Delayed more than three hours while troubleshooting problems with the docking mechanism holding a Soyuz spacecraft to the International Space Station, Russian flight controllers called off an attempt to bring three crew members back to Earth Friday pending additional work to resolve the malfunction.
The unprecedented glitch with the normally reliable docking mechanism means outgoing station commander Alexander Skvortsov, flight engineer Mikhail Kornienko, and NASA astronaut Tracy Caldwell Dyson will have to spend at least one and possibly two more days in orbit.
It was not clear what caused a lack of response with hooks on the space station side of the docking interface that are designed to release on command. But Expedition 25 flight engineer Fyodor Yurchikhin, examining the docking interface later from inside the space station, reported finding a small gear floating from the mechanism when he removed a cover.
"Right under the cover, I could see...there is a small thing, it looked like a gear," he said. "It was under the cover of the panel so I could actually see it for a second. I am trying to reach under it, but the docking mechanism is in the way. But there was some small object that was floating there. That I can confirm...It's very small, it was looking very much like a spiral, like a gear with teeth."
He later recovered the object, confirmed it was a small gear-like component, and downlinked photos to Russian flight controllers. But it was not immediately clear whether the object came from the docking system or had anything to do with its failure to respond to commands.
Skvortsov, Kornienko, and Caldwell Dyson remained inside the Soyuz TMA-18 spacecraft while troubleshooting continued.
They had hoped to undock from the station's upward-facing Poisk module at 9:35 p.m. EDT Thursday, setting up a landing in southern Kazakhstan at 12:55 a.m. Friday (10:55 a.m. local time) to close out a 175-day stay in space.
The trio entered the Soyuz TMA-18 spacecraft late Thursday afternoon and closed the main hatch at 6:35 p.m. They immediately ran into problems getting a tight seal and were forced to open the Soyuz hatch again for a quick inspection. The hatch later was sealed, but Yurchikhin had problems confirming a tight fit with the hatch on the station side of the interface.
After an extended leak check, flight controllers in Moscow decided the docking interface was tight and leak free.
As the countdown ticked toward undocking, commands were sent to open hooks on the Poisk side of the interface. But the mechanism failed to respond.
Unable to figure out what might be causing the problem, chief flight director Vladimir Solovyov in the Russian mission control center ordered a one-orbit wave off pending additional troubleshooting. That later was extended to two orbits.
Skvortsov and his crewmates only had three opportunities on successive orbits to make it back to Kazakhstan on Friday. The station fliers were hoping to get away on their third and final opportunity, undocking around 12:40 a.m. EDT Friday. That would have set up a four-minute 21-second de-orbit rocket firing at 3:14:35 a.m. with landing in northern Kazakhstan near Arkalyk expected around 4:05 a.m. (2:05 p.m. local time).
But engineers were unable to resolve the problem with the docking mechanism and the Russians called off the undocking attempt. Skvortsov, Kornienko, and Caldwell Dyson were cleared to doff their pressure suits, open the Soyuz hatch and return to the space station.
"Fyodor, well, we're not going to have another attempt today for the undocking," a flight controller called from the Russian mission control center. "Why don't you give the guys the go for opening the hatch and coming back to the ISS. All the details will be given later ... about the planned undocking either tomorrow or the day after tomorrow."