A technician checks cables and wires that will be used in the Time Domain Reflectometry or TDR test.

On Launch Pad 39A, a technician checks cables and wires that will be used in the Time Domain Reflectometry, or TDR, test on engine cut-off sensors, or ECO, in space shuttle Atlantis' external tank. The test equipment -- blue monitor at left-- will be used to validate the circuit on the test wiring before hooking it up to the test box. The shuttle's planned launches on Dec. 6 and Dec. 9 were postponed because of false readings from the part of the ECO system that monitors the liquid hydrogen section of the tank. The liftoff date from NASA's Kennedy Space Center, Florida, is now targeted for Jan. 10, depending on the resolution of the problem in the fuel sensor system. Photo credit: NASA/Kim Shiflett