International Space Station (ISS) astronauts apparently cleared the way for station assembly to continue through two more space shuttle visits Jan. 30, replacing a key piece of power-generating gear at one end of the main station truss.

Expedition 16 Commander Peggy Whitson and Flight Engineer Dan Tani also collected some more clues in the continuing mystery of what has fouled the starboard solar alpha rotary joint (SARJ) with metallic debris, taking photographs and pulling debris samples from previously uninspected sections of the 10-foot-diameter geared mechanism.

In a high-altitude repair job intended to squeeze enough power out of the malfunctioning starboard solar array system to support systems and science on two more pressurized laboratory modules, Whitson climbed into the truss structure to pull a failed bearing motor roll ring module (BMRRM) and replace it with a spare.

Tani assisted her from outside the truss structure, drawing on a serendipitous training session on the ground long before the Dec. 8 failure of the malfunctioning 200-pound "broom," which rotates one half of the starboard solar array wing along its long axis to gain the best solar angle on its power-producing cells.

After overcoming a brief breakdown of communications with Mission Control Center in Houston by switching to a backup S-band link, the pair installed the spare unit, reconnected its power cables and bolted it down. Because the 160 volts generated by the array couldn't be switched off, for safety the pair had to wait until the orbiting station entered the Earth's shadow to handle the BMRRM and its electrical connectors.

Working against the clock in the roughly half-hour of darkness available on each orbit, Whitson managed to pull and replace the BMRRM and connect all but one of the four power and data cables linking the BMRRM to the station grid before time ran out on the first "eclipse." She quickly made the final connection when the station re-entered darkness an hour later.

As soon as Whitson and Tani reinstalled thermal covers and were clear of the area, controllers in Houston began checking out the new BMRRM, which performed well during initial tests.

"Ah, I see it moving," Whitson radioed as the array started moving in a 360-degree test. "You can see where it's changing angles. Yay, it works!"

After replacing the BMRRM, Whitson and Tani moved back inboard on the truss to continue inspections of the starboard SARJ. Normally the mechanism rotates the entire 240-foot-long solar array wing around its end of the truss like a propeller to get the best solar angle.

With both of the "beta" gimbals on the starboard end of the truss working again, power production should be adequate for Europe's Columbus laboratory module set for launch next month, a "hand" for the Canadian-built station robotic arm and a Japanese pressurized logistics module to be launched in March, and the big Japanese Kibo module set to fly in April.