Shuttle Columbia rolls to pad 39A on May 16, 1990, with sistership Discovery at nearby pad 39B. It marked only the second time in space shuttle history both pads had been occupied. Photo: NASA-JSC

NASA is keeping open the option of putting two shuttles on the Kennedy Space Center's two launch pads at the same time during hurricane season. But such decisions will be made on a case-by-case basis, balancing the demands of space station assembly against potential disruptions due to approaching storms.

If delaying a second shuttle's trip to the pad will not impact its eventual launch date, NASA likely will keep the craft in doors until the other shuttle is safely off the ground, James Halsell, manager of shuttle launch integration, told Spaceflight Now.

But if such a roll-out delay threatened to disrupt station assembly or derail some high-priority objective, NASA likely would press ahead with moving the second shuttle to the pad, running the risk of additional disruptions if a hurricane forced engineers to move both orbiters back to the protection of the Vehicle Assembly Building.

The shuttle Atlantis currently is mounted atop pad 39B awaiting liftoff Sept. 8 on a space station outfitting mission. The shuttle Discovery, meanwhile, is stacked and ready for rollout to pad 39A for launch Oct. 5 on another station assembly flight.

Discovery had been scheduled for roll out Monday, but the approach of Hurricane Debby last week prompted NASA managers to reconsider the wisdom of mounting two shuttles on their seaside firing stands during the height of hurricane season.

At issue was how long it would take to haul two space shuttles back to the protection of NASA's hurricane-rated VAB and how far in advance of an approaching storm such a roll-back decision would have to be made.

United Space Alliance, the shuttle program's prime contractor, operates the two crawler-transporters used to haul shuttles to and from pads 39A and 39B. But due to previous staff reductions, there currently are not enough trained personnel to operate both crawlers at the same time.

Space shuttle Discovery is hoisted upright inside the Vehicle Assembly Building last week for mating to the external tank and solid rocket boosters. Photo: NASA-KSC

With two vehicles on the pad, Halsell said, preparations for roll back would have to begin 56 hours before the arrival of 40-knot winds. With one vehicle on the pad, preparations would have to begin 40 hours in advance.

And that difference could be critical. Had two shuttles been on the pad during the approach of Hurricane Debby, NASA managers could have been forced to order a roll back, which, in turn, could have delayed the next flight.

As it turned out, Debby broke up and posed no threat. But NASA managers might not have known that 56 hours before the predicted arrival of 40-knot winds.

"The (hurricane} policy hasn't changed, that is, the program feels comfortable with having two vehicles on pad simultaneously," said Halsell.

"The special circumstances this time were A) it was the very peak of the hurricane season and B) we can still make our launch date and avoid having two vehicles on the pad simultaneously without paying an unacceptable cost."

In the case of Discovery, engineers had about two weeks of contingency time built into the processing schedule. Not counting the Labor Day holiday, Halsell said, the decision to delay roll out only cost four days of weekday processing.

"If the situation had been different, that is, we couldn't assure ourselves we could hold the launch date or if it were not at the peak of hurricane season, the decision could have gone the other way," Halsell said.

"On flip side of that, we wanted to make sure we weren't guilty of over managing ourselves into another tough work situation for the Kennedy Space Center."

He said USA expects to have two full crawler crews in place by the 2001 hurricane season.