CAPE CANAVERAL, Fla. -- America's newest spaceflight duration champs are ready to come home.

STS-111

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Having spent a record-breaking six months in Earth orbit aboard the International Space Station, astronauts Dan Bursch and Carl Walz on Wednesday both said they are looking forward on Monday to a family reunion and pizza.

"What about me? I want the same. Maybe twice," said Russian cosmonaut Yuri Onufrienko, commander of the Expedition Four crew that included Bursch and Walz.

Launched into orbit in December, the pair of Americans late Tuesday surpassed the previous U.S. spaceflight record of 188 days and four hours. Shannon Lucid held that mark thanks to a 1996 stay aboard the Russian space station Mir.

The Expedition Four crew was replaced by the Expedition Five crew which includes Valery Korzun, Sergei Treschev and Peggy Whitson.

If shuttle Endeavour lands as scheduled on Monday, the new record for the longest American space mission will be 193 days and 17 hours.

"It's certainly not something that we set out to do, to break a record like this," Bursch said. "We all miss our families but we're really happy that everything's gone really well. And we'll be happiest if we know that folks on the ground are proud of what we've done."

For Walz, who is making his fifth flight, the new record made him NASA's most experienced astronaut. If Endeavour returns to Earth Monday he will have racked up more than 223 days in space, again taking an American record away from Lucid.

But those numbers still pale in comparison to the Russian spaceflight endurance records.

Cosmonaut Valery Polyakov, a medical doctor who spent 438 days aboard Mir in 1994-1995, has the record for the longest single mission.

Cosmonaut Sergei Avdeyev is the most experienced human in space, with 748 days during three spaceflights in 1992-93, 1995-96 and 1998-99.

And despite that experience, humans have a lot more to learn about long-duration spaceflight before embarking on a round-trip to Mars, which could last as long as three years according to some mission models.

"We have some new technology that would promise to get us to Mars much quicker than that and I think that's important," Bursch said. "When I think back of the old wooden sailing ships, when sailors would go out on whaling ships for years at a time before returning, I don't know how they did it. But eventually the speed of transportation increased."

New plasma-based rocket engines are being tested that would greatly increase a Mars-bound spaceship's speed, technology that is being researched by scientists that include Endeavour spacewalker Franklin Chang-Diaz.

"What we need to do is move into those kinds of technologies that would enable us to travel pretty much anywhere in the solar system within a reasonable amount of time so we can come back and tell the story," Chang-Diaz said.

When those missions happen, the astronauts say it won't be the physical challenges that will be the most difficult to overcome.

"Without a shadow of a doubt, in my opinion, the biggest challenge would be mental and psychological," Bursch said.

Getting along with your crewmates would be another.

"If you think about taking a family trip, whether it's with your spouse or with your family, and never getting out of the car, you can imagine some problems are going to crop up no matter how well you get along," Bursch said.

Staying occupied with things to do is the key.

"You really want to be busy and have lots of scientific experiments to do," Walz said.

Still ahead for the next few days: A final spacewalk to repair a faulty joint in the station's robot arm is planned for Thursday, the Italian-built Leonardo supply module is to be returned to Endeavour's cargo bay on Friday and Endeavour is to undock Saturday.

Mission managers reported late Wednesday that Leonardo had been completely unloaded and then filled back up with everything it is supposed to carry home to Earth, a feat that was expected to take until Thursday to complete.