While Discovery landed safely at the Edwards Air Force Base in California, its liftoff last month was not as smooth.

The first scheduled launch, on July 13, was postponed after a fuel gauge malfunctioned just two hours before liftoff in Cape Canaveral, Florida. The sensors protect the shuttle's main engines by triggering their shutdown in the event that fuel runs unexpectedly low.

NASA experts worked furiously for the next two weeks to figure out what was wrong with the fuel sensor, one of four. But the space agency decided to go ahead with the launch even if a fuel gauge malfunction reoccurred.

On the second launch attempt, on July 26, the fuel gauge mysteriously worked again, but another unpleasant surprise awaited NASA.

As Discovery took off, a large piece of insulating foam peeled off the external fuel tank - a chilling reminder of the cause of the Columbia disaster.

A piece of insulation foam had fallen from Columbia's external tank during liftoff, causing a gash that allowed superheated gases to penetrate the shuttle during its disastrous re-entry on February 1, 2003, killing seven astronauts.

Thankfully for Discovery's seven crew members, the foam did not strike the shuttle. But the incident prompted NASA to call off future launches.

The Atlantis shuttle is ready to launch as early as September 22 for another mission to the International Space Station, if the foam problem is believed fixed once and for all.

"We're going to try as hard as we can to get back in space this year," said NASA administrator Michael Griffin. "But we're not going to go until we're ready to go."

NASA took extraordinary precautions to ensure that Discovery would safely return to Earth.

While in orbit, docked on the space station, the shuttle was thoroughly inspected with cameras that allowed NASA experts to check it for damage.

The inspection led to an unprecedented spacewalk under the shuttle as US astronaut Stephen Robinson removed two protruding pieces of fiber that risked overheating during reentry.

NASA considered conducting another spacewalk when it discovered a tear in a thermal blanket on the shuttle skin just under Commander Eileen Collins' cockpit. But it eventually decided that a repair was unnecessary for a safe return.

In the end, nature delayed Discovery's return to Earth as bad weather forced it to stay in orbit an extra day. It finally landed in California instead of Cape Canaveral due to the weather.

The problems with foam, fuel sensors and protruding fibers should give NASA plenty of work after it finishes celebrating the successful Discovery mission.

"This flight was tremendous," said Bill Gerstenmaier, who has been tasked with leading the probe into the foam problem.

"We have got data now we have never had before," he said. "So we have a tremendous chance to learn from this exercise, so we can really take our knowledge base of how we apply foam to tank, how we ensure that it doesn't come off."

But some critics, including in Congress where NASA's budget is decided, are losing patience with the aging shuttle.

The shuttle fleet - which made its maiden voyage back in 1981 - is slated for retirement in 2010 and will be replaced by a more modern space vehicle.

"If the problems take a long time to be solved then we have to rethink everything," warned Representative Sherwhood Boehlert, a New York Republican who chairs the House Science Committee. "Maybe the shuttle will be no more."

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.

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