CAPE CANAVERAL, Fla. -- Space Station Alphas first full-time tenants are busy this week getting outpost systems up and running, working long days in advance of the arrival of their first visitors -- a construction crew set for launch Thursday aboard NASAs shuttle Endeavour.

A month after their launch from Baikonur Cosmodrome in Kazakhstan, U.S. astronaut Bill Shepherd and two Russian cosmonauts -- Yuri Gidzenko and Sergei Krikalev -- are pressing ahead with efforts to bring key station systems to life.

Station commander Bill Shepherd (left) and cosmonauts Sergei Krikalev and Yuri Gidzenko speak with Mission Control in Houston on Tuesday in this NASA TV image.

The biggest challenge so far: The staggering amount of work on a day-to-day basis. "To me, the biggest challenge is trying to pack 30 hours into an 18-hour work day," Shepherd told reporters in a space-to-ground interview Tuesday. Still, he added: "I think this crew is doing a great job of climbing any mountain no matter how tall it is."

Shepherd and company arrived at the station Nov. 2 and since then, have been starting up crucial computer control, life support and other systems at the outpost. The process has been a bit tedious, routinely cutting in to the crews allotted eight-hour sleep periods.

Normal sleep shifts are "possible," Krikalev said, "but practically, we have less sleep because a lot of things need to be done, especially in the first weeks of this mission."

The Alpha crew, meanwhile, is looking forward to the scheduled arrival on Saturday of the Endeavour astronauts, who plan to mount a $600 million electrical power tower atop the station.

Limited power supplies have prevented the Alpha crew from opening up one of three pressurized wings at the station, but that problem should be rectified once the new U.S. electrical system is added to the outpost.

Initial difficulties aside, Alphas inaugural tenants say their four-month mission not only is critical to the $60 billion station construction project but to the future of human exploration. Said Shepherd: "Were hoping, in the sense of space history, that well have one because of this mission."