Experts answer the question 'What is a spy balloon? Is it bad for an artificial satellite?'

On February 4, 2023, the U.S. Air Force shot down a ``

mysterious balloon that flew from China to the sky over the United States ,'' and it became a big topic in Japan. The US Department of Defense claims that this balloon is a ``Chinese reconnaissance balloon,'' but questions such as ``What is a reconnaissance balloon in the first place?'' Ian Boyd , an aerospace engineering professor at the University of Colorado Boulder in the United States, explains the question.

Chinese spy balloon over the US: An aerospace expert explains how the balloons work and what they can see

On February 2, 2023, the US Department of Defense revealed that a mysterious balloon from China was flying over the United States and that authorities are continuing to monitor it. The balloon crossed the Aleutian Islands at the end of January, invaded the sky above Alaska, passed through Canadian territory, and entered the sky above Montana, USA. The altitude at which the balloon is flying is about 60,000 feet (about 18,000 meters), which is higher than a commercial aircraft, so it does not pose a physical threat, but Montana has an intercontinental ballistic missile equipped with a nuclear warhead. President Joe Biden had issued a shoot-down order as of the 1st because there are many important military bases such as Malmstrom Air Force Base where missiles are deployed.

Chinese officials confirmed the balloon was made in China, but claimed it was a privately owned meteorological research object and that it was hit by a westerly wind that deviated from its planned course. And on February 4th, the US Air Force shot down a balloon flying over the Atlantic Ocean using an air-to-air missile, and after that the authorities are working to recover the wreckage scattered on the ocean.

The US military shot down a Chinese reconnaissance balloon that crossed US airspace, the Chinese Ministry of Foreign Affairs protested - GIGAZINE

In addition to objecting to the US military's use of force to solve the problem, Chinese authorities have protested that ``balloons do not belong to the United States'' about US authorities collecting the wreckage. In addition, Chinese balloons have also been confirmed over Costa Rica in Central America, and Chinese authorities explain that private balloons have deviated from the planned course like the American ones, but the US Department of Defense said that a series of balloons claims to be part of China's military surveillance program .

◆What is a spy balloon?
The idea of using a balloon to monitor the enemy from the sky was not born recently, and in 1794 there was a case in which the French army launched a balloon to monitor the enemy army in the French Revolutionary War . “A spy balloon is literally a gas-filled balloon that flies as high as a commercial aircraft,” Boyd said. Towards the ground, we collect all the information that is happening on the ground by photography and image processing.'

What are the benefits of using spy balloons instead of spy satellites?
In modern times, artificial satellites are the mainstream means of monitoring opponents from the sky, and Mr. Boyd says that artificial satellites can be divided into two types. The first is a low-Earth orbit satellite that orbits at a relatively low altitude of less than 2000 kilometers, and has the advantage of being able to photograph things on the ground more clearly than satellites that orbit more distantly. However, since low-earth orbit satellites continue to move around the earth at a pace of about 90 minutes, they are not suitable for missions that continuously monitor the same point.

The second is geostationary orbit satellites that orbit higher than low earth orbit satellites. A geostationary orbital satellite, 35,786 kilometers above the equator, orbits at the same speed as the earth's rotation, so it appears to be stationary from the ground. Therefore, it is possible to continuously monitor the same point, but it is much farther than a low-orbit satellite, so the accuracy of the image is inferior.

Spy balloons can solve the challenges of these two types of satellites. First, balloons fly much lower than satellites, so they can see ground targets more clearly. And since the balloon moves relatively slowly, it is possible to monitor the same point continuously to some extent. However, Boyd said, 'But balloons are relatively easy to target and not completely controllable, so balloon espionage is not usually done these days.'

What kind of surveillance is possible with spy balloons?
It's still unclear what equipment was on board the downed Chinese balloon, but a typical spy balloon is equipped with various types of cameras. In recent years, cameras that capture not only the visible spectrum that can be seen by the human eye, but also the electromagnetic spectrum that is invisible to the naked eye, such as infrared rays, have been developed, so spy balloons may be able to shoot targets on the ground even in dark nights.

◆ How do spy balloons move?
Most balloons move with the wind, making it difficult for unmanned balloons to control their destination precisely, even though they have the navigational ability to change altitude to catch a particular wind. John Kirby, director of strategic public affairs at the White House National Security Council, said the balloon had a propeller and a rudder, but

that it had limited maneuverability at the altitude it was flying. is shown.

◆From what altitude is space in the sky, and how far does the country have rights?
In response to this question, Mr. Boyd said, ``There is an internationally recognized boundary line called the Carman Line at 100 kilometers above the ground.The balloon was well below it, so it was definitely in American airspace.'' said.

◆Is there a country that actually uses spy balloons?
The United States seems to have flown many spy balloons over the Soviet Union in the 1940s and 1950s, but eventually they were replaced by reconnaissance aircraft, and eventually satellites began to take on reconnaissance missions. The fact that the balloon that flew to the United States caused a big fuss this time also shows that spy balloons are rarely used in recent years.

But Boyd points out that the US Department of Defense has spent decades studying whether modern technology can do things that balloons of the past couldn't do. He argued that countries other than the United States would also periodically reassess spy balloons.

Were the balloons that China flew really practical spy balloons?
Boyd said the balloon was part of China's frequent incursions into other countries' territorial waters and airspace, including in the South China Sea, as well as its military exercises. “This balloon poses no threat to the United States. I see the balloon as a political message,' he said.

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