The balloon above the US was “the size of three buses” and had a visible “technology bay”, US media reported, including solar panels to power the surveillance device.
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.
Why is China doing this?
China may have sent a spy balloon over a major US nuclear missile silo complex simply to show that it could. It has far more advanced methods of surveillance and espionage to glean information.
By comparison, sending a spy balloon – technology that has been around for decades – is rather unsophisticated.
Alexander Neill, an analyst at Hawaii’s Pacific Forum think tank, said the balloon’s intelligence gathering was likely limited, suggesting its real intention may have been more political.
“China has its own constellation of spy and military satellites that are far more important and effective in terms of watching the US, so I think it is a fair assumption that the intelligence gain is not huge,” Mr Neill said.
China has continued to claim that the balloon was merely a weather research “airship” that had been blown off course.