The successful mission of the Space Shuttle Atlantis Sept. 9-21 showed that the safeguards put in place to prevent the kind of accident that destroyed the Columbia orbiter are working well enough to let NASA go back to launching shuttles at night when necessary. Shuttle managers took an initial step in that direction late Sept. 28. When the agency’s Program Requirements Change Board meets Oct. 5 at the Johnson Space Center in Houston they should formalize the change.

Banning nighttime shuttle launches was one of the recommendations of the Columbia Accident Investigation Board. The idea was to make sure NASA has the best photographs possible to assess whether insulating foam falling off the shuttle’s external tank — something that still happens during every launch — had damaged any critical parts of the orbiter.

Foam damage, of course, is what doomed Columbia and its crew. A large piece of foam that had shaken loose from the tank during liftoff punched a hole in the leading edge of one of Columbia’s wings . That breach allowed hot plasma to stream into the wing when Columbia re-entered Earth’s atmosphere. The orbiter broke up over Texas, killing the crew.

To make sure the heat-resistant shielding on the leading edges and underbellies of shuttles are in good enough shape to safely re-enter the atmosphere in future missions, NASA accepted the accident board’s recommendation to launch only during the day so that cameras could closely monitor foam shedding .

But that was not the only measure adopted to make sure no damaged orbiter tried to re-enter the atmosphere . NASA also built extensions for the shuttle’s robotic arms so that a high-resolution camera can examine every centimeter of a shuttle’s exterior on orbit to make sure it has not sustained any damage. Spacewalking astronauts can also conduct their own close-up examinations.

In the three shuttle flights since Columbia, those examinations have given NASA and its astronaut crews a full picture of the condition of their orbiter.

During the Atlantis mission the camera system was used twice: Once for the now-routine examination of the orbiter’s exterior on orbit; and a second time after ground-based radar spotted two unidentified objects floating near Atlantis.

While there are still many things that can go wrong during a shuttle mission, NASA seems to have a very good system for assessing foam damage. If any serious damage is found — and so far none has been — the crew can either conduct repairs on orbit or return to the international space station to wait for a rescue spacecraft. The on-orbit inspection system has proven itself good enough that mandating daytime launches for monitoring purposes is no longer necessary.

Agency officials have in fact said the daytime launch restriction might be lifted once they have a few successful missions with the new safety procedures under their belts. So it was not surprising when shuttle launch officials agreed Sept. 28 to move up the target launch date for the Space Shuttle Discovery on mission STS-116 from Dec. 14 to Dec. 7 at roughly 9:38 p.m. eastern time .

But they still need to get the Program Requirements Change Board to formally waive the post-Columbia daylight launch

The crew of Atlantis did a great job getting assembly of the international space station back on track, but as NASA Administrator Mike Griffin noted after the crew had returned to Earth, nearly 50 percent of the station’s hardware has yet to be launched.

The shuttle’s history shows that unexpected problems and delays frequently occur. The ability to launch at night will give NASA some sorely needed schedule flexibility and a greater chance of completing all of the launches necessary to complete assembly of the space station by 2010, when the agency intends to mothball the shuttle fleet.

The road ahead is tough enough without imposing a constraint on shuttle operations that is no longer needed to assure the crew’s safety.