U.S army shoot down what US officials called a Chinese surveillance balloon off the coast of South Carolina on February 4, 2023. Officials say the US Navy plan to recover debristhat is in shallow water.
The United States and Canada tracked the balloon as it crossed the Aleutian Islands, crossed Western Canada, and entered U.S. airspace via Idaho. U.S. Department of Defense officials confirmed on February 2, 2023 that the military has track hot air balloon as it flew over the continental United States at about 60,000 feet, including over Malmstrom Air Force Base in Montana. The base houses the 341st Missile Wing, which operates nuclear intercontinental ballistic missiles.
The next day, Chinese officials admit that the balloon is theirs but denied it was for spying purposes or for infiltrating US airspace. U.S. Secretary of State Antony Blinken says the hot air balloon intrusion brought him to Beijing trip cancellation. He was scheduled to meet Chinese Foreign Minister Qin Gang on February 5 and 6.
The Pentagon reported that a second China hot air balloon have been seen throughout Latin America. On February 4, officials told reporters that China’s third surveillance balloon was operating somewhere else in the world and that the balloons were part of China’s military surveillance program.
Tracking enemies from a hot air balloon dates back to 1794, when the French used a hot air balloon to track the Austrian and Dutch armies during the Battle of Fleurus. We asked the aerospace engineer Iain Boyd of the University of Colorado Boulder to explain how the spy balloon works and why people will use it in the 21st century.
What is a spy bubble?
A spy balloon is literally a gas-filled balloon that is flying pretty high in the sky, more or less where we fly commercial planes. It has some sophisticated cameras and imaging technology on it, and it points all that equipment to the ground. It is gathering information through photography and other images of whatever is happening on the ground below it.
Why would someone want to use a spy balloon instead of just a spy satellite?
Satellites are the preferred method of spying from above. Spy satellites are above us today, usually in 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’re still hundreds of miles away from us. For pictures and photography, the closer you are to something, the more clearly you can see it, and this also applies to espionage. Satellites in low Earth orbit have the advantage that they are closer to Earth so they can see things more clearly than satellites that are farther away.
The disadvantage of these low-Earth orbit satellites is that they are constantly moving around the Earth. It takes them about 90 minutes to make one orbit around the Earth. That turned out to be pretty quick when it came to taking clear pictures of what was going on below.
The second type of satellite orbit is called geosynchronous orbit, and that’s much further away. It has the disadvantage that it’s harder to see things clearly when you’re very, very far away. But they have the advantage we call persistence, which allows satellites Take pictures continuously. In those orbits, you’re essentially always observing exactly the same piece of land on Earth’s surface because the satellite moves exactly the same way the earth rotates – it rotates at the same speed.
A ball in some ways gets the best of them. These balloons are much closer to the ground than any satellite, so they can see even better. And then, of course, the balloons are moving, but they’re moving relatively slowly, so they also have a degree of persistence. Today, however, reconnaissance is not usually done with balloons as they are relatively easy targets and cannot be fully controlled.
What types of spy balloons are capable of monitoring?
I don’t know what’s on this particular balloon, but it’s likely that different types of cameras collect different types of information.
Nowadays, imaging is conducted on different areas of the electromagnetic spectrum. Humans see within 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 photo. That’s one of the things spy planes do. They take regular photos, although they have a very good zoom so they can pretty much magnify what they’re seeing.
But you can also collect different types of information in other parts of the electromagnetic spectrum. Another pretty well known one is infrared. If it’s night, a camera operating in the visible part of the spectrum won’t show you anything. All will be in the dark. But an infrared camera can pick up things from heat in the dark.
How do the balloons navigate?
Most of these balloons actually fly in the direction the wind is blowing. There might be a bit of navigation, but definitely no people on them. They are at the mercy of no matter what the weather is. They sometimes have a guide device that changes the height of the balloon to catch the wind in specific directions. According to reports, US officials said China’s surveillance balloon has propellers to help steer it. If this is confirmed, it means that its operator will have more control over the path of the balloon.
What are the limits to a country’s airspace? At what height does it become space and anyone has a right to be there?
There is an internationally accepted boundary called The Kármán . line at an altitude of 62 miles (100 km). This balloon is much lower than that, so it’s absolutely, definitely in US airspace.
Which countries are known to be using spy balloons?
The Pentagon has had programs over the past few decades studying what could be done with balloons that was previously impossible. Maybe they’re bigger, maybe they’re higher up in the atmosphere making it harder to shoot down or neutralize. Maybe they could be more persistent.
The widespread interest in this case shows its unusual nature. Some would expect any country to actively use spy balloons these days.
The United States flew many hot air balloons over the Soviet Union during the 1940s and 1950s, and these were eventually replaced by high-altitude reconnaissance aircraft, the U-2and then they were replaced by satellites.
I’m sure some countries around the world have periodically returned to re-evaluate: Is there anything else we can do now with balloons that we couldn’t do before? Do they bridge the gap we have with satellites and planes?
What does that say about the nature of this hot air balloon, which China claims is its own?
China has been complaining for years about American spies to China by satellite, by ship. And China is also famous for participating in slightly provocative behaviorlike in South China Sea, sailing close to the boundaries of other countries and swinging his sword. I think it falls into that category.
Hot air balloons do not pose any real threat to the United States. I think sometimes China is just testing to see how far they can push things. This is not really very advanced technology. It does not serve any real military purpose. I think it’s more likely to be some kind of political message.
Iain Boyd is a professor of Aerospace Engineering Science at the University of Colorado Boulder.
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