NASA to Attempt Space Shuttle Launch on Sunday
In the late afternoon shadows, space shuttle Atlantis is still poised on the pad after its launch on mission STS-122 was postponed on Dec. 6, 2007.
Credit: NASA/George Shelton.

CAPE CANAVERAL, Fla. - NASA will attempt to launch the shuttle Atlantis and a European-built lab toward the International Space Station (ISS) on Sunday despite suspect sensors inside the orbiter?s orange external tank, top mission managers said today.

Atlantis and its STS-122 crew are set to rocket spaceward from their seaside launch pad at NASA?s Kennedy Space Center at about 3:20 p.m. EST (2020 GMT) with stricter flight rules in place to compensate for the spacecraft?s erratic fuel tank sensors.

?We had basically a unanimous decision to go forward,? NASA shuttle program manager Wayne Hale told reporters here in an afternoon briefing.

Commanded by veteran shuttle astronaut Stephen Frick, the spaceflight has been delayed since Thursday, when two of four engine cut-off (ECO) sensors inside the liquid hydrogen portion of Atlantis? 15-story external tank failed a standard countdown check. A third sensor also gave erroneous readings once the tank was drained of its liquid hydrogen and liquid oxygen propellant.

According to the agency?s flight rules, at least three of the four sensors, which serve as a backup system to ensure Atlantis? three main engines shut down before its fuel tank runs dry, must check out during tests before a shuttle can launch spaceward.

Mission managers decided today to impose even stricter guidelines, which call for all four of the sensors and a set of voltage meters that monitor their performance, to function properly before a launch attempt can go forward. They also curtailed Atlantis? five-minute launch window to just one minute in order to conserve fuel and ensure the shuttle?s fuel tank has enough propellant to reach orbit should the sensors fail during liftoff.

While some shuttle engineering groups did suggest possible troubleshooting methods, none voted to abandon Sunday?s launch attempt, mission managers said. Launch controllers plan to begin fueling Atlantis with the more than 500,000 gallons (1.9 million liters) of super-chilled liquid hydrogen and liquid oxygen propellant at about 5:55 a.m. EST (1055 GMT).

?We?ll fill up the tank and we?ll see what we get,? said LeRoy Cain, head of Atlantis? mission management team. ?If we meet our criteria, we?ll go fly and if we don?t, we?ll scrub and we?ll get a good tanking test and we?ll go forward from there.?

Intermittent glitches with the fuel sensors have plagued NASA since 2005, when the space agency resumed shuttle flights after the Columbia tragedy. Despite some design modifications and the new voltage meters, the sensors continue to behave erratically for reasons engineers have yet to understand.

?I would like to quit talking about ECO sensors,? Hale said, adding that he has directed engineering team to reevaluate the sensor system for signs of the glitch. ?We?re going to have to pursue it at an even more vigorous level.?

The agency also plans to upgrade equipment in space shuttle main engines and revisit protocols overseeing external tank propellant reserves to increase flight safety, Hale added.

Atlantis? seven-astronaut crew will deliver the European Space Agency?s Columbus laboratory to the ISS during a planned 11-day mission. Current forecasts predict an 80 percent chance of good weather at launch time, with low clouds and nearby rain showers posing the only concern.

?I can tell you that the launch team is extremely excited about having the opportunity to make a launch attempt tomorrow,? said Doug Lyons, NASA?s STS-122 shuttle launch director.

NASA must launch Atlantis by Thursday in order to fly the STS-122 mission to sun angles become unfavorable for docked operations. If the shuttle cannot launch Sunday, the next opportunity opens up on Monday at 2:55 p.m. EST (1955 GMT).

Atlantis? STS-122 mission will mark NASA?s fourth shuttle flight of 2007 and the second this year to deliver a new orbital room to the high-flying space station.

NASA is broadcasting Atlantis' STS-122 mission?s Sunday launch live on NASA TV beginning at 5:00 a.m. EST (1000 GMT). Click here for SPACE.com's shuttle mission coverage and NASA TV feed.

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