The critical re-entry stage begins a little over one hour before landing which is planned for 4:46 am local time or approximately 18:46 AEST.
Weather forecasts were favorable for the planned touchdown at Kennedy Space Centre, but NASA said that if needed, the landing could be postponed by up to two hours.
Should the touchdown be scrubbed, Discovery has until Wednesday to land, either at the Florida seashore space centre or at an alternate landing strip in California or New Mexico.
Commander Eileen Collins and Pilot James Kelly both said they had no worries about the scheduled pre-dawn landing in Florida, and that Discovery was in great shape.
They tested the systems that will be used for re-entry into the Earth’s atmosphere, as their five crewmates packed up in preparation for the critical phase of the mission.
Managers at NASA hailed what they said was the complete success of the first space shuttle flight since the February 1, 2003 Columbia disaster.
Despite the optimism, Discovery will be grounded with the rest of the fleet once it returns to Earth because the flight demonstrated the US space agency had failed to fix the problem that doomed Columbia.
The mission was largely designed to test changes made to the shuttle since the Columbia disaster, including improvements meant to prevent insulation foam from breaking off upon launch.
Crew members said their thoughts would be with the seven astronauts who lost their lives when Columbia burst into flames just minutes ahead of planned landing.
But Commander Collins stressed that the Discovery crew will concentrate on getting home safely.
When they gave the green light for Discovery’s landing, NASA managers said a tear on the cockpit’s thermal blanket should not compromise the shuttle’s safety as it re-enters the atmosphere.
They also said the orbiter suffered no significant damage when foam insulation fell off its external fuel tank as the shuttle blasted into orbit on July 26.
The same problem doomed Columbia, as the debris hit the orbiter’s left wing, causing a crack that eventually allowed superheated gases to penetrate the structure upon re-entry into the atmosphere.