Washington  - Astronauts were steering a new solar panel into place using robotic arms on Wednesday ahead of a spacewalk to install the segment aboard the International Space Station (ISS).

The panel is part of a truss segment that will complete the backbone of the station and boost its energy capacity, allowing the crew size to double to six astronauts.

Astronauts used the station's robotic arm to lift the piece out of the space shuttle Discovery's cargo bay and were handing it off between both crafts' arms in a complex, six-hour process until it was in position ahead of Thursday's planned spacewalk.

Two Discovery spacewalkers are to install the panel with help from the station's robotic arm. The spacewalk is scheduled to begin at 1713 GMT Thursday.

Discovery docked Tuesday with the ISS, bringing the fourth and final solar panel that will enable the ISS crew to grow from three to six astronauts.

Three spacewalks are planned to install the solar panels and conduct other construction projects.

The mission delivered Japanese astronaut Koichi Wakata, who officially joined the permanent crew on the orbiting space station later Tuesday. He replaces US astronaut Sandra Magnus, who now joins the Discovery crew for the flight back to Earth.

The shuttle launched Sunday after weeks of delays to inspect and study the hydrogen fuel valves and a later leak in a fuel vent.