Written by Derek Kessler on
Tuesday, 18 December 2007
After puzzling over the cause of repeated failures in the engine cut-off fuel sensors in the external fuel tank of the space shuttle Atlantis, NASA engineers have tracked the problem to an electrical connection that bridges the space between the tank and the shuttle. The problem was not discovered until the tank was filled with 500,000 gallons of super-chilled fuel this morning, leading engineers to hypothosize that thermal contractions are causing a disconnect that resulted in incorrect readings during pre-launch fueling attempts.
NASA tried twice earlier this month to launch Atlantis, but when the ECO sensors failed to register proper readings during fueling they chose to abort. The sensors measure the level of crygonic liquid hydrogen inside the tank and serve as emergency cut-off switches for the space shuttle's three main engines in the event of a sudden loss of fuel. If the engines were to fire without fuel it would result in catastrophic, if not fatal, damage to the shuttle.
The connector currently under scrutiny measures just 1.5 inches wide by 4 inches long. NASA engineers used tools similar to those used by telephone line repairmen when tracking down breaks in lines. They tested individual segments of the electrical conduits between the ECO sensors and the shuttle for conductivity and found the open circuit at the bridge between the tank and the shuttle.
Engineers will meet tomorrow to discuss the data they have collected and determine how best to correct the defective joint. They have around ten days to complete any repairs before prep work for the next launch window for Atlantis - January 10 - must begin. If they have to go inside the fuel tank to repair or modify any systems, the shuttle will have to stand down and return to the massive Vehicle Assembly Building for unmounting from the fuel tank. This would cause a large delay in the launch of Atlantis and result in a ripple of delays through the entire shuttle launch schedule.
After puzzling over the cause of repeated failures in the engine cut-off fuel sensors in the external fuel tank of the space shuttle Atlantis, NASA engineers have tracked the problem to an electrical connection that bridges the space between the tank and the shuttle. The problem was not discovered until the tank was filled with 500,000 gallons of super-chilled fuel this morning, leading engineers to hypothosize that thermal contractions are causing a disconnect that resulted in incorrect readings during pre-launch fueling attempts.
