With no technical troubles being addressed and an improving weather forecast, the countdown continues at Kennedy Space Center for Thursday evening's planned launch of shuttle Endeavour to ferry a new crew to the international space station.

Liftoff remains targeted for 7:41 p.m. EST (0041 GMT Friday), the optimum time during a 10-minute window extending from 7:36 to 7:46 p.m. EST. The exact timing will be revised 90 minutes before launch based upon the latest radar tracking of the space station's orbit.

"The countdown is continuing in progress, work is right on the timeline and we are not tracking any significant issues," NASA test director Pete Nickolenko said today.

"Our vehicle and ground systems continue to perform very well. Everyone here is focused, we are ready and we are looking forward to the launch of Endeavour on Thursday evening."

At launch pad 39B, the cryogenic reactants have been loaded into storage tanks beneath Endeavour's payload bay for the ship's three electricity-generating fuel cells. Technicians have also closed the shuttle's two 60-foot long payload bay doors for flight and checked out the onboard avionics.

Work is underway today to finish prepping Endeavour's three liquid-fueled main engines and securing launch pad systems.

Tonight, the massive rotating service structure will be retracted away from the shuttle at about 11:30 p.m. EST as activities begin in earnest for filling the shuttle's bullet-shaped external fuel tank.

The three-hour process of loading a half-million gallons of liquid oxygen and liquid hydrogen into the external tank is due to begin at around 10:30 a.m. EST Thursday.

The weather forecast for launch time is calling for just a 30 percent chance of conditions prohibiting liftoff. The only concern involves thunderstorm cloud tops, called anvil clouds. If such clouds drift within 10 miles of the pad, the launch has to be delayed because of the possibility of rocket-triggered lightning striking the shuttle as it climbs into the sky.

"The single concern we have right now is the slight chance of thunderstorm anvils if we get storms in the Gulf of Mexico," said Ed Priselac, the shuttle weather officer. "The way it appears right now, it'll probably be too far west for the anvils to reach us, but we are keeping the 30 percent (of bad weather) that could occur."

At launch time the conditions are expected to include a few clouds at 3,000 feet, scattered clouds at 20,000 feet, seven miles visibility, southeasterly winds from 130 degrees at 12 gusting to 18 knots and a temperature of 74 degrees F.

Should the launch delay to Friday or Saturday for some reason, there is only a 10 percent chance of bad weather each day.

For a complete preview of this shuttle mission and the challenges facing the space station project, checkout our comprehensive eight-part report.