What are spy balloons and what is their purpose?

Tensions between the United States and China heightened Friday when U.S. officials publicly identified a Chinese surveillance balloon drifting across the country. 

The Chinese Foreign Ministry confirmed that the balloon belongs to China but have claimed that it is a weather balloon that went off course as a result of the wind. U.S. officials have rejected that claim. 

The U.S. has still not shot down the balloon, though, citing concerns that people on the ground could be in harm’s way as a result. It was first spotted over Montana on Wednesday and has moved across the continent, being seen in northeast Kansas on Friday afternoon. 

Surveillance balloons have been used by many countries over the years — well before satellites existed — and continue to be used in certain situations for intelligence-gathering. 

The Guardian reported that modern spy balloons include a certain piece of surveillance equipment — like a camera or a radar — held below a balloon that is guided by wind currents. But Brig. Gen. Pat Ryder, the Pentagon press secretary, said in a briefing that this balloon has some ability to maneuver itself. 

These types of balloons usually operate somewhere between 80,000 to 120,000 feet above the ground, which is much higher than the height commercial airlines fly to, according to The Guardian. China’s balloon has reportedly been traveling at 60,000 feet in the air, still much higher than the roughly 40,000 feet planes can reach.

Although satellites have become much more prominent in modern times, using high-altitude balloons still provides some advantages.

Timothy Heath, a senior international defense researcher for the RAND Corporation, said balloons are tough to detect because they do not have much metal, presenting a difficulty to radar sensors. They are also less predictable once discovered, he said.

Politico reported that balloons are also much cheaper to create and operate than satellites, and they can carry more than a drone can. The balloons can also travel long distances without needing to receive additional fuel and can stay over a specific area for a longer period of time than a satellite that orbits Earth. 

The use of spy balloons reportedly dates back to as early as the 1700s during the French Revolution and has played key roles in military and intelligence operations. 

The New York Times reported that the Union and Confederate armies used balloons during the Civil War. Both sides experienced some logistical issues, but Thomas Paone, a curator at the National Air and Space Museum in Washington, D.C., told the Times that this was the first time in U.S. history that an organized military effort to use balloons for surveillance happened. 

Japan also sent 9,000 military balloons with bombs attached to the United States during World War II, but only six people in the U.S. were killed when they came in contact with one in May 1945, according to the Times. 

NASA also uses balloons for observing parts of Earth, sending one to the top of the atmosphere in 2015. Politico reported that the agency’s use of helium balloons goes back to the 1950s.