A US Air Force jet that can navigate using tiny variations in Earth鈥檚 magnetic field will take a test flight next month. The technology could be used on aircraft as an alternative to GPS, which is easier to interfere with than magnetic field sensors.
The USAF鈥檚 Position, Navigation and Timing programme is using a combination of sensors in a modular AgilePod, a device that can be easily mounted beneath a plane. In the tests, the AgilePod will also carry cameras for visual navigation and equipment for radio navigation using transmitters with known locations such as TV masts. However, adding magnetic navigation is new.
A simple compass needle aligns with the strong magnetic field produced by Earth鈥檚 liquid-iron core, but a more sensitive magnetometer can also pick up fainter magnetic fields embedded in rocks that make up Earth鈥檚 crust. These fields have a pattern as complex and distinctive as topography. By measuring the strength and direction of the crustal field and how it changes during a flight, you can work out where you are in the magnetic landscape.
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at the Air Force Institute of Technology in Ohio demonstrated magnetic navigation in 2017. He used data from a sensitive airborne magnetometer to locate a plane with an average error of just 13 metres over a 1-hour flight. However, this technique required an accurate magnetic map of the area below.
鈥淢agnetic navigation is always possible to some level of accuracy, but the greatest accuracies require the highest resolution maps,鈥� says Canciani. Sourcing such maps for other countries, especially those hostile to the US, may not be easy.
Other challenges are shielding the sensor from magnetic fields generated by the plane and its electronics, and finding a sufficiently robust, compact magnetometer. However, unlike GPS, magnetic navigation is difficult to jam or spoof.
Visual navigation only works when landmarks are visible, and radio navigation requires known radio transmitters, whereas magnetic navigation will work over the ocean where there are neither. The three systems should complement each other, according to lead researcher Andy Cottle at the Air Force Research Laboratory, also in Ohio.
A USAF T-38 jet with an AgilePod combining the three navigation sensors will carry out a series of test flights in August, and the results will determine how the technology is developed.
