Shuttle Discovery in orbit.
The space shuttle Discovery was forced to postpone landing in Florida Monday morning because of low clouds and poor visibility. NASA has set the first landing since the 2003 Columbia disaster for early Tuesday, at 5:07 a.m., ET.
The space agency also announced two alternative landing sites, should the Florida landing be deemed untenable. They are Edwards Air Force Base in California and White Sands Space Harbor in New Mexico. Officials say each site offers two chances for landing Tuesday.