Two Americans floated outside the International Space Station to start a spacewalk with the primary goal of freeing a rail car that was jammed outside the orbiting lab.
NASA's one-year spaceman, Scott Kelly, and astronaut Timothy Kopra exited the space station's hatch early Monday ahead of schedule.
The spacewalk was unplanned.
NASA managers want them to move the rail car so a cargo ship filled with almost three tons of food and supplies can dock on Wednesday.
Engineers believe a stuck brake handle is to blame. The rail car needs to move about four inches (10 centimeters) so it can be latched into place.
The mobile transport system is normally used to transport people and equipment, including the station's big robot arm. It's the seventh spacewalk of the year.
