"The very first maneuver was completed successfully," Hoshide told Japanese flight controllers near Tokyo.
Full deployment of the 33-foot arm will be done after Discovery leaves the station next week. However, it won't be used for any actual work until after the launch into orbit next year of the billion-dollar lab's third and final section - a "porch" for exterior experiments - and a second, smaller robotic arm.
After he and Nyberg finished testing the robotic arm, Hoshide reflected on what Kibo means for Japan.
"It's a big milestone. We have our own house here now," Hoshide said during a series of media interviews Saturday.
The initial deployment of the robotic arm provides room for astronauts Michael Fossum and Ronald Garan Jr. to finish some final outfitting of the lab on Sunday during their third and final spacewalk of the current shuttle mission.
On Saturday, Fossum and Garan got word that an extra task had been added to the spacewalk.
Fossum will collect samples of grease and small amounts of debris detected on a solar wing rotating joint on the space station's left side.
The grease and debris will be analyzed by engineers back on Earth to see if it can help them figure out what caused a similar joint on the right side of the station to be clogged with metal shavings.
The right side joint has been used only sparingly since last fall, hampering energy production. The joints enable the space station's solar arrays, which provide electrical power, to rotate and track the sun.
The left side joint is working normally, but engineers are trying to prevent it from experiencing problems, as well. Fossum said he wasn't worried about the joint.
It "looks to be in pretty darn good shape," he said.
Fossum and Garan also planned to replace an empty nitrogen gas tank during Sunday's spacewalk.
Kibo, Japanese for hope, was delivered by the shuttle and installed on the space station this week.
The attic - a 14-foot shed, or closet, for spare tools and equipment - was put atop the 37-foot lab on Friday. It had been in a temporary location at the space station since being delivered by another shuttle crew in March.
Kibo is the largest of the nine rooms now at the space station, including the two other labs, belonging to NASA and the European Space Agency.