Spaceflight Now




Engineers troubleshoot last-minute shuttle issues
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: December 5, 2006

After a lengthy launch-minus-two-day review, NASA managers tonight tentatively cleared the shuttle Discovery for liftoff Thursday night, weather permitting, pending resolution of two last-minute technical issues. The issues do not appear to be show stoppers, but engineers are collecting additional data to make sure.

"We're on track and on target for Thursday," said LeRoy Cain, chairman of NASA's launch-site Mission Management Team. "All in all, we're in great shape."

Discovery's liftoff on NASA's third shuttle mission of 2006 - the agency's first night launch since 2002 - is targeted for 9:35:49 p.m. The forecast calls for a 60 percent chance of favorable weather.

The goal of the 117th shuttle flight is to re-wire the international space station to take advantage of newly installed solar arrays in a complex transition from an interim power system, used during the initial stages of construction, to the station's permanent system.

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"Many of us consider this the most challenging flight that the international space station will have done since we began the effort of assembling the ISS," said space station Program Manager Mike Suffredini.

"Now I need to tell you guys, when you look at the space station when the shuttle leaves, it's not going to look hardly any different than when they got there. But it will be a dramatically different vehicle inside when we finish all the reconfigurations. So this is a big flight for us and we're looking forward to it."

The Discovery astronauts need to rendezvous and dock with the station on their first opportunity - flight day three - to accomplish all of the mission's objectives. For a launch Thursday, that means a docking Saturday evening.

Given a successful reboost of the space station Monday, Discovery's crew now has flight-day-three docking opportunities through Dec. 26, the end of the 2006 launch window, should the flight be delayed.

In addition, engineers successfully uplinked and tested new software today designed to detect and automatically correct motor-gear tooth misalignments in a massive rotary joint designed to rotate the station's huge solar arrays to keep them face on to the sun.

Engineers ran into problems with the software last week and while the rotary joint motors can be readjusted using ground commands, the software works much faster, a potential factor in Discovery's already complicated mission.

Today, engineers successfully tested a software patch to correct the problem and Suffredini said the new tool will be available to resolve any misalignments that might otherwise interrupt critical activities.

But Discovery will not be formally cleared for launch until engineers resolve two last-minute issues that were left open at the end of the L-minus two-day review:

  • A brief, half-second electrical transient was noted early today when engineers were configuring the shuttle's electrical power systems for launch. Cain said he asked engineers to work through the night to collect data showing whether the brief surge could have caused problems for any of the electrical systems in the orbiter, the external tank or the ship's twin solid-fuel boosters. Cain said a preliminary assessment indicates the shuttle's systems were not affected by the transient, but additional data is needed to make sure.

  • A recent engineering test uncovered a potential issue with an adhesive used to bond insulation in the joints between solid-fuel booster segments. The adhesive is associated with so-called J-seals, a post Challenger safety improvement, but Cain said the test results were new and not yet fully understood. Engineers are studying the test data to determine if there are any concerns about the joints in Discovery's boosters.
"With respect to the solid motor joint adhesive, I don't think I would even call it suspect because I don't know enough to be able to even put an adjective or a characterization of it," Cain said. "What we know is there is a test out there, or the results of a test, we need to look further at to determine whether or not we have any concerns. That's really and truly where we are. We don't even know enough to know if we have a concern.

"I wouldn't want to speculate, really, on either one of those problems as to where they might lead, but you can be certain we'll follow the data."

The only other issue of any significance is the weather. Forecasters now say a cold front expected to pass through Central Florida Thursday has a 40 percent chance of leaving low clouds in its wake that could cause a delay.

The forecast for Friday and Saturday is 60 percent no-go both days.

NASA's scrub/turnaround options permit seven launch attempts between Dec. 7 and Dec. 17, the end of the currently approved launch window. A launch on Dec. 17 would result in a landing before the end of the year and still provide two contingency days for bad weather or other problems.

Launches after Dec. 17 are possible - the station's orbit permits launchings as late as Dec. 26 - but NASA managers would have to agree on flying Discovery over the new year transition if it came to that.

In any case, the launch team's normal scrub-turnaround policy calls for four launch attempts in five days - Dec. 7, 8, 10 and 11. That includes one 48-hour stand down to top off on-board supplies of liquid hydrogen between the second and fourth attempts.

After that, alternating hydrogen and oxygen top-offs would result in launch opportunities Dec. 13, 15 and 17.

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