Space shuttle Discovery is making final orbits of its final mission, as the craft's six-member crew makes last-minute preparations for landing at the Kennedy Space Center at 11:57 a.m. Eastern Standard Time.
Since Discovery's launch on Feb. 24, the orbiter's performance has been virtually flawless, mission managers say, given a dearth of technical glitches during the 13-day trip to the International Space Station (ISS).
"I would be hard-pressed to find a mission of any one of the orbiters that has been cleaner," said LeRoy Cain, who heads the shuttle mission management team, during a briefing Tuesday.
Starting with the launch and ascent, "the entire system has been as clean or cleaner, and the performance has been as good or better than any that we've every flown," he said, referring not only to the shuttle's performance on orbit, but also to the performance of the entire system – from ground support activities to the engines and external fuel tank, which has been modified since the Columbia accident in 2003 to reduce the risk that the orbiters would be damaged by ice and foam insulation that the tanks shed during ascent.
Tuesday evening, the mission management team cleared Discovery's thermal-protection system for reentry after a final inspection of the tiles and other heat-protected surfaces revealed no damage that would endanger the orbiter and crew.
The inspection is one of three that astronauts make of the thermal protection system during visits to the space station – a regime put in place after the Columbia tragedy.
During this mission, Discovery delivered the final US segment to the station, an Italian-made cargo container that engineers converted into a permanent storage module for the orbiting outpost. The crew also delivered a storage platform for the station's exterior, as well as Robonaut 2, the upper half of a humanoid robot that designers say will eventually become a silent seventh ISS crew member.
Discovery's crew got their wake-up call at 3:23 a.m. EST Wednesday and began final preparations for reentry and landing.
The orbiter is slated to swing tail-first and fire its orbital-maneuvering engines at 10:52 a.m. EST, roughly an hour before the scheduled touchdown. The deorbit burn, which will last about two minutes, slows the craft by about 180 miles an hour, enough to allow Earth's gravity to take firm hold on the orbiter and draw it home.
The craft will reenter Earth's atmosphere over the South Pacific, head north across Central America and up the east coast of the Yucatan Peninsula, then make its final pass over Florida's west coast en route to the Kennedy Space Center and, eventually, a berth at the Smithsonian Institution's Air and Space Museum in Washington.