The US military shot down a Chinese surveillance balloon on February 4, 2023 off the coast of South Carolina to US officials. Officials said the US Navy plans to recover the wreck, which lies in shallow water.
The US and Canada tracked the balloon as it crossed the Aleutian Islands, passed over western Canada and entered US airspace over Idaho. US Department of Defense officials confirmed on February 2, 2023, that the military was tracking the balloon as it flew over the continental US at an altitude of about 60,000 feet, including Malmstrom Air Force Base in Montana. The base houses the 341st Missile Wing, which operates nuclear intercontinental ballistic missiles.
The next day, Chinese officials acknowledged that the balloon was theirs but denied that it was for espionage or for entering US airspace. US Secretary of State Antony Blinken said the balloon intrusion prompted him to cancel his trip to Beijing. He was scheduled to meet Chinese Foreign Minister Qin Gang on 5 and 6 February.
The Pentagon has reported that a second suspicious Chinese balloon has been spotted over Latin America. On 4 February, officials told reporters that a third Chinese surveillance balloon was operating elsewhere in the world, and that these balloons were part of the Chinese military surveillance program.
Monitoring an enemy from a balloon dates back to 1794, when the French used a hot air balloon to track Austrian and Dutch troops at the Battle of Fleurs. We asked aerospace engineer Ian Boyd of the University of Colorado Boulder to explain how spy balloons work and why anyone would use them in the 21st century.
What is a spy balloon?
A spy balloon is actually a gas-filled balloon flying high enough in the sky, more or less where we fly commercial airplanes. It has some sophisticated cameras and imaging technology, and it’s pointing all of that equipment down at the ground. It is gathering information through photography and other imaging of what is happening on the ground below.
Why would someone want to use spy balloons instead of just using spy satellites?
Satellites are the preferred method of spying from overhead. Spy satellites are above us today, usually on one of two different types of orbits.
The first is called Low Earth Orbit, and, as the name suggests, those satellites are relatively close to the ground. But they are still several hundred miles above us. For imaging and taking pictures, the closer you are to something, the more clearly you can see it, and the same applies to spying. Satellites that are in low Earth orbit have the advantage that they are closer to Earth so they are able to see more clearly than satellites that are further away.
The disadvantage of these low earth orbit satellites is that they are constantly revolving around the earth. It takes about 90 minutes for them to orbit the Earth. It turned out to be very fast in terms of taking clear pictures of what’s happening below.
The second type of satellite orbit is called a geosynchronous orbit, and it is very distant. The disadvantage is that it’s hard to see things clearly when you’re too far away. But they have the advantage of what we call persistence, allowing satellites to capture images continuously. In those orbits, you’re essentially looking at the exact same piece of land on Earth’s surface at all times because the satellite moves exactly as the Earth rotates – it rotates at exactly the same speed.
A balloon gets the best of them in some ways. These balloons are much closer to the ground than any satellite, so they can see even more clearly. And then, of course, the balloons are moving, but they’re moving relatively slowly, so they also have some degree of persistence. However, these days spying is not usually done with balloons as they are relatively easy targets and not fully controlled.
What types of surveillance are spy balloons capable of?
I don’t know what’s in this particular spy balloon, but it likely has a variety of cameras collecting different types of information.
These days, imaging is done in different regions of the electromagnetic spectrum. Humans see in a certain range of this spectrum, the visible spectrum. And so if you have a camera and you take a picture of your dog, that’s a visible picture. It’s one of those things that spy planes do. They take regular pictures, although they have great zoom capabilities to magnify whatever they are looking at.
But you can also collect different types of information in other parts of the electromagnetic spectrum. Another fairly well known is infrared. If it’s night time, a camera operating in the visible part of the spectrum won’t show you anything. It’s all about to get dark. But an infrared camera can pick up things in the dark by heat.
How do these balloons navigate?
Most of these balloons literally go where the wind blows. There might be a bit of navigation, but certainly not the people aboard. Whatever the weather, they are at their mercy. They sometimes have guiding devices that change the height of the balloon to catch winds going in particular directions. According to reports, US officials said the Chinese surveillance balloon had propellers to help it steer. If confirmed, it means the operator will have more control over the balloon’s path.
What are the boundaries of a country’s airspace? At what height does it become space and one has the right to live there?
At an altitude of 62 miles (100 km) there is an internationally accepted boundary called the Karman Line. This balloon is well below that, so it’s absolutely, definitely in US airspace.
Which countries are known to use spy balloons?
The Pentagon has had programs over the past few decades to study what could be done with balloons that could not be done in the past. Maybe they’re bigger, maybe they can go higher up in the atmosphere so it’s more difficult to shoot them down or disable them. Maybe they could be more persistent.
The widespread interest in this phenomenon reflects its unusual nature. Few would expect any country to be actively using spy balloons these days.
The US flew many balloons over the Soviet Union in the 1940s and 1950s, and they were eventually replaced by high-altitude spy airplanes, the U-2s, and later by satellites.
I’m sure many countries around the world have gone back from time to time to reevaluate: are there other things we can do with balloons now that we couldn’t do before? Do they close some of the gap with the satellites and airplanes we have?
What does that say about the nature of this balloon, which has been confirmed by China?
China has been complaining about US spying on China through satellites, ships for many years. And China has also been known to engage in some provocative behavior, such as sailing and sword fighting close to other countries’ borders, in the South China Sea. I think this falls into that category.
There is no real threat to the US from the balloons I think sometimes China is just experimenting to see how far they can take things. It’s not really very advanced technology. It is not serving any real military purpose. I think it’s more likely to be a political message of some sort.
Ian Boyd is Professor of Aerospace Engineering Science at the University of Colorado Boulder.
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