Entry Flight Director Norm Knight expects a "very difficult weather day" for the shuttle Endeavour's planned landing Sunday night at the Kennedy Space Center, with low clouds and showers in the vicinity. Conditions are expected to be even worse Monday, but forecasters expect good conditions at Edwards Air Force Base, Calif., if a one-day wave off is required.

Despite the gloomy forecast, Knight said NASA would be staffing both landing sites Sunday night in an attempt to get Endeavour down on time on one coast or the other.

"We're really not going to know until we get down to the wire," he told reporters early Sunday. "I anticipate that about an hour prior to the deorbit burn we'll have a pretty good idea what the weather looks like and make a decision at that point."

Commander George Zamka and his crewmates have two landing opportunities at Kennedy on Sunday and two at Edwards on four successive orbits. Here are the latest times (in EST and mission elapsed time):

DATE/TIME.....DD...HH...MM...SS...EVENT

02/21
09:14:52 PM...13...17...00...45...Deorbit ignition (orbit 217)
10:20:37 PM...13...18...06...30...Landing at Kennedy Space Center
10:50:52 PM...13...18...36...45...Deorbit ignition (orbit 218)
11:55:50 PM...13...19...41...43...Landing at Kennedy Space Center

02/22
12:20:31 AM...13...20...06...24...Deorbit ignition (orbit 219)
01:25:41 AM...13...21...11...34...Landing at Edwards AFB
01:56:41 AM...13...21...42...34...Deorbit ignition (orbit 220)
03:00:56 AM...13...22...46...49...Landing at Edwards AFB

The latest forecast from the Spaceflight Meteorology Group at the Johnson Space Center in Houston calls for broken decks of clouds at 6,000, 12,000 and 25,000 feet and a chance of showers within 30 nautical miles of the runway. The forecast for Edwards calls for rain and broken decks at 3,000 and 6,000 feet.

"As far as the landing strategy goes, we're definitely going to try two KSC opportunities (Sunday)," Knight said. "We have Edwards called up, the site's ready to support. ... The forecast right now doesn't look good for Sunday, but we're going to be looking hard at the weather and if an opportunity exists for Edwards, we'd probably take a shot at it."

If the weather doesn't cooperate, Zamka and his crewmates will spend an extra day in space and try again on Monday. Endeavour has enough on-board supplies to remain in orbit until Tuesday at the latest, but NASA typically reserves the final landing opportunity to protect against technical problems.

"For end of mission plus one, which is Monday, for KSC the current forecast indicates the site is degrading," Knight said. "That system that's moving across the central U.S. encroaches Florida and it brings thunderstorms, rain, high crosswinds and (low) ceilings to the site. So if the forecast holds true for KSC, it doesn't look good for Monday.

"Edwards, on the other hand, looks pretty good," he said. "That low pressure that was pretty much centered on top of them on Sunday moves off to the east and it leaves some very nice weather for landing if we need it on end of mission plus one."

He said forecasters with the Spaceflight Meteorology Group were confident Edwards would be available Monday.

Even so, Sunday night "is going to be a very difficult weather day," Knight said. "We're going to play it by ear. Again, it's going to go down to the wire and if we don't land (Sunday), if we wave off, we'll look at our end-of-mission-plus-one weather and try to get on the ground (Monday)."

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