NASA Targets Saturday for Space Shuttle Launch

CAPE CANAVERAL, Fla. - NASA is now targeting a weekend launch for the space shuttle Atlantis and a new European lab after a fuel tank sensor glitch prevented a Thursday liftoff, mission managers said.

Atlantis is slated to launch Europe?s Columbus laboratory and a seven-astronaut crew no earlier than Saturday at 3:43 p.m. EST (2043 GMT), but only if mission managers decide tomorrow that the risk of flying without two of four vital fuel tank sensors is acceptable, said LeRoy Cain, head of Atlantis? STS-122 mission management team.

?We?ve done everything we can to maintain the possibility of launching on Saturday,? Cain told reporters in an evening briefing here at NASA?s Kennedy Space Center.

NASA called off Atlantis? planned 4:31 p.m. EST (2131 GMT) launch toward the International Space Station (ISS) early this morning, when two of the four Engine Cut-Off (ECO) sensors in the liquid hydrogen portion of the shuttle?s 15-story fuel tank failed a standard countdown test.

NASA flight rules call for three of the four fuel gauge sensors, which serve as a backup system to shut down a shuttle?s three main engines before its hydrogen supplies run dry, to be working properly in order to launch. Similar sensor issues have afflicted recent NASA shuttle launches, most recently in September 2006.

U.S. space shuttles consume more than 500,000 gallons (1.9 million liters) of cryogenic liquid hydrogen and liquid oxygen propellant to make the 8.5-minute launch into orbit.

Cain said late Thursday that a set of new instruments which watches over the ECO sensors may offer extra data that could allow flight controllers to launch Atlantis and its STS-122 crew Saturday if two of four sensors performing as designed. Engineers currently suspect an open circuit somewhere between an electronics box inside Atlantis and its fuel tank, and not the sensors themselves, is the source of the glitch.

?It was slightly different than things we?ve seen before,? Cain said of the glitch, adding that analysis teams simply ran out of time today. ?What all that means to us is, it?s still a little bit new and we want to sleep on it.?

Atlantis? fuel tank sensor glitch marred what appeared to be an otherwise flawless countdown, with the weather forecast predicting clear skies and a 90 percent chance of favorable launch conditions.

?The countdown had been going very smooth,? said NASA shuttle launch director Doug Lyons. ?The weather was perfect. Everything was lining up for a perfect launch on our first attempt.?

Atlantis? launch scrub ended NASA?s 2007 streak of on-time shuttle launches that stretched across three missions that lifted off on the first try in June, August and October, respectively.

Commanded by veteran shuttle flyer Stephen Frick, Atlantis? seven-astronaut crew will deliver the European Space Agency?s (ESA) Columbus laboratory to the ISS. The delay disappointed hundreds of ESA officials who have spent more than two decades building Europe?s first permanent human spaceflight laboratory to fly.

?In the big picture, it?s not a setback,? said Alan Thirkettle, the ESA?s space station program manager, of the delay. ?[But] it is disappointing because we have 750 people over here.?

The visitors are ESA Columbus program officials and supporters who have toiled over the module?s 20-year history to see it reach the ISS. They will return to Europe aboard a charter jet late Friday, whether or not Atlantis makes a new launch attempt, Thirkettle said.

NASA must launch Atlantis to the space station by Dec. 13 or else stand down to Jan. 2, when the angles between the orbital laboratory?s expansive solar arrays and the sun are more favorable to support a visiting shuttle crew.

Atlantis? STS-122 mission will mark NASA?s fourth space shuttle flight to the ISS this year, and the second to haul a new orbital room to the high-flying orbital laboratory. If Atlantis cannot launch on Saturday, a third attempt could be made as early as Sunday at 3:20 p.m. EST (2020 GMT), with current weather forecasts predicting a 70 percent chance of acceptable flight conditions.

NASA will broadcast Atlantis' STS-122 mission live on NASA TV. Click here for SPACE.com's shuttle mission coverage and NASA TV feed.

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