Astronauts to test-drive railway

First movement test of new railway should come Monday

Atlantis astronaut Lee M.E. Morin wore a 35 mm camera during a weekend spacewalk at the orbiting international space station. On Monday, a newly installed section of railway is to be tested.

(CNN) -- Earth orbit's first railway is about to get its initial trial. Space shuttle Atlantis astronauts soon should venture outside for a fourth time in their ongoing mission, to hook up the railway.

They've completed the most difficult task of their 11-day mission, attaching a $600 million beam to the international space station. The 13.5-ton girder will serve as the backbone for future research and construction projects on the exterior of the space station, as well as house a depot for a small railway on the orbiting complex.

The Atlantis crew, which moved the massive truss to the space station on Thursday, conducted their second and third space walks during the weekend to complete installation of the structure -- a squat, metal, three-dimensional trapezoid brimming with electrical wires, cables and computers. A fourth and final walk is on NASA's agenda for the mission.

Also during the Sunday trip outside, the spacewalkers positioned a $190 million railcar on a rail segment attached to the truss.

•  Shuttle mission guide  •  CNN Presents: what makes the shuttle fly Movies:  •  Atlantis returns to earth  •  Atlantis leaves space station  •  CNN's Miles O'Brien talks with shuttle crew  •  CNN's John Zarrella previews the mission  •  Watch the launch from Kennedy Space Center  •   NASA animation of completed space station railroad More resources:  •  Cult 3-D model of the space shuttle  •  Milestones in space shuttle history  •  Space: The final frontier for railroads

With the addition of new segments in the coming years, the railway should stretch the length of a football field, allowing the station's robotic crane to move from one end of the sprawling modular complex to the other.

The new railcar should move for the first time on Monday, the eighth day of the mission, currently running on-schedule. A test is planned to move it up and down the first length of track, which extends about 44 feet (13 meters).

Mission winding down

After a week-long rendezvous, Atlantis should undock from the station on Wednesday. Shuttle astronauts expect to return to the Kennedy Space Center in Florida two days later.

Besides nearly $1 billion in heavy hardware, the shuttle took along sensitive scientific experiments. One known as the Photosynthetic Experiment and System Testing and Operation, or PESTO, could lead to better space food.

The wheat growth project, which will remain on the station at least two months, could help scientists determine how to grow grains in space, raising the prospect of astronauts baking their own bread.

The shuttle astronauts are the first visitors to the space station since its current crew of two Americans and one Russian arrived in December. The station residents expect to return home this summer.