Sunday, August 23, 2009

Live At KSC: Discovery Gets A "Go" For Launch

NASA gave Discovery and seven astronauts a green light for flight today after a readiness review that included a lengthy discussion about the failure of one of the shuttle's nine power control assemblies.

The 18-story spaceship and its crew remain slated to blast off from launch pad 39A at Kennedy Space Center at 1:36 a.m. Tuesday -- the middle of a 10-minute window during which Discovery can be propelled onto a ground-up rendezvous with the International Space Station.

The weather forecast still is the same. There is an 80 percent chance conditions will be acceptable for liftoff at launch time.

However, meteorologists and mission managers will be keeping close tabs on the weather around 4 p.m. Monday, when external tank propellant-loading operations are scheduled to begin. There is a 40 percent chance of lightning within five miles of the pad -- conditions that would prohibit fuel-loading. NASA Launch Director Pete Nickolenko said engineers would have to begin tanking by 7 p.m. in order to make a launch attempt early Tuesday.

NASA mission managers had one key issue to address in the L-2 Mission Management Team briefing at KSC today.

One of three forward power control assemblies on Discovery failed after the shuttle was rolled out to pad 39A. The electronics box, which routes power from the shuttle's fuel cells to spaceship systems, was replaced with a spare. But two other boxes recently failed during laboratory testing at Johnson Space Center in Houston, prompting engineering analyses and debate.

Mike Moses, chairman of the Mission Management Team and manager of shuttle launch integration at KSC, said engineers and managers spent an hour talking about the issue.

The prime concern is that a failure might prevent shuttle steering thrusters from being turned on in flight. Consequently, NASA already has powered up jet drivers that route commands to the thrusters on the shuttle's nose and will keep them powered up through docking at the station to make sure they can be operated as needed.

The devices will be turned off once the shuttle docks at the station to prevent an inadvertent jet firing that could rip a docked shuttle and the station apart -- a normal precaution. Moses said the mode of failure seen on Discovery's failed unit and the two others could not induce an inadvertent jet firing while the shuttle is docked at the station.

There is some concern that a failure might prevent jet drivers from being powered up after the shuttle departs from the station. Moses said Discovery in that case could perform an atmospheric reentry using aft steering thrusters alone. A fly-around of the station would be scrapped in that event.

NASA is facing an Aug. 30 deadline to launch Discovery or delay the mission until mid-October. Senior officials say NASA would yield to the debut launch of a robotic Japanese cargo carrier on Sept. 10 and a Russian crew exchange mission in late September.

The tanking forecast for launch attempts on Wednesday and Thursday improve. There is only a 20 percent chance weather would prevent tanking prior to a launch attempt on Wednesday and a 10 percent chance in advance of an attempt on Thursday.

Nickolenko said shuttle launch history shows that there is a 96 percent chance that Discovery and its astronauts will be launched within the first four attempts.

Coming up early Monday: The Rotating Service Structure at pad 39A will be retracted away from the shuttle around 5 a.m. You can watch live here in The Flame Trench. Click the NASA TV box on the right side of the page to launch our NASA TV viewer and live coverage. Be sure to refresh this page, too, for periodic updates.

1 comment:

Anonymous said...

I'm working the, go Discovery !