While NASA prepares to roll the Space Shuttle Discovery out to its launch pad, a team of engineers are working through a mountain of safety waivers to ensure the orbiter is safe for flight.

For every aspect of a shuttle or shuttle flight that falls outside the precise flight-safety rules that date back to the 1970s, a waiver must be granted for a mission to go forward. In theory, the safety issues that necessitate the waiver get addressed for subsequent missions, but in reality they have stacked up over the years.

With the target launch date for Discovery getting closer, NASA officials are scrambling to separate those waivers that are no longer relevant from those that are. They then have to evaluate the remaining waivers to determine whether the issue in question must be addressed before the orbiter can be cleared to fly.

“We’re very close, but I don’t know if we’re going to have every one examined [by launch day],” NASA’s space shuttle deputy manager Wayne Hale told reporters March 30 . “We will likely have some handful of [safety] waivers for the flight.”

As part of the return-to-flight efforts, NASA has turned waiver approval over to an Independent Technical Authority (ITA), which is separate from the shuttle program and headed by the agency’s chief engineer, Rex Geveden.

“In the case of Columbia, [the shuttle] program office really owned all the technical requirements, but also evaluated itself on them, and that’s the thing,” Geveden said in an interview . “You really ought to have an independent panel so that you can look at [waivers] without the pressure of cost and schedules.”

Space Shuttle Columbia and its crew were lost Feb. 1, 2003, when damage incurred during launch triggered a string of events that caused the orbiter to break up during re-entry over Texas. Since then, the agency’s three remaining orbiters have been grounded.

Discovery, NASA’s first shuttle to launch since Columbia , currently is slated to lift off no earlier than May 15 .

“The waiver system at NASA prior to Columbia was inappropriate,” Hale said. “We had a huge number of waivers that clogged the system, not allowing us to sift out the safety concerns.”

Before Columbia launched in January 2003, about 6,000 waivers sat on the orbiter’s books, and in most cases there were no plans to address or eliminate them from the roster, Hale added.

“There has been a lot of energy spent over what will constitute a waiver,” Geveden said, adding that flight-rule changes or other emergencies may spur new waivers. “It’s not just designs and drawings.”

Since the Columbia disaster , shuttle and ITA officials have managed to weed out hundreds of waivers that were simply obsolete since they referred to components that were no longer used aboard shuttles. Hundreds more were thrown out because they were impractical; one arcane requirement called for a waiver for each piece of flight hardware that emits electromagnetic interference.

“Even your watch emits some interference,” Hale said, adding that the regulation was written in the 1970s, before laptop computers were regular items on flight manifests. “[And] some of these waivers were based on designs of the shuttle before the first orbiter flight.”

According to the most recent edition of NASA’s return-to-flight implementation plan, a large number of waivers could be unavoidable if the space agency were forced to launch a rescue shuttle to pick up a stranded crew at the international space station.

“If you have to change a flight rule in the middle of a flight, like in a ‘safe haven’ contingency, then that will be looked at by the Technical Authority,” Geveden said.

But some waiver habits, it seems, are hard to shake.

“As we were rolling Discovery over, some engineers came to me with a sheaf of waivers for minor issues,” Hale said.

One of the waivers, he added, concerned a blemish on a seal, which an engineer wiped away with a cloth. Since the engineer addressed the smudge on his own before seeking approval from hardware designers, the procedure technically required a waiver.

“A waiver implies that something has a safety concern,” said Hale, adding that he expects at least a few true safety waivers to be addressed for Discovery’s flight. “And I also want to make sure that every one of those has a retirement plan.”