Aboard the complex, one crew prepared for a return to Earth while another focused on taking the helm in orbit.
Expedition 12 Commander Bill McArthur, Flight Engineer Valery Tokarev and Brazilian astronaut Marcos Pontes head home Saturday, closing hatches as they leave the station at 1:35 p.m. EDT. They will undock their Soyuz spacecraft at 4:28 p.m. EDT. That sets the stage for a deorbit burn at 6:58 p.m. EDT to drop the 15,000-pound spacecraft out of orbit. The Soyuz will parachute to a landing at 7:48 p.m. EDT on the steppes of Kazakhstan.
Expedition 12's homecoming preparations began in earnest after last week's arrival of the 13th station crew, Commander Pavel Vinogradov and Flight Engineer Jeff Williams, who arrived with Pontes, Brazil's first astronaut. Pontes will have spent eight days on the station conducting experiments as part of a commercial agreement with the Russian Federal Space Agency.
This week began with a partially completed "campout" by McArthur and Williams in the Quest Airlock. The planned overnight stay in the airlock tested procedures that can shorten the time needed to prepare for future spacewalks.
Quest was sealed off from the rest of the station at 6:45 p.m. EDT Monday with McArthur and Williams inside, and its air pressure was later lowered to 10.2 pounds per square inch. The rest of the station remained at the normal air pressure of 14.7 pounds per square inch. An overnight stay at the lower air pressure helps purge nitrogen from the body, a necessary step to avoid decompression sickness. McArthur and Williams were awakened four hours into their sleep in the airlock by an error tone.
The tone was generated by software that monitors the composition of air on the station. Flight controllers opted to end the campout test Tuesday at 12:43 a.m. EDT, open the airlock hatch to the station, and allow the crew to go back to sleep. Despite the glitch, all of the test objectives were achieved. Engineers are reviewing data to determine whether changes are needed to use the technique during the STS-115 shuttle mission later this year. Engineers could decide to repeat the test at another time.
On Wednesday, Williams trained with the station's robot arm, Canadarm2. Late this week, McArthur briefed Williams on payload operations in the Destiny laboratory while Tokarev, the Soyuz commander, stowed equipment and payloads in the Soyuz for the trip home. Tokarev also reviewed procedures for the undocking, entry and landing with flight controllers at the Russian Mission Control Center outside Moscow.