Boeing technicians remove the cover from a Control Moment Gyroscope (CMG) in the Space Station Processing Facility in July 1998. Photo: NASA/KSC

NASA managers are re-assessing the agency's hurricane protection strategy while troubleshooting a possible problem with stabilizing gyroscopes bound for the international space station in October, NASA officials said Friday.

As a result, the shuttle Discovery's move from its processing hangar to the nearby Vehicle Assembly Building for attachment to an external fuel tank and two rocket boosters is on hold pending meetings next week to resolve both issues.

But Discovery's processing schedule includes more than two weeks of contingency time and NASA managers are optimistic about meeting the shuttle's Oct. 5 launch target.

Discovery currently is scheduled for blastoff one month after the Sept. 8 launch of shuttle Atlantis on a space station outfitting mission. Discovery's payload is the Z1 truss, which houses four control moment gyroscopes.

The gyros will provide stability and a fuel-efficient way to reorient the station when needed.

But engineers are studying a possible problem with the epoxy used to hold sensors in place that monitor the speed of the spinning gyros.

"During some thermal acceptance testing of some spare control moment gyroscope components, what's called the Hall effect sensor -- the sensor that's used to measure the wheel speed of the gyroscopes -- failed at extremely cold temperatures," said NASA spokesman James Hartsfield.

"At present, for prudence, engineers are working under the assumption the gyros on (the Z1 truss) could be susceptible to a similar failure," he said.

Michele Brekke, launch manager for mission STS-92, told Spaceflight Now each of the four control moment gyroscopes on the Z1 truss is equipped with two Hall effect speed sensors.

At extremely low temperatures -- around 60 degrees below zero Fahrenheit -- the epoxy in question can contract to the point of failure. During normal operations, heaters in the gyros will keep the systems well above zero degrees.

But the gyros in the Z1 truss will not be activated until after the U.S. laboratory module Destiny is attached to the station early next year. Until the lab gets there, the gyros will be dormant and so-called survival mode heaters will be used to provide minimal heating.

Under the current heater operations plan, the survival heaters would be cycled on and off to minimize power consumption during the five-month wait for arrival of the lab module. As a result, Brekke said, the Z1 gyros could, in fact, experience temperatures as low as those that caused the debonding.

One possible solution to the problem is to reset the thermostat in the survival heater system to ensure temperatures never fall low enough to cause any damage.

That would take about two weeks, but the work could be done in parallel with normal shuttle processing and would not necessarily impact Discovery's planned Oct. 5 launch target.

"The leading option is to go in and reset the thermostat on the survival heaters to a higher setting," Hartsfield said. "Resetting these thermostats is something that would take about two weeks but it wouldn't have an impact on the launch."

Brekke agreed, saying "there's about two weeks of margin in the flow and we can rephase our rolling (the shuttle to the pad) and taking the Z1 to the pad and absorb about two weeks of slip and still meet the launch date."

It is fairly rare for NASA to have two shuttles on the exposed seaside launch pads at Kennedy Space Center. The second time was in 1990 when Discovery blasted off carrying the Hubble Space Telescope as Columbia stood by. Photo: NASA/KSC

On another front, James Halsell, a veteran shuttle commander recently put in charge of shuttle processing at the Kennedy Space Center, is overseeing a separate review of the agency's hurricane protection strategy.

At issue is the wisdom of having two shuttles on the launch pad at the same time at the height of hurricane season.

The shuttle Atlantis currently is mounted atop pad 39B awaiting launch to the space station on Sept. 8. NASA managers had planned to roll Discovery to the Vehicle Assembly Building on Monday and out to pad 39A on Aug. 28 to prepare if for launch on mission STS-92.

The concern is how much time it would take to move two shuttle "stacks" back to the protection of the Vehicle Assembly Building in the event of an approaching hurricane.

NASA recently completed "safe haven" modifications to the VAB enabling the building to house three completed shuttle vehicles at the same time if necessary.

While NASA has two crawler-transporters for moving shuttles, the agency does not have enough trained operators to run two rollback operations at the same time. Instead, an approaching hurricane could force transporter personnel to make back-to-back rollbacks with minimal time for rest between operations and forcing NASA managers to make a rollback decision far in advance.

"The issue with having two orbiters at the pad simultaneously, there's just one ground crew that would have to bring them back if you had a hurricane coming," Hartsfield said. "That's kind of the issue that's of concern."

He said agency managers expect to resolve the hurricane issue early next week. But a final decision on when to move Discovery to the pad likely will be put off until the Z1 truss issue is resolved later in the week.