National Security Council strategic communications coordinator John Kirby told reporters that there are several factors – like their altitude and speed – that make detecting the spy balloons difficult, saying that the ways to track them are “not constant.”
“They fly very, very high, very, very slow and in order to track, you’ve got to run the traps along many different lines of information and technology,” Kirby said. “Their dynamics, their trajectory, their flight behavior complicates the ability to know exactly where one is at any particular moment in time depending on where it is over the Earth’s surface.”