Q&A with Keith Gendreau, principal investigator of the first X-ray space communications experiment (members only)

Two Russian cosmonauts used the International Space Station’s Poisk docking compartment as an airlock for the first time Wednesday in a six-hour 48-minute spacewalk to begin preparing the nearly identical Pirs module for removal next year. A new laboratory module will be parked in its place later.

Space station commander Scott Kelly and Kjell Lindgren carried out a tedious seven-hour 16-minute spacewalk Wednesday, installing cables needed for a new docking mechanism, mounting insulation panels on a physics experiment to improve cooling and lubricating the latching mechanism of the station’s robot arm.

Liftoff of a previously-flown Falcon 9 rocket from NASA’s Kennedy Space Center with a European-built television broadcast satellite has been pushed back from Saturday until at least next Wednesday night, officials said.