The US space shuttle Endeavour is closing in on the International Space Station and the astronauts will begin rendezvous operations in preparation for docking at 1:53 p.m., NASA announced.

About an hour before docking, Commander Scott Kelly and Pilot Charles Hobaugh will guide the shuttle through a backflip maneuver to allow the station Expedition 15 crew to collect digital images of its heat shield

Endeavour is delivering a new segment of the Integrated Truss Structure. The Starboard 5 (S5) truss will be attached to end of the Starboard 4 truss structure on Saturday. The installation and activation of the S5 sets the stage of the Starboard 6 segment and its solar arrays.

Meanwhile NASA engineers are trying to determine whether foam insulation that broke off the fuel tank damaged the ship.

Nine pieces of foam insulation broke off Endeavour's fuel tank during liftoff Wednesday evening, and three pieces appeared to strike the shuttle, said John Shannon, chairman of the mission management team. None is believed to have been big enough to cause critical damage, he added.

Astronauts aboard the space shuttle Endeavour spent their first full day in space on Thursday inspecting the craft for any damage sustained during take-off. They used a robotic arm to examine the outside of the shuttle.

"Whether it caused damage or not, we will find out in great detail" during Friday's rendezvous, Shannon said Thursday night. "The report initially was that you got a spray of debris from this area and, of course, that brings up images of Columbia and the spray you saw there, and I would tell you this was not even remotely of the same magnitude.

Mission Specialist Barbara has operated the robotic arm during the inspection. In a message sent on Thursday Morgan said she was having a great time and was looking forward to docking and seeing the Expedition 15 crew.

"When we first came to orbit it took a little getting used to," Morgan said. "I felt like I was upside down the whole time." She joked that when you put something aside, it floats off and you have no idea where it went. "We’ll have to do a treasure hunt later."

Morgan waited 22 years to reach space. She was the second teacher chosen to participate in the space programme and watched as the space shuttle Challenger exploded on takeoff in 1986. She trained as the substitute for Christa McAuliffe, the teacher who died along with six NASA astronauts.

While the Endeavour is docked to the ISS, Morgan will operate the shuttle's robotic arm during the installation of a solar panel. Morgan sees no distinction between her roles as astronaut and teacher.

"To me space exploration is all about open-ended, never-ending opportunities for our young people," she said. "That is what teaching is all about, too. There are no boundaries. The opportunities are there. You have just to wish to seize them."