"The planned undocking was prevented when commands being sent to disengage the hooks and latches holding the Soyuz TMA-18 spacecraft failed", NASA Mission Control told this reporter this morning. "The spacecraft remains securely docked to the Poisk module."
The Russian Poisk module is home to the docking port in which the Soyuz craft is docked.
At this time, engineers both in Moscow and at the Johnson Space Center south of Houston, are working to uncover the issue.
Several I spoke with at the American space agency feel that the issue is electrical, however more time is needed to understand exactly where the problem lies.
On Thursday evening, as the hatch from the station to the Poisk was being closed, controlers did not receive the proper indication early on that the small switches latched to seal the compartment for undocking. They later received good confirmation following several leak checks.
The departing expedition 24 of commander Alexander Skvortsov, and flight engineersTracy Caldwell Dyson and Mikhail Kornienko returned from their Soyuz and reentered the space station at about 12:30 am following the undocking scrub.
The trio then spent time exercising and discussing the issue at hand with their fellow crew members Doug Wheelock, Shannon Walker and Fyodor Yurchikhin for a meal and then began their sleep period at about 3 am.
Moscow has now rescheduled undocking for 10:02 pm EDT tonight (0202 GMT). The daytime landing would then occur two orbits later at 1:21 am Saturday morning on the desert floor of Kazakhstan near the town of Arkalyk (11:21 am local time).
Today marks the expedition 24 crew's 176th day in space since their launch on April 2; and their 174th day living aboard the space station.
Wheelock, Walker and Yurchikhin complete the current 25th expedition crew, and following the Soyuz undocking tonight, will be alone for two weeks until a new crew arrives.