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.

The capture came after Northrop Grumman engineers adjusted the sensitivity of main engine fault detection software that prematurely triggered shut downs during two rendezvous thruster firings Tuesday.

A Soyuz rocket carrying a Russian commander, a NASA co-pilot and a United Arab Emirates guest cosmonaut blasted off from Kazakhstan Wednesday, chased down the International Space Station and glided in for a picture-perfect docking, kicking off an unprecedented end-of-year schedule that includes up to a dozen spacewalks.