127° E;37° N], Figure 7 shows performance in position error and protection levels achieved on September 4, 2002.

This approach has also high interest in the frame of geographical extension of KASS service, for instance the APV I coverage is extended. Table 2 shows the comparison between the APV I availability with the seven KRS and 12 KRS networks.

Again, in all maps the integrity target is held with a good margin:

• The maximum satellite Safety Index is 0.92.

• The maximum Ionospheric Grid Point Safety Index is 1.33.

CAT I Performances Reached with Reference Station Extension (Narrow Network)

The third extended configuration considers the introduction of Galileo measurements and additional reference stations located outside the South Korea landmass to build a narrow station network.

Added KASS reference stations are depicted in Figure 8. Five new reference stations are considered: Shangai, Dalian, Mudanjiang (China), Izumo and Goto Tsubaki (Japan).

Figure 9 shows the availability performance results with a satellite monitoring performed using measurements with a minimum of 15° elevation. 

Here again, in all maps the integrity target is held with a good margin:

• The maximum satellite Safety Index is 0.87.

• The maximum Ionospheric Grid Point Safety Index is 0.85.

Focusing on the Incheon Airport location [127° E;37° N], Figure 10 shows the performances achieved on Sept. 4, 2002.

Much like the previous cases, the VPL remains around 15 to 25m, except for a spike around 5 p.m. The HPL remains around 10m the entire day. The narrow network extension has a benefit aspect on the navigation error NSE, mainly because of better ionosphere corrections accuracy.

Conclusion

The experimentation shows the KASS system evolution makes it possible to achieve the CAT I operational approach. The system’s adherence to architectural principles warrant its ability to meet the TTA requirements. Leveraging the Galileo system, the introduction of new GNSS measurements with the unchanged KRS network results reduces ionosphere integrity bounds, further enhancing the legacy system’s overall availability below the vertical alert limit compatible to CAT I. The study has also envisaged the addition of new external reference stations whose results have established a significant impact on satellite monitoring. With these new adjunctions, the KASS system would improve its capabilities to provide effective and accurate positioning services, proposing for safer and more efficient navigation in the CAT I operational approach.

References 

(1) “Standards and Recommended Practices (SARPS) Annex 10 to the Convention on International Civil Aviation,” Volume I, up to Amendment 86, July 2006, ICAO (International Civil Aviation Organization). 

(2) Houllier, Carolle, Authié, Thierry, Comelli, Guillaume, Lee, ByungSeok, Lee, Eunsung, Yun, Youngsun, SIN, Cheon Sig, “KASS: The Future of SBAS in Korea.” Inside GNSS, Junary–February 2023, pp 50-57

(3) Thierry Authié, Mickael Dall’Orso, Sébastien Trilles, Heonho Choi, Heesung Kim, Jae-Eun Lee, Eunsung Lee, Gi-Wook Nam, “Performances Monitoring and Analysis for KASS,” In Proc. of ION GNSS+, pp 958–978, 2017

(4) “Minimum Operational Performance Standards (MOPS) for Global Positioning System/Wide Area Augmentation System Airborne Equipment,” RTCA/DO-229D with Change 1, February 1, 2013.

Authors

Thierry Authié is a specialized engineer in space flight dynamics, precise orbit determination and navigation. He received his MS degree in Applied Mathematics from the INSA, Toulouse (France) in 2004. He currently works on SBAS and navigation algorithm at Thales Alenia Space.

Guillaume Comelli
is a system engineer and system architect at Thales Alenia Space. He received his MS degree in electrical engineering from the INSA, Lyon (France) in 1994. He has been the Technical Manager for the KASS program since 2019.

Sébastien Trilles is an expert in orbitography and integrity algorithms at Thales Alenia Space in Toulouse, France. He holds a PhD in Pure Mathematics from the Paul Sabatier University and an advanced MS in Space Technology from ISAE-Supaero. He heads the Performance and Processing Department where high precise algorithms are designed as orbit determination, clock synchronization, time transfer, reference time generation, integrity and ionosphere modelling algorithms for GNSS systems and augmentation.

ByungSeok Lee received a BS degree in electric and electrical engineering, a MS degree and a PhD in electrical and computer engineering from University of Seoul, Seoul, Korea, in 2002, 2009, 2015, respectively. He has conducted research related to a Global Navigation Satellite System (GNSS) including the Satellite Based Augmentation System (SBAS) in Korea Aerospace Research Institute. He was in charge of the KASS program from November 2020 to February 2024. He is currently responsible for the entire KASS operation and maintenance.

Minhyuk Son received his BS and MS degrees in electrical engineering from Daegu University, South Korea, in 2009, and 2011, respectively. He joined the Korea Aerospace Research Institute in 2011 and is currently in charge of operation safety technology development for KASS.

Cheon Sig SIN received a BS degree in electric and electrical engineering from Hanyang University, and a MS degree from Chungnam University, Korea in 1990, 2000 respectively. He conducts research related to a GNSS Signal Interference Detection and Mitigation Technology and Global Navigation Satellite System (GNSS) including the Satellite Based Augmentation System (SBAS) in Electronics and Telecommunication Research Institute. He has been in charge of the GK-3 SBAS Payload Development program since April 2021.

The post Achieving CAT I Service with KASS appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

PAUL ANDERSON, GEORGE SCHMITT, FURQAN AHMED, PATRICK SHANNON, TRUSTPOINT INC.

A 2007 Inside GNSS article examined C-band as a future for GNSS signals, with authors outlining its advantages and disadvantages when compared to L-band in context of the Galileo system and its potential role. Nearly 20 years later, we reexamine the cost/benefit trades for C-band for navigation in the context of the NewSpace economy and future commercial GNSS systems operating in low Earth orbit (LEO). In that time, C-band has become critical for resilient PNT, with TrustPoint beginning to deploy a proliferated LEO constellation of microsatellites broadcasting next-generation navigation signals in the 5010 to 5030 MHz Radionavigation Satellite Service (RNSS) allocation at C-band. TrustPoint’s future LEO GNSS service will enable rapid time-to-first-fix, meter and sub-meter positioning accuracy, improved jamming resistance due to frequency selection, diversity and increased signal strength, and an encrypted, spoof tolerant signal with built-in authentication.

The Paradigm Shift of Commercial GNSS

Over the past 50 years, the U.S. GPS and international GNSS counterparts have provided invaluable services in support of commercial, civil government, and military operations across the globe. Given the crucial role they play, it is difficult to envision a world without the ever-present support of these services streaming down from space. Recent reports estimate the global installed base of GNSS-enabled devices is projected to grow from 5.6 billion units in 2023 to almost 9 billion units across all markets by 2033, with the number of GNSS devices shipped per year increasing from 1.6 billion in 2023 to 2.2 billion units in 2033. As humanity exits the first complete epoch of the information age and boldly leans into the age of autonomy and ubiquitous connectivity, there is an expectation that GNSS-enabled devices will further proliferate and continue integrating more broadly and deeply into our way of life.

While humanity finds tens, if not hundreds, of new applications for GNSS every year, and develops an analogous number of unique receivers, the update rate for the satellite systems and the signals they transmit follow closer to decadal timeframes. This slow rate of technical progress is driven by a variety of factors, including the high costs of government system development, limited spectrum availability, and strict backwards compatibility requirements. Unfortunately, this rate of technical progress is severely outpaced by adversarial activity, new application requirements, and technologies from adjacent markets readily available for integration into the larger GNSS ecosystem. In response to this reality, TrustPoint has architected a responsive, resilient and evolutionary LEO PNT system and signal paradigm that enables rapid service upgrades to achieve receiver forward compatibility.

To date, all space-based PNT systems and services have been funded, owned and operated exclusively by world governments with significant budgets, lengthy schedules, and public Interface Control Documents (ICDs). A new era of space-based alternative PNT (A-PNT) is dawning with the emergence of venture-backed commercial companies seeking to fill capability gaps of heritage GNSS services with new technologies and solutions targeting a $260 billion plus total addressable market in navigation and location-based services enabled by commercial satellite platforms and advancements in microelectronics technology. This is a paradigm shift in that GNSS users will soon have access to commercial “PNT-as-a-Service” in addition to the heritage GNSS systems owned by world governments. Novel A-PNT business models and pricing strategies, proprietary signal ICDs, and service-level agreements specifying signal availability and signal-in-space accuracy will become standard—and this will fundamentally change the way global users subscribe to and access next-generation A-PNT services enabling secure, resilient and high-accuracy time and position solutions.

TrustPoint is deploying a purpose-built, commercial A-PNT service using a proliferated LEO constellation of microsatellites broadcasting next-generation navigation signals in the 5010 to 5030 MHz RNSS allocation at C-band. TrustPoint’s commercial, dual-use LEO PNT system and C-band service will enable rapid time-to-first-fix, meter and sub-meter positioning accuracy, improved jamming resistance due to frequency selection, diversity and increased signal strength, and an encrypted, spoof-tolerant signal with built-in authentication for all users. The solution is made possible by our constellation of low-cost LEO microsatellites that leverage commoditized space platforms, rideshare launch services, and patented innovations in navigation signal generation and processing at the RF physical and navigation data layers, enabling next-generation commercial GNSS services made possible by smaller wavelengths, smaller satellites and smaller orbits.

In this article, we summarize the cost and benefit trades of C-band versus L-band at LEO versus medium Earth Orbit (MEO), inclusive of considerations for space segment design, architecture, and size, weight, power, and cost (SWaP-C); signal and service design; and attenuation effects and path delay. 

Commercial Space Segment Considerations

Why is it that after 50 years of satellite navigation technologies and services, LEO PNT has only become relevant in the past 5 years? The answer could lie in the trifecta of (1) the commoditization of microsatellite platforms spurred by the “NewSpace” ecosystem dominated by commercial players; (2) continued miniaturization of software-defined radios and other analog and digital electronics; and (3) the routine availability of low-cost rideshare launch opportunities to common LEO orbits. TrustPoint is leveraging all three of these factors to enable a commercially-funded space segment that is both affordable and high-capability—a combination that wasn’t possible at the scale needed for a new LEO PNT system even 5 years ago. Proliferated LEO architectures comprised of small-but-capable satellites have been technically, cost-prohibitively, or politically out of reach for First World governments, let alone commercial enterprises seeking to generate revenue from new PNT service offerings. As space technologies within the NewSpace economy have continued to relentlessly evolve on accelerated timelines, bootstrapped by venture capital and driven by new use cases arising from humanity’s increasingly interconnected and autonomous future, it is now possible for a commercial business to pursue—in fact, succeed in—delivering space-based LEO PNT services.

Proliferated LEO Constellation. Design and analysis of proliferated LEO constellations for alternative PNT is well-studied in the literature and may be considered a solved problem, see for example [3, 4,5]. The key consideration with lowering the orbital altitude of a PNT system from GNSS MEO altitudes (19,000 to 24,000 km) down to LEO altitudes (500 to 1,000 km) is the number of satellites required to provide persistent four-in-view (“4-fold”) coverage increases exponentially as the altitude decreases, specifically according to this summary relation for minimum number of satellites:

where K=4 for four-in-view coverage, and θ is the Earth central angle. Assuming a 10° minimum elevation angle for a terrestrial user accessing a LEO constellation at 550 km, θ=15°, which translates to more than 400 satellites required to maintain persistent, global 4-fold coverage at the minimum orbit inclination i_min=90–θ=75 deg. This can be reduced by combining multiple “shells” where each shell is defined as a unique altitude, inclination, number of planes, and number of satellite slots per plane. Heterogeneous combinations of shells can then provide superior coverage properties for PNT applications in terms of common metrics such as 4-fold daily availability, 4-fold recovery time in the event of intermittent outage, and the variants of Dilution of Precision (DOP).

Given the significant number of minimum satellites required for LEO PNT coverage when compared with the order of magnitude fewer satellites used in heritage GNSS constellations, the prudent system architect must trade optimal constellation geometry and coverage properties to improve the system cost and operational considerations. The availability of commoditized rideshare launch opportunities has spurred dramatic reductions in launch cost per kilogram of upmass, but these rideshare launch opportunities target standard Sun-Synchronous and mid-inclination destinations, so cost savings for leveraging rideshare launch are only realized if the operational orbits for the LEO PNT system are “close” to these standard dropoff locations. Higher altitude LEO orbits above 700 km, or non-standard LEO orbits such as elliptical orbits, carry additional requirements for last-mile delivery services via Orbital Transfer Vehicles (OTVs) or expensive dedicated launch services.

In addition, with an increasingly congested space environment, the number of planes, inter-plane phasing, and intra-plane phasing must be carefully considered in light of operational and spaceflight safety constraints, namely (1) access to routine ground station contacts for telemetry, tracking and command (TT&C); (2) routine collision avoidance course of action assessment (arising from both external conjunctions and self-conjunctions amongst satellites in the same LEO constellation); and (3) sufficient end-of-life deorbit to ensure compliance with flowdown regulatory requirements from the cognizant licensing authority. A lack of consideration for any of these items can lead to significantly higher incurred costs for LEO system development, deployment, operation, and sustainment, which are especially critical for commercial entities in the process of developing new LEO PNT systems and services.

The deployment of hundreds of satellites necessarily takes time, so another important consideration is not only the final end-state constellation design, but the roll-out plan for various phases of the constellation deployment, which impacts coverage and system performance over time. At full operational capability (FOC), constellation management pivots from deployment to sustainment, and given that 3 to 5 years of design life is typical for low-cost LEO microsatellites, upwards of 20% of the constellation capacity may need to be replaced on an annual basis, depending on satellite reliability, orbital altitude, space weather conditions, and the solar cycle (which impacts atmospheric density and therefore the rate at which LEO orbits decay due to atmospheric drag). This underscores the importance of minimizing the total cost per satellite delivered to orbit, while maximizing production capacity to ensure routine readiness of replacement batches of satellites that are acceptance tested, flight-ready, and standing by for launch.

Commoditized Microsatellites. The global small satellite market grew from $5.4 billion in 2023 to $6.6 billion in 2024, and is projected to grow to $14 billion by 2028, driven by both NewSpace incumbents and new LEO constellation entrants in the areas of SATCOM, EO/IR imagery, RF sensing, SAR, and PNT [6]. Small satellites comprised 93% of all spacecraft launched from 2014 to 2023, accounting for 41% of total upmass, given the 25x increase in the number of small satellites launched per year from 2014 (115) to 2023 (2,860) [7]. These trends have been enabled by the increasing commoditization of satellite components, subsystems and entire platforms with competitive price points, sub-12-month lead times, and increasing capability densities for performing diverse mission sets. What was once only feasible with a government-class budget and schedules measured in years—or even decades—is now doable for venture-backed commercial startups with small budgets and schedules measured in months.

From 2022 to 2023, TrustPoint reviewed 16 CubeSat-class platforms (3U, 6U and 12U, where 1U is defined as a 10x10x10 cm cube) offered as commercial-off-the-shelf (COTS) products by commercial bus providers both in the U.S. and internationally. These platforms ranged from Technology Readiness Level (TRL)-6 to TRL-9, and were scored based on SWaP available to the payload, ease of integrating a propulsion system, and lead times and unit pricing for various quantities of identical units. For an RF payload, the size and weight can, in general, be optimized, but power consumption is directly related to the duty cycle that is allowable for signal transmission—indeed, “P” is the most challenging dimension of SWaP for a PNT application. As shown in Figure 1, these 16 reviewed CubeSat platforms can be grouped into four categories on the basis of Orbit Average Power (OAP) available to the payload and the unit cost per platform at small quantities. Our survey confirmed strong advancements in CubeSat technologies over the last 3 to 5 years, specifically 2 to 3x increases in OAP available to the payload and 30% to 50% reductions in platform cost. Furthermore, our assessment identified multiple bus providers in the “pack leader” category who are aggressively pushing toward higher capability at a lower price point by means of vertical integration and continuous innovation in bus technology stacks, and preparing parallel production lines and supply chains to enable an additional 20% to 30% unit cost reduction for the large quantities required for fielding a proliferated LEO constellation.

Multiple high-performance CubeSat platforms in the $200,000 to $300,000 range are now available, inasmuch as the PNT payload being integrated with the commercial bus conforms to standard mechanical, electrical and thermal interface requirements. This price point per constellation node is multiple orders of magnitude beneath the price tag of a single GNSS MEO satellite. Given the cost of a single GPS Block III satellite is estimated at $250 million, a $250,000 price point per LEO CubeSat is a 1/1000x reduction that trades the larger available SWaP and 2 to 3x increased design life of a heritage MEO satellite for the dramatically reduced unit cost per commercial LEO microsatellite.

Low SWaP C-Band PNT Payload. Thanks to the realization of Gordon Moore’s (co-founder of Intel) famous 1965 prediction that the number of transistors on microchips would double approximately every two years, the SWaP of commercially available microelectronics has significantly reduced over the past 50 years of satellite navigation technologies. The semiconductor industry has continuously innovated to shrink the size of transistors to fit more onto single microchips, thereby increasing transistor density per integrated circuit and leading to electronics with higher efficiency, increased compute performance, and lower cost per chip. “Moore’s Law” has significantly influenced the miniaturization of software-defined radios over time [9] and has driven significant SWaP reductions and performance increases in foundational microelectronics for mobile phones, GNSS user equipment (Figure 2), and myriad other technologies.

Similarly, the advancements resulting from Moore’s Law can be leveraged to develop a low SWaP commercial PNT payload for integration into a commercial microsatellite bus with standard interfaces. TrustPoint’s C-band PNT payload is CubeSat compatible and less than 2 kg in mass, providing stable, high-power C-band transmission capability, onboard navigation message generation, and precision GPS-independent timekeeping—all packaged in a form factor that fits in the palm of your hand. Leveraging low-cost, widely-available COTS products integrated in a proprietary electromechanical configuration that is space-qualified for moderate LEO orbits, TrustPoint has designed, integrated, tested and launched the first purpose-built, commercial microsatellites capable of transmitting next-generation C-band LEO PNT signals as both a complement to GPS /GNSS and an independent A-PNT source.

Commoditized Launch. Deployment and sustainment of a proliferated LEO constellation of hundreds of satellites necessitates low-cost, reliable and timely space launch services. Over the last 5 years, commoditized rideshare launch services from multiple commercial launch providers have been introduced into the market and matured, driving orders of magnitude reductions in launch pricing that have made access to LEO affordable for non-government entities. Commercial offerings such as SpaceX’s SmallSat Rideshare Program, with its Transporter and Bandwagon mission series, have provided unprecedented routine access to standard LEO orbits including Sun-Synchronous Orbit (SSO) and mid-inclination, at sub-$5,000 per kilogram pricing (Figure 3). Coupled with orbital transfer vehicles (OTVs) that provide “last-mile” delivery services to specific orbital slots, entire planes of a proliferated LEO constellation can be populated from a single launch opportunity at a fraction of the cost of a single heritage GNSS satellite, which requires a dedicated launch service to a single orbital slot in MEO. 

As additional medium-lift and heavy-lift class launch vehicles emerge and become viable in the commercial space ecosystem within the next 5 years, e.g., SpaceX’s Starship, Rocket Lab’s Neutron, Blue Origin’s New Glenn, and others, the launch cost per kilogram is projected to continue decreasing, enabling affordable LEO constellation deployment and sustainment. System design considerations and optimizations such as standard satellite form factors compatible with industry-standard separation systems, standard LEO orbits at moderate altitudes, and advance bulk buys of launch capacity have the potential to further reduce launch pricing at the scale necessary for proliferated LEO PNT.

Geographic Diversity. From LEO altitudes, a single satellite transmits to less than 10M km2 of effective surface area, whereas a single GNSS satellite at MEO transmits to 200M km² of surface area (Figure 4). At first glance, this 20x increased Field-of-View for GNSS from MEO appears to put LEO PNT systems at a disadvantage—but GPS was optimized for global “one-size-fits-most” PNT, and this approach is no longer effective for increasing numbers of civil, commercial, and military users and applications demanding flexibility and bespoke services in uncertain and evolving environments. The smaller footprint of LEO satellites, coupled with end-to-end software and firmware reprogrammability by design, provides an advantage in that signal parameters can be dynamically varied over different parts of Earth. On the same orbit revolution, a TrustPoint satellite can service the Continental United States with a given signal, then Asian markets with a different signal, and then mainland European markets with yet a different signal. The flexibility of this PNT-as-a-Service business model has nascent dual-use commercial and defense applications, and further is a wartime deterrent in that reconstitution of degraded PNT capability is as rapid as an on-orbit software update, or command uplink to increase the number of satellites tasked with transmitting a desired signal over the impacted area as a countermeasure.

Angular Velocity. According to Keplerian motion, the orbital speed of a circular LEO orbit is about twice as fast as a circular MEO orbit. Range rates between terrestrial users and LEO satellites depend on factors such as the latitude of the user and the altitude and inclination of the satellite, and are on the order of 10 to 15x faster than range ranges that are typical for GNSS satellites (Figure 5, left). The result is single LEO satellite accesses are on the order of 5 to 10 minutes as compared to 3 to 4 hours during which single GNSS satellites are in view from a given terrestrial user in the absence of line-of-sight obstructions. Because the Doppler shift of the carrier frequency is directly proportional to both the range rate and the carrier frequency, it follows that the increase in range rate for LEO orbits, coupled with the increase in frequency from L-band to C-band, leads to Doppler shift that is 30x greater for C-band LEO than the Doppler shift that is typical for L-band GNSS from MEO (Figure 5, right).

Although increased angular velocity makes signal acquisition more challenging, and drives requirements for advanced acquisition techniques and increased data rates to ensure rapid time-to-first-fix (TTFF), increased range rates resulting from faster orbital speeds in LEO have the benefit of rapidly-changing overhead geometries that reduce outages for urban canyon users, and have the potential to accelerate carrier phase ambiguity resolution timelines. Given a LEO satellite has a 10x faster range rate than a MEO satellite, and the L-band wavelength is approximately f_C1/f_L1 = 3.2x longer than the C-band wavelength (6 cm), the resulting rate of change in carrier phase for TrustPoint’s C1 signal is 30x faster than for L-band GNSS from MEO, which has implications for cycle slip detection and integer ambiguity resolution.

Signal and Service Design Considerations

Frequency Diversity. As the RNSS allocation in L-band becomes increasingly congested with current and planned GNSS signals in MEO and LEO, the international GNSS community has begun to consider alternative frequencies for satellite navigation services, specifically unused RNSS allocations at C-band. In addition to L-band congestion driven by future GNSS signals, the criticality of frequency diversity also emerges from global proliferation in GNSS L-band jamming and spoofing threats. Electromagnetic Interference (EMI) at L-band is becoming increasingly prevalent worldwide as low-cost COTS hardware and open-source software enable turnkey GNSS degradation, denial and spoofing capability for bad actors, impacting civil, commercial, military, and even LEO satellite users. The global GPS anti-jamming system market size was estimated at $4.3 billion in 2021 and is expected to grow to $6.1 billion by 2028 as commercial providers of GNSS chips, receivers and augmentation services continue to implement hardware/software solutions for GNSS jamming and spoofing mitigation. However, the prevalent commercial user base of L-band GNSS does not use bespoke anti-jam or anti-spoof equipment due to higher relative cost or SWaP constraints, leaving sectors such as critical infrastructure and commercial aviation susceptible to EMI threats as a result of their continued dependence on low-power, unencrypted heritage signals at L-band, specifically GPS L1 and L2.

To address demand signals for PNT frequency diversity from the civil, commercial and military markets, TrustPoint has filed for global spectrum rights at the ITU for the C-band RNSS/RDSS allocation, and has developed a next-generation A-PNT service and signal set purpose-built for reconfigurability and enabling our vision of PNT built on signals at smaller wavelengths transmitted from smaller orbits (LEO). In future multi-source user equipment built on open architectures and data standards, incorporating C-band A-PNT signals alongside existing L-band GNSS signals, and signals of opportunity from Ku/Ka-band SATCOM systems, offers the potential for significant improvements in PNT service availability and resiliency through diversification of architectures.

Received Signal Power. For equivalent distance, Free Space Path Loss (FSPL) at C-band is a factor of (f_C1/f_L1)² = 10.2x stronger (10 dB) than at GPS L1. The downside of increased FSPL at C-band is that Received Signal Strength (RSS) at the user will be reduced accordingly, unless the loss is compensated for elsewhere in the transmit side of the architecture. For TrustPoint, the 10 dB loss from increasing the carrier frequency from L-band to C-band is compensated for by lowering the space segment to 500 to 700 km LEO altitudes, for which the FSPL at the equivalent carrier frequency is reduced by 31 dB at zenith and 23 dB at 10° elevation angle, assuming a reference LEO altitude of 550 km. Therefore, the net effect of shifting the space segment from L-band MEO to C-band LEO is a +21 dB gain at zenith and +13 dB gain at 10° elevation, when considering the combined effects of carrier frequency, orbital altitude, and FSPL only. This power margin can then be allocated directly into the required minimum RSS at the user, or the prudent system architect could choose to trade this margin to decrease transmit EIRP requirements, and in doing so take advantage of SWaP reductions in the space segment.

A notional comparison of RSS at the input to the user antenna for L-band MEO, C-band MEO and C-band LEO cases is provided in Table 2. To achieve the same -158 dBW RSS as the L-band MEO, the C-band MEO system requires a kilowatt-class transmitter to compensate for the increased free space path loss and tropospheric attenuation at C-band. Transmit hardware of this class carries material technical challenges including larger SWaP, higher development and production costs, and significant thermal management considerations. Conversely, the C-band LEO system achieves -158 dBW RSS with only a 15 W (11.8 dBW) transmitter and 8 dBi gain antenna, both of which are microsatellite-compatible with multiple existing hardware solutions on the market today.

Signal Security. TrustPoint’s C-band A-PNT signal incorporates commercial best practices in cryptographic confidentiality of navigation message data, and time-delayed cryptographic authentication of the same data to mitigate spoofing attacks. This includes the use of the Advanced Encryption Standard [11] and a navigation data authentication method similar to the lower-overhead TESLA method [12]. Encryption keys rotate regularly to protect the integrity of the C-band service and deter unauthorized access. Authentication of navigation message data ensures the data as received by the user is signed by TrustPoint and thus approved for use in forming corrected pseudorange observables supporting Position, Velocity and Time (PVT) solutions. This is a counterpoint to the heritage GPS L1 and L2 signals, which do not inherently offer either confidentiality or authentication protections for users.

Advanced Data Elements. One of the benefits of designing a commercial LEO PNT system and service is the ability to clean-sheet the navigation message structure and enable the opportunities for civil, commercial and military users to embed bespoke data of their choosing within the constraints of the defined message structure. Data rates need not be as high as commercial Ku/Ka-band SATCOM services to provide the dual-use commercial benefits and military utility of embedding GNSS integrity, clock and ephemeris corrections, and/or other augmentation information within the LEO PNT navigation message.

C-Band Attenuation and Propagation Delay Considerations

How do the signal attenuation and propagation delay differ between the C-band LEO GNSS and the L-band MEO GNSS? Table 3 provides a quantitative, side-by-side comparative analysis of RF attenuation and path delay considerations for these two approaches. C-band LEO GNSS benefits from superior FSPL and significantly lower ionospheric effects (attenuation and delay), incurs modestly increased losses due to tropospheric effects, and is more resilient to multipath errors as a result of the combination of shorter wavelengths at C-band and faster geometry changes at LEO.

Next Generation PNT

This article on LEO GNSS at C-band has outlined macroscopic cost and benefit trades for a commercial LEO GNSS system and service in the 5010 to 5030 MHz band, inclusive of space segment architecture, signal and service design, and RF attenuation and propagation delay considerations. Notably, TrustPoint’s vision for next-generation PNT services supporting humanity’s interconnected, autonomous and augmented future is one in which cooperative C-band LEO PNT services are an independent and trusted input into intelligent multi-source PNT fusion engines leveraging commercial PNT signals, heritage GNSS signals, signals of opportunity, and local sensors for resilient PNT that benefits from diversification of architectures and modalities.

The authors of the 2007 Inside GNSS article, “A Role for C-Band?”, leave their readers with the following prospects for a future C-band system:

“Could we not perhaps apply similar ideas to C-band in order to avoid the high power figures that are needed to compensate for the higher propagation losses of the C-band? Another approach might be to design C-band satellites that only serve users in certain locations and then allow satellite transmissions only while flying over those designated regions and for selected periods of time. Such a time-multiplexing could indeed prove to be interesting one day. Equally interesting would be to use special C-band-emitting satellites with LEO orbits to cope with the problem of signal power loss and navigation data transmission.”

Now, 18 years later and in the context of a commercially-driven NewSpace ecosystem, TrustPoint is doing just that—and C-band for LEO PNT isn’t just “interesting”; it is critical for resilient PNT in the face of global proliferation in L-band GNSS jamming and spoofing. 

References 

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(2) EU Agency for the Space Programme (2024). EUSPA EO and GNSS Market Report 2024. Technical Report, EU Agency for the Space Programme.

(3) Prol, F. S., Ferre, R. M., Saleem, Z., Valisuo, P., Pinell, C., Lohan, E. S., Elsanhoury, M., Elmusrati, M., Islam, S., Celikbilek, K., Selvan, K., Yliaho, J., Rutledge, K., Ojala, A., Ferranti, L., Praks, J., Bhuiyan, M. Z. H., Kaasalainen, S., and Kuusniemi, H. (2022). Position, Navigation, And Timing (PNT) through Low Earth Orbit (LEO) Satellites: A Survey on Current Status, Challenges, and Opportunities. IEEE Access, 10:83971–84002.

(4) Morales Ferre, R., Praks, J., Seco-Granados, G., And Lohan, E. S. (2022). A Feasibility Study for Signal-In-Space Design for LEO-PNT Solutions with Miniaturized Satellites. IEEE Journal on Miniaturization for Air and Space Systems, 3(4):171–183.

(5) More, H., Gerardi, R., Stallo, C., Sanctis, M. D., And Cianca, E. (2022). PNT through Optimised LEO Constellation and INS. In Proceedings of the 35th International Technical Meeting of the Satellite Division of the Institute of Navigation (ION GNSS+ 2022), Pages 1428–1441, Denver, Colorado.

(6) The Business Research Company (2024). Small Satellite Global Market Report 2024. Technical Report, The Business Research Company.

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(16) ITU-R (2022). Attenuation by Atmospheric Gases and Related Effects (Recommendation P.676-13).

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Authors

Dr. Paul Anderson is Lead Systems Engineer for TrustPoint, where he leads the development and deployment of proliferated space and ground segments enabling TrustPoint’s commercial C-band PNT services. He brings more than 12 years of experience in astrodynamics, state estimation, space systems engineering, and IV&V across the program lifecycle. He joined TrustPoint from VOX Space, subsidiary of Virgin Orbit, where he led systems engineering for microsatellite launch integration and responsive mission execution. Prior to VOX Space, he led technical teams at The Aerospace Corporation in support of the GPS space and ground segments, multi-source PNT, and RF geolocation. He brings a mission-driven, technically oriented, people-focused approach in pursuit of 100% mission success at scale. He holds a Ph.D. in Aerospace Engineering Sciences from the University of Colorado Boulder.

George Schmitt is Signals and Processing Lead for TrustPoint, where he drives the company’s waveform design, RTL development, and advanced signal processing efforts, bringing more than 30 years of expertise in digital signal processing, secure communications, and RF system design. His career includes senior technical roles at The Aerospace Corporation, where he developed resilient satellite and ground communication systems for the DOD and intelligence community, and technical leadership positions at Naval Research Laboratory and Orbital Sciences, where he led rapid prototyping on FPGA and GPU platforms. Known for his deeply analytical and hands-on approach, his technical skills span VHDL, Verilog, MATLAB, encryption, radar, comm, and PNT waveform design, and high-speed data protocols. He holds a B.S. in Mathematics and Computer Science from the Massachusetts Institute of Technology.

Dr. Furqan Ahmed is a Senior GNSS Scientist at TrustPoint, where he focuses on the development of PVT engines, channel modeling for LEO PNT signals, and simulation of GNSS observations for TrustPoint’s commercial C-band PNT services. He also contributes to payload software development for TrustPoint’s LEO satellites. Previously, he worked in the GNSS positioning engine teams at Qualcomm and Garmin. Prior to joining the PNT industry, he spent time in academia where his research focused on geodetic and atmospheric applications of GNSS. He holds a Ph.D. in Engineering Sciences from the University of Luxembourg.

Patrick Shannon is CEO and co-founder of TrustPoint. Prior to co-founding TrustPoint, he was the VP of Business Development and Operations at Astro Digital where he was responsible for strategy formulation, business development, and product management. During his tenure at Astro Digital, he directly led five satellite programs and a 400% increase in revenue over a three-year period. Before that, he was VP of Business Development at SpaceQuest, where he drove company strategy and oversaw all contract and internal R&D program execution. He got his start as a satellite systems engineer at Orbital Sciences, later transferring to the Corporate Strategy group supporting M&A and government relations. He holds a BS in Aerospace Engineering from MIT and a MS in Management Science and Engineering from Stanford University.

The post The Case for LEO GNSS at C-Band appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

This service offers free real-time precise positioning corrections to all Galileo system users. The first version of the HADG, also developed by GMV, is currently operational and provides users with the Initial Service (Phase 1) of the HAS.

The new contract, with a duration of up to 45 months and a budget of up to 12 million euros, includes the design, development, deployment, support to commissioning and, optionally, maintenance of an improved version of the HADG. This new version will also incorporate the new functionalities required to deliver the services planned for Phase 2 (Full Service) of the HAS deployment.

Specifically, the new version of the HAS data generator will:

• Improve the performance level of Service Level 1 (SL1): The deployment of a new version of GMV’s magicPPP^® algorithms for precise corrections calculation and the expansion of the ground station network will provide global coverage and enhance the accuracy and availability of the SL1 service.

• Implement a new Service Level 2 (SL2): This is a new regional service that will be available only in Europe. By transmitting atmospheric corrections, it will make it possible to reduce the convergence time required to achieve maximum accuracy at user-level.
• Implement a new functionality for the authentication of HAS corrections transmitted through the Galileo constellation, thereby increasing user security and confidence in the service.

Since 2020, GMV has led the development of the Galileo HAS data generator following the award of the first contract with EUSPA. Since its operational launch in January 2023, the Galileo HAS service has provided accuracy for advanced applications in sectors such as navigation, agriculture, geodesy, and autonomous driving. In the new contract, GMV maintains its role as the main contractor and leader of an industrial consortium that includes atmospheric modelling experts from the Polytechnic University of Catalonia (UPC) and cybersecurity specialists from Sidertia.

According to Miguel Romay, General Manager of Satellite Navigation Systems at GMV: “The new contract to evolve the Galileo HAS service consolidates GMV’s commitment to technological excellence and its leadership capacity in key projects for Europe. This achievement reinforces GMV’s role in Galileo and allows the company to continue innovating to offer transformative solutions that benefit society.”

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