The STS-121 astronaut crew are due back on Earth at 9:14 a.m. EDT (1314 GMT) today at the Kennedy Space Center's  Runway 33. And everything looks just fine! “We’ve inspected the vehicle and we understand the [heat shield] more than we have on any other mission,” NASA’s reentry flight director Steve Stitch. “The vehicle is totally clean for reentry.”

Everything except the weather, that is. “Hopefully the weather will be great in Florida tomorrow,” pilot Mark Kelly. Mission controllers are hoping the skies would clear up despite forecasts of rain showers close to a 30-mile (48-kilometer) zone around the shuttle's landing site. The Discovery cannot land under rainy conditions because of possible damage to the thousands of black ceramic tiles that protect the orbiter’s belly from the searing heat of reentry.

If all goes well, Kelly and STS-121 commander Steven Lindsey will fire Discovery’s engines at about 8:07 a.m. EDT (1210 GMT) slowing it down for its hour-long drop toward Earth. But if weather conditions do interfere, NASA could could order the delay of the Discovery’s reentry for about 90 minutes. That's enough for the crew to make one last circle around Earth before firing Discovery’s engines for its second attempt at 9:43 a.m. EDT (1343 GMT) for a landing at 10:50 a.m. EDT (1450 GMT).

If Discovery fails to land as scheduled, flight controllers will activate the alternate landing sites at Edwards Air Force Base in California’s Mojave Desert and the Northrup Strip at White Sands Space Harbor in New Mexico. NASA said they expect to bring the shuttle home by Wednesday at the latest. Discovery’s planned landing activities will be broadcasted live on NASA TV beginning at 1:08 a.m. EDT (0508 GMT).