Expedition 6 commander Kenneth Bowersox formally turned over command of the international space station to Expedition 7 commander Yuri Malenchenko today, closing out an extended five-and-a-half-month mission and setting the stage for landing this evening aboard a Russian Soyuz spacecraft.

Bowersox, science officer Donald Pettit and flight engineer Nikolai Budarin originally planned to return to Earth in March aboard the shuttle Atlantis, which was to ferry up their replacements: Expedition 7 commander Malenchenko, Edward Lu and Alexander Kaleri. But those plans went up in smoke in the wake of the Feb. 1 Columbia disaster.

With the shuttle fleet grounded, Bowersox and company were forced to extend their mission and to wait for the arrival of Malenchenko and Lu last Monday aboard a fresh Soyuz. With station assembly on hold, Kaleri is awaiting assignment to a future mission.

Despite the disruption to their timeline and the personal tragedy of the Columbia disaster, Bowersox said today "I couldn't be prouder to be a member of the Expedition 6 crew, along with Nikolai and Don."

"Over the last five-and-a-half months we've experienced some really sad moments and some extremely happy moments," he said during a formal change-of-command ceremony. "But most important is we have managed to stay together as a crew. Each one of us has put individual interests aside, put the interests of the crew first.

"When we started the mission, we had three goals," he said. "The first was to demonstrate international cooperation. The second, maintain and assemble the station and the third, to further the science activities aboard ISS. With the help of our huge international team on the ground, we've accomplished that mission.

Turning to Malenchenko and Lu, Bowersox said: "Ed, Yuri, you guys have to be the two luckiest guys who come from the planet Earth today."

"Over the next six months, you get to live aboard this beautiful ship. It's huge in size, it's tremendous in capability, it's an environment rich for discovery. I wish you well and I hope your expedition goes as wonderfully as ours has. I wish you many, many fantastic memories. Yuri, I'm ready to be relieved."

"I relieve you of command," Malenchenko said.

"I stand relieved."

Malenchenko said he was "very happy to be here on board the international space station, very proud. Thanks all for (the) opportunity and thank you, Sox, for your command. The station is in great shape."

Bowersox, Pettit and Soyuz commander Budarin plan to undock from the space station's Pirs airlock module at 6:40 p.m. At a distance of about 19 miles from the station, Budarin plans to fire the Soyuz TMA-1's braking rockets at 9:12:27 p.m. for a landing at 10:06:48 p.m. in Kazakhstan near the town of Arkylyk.

NASA Administrator Sean O'Keefe congratulated the Expedition 6 crew today for a successful mission and jokingly asked how they wanted their steaks cooked when they got back to Earth. Bowersox passed, but Pettit said he'd like one cooked medium rare. Budarin promptly said, "Rare. Two steaks."

Bowersox and Pettit are the first NASA astronauts to make a descent in a Russian spacecraft.

"For me, I'm actually going to miss station quite a lot," Bowersox said earlier this week. "I feel a little bit like I'm being kicked out of my apartment for not paying my rent. But when I get back to Earth the best part's going to be to be able to hug my wife and hug my kids."

Said Pettit: "I've got two little boys that turned two early on this mission. So they're in the middle of their twos now and they're talking sentences and I've never heard them, or been when them when they could talk. So I'm really anxious to be with them and my wife and I'm looking forward to getting some good home cooking again, too."

Assuming an on-time touchdown, the Expedition 6 crew will have spent 161 days, 23 hours and 10 minutes off planet since launch aboard the shuttle Endeavour on Nov. 23.

"I'm actually sort of excited about it," Bowersox said of the unexpected opportunity to land in a Soyuz. "I've been looking down quite a bit here from orbit, looking down on Kazakhstan and it's a beautiful country. It's very exciting for me, I went through a lot of training there in Star City (Russia) and I always thought 'oh, I'm doing this training and I'm never going to get to use it in the Soyuz.' And now we're going to use it. So I think it's going to be a very, very interesting life experience."

In the wake of the Columbia disaster, NASA and the Russian space agency discussed a variety of options for keeping the station manned until shuttle flights could resume.

In the end, the only viable option was to replace Expedition 6 with a two-man "caretaker crew" and to launch that new crew on a Soyuz rotation flight already scheduled for launch April 25. While three astronauts are needed to maximize science and assembly operations on the station, not enough water could be delivered to the outpost in the absence of routine shuttle visits.

At the time of the Columbia disaster, Malenchenko, Kaleri and Lu already were in training to replace Bowersox, Budarin and Pettit. After lengthy negotiations between NASA and the Russians, Malenchenko and Lu were named to fly on the April Soyuz rotation flight for a six-month stay aboard the station.

During a news conference the week after the Columbia disaster, Bowersox said the absence of a third crew member will "change the dynamic of how you support each other emotionally. It's really nice where if two people are getting a little bit irritated, well one of them can go and talk to the third or the third can act as a referee. It's sort of like with our international partnership. The more people, the more partners you have the more work is required to maintain that partnership but the stronger you are because you have more bodies, more hands to get things done."

But Lu said this week he doesn't expect any problems.

"I think we will be able to do just fine," he said. "Yuri here is quite experienced and he's actually lived on the Mir for three months. ... There is, of course, the problem Ken mentioned, we don't have shuttles coming up which have the capability to bring huge amounts of supplies up here. So we will have to conserve a little bit on some things. But I don't think it'll be that bad."

While the ISS-8 crew has not yet been named, it is expected to be made up of Kaleri and Michael Foale, who trained as backups to Malenchenko and Lu. Launch is targeted for around Oct. 18. By the time the ISS-8 increment is over in mid April 2004, NASA hopes the shuttle will be flying again.

"The biggest impact is to assembly," Bowersox said of the interruption in shuttle flights. "It's going to delay the rest of the assembly of the truss and the additional laboratory modules we want to bring up here. The second effect is, it's going to hinder resupply for crews who are maintaining and living on board the station. Of course, we want to get the shuttle flying again as soon as we can and continue on with our station program."

Today's re-entry and landing will be the first by an upgraded Soyuz TMA spacecraft, equipped with more up-to-date computers and displays, an improved braking rocket system and slightly larger seats to accommodate more U.S. astronauts.

"We've done a heap of training for both Soyuz and shuttle entries and either one is fine with us," Pettit said earlier this week. "It happens that for the end of our mission we're going in with a Soyuz due to circumstances we're all aware of. And I don't think there's any extraordinary angst about the particular entry we're planning to do here versus any entry you would do where you have to get rid of the energy of orbit and land on the surface of the Earth with zero velocity."

Malenchenko, Mir veteran, offered a bit of advice on what Bowersox and Pettit could expect.

"Landing by shuttle is like (a) comfortable landing by commercial plane," he said in English during a news conference. "When you make landing by Soyuz, it's a very unusual mode, temperatures, Gs, vibration and finally by parachute. But it's very safe and finally you reach ground, which is most important. And in a few seconds, you see friends, good people and everything you want."

A detailed timeline of major re-entry events is available here.

The Soyuz TMA spacecraft is made up of three sections: A propulsion and instrumentation section equipped with two solar arrays; a descent module where the crew sits during launch and re-entry; and an orbital module equipped with the docking system used to connect to the space station.

Bowersox, Budarin and Pettit will return to Earth later today in the descent module, which weighs 6,393 pounds and has a habitable volume of 141 cubic feet. Only about 110 pounds of cargo or experiment samples can be accommodated.

The Soyuz TMA is an upgraded version of the Soyuz TM-series spacecraft. Today's landing will be its first. Here's a bit of background on the upgrades from NASA's space station website:

Source: NASA

The Soyuz TMA spacecraft is a replacement for the Soyuz TM, which was used from May 1986 to November 2002 to take astronauts and cosmonauts to Mir and then to the International Space Station beginning in November 2000.

The TMA increases safety, especially in descent and landing. It has smaller and more efficient computers and improved displays. In addition, the Soyuz TMA accommodates individuals as large as 1.9 meters (6 feet, 3 inches tall) and 95 kilograms (209 pounds), compared to 1.8 meters (6 feet) and 85 kilograms (187 pounds) in the earlier TM. Minimum crew member size for the TMA is 1.5 meters (4 feet, 11 inches) and 50 kilograms (110 pounds), compared to 1.6 meters (5 feet, 4 inches) and 56 kilograms (123 pounds) for the TM.

Two new engines reduce landing speed and forces felt by crew members by 15 to 30 percent and a new entry control system and three-axis accelerometer increase landing accuracy. Instrumentation improvements include a color "glass cockpit," which is easier to use and gives the crew more information, with hand controllers that can be secured under an instrument panel. All the new components in the Soyuz TMA can spend up to one year in space.

New components and the entire TMA were rigorously tested on the ground, in hangar-drop tests, in airdrop tests and in space before the spacecraft was declared flight-ready. For example, the accelerometer and associated software, as well as modified boosters (incorporated to cope with the TMA's additional mass), were tested on flights of Progress unpiloted supply spacecraft, while the new cooling system was tested on two Soyuz TM flights.

Descent module structural modifications, seats and seat shock absorbers were tested in hangar drop tests. Landing system modifications, including associated software upgrades, were tested in a series of airdrop tests. Additionally, extensive tests of systems and components were conducted on the ground.

"Congratulations, Ken, and to Don and Nikolai for a fantastic expedition," O'Keefe radioed before hatch closure. "You all did a superb job. We're looking forward to welcoming you all home in a couple of hours."

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