Image: Troubleshooting
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Russian cosmonaut Fyodor Yurchikhin checks connections between the International Space Station's Poisk module and a Soyuz spacecraft after a technical glitch prevented the Soyuz's undocking on Thursday.
By Space.com managing editor
updated 9/24/2010 1:23:30 AM ET 2010-09-24T05:23:30

An undocking system malfunction on the International Space Station has delayed the return to Earth for three astronauts in a Soyuz capsule by at least one day as Russian engineers try to understand what went wrong.

The problems began late Thursday when a set of hooks and latches on the space station's Russian Poisk docking port refused to release their grip on the astronauts' Soyuz spacecraft linked to the port.

The Soyuz crew — two Russian spacefliers and one American — had hoped to undock and land on the steppes of Kazakhstan in Central Asia early Friday morning local time. They are now slated to land no earlier than early Saturday.

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bbFlight controllers were unable to command the hooks into the undocking position, causing hours of delays and ultimately forcing the astronauts to abandon their undocking and landing plans for the day.

Russian engineers suspect that an open electrical circuit may be to blame, NASA officials said. [Graphic – Inside and Out: The International Space Station]

"Well, we're not going to have another attempt today for the undocking," a Russian flight controller radioed the station crew. "We're going to give the guys the go for the opening of the hatch and coming back into the ISS."

A fleet of 12 Russian recovery helicopters and other aircraft were gearing up for the astronauts' return to Earth at the time.

Russian engineers at the station's Mission Control near Moscow plan to try undocking the spacecraft late Friday.

The Soyuz TMA-18 spacecraft had been slated to leave the space station at 9:34 p.m. ET Thursday, bringing two cosmonauts and one American astronaut back to Earth after six months in orbit. Aboard the craft were American astronaut Tracy Caldwell Dyson and Russian crewmates Alexander Skvortsov and Mikhail Kornienko.

Russian cosmonaut Fyodor Yurchikhin and two NASA astronauts — Douglas Wheelock and Shannon Walker — are remaining behind on the International Space Station to complete their own space mission.

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While troubleshooting the glitch, Yurchikhin found a gear with two broken teeth, though it is unclear what role, if any, the broken part may have played in the evening's troubles.

The space station's Poisk docking port is on the top of the orbiting laboratory's Russian segment. It was delivered last year and was first used by visiting Russian spaceships earlier this year.

The stuck hooks are on Poisk side of the docking port. These hooks, along with others on the Soyuz side, ensure that the spacecraft and station are securely attached while docked.

During the undocking attempts, Russia's Mission Control center radioed words of encouragement to the Soyuz crew, telling the astronauts they could take off spacesuit gloves and get comfortable while they waited.

Skvortsov, who is commanding the Soyuz trip to Earth, said he and his Soyuz crewmates were doing well.

The scrapped undocking attempt capped a night of delays for the space station's full six-person crew. Earlier in the night, they had trouble sealing the hatch cover on the Poisk module docking port.

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