Explainer: Why the fuss over falling debris from China's most powerful rocket

China launched into orbit last month the first piece of a permanent space station using its most powerful rocket, but international focus has fallen instead on the re-entry of debris which critics say has been shrouded in secrecy.

What happened?

The Long March 5B rocket successfully delivered its payload into orbit on April 29, in the first of 11 missions needed to complete China's first permanent space station by 2022.

Media reports warned of an "uncontrolled"...