BLOGGER NOTE: Countdown clocks are ticking backward at Kennedy Space Center as NASA gears uo for the planned 11:59 p.m. launch of shuttle Discovery and seven astronauts on an International Space Station outfittin mission. The stalled countdown resumed at T-Minus 11 hours and counting at 8:34 a.m.
NASA plans to retract a towering gantry from around shuttle Discovery early today as engineers prepare to present managers with solid rationale to go fly despite a suspect main propulsion system valve and what appears to be a faulty sensor.
Discovery and seven astronauts are tentatively scheduled to blast off from Kennedy Space Center's Launch Complex 39A at 11:59 p.m. The weather forecast for launch calls for a 60 percent chance of acceptable conditions.
Mission managers will meet at noon and be briefed by engineers who are developing secondary means to ensure the suspect liquid hydrogen fill-and-drain valve closes as intended if a presumably faulty sensor fails during external tank propellant-loading operations that would begin at 2:34 p.m. today.
But first, the Rotating Service Structure at launch pad 39A is scheduled to be retracted away from Discovery sometime between 5 a.m. and 7 a.m. today -- depending on when some work at the pad is finished.
Technicians are replacing Tyvek covers on the Forward Reaction Control System jets on the nose of the orbiter. A seven-day life will expire on Saturday and NASA wanted to complete the work to clear the way for what could be three launch attempts within 48 hours.
NASA aims to fly at 11:59 p.m. Friday but also would have opportunities to launch at 11:33 p.m. Saturday and 1:11 p.m. Sunday. After that, Discovery's mission would be postponed until mid-October to make way for a busy slate of Japanese and Russian missions to the international outpost in September and the first two weeks of October.
The service structure rollback will be the second this week. The gantry moved away from Discovery early Monday for an initial launch attempt early Tuesday that was scrubbed as a result of thunderstorms. A second launch try Wednesday was scrapped Tuesday afternoon when the valve problem cropped up near the end of external tank propellant-loading operations.
NASA managers on Thursday decided to pass up a launch opportunity at 12:22 a.m. today so engineers could make certain the critical valve will work as intended.
Tests on Wednesday showed the valve and a sensor designed to indicate when it is closed were both working properly. But managers said engineers needed more time to develop a strategy for handling a repeat if the same type of valve trouble that forced the launch scrub earlier this week cropped up yet again.
NASA plans to pick up Discovery's stalled launch countdown at 8:34 a.m.. The propellant-loading operation would be complete about 5:30 p.m.
The Discovery astronauts would suit up around 7:39 p.m. and depart crew quarters at the Kennedy Space Center Operations & Checkout Building and arrive at the 195-foot-level of the launch tower at 8:39 p.m.
The Close Out Crew would assist the astronauts as they crawled through the side hatch of the orbiter and strapped into their seats on the flight deck and middeck of the spaceship. The side hatch would be closed for flight at 9:54 p.m.
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