The crew of Atlantis pose for a picture at the launch pad on Wednesday. Photo: NASA-KSC

The U.S. space agency lifted its tattered security blanket on Wednesday and revealed the official time for Thursday's planned launch of space shuttle Atlantis: 5:12:51 p.m. EST -- just one second earlier than amateur satellite observers had predicted and posted on the internet.

NASA officials had refused to reveal the launch time until today for security reasons, but they have continued to openly release orbital data that has allowed amateur satellite observers to determine the launch time to within a few minutes and, in one case, to within one second of the actual time.

Space agency spokesman George Diller said the full 10-minute launch window opens at 5:07:52 p.m. (22:07:52 GMT) and closes at 5:17:50 p.m. (22:17:50 GMT). The preferred liftoff time is 5:12:51 p.m. EST (22:12:51 GMT). The mission is due to end with a landing at the Kenney Space Center on April 15, 2002 at 1:21 p.m. EDT (1721 GMT).

The news blackout imposed on the countdown has been partially lifted, too. But the astronauts' launch day activities -- including their traditionally broadcast pre-launch meal -- will take place largely in the dark.

The space agency does not plan say anything about the crew until after they arrive at the launch pad tomorrow afternoon. For that reason the space agency will curtail its usual countdown coverage on NASA Television. Its broadcast is not expected to start until the astronauts are ready to board the shuttle.

NASA was prepared to say that the three-hour process of loading 528,000 gallons of super-cold, explosive propellants into the shuttle's external fuel tank would begin around 8:15 a.m. EST.

The gantry-like rotating service structure is scheduled to be pulled back from around Atlantis Wednesday evening as technicians make final preparations for fueling.

Meanwhile, managers meeting this afternoon cleared the last remaining issue that was being addressed by engineers -- the Power Drive Units used on the shuttles to close the flapper doors on the belly of the orbiter after external tank jettison. NASA said the issue has been resolved and there is no concern with the hardware on Atlantis.

The launch weather officers are calling for a 60 percent chance of acceptable conditions due to showers and thunderstorms in the area.

The main goal of Atlantis' mission is to deliver the so-called S0 truss. It will form the central portion of the station's backbone, the eventual nine-piece truss supporting power and cooling systems for the expansion of the orbiting complex.

Atlantis' crew is led by commander Mike Bloomfield, with rookie pilot Stephen Frick, flight engineer Ellen Ochoa and spacewalkers Jerry Ross, Steve Smith, Lee Morin and Rex Walheim. Ross will be making a record-setting seventh space flight, the most of any astronaut in history.