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Discovery Heads Back To Earth

Space shuttle Discovery unhitched Saturday from the orbital outpost its astronauts called home for nine days, readying itself for the long, dangerous journey back to Earth.

There were hugs and handshakes as Discovery's astronauts said their goodbyes to the astronaut and cosmonaut who live aboard the international space station. The crews then closed the hatches between the ship and orbiting lab.

CBS News Correspondent Lee Cowan reports that, with future flights grounded indefinitely, it could be a while before the space station gets another visit — and the clock is ticking.

The station itself is only half finished, and there are promises that have to be kept to the agency's international partners before the shuttle are retired five years from now.

Astronaut Scott Parazynski — who is scheduled to install a new truss on the space station next year — told Cowan that the project is crucial to NASA's larger mission.

"We're also going to be using the laboratory of the space station to develop the technologies that will take us back to the moon, not just to visit, but to stay," Parazynski said.

Before the spacecraft left for good, Discovery's astronauts planned to fly a farewell loop around the station, then fire the shuttle's jets to reposition the spacecraft and prepare for the voyage home.

Discovery's astronauts are scheduled to complete their 13-day mission Monday when the first shuttle to return to space since the 2003 Columbia tragedy is set to land in Florida.

"We are so happy to have spent the time up here," Discovery's commander Eileen Collins told the station's two crew members, who have been there since April. "These are memories that we will have forever."

Discovery's seven astronauts spent a day longer than originally planned aboard the station to bring over additional supplies, such as paper, laptop computers and surplus food and batteries. Discovery is the first shuttle to visit the station since 2002.

Meanwhile, a former astronaut spoke highly of the Discovery crew, while criticizing the U.S. space program. CBS News Correspondent Larry Miller reports that Apollo astronaut Buzz Aldrin says the Discovery shuttle crew knows its craft inside and out and he does not think they will be nervous on the return journey to earth.

Miller adds that in a recent interview with the BBC, Aldrin was critical of the shuttle program. He said it's now time to change the way people travel into space. The second man to walk on the moon refused to say whether this should be the last shuttle mission, but said it's time for the United States to make a hard decision on how to go forward.

NASA is investigating whether repairs to a small crack in the foam on Discovery's fuel tank may have caused a 1-pound section of the insulation to break off during liftoff, officials said late Friday.

The shallow crack, just six-tenths of an inch long and two-tenths of an inch wide, was sanded away at the Louisiana manufacturing plant before the tank was shipped to Cape Canaveral, Fla. No new foam was applied to the spot.

It's a common repair procedure, NASA officials said.

What's intriguing, officials said, is that the repair was made to the approximate area where the big chunk of foam came loose during Discovery's launch on July 26. They cautioned, however, that there is no evidence yet that the repair contributed to the foam loss.

The external fuel tank was redesigned following the 2003 Columbia tragedy, but no improvements were made to the area where the foam came loose. Lockheed Martin Corp. built the tank at its Michoud Assembly Facility in New Orleans.

Unlike with Columbia, which was smacked in the wing by foam that broke off during liftoff, this large chunk of foam missed Discovery. Nonetheless, NASA has suspended all future space shuttle flights until the problem is resolved.

Among the many theories being investigated, besides the crack: whether a mistake was made in the manual spraying of the foam, whether the new environmentally friendlier foam that was used in that area was defective, whether too many people handled the foam and tank, and whether the foam was damaged during the tank's shipment to Florida.

Space station program manager Bill Gerstenmaier, who is heading up the investigation, said he expects to get his first technical briefing on the matter Tuesday.

The tank lost four or so pieces of foam that were bigger than NASA wanted to come off.

"The amazing thing is, well, not amazing, but the good thing is almost all of the tank changes worked. Some didn't," NASA Administrator Michael Griffin said earlier Friday. "So what's the difference between the ones that did and the ones that didn't?"

The earliest that the next shuttle could launch is Sept. 22, but that's only "if next week, the guys have a eureka moment on the foam and spot why this big chunk came off," Griffin said.

Many speculate it could be next year before another shuttle flies, if the cause proves elusive.

The shuttle is scheduled to land back at Cape Canaveral, Fla., before dawn on Monday.

Friday's activity came a day after NASA gave the all-clear for Discovery to return to Earth, concluding that there was no need to send the astronauts out on another spacewalk to repair a torn thermal blanket near a cockpit window.

The damaged 20-inch-long, 4-inch-wide insulation blanket just below commander Eileen Collins' cockpit window was the only remaining question mark about the shuttle's condition prior to re-entry and landing early Monday morning, CBS News Space Consultant Bill Harwood reports.

Mission managers could not guarantee that a piece of the blanket wouldn't rip and slam into the spacecraft during re-entry, but said the chances were slim.

"We have assessed the risk to the very best of our engineering knowledge and we believe that it is remote, small, whatever adjective you want to put with that," deputy shuttle program manager Wayne Hale said. "And the remedy that might be called for to try to make this better would be worse."

Had blanket repairs been necessary, the work would have come during a fourth spacewalk. It would have been the second time during Discovery's 13-day mission that astronauts were called on to repair their spacecraft's thermal protection shield.

During unprecedented repairs earlier this week, Robinson went beneath Discovery's belly to remove two protruding strips of tile filler that engineers thought could lead to dangerous overheating during the trip home.

CBS News Correspondent Peter King reports that NASA had worried some of that lightweight material could shred and damage the orbiter. A different kind of debris hit Columbia two-and-a-half years ago, causing the spacecraft to break apart over Texas as it headed to Florida.

Columbia was doomed by a 1.67-pound piece of insulating foam that fell from its external tank during launch. The foam pierced a hole in the spacecraft's left wing and as it re-entered the Earth's atmosphere, searing gases melted the wing from the inside out causing the ship to disintegrate. The seven astronauts on board were killed.

Discovery is the first shuttle to return to orbit since the tragedy.