The first major task will be the closing of Columbia's cargo bay doors at about 6:40 this evening, followed by the astronauts climbing into their launch and entry suits shortly before 8 p.m. The entry flight control team led by Flight Director John Shannon will receive updated weather forecasts throughout the late afternoon and evening before a "go-no go" decision for the deorbit burn is issued around 9 p.m.
There are two opportunities to land Tuesday night. The first begins with a deorbit burn on orbit 79 at 9:19 p.m. with a landing at 10:20 p.m. at Kennedy Space Center Florida. Columbia's orbital maneuvering engines will fire, slowing the 100-ton spacecraft by 250 feet per second, enough to drop it into the atmosphere halfway around the world. Columbia's unpowered glide through the atmosphere will heat a plasma layer around the heat-protecting tiles and creating a brilliant streak across the night sky for many ground observers. The Orbiter will cross Baja California and northwest Mexico, bisect Texas from west to east and pass over southern Louisiana on its way to Florida. Weather permitting, ground observers will be able to see the entry path about 100 miles on each side of the track. Columbia will cross Texas between 10 and 10:05 p.m. and a few minutes later will overfly Louisiana. Present plans call for a right turn to line up with runway 33, a southeast to northwest landing.
The second opportunity is one orbit later with an engine firing at 10:54 p.m. CDT and a landing at KSC at 11:55 p.m. The groundtrack is similar to the previous orbit's entry path.
Edwards Air Force Base will not be called up for support Tuesday night because of the good chances for landing at KSC.
Flight controllers will be keeping an eye on the weather in Florida. The primary threat to ending Columbia's mission at the Shuttle Landing Facility there is the possibility of thunderstorms within 30 miles, most likely to the west. Winds and cloud cover were not a concern leading up to the engine firing.
If Columbia lands at Kennedy Space Center it will be the 12th night landing in the Shuttle program's history. Five of those have been at Edwards Air Force Base in California and the rest have been at KSC. There have been 18 consecutive landings at KSC and 25 of the last 26 have been there. The last Edwards landing was in March 1996 with the STS-76 mission.
Additional opportunities for landing will be available on Wednesday at both landing sites if weather prevents Columbia from coming home tonight.
If Columbia lands this evening, the astronauts are due back at Ellington Field in Houston around mid-morning on Wednesday. An exact time for crew arrival will be firmed up after landing.
Columbia is orbiting the Earth every 90 minutes at an altitude of 179 statute miles with all systems operating normally.