Space Shot Redux: Shuttle Discovery Set for Night Launch

NASA's space shuttle Discovery shines in the night during its first launch attempt on Dec. 7, 2006. CREDIT: NASA/George Shelton.

This story was updated at 12:58 p.m. EST.

CAPE CANAVERAL, Fla. - NASA is once more preparing to launch the shuttle Discovery and its seven-astronaut crew tonight after low clouds thwarted a Thursday evening liftoff.

NASA mission managers decided earlier today to continue preparations for today's planned space shot, though fueling operations for Discovery's external tank were been delayed from this morning to midday.

"We haven't started tanking yet, we'll be doing that in in the next few minutes, but we are going to make an attempt tonight," NASA spokesperson Bruce Buckingham said here at the Kennedy Space Center.

Launch is currently scheduled for 8:47:34 p.m. EST (0147:34 Dec. 10 GMT), though threatening weather could prevent liftoff. Weather permitting, the launch may be visible to viewers along the U.S. eastern seaboard [Map].

Led by commander Mark Polansky, the five-man, two-woman crew of STS-116 are tasked with delivering a new portside piece of the International Space Station (ISS) and rewiring the orbital laboratory's electrical grid.

Wrangling weather

Launch controllers decided to forgo a Friday attempt to loft Discovery after a bleak weather forecast of low clouds, rain showers and high crosswinds gave only a 1-in-10 chance of the shuttle lifting off.

"We have high winds on Friday that will not allow us to launch, so the decision has been made to perform a 48-hour turnaround and the next launch attempt will be on Saturday," NASA launch commentator Bruce Buckingham said after Thursday night's launch scrub.

Low clouds, showers and crosswinds are still predicted for tonight's launch attempt, but chances of favorable conditions are slightly better at 30 percent. The weather outlook continues to improve for Sunday, with a 40 percent favorable forecast.

If NASA decides to attempt launches both tonight and on Sunday, they will have to stand down on Monday to top off liquid oxygen in the shuttle's fuel cells, which evaporates if not used, NASA officials said. Under this scenario, launch attempts would resume again on Tuesday, Dec. 12.

NASA's standard approach is to try two launch attempts and then stand down for one to refuel either the liquid hydrogen or liquid oxygen, NASA spokesperson June Malone told SPACE.com.

"Sometimes you can try three in a row, but a lot of that has to do with the fuel cells and how much fuel we have on board," Malone said. "Also, ground crew rest is an issue, so you don't overtax the organization of the people."

Tuesday's weather forecast is the most favorable yet, with a 60 percent chance that conditions will permit the shuttle to lift off. After Tuesday, another cold front is expected to move into central Florida, possibly bringing with it thick cloud cover and showers that could once again hinder launch.

Space station bound

During their spaceflight, Polansky and his STS-116 crewmates will perform what NASA has oft described as the most challenging ISS construction mission to date.

Three spacewalks are scheduled for the 12-day spaceflight. One of them will be dedicated to the installation of a new piece of the station's portside truss. The other two are set aside for a complicated rewiring task of the space station's electrical grid that will involve a heavily choreographed power-down of its different sections, as well as the activation of the orbital laboratory's thermal cooling system.

"We're going to do the largest power down of the space station during this flight," NASA launch director Michael Leinbach told reporters in a prelaunch news briefing. He added that during the two space station rewiring spacewalks, NASA ground control will send an excess of 4,500 commands to the space station, compared to only about 800 commands on a normal day.

"That's the most we've ever done," he said.

Set to ride into space with Polansky today are: Discovery shuttle pilot William Oefelein and mission specialists Robert Curbeam, Nicholas Patrick, Joan Higginbotham, Sunita Williams and European Space Agency (ESA) astronaut Christer Fuglesang, Sweden's first spaceflyer to bound for orbit. With exceptions of Polansky and Curbeam, all five STS-116 astronauts are making their spaceflight debut today.

Williams will relieve European Space Agency astronaut, Thomas Reiter, who has been aboard the orbital laboratory since July. Reiter will ride back to Earth aboard Discovery in Williams' place.

Discovery's launch window currently runs from Dec. 7 to 17. Additional flight opportunities exist through Dec. 26, but only if mission managers approve the shuttle for flight over the year-end switch from 2006 to 2007.

NASA will broadcast Discovery's launch countdown and planned liftoff on NASA TV beginning at about 2:30 p.m. EST (0730 GMT). You are invited to follow the countdown's progress using SPACE.com's feed, which is available by clicking here.

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