A Russian Soyuz capsule carrying three of the International Space Station's six crew members suffered an unexpected communications blackout just before plunging back into Earth's atmosphere, completing a nail-biting descent in radio silence with repeated calls from flight controllers near Moscow going unanswered.
Finally, recovery crews spotted the Soyuz TMA-21's braking parachute, communications with ground crews were established and the spacecraft touched down in Kazakhstan at 9:59 a.m. local time Friday (8:59 p.m. PT Thursday), tipping over on its side as it closed out an expedition lasting 164 days since launch April 4 from the Baikonur Cosmodrome.
Russian recovery crews, along with NASA flight surgeons and space station program managers, were standing by to help Soyuz commander Alexander Samokutyaev, Andrey Borisenko, and NASA flight engineer Ronald Garan out of the cramped descent module as they begin their re-adaptation to gravity after five-and-a-half months in space.
All three men appeared relaxed and in good spirits as they rested in recliners near the scorched descent module, smiling and chatting with recovery crews. Borisenko, the last of the three to be pulled from the spacecraft, flashed an enthusiastic thumbs-up.
There was no immediate explanation for the communications dropout. The repeated, unanswered calls from mission control near Moscow were eerily reminiscent of the fruitless calls to the shuttle Columbia during the orbiter's ill-fated descent to Earth in 2003.
But the Soyuz TMA-21 spacecraft completed its return to Earth safely, if in near silence, and all three crew members appeared to be in good health.
The three remaining crew members on the space station originally expected to be welcoming three fresh fliers aboard on September 24. But launch of the Soyuz TMA-22 spacecraft carrying Anton Shkaplerov, Anatoly Ivanishin, and NASA flight engineer Dan Burbank was put on hold pending resolution of a third-stage failure August 24 that triggered the destruction of a Soyuz-U rocket carrying an unmanned Progress supply ship.
The Soyuz-U and the Soyuz-FG rocket used to launch manned missions use virtually identical third stages.
Engineers have traced the Soyuz-U engine failure to a kerosene fuel line blockage that disrupted the operation of a turbopump used to feed propellants to the main combustion chamber. A Russian commission investigating the failure reportedly has raised questions about quality control. But it's not yet clear how that issue will be resolved.
During a weekly program planning meeting Thursday, Russian managers told their NASA counterparts they hope to launch another Progress supply ship on October 30. If that goes well, they plan to press ahead with launch of the Soyuz TMA-22 spacecraft carrying Shkaplerov, Ivanishin, and Burbank on November 14, setting up a docking two days later.
The three current space station crew members must return to Earth by November 22 at the latest or they will be faced with landing at night, which is a violation of Russian safety guidelines. If Burbank's launch is held up much beyond November 14, station managers could be faced with the prospect of bringing the current crew home as planned and leaving the lab complex unmanned.
Procedures are being developed to safely "de-man" the station and operate it from the ground if the Soyuz rocket problem takes longer than expected to resolve. NASA managers are hopeful it won't come to that, but the margin is razor thin.