French astronaut Jean-Loup Chretien and a Soviet colleague left the orbiting Mir station Friday for a spacewalk to test construction techniques, Tass said. The official news agency said Chretien and Alexander Volkov, who rocketed into space Nov. 26, unfolded a carbon plastic structure and fastened it to a platform they will assemble on Mir's shell. If proved reliable, the platform could be used to house antennas and telescope mirrors. During the walk, Chretien and Volkov deployed a unit with various materials and coatings to test how they withstand exposure to the space environment. The unit will have to withstand sharp temperature fluctuations and solar radiation. It is to remain in place for six months and then be brought back to Earth for study.