Shuttle program manager Wayne Hale said, "I find this extremely frustrating. We frankly have done everything that we know to do to improve that system."

Two of the four sensors on the liquid hydrogen tank (there are also four sensors on the liquid oxygen tank within the ET) failed during a preflight test. A third one had intermittent problems later. Even if these three sensors worked in the future, there is always the risk they would fail during launch—a risky proposition to say the least.

If left as is during ascent the faulty sensors could automatically shut off the three Space Shuttle Main Engines (SSMEs) if they mistakenly thought the hydrogen tank was empty (when they weren’t). Shutting off the main engines prematurely could force an emergency landing back at the Kennedy Space Center or one of its contingency (emergency) landing sites around the world.

In addition, the sensors could fail to detect a nearly empty hydrogen tank (when it was really empty) and leave the main engines on without fuel feeding the main engines. Such a condition could eventually destroy the engines, which would lead to a loss of the shuttle and its astronaut crew.

Based on fuel gauge sensors placed on the 1960s Apollo/Saturn spacecraft, the sensors have been causing intermittent problems since 2005.

Earlier NASA officials were thinking of flying with only two good sensors, but that scenario was dismissed as too dangerous. The NASA Astronaut Office, located at the NASA Johnson Space Center in Clear Lake City, Texas, has suggested that the rule be strengthened, rather than weakened, so launches occur only when all four sensors are working normally. Currently, at least three of the four sensors must be working properly before a launch can proceed, at least according to NASA procedures and rules.

Another meeting on Saturday, December 8, 2007, will decide this proposal and other suggestions put forth on this mission. NASA has until Wednesday, or Thursday at the very latest, in 2007 to launch space shuttle Atlantis to the space station. If unable to launch, the mission will be delayed until January 2008.

Hale concluded, “We don't want to get launch fever. Even though the Columbus [European Space Agency’s scientific laboratory module] 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 at least as safe as it ever is in this normally risky business." [Marcia Dunn, Associated Press “NASA delays shuttle launch until Sunday”]

{moscomment}

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