The crew of the shuttle Atlantis made their final preparations for a return to Earth Wednesday after a 12-day resupply mission to the International Space Station.
NASA officials gave the green light for a return to Florida's Kennedy Space Center after an inspection on Monday of the shuttle's heat shields.
The crew has two windows for its landing, in the event bad weather scuppers the first one, set for 8:48 am (1248 GMT).
A NASA spokesman said weather forecasts were mixed for the area on Wednesday morning with a risk of rain hitting the coast.
If the weather forces a delay, the US space agency has planned for two more attempts on Thursday again at Kennedy, and a further back-up landing Friday at Edwards Air Force Base in California.
The shuttle uncoupled from the Space Station on Sunday after successfully delivering tons of supplies.
The trip back to Earth caps the 25-year career of one of NASA's iconic spacecrafts, which has logged some 115 million miles (185 million kilometers).
Only two more shuttle launches remain -- one in September for Discovery and the final blast off for Endeavour in November -- before the curtain falls on this era of human spaceflight.
The United States will then have to rely on Russia to take astronauts to the station aboard three-seater Soyuz spacecraft until a new fleet of commercial "space taxis" is operational.
Explore further: Atlantis to undock from ISS on final mission