Malfunction Delays Space Station Astronauts' Return to Earth

A malfunction with a spacecraft docking mechanism delayed the return of three astronauts from the International Space Station (ISS) to Earth late Thursday.

Astronauts on Friday were able to successfully repair the problem that prevented two Russians, Alexander Skvortsov and Mikhail Kornienko, and American Tracy Caldwell Dyson from undocking the Soyuz TMA-18 spacecraft from the ISS on Thursday, according to NASA. They were scheduled land in Kazakhstan early Friday local time.

Soyuz TMA-18 is now scheduled to undock at 10:02 pm EDT Friday and make the trip back to Earth, landing Saturday in Kazakhstan if all goes according to schedule. Their departure will leave three astronauts aboard the ISS.

The docking problem is the second notable system failure astronauts aboard the ISS have encountered in as many months. Last month NASA sent astronauts on an emergency spacewalk to repair a failed cooling system.

Astronauts on the ISS noticed the problem when they tried to unlock the spacecraft Thursday and hooks attaching its Poisk module to the ISS failed to open. Mission controllers in Moscow also did not receive the "hatch locked" signal from the module letting them know the operation had completed successfully, according to NASA.

While troubleshooting the problem, Flight Engineer Fyodor Yurchikhin found a small star-shaped gear with two broken teeth, but it's unclear whether this prevented the hooks from unlocking. Experts are currently evaluating whether the part is related to the problem, according to NASA.

Overnight, Yurchikhin and crew members installed a series of jumper cables to open the Poisk module hooks and latches. They were left open overnight in preparation for Friday's second attempt at undocking.

Skvortsov, Dyson and Kornienko arrived at the ISS in April when the Soyuz TMA-18 first docked with the ISS. They are crew members of Expedition 24, which began in June and conducted a variety experiments in human research; biology and biotechnology; physical and materials sciences' technology development; and Earth and space sciences.