Shuttle engineers are gearing up to refuel the shuttle Discovery for launch tonight at 8:47:34 p.m. to kick off a critical space station mission. Retraction of a huge service gantry ran behind schedule this morning, but a NASA spokesman said the work was expected to be completed in time to support fueling operations, scheduled to begin at 10:52 a.m.

Weather remains the only major concern, with launch forecasters at the Air Force 45th Space Wing predicting a 70 percent chance of high crosswinds and low cloud decks that could force another delay. The ods are 60 percent "no-go" Sunday and Monday.

"High pressure is dominating the Eastern U.S., inducing a strong pressure gradient over Central Florida," according to the morning forecast. "Over the course of the next several days the winds will gradually decrease and veer clockwise as the high pressure area migrates east.

"Also, the easterly flow causes low clouds and isolated showers moving onshore across the launch complex and Shuttle Landing Facility (SLF). Our primary concerns for launch day are SLF crosswinds, a low cloud ceiling, and isolated showers."

The Spaceflight Meteorology Group at the Johnson Space Center, responsible for predicting landing conditions in case of an emergency return-to-launch-site abort, predicts scattered clouds at 4,000 feet, a broken deck at 20,000 feet and a chance for showers and an out-of-limits broken deck at 4,000 feet.

SMG also predicts winds out of 60 degrees at 12 knots gusting to 18, a direct crosswind on shuttle runway 15/33. NASA's launch limit is 15 knots.

An initial attempt to launch Discovery Thursday night was scrubbed at the last minute by low clouds over the launch pad. NASA managers decided to skip a Friday opportunity because of a 90 percent "no-go" forecast. As it turned out, SMG was observed and forecast "go" Friday night and it appeared to the untrained eye that Discovery's crew would have had a shot at getting off had NASA opted for a 24-hour turnaround instead of 48.

But that's hindsight. Florida's coastal weaher is notoriously difficult to predict, reinforcing former Launch Director Bob Sieck's observation that on any given day, the odds of launch are 50-50.

Here is a timeline of today's countdown activities (in EST):

DATE/EST......EVENT
_________________________________________________________________

Sat  12/09/06

08:52:00 AM...Begin 2-hour built-in hold (T-minus 6 hours)
09:02:00 AM...Safe-and-arm circuit test
09:42:00 AM...Mission management team tanking meeting
09:52:00 AM...External tank ready for fueling
10:52:00 AM...Resume countdown (T-minus 6 hours)

10:52:00 AM...LO2, LH2 transfer line chilldown
11:37:00 AM...Hydrogen ECO sensors go wet
11:42:00 AM...LO2 fast fill
11:52:00 AM...LH2 fast fill
01:52:00 PM...Fueling complete

01:52:00 PM...Begin 3-hour built-in hold (T-minus 3 hours)
01:52:00 PM...Closeout crew to white room
01:52:00 PM...External tank in stable replenish mode
02:30:00 PM...NASA TV coverage begins
03:08:00 PM...Astronaut photo opportunity (time approximate)
04:27:00 PM...Astronauts don pressure suits
04:52:00 PM...Resume countdown (T-minus 3 hours)

04:57:00 PM...Crew departs O&C building
05:27:00 PM...Astronauts strap in
06:32:00 PM...Hatch closure

07:32:00 PM...Begin 10-minute built-in hold (T-minus 20m)
07:42:00 PM...NASA test director countdown briefing
07:42:00 PM...Resume countdown (T-minus 20m)

07:43:00 PM...Backup flight computer to OPS 1
07:47:00 PM...KSC area clear to launch

07:53:00 PM...Begin final built-in hold (T-minus 9m)
08:03:34 PM...NTD launch status verification
08:38:34 PM...Resume countdown (T-minus 9m)

08:40:04 PM...Orbiter access arm retraction
08:42:00 PM...Launch window opens (actual: 8:42:34 p.m.)
08:42:34 PM...Hydraulic power system (APU) start
08:42:39 PM...Terminate liquid oxygen replenish
08:43:34 PM...Purge sequence 4 hydraulic test
08:43:34 PM...Inertial measurement units to inertial
08:43:39 PM...Aerosurface movement check
08:44:04 PM...Main engine steering test
08:44:39 PM...Oxygen tank pressurization
08:44:59 PM...Fuel cells to internal reactants
08:45:04 PM...Clear caution-and-warning memory
08:45:34 PM...Crew closes visors
08:45:37 PM...Hydrogen tank pressurization
08:46:44 PM...Solid rocket booster joint heater deactivation
08:47:03 PM...Shuttle computers take control of countdown
08:47:13 PM...Booster steering test
08:47:27 PM...Main engine start (T-6.6 seconds)
08:47:34 PM...Booster ignition (LAUNCH)

Video coverage for subscribers only:
VIDEO: LONGER LENGTH MOVIE OF THE SCRUB PLAY
VIDEO: SCRUB CALLED DUE TO LOW CLOUDS PLAY
VIDEO: ASTRONAUTS DEPART QUARTERS FOR PAD PLAY
VIDEO: CREW FINISHES DONNING SPACESUITS PLAY
VIDEO: ASTRONAUTS IN DINING ROOM THURSDAY PLAY
VIDEO: PAD'S ROTATING SERVICE STRUCTURE ROLLED BACK PLAY

VIDEO: POST-ARRIVAL COMMENTS FROM THE CREW PLAY
VIDEO: ASTRONAUTS ARRIVE IN WAVE OF T-38 JETS PLAY
VIDEO: BIOGRAPHIES OF THE DISCOVERY ASTRONAUTS PLAY
VIDEO: NARRATED STS-116 MISSION PREVIEW MOVIE PLAY

VIDEO: WEDNESDAY'S SHUTTLE BRIEFING IN ITS ENTIRETY PLAY

BRIEFING SOUNDBITES:
VIDEO: THE ISSUES DISCUSSED AT FRR PLAY
VIDEO: NOT YOUR FATHER'S FRR PLAY
VIDEO: READY TO RESUME NIGHT LAUNCHES PLAY
VIDEO: LAUNCH PREPS PROCEEDING WELL PLAY
VIDEO: YEAR-END ROLLOVER CONCERNS PLAY
VIDEO: REASSESSING TANK FOAM RISK PLAY
VIDEO: STATION SOLAR ARRAY DRIVE SYSTEM PROBLEM PLAY
VIDEO: PRESSURIZATION PRECAUTIONS AT THE PAD PLAY

VIDEO: OVERVIEW OF STS-116 MISSION PLAY
VIDEO: SHUTTLE/ISS PROGRAM PERSPECTIVE PLAY
VIDEO: PREVIEW OF MISSION'S SPACEWALKS PLAY
VIDEO: ASTRONAUTS' PRE-FLIGHT NEWS BRIEFING PLAY

VIDEO: COVERAGE OF PRACTICE COUNTDOWN ACTIVITIES PLAY

VIDEO: DISCOVERY ROLLS TO THE PAD PLAY
VIDEO: DISCOVERY MATED TO TANK AND BOOSTERS PLAY
VIDEO: SHUTTLE HOISTED VERTICALLY INSIDE VAB PLAY
VIDEO: DISCOVERY HAULED FROM HANGAR TO VAB PLAY
VIDEO: PORT 5 TRUSS PAYLOAD PACKED UP PLAY
VIDEO: CREW VISITS KENNEDY SPACE CENTER PLAY
VIDEO: EXTERNAL FUEL TANK MATED TO BOOSTERS PLAY
MORE: STS-116 VIDEO COVERAGE
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