What is a spy balloon, and why is China being accused of flying one over the U.S.?

The Pentagon announced on Thursday that it was tracking a suspected spy balloon flying in U.S. airspace. Defense officials said they had “very high confidence” that it belonged to China and that it was “significantly above ... civilian air traffic.”

On Friday, military officials confirmed that "another Chinese surveillance balloon" was seen flying above Latin America.

A spokesperson for the department said officials had been observing the balloon over the U.S. — spotted by local residents in Billings, Mont. — for several days, but said it was not shot down over concerns about the damage it could cause.

“We did assess that it was large enough to cause damage from the debris field if we downed it over an area,” the official said. “We had been looking at whether there was an option yesterday over some sparsely populated areas in Montana. But we just couldn’t buy down the risk enough to feel comfortable recommending shooting it down yesterday.”

A balloon flies in the sky over Billings, Mont.
A balloon over Billings, Mont., on Wednesday, in an image obtained from social media. (Chase Doak via Reuters) (Chase Doak via REUTERS)

On Friday morning, the Chinese Foreign Ministry claimed that the suspected surveillance balloon was an unmanned “civilian airship” used for weather research. In a statement, the ministry said it regretted the “unintended entry of the airship into US airspace due to force majeure,” and that, “affected by the Westerlies and with limited self-steering capability, the airship deviated far from its planned course.”

Montana is home to one of the United States’ three nuclear missile silo fields, at Malmstrom Air Force Base. A senior defense official said the U.S. is confident the balloon was being flown over sensitive sites to collect information.

The discovery of the balloon came days before Secretary of State Antony Blinken was to visit China — the highest-ranking member of the Biden administration to do so. But on Friday it was announced that the diplomatic trip was postponed. In a call to his counterpart, Foreign Minister Wang Yi, Blinken said the balloon was “an irresponsible act and a clear violation of U.S. sovereignty and international law that undermined the purpose of the trip.”

What is a spy balloon?

Spy balloons have been around for centuries, initially deployed for military use in the 18th century. They were used as a form of observing enemy armies and gathering intelligence. Balloons were used again in World War I and even as late as the Cold War, and their use has been revived in recent years, despite the use of global satellite technology.

A modern surveillance balloon works at high altitude, reaching at least 60,000 feet and often 80,000 to 120,000 feet. The balloon flying over the U.S. is flying around 60,000 feet over the center of the country, officials said.

An observation balloon at Van Cortland Park in New York City in 1919
An observation balloon at Van Cortland Park in New York City during a field artillery demonstration in 1919. (HUM Images/Universal Group via Getty Images) (HUM Images/Universal Images Grou)

They are made in a variety of sizes and have their own propulsion system. To generate power, most balloons are equipped with solar panels, as their high altitude allows good access to solar energy. A photographer with the Billings Gazette who saw the balloon said a solar array appeared to be hanging from the bottom.

Last July, the Pentagon confirmed to Politico that during one of its surveillance missions, 25 balloons were used in its demonstration. Since 2020, the Pentagon has invested close to $4 million in projects with balloons, and it intends to spend $27.1 million this year, according to budget documents reviewed by the news outlet.

How do spy balloons work?

“Surveillance balloons are designed to stay stationary in the upper atmosphere for up to 20 months,” Patrick Bury, a senior lecturer in security at the University of Bath in England, told Yahoo News. “And because they are kitted out with these advanced optics, they can download the information they want via a secure network.”

Has the balloon moved?

Officials said on Friday that the balloon changed course and has been moving eastward toward the central U.S. This demonstrated that it has the ability to maneuver, according to military officials. However, during a press briefing, Air Force Brig. Gen. Patrick Ryder refused to answer precisely how it was being moved and who or what was in control of its flight path. The Pentagon expects the balloon to continue to float over the U.S. for the next couple of days.

Air Force Brig. Gen. Patrick Ryder
Pentagon spokesman Air Force Brig. Gen. Patrick Ryder at a media briefing on Friday. (Alex Brandon/AP) (AP)

Why use a spy balloon instead of a satellite?

According to Bury, surveillance balloons can be equipped with the same kind of surveillance devices as a satellite, but at a much lower cost.

A senior defense official said it was unlikely the balloon could provide additional surveillance data versus what China could get from a low-altitude satellite.

Why now?

Bury said, “Speaking as a security analyst, I would say that this is quite the coincidence that the balloon is turning up over nuclear bases.”

“So my own thoughts are that the U.S. is very aware that they’re there and has been for a while,” he added. “And China is very aware that the U.S. knows that they’re there, and the Chinese have decided to potentially send a message.” The balloon situation this week comes after the U.S. expanded its military presence in the South China Sea after opening new bases in the Philippines.