Coming 136 days after Shepherd and company boarded the station, the hour-long flyaround followed the first changing-of-the-guard at the international outpost.

Veteran cosmonaut Yuri Usachev took command of the complex late Sunday as he and two American flight engineers -- Susan Helms and Jim Voss -- set sail on the second station expedition, a planned four-and-a-half month outpost tour.

"This is a pretty monumental event: the exchange of the Expedition One crew with the Expedition Two crew," said NASA deputy project manager Bill Gerstenmaier.

Added NASA flight director Wayne Hale: "It's a page in history."

With the world's only other space station -- Mir -- due for a fiery finale this week, the Expedition Two crew is embarking on a mission aimed at prepping the new international outpost for further construction.

The first order of business: Finishing up the activation of sophisticated computer workstations critical to controlling the station's Canadian-built robot arm, which is to be delivered to the outpost by a visiting shuttle crew next month.

The 57-foot (17-meter) construction crane will play a key role in almost all future assembly work at the growing outpost.

"It's extremely important to the future of the space station," said Voss. "It's what's going to allow us to construct the greater portion of the station from now on."

Also on tap this week: The activation of a dish-shaped antenna designed to send back high-quality audio and video signals through NASA relay satellites.

Set up by spacewalking assembly workers last October, the Ku-band antenna will reduce reliance on widespread Russian ground stations and replace a comparatively primitive U.S. communications system aboard the outpost.

What's more, the antenna will enable the new station crew to beam back reams of scientific data, a capability key to starting up research aboard the outpost.

All that work is scheduled to pick up Wednesday as Shepherd and his crew -- which includes cosmonauts Yuri Gidzenko and Sergei Krikalev -- head for a 12:56 a.m. EST (05:56 GMT) landing here at Kennedy Space Center.

Weather permitting, that is.

The early forecast calls for a chance of high winds and rain showers, conditions which might prompt mission managers to keep Discovery, its four astronauts, and the Expedition One crew aloft for at least an extra day.

Once back on Earth, Shepherd and company face several months of physical therapy as their bodies readapt to life in normal gravity. Space medicine specialists expect them to be weak and woozy after at least 141 days in weightlessness, and even walking will be a chore.

Said NASA flight surgeon Terry Taddeo: "It's going to be as if they are encountering gravity all over again for the first time."