The docking was delayed more than 10 minutes as the astronauts were waiting for the shuttle to emerge from the Earth's shadow for the docking unit to be illuminated by the sun.
The shuttle will deliver a seven-member crew, a space station segment and 5,800 pounds of cargo and supplies to the space outpost Friday for an 11-day assembly mission, designated STS-118.
During three scheduled spacewalks, the astronauts - Commander Scott Kelly, Pilot Charlie Hobaugh, mission specialists Tracy Caldwell, Barbara Morgan and Alvin Drew, and veteran astronauts Rick Mastracchio and Dafydd Williams of the Canadian Space Agency - will attach a truss segment, install a new gyroscope and an external spare parts platform to the station, and test a new power transfer system.
The new system enables electricity supply for docked shuttles from the ISS, which allows shuttles to remain in orbit longer. If the system works as expected, three days and a spacewalk will be added to the mission.
Teacher-turned-astronaut Barbara Morgan will also conduct some educational experiments. Morgan was the backup to Christa McAuliffe, the teacher-turned astronaut who was killed when the shuttle Challenger exploded on lift-off in 1986.
Shortly before Endeavour's liftoff, NASA experts discovered an abnormal leak rate in the cabin, which was rectified after an air pressure-relief valve was replaced with one from the Atlantis shuttle.
