The space shuttle is expected to dock with the ISS on March 17. Its seven crew, commanded by Lee Archambault and include Koichi Wakata, the first Japan Aerospace Exploration Agency's resident station crew member. He will replace NASA astronaut Sandra Magnus as part of the ISS' Expedition 18 crew.

The space shuttle Discovery takes off from launch pad 39A at the Kennedy Space Center in Cape Canaveral, Florida March 15, 2009. Mission STS-119 will carry a crew of seven astronauts to the International Space Station. [Xinhua]

Discovery's mission will feature three spacewalks to help install the S6 truss segment to the starboard, or right side of the station and the deployment of its solar arrays. The arrays will provide the electricity to fully power science experiments and support the station's expanded crew of six in May.

The truss is a high-tech girder structure made up of 11 segments. It provides the backbone for the station, supporting the US solar arrays, radiators and other equipment. To install the S6 truss segment, the station's robotic arm must extend its reach just about as far as it will go (about 57 feet or 17.4 meters), leaving it with very little room to maneuver. The S6 truss segment weighs a little more than 31,000 pounds or 14,061 kg. After S6 installation, the truss will be 335 feet (102 meters)long.

Each solar array wing has two 115-foot-long (35 meters) arrays, for a total wing span of 240 feet (73 meters), including the equipment that connects the two wings and allows them to twist as they track the sun. Altogether, the station's arrays can generate as much as 120 kilowatts of usable electricity -- enough to provide about forty-two 2,800-square-foot (260 square meters) homes with power. The addition of the S6 will nearly double the amount of power for station science -- from 15 kilowatts to 30 kilowatts.

The flight will also replace a failed unit for a system that converts urine to potable water.