Shuttle engineers are gearing up today for the start of the shuttle Atlantis' countdown to blastoff Friday on a mission to deliver a new set of solar arrays to the international space station. With forecasters predicting a 70 percent chance of good weather, the countdown is scheduled to start at 9 p.m. this evening, targeting a launch attempt at 7:38:02 p.m. Friday.

"All our systems right now are in great shape, we're tracking no constraints that are show stoppers," said NASA Test Director Steve Payne. "The teams are ready and everybody's eager to launch. We're looking forward to a safe and successful assembly mission."


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Shuttle weather officer Kathy Winters said today she expects a 70 percent chance of acceptable weather Friday, Saturday and Sunday, with the only concern being possible showers or thunderstorms in the area. The weather at emergency runways in California, Spain and France also is expected to be good.

"We do expect to see some afternoon thunderstorms in the area on launch day but by launch time, all that weather should move inland with the sea breeze," Winters said. "So for the coast here, the weather looks reasonably promising for launch."

Atlantis originally was scheduled for liftoff on mission STS-117 on March 15, but the flight was put on hold after a freak hail storm Feb. 26 that caused extensive damage to the protective insulation on the shuttle's external fuel tank. Repairing the tank was a major technical challenge, but NASA managers say they are satisfied the repairs will stand up to the thermal and aerodynamic rigors of launch.

"We are relieved that we're finally there," Payne said. "It's been a long waiting period and as you probably know, whenever you're ready to go and you have to stop and wait for a few months, it's a disappointment. But once you spool back up and everything's ready, and it looks like everything's falling into place nicely, the team's really excited and we're ready to get off the ground."

A detailed countdown timeline is posted here. Here are highlights (in EDT and hours and minutes to launch):

HH...MM...SS....EDT..........EVENT

Tue  06/05/07

...............08:30:00 PM...Call to stations
70...32...00...09:00:00 PM...Countdown begins

Wed  06/06/07

54...32...00...01:00:00 PM...Begin 4-hour hold
50...32...00...05:00:00 PM...Resume countdown
49...02...00...06:30:00 PM...Fuel cell oxygen loading begins
46...32...00...09:00:00 PM...Fuel cell oxygen load complete
46...32...00...09:00:00 PM...Fuel cell hydrogen loading begins
44...02...00...11:30:00 PM...Fuel cell hydrogen loading complete

Thu  06/07/07

43...02...00...12:30:00 AM...Pad open; ingress white room
42...32...00...01:00:00 AM...Begin 4-hour hold
38...32...00...05:00:00 AM...Countdown resumes
38...32...00...05:00:00 AM...Main engine preps
36...02...00...07:30:00 AM...Tile inspection
30...32...00...01:00:00 PM...Begin 13-hour 42-minute hold
27...42...00...03:50:00 PM...JSC flight control team on station
26...32...00...05:00:00 PM...Communications system activation
26...02...00...05:30:00 PM...Crew module voice checks
21...02...00...10:30:00 PM...Rotating gantry moves to park position

Fri  06/08/07

16...50...00...02:42:00 AM...Resume countdown
16...30...00...03:02:00 AM...Pad clear of non-essential personnel
15...40...00...03:52:00 AM...Fuel cell activation
11...50...00...07:42:00 AM...Begin 2-hour hold (T-minus 6 hours)
11...05...00...08:27:00 AM...Mission management team tanking meeting
09...50...00...09:42:00 AM...Resume countdown (T-minus 6 hours)
09...50...00...09:42:00 AM...Liquid oxygen, liquid hydrogen transfer line chilldown
09...40...00...09:52:00 AM...Main propulsion system chill down
09...40...00...09:52:00 AM...LH2 slow fill
09...10...00...10:22:00 AM...LOX slow fill
09...05...00...10:27:00 AM...Hydrogen ECO sensors go wet
09...00...00...10:32:00 AM...LOX fast fill
08...50...00...10:42:00 AM...LH2 fast fill
07...35...00...11:57:00 AM...LH2 topping
06...55...00...12:37:00 PM...LH2 replenish
06...50...00...12:42:00 PM...LOX replenish
06...50...00...12:42:00 PM...Begin 3-hour hold (T-minus 3 hours)
06...50...00...12:42:00 PM...Closeout crew to white room
06...50...00...12:42:00 PM...External tank in stable replenish mode
06...02...00...01:30:00 PM...NASA TV coverage/commentary begins
05...47...00...01:45:00 PM...Crew photo opportunity on NASA TV
03...50...00...03:42:00 PM...Resume countdown (T-minus 3 hours)
03...45...00...03:47:00 PM...Crew departs O&C building
03...15...00...04:17:00 PM...Crew begins boarding Atlantis
02...25...00...05:07:00 PM...Astronaut comm checks
02...10...00...05:22:00 PM...Hatch closure
01...10...00...06:22:00 PM...Begin 10-minute hold (T-minus 20m)
01...00...00...06:32:00 PM...NASA test director countdown briefing
01...00...00...06:32:00 PM...Resume countdown (T-minus 20m)
00...05...00...07:32:00 PM...Launch window opens
00...02...55...07:35:07 PM...LO2 tank pressurization
00...02...35...07:35:27 PM...Fuel cells to internal reactants
00...01...57...07:36:05 PM...LH2 tank pressurization
00...00...07...07:37:55 PM...Main engine start (T-6.6 seconds)
00...00...00...07:38:02 PM...SRB ignition (LAUNCH)