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.
"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:
"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.