GPS satellites could be used as a global monitoring system for detecting intercontinental ballistic missiles. The principle was demonstrated last week when researchers identified the atmospheric disturbances caused by North Korea’s largest intercontinental missile test yet in satellite data.
The researchers posted an on Twitter – a big moment for an open-source intelligence project that has worked to detect missile and rocket launches for the past two years. Volunteers have developed computer software to detect disturbances in the earth’s atmosphere by measuring global navigation satellite signals travelling between satellites and ground stations.
“It would be wonderful if this could be a truly global network,” says Tyler Nighswander at Theori, a cybersecurity company in Texas.
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The idea of actively tracking missile and rocket launches through disturbances in the ionosphere – part of the upper atmosphere filled with charged particles – came from at the James Martin Center for Nonproliferation Studies in California. He then asked for help from the online open-source intelligence community, which aims to make better use of publicly available information for intelligence purposes.
Nighswander and at Rice University in Texas took up the challenge. They first had to find a global navigation satellite system – in this case Japan’s GEONET system – that publicly shared data on at least an hourly basis. GEONET’s network of ground stations includes more than 1300 owned by the government and 3000 operated by the Japanese multinational company Softbank, says , formerly at Hokkaido University in Japan, who was not involved.
Next, the researchers created computer software to detect changes in the ionosphere. They drew on decades of previous studies by Heki and others showing how rocket launches can impact the ionosphere – the water vapour in rocket exhaust interacts with and depletes the ionosphere’s charged particles, while related acoustic shock waves can push particles around.
The total number of charged particles can affect radio signals, with different signal frequencies passing through at different speeds. By measuring the precise delay between satellite signals on two different frequencies, it is possible to measure the number of charged particles and detect changes over time.
The researchers developed algorithms to identify these changes. The rate of false detection alarms is “quite low” because a large ballistic missile looks different from natural ionospheric phenomena, but the method can still miss low- and intermediate-range ballistic missiles with lower trajectories that don’t leave a similar trail in the ionosphere, says Nighswander.
The result is a system that can get the time and rough geographic location of a missile or rocket launch. But more data from multiple points of view – such as from South Korean stations – would be required to reconstruct the flight path of a North Korean missile.
“I think this is very powerful,” says at National Cheng Kung University in Taiwan. Lin has previously observed ionospheric disturbances associated with rockets such as the SpaceX Falcon Heavy, but he described the success in detecting a North Korean ballistic missile as “very impressive”.
The open-source intelligence project could eventually harness global navigation satellite systems that share data in real time. That would provide an alternative to waiting for governments with military-grade missile-warning satellites to share information – especially when it concerns more secretive countries such as North Korea.
