HOUSTON — Astronauts Sunita Williams and Akihiko Hoshide overcame a jammed bolt to secure a critical power system switching unit to the outside of the International Space Station during a Sept. 5 spacewalk, enabling much-needed solar energy to return to the orbiting science lab’s electrical grid.

The bolt jammed during an Aug. 30 spacewalk in which Williams and Hoshide attempted to replace the failing Main Bus Switching Unit-1 with a spare. The MBSU-1 is one of four similar circuit boxes that distribute power generated by the station’s eight outstretched solar panels to internal as well as external electrical components, including life support systems, communications gear and science experiments.

The temporary absence of the switching unit prevented power from two of the solar panels from entering the power grid, leaving the six-member station crew with just 75% of normal current and forcing them to impose conservation measures.

Power should be flowing from the new switching unit into the power grid on Sept. 6, following a checkout.