Endeavour Countdown, Fueling to Resume Tuesday

NASA on Tuesday plans to finish up repairs to a leaking launch pad vent line and resume a countdown to the launch of space shuttle Endeavour, now set for 5:40 a.m. Wednesday.

Mission managers are confident a replaced quick disconnect valve and seals will prevent the vent line from leaking hydrogen gas during fueling of the external tank, a problem that scrubbed Saturday's launch attempt.

"The repair is work is going well," Steve Payne, NASA test director, said Monday afternoon at Kennedy Space Center. "Our teams have been working very hard over the last couple of days to get this piece of equipment fixed."

KSC workers on Monday reattached the vent line to Endeavour's external tank. The line routes excess gas to a flare stack to be burned off safely.

Leak checks and tests of electrical connections are scheduled to take place overnight, with final prelaunch closeouts not until 3 p.m.

Earlier, at 10:15 a.m., the shuttle will be revealed again on launch pad 39A when the pad's rotating service tower is opened to its launch position.

The countdown clock should start ticking at 1:15 p.m. at T minus 11 hours, a total that includes several built in pauses before liftoff.

The ultimate test of the repair's success will come with the loading of 500,000 gallons of liquid hydrogen and liquid oxygen, scheduled to begin at 8:15 p.m. and take about three hours.

NASA TV will provide live commentary of the fueling process, which you can watch here - just click on the NASA TV still image on the right side of the page.

If fueling is successful, the seven-person Endeavour crew led by mission commander Mark Polansky would climb into the shuttle's crew cabin at 2:20 a.m. Wednesday.

Wednesday is probably Endeavour's only chance to launch a 16-day mission to the International Space Station before July.

A NASA mission to send two satellites to the moon hopes to lift off on an Atlas V rocket as early as Thursday afternoon from Cape Canaveral Air Force Station.

The shuttle could consider launching Sunday, a plan that would require shortening the mission by a day and eliminating the last of five planned spacewalks.

After that, for a period of several weeks, the sun's angle to the space station won't provide enough power or dispel enough heat to support the shuttle mission.

The weather forecast Wednesday morning is good, with an 80 percent chance of favorable conditions for the launch at KSC and good conditions at U.S. and overseas emergency landing sites, according to Patrick Air Force Base's 45th Weather Squadron.

Click here for the official forecast.

The percentage chance of good weather is the same for Tuesday evening's external tank fueling operations.

The forecast for the Atlas V launch is a bit worse. From Thursday through Saturday, there is a 60 percent chance of good enough weather, with concern about afternoon thundershowers developing.

An Atlas V launch as early as Thursday is probably only possible if Endeavour's launch srubs before midnight Tuesday, because of another gas leak or some new problem. The first of three opportunities on Thursday, each 10 minutes apart, would be at 5:12 p.m.

On Friday, the first opportunity would be 6:41 p.m., followed by 6:51 p.m. and 7:01 p.m.

IMAGE NOTE: After rollback of the rotating service structure on launch pad 39A at Space Center on Friday, space shuttle Endeavour, with its external fuel tank and solid rocket boosters, were poised for launch. The RSS is scheduled to roll back again Tuesday morning in preparation for a Wednesday launch. Photo credit: NASA/Jim Grossmann