Ruling out a strike by space debris or a micrometeoroid, Russian engineers say a small now-plugged leak in a Soyuz crew ferry ship docked to the International Space Station was the result of a hole drilled into the wall of the spacecraft’s upper compartment, an apparent case of human error.

The spacecraft was originally scheduled to dock with the International Space Station the morning of Wednesday, Sept. 17. An alternate plan is in the works.

The International Space Station’s first three-man crew moved in on Nov. 2, 2000, 15 years ago Monday, the first of 45 expeditions to date that have logged a decade and a half of continuous human presence in low-Earth orbit.