A small water leak cropped up in one of the hoses designed to keep NASA astronaut Jack Fischer’s spacesuit cool while he waited to begin today’s 200th spacewalk on the International Space Station. That had a domino effect on the preparations, drawing down battery power and forcing NASA to trim back the time allotted to the outing from six and a half hours to a little more than four hours. The schedule still gave Fischer and NASA’s Peggy Whitson enough time to accomplish the spacewalk’s primary task: replacing the ExPRESS Carrier Avionics box, which provides electricity and data connections to science experiments and spare parts mounted on the space station’s exterior. The spacewalkers also installed a data connector for the Alpha Magnetic Spectrometer, the station’s cosmic particle detector. It was the first spacewalk for Fischer, the ninth for Whitson (America’s most experienced astronaut), and the 200th for the station since 1998.