S118-E-07463 (13 Aug. 2007) --- Astronaut Dave Williams, STS-118 mission specialist representing the Canadian Space Agency, gets assistance from astronaut Tracy Caldwell (out of frame) as he prepares for extravehicular activity to work on the International Space Station. This will mark the second spacewalk for the Endeavour crew and the second for Williams in three days. He will again be joined by astronaut Rick Mastracchio for the EVA.