Shuttle cleared for landing after crisis over rudder part seen floating off into space

Nasa engineers said the loss of a metal clip yesterday posed no threat to the shuttle's landing after a two-week mission in which it delivered a new Japanese lab to the international space station.

The clip broke loose during a routine check of the flight systems needed for today's descent.

Goodbye: Discovery viewed from the International Space Station after undocking, and below, the ISS as seen from the shuttle

In this image provided by NASA backdropped by a blue and white part of Earth, the International Space Station is seen from Space Shuttle Discovery as the two spacecraft begin their relative separation on Wednesday June 11, 2008. Earlier the STS-124 and Expedition 17 crews concluded almost nine days of cooperative work onboard the shuttle and station.(AP Photo/NASA)

Space shuttles have returned to Earth in the past with clips missing from the rudder, which opens like a book to serve as a brake, slowing the craft down from its high re-entry velocity.

The V-shaped spring tabs, just 2.5in by 1in, protect that area from the intense heat of lift-off by providing a seamless barrier down the back edge of the rudder, or tail, panels.

Engineers suspect this clip, or tab, came loose during the vibrations of launch on May 31, and it wasn't until the brake panels were opened for checking yesterday that it floated away.

Ever since the Columbia tragedy five years ago, any shuttle part seen floating away in orbit is quickly and intensely studied by Nasa.

A protrusion in the same area at the tail, reported by the Discovery astronauts around the same time, was also found to be harmless.

The one that got away: Nasa's LeRoy Cain shows the size of the missing rudder clip

The weather today also looked favourable for landing at Florida's Kennedy Space Centre, with light winds and - on the second of two possible timeslots - slight showers.

'Right now it looks pretty good,' Mission Control in Houston said.

Discovery's crew of seven is returning after delivering and installing the new lab named Kibo, Japanese for hope, to the space station.

Besides delivering the lab, the shuttle also dropped off Gregory Chamitoff, the station's newest crew member. He traded places with Garrett Reisman, who lived on the station for three months. Chamitoff will stay for six months.

The 37ft lab, about the size of a bus, is the biggest room at the space station. Kibo also has a storage closet and a 33ft robotic arm.

A final section - a 'porch' for exterior experiments - and a second, smaller robotic arm will be delivered next year.

Discovery also delivered a pump that fixed the space station's malfunctioning toilet.