The crews of Discovery and Alpha gather for a joint news conference. Photo: Spaceflight Now/NASA TV

The first commander of the international space station says he's not looking forward to returning to Earth's gravity after 141 days in space. But he's proud of his crew's work to activate the outpost and looking forward to seeing his wife and his two dogs again.

"We basically put the space station in commission," commander William Shepherd told reporters today. "We have taken something that was an uninhabited outpost and we now have a fully functional station where the next crew can do research. And I think that's the substance of our mission."

Shepherd and Mir veterans Yuri Gidzenko and Sergei Krikalev were launched to the international space station Oct. 31 aboard a Russian Soyuz rocket, becoming the lab's first full-time crew.

They have been replaced by Expedition Two commander Yury Usachev, James Voss and Susan Helms, who took off aboard the shuttle Discovery on Feb. 8.

Asked if he was looking forward to returning to Earth's gravity, Shepherd said "to be honest, I'm not that anxious to see what it's going to be like."

"Sergei and Yuri have done this before and they're telling me it's going to be arduous," Shepherd said. "I know my wife is going to be anxious to see me and I'll be happy to get home on time if Captain (James) Wetherbee and the Discovery crew can arrange that."

Asked what he looked forward to the most, the former Navy SEAL commando said "the first thing I plan on doing when I get back to Earth is say 'hi' to my wife and playing with my two dogs."

Gidzenko agreed, saying "I'm going to meet with my family, my wife and my son, and maybe a little bit later I'm going to take a shower."

Along with delivering the station's second crew, Discovery also carried some five tons of supplies and equipment to the complex, including the first suite of scientific experiments and the computer workstations needed to operate the station's robot arm after it is attached next month.

Unloading the Italian-built Leonardo cargo carrier went faster than expected, but the astronauts - and engineers on the ground - ran into problems while reloading it with a ton of trash and discarded equipment.

Lead flight director John Shannon said it's not enough to simply get the hardware and trash into Leonardo. A detailed inventory must be maintained so engineers on the ground can consider how much each item weighs, where it is located and how it might affect the shuttle's overall balance.

As a result, NASA managers decided Thursday to extend the flight by one day to give the astronauts and engineers more time to complete the complex stowage work.

"In zero G, things float away, you can't set it beside you and stack it up," said lead flight director John Shannon. "The other part of it is, you can't accurately assess the weight in zero G.

"So on the ground, we have to keep a real close tally on what's going in each box and each bag, add up the weights and then do our structural assessment to make sure that bag, when we hit Earth's gravity, is not going to weigh so much it will hurt that bag or the platform that we strap it to."

As it now stands, the Leonardo module will be undocked from the station and re-berthed in Discovery's cargo bay overnight Saturday and the shuttle will undock around 11:30 p.m. Sunday. Landing back at the Kennedy Space Center is targeted for 12:55 a.m. Wednesday.

Before Discovery departs, however, the Expedition One crew must thoroughly brief Usachev and his crewmates on the station's operation and idiosyncracies.

"The top several items we're discussing are how the crew and the vehicle need to be organized for all kinds of contingencies and probably," Shepherd said.

"From the aspect of controlling the ship, how we work with computers and communications. Those are the major areas we've covered so far and our discussions are ongoing today and tomorrow."

For her part, Helms said she and her crewmates "have a lot of catch up to do in order to figure out where everything is."

"These guys have had months to get organized and they've done an outstanding job of putting things where they belong," she said.

"So Jim, Yury and I need to get up on the step and try to figure out where all this stuff is so that once these guys leave in a day or two, we're going to be able to find what we need to continue to work," she said. "They've set an example and it's going to be a struggle to try to match it." While she's only be aboard the station for one day, her impressions "have been nothing but favorable and we owe a lot of that to the condition of the ship based on how Expedition One left it."

"It's much more spacious than I had imagined," she said. "I expected to have just a couple of things that would be unexpectedly negative but it's turned out everything has been absolutely positive and I just can't believe how much room we're going to have to spread out here and get to work."

Voss said he's looking forward to spending four-and-a-half months aboard the outpost.

"That is a long time to be away from home no matter where you are, if you're just on a business trip or you're in space," he said. "But I'm looking forward to the work we're going to be doing up here.

"We're going to be activating some more systems on the station, there'll be several shuttle flights and a Soyuz flight that will come up here.

"We have a lot of work to do and I like working, so I'm just anxious to get started and greatly looking forward to it," he said. "I'm hoping it's going to be a great four-and-a-half months for Susan, Yury and myself."

Back on Earth, meanwhile, Shepherd, Gidzenko and Krikalev will be working through extensive physical therapy to re-adapt to gravity.

Shepherd said he would like to fly in space again, but not necessarily on the international space station.

"I've been wrestling with that question a lot," said. "I do think I would like to fly again in space but I'd like to do it on a vehicle that's going to go somewhere.

"I think we should be making plans to have vehicles built somewhat along the lines of this station but that have another destination away from the Earth in mind."