Space station's railcar slightly off track CAPE CANAVERAL - (AP) -- Astronauts sent the international space station's new railcar rolling slowly down a short stretch of track Monday, but it quickly hit a snag that interrupted the inaugural run of the first permanent railroad in orbit. NASA blamed the problem on weightlessness. Engineers suspect the one-ton car floated ever so slightly off the rail, causing the magnetic sensors on the bottom of the car to lose contact with a pair of iron strips in the aluminum tracks. The railcar will eventually be used during the next stages of the space station's construction. The track runs along a 44-foot girder that space shuttle Atlantis' astronauts delivered and bolted to the orbiting outpost last week. The problem cropped up after the empty flatcar moved down 17 feet of track at a snail's pace of less than a half-inch per second. Right on cue, the car stopped at a work station and was automatically latching itself down when everything came to a halt. Ground controllers took over manual control and, a few hours later, were able to latch the railcar to the track. Space station astronaut Carl Walz sent another computer command from inside to get the railcar moving again. The railcar smoothly rolled 26 feet to a second work station, where the same thing happened. Again, ground controllers had to take over manual control to secure the car. Later Monday, Walz commanded the railcar to move for the third and final time, back down the same 26 feet of track. ''The train's leaving the station,'' he called out. It got to where it was going, but the automatic latching system shut down again and ground controllers had to step in as before. ''I think what we're finding out as we go through this is how the mobile transporter works in zero-g,'' said Ben Sellari, a NASA manager. Engineers may adjust the computer software sometime if it becomes more of a nuisance, he said. There is no danger of the $190 million railcar rolling off the track because of rings on both ends of the 44-foot girder, Sellari said. The first use of the railcar is set for late summer. The railcar is needed to transport the space station's 58-foot robot arm from one end of the outpost to the other as more girders are installed. Atlantis' astronauts plan a fourth and final spacewalk today to finish installing the girder.