CAPE CANAVERAL, Fla. -- Astronauts on the International Space Station (ISS) continued unpacking the Italian-built "moving van" Monday and completed another step in assembling the outpost.

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The crews also attempted to ceremoniously turn over command of the ISS to Russian cosmonaut Valery Korzun, but were unceremoniously interrupted by a fire alarm as the event began.

One of 10 sensors inside the Russian Zarya module detected smoke setting off an alarm that quickly put a halt to the festivities inside the U.S. Destiny module.

The station crewmembers quickly left the scene, broadcast live on NASA TV, to check out the situation.

"It was a false alarm," Expedition Four commander Yuri Onufrienko reported to Mission Control in Moscow moments later. "Everything is OK and everything is under control."

Onufrienko blamed the alarm on dust kicked up in the air from the many boxes and other containers being moved around within the station during this resupply mission.

The ceremony, in which Onufrienko was to hand over the ship's log to Expedition Five commander Valery Korzun will be rescheduled, possibly for late Monday. Official change of command took place last Friday, soon after Endeavour docked to the station.

Until the fire alarm went off, NASA officials had called Monday a relatively quiet day in space.

"We're really enjoying ourselves here," Endeavour commander Ken Cockrell told French officials and reporters during an earlier VIP event.

Most of the day was spent finishing the task of unloading the Leonardo supply module. It was loaded with nearly three tons of equipment and supplies intended for use by the Expedition Five crew of Korzun and flight engineers Sergei Treschev and Peggy Whitson.

Leonardo was carried into space within shuttle Endeavour's cargo bay. On Saturday it was lifted from the bay and attached to the station's Unity node so it could be unloaded.

The goal for the 10 humans in space during the next few days is to fill Leonardo with about two tons of trash, unneeded equipment and completed experiments. The module will return to Endeavour's cargo bay on Friday, setting the stage for undocking on Saturday and a landing back in Florida on Monday, June 17.

The day began with the temporary attachment at 9:13 a.m. EDT (1313 GMT) of a work platform to a rail car atop the station's main truss.

When that truss is eventually built out, the rail car -- which is called the Mobile Transporter (MT) -- and its attached work platform -- known as the Mobile Base System (MBS) -- will be able to move along the entire truss span. The truss will stretch out longer than a football field.

At the same time, the station's Canadian robot arm will be able to connect itself to the MBS and travel with the rail car, hauling large station components with it to assist in the outpost assembly effort.

Spacewalking astronauts Franklin Chang-Diaz and Philippe Perrin plan to permanently bolt the platform to the rail car on Tuesday, as well as make all the appropriate electrical and data cable connections.

Staged from the station's Quest airlock, the mission's second spacewalk is set to begin at 11:08 a.m. EDT (1508 GMT) and last about six hours.