Artist’s impression of the CACI/York Space DemoSat scheduled to launch in January 2023. (Credit: CACI)
CACI International, a U.S. defense contractor, plans to demonstrate a supporting navigation technology for military use as part of its DemoSat launch in January 2023.
CACI will launch two demonstration payloads on a York Space Systems satellite scheduled to fly to low Earth orbit in January aboard the SpaceX Transporter 7 rideshare.
The payload will contain an alternative positioning, navigation and timing solution that will work in a contested space domain. It is designed to support rather than replace GPS.
The technology is two-way time transfer and clock modeling technology. Two-way time transfer has been used for years on the ground, but in this case will be used in space. The low size, weight and power (SWaP) space-based PNT is expected to significantly improve multi-platform remote sensing.
If the experiment is successful, CACI plans to offer the two-way time transfer PNT service to the military and other government agencies.
CACI has completed the critical design review for the DemoSat. CACI and its partner York Space Systems will also demonstrate a tactical intelligence, surveillance and reconnaissance (TacISR) payload. The TacISR payload identifies and captures key signals of interest and operates with CACI’s Beast ground receiver to demonstrate real-time radiofrequency geolocation for deployed U.S. forces.
“CACI expertise, systems, and technology help our customers maintain dominance in the increasingly contested space environment,” said Mike Hale, executive vice president of CACI’s Advanced Solutions Group. “We are very proud that CACI is launching a DemoSat payload into orbit – distinguishing our mission technology and transformative solutions for customer success.”
In January’s issue, he listed 10 questions from a PNT expert perhaps unfamiliar with eLoran.
These are important questions that must be asked of any technology, especially one under consideration to augment and back up our essential, but very weak and vulnerable, GNSS signals.
Yet the expert’s concerns pale in comparison to the essential questions about GNSS and PNT facing the United States and the West.
While I look forward to answers to the “10 questions” as a part of our ongoing professional dialogue, there are two important points of context we all need to keep in mind.
A Broad Consensus
First, Mr. Luccio’s assertion about eLoran being a part of the solution is more than reasonable. It also has a lot of impressive support from a wide variety of authoritative sources.
In 2008 and 2015, after much study each time, the U.S. government decided on and committed to building eLoran systems. Also, the U.S. government-sponsored National Space-based Positioning, Navigation and Timing (PNT) Advisory Board recommended eLoran in 2010 and 2018 as a part of securing the nation’s critical PNT capability.
In 2021, the U.S. Department of Transportation told Congress that wide-area terrestrial broadcast was a necessary part of a national PNT architecture. They later commented that infrastructure required per coverage area would be a key selection criterion for that broadcast technology. In other words, a system like eLoran.
Overseas, support for Mr. Luccio’s statement on eLoran is even stronger.
The United Kingdom has long endorsed eLoran and operates an eLoran transmitter as a timing reference.
Russia operates Chayka, a version of Loran.
Available information points to Iran’s terrestrial PNT system being a form of Loran or eLoran.
China and South Korea have long had Loran-C systems, and both are in the process of upgrading to the eLoran standard.
Each of these countries has publicly announced that it operates Loran/eLoran as a matter of national security in case space-based systems are jammed or destroyed, and to generally avoid overdependence on space-based PNT signals.
So, Mr. Luccio’s assertion was not at all revolutionary. Given all the studies, recommendations and existing uses, it would be surprising if he did not consider eLoran a part of the solution.
The Important Questions
Second, modern keying, encryption, authentication and other tech advances will help make all PNT technologies much safer and more resilient than they would have been decades ago, Loran and eLoran included.
Yet all will still have their strengths and weaknesses.
The most important questions we must ask are about how to establish the right level of national PNT security. These include:
What is the right combination of technologies and systems with different delivery and failure modes that complement and reinforce GNSS and each other?
How can the systems be efficiently and effectively implemented?
How can the services they provide be easily accessed and widely adopted to ensure all parts of society are protected?
Countries such as China have answered these questions and are well down the path to implementation and wide adoption. Their robust national PNT architectures support easier rollout of 5G, rural broadband and other systems. They also serve as solid tech infrastructure upon which to build myriads of technologies and applications yet to be conceived.
Those nations not so advanced must accelerate their efforts. Otherwise, they must resign themselves to perpetually coping with GNSS vulnerabilities, including the possibility of attacks, and an eventual second or third place in the world because of their shortsightedness.
In its closing days, the Trump administration issued several new policy documents affecting positioning, navigation and timing (PNT) issues.
Some have questioned the long-term impact of these, given the significant policy differences between the previous and current administrations. Yet policies in relatively non-controversial areas such as PNT are generally developed by career personnel who tend to remain in place from administration to administration. While they must adhere to the philosophical tenets of extant elected officials, these policies tend to endure longer than others.
Even if this weren’t the case, considering the wealth of other issues the new administration is grappling with, these new policies could remain in force for some time, even if the new regime ultimately decides to change them.
Several themes run through many of the documents. These include:
Space-based PNT is vulnerable and must be protected.
The first of these late-term documents to be published was the National Space Policy issued on Dec. 9, 2020. Highlights and possible impacts for the PNT community include:
A goal to “Promote and incentivize private industry” could have implications for low-Earth orbit (LEO) PNT services.
A goal to “Increase the assurance of national critical functions” could include GPS/PNT resilience.
A pledge to “Safeguard space components of critical infrastructure” undoubtedly includes GPS. The section also has ominous statements about U.S. responses to purposeful interference and tasks the Defense and Homeland Security secretaries with having those responses ready.
Another pledge to “Maintain and Enhance Space-based Positioning, Navigation and Timing (PNT) Systems” is followed by eight explanatory paragraphs, many of which repeat previous policy. One new item is a promise to invest in detection and mitigation of harmful interference. A mention is also made of the need for multiple and diverse PNT sources, and responsible use of PNT, echoing the February 2020 Executive Order on the subject. Both of the latter two mentions were in the context of critical infrastructure and mission essential functions versus the security of the nation and economy as a whole.
Congress mandated a GPS backup technology demonstration in 2017, and $10 million was subsequently provided for that purpose. Various internal government delays resulted in the project not getting underway until March 2019. It concluded about a year later.
While some people have been critical, it is important to remember the report documents 11 vendor demonstrations, not engineering tests. Technologies were demonstrated in different locations and under differing conditions.
There is no silver bullet for meeting the nation’s needs. It must be a system of systems.
Also, the amount of effort and equipment in the demonstrations depended in some cases upon infrastructure available and the amount of money the government and vendors were able to spend. This meant that at least one technology was “demonstrated” mostly by explaining the concept, and other vendors were able to only partially demonstrate their technologies.
All of that said, the report offers valuable information about how America should make its national PNT much more resilient and reliable. First, it reinforces DOT’s message that there is no silver bullet for meeting the nation’s needs. It must be a system of systems. Second, the report goes further and says what that system of system should look like: “Those technologies are LF and UHF terrestrial and L-band satellite broadcasts for PNT functions with supporting fiber-optic time services to transmitters/control segments.”
From a policy perspective, this is a huge step forward. It resolves previous ambiguity and positions the nation to establish a resilient PNT architecture, one that will do more than be a “GPS backup.” It will be an architecture that will better support current applications and better enable emerging ones like autonomy, 5G and “NextG.”
Published one hour and fourteen minutes before the end of the administration on inauguration day, this plan was mandated as part of the February 2020 Executive Order on responsible use of PNT. By taking a comprehensive look at how we can do better, it provides an interesting outline of the challenges associated with America’s current over-reliance on GPS. While not a policy or directive document, it does suggest two or three departments and agencies that might be tasked with addressing each challenge.
It also addresses the need for interference detection and monitoring, and diverse sources of PNT.
This directive was published five days before the end of the administration and replaced the previous policy, 2004’s NSPD-39.
While the old policy calls for performance monitoring of GPS signals, the new one also has investment in interference detection and monitoring as a goal.
Perhaps the most significant change in the new policy was the absence of the words “backup capability” and the lack of a mandate for DOT to lead its establishment. Yet the policy hammers home multiple times the need for more than GPS as a source of PNT. And it doesn’t abandon the idea of government involvement in making that happen.
In addition to reinforcing Executive Order 13905 on responsible use of PNT, the directive defined a new (for presidential policies) term. “Alternative PNT Service” was described as “a PNT service that has the capability to operate completely independent of, or in conjunction with, other PNT services.” The directive goes on to say that “Multiple, varied PNT services used in combination may provide enhanced security, resilience, assurance, accuracy, availability and integrity. An alternative PNT service allows a user to transition from the primary source of PNT signals in the event of a disruption or manipulation.”
And while the policy does not say the government will establish or support an alternative PNT service, it comes pretty close. One of its goals is “Invest in… as appropriate, alternative sources of PNT for critical infrastructure, key resources, and mission-essential functions.”
It goes on to task the departments of Defense, Homeland Security and Transportation with making that happen.
So “backup” is out, “alternative PNT” is in. We agree words are important and are happy to have the new words. Let’s hope the new administration will match the new words with action (as appropriate).
An artist’s concept of a GPS IIR-M satellite in orbit (courtesy of Lockheed Martin).
For more than 41 years, many of us who were there in the beginning have been discussing the attributes, capabilities, enabling features and shortcomings of GPS and other space-based PNT (position, navigation and timing) systems. You have likely heard most of them; historically they go something like this:
The signal is weak.
The signal is easily jammed.
The signal can be spoofed.
The signal is subject to atmospheric perturbations.
The signal doesn’t penetrate buildings.
The signal doesn’t penetrate dense canopies (urban or natural).
I am sure you have heard most of these. Now, allow me to update the situation with some of the developments enabled by modern signals, new techniques, and multi-frequency, multi-GNSS (Global Navigation Satellite System) “all-in-view” receivers. All of the above bulleted statements are still true, but to a lesser extent, virtually each day. As some well-known pop musicians once sang, “It’s getting better all the time.”
Today, multi-GNSS signals in a fully modern multi-GNSS receiver can to some degree resist interference — intentional (jamming) or unintentional — and spoofing. It is extremely difficult for a jammer or spoofer to disrupt GPS, GLONASS, Galileo and BeiDou all at the same time. And more help is on the way.
Today, multi-GNSS signal corrections remove a large amount of error due to atmospheric perturbations and can sometimes deliver centimeter and millimeter accuracy in real time (in the case of short-baseline real-time kinematic (RTK) using only L1 carrier-phase as data, and/or in some other special situations.)
Today, multi-GNSS signals and augmentation signals show some improvement in penetrating dense canopies and canyons by virtue of their multiplied numbers and dispersed geometry.
Today, new ground-based technologies show promise at penetrating buildings to provide indoor location. When combined with GPS/GNSS, this is starting to get us closer to the Holy Grail, the ubiquitous PNT solution.
Debate
The future looks bright for PNT solutions, ground and space-based. I know it all sounds like a debating society, and you may have heard some of these arguments before. My point, my premise if you will, or bottom-line-upfront in military parlance, being: the GPS (space-based) limitations of the past are gradually giving way to the improved multi-GNSS capabilities of today and the combined ground-based and space-based PNT technologies of the present and rapidly arriving future.
Unfortunately, there are many uninformed so-called PNT pundits who love to posture for the press — and who are living in the past. The future is right in front of them, or in many cases in their hands, and they cannot or will not acknowledge its existence.
It’s all in the numbers
Current estimates are that more than 4 billion users depend on PNT daily for position, navigation and timing, or the multitude of services each of these resources enables. More than half of that number is attributable to smartphone users, which means, at a minimum, more than 2 million PNT users have a two-way communications device incorporated into their PNT receiver/sensor.
Let’s look at current high-end smartphones as examples of commercial multi-frequency, multi-GNSS “all signals available” devices. The user has a true multi-GNSS device incorporating:
GPS — Global Positioning System, United States government
GLONASS — Globalnaya Navigazionnaya Sputnikovaya Sistema, the Russian space-based PNT system
BeiDou — the Chinese BeiDou Navigation Satellite System, a regional system now, soon to be global (2020 the advertised date).
with augmentations such as
WAAS — U.S. Wide Area Augmentation System
EGNOS — European Geostationary Navigation Overlay Service
Other SBAS — additional Satellite-Based Augmentation System signals by region
Wi-Fi — Signals compatible with a set of broadband wireless networking standards.
The latest high-end smartphones incorporate an inertial system, a digital compass, a rate gyro, and a pressure sensor integrated with pedometer software that keep track of position, heading and velocity when external signals are lost. Add cellular tower and network-enabled positioning and timing technology, and you have a two-way communications and PNT-based multi-GNSS sensor that, as long as it has power, is never lost.
Atomic numbers
The rubidium-based (atomic-reference system) timing signals from GPS satellite vehicles (SV) are among the most stable timing frequencies ever broadcast from space. The true accuracy of the signal in space is classified, but approaches an accuracy 10 times better than what was once thought to be adequate for our warfighters.
The best clocks in any current GNSS system are the passive hydrogen masers of Galileo. Thus a PNT set-up that adds Galileo to GPS improves in more ways than one.
Ephemeris numbers
Twenty-five years ago, the U.S. military kept track of GPS satellite orbit locations (known as the ephemeris of the satellite) using actual GPS measurements at the control segment tracking stations. The GPS satellite ephemeris was known to a much lesser degree of accuracy than now. At the time, that accuracy was considered good enough.
Today, the ephemeris is known much more precisely, and this can be on the order of some centimeters. This has to do with not only the location of the satellite’s center of mass (c.o.m.), but the actual location from which the signal is broadcast. The position of the satellite’s broadcast antenna is known reasonably well most of the time, by very high-end users, after correcting for the arm lever between the c.o.m. and the antenna phase center. The c.o.m. itself can vary by some centimeters over time because of depletion of onboard expendables, but here we are getting into very high-order minutiae.
Suffice it to say that certain multi-GNSS scientific high-precision receivers today are used to measure tectonic movements on the order of centimeters over the course of a full year.
Number of signals
Just recently, with the addition of certain QZSS signals (the Japanese Quasi-Zenith Satellite System) along with the Indian (GAGAN) and Russian (SDCM) equivalents of WAAS and EGNOS, the number of multi-GNSS PNT signals available to a truly international multi-GNSS receiver exceeds 200. For example, one set of global commercial receivers routinely receive and process more than 190 PNT signals in a six-hour period. The receivers are both static and dynamic, and they are networked. The static receivers know their actual location to within millimeters, and use this location as a truth set from which all other signal data is compared.
Accuracy numbers
For our example (and all parameters are software-defined and user-programmable), the location parameter may be set at 10 centimeters, meaning that any position derived from PNT signals or augmentations that differ by more than 10 centimeters from the “truth set” are immediately rejected, and that data is broadcast on the systems network, which keeps the dynamic receivers in sync as well.
The individual receivers each contribute to their own and a networked website with metadata usable by Kalman filters to which other users may choose to subscribe. This makes the multi-GNSS receivers not only receivers, but system and PNT monitors and sensors that can detect jamming, interference and spoofing attempts, which are reported.
This monitoring and tracking system is constantly evolving and incorporating new technologies while becoming more secure everyday. This is not a totally new concept, as the core system is a mature enterprise system that has been in operation and commercially viable for more than seven years.
This should be comforting information for those of you who stay up at night worrying about the safety of autonomous vehicles on land, sea and in the air.
Don’t let me give you the impression that GPS is just waiting around for other GNSS to come to its aid. GPS is aggressively modernizing itself. In Air Force parlance, “GPS III space vehicles will introduce new capabilities to meet higher demands of both military and civilian users.” As stated by GPS III contractor Lockheed Martin, the modernized system will:
• Deliver signals three times more accurate than current GPS spacecraft.
• Provide military users up to eight times improved anti-jamming capabilities.
Augmentations and improvements
The bottom line is that a greatly increased number of space-based PNT platforms — along with quantum improvements in computing power, cheap non-volatile memory and software-defined capabilities — have produced a multi-GNSS PNT capability that increases availability via sheer numbers, with more security and reliability on the way.
A pair of LocataLite transmit antennas overlook a section of the White Sands Missile Range blanketed by the Locata high-precision ground-based positioning system.
We are rapidly developing a PNT system that goes far in countering the naysayers. It takes advantage of augmentations and complimentary systems such as newer versions of Loran, (Long-Range Navigation System) and local PNT implementations such as Locata, just to name a couple of examples.
These ground-based systems are critical to the future of PNT, and have very strong signals. For instance, eLoran is extremely difficult to jam, if not actually unjammable. If a monstrous sunspot were to temporarily knock out the majority of space-based systems, the ground-based systems would more than likely still be available, if — big if here — they are fully developed. At the moment, this is not a sure thing. It is a work in progress.
Ground-based augmentations and complimentary/backup systems can in the future add a level of security for GPS and other space-based PNT systems: Why bother trying to knock out these space-based systems when there is a suitable and readily available ground-based system as a backup?
The U.S. government maintains a number of monitor stations around the globe. However, it has not historically taken advantage of the incredible capabilities of multi-GNSS receivers and sensor technology. Although NASA and other U.S. non-military agencies have been involved with multi-GNSS — specifically the Russian GLONASS — for the past 20 years or so, the use has not been widespread. Fortunately, recent changes now permit multi-GNSS receivers for government users, including the military, in certain non-targeting activities, and the government would do well to take advantage of the changes. The good news is that the majority of the capability is in the receiver design, a capability on which the current director of the GPS Directorate at the Space and Missile Systems Center (SMC) “made his bones.”
To all those critics who take every opportunity to denigrate space-based PNT, both inside and outside the government, I say: Pay attention to multi-GNSS. Stop your diatribes, because the future is arriving. Secure space-based PNT systems are here to stay.
They continue to improve and become more secure as they incorporate space- and ground-based augmentations, new PNT technologies, software-defined capabilities, multi-GNSS signals, and enhanced computing. “It’s getting better all the time.”
Allow me to repeat myself all over again. Space-based PNT is here to stay.
Until next time, happy navigating, and remember: GPS is brought to you free of charge by the United States Air Force.
