NASA postpones Atlantis launch after fuel tank sensor problem

William Atkins
Thursday, 06 December 2007 20:37

Science - Space

NASA officials report on Thursday, December 7, 2007, that ground controllers were getting bad readings in two of the four hydrogen fuel gauge sensors from the external tank (ET).

These readings were discovered while NASA workers were filling the ET with liquid hydrogen in preparation for the launch. The sensors tell ground controllers the amount of hydrogen fuel left in the tanks so the shuttle’s three main engines—or Space Shuttle Main Engines (SSMEs)—shut down before the fuel is exhausted.

While filling the hydrogren tank, the two sensors did not sense any hydrogen.

Each SSME generates about 400,000 pounds of force (thrust) during liftoff of the space shuttle as it burns liquid hydrogen and liquid oxygen contained with the external tank (ET). Once the SSMEs turn off, the ET is jettisoned into the Atlantic Ocean.

When the troublesome sensors were discovered they prevented the launching of space shuttle Atlantis on its intended liftoff on Thursday, December 6, 2007. NASA flight rules require that at least three sensors be working nominally (normally) before a launch can take place.

The STS-122 mission can afford to wait until December 13 for its launch. Past this date, the space station cannot generate enough energy from sunlight to keep both it and the space shuttle running smoothly.

The launch is now scheduled for Friday, December 7 at 4:09 p.m. EST (2109 GMT). If the Friday launch is also scrubbed, then a third attempt will occur on Saturday, December 8 at 3:43 p.m. EST (2043 GMT).

More information about the STS-122 mission is found at the article “Scientific expansion of space station prime goal of STS-122.”

UPDATE: NASA officials announced that the problem with the fuel tank sensors was due to an open circuit, preventing the sensors to make any type of readings. The two sensors are working properly, which should provide a "GO" for Friday's launch of the space shuttle Atlantis and its STS-122 crew to the International Space Station for its important installation of the ESA Columbus scientific laboratory.