So far, the US military has shot down four high-altitude flying objects that have entered the US and Canadian airspace. Today, this has raised a lot of questions from scientists and engineers about the technologies used, their purpose, and their origin. Business magazine B-MAG understands the technology of spy balloons. What are the prospects for such old flying objects if new technologies are applied to them?
The first of these objects, a Chinese balloon, was shot down by a fighter plane on 4 February. While China says the balloon was used for weather monitoring, US officials say the object was used for surveillance and reconnaissance. Knowing the technology in this area gives us some clues about what might be going on.
It is assumed that the balloon carried new equipment with technology to collect intelligence signals, although this has yet to be confirmed. The wreckage was recovered from US territorial waters off the coast of South Carolina and will be brought ashore for analysis.
Three more targets were shot down between February 10 and 12 over Deadhorse in Alaska, near the Yukon in Canada, and over Lake Huron near the US-Canada border.
Signal Intelligence, or “Sigint”, refers to electronic data, which may consist of conversations, written communications, or data from weapons or radar systems. Signal intelligence is usually collected by satellites, but may also be collected from aircraft flying in international airspace.
Typically, satellites that collect information are located in low Earth orbit (LEO) – say, at an altitude of 500 to 1000 km – or in geostationary orbit at a much higher altitude – 36,000 km. While this type of intelligence gathering using satellites is efficient and quite effective, there are some limitations.
A satellite in low Earth orbit will make a full orbit around the Earth in 70–100 minutes, but it will not pass the same point on Earth in 14–20 hours depending on altitude. This is due to the fact that our planet is also moving. But even in this case, the satellite will be visible on Earth for no more than 20 minutes, which is called the “stay time”. Increasing the number of satellites helps, but there will still be large time gaps in coverage.
Theoretically, a geostationary satellite can have a constant residence time. But because it is located about 36,000 km from the Earth’s surface, it can miss important but weak signals.
The US military is developing signals – electronic data transmissions with a low probability of interception. This makes it difficult for both Chinese and other spy satellites to collect data. During the 24 hours, there will be large periods of time when the signal collection is not possible – the time of silence.
China has tried to close these gaps. In 2020, the country launched three new Yaogan-30 series reconnaissance (spy) satellites into a 600 km orbit as part of a wider network, or “constellation”, called Chuangxin-5 (CX-5), bringing the number of satellites in the network to 21.
Old balloons with new technology
Take for example the hot air balloon that was shot down on February 4th. Following the object’s trajectory over the United States, one can see that it flew past several critical defense installations, including nuclear-tipped intercontinental ballistic missile (ICBM) silos in Montana.
The balloon flew over the United States at an altitude of 20-30 km and was able to move in the jet streams of the upper atmosphere. Obviously, the advantage of collecting intelligence signals was that its time in the air could be several hours, and its proximity to the surface of the Earth ensured that it could, if spying, collect very weak signals.
Thus, a balloon that can go undetected would be an ideal platform to increase the collection of signals from both satellites and aircraft. Many countries have been using balloons for intelligence gathering for at least 200 years, so the idea is not new and the benefits are well known.
Modern technology has given this intelligence-gathering method new life, as we have also seen in the use of small aircraft – or “microdrones”. Going unnoticed for a significant period of time is a key condition for success. How this was possible in the United States is an interesting question, given that the country has one of the best air defense systems in the world.
One possible answer lies in the development of radars for ground and airborne early warning radar systems (AEWs). To reduce interference on the radar, static objects such as mountains and towers are removed from the radar returns using a natural effect known as “Doppler shift”. When a train passes you, the pitch of its whistle seems to change as it moves away from you. This is an everyday demonstration of the Doppler shift of sound waves.
Doppler capability is common to all defense radars as they target air and missile threats. A balloon or inflatable object can move at a speed less than the Doppler threshold and thus remain undetected.
Radar interference
This deficiency in detection capabilities was recognized by NORAD (North American Air Defense Command) and the radars were reconfigured to see targets at very low speeds. However, interference will increase, which may be one of China’s goals to reduce the effectiveness of air defense radars.
Another difficulty in detecting lies in the material from which the balloons or objects are made. Plastics and synthetic inflatable fabrics have no or very low radar reflectivity, which adds another plus to their classified performance. The balloon that caused the current controversy and controversy in the US was first spotted visually rather than detected by air defense systems.
But later sightings of aerial objects over Canada and Alaska were the result of intensive surveillance. What they are is not yet reported and it is classified.
Once this is established, the key question will be whether these facilities were designed to infiltrate the US defense system in order to collect more accurate intelligence signals, or whether they were a test of US air defense systems. We will know about it or not when the results of the analysis of the wreckage of the balloons become known.