China has put new focus on airships hovering in a part of the sky just before outer space. Although Beijing says they're scientific, analysts say the data helps the country develop advanced weapons.

The air defense center was created in the 1950s, as a counter to a rival superpower. Now NORAD is front and center again, prompting questions about what it does — and how it copes with modern threats.

The U.S. military started tracking more airborne objects it calls "low speed clutter" after shooting down the Chinese balloon. The National Weather Service says it launches about 184 balloons a day.

"Crews have been able to recover significant debris from the site, including all of the priority sensor and electronics pieces identified," U.S. Northern Command said.

FBI and State Department officials gave reporters an update on some of what the U.S. has learned so far about the balloon.

Chinese surveillance balloons have flown over the U.S. at least four times in recent years. But the U.S. didn't learn about these cases until the intelligence community discovered them afterwards.

The suspected Chinese spy balloon was noticed in Montana and slowly crossed the U.S. China expressed its "strong dissatisfaction and protest" over the downing.