When a piece of insulating foam more than half the weight of the one that doomed the Columbia broke off from the shuttle Discovery’s external fuel tank this week, it not only raised questions about the safety of future shuttle flights, but also called into question the competence and engineering judgment of NASA, its contractors and its oversight boards.

NASA took the only reasonable step by announcing that it would ground the shuttle fleet indefinitely while it tried to identify and fix the foam-shedding problem. Fortunately, that piece of foam seems to have missed the shuttle, but this may have been a very close call. Had the foam broken off 40 seconds earlier, it could have hit the orbiter and poked a hole in the shuttle’s fragile protective skin. If that had happened, the astronauts would have been in grave peril. This incident says nothing good about the meticulous process by which the shuttle was repaired and determined to be ready for flight. NASA pronounced the tank the safest and most reliable ever built. NASA had identified the area on the tank that shed the foam as a potential risk, but as one that could wait to be corrected. Either NASA’s engineering judgments is still flawed, or the aging shuttles, with their millions of parts, are just too complex to be fully understood. — The New York Times