Flight Engineer Fyodor Yurchikhin inspects balky Russian segment docking mechanism. (Photo credit/NASA TV)
Russia's Mission Control called off attempts by the International Space Station's Expedition 24 crew to land early on Sept. 24, after Alexander Skvortsov, Mikhail Kornienko and Tracy Caldwell Dyson encountered problems unlatching the docking mechanism that secured their Soyuz TMA-18 spacecraft to the orbiting science laboratory.
The decision to postpone further landing attempts for at least 24 hours was made at 12:13 a.m. EDT.
The three fliers were tentatively scheduled for a second undocking attempt today at 10:02 p.m. EDT, followed by a landing under parachute on the southern plains of Kazakhstan on Sept. 25 at 1:21 a.m. EDT.
The new landing schedule depends on efforts by station flight engineer Fyodor Yurchikhin to bypass what appeared to be a faulty microswitch in the circuitry of the latching mechanism.
Skvortsov, Kornienko and Caldwell Dyson were originally scheduled to touchdown in Kazakhstan on Sept. 24 at 12:55 a.m. EDT.
However, after boarding their spacecraft on the evening of Sept. 23, the Soyuz crew encountered difficulties carrying out a series of leak checks on the hatches separating the Soyuz and the station's year old Russian Poisk docking module. During prolonged troubleshooting, Yurchikhin opened and closed the hatches several times.
The activities led to a delay in scheduled commands from Russia's Mission Control, which were to release a series of hooks and latches on the Poisk side of the docking mechanism in time for the Soyuz crew to depart at 9:34 p.m. EDT.
Skvortsov, the Soyuz commander, then attempted unsuccessfully to transmit the unlatching commands.
During the final hour of troubleshooting, Yurchikhin discovered a small circular metal gear with two missing teeth on the Poisk side of the apparatus. However, the significance of the find was not immediately clear.
Skvortsov, Kornienko and Caldwell Dyson began their mission with an April 2 lift off aboard the Soyuz TMA-18.
Their ultimate departure will leave the orbital base staffed by Americans Doug Wheelock and Shannon Walker and Yurchikin for two weeks.
Russia's Soyuz TMA-01M is scheduled to lift off from the Baikonur Cosmodrome with Alexander Kalari, Oleg Skripochka and American Scott Kelly on Oct. 7 and dock with the station two days later.
Expedition 24 was marked by unusual drama late on July 31, when an electrical short in an external U.S. coolant pump on the starboard section of the station's solar power truss crippled half of the vital external thermal control system. The shutdown triggered late-night alarms aboard the outpost and kicked off a near three week, around-the-clock campaign led by NASA station program managers and Mission Control to recover Loop A of the dual loop cooling system.
The breakdown was accompanied by a powerdown of non essential avionics, life support systems and scientific research.
NASA responded with spacewalks by Wheelock and Caldwell Dyson on Aug. 7, 11 and 16. The spacewalkers managed to replace a failed coolant pump module with a spare that has been pre-staged on the station.