The smooth landing of the Discovery ended a flight that was successful in almost every respect but one: the dislodging of a big chunk of foam, like the one that doomed the Columbia. It’s astronauts performed superbly during their two-week mission. The flight achieved its prime aim.

This was the most scrutinised shuttle flight ever, with the vehicle undergoing close inspection while still in orbit. New sensing and photographic equipment to look for potentially perilous damage to the sensitive external skin proved valuable. The flood of images and NASA’s openness in discussing its uncertainties about potential hazards sometimes made it appear that the shuttle was about to fall apart. In the end the damage was tolerable. A much-touted space walk to repair the shuttle’s skin — the first of its kind — moved an astronaut close enough to pluck out some protruding material with his hand.

The biggest concern was the nearly one-pound piece of foam that fell off the external tank during lift-off and several other pieces of foam debris that exceeded NASA’s size limit. NASA has not yet solved the foam-shedding problem. This fli-ght and the visible uncertai-nties of its managers left the unsettling impression that there is a lot NASA doesn’t know about the performa-nce of the spacecraft it has relied on for the past quarter-century. — The New York Times