A NASA spokeswoman said Wednesday that a measuring gauge came apart. The tool may have struck Discovery's external fuel tank as it fell. The mishap occurred Tuesday night during repair work.
Spokeswoman Candrea Thomas says the metal gauge is small. It was tethered properly to a worker, but came apart and some pieces fell.
This week, workers are replacing a shuttle seal to prevent another hydrogen gas leak. Leaking gas halted Discovery's countdown in November. Fuel tank cracks contributed to the lengthy delay.