NASA Mulls Sunday Launch Plan for Shuttle Atlantis
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 engineers are meeting today determine whether to go forward with the planned Sunday launch of the space shuttle Atlantis despite a suspect fuel tank sensor system.

Top mission managers are meeting to decide whether to proceed with a Sunday afternoon launch for Atlantis with some stricter flight rules in place, or take more time to study an intermittent glitch with fuel gauge sensors at the bottom of the orbiter?s 15-story external tank.

?The proposal?s on the table,? NASA shuttle program manager Wayne Hale said late Friday. ?We?re very cognizant of the fact that you don?t like to accept risk at the launch site.?

Commanded by veteran shuttle flyer Stephen Frick, Atlantis? STS-122 crew is charged with delivering the European Space Agency?s Columbus laboratory to the International Space Station (ISS). A Sunday launch attempt, if approved, would lift off at about 3:21 p.m. EST (2021 GMT), with current forecasts predicting an 80 percent chance of good weather.

Mission managers called off a Thursday launch attempt after two of four engine cut-off sensors in the liquid hydrogen portion of the shuttle?s fuel tank failed a standard check. A third sensor also acted later as the fuel tank was drained. NASA flight rules call for three of the four sensors to be working properly in order to launch.

?We pretty much came to the conclusion that we are in an area that we have got a suspect system,? said Hale, adding that the sensors are based on 1960s, Apollo-era technology.

The sensors serve as a backup system to shut down Atlantis? three main engines before its propellant supply runs dry. Space shuttles consume more than 500,000 gallons (1.9 million liters) super-chilled liquid hydrogen and liquid oxygen propellant during launch.

NASA has wrangled with the fuel sensor glitches since the agency resumed shuttle flight in 2005 following the Columbia tragedy. After modifying the sensors and adding extra monitoring devices to ensure they work properly, NASA is still at a loss to explain their intermittent behavior.

?We?d like to have certainty,? Hale said. ?We would like to know root cause.?

For Sunday?s launch attempt, NASA is looking at tightening the sensor rule to require all four units to be working properly before attempting a liftoff. As an extra measure, they may also shorten the daily five-minute launch window to one single minute to conserve fuel in case the suspect sensors fail during flight.

?We don?t want to get launch fever,? Hale said. ?Even though the Columbus is out there loaded in the payload bay and everybody is anxious for us to launch that guy, we want to make sure that when we go launch, it is safe or as safe as it ever is in this normally risky business.?

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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