CAPECANAVERAL, Fla. - All that stands between six astronauts in space and a warm Florida landing are about 200 miles (321 kilometers) and the hint of rain.
NASA's STS-121astronaut crew and their space shuttle Discovery up in orbit are due back onEarth at 9:14 a.m. EDT (1314 GMT) today, when the spacecraft's newtires are expected to touchdown on Runway 33 here at the Kennedy SpaceCenter (KSC) landing facility.
"We've inspectedthe vehicle and we understand the [heat shield] more than we have on anyother mission," NASA's reentry flight director Steve Stitch told reportersSunday. "The vehicle is totally clean for reentry."
Discovery'santicipated landing comes after a busy 13-daymission that not only completes NASA's return to flight tests, but also increasedthe crew size of the International Space Station (ISS), readied the orbital labfor future construction. The mission marked NASA's second shuttle flight since the2003 Columbia accident.
"Hopefullythe weather will be great in Florida tomorrow," STS-121 pilot MarkKelly said Sunday.
All eyeswill be on the weatherthis morning to ensure that Discovery won't run into rain or other unfavorableconditions.
Mission controllers are hoping for clearskies, though forecasts predict that some rain showers may creep too close to a30-mile (48-kilometer) zone around Discovery's landing site. The space shuttlecannot land in rain because it could damage the thousands of black ceramictiles that protect the orbiter's belly from the searing heat of reentry.
"Myexperience that at the Kennedy Space Center, it's always a challenge," Stitchsaid of Florida's weather on Sunday. "I think we have a pretty good shot atgetting into Kennedy tomorrow."
If all goeswell, Kelly and STS-121 commander StevenLindsey will fire Discovery's engines at about 8:07 a.m. EDT (1210 GMT) toslow the spacecraft and begin its hour-long drop toward Earth. That maneuverwould deliver Discovery and its six-astronaut crew to a 9:14 a.m. EDT (1314GMT) landing after 202 orbits around Earth.
Should raincloud that initial attempt, Stitch and his flight control team could orderDiscovery's crew to hold off for about 90 minutes, though the forecasts callfor deteriorating weather conditions for a second pass.
That wouldcall for the crew to make one last circle around Earth before firing Discovery'sengines at 9:43 a.m. EDT (1343 GMT) for a landing at 10:50 a.m. EDT (1450 GMT),NASA said.
Stitch saidthat Discovery's crew will only attempt to land at KSC today since the site ishome to NASA's three-shuttle fleet.
A KSClanding would minimize the amount of time needed to once-more ready Discovery forflight, first to serve as a potential rescue ship - if needed - for NASA's STS-115shuttle mission to slated for an Aug. 28 launch, then as the primary vehicle forthe STS-116 mission to the ISS in December.
"We try toget into Kennedy because it helps us get ahead a little bit on our turnaround,"Stitch said. "That's where all our maintenance facilities are, so we like toland there if we can safely."
IfDiscovery does not land today, flight controllers will activate alternatelanding sites at Edwards Air Force Base in California's Mojave Desert andNorthrup Strip at New Mexico's White Sands Space Harbor with the aim ofbringing the shuttle home by Wednesday at the latest.
Stitch saidthat KSC will be the prime landing site for any Tuesday attempt, with Edwardsas a backup should the whether go foul. Northrup Strip is reserved only for theworst-case scenario of poor weather at both KSC and Edwards, he added.
Spaceshuttle landings at Edwards or Northrup Strip typically require about sevenextra days, and an additional $1 million to transport an orbiter back to itshangar at KSC.
NASAofficials said shuttle workers already have a challenging schedule of about 110days to ready Discovery for its STS-116 launch on Dec. 14, with only five extradays of padding in case of delays.
"The standardjoke is that I asked Steve Lindsey to make sure that he brought home my vehiclein good condition, and that he didn't prang it on the runway," NASA astronautMark Polansky, NASA's STS-116 mission commander, told SPACE.com before today'slanding attempt. "He promised to do the best he could."
Discovery'splanned landing activities will be broadcast live on NASATV beginning with crew wakeup at 1:08 a.m. EDT (0508 GMT). You are invitedto follow the progress of Discovery's STS-121 crew via SPACE.com's NASA TV feed, whichis available by click here.
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