When four astronauts set off on their historic trip around the moon in NASA’s 16.5-foot-wide Orion spacecraft, they knew they’d be testing a known flaw with their spacecraft — one that had some experts urging the space agency not to fly the mission with humans on board. NASA remains confident it has a handle on the problem and the vehicle can bring the crew home safely. The issue relates to a special coating applied to the bottom part of the spacecraft, called the heat shield. It’s a crucial piece of hardware designed to protect the astronauts from extreme temperatures as they’re descending back to Earth during the final stretch of their moon-bound mission called Artemis II....