The landing was to have been at 9.46am (BST) and was initally delayed until 11.21am before it was finally put off until tomorrow - leaving the astronauts circling the earth for another day.
Earlier, the classic hit <i>Come On, Eileen</i> gave an unusual wake-up call to Discovery Commander Eileen Collins and the rest of her crew ahead of their return to Earth.
She thanked Mission Control for playing the Dexy's Midnight Runners anthem, which roused the seven-strong team eight hours before their scheduled landing.
The plunge back into the Earth's atmosphere has not been attempted since the Columbia disintegrated minutes from landing in early 2003, killing all seven astronauts on board.
Nasa insists it is not deeply concerned about the dangerous re-entry, even though Discovery's 13-day mission has been fraught with problems.
Tensions have run high ever since take-off, when a piece of insulating foam broke off the external fuel tank.
Unlike Columbia, which was doomed by a similar problem, Discovery narrowly missed being hit by the large chunk of foam.
However, the wing sensors and extensive video coverage clearly showed material hanging from the shuttle's underside, and Nasa, at pains to avoid another fatal catastrophe, ordered a space walk.
Astronaut Stephen Robinson made the first-ever orbital repair, gently pulling two strips of thermal tile "grout" away from the shuttle's heat shield.
The effort was a hailed a success, but that did not stop Nasa grounding its fleet until the problem is resolved.
The space agency is confident that all should go according to plan this morning as Discovery is guided toward the Kennedy Space Centre.
Commander Collins admitted that the Columbia was on her mind but said all thoughts would be focused solely on landing safely.
"We're all going to be very focused on the job at hand," she said. "It's time to come home and keep working on getting the shuttle better and ready to fly in the future."
Her co-pilot, James Kelly, said he did not have any concerns about re-entry and noted that never before have astronauts or flight controllers known so much about the condition of a returning shuttle.
"I guess you almost have to thank the Columbia crew," he said. "The sacrifices they made allowed us to get a lot smarter about it, get a lot of tools on board that we could use to look at the vehicle."
The Discovery's seven-man crew achieved its goals of refilling the station with much-needed supplies, carrying out repairs and unloading some two years worth of rubbish.
It left the international space station in the early hours of Saturday morning, photographing the outpost before making final preparations to head home.
In the final hours before landing the shuttle will slow down from around 17,500mph to 200mph.
It will take around 90 minutes to orbit the Earth as two engines are fired off to slow it down.
A Nasa spokesman said: "We are no more concerned than we ever would be about this landing. If anything we are more confident than ever given the thorough inspections to the heat shield."Reuse content