Astronauts Jim Kelly, Andy Thomas and Paul Richards speak from the Destiny module on Saturday. Photo: Spaceflight Now/NASA TV

It's too soon to say how history will remember the doomed Mir space station. But astronauts and cosmonauts aboard the international space station said today the sprawling new complex would have been impossible to build and operate without Mir's trailblazing 15 years in space.

"We developed invaluable techniques on Mir, we gained experience, we gained, for example, experience in docking to the station, orbiter dockings, both (mission control centers) in Moscow and in Houston learned to work together," said Sergei Krikalev, wrapping up a 141-day stay in space.

"All this joint experience now finds its use in the ISS, including the experience that we gained working on Mir. Even when we unpack here on the station and unstow a lot of cargo, we use the techniques we developed on Mir."

Mir currently is expected to end its illustrious career with a flaming plunge back to Earth on March 22. Five of the 10 astronauts and cosmonauts currently aboard the international space station visited Mir during earlier missions and they unanimously lament its passing.

"I feel that I left a part of myself on the station," said Yury Usachev, commander of the new station's second crew. "But we have moved on and we're working with a new station now.

"I think some time needs to pass to be able to give a good estimate of the results of the work of Mir and our work on the station. After some time, we'll be able to fully appreciate Mir. I think it deserves appreciation."

The combined shuttle-station crews worked overnight Friday and today to complete stowing about a ton of discarded equipment and trash in an Italian-built cargo module for return to Earth.

If all goes well, astronaut Andrew Thomas, operating Discovery's 50-foot-long robot arm, will detach the Leonardo cargo module from the station at 12:52 a.m. Sunday and remount it in the orbiter's cargo bay about an hour later to complete the final major objective of the 103rd shuttle mission.

Discovery is scheduled to undock from the station at 11:32 p.m. Sunday and land back at the Kennedy Space Center around 12:55 a.m. Wednesday.

On board will be the space station's first full-time crew: Commander William Shepherd, Sergei Krikalev and Yuri Gidzenko.

"I have a feeling that we have completed a very important task, we have done a good job," Krikalev said today. "We started training in 1996 and we concentrated all our efforts on preparing for this flight. Now this flight is almost over and in a way, it makes me sad because this is a stage in our lives that has been completed.

"However, our work was good, we were able to work here without any disasters, there haven't been any serious problems on the ISS and I'm sure the program will continue developing."

Thomas, who spent nearly five months aboard Mir in 1998, told a reporter today the old station's demise is "kind of sad, it's the passing of a veteran spacecraft."

"Mir suffered a lot of problems, but it was nonetheless remarkably successful and it was a great technical triumph and a great achievement," Thomas said. "I was very priviledged to serve on it and I look back on it with great fondness.

"I'm going to be sorry that Mir is being deorbited, but that is, of course, the inevitable consequence of progress," he said. "Because of the lessons learned on Mir, we now have this vehicle here. So we've gained a lot from that Mir experience, but I will be sorry to see it go nonetheless."

Thomas was the seventh and final NASA astronaut to make a long-duration visit to Mir, giving him a somewhat unique perspective on the Russian station and the new international outpost.

"I had the priviledge to live on the Mir space station for several months a few years back and it had a quite a bit of room, too," he said. "In fact, in terms of physical volume, it was probably comparable to what we have here.

"But these modules here are quite a bit wider than I had on Mir, we have a lot more space and headroom, as you can plainly see. And after being in the shuttle, it's quite a change to come into this area and have the freedom to move around that we have in here. It's been kind of a kick, actually, to be able to float.

"And, you know, we can do things like this," he said, flipping upside down, "and have a lot of fun with it."

Said Richards of his first impression of the new station: "It's akin to having a long car trip and then finally stopping at a hotel and being able to stretch out and stretch your legs, but this time in all directions."

For his part, Usachev said he was amazed at the uncluttered volume of the new station in its early stages of construction.

"It is sort of atypical of what we're used to, size wise," he told a Russian reporter today. "Here, we can float around, we can see how much space there is here. When we first docked and entered the space station, i was amazed to see how long the station is because of the modules that are docked together. You feel different with so much space.

"As far as the Russian segment is concerned, we're a little bit more familiar with it. It's not much different from Mir. However, the American segment is very different from what we're used to. We're looking forward to the (Discovery) crew leaving and starting working on our own."

Departing Soyuz pilot Gidzenko said Mir's demise is "a pitty ... but nothing lasts forever and I think it is true about Mir as well."

"The fact that the station has to be deorbited is not something that we can decide," he said of the on-board crews. "But of course, it is our home and we're losing it at this time."

Television images from Mir during its final years showed a very cluttered spacecraft, with equipment lashed to every available bit of wall space and forests of electrical cables and air ducts running between modules like thick vines.

The new station, in contrast, appears much roomier in large part because that ducting is not so prevelent and the shuttle has the capability to bring discarded items back to Earth, a capability far beyond that of Russia's much smaller Soyuz ferry craft.

"Mir, of course, when I got there was 15 years old and it had 15 years of equipment and miscellaneous junk, basically, stored in it still because there was not much down-mass capability," Thomas said. "So that contributed to that sense of confinement and there wasn't that much room.

"But here, of course, by comparison it's very spacious. Because we have the shuttle, we can take goods to and from (the station) and keep that sense of spaciousness, we won't accumulate equipment up here the way they did on Mir.

"This module we're in right now is about the size of a bus, it's very spacious, it has racks of equipment down each side, it's going to be an interesting place to do scientific investigations," he said. "There's no doubt about that. It's really a very novel approach to doing science that's going to have an impact in future years."

Asked to summarize Discovery's current mission, Thomas said "this has been an amazingly productive flight."

"I think it's a very historical flight in the sense that we're bringing up the first exchange crew to the international space station, we're bringing the first crew home, who basically commissioned and outfitted the space station from its inception, we're bringing them back to Earth and leaving a new crew in residence to take their place.

"We brought up hardware to support the continued assembly and operations of the space station, we brought up supplies and equipment for the next crew, so it's really been a very productive and action-packed flight and we've gotten a lot out of it."