The countdown has been smooth and there's a 90-percent chance of favorable weather for a night launch of shuttle Endeavour on the arduous, 16-day mission.
Endeavour and its seven-member crew will deliver the first installment of Japan's space station lab, Kibo. It will also deposit a Canadian two-armed robot designed to assist spacewalking astronauts at the orbiting complex. In all, five spacewalks are planned.
It's only the second scheduled night launch since the 2003 Columbia disaster. Early on, NASA preferred day launches to make it easier to gather images of an ascending shuttle and its external fuel tank.
