Entry flight director Wayne Hale, faced with deteriorating weather at the Kennedy Space Center, called off a second attempt to land the shuttle Endeavour today at the Kennedy Space Center and delayed re-entry at least 24 hours. NASA's Spaceflight Meteorology Group is predicting solidly "no-go" conditions Thursday, raising the prospect of a delay to at least Friday and possibly longer.

"Yeah, unfortunately we weren't able to get the weather we needed," astronaut Duane Carey radioed from mission control. "The latest forecast came in with 6,000-foot ceilings, which is not going to help us."

Commander James Wetherbee and his six crewmates then began backing out of their deorbit checklist and rigging the shuttle for at least one more day in space.

For returning space station astronauts Valery Korzun, Sergei Treschev and Peggy Whitson, the decision means a 183rd day in orbit and a frustrating delay for long-awaited reunions with families and friends.

While forecasters predicted the possibility of low clouds and showers earlier today, they appeared optimistic the weather would cooperate as the morning wore on and the expected clouds and rain failed to materialize.

But less than 45 minutes before Wetherbee and pilot Paul Lockhart planned to fire the shuttle's twin braking rockets to drop out of orbit, a deck of low, broken cloud cover began developing southwest of the Kennedy Space Center. At 2:20 p.m., Hale reluctantly waved off the shuttle's first landing opportunity.

At 2:41 p.m., when the braking rockets had been scheduled to fire, the shuttle runway was observed "no go" and forecast to be unacceptable an hour later, when Endeavour would have been making its final approach for a landing at 3:48 p.m.

A second deorbit opportunity was available one orbit later, at 4:19 p.m., but the clouds remained broken, obscuring visibility to the runway and violating NASA's conservative flight safety rules. At 3:55 p.m., Hale told Wetherbee to stand down.

NASA's mission management team met late today to assess the weather and various options for bringing Endeavour back to Earth. As expected, the forecast for Thursday remains bleak, but NASA will not rule out a possible landing until a meeting early Thursday morning to check the latest weather forecast.

As of this evening, the forecast calls for broken decks of clouds at 3,000, 6,000 and 25,000 feet, winds out of the west-southwest at 13 knots with peaks to 20 and showers and thundershowers in the vicinity.

"Obviously not looking real good," astronaut Duane Carey radioed from mission control. "However, we will give it an attempt, we're going to have weather briefings and give it the whole nine yards and look at it real good tomorrow before we give up. But quite realistically, we think tomorrow might be a real light day for you guys. ... We're looking at the weather to get considerably better by Friday."

"OK, Houston," commander James Wetherbee replied from Endeavour. "So understand we will possibly get a weather briefing in the morning before we do anything?"

"That's correct. We'd like to give you guys a realistic idea of what our chances are before we start marching down any paths tomorrow. But we're certainly not going to give up on tomorrow at this point."

"OK, thank you very much," Wetherbee said. "The Cape weather folks and Houston weather folks are about the best in the world, so they are generally pretty accurate."

"Yeah, Endeavour, and if it'll make you feel any better it turns out their calls today were spot on. The flight director here just wanted me to remind you it is looking fairly pessimistic for tomorrow."

Interestingly, plans to launch an unmanned Atlas 2 rocket this evening at 9:42 p.m. from the nearby Cape Canaveral Air Force Station remain on track, with forecasters predicting an 80 percent chance of acceptable weather. The goal of the flight, which is not subject to the same flight rules as a space shuttle, is to put a new NASA communications satellite in orbit. NASA television coverage begins at 8 p.m.

If the weather permits a Thursday landing for Endeavour's crew - and no one is optimistic at this point - the astronauts would have two opportunities on successive orbits:

EVENT......................EST

Deorbit rocket firing......01:49 p.m.
Landing....................02:54 p.m.

Deorbit rocket firing......03:26 p.m.
Landing....................04:30 p.m.

Endeavour has enough on-board supplies of fuel, water, air, food and electrical power to remain in orbut until Sunday afternoon in a worst-case scenario. But going into today, the shuttle only had enough propellant to make six deorbit attempts. Two of them were used up today, leaving enough fuel for just four more attempts over the next four days.

The forecast for Friday had been favorable, but the approach of the frontal system expected to sweep through central Florida on Thursday has slowed and rainy weather associated with the front may still be lingering in the area at landing time Friday.

NASA did not activate the shuttle's backup landing site at Edwards Air Force Base, Calif., for today's landing attempt and the Mojave Desert weather is predicted to be "no go" on Friday. If the weather on both coasts actually plays out that way, Endeavour's crew could be in orbit until this weekend.

So why not activate Edwards for a possible Thursday landing attempt? NASA program managers, sources say, are "hard over" to get Endeavour back to the Kennedy Space Center to avoid the ground processing delays - and the $1 million price tag - associated with landings in California.