Space shuttle cleared for landing

CAPE CANAVERAL - Nasa cleared space shuttle Atlantis to return to Earth today, confident that unidentified objects spotted floating near the spaceship did not result from damage to its heat shield or other critical equipment.

Atlantis' homecoming from an 11-day construction mission at the International Space Station had been planned for yesterday, but was delayed a day so the crew could make an unprecedented third inspection of their ship.

Nasa was concerned the objects might be debris from something that had struck and damaged the shuttle. Since the 2003 Columbia disaster, the result of an impact by debris shed during launch, Nasa has been particularly careful to ensure the shuttles are in good shape before allowing them to return to Earth.

With its protective heat shield damaged by the debris, Columbia broke apart as it attempted to fly through the atmosphere for landing, killing all seven astronauts aboard.

Atlantis' touchdown at the Kennedy Space Centre in Florida was rescheduled for 6.21am local time Thursday (10.21pm NZT).

The extra inspection was prompted by video showing a mysterious dark object flying near the shuttle on Tuesday. A second item was later spotted by one of Atlantis' astronauts and photographed, then three more flew by the shuttle's windows on Wednesday.

Atlantis astronauts used a camera on the spacecraft's 15m robot arm to scan the heat shield for damage and then added a longer, sensor-laden extension boom for close-up study.

"It was a very thorough and intense investigation," shuttle programme manager Wayne Hale said. "Nothing is missing ... There is no damage."

Nasa conducted two test flights to refine its post-Columbia safety upgrades before Atlantis' mission. The shuttle's current trip is the first of at least 15 flights to complete the half-finished International Space Station by 2010, when the shuttles will be retired.

Atlantis' crew had installed a US$372 million ($571 million) solar power unit and truss structure at the space station before the first object was spotted.

Engineers believe the item is a spacer, a small piece of rigid plastic inadvertently left between pieces of ceramic tile on the shuttle's belly. Earlier inspections had shown plastic bits protruding from Atlantis' underside that were gone during Wednesday's inspections.

"This is most likely the culprit," Hale said. "We don't know for sure. We will probably never know."

Nasa believes the spacer could have worked its way out from vibrations during the routine in-flight check of the shuttle's hydraulic system.

"Little things come out in space," Hale said. "Over the years, we have chased many, many, many of these things and rarely have been able to pinpoint where they came from."

"Sorry we're being a litter bug here," he added.

The inspections came on a busy day in space as a Russian Soyuz spacecraft docked at the station bringing new crew members cosmonaut Mikhail Tyurin and US astronaut Michael Lopez-Alegria, and Anousheh Ansari, an Iranian-born American businesswoman and the world's fourth space tourist.

Soyuz could be seen in television shots creeping toward the space outpost 352km above Earth before docking with a gentle bump. Its crew opened the hatch and was met with big hugs and smiles from the current station residents, Pavel Vinogradov, Jeff Williams and Europe's Thomas Reiter.

"It was a smooth ride," said Ansari, the first woman space tourist, a wealthy entrepreneur believed to have paid the Russian space agency US$20 million for her trip.

Ansari will return home in a week with Vinogradov and Williams, who are wrapping up a six-month stay in space.

- REUTERS