Chinese spy balloons: aerospace expert explains how they work and what they can see

On February 4, 2023, the US military shot down a so-called Chinese reconnaissance balloon off the coast of South Carolina.

The United States and Canada followed the balloon’s path as it crossed the Aleutian Islands, passed 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 US mainland at an altitude of about 60,000 feet, hovering over Malmstrom Air Force Base, Montana. The base is home to the 341st missile wing, which operates nuclear-powered intercontinental ballistic missiles.

The following day, Chinese officials claimed the balloon was theirs, but denied that it was intended for espionage or to enter US airspace. US Secretary of State Anthony Blinken said the balloon raid caused him to cancel his trip to Beijing. He was scheduled to meet Chinese Foreign Minister Qin Gan on February 5-6.

The Pentagon said a second, believed to be Chinese, balloon has been sighted over Latin America. On February 4, officials told reporters that a third Chinese observation balloon was operating in another part of the world and that the balloons were part of China’s military surveillance program.

Balloon observation of the enemy dates back to 1794, when the French used a balloon to track Austrian and Dutch troops at the Battle of Fleurus.

Aerospace engineer Ian Boyd of the University of Colorado Boulder explains how spy balloons work and why someone would use them in the 21st century.

What is a spy ball?

A spy balloon is literally a gas-filled balloon that flies quite high in the sky, roughly where commercial airliners fly. It has sophisticated cameras and imaging technology, and all of these tools point straight down. Gather information through images of what is happening on the ground.

Why would anyone use spy balloons instead of satellites?

Satellites are the preferred method of spying from the sky. Currently, spy satellites fly over our heads mainly in two types of orbits.

The first is called Low Earth Orbit, and as the name suggests, these satellites are relatively close to the earth. But they are still a few hundred kilometers above us. In photography and still photography, the closer you are to something, the more clearly you see it, and this applies to surveillance as well. The advantage of satellites in low Earth orbit is that they are closer to Earth, so they can see things more clearly than satellites further away.

The disadvantage of these low orbit satellites is that they are constantly moving around the Earth. It takes them about 90 minutes to make a complete revolution, too fast to take clear pictures of what’s happening below.

The second type of satellite orbit is called geostationary orbit and is much further away. Its disadvantage is that it is more difficult to see things clearly. But they have the advantage we call persistence, which allows the satellites to continuously capture images. In these orbits, you always see exactly the same part of the earth’s surface, because the satellite moves with the Earth, rotates at the same speed.

In a way, a balloon is the best solution. They are much closer to the earth than any satellite, so they see more clearly. And of course the balloons move, but they move relatively slowly, so they also have some persistence. However, balloon espionage is not common today because balloons are relatively easy targets and not completely controllable.

What types of surveillance are spy balloons capable of?

I don’t know what technology is used in this particular spy balloon, but they are probably different types of cameras that collect different information.

Today, images are obtained in different areas of the electromagnetic spectrum. People see in a certain range of this spectrum, the visible spectrum. So if we have a camera and we take a picture of our dog, the result is a visible image. This is one of the tasks of spy planes. They take normal photos, although they have very good zoom options to be able to zoom in a bit on what they see.

But different types of information can be obtained in other parts of the electromagnetic spectrum. The most famous of them is infrared. If it’s night, a visible camera won’t show us anything, because everything will be dark. But an infrared camera can pick up heat radiation in the dark.

How do these balloons fly?

Most of these balloons go literally where the wind blows. There may be little navigation, but there are definitely no people on board. They are at the mercy of the weather. They sometimes carry guidance devices that change the height of the balloon to pick up the wind blowing in a particular direction. US officials said the Chinese reconnaissance balloon had propellers to help it steer. If this is confirmed, it would mean that your operator will have a lot of control over the trajectory of the balloon.

What are the boundaries of the country’s airspace?

There is an internationally recognized limit called the Karman line at 100 kilometers. This balloon was well below that limit, so it was in US airspace.

Which countries use spy balloons?

In recent decades, the Pentagon has had programs to explore what new things can be done with balloons. Maybe they’re bigger, maybe they can go higher into the atmosphere to make them harder to shoot down or incapacitate. Maybe they can be more assertive.

The great interest generated by this incident illustrates its unusual nature. Few people expected that today the country would actively use spy balloons.

The United States flew many balloons over the Soviet Union in the 1940s and 1950s, which were later replaced by U-2 high-altitude spy planes and then satellites.

I’m sure a number of countries have periodically rethought the use of balloons: is there anything we could do with balloons now that we couldn’t do before? Do they fill our gaps with satellites and aircraft?

What does the incident with this balloon mean, which China has confirmed is its own?

China has been complaining for years that the US has been spying on it from satellites and ships. China is also known for its somewhat provocative behavior, swimming close to the borders of other countries and “rattling weapons”. I think this incident falls into that category.

The balloon poses no real threat to the US. Sometimes China is just experimenting to see how far it can go. It’s not very advanced technology. It serves no real military purpose. I think some kind of political message is much more likely.

Ian Boyd, Professor of Aerospace Engineering, University of Colorado Boulder

This article was originally published on The Conversation. Read the original.