Using the microgravity science glovebox, Williams began the second of three sessions Wednesday of the Pore Formation and Mobility Investigation experiment. This experiment studies bubbling that occurs in weightlessness as liquids cool and solidify.
Williams will begin his first Saturday Science activity this weekend with the Cellular Biotechnology Operations Support Systems Fluid Dynamics Investigation. This is a series of experiments to improve fluid mixing techniques and to control bubble distribution for cell culture in orbit.
On May 4, ISS Progress 21 engines were used to reboost the station. Afterward, an error message indicated the Zvezda Service Module computers couldn't command the Progress engines to reconfigure for normal operations. The reboost was not affected. Engineers have determined the most likely cause of the message was a software error, which will be corrected. Meanwhile, a procedural change will allow the Progress thrusters to be used. Vinogradov and Williams continued to unpack supplies from that cargo vehicle.
Last week, engineers detected a small reduction of nitrogen pressure in the liquids unit of the oxygen-generating Elektron. To isolate the source of the leak, Russian flight controllers asked Vinogradov to turn off the machine. They have identified the small leak and plan to operate the Elektron as needed. A spare liquids unit is onboard.
The Elektron will remain deactivated until after a June 1 spacewalk. Engineers originally had planned to turn it off next week to reconfigure ventilation lines and to install a new hydrogen vent before the extravehicular activity. Meanwhile, oxygen from tanks in the ISS Progress 20 cargo vehicle is being added to the station's cabin.
On Thursday, Williams practiced using the station's robotic arm. He and Vinogradov spoke Wednesday with reporters from the StarDate syndicated Radio Network and WISN-TV of Milwaukee.