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What To Do When China And Russia Jam GPS? Use The Earth’s Magnetic Field



GPS is in trouble. Once a navigational miracle, GPS is now vulnerable to jamming and spoofing. Multiple nations – including China and Russia — have devised anti-GPS systems, from jammers to weapons that target GPS satellites. Even civilians can purchase GPS jammers of questionable legality.

Currently, the U.S military depends on GPS for accurate navigation and – equally important – accurate targeting of smart weapons. If GPS can’t be trusted, then the Pentagon will need a reliable substitute.

That’s why the U.S. Navy is looking for a GPS substitute: using the Earth’s magnetic field for navigation. The project – called Positioning Using Magnetic Anomalies Correlation of Earth (PUMACE) – used anomalies in the Earth’s magnetic field to determine location.

“GPS utilizes weak radio frequency (RF) signals from distant satellites and are subjected to intentional and unintentional interference,” says the Navy’s research solicitation. “Navigation based on the Earth’s magnetic field promises a more robust all-weather passive navigation with no dependence on new infrastructure.”

The Navy wants a magnetic sensor for ships and submarines that is accurate to at least 30 meters (32.8 feet) and ideally 15 meters (16.4 feet). It should weigh less than 15 pounds and use less than 5 watts of power.

The Air Force Institute of Technology has already tested magnetic anomaly navigation, in which scalar magnetometer sensors measure differences in the magnitude of magnetic fields as the sensor passes by them, and then compares these readings with known readings on magnetic field maps. Animals such as turtles and birds already appear to use to some form of magnetic navigation.

However, the Navy wants to refine the process further. “Challenges remain in the availability of precise maps of the Earth’s crustal magnetic field,” the Navy solicitation noted. “The presence of larger core fields, as well as temporal variations, can further limit the precision of position accuracy. Additionally, locally induced magnetic fields of the ship itself must also be considered in the determination of position.”

Models of the Earth’s magnetic field tend to focus on the field generated by our planet’s core, rather than the Earth’s crust. “Crustal field variation sensing could result in accurate positioning; however, because the crustal field is so weak in comparison to core fields, it also requires advanced vector sensors,” the Navy said. “Current-generation sensors are limited because they are scalar sensors and, therefore, not capable of sensing minute variations of the Earth’s crustal field.”

PUMACE aims to develop a system accurate and reliable enough to assist and correct any errors  inertial navigation systems (INS), which also function independently of GPS. “This family of sensors can promise robust positioning using integrated systems that are capable of blending alternate positioning sensor data as a re-set of the INS for continued accurate platform navigation holdover without GPS dependency,” said the Navy. “In addition to INS aiding, the data can be used as another sensor source for integrity evaluation within the Position, Navigation, and Timing (PNT) suite.”

Phase I of the project calls for determining the feasibility of measuring anomalies in the Earth’s magnetic field, and of the sensors required for this. Phase II and III will involve developing technical specifications and a working prototype.

Regardless of whether PUMACE is successful, the U.S. military will need to find jam-proof alternatives to GPS. Not only do precision-guided weapons require an accurate navigation system, but so does the American way of war, which depends on tight and precise coordination of air, land, sea and space forces separated by great distances. U.S. adversaries are well aware of this vulnerability, and will seek to exploit it.

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