"Copy, wheels stop Endeavour. Welcome back to Earth," replied astronaut Bill Oefelein from Mission Control at the Johnson Space Center in Houston. "Congratulations on a very successful and very safe assembly, repair and crew rotation mission to the International Space Station. And a special welcome home to the Expedition Four crew after your record stay aboard the ISS."

"OK, Billy-O, thanks for the support. Thanks for hanging with us for the last two days getting us down," Cockrell said.

"It's great to be back on planet Earth," Bursch added from his couch in the shuttle crew cabin's middeck.

The previous record holder was Shannon Lucid, who spent 188 days in Earth orbit during a 1996 tour aboard the Russian space station Mir. She is now NASA's chief scientist based in Washington, D.C.

With his safe return, Walz broke another Lucid record to become NASA's most experienced astronaut in terms of total time spent in space. That mark is now 231 days, earned during five flights.

Bursch is in second place with 227 days, while Lucids total time in space is 223 days.

Along with Russian cosmonaut Yuri Onufrienko, the Expedition Four crew spent the past six months living and working aboard the International Space Station (ISS).

Their tenure saw the addition of the S-Zero truss and a new rail car and work platform that will allow the station's Canadian robot arm to continue building out the multinational complex.

A new Soyuz lifeboat -- whose crew included South African space tourist Mark Shuttleworth -- was delivered in April and the pace of science operations took another step up.

Each of the station crewmembers also took turns going outside as they staged a trio of spacewalks in Russian spacesuits to assist in the outpost assembly effort.

"I can't tell you what a fantastic voyage this was," Bursch said shortly after Endeavour undocked from the ISS on Saturday, leaving behind the new Expedition Five crew of Valery Korzun, Sergei Treschev and Peggy Whitson.

Life on Earth

All three of the station veterans asked for pizza as their first meal back on Earth and looked forward to a reunion with their families. Unfortunately their families were in Florida to watch them land, so the reunion will be delayed a couple more days.

Although the Expedition Four team is back on the ground, their mission won't be fully complete until the three astronauts get used to living in normal gravity again. NASA medical specialists say that process should take about 45 days, sometimes longer, to complete.

"It's all individualized. You don't push the crewmember faster than they can," said Dr. Terry Taddeo, a NASA flight surgeon.

All space travelers lose bone mass and their muscles weaken, so the rehabilitation drill starts with simple stretching and gentle massages. From there it is on to aquatic exercising, long walks, jogging and resistance training on weight machines, Taddeo said.

Astronauts most commonly want to know when they can drive or fly again, but there's no test to objectively show when a crewmember won't suddenly get dizzy or will no longer feel like the world is spinning. That becomes a decision for the astronaut and their doctor together, he said.

The veteran fliers also will have to relearn simple tasks such as turning corners without falling, or remembering to put objects such as a pencil down on the table instead of releasing it in the air, expecting it to float.

The Expedition Four increment originally was planned to last about five months, but the two Americans and one Russian got a bonus month in space thanks to a last-minute change in the flight plan for their ride home.

Ambitious plan

Tasked with goals of crew exchange, delivering fresh supplies in the Italian Leonardo "moving van" and staging two station assembly spacewalks, Endeavour's STS-111 mission was full from the start.

"At that time there was already a lot of folks here at JSC who know a lot about how we fly people in space that thought we were biting off more than we could chew with this flight plan," said shuttle flight director Paul Hill.

Then a problem cropped up with a joint on the station's Canadian robot arm that threatened to grind future space station assembly operations to a halt.

NASA mission managers on March 20 decided that surgery was in order and they added a third spacewalk to the already busy mission, which was then delayed a month to accommodate the extra training and time needed to load the required replacement hardware aboard the shuttle.

Exactly 100 days after the Canadarm2 problem was first detected, spacewalkers Franklin Chang-Diaz and Philippe Perrin -- a French space agency astronaut -- executed the operation without incident, giving the crane a new wrist roll joint.

For an agency that historically is used to planning its missions months, if not years, ahead of time, the success was particularly sweet, with some officials privately calling it nothing short of a miracle.

"It looked very easy, but it took a lot of smart people, a lot of hard work and they did a super job," Hill said.

In fact, every goal of Endeavour's mission was accomplished without incident, including delivering more than four tons of equipment and supplies to the station and returning more than two tons of garbage to Earth.

Another highlight came as rookie Endeavour pilot Paul Lockhart flew the shuttle around the station after undocking and provided everyone in space and on the ground with some of the most spectacular images yet of the evolving laboratory complex.

Weather woes

The only trouble Endeavour and its crew had was in getting into space, and then returning home again.

First set for launch May 30, Florida's notorious afternoon thunderstorms and a relatively minor technical problem with a valve conspired to delay the launch one week to June 5.

However, another round of bad weather kept the shuttle up an extra three days -- something that Endeavour's skipper likely won't be allowed to forget for the rest of his career.

Cockrell had the same thing happen to him during his two previous flights as commander. A 1996 mission ended in Florida after the third try, while a Februrary 2001 trip into space repeated what happened this week: landing in Calfornia on the third day after two days of bad weather in Florida.

It will now take about a week for a team of Kennedy Space Center-based workers to prepare Endeavour for its cross-country ferry flight home.