The crew aims for touchdown at NASA's Kennedy Space Center in Florida at 1248 GMT with no threat from the huge ash cloud from an erupting Icelandic volcano that has shut down air traffic over Europe, the US space agency said.

"Iceland's erupting volcano won't affect Discovery's landing Mon (Monday). Reentry course isn't near ash cloud," read a message from the Kennedy Space Center on micro-blogging service Twitter.

Over a 14-day mission, Discovery's seven-member crew delivered nearly eight tons of scientific equipment and other supplies intended to fortify the orbiting science laboratory for operations beyond NASA's final shuttle launch.

If scheduling holds, Discovery will lift off for the space station on September 16 for the final flight of the remaining three shuttles.

The United States will then rely on Russia for transportation of astronauts to the station until a new fleet of commercial space taxis is operating, a controversial policy that President Barack Obama re-enforced during a visit to the shuttle's Florida landing site last week.

Monday's forecast at Cape Canaveral includes overcast skies and a chance of showers, but shuttle commander Alan Poindexter and his crew have a backup landing opportunity in Florida later in the morning at 1423 GMT.

The astronauts took power conservation measures Sunday in case Mother Nature delays their return by a day.

"The weather situation is always fluid, and we will keep watching it," Mission Control in Houston told Discovery.

The shuttle is provisioned to remain in orbit until Wednesday if necessary, said Bryan Lunney, NASA's supervising flight director.

Monday's descent will follow a rare northwest to southeast course over the United States, leaving a glowing contrail visible to observers across several states should skies remain clear.

Discovery lifted off on April 5. The astronauts docked with the space station two days later, overcoming a communications antenna failure that crippled their rendezvous radar.

The linkup united 13 US, Russian and Japanese astronauts from the two craft for 10 days. Four were females, the most women in space at one time.

Over the course of three spacewalks, astronauts replaced a bulky external coolant tank. The ammonia reservoir circulates a coolant through outstretched radiators to disperse the heat generated by the station's internal electronics, including the life-support systems.

The science hardware delivered by Discovery included an Earth observations rack to hold cameras and spectral scanners for studies of the atmosphere, land forms, coastal areas as well as weather-induced crop damage. Another new experiment will measure changes in muscle and joint health of astronauts during their long exposures to weightlessness.

A new freezer will hold blood and other specimens collected for experiments.

During his April 15 visit to Kennedy, Obama made no mention of a shuttle program extension, disappointing some in Congress and those employed by the multi-billion-dollar space flight program.

At NASA, the looming reality that the United States will soon be unable to launch its own astronauts for the first time in three decades has begun to sink in.

"I'm sure that it's running through people's minds, but we are professionals and we are working really hard on the missions in front of us," said Richard Jones, lead NASA flight director for the Discovery mission.

"As we get closer, that will be forefront on people's minds."

Discovery's pilot Jim Dutton, who was making his first and possibly last space flight, echoed the sentiments.

"I think everyone feels a little bittersweet," Dutton said. "We love the shuttle, but we have to press on into the future."

earlier related report
Leonardo Returned to Discovery, Crew Prepares for Undocking
Space shuttle Discovery astronauts secured the Multi-Purpose Logistics Module Leonardo in the cargo bay Friday morning, wrapping up its delayed move from the International Space Station.

Leonardo had spent the crew's night at the end of the station's Canadarm2 just above Discovery's payload bay after balky bolts delayed its departure from the orbiting laboratory's Harmony module. Mission Specialists Stephanie Wilson and Naoko Yamazaki used the arm to cover the final feet of the first stage of Leonardo's trip home.

Mission Specialist Dorothy Metcalf-Lindenburger activated latches to secure Leonardo in the cargo bay at 3:15 a.m. EDT.

Next Wilson, Metcalf-Lindenburger and Discovery Pilot James P. Dutton Jr. teamed up to begin the late inspection of the shuttle's thermal protection system. Working in shifts with some help from Commander Alan G. Poindexter and Yamazaki, they used Discovery's robotic arm and the orbiter boom sensor system to look at reinforced carbon-carbon of the wing leading edges and the nose cone, as well as the heat-resistant tiles.

The inspection, scheduled for about seven hours, was finished almost three hours ahead of schedule. It was done while the shuttle was still docked so the images could be sent down by the station's high-data-rate system. Discovery's high-data-rate Ku band antenna is not working.

Discovery is scheduled to undock from the station a little before 9 a.m. on Saturday. The first landing opportunity at the Kennedy Space Center in Florida is at 8:48 a.m. on Monday.

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