The Discovery astronauts spent the day loading the Leonardo cargo module with trash and discarded equipment from the international space station while the lab's departing crew members briefed their replacements on the finer points of operating the growing outpost.

Completing this handover process is critical, flight controllers say, to make sure Expedition Two commander Yury Usachev, James Voss and Susan Helms are up to speed on the station's complexities and idiosyncracies before Discovery departs Saturday.

Expedition Two astronaut Jim Voss assembles the space station robotic arm control post inside the Destiny lab. The Canadian-made arm is scheduled to be delivered at the station next month. Photo: Spaceflight Now/NASA TV

"Right now, the best way to describe them is up to their necks in trying to figure out exactly how Alpha works and trying to get as much of the handover done as possible," said shuttle pilot James Kelly.

"They're right now trying to learn the ropes of the international space station from the Expedition One crew. They are zooming back and forth trying to figure out everything that goes on."

At the same time, Kelly and his three shuttle crewmates are racing the clock to repack the Leonardo cargo module with trash and discarded equipment that's no longer needed on the station.

Some 9,650 pounds of equipment and supplies carried into orbit inside the module have now been transferred into the space station, including the first suite of science experiments, computer work stations for operating the lab's robot arm, a compact medical facility and components of the station's Ku-band communications system.

"We are working on the Leonardo, repacking that to go back in the Discovery's payload bay and bring it back home," Kelly said. "And once that's done, we'll round up the seven of us that are coming home, which is the four of us that went up and the three from the Expedition One crew, and we'll do an undock and hopefully a fly-around."

"We're bringing back a whole bunch of logistics and supplies that are no longer necessary and frankly, a lot of trash and things like that that we want to clear out of station.

From a payload bay camera on Discovery looking up at the space station, the Leonardo cargo module is seen docked to the Unity node right below the Soyuz capsule. Photo: Spaceflight Now/NASA TV

"Obviously, when new things come up, there's packaging materials, foam and bags and all those kind of things, which we don't want to leave inside the station cluttering it up," he said.

NASA flight controllers say the mission is proceeding on schedule with no problems of any significance.

"We had 10 astronauts working really hard today," said lead flight director John Shannon. "The Expedition One/Expedition Two crew members are spending most of their time right now doing handover tasks.

"The Expedition One team is working very hard teaching the Expedition Two team all they need to know about the workings of space station Alpha.

"The four shuttle crew members that are left have spent most of their time doing transfers from the Leonardo module," Shannon said. "They got it all unpacked and they're working very hard on the return stowage."

Shannon said he was struck by how large the international space station has become and how much volume is available in Leonardo to carry equipment up and down.

"It really brings home the fact that this is the largest space station ever put in Earth orbit," he said. "And if you saw (Expedition One commander) Bill Shepherd's video of him translating through the lab, the node and into Leonardo, you get an idea of how immense this is.

"Also, how much stowage we can put in Leonardo. It's very impressive, but it's quite a daunting task over the next couple of days to get all the stowage put back in Leonardo. But we're sure happy we have that capability." If all goes well, the Italian-built cargo module will be detached from the space station early Saturday and reberthed in Discovery's cargo bay. The shuttle is scheduled to undock from he station around 10:54 p.m. Saturday evening.