Posted: Sat, Mar 8, 2008, 3:51 PM ET (2051 GMT)

NASA started the countdown early Saturday morning for the launch of the space shuttle Endeavour on its mission to the International Space Station. The countdown clock started Saturday at 3 am EST (0800 GMT) in advance of a launch scheduled for 2:28 am EDT (0628 GMT) Tuesday, March 11. Shuttle managers said Saturday that they are not working any technical issues, after determining that a UHF radio that had failed some earlier tests did not need to be repaired or replaced. Forecasters are calling for a 90 percent chance of acceptable weather for the launch. During the 16-day STS-123 mission the shuttle will deliver the first component of the Japanese lab module Kibo as well as install the Canadian robotic arm system Dextre on the ISS.