Video: Soyuz MS-01 leaves the space station for landing

Russian investigators believe a malfunction during separation of the Soyuz rocket’s four liquid-fueled first stage boosters two minutes after liftoff from Kazakhstan led to an emergency landing of a two-man crew heading for the International Space Station, officials said Friday.

Picking up where they left off last week, two space station astronauts ventured back outside the outpost Wednesday to continue the replacement of aging batteries in the lab’s solar power system. Two more spacewalks later this month should complete the multi-year project.

A miniature cargo return vehicle carried aboard a Japanese supply ship splashed down in the Pacific Ocean earlier this month in the first test of a new capsule to bring home experiment samples from the International Space Station.