HOUSTON, July 28: The shuttle Discovery astronauts boarded the International Space Station high above the Earth on Thursday, the first shuttle crew to visit since the Columbia disaster and now because of new safety concerns, possibly the last for some time.

At Mission Control in Houston, Nasa said it is confident it can fix problems with the space shuttle’s fuel tank, which shed four large pieces of insulating foam during launch from the Kennedy Space Center in Florida on Tuesday, a recurrence of a dangerous flaw the US space agency thought it had fixed.

“No one is folding their tents. No one is down in the mouth. All I see from the team is extreme determination to go and fix that problem,” John Shannon, the space shuttle flight operations manager, said at a news conference.

“I think we can get the tank in good shape to fly again.” He added that so far the ship appears in good shape for landing on Aug. 7.

As Nasa managers grappled with the foam problem, Discovery and the space station, each weighing more than 100 tons, linked up with barely a bump when commander Eileen Collins slowly guided the shuttle in.

Following US Navy tradition, astronaut John Phillips on the space station rang a ship’s bell to welcome the shuttle crew aboard.

“Discovery arriving,” Phillips called out, as Collins, pilot Jim Kelly, flight engineer Steve Robinson, Japan’s Soichi Noguchi and astronauts Andy Thomas, Charles Camarda and Wendy Lawrence floated into the station’s Destiny laboratory module.

This flight was supposed to have been a triumphant return of the shuttle to the space station for the first time since November 2002, but Nasa’s surprise decision to ground the rest of the aging orbiter fleet took the glow off.

The US space agency said the flying debris captured on video at Discovery’s launch was too similar to what brought down shuttle Columbia on Feb. 1, 2003, and showed that the debris problem was not fixed after 2 1/2 years of work and more than $1 billion in safety improvements.

Video of the launch shows the foam floating harmlessly away from the shuttle although engineers were still reviewing images and sensor data taken during liftoff, Shannon said.

Nasa officials said they do not know when shuttles will fly again. Atlantis was scheduled to launch in September.

A 1.67 pound piece of insulating foam from Columbia’s external fuel tank broke loose at launch on Jan. 16, 2003, and struck the left wing, causing a hole in the heat shield that doomed the shuttle during re-entry 16 days later.

As Columbia glided toward Florida, superheated gases from the earth’s atmosphere entered the breach and broke the ship apart over Texas, killing its seven astronauts.

Engineers have determined that the biggest piece of foam that fell from Discovery’s tank weighed 0.9 pounds (0.48 kg). The foam is part of a ramp that runs alongside the tank to protect cables, electrical connections and pressure hoses.

Nasa redesigned parts of the tank after the Columbia accident, but did not make any changes to the ramp.

“We didn’t think the ramp was a problem,” Shannon said. “Obviously we were wrong.”

In space, the seven astronauts on Discovery, which flew its first mission in 1984, went about their business with nary a word about problems on Earth.

In a manoeuvre planned before launch, Collins steered Discovery into a slow back flip 600 feet below the space station while station crew members Sergei Krikalev and Phillips snapped pictures of Discovery’s damaged tiles.

The photos will be used to determine if Nasa is correct in thinking the shuttle is OK to return home. More inspections were scheduled for Friday.

Discovery is scheduled to stay a week at the station, during which time its crew will hand over 15 tons of supplies ranging from food to light bulbs to new laptop computers and pick up 13 tons of junk to carry back to earth.—Reuters