The seven astronauts woke up at 0738 GMT and at around 0908 GMT began reviewing their checklist for the rendezvous operations, in just the second flight since the 2003 Columbia tragedy, the Johnson Space Center said in Houston, Texas.

 Before docking to the ISS, Commander Steven Lindsey will flip the shuttle to allow the two ISS crewmembers to photograph Discovery's heat shield for any cracks that could endanger its return to Earth.

 The backflip will take place about 180 metres (600 feet) below the ISS before docking at 1452 GMT.

 The 360-degree maneuver was first conducted last year in the first flight since the Columbia accident, which was caused by debris that pierced the shuttle's heat shield during liftoff. The shuttle broke apart as it returned to Earth killing all seven on board.

 During pre-docking preparations, Discovery's crew reactivated a thruster that had been turned off after its heater failed before Tuesday's shuttle launch at Cape Canaveral, Florida. The jet allows Discovery to make small maneuvers as it approaches the ISS.

 The shuttle flew in a position that allowed sun rays to keep the small jet warm, NASA officials said.

 "That was effective to this point," said a Johnson Space Center mission commentator.

 The 115th shuttle mission is bringing supplies and equipment to the ISS and will drop off European Space Agency astronaut Thomas Reiter of Germany, who will join ISS commander Pavel Vinogradov of Russia and flight engineer Jeffrey Williams of the US.

 NASA officials said the Discovery crew could take refuge in the ISS and wait for a rescue mission if the shuttle is found to have suffered irreparable damage.

Agence France Presse