Engineers at the Kennedy Space Center began pumping a half-million gallons of supercold liquid oxygen and liquid hydrogen rocket fuel into the shuttle Atlantis' repaired external tank today at 9:55 a.m., setting the stage for launch at 7:38 p.m. on a space assembly mission. This will be NASA's first shuttle flight of 2007, thanks to a three-month delay to fix hail damage.

The three-hour fueling process, carried out by remote control from the firing room 3.2 miles from launch pad 39A, should be complete around 1 p.m. NASA television coverage is scheduled to begin at 1:30 p.m. followed by a traditional dining room photo opportunity with the crew.

Wearing bright orange pressure suits, commander Rick Sturckow, pilot Lee Archambault, flight engineer Steve Swanson, Patrick Forrester, Danny Olivas, Jim Reilly and space station astronaut Clay Anderson are scheduled to depart crew quarters at 3:47 p.m. and head for the pad.

Sturckow will strap into the front left seat on Atlantis' flight deck with Archambault to his right. Swanson will sit behind and between the two pilots with Forrester to his immediate right. On the shuttle's lower deck, Olivas will strap in just in front of the ship's side hatch. Reilly and Anderson will take seats just behind and to the right of Olivas.

Launch is targeted for roughly the moment Earth's rotation carries the launch pad into the plane of the space station's orbit. As of this writing, the "in-plane" launch time is 7:38:04 p.m. That might be adjusted by a few seconds during a final hold at the T-minus nine-minute mark based on a final analysis of the station's orbit. Today's launch window will close at 7:43:04 p.m.

There are no technical problems at pad 39A and officials say the forecast remains unchanged, with a strong sea breeze expected to push afternoon thundershowers well inshore. Shuttle weather officers in Florida are predicting an 80 percent chance of acceptable conditions today and they upgraded the forecast for Saturday to 80 percent "go" as well.

"An upper level low off the east coast of Florida is creating a broad shield of mid clouds and rain showers along the Space Coast," the weather office said in its morning forecast. "This low and the associated showers should gradually move southwest allowing drier mid-level air to move in by launch time. At the surface, easterly winds will allow the sea breeze and its associated weather to push inland by early afternoon.

"Upper level winds are forecast to be from the east today, so anvils from any inland thunderstorms that develop should remain inland by launch time. By Saturday afternoon the upper level low is forecast to be over southern Florida, creating favorable conditions for launch; therefore, the 24-hour forecast probability of KSC weather prohibiting launch is decreased to 20%. Our primary concern for launch day is cumulus clouds."

The forecast from the Spaceflight Meteorology Group at the Johnson Space Center in Houston, which focuses on landing weather in case of an emergency that might force a quick return to Earth, calls for scattered clouds at 3,000, 10,000 and 25,000 feet with winds out of 100 degrees at 8 knots gusting to 12. The crosswind component at the shuttle's emergency runway is just 9 knots well within NASA's launch guidelines. Likewise, the weather at emergency landing sites in California, New Mexico, Spain and France is forecast "go."

Here is the remainder of today's countdown, along with the ascent timeline (in EDT):

EDT...........EVENT

12:42:00 PM...Begin 3-hour built-in hold (T-minus 3 hours)
12:42:00 PM...Closeout crew to white room
12:57:00 PM...Astronaut support personnel comm checks
01:30:00 PM...NASA TV coverage begins
01:45:00 PM...Astronaut photo opportunity
03:07:00 PM...Final crew weather briefing
03:17:00 PM...Astronauts don pressure suits
03:42:00 PM...Resume countdown (T-minus 3 hours)

03:47:00 PM...Crew departs O&C building
04:17:00 PM...Crew ingress
05:07:00 PM...Astronaut comm checks
05:22:00 PM...Hatch closure
06:07:00 PM...White room closeout

06:22:00 PM...Begin 10-minute built-in hold (T-minus 20m)
06:32:00 PM...NASA test director countdown briefing
06:32:00 PM...Resume countdown (T-minus 20m)

06:33:00 PM...Backup flight computer to OPS 1
06:37:00 PM...KSC area clear to launch

06:43:00 PM...Begin final built-in hold (T-minus 9m)
06:54:04 PM...NASA test director launch status verification
07:29:04 PM...Resume countdown (T-minus 9m)

07:30:34 PM...Orbiter access arm retraction
07:33:04 PM...Hydraulic power system (APU) start
07:33:09 PM...Terminate LO2 replenish
07:34:04 PM...Purge sequence 4 hydraulic test
07:34:04 PM...IMUs to inertial
07:34:09 PM...Aerosurface movement check
07:34:34 PM...Main engine steering test
07:35:09 PM...LO2 tank pressurization
07:35:29 PM...Fuel cells to internal reactants
07:35:34 PM...Clear caution-and-warning memory
07:36:04 PM...Crew closes visors
07:36:07 PM...LH2 tank pressurization
07:37:14 PM...SRB joint heater deactivation
07:37:33 PM...Shuttle computers take control of countdown
07:37:43 PM...SRB steering test
07:37:57 PM...Main engine start (T-6.6 seconds)

07:38:04 PM...SRB ignition (LAUNCH)

07:38:14 PM...Shuttle roll maneuver begins (alt: 796 feet)
07:38:22 PM...Roll maneuver ends (alt: 3,294 feet)
07:38:37 PM...Engine throttle down to 72 percent (alt: 11,405 feet)
07:38:47 PM...Maximum aerodynamic pressure (684 psf; alt: 20,122 feet)
07:38:53 PM...Main engine throttle up to 104.5% (alt: 25,601 feet)
07:40:09 PM...Booster separation (alt: 30.2 statute miles; velocity: 2,982 mph)
07:40:19 PM...Starts OMS rocket assist		
07:40:51 PM...Trans-Atlantic abort window opens (alt: 44.6 sm; vel: 3,533 mph)
07:42:01 PM...Return to launch site abort window closes	
07:43:21 PM...Abort to orbit window opens (alt: 67.5 sm; vel: 7,245 mph)
07:43:51 PM...Shuttle rolls to heads up orientation
07:44:21 PM...Press to MECO (alt: 67 sm; vel: 9,536 mph)
07:45:05 PM...Single-engine press to main engine cutoff
07:45:26 PM...3G limiting (alt: 64.3 sm; vel: 13,009 mph)
07:46:22 PM...Trans-Atlantic abort window closes
07:46:28 PM...Main engine cutoff command (alt: 64.7 sm; vel: 16,942 mph)
07:46:34 PM...Zero thrust