Why were astronauts aboard the International Space Station recently ordered by NASA to take cover in their escape capsule?

Answer: A piece of "space junk" was passing near the station. According to the AP, "The debris — estimated to be about 6 inches square — is from a Chinese satellite that was deliberately destroyed in 2007 as part of a weapons test. It was projected to pass within three miles of the space station, warranting a red threat level, NASA's highest."