Discovery's belly tiles were imaged by cameras on the International Space Station (ISS) as it moved into dock.

Video footage caught foam peeling off Discovery's external tank on launch and Nasa wants to be sure there are no holes on the vehicle's underside.

Until the foam issue can be fixed, shuttles will not lift-off, Nasa says.

Tuesday's shedding foam is not thought to have hit Discovery, but two heatshield tiles do appear to be broken underneath the vehicle.

However, the first reports of the ISS investigation indicated there were no major areas of damage to contend with.

It was a suitcase-sized piece of foam that fell off the Columbia shuttle during its launch and punched a hole in the wing.

The damage did not present problems in orbit, but as the vehicle tried to re-enter Earth's atmosphere on 1 February 2003, super-heated gases entered the wing and tore the orbiter apart.

Flight suspension

Managers announced the suspension of all shuttle flights on Wednesday evening EDT after more than a day analysing video and still images of Discovery's flight to orbit.

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A 15cm (six-inch) piece of foam came away from the tank bipod area, where engineers carried out important modifications post-Columbia, and smaller pieces from the acreage foam just below it.

"You have to admit when you're wrong and we were wrong. We have to do some more work here," said shuttle programme manager Bill Parsons.

"Until we fix this, we're not ready to go fly again."

Shortly after 0600 EDT (1100 BST; 1000 GMT) on Thursday, Discovery performed a three-quarter-of-a-degree per second, 360-degree backflip as it closed in on the ISS.

Russian cosmonaut Sergei Krikalev and US astronaut John Phillips, who were positioned in the station's Zvezda service module, took digital images through 400mm and 800mm lenses.

The pictures should have provided resolution of up to 2.5cm (one inch), good enough to "read the serial numbers on the tiles," according to flight director Paul Hill.

Discovery's docking with the ISS was completed at 0718 EDT (1218 BST; 1118 GMT) above the South Pacific just west of Chile.

Robotic arm

On Wednesday morning EDT, Discovery crew members used the Orbiter Boom and Sensor System (OBSS) to inspect the shuttle's wing and nosecone leading-edge panels.

The OBSS is expected to further inspect "areas of interest" on Friday. These will likely include the two damaged shielding tiles. A rectangular tile near the nose landing-gear doors and a square "chine" tile further toward the aft (back) end of Discovery both appeared to be damaged.

Luckily, the shuttle was nearly out of the atmosphere when the foam broke free, so there was not enough air to accelerate the debris to dangerous speeds.

Nasa spent months changing the way the insulation was applied to the tank. It was thought only small pieces of debris would come off during Discovery's launch.

Mission controllers have since played back astonishing footage shot from Discovery's flight deck by astronaut Soichi Noguchi of the external tank tumbling to Earth after separation.

Discovery is due to touch down at Kennedy Space Center on 7 August at 0546 EDT (0946 GMT; 1046 BST).