Key Points
- US security experts say China's decision to use a spy balloon not a satellite is aggressive and puzzling.
- China said the balloon was deployed for civilian meteorological and scientific purposes.
- Spy balloons are cheaper to launch than satellites and can spend more time over a target area.
A suspected Chinese surveillance balloon — or spy balloon — has been flying across the United States for several days, causing .
Washington has called the presence of the spy balloon a "clear violation" of US sovereignty.
"The presence of this balloon in our airspace … is a clear violation of our sovereignty as well as international law. It is unacceptable this occurred," White House spokesperson Karine Jean-Pierre said.
Security experts say it also appears to mark a more aggressive — albeit puzzling — espionage tactic than relying on satellites and the theft of industrial and defence secrets.
Both the United States and China have for decades used surveillance satellites to keep an eye on each other from the air. But China's recent balloons — a White House official said this week's episode was not the first — have some in Washington scratching their heads.
"In a way, it's more amateurish," said former White House national security adviser John Bolton. "Do the cameras in their satellites not have high enough resolution that they have to send a balloon over?"
So what's going on, what exactly are spy balloons and why are they useful?
Why did China do it and why hasn't the US taken it down?
China said the balloon was for civilian meteorological and scientific purposes that strayed into US airspace, on Saturday accusing US politicians and media of taking advantage of the situation to discredit China. It has previously rebuffed accusations of espionage and said the United States holds a Cold War mentality and hypes up the "China threat".
The US says the spy balloon has demonstrated a "capability to manoeuvre", which challenges China's assertion that it was blown off course.
Military leaders considered shooting down the high-altitude surveillance balloon on Wednesday but eventually recommended against this to President Joe Biden because of the safety risk from debris, officials said.
Mike Rounds, a Republican member of the US Senate Armed Services Committee, told Fox News it would be good to recover the balloon to see "if it was designed to actually collect data or if it was designed to test our response capabilities".
Andrew Antonio, co-founder of high-altitude balloon startup Urban Sky, said the wind currents high-altitude balloons depend on for steering on long-distance trips were least favourable in the winter, suggesting China's intentions might not have been to target any specific location in the United States.
"Specifically targeting a certain military base with that balloon from a launch in China, in January or February, in the northern hemisphere, is very difficult to do, if not impossible," Mr Antonio said, speculating that the balloon's venture into US airspace could have been the result of a failed experiment, or some failure in its self-termination system.
Adding to the questions on Friday night, a Pentagon statement said another Chinese balloon was observed over Latin America.
A huge, high-altitude Chinese balloon has sailed across the US, drawing severe Pentagon accusations of spying despite China's firm denials. Source: AAP / Anna Griffin/AP
When did spy balloons come about?
Using high-altitude balloons for spying and other military missions is a practice that dates to the middle of the last century.
During the Second World War, the Japanese military tried to loft incendiary bombs into US territory using balloons designed to float in jet stream air currents. No military targets were damaged, but several civilians were killed when one of the balloons crashed in an Oregon forest.
Just after the war, the US military started exploring the use of high-altitude spy balloons, which led to a large-scale series of missions called Project Genetrix. The project flew photographic balloons over Soviet bloc territory in the 1950s, according to government documents.
A White House official has said spy balloon activity had "been observed over the past several years, including in the prior administration — we have kept Congress briefed on this issue".
Could they crash into planes?
The Pentagon told reporters on Thursday the balloon was at an altitude well above commercial air traffic and did not present a military or physical threat to people on the ground.
Spy balloons typically operate at 24,000-37,000 metres, well above where commercial air traffic flies — airliners almost never fly higher than 12,000 metres.
The highest-performing fighter aircraft typically do not operate above 20,000 metres although spy planes such as the U-2 have a service ceiling of 24,000 metres or more.
Why are spy balloons useful?
The advantages of balloons over satellites include the ability to scan wide swathes of territory from closer in, and to be able to spend more time over a target area, according to a 2009 report to the US Air Force's Air Command and Staff College.
Unlike satellites, which require space launchers that cost hundreds of millions of dollars, balloons can be launched cheaply.
The balloons are not directly steered, but can be roughly guided to a target area by changing altitudes to catch different wind currents, according to a 2005 study for the Air Force's Airpower Research Institute.
How else have China and the US spied on each other?
FBI Director Christopher Wray said in 2020 that the greatest long-term threat to US information and intellectual property was "the counterintelligence and economic espionage threat from China".
China's alleged clamour for American trade secrets has been so sweeping that the FBI estimated last October that it was opening a new Chinese counter-intelligence operation every 12 hours.
A more common spying tactic by China in recent decades, experts say, has been to use graduate students and other individuals with ties to China to gain access to sensitive materials by studying at research universities, working at technology companies or hacking into their computer networks.
"The problem with China is far more in the academic, scientific world," said Mark Zaid, a Washington lawyer who is involved in various national security cases.
"There is no doubt that that dynamic is changing and the Chinese are becoming more aggressive for whatever reason."
The United States has also been accused of spying by China.
Before the use of spy satellites, the United States used high-altitude aircraft that could not easily be shot down and flew them over the Soviet Union, China and Cuba, for example.
US-China relations plunged in April 2001 when a US Navy EP-3E signals intelligence aircraft collided with a Chinese fighter jet in mid-air over the South China Sea about 110km away from China's Hainan province.
In 2009, the Pentagon said five Chinese ships including a naval vessel harassed US Navy ship the USNS Impeccable, an unarmed ocean surveillance vessel, in international waters off Hainan. China said the US ship was carrying out an illegal survey off the island province.
