Current US Military GPS vs. Civilian GPS and Access by Non-American Armies
The Global Positioning System (GPS), a ubiquitous technology that touches the daily lives of billions of people worldwide, is a masterpiece of modern engineering. Originating as a US Department of Defense (DoD) project, GPS has since revolutionized navigation and timing services. It’s used in diverse applications from guiding cars, ships, and aircraft to enabling accurate time-stamping for financial transactions. This article seeks to explore the inherent differences between military and civilian GPS, focusing on the access non-American militaries have to US military GPS.
Civilian GPS vs. Military GPS
Despite the common assumption, the US military GPS and civilian GPS are not two entirely separate systems. They are part of the same satellite constellation, and the distinction arises from the way receivers decode and use the signals broadcast by these satellites.
GPS receivers determine their location by calculating the time it takes for signals to arrive from satellites overhead. The User Range Error (URE) of the GPS signals in space, which indicates the degree of signal accuracy, is the same for both the civilian and military GPS services. So, fundamentally, both forms of GPS use the same core technology to provide positional information. The primary difference lies in the number of frequencies used, the level of precision offered, and signal encryption, among other things.
Most civilian GPS devices use only one GPS frequency — the L1 frequency, which carries the Coarse/Acquisition (C/A) code and the L1 civilian (L1C) signal. The civilian GPS, thus, offers positional accuracy in the range of a few meters, typically around 5–10 meters.
Military receivers, on the other hand, use two frequencies — L1 and L2. By utilizing two frequencies, the military GPS can correct signal distortions caused by Earth’s atmosphere — a phenomenon known as ionospheric delay. This use of dual frequencies improves positional accuracy down to about a meter or less. In addition to this, military GPS signals employ the Precise Positioning Service (PPS), an encrypted data stream that provides resistance to jamming and spoofing, thereby enhancing reliability and security.
This dual-frequency equipment is available for civilian use, but its cost, size, and power requirements have largely restricted it to professional applications such as surveying, mapping, and aviation.
The civilian and military GPS also had a significant divergence in the past because of a feature called Selective Availability (SA). Until May 2000, the US government used SA to intentionally degrade the accuracy of the civilian GPS service as a national security measure. However, this practice was ended under the direction of President Bill Clinton to make GPS more responsive to civil and commercial users worldwide. Since then, the accuracy of civilian GPS has improved significantly.
Access to US Military GPS by Non-American Armies
While the GPS service is globally accessible to anyone with a GPS receiver, certain restrictions apply to the export of some civilian receivers from the United States, particularly those capable of functioning above specific altitudes and speeds. These restrictions have been put in place due to concerns about the potential misuse of GPS technology in Intercontinental Ballistic Missile (ICBM) guidance systems and high-speed aircraft. However, these restrictions do not apply to units or components exported from other countries, leading to a growing trade in GPS units from non-US sources.
When it comes to foreign militaries, selective access to US military GPS is granted. Selected foreign military services have access to the Defense Advanced GPS Receiver (DAGR), a military-grade, dual-frequency receiver that can decode the encrypted P(Y)-code GPS signals used by the US military. DAGR, a handheld, single-channel device, provides precise positional, velocity, and timing data to the user.
In recent years, the advent of the M-Code, a new military GPS signal, has made headlines. M-Code is a critical element in modernizing the current GPS service and enhancing its warfighting effectiveness. It is designed to improve the security of military GPS signals, providing better anti-spoofing and anti-jamming capabilities.
Following the approval by the US Congress, the GPS Directorate started to provide M-Code Early Use (MCEU) capability to the warfighter. Moreover, plans were set into motion to facilitate access to M-Code-enabled GPS user equipment to foreign nations. As of the data available in 2020, there were plans to facilitate access to M-Code-enabled GPS user equipment to 58 authorized nations. This step was taken with the aim of improving interoperability with equipment and operations of US allies, thus enhancing navigation warfare effectiveness for allied operations.
In conclusion, while the GPS service is globally accessible, the US military GPS offers increased accuracy and security features. Non-American militaries can gain access to these features through specific channels and agreements. These cooperative measures not only underline the strategic partnerships between the United States and its allies but also significantly enhance global interoperability and effectiveness in navigation warfare operations.
As GPS technology continues to evolve and the applications of this technology expand, the differences between civilian and military GPS may become even more nuanced. The US’s GPS III program, for instance, promises to bring even more significant advancements in GPS capabilities. It is a fascinating field to watch as new developments in GPS technology continue to shape the world in which we live.
