First, a grease gun inside her tool bag leaked, coating everything inside with a film of lubricant. While she was trying to clean it up in the absence of gravity, the whole bag floated away.

Stefanyshyn-Piper and Steve Bowen were outside the space station on the scheduled six-hour spacewalk, the first of the space shuttle Endeavour's stay at the station.

After completing a few preliminary tasks, Stefanyshyn-Piper was beginning the job of cleaning and lubricating the gears of the station's malfunctioning starboard Solar Alpha Rotary Joint, or SARJ, when she discovered the grease gun leak and then lost the bag.